SN
SNZ PAS 5311:2021
Z
P
A
STANDARDS NEW ZEALAND
S
PUBLICLY AVAILABLE SPECIFICATION
5
31
1:2
Biomass boiler
0
21
systems for
small and medium
heat loads

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SNZ PAS 5311:2021
TECHNICAL ADVISORY GROUP REPRESENTATION
This publicly available specification was prepared by the P5311 Biomass Boilers Technical Advisory Group (TAG).
The membership of the TAG was approved by the New Zealand Standards Executive.

The TAG consisted of representatives of the following nominating organisations:

Bioenergy Association of New Zealand
Carbon and Energy Professionals New Zealand
Coal Action Network Aotearoa
Energy Efficiency and Conservation Authority
Great South
Scion
Toimata Foundation, Enviroschools
University of Otago, Otago Energy Research Centre
WorkSafe New Zealand
ACKNOWLEDGEMENT
Standards New Zealand gratefully acknowledges the contribution of time and expertise from all those involved in
developing this specification.
COPYRIGHT
The New Zealand Standards Executive owns the copyright in this document. You may not reproduce any part of it
without prior written permission of the New Zealand Standards Executive, unless your actions are covered by Part 3 of
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We will vigorously defend the copyright in this publicly available specification. Your unauthorised use may result in
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injunctive relief and/or an account of profits.
Published by Standards New Zealand, PO Box 1473, Wellington 6140.
Telephone: (03) 943 4259, Website: www.standards.govt.nz.
AMENDMENTS
No.
Date of issue
Description
Entered by, and date
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Copyright Standards New Zealand

SNZ PAS 5311:2021

Publicly Available Specification
Biomass boiler systems
for small and medium
heat loads
Copyright in SNZ PAS 5311 is Crown copyright, administered by the New Zealand Standards Executive. Access to this standard has been sponsored by the Energy
Efficiency and Conservation Authority under copyright license LN001390. You are permitted to view and print this standard free of charge (subject to printing costs) for your
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Copyright Standards New Zealand
ISBN (Print) 978-1-77686-638-0
ISBN (PDF) 978-1-77686-639-7

TECHNICAL ADVISORY GROUP REPRESENTATION
ACKNOWLEDGEMENT
NOTES
COPYRIGHT
These 3 titles are here for the auto TOC (they are actual y on the IFC)

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link to page 6 link to page 6 link to page 6 link to page 9 link to page 11 link to page 11 link to page 12 link to page 13 link to page 13 link to page 13 link to page 14 link to page 14 link to page 17 link to page 19 link to page 19 link to page 21 link to page 22 link to page 23 link to page 24 link to page 24 link to page 25 link to page 26 link to page 28 link to page 28 link to page 29 link to page 30 link to page 30 link to page 30 link to page 33 link to page 34 link to page 34 link to page 34 link to page 35 link to page 35 link to page 36 link to page 36 link to page 38 link to page 40 link to page 42 link to page 43 link to page 43 link to page 4 SNZ PAS 5311:2021
CONTENTS
Technical advisory group representation �� ii
IFC
Acknowledgement �� ii
IFC
Copyright �� ii
IFC

Referenced documents �� v
Latest revisions �� vii
Review �� vii
Foreword ��viii
Section
1 GENERAL ��1
1�1 Scope ��1
1�2 Objective ��2
1.3
Definitions ��2
1�4 Abbreviations ��5
2 OVERVIEW ��7
2�1
What is a biomass boiler system? ��7
2�2
Where to start? Evaluation of options ��9
2�3
Biomass fuel ��10
2�4
Fuel quality characteristics that effect boiler performance �� 11
2�5
Fuel management and storage ��12
2�6
Biomass boilers ��12
2�7
Operation, maintenance, and safety ��13
2�8
Attributes of biomass boiler systems �� 14
2�9
Scoping and conceptual assessment ��16
2�10 Consenting ��16
2�11  Checklist for biomass boiler systems �� 17
3
TECHNICAL SPECIFICATION ��18
3�1 General ��18
3�2
Biomass fuel ��18
3�3 Chip ��21
3�4
Hog fuel ��22
3�5 Pel ets ��22
3�6 Briquettes ��22
3�7
Herbaceous fuels ��23
3�8
Specifying the right fuel ��23
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3�9
Fuel supply contracts��24
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3�10  Fuel management and storage ��24
3�11  Equipment selection ��26
3�12  Capacity ratings ��28
3�13  Operation, maintenance, and safety ��30
3.14 Consenting, financial life cycle, and environmental and
social assessment ��31
COPYRIGHT © Standards New Zealand
iii

link to page 48 link to page 48 link to page 50 link to page 30 link to page 33 link to page 37 link to page 46 link to page 49 link to page 19 link to page 20 link to page 20 link to page 20 SNZ PAS 5311:2021
Appendix
A
Wood fuel value by moisture content (Informative) ��36
B
Other resources (Informative) ��38

Table

1
Fuel type features for heating systems covered by this specification ��18
2
Fuel specifications ��21
3
Indicative fuel densities ��25
4
Financial example comparison ��34
A1 Indicative moisture content and energy ��37
Figure
1
Stoker biomass boiler system ��7
2
Wood chips ��8
3
Wood pellets ��8
4
Hog fuel ��8
Copyright in SNZ PAS 5311 is Crown copyright, administered by the New Zealand Standards Executive. Access to this standard has been sponsored by the Energy
Efficiency and Conservation Authority under copyright license LN001390. You are permitted to view and print this standard free of charge (subject to printing costs) for your
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iv
COPYRIGHT © Standards New Zealand

SNZ PAS 5311:2021
REFERENCED DOCUMENTS
Reference is made in this document to the fol owing:
New Zealand standards

NZS 1170:----
Structural design actions

Part 5:2004
Earthquake actions – New Zealand
Joint Australian/New Zealand standards
AS/NZS 1170:----
Structural design actions

Part 2:2011
Wind actions
AS/NZS 4536:1999
Life cycle costing – An application guide
AS/NZS 3598:----
Energy audits

Part�2:2000
Industrial and related activities
International standards
ISO 17225:----
Solid biofuels – fuel specifications and classes

Part 1:2014
General requirements

Part 2:2014
Graded wood pel ets

Part 3:2014
Graded wood briquettes

Part 4:2014
Graded wood chips

Part 5:2014
Graded firewood

Part 6:2014
Graded non-woody pel ets

Part 7:2014
Graded non-woody briquettes (new draft standard 2020)

Part 8:2016.
Graded thermal y treated and densified biomass fuels

Part 9:2020
Graded wood hog fuel and wood chips for industrial use
ISO 17831:----
Solid biofuels – Determination of mechanical durability of
pel ets and briquettes

Part 1:2015
Pel ets

Part 2:2015
Briquettes
ISO 17827:----
Solid biofuels – Determination of particle size distribution
for uncompressed fuels

Part 1:2016
Oscil ating screen method using sieves with apertures of
3�15mm and above
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Efficiency and Conservation Authority under copyright license LN001390. You are permitted to view and print this standard free of charge (subject to printing costs) for your
unless your actions are covered by Part 3 of the Copyright Act 1994. For queries about copyright, please contact Standards New Zealand at [email address]
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Part 2:2016
Oscil ating screen method using sieves with apertures of
Copyright Standards New Zealand
3�15mm and below
COPYRIGHT © Standards New Zealand
v

SNZ PAS 5311:2021
Other publications
Bioenergy Association. Solid Biofuel Classification Guidelines. Bioenergy Association
Technical  Guide  01.  2015.  Available  at  https://www.usewoodfuel.org.nz/documents/
resource/TG01-Solid-Biofuel-Classification-Guidelines.pdf  (accessed  23  November

2020).

Bioenergy Association. Standard Methods for Verifying the Quality of Solid Biofuels.
Bioenergy Association Technical Guide 05. 2015. Available at https://www.usewoodfuel.
org.nz/resource/tg05-verifying-solid-biofuel (accessed 1 March 2021).
Bioenergy  Association.  Contracting  to  Deliver  Quality  Solid  Biofuel  to  Customers.
Bioenergy Association Technical Guide 06. 2015. Available at https://www.bioenergy.
org.nz/documents/resource/Technical-Guides/TG06-Contracting-to-deliver-quality-
wood-fuel.pdf (accessed 23 November 2020).
Bioenergy Association. Consultant/specifier practice paper for wood fuel industrial and
commercial heating systems. Bioenergy Association Technical Guide 10. 2015. Available
at https://www.usewoodfuel.org.nz/resource/tg10-specifier-practice-paper (accessed
4 March 2021).
Bioenergy Association. Best practice guideline for life cycle analysis of heat plant
projects. Bioenergy Association Technical Guide 14. 2018. Available at https://www.
bioenergy.org.nz/documents/resource/Technical-Guides/TG14-guideline-for-lifecycle-
analysis-of-heat-supply-projects-181031.pdf (accessed 23 November 2020).
Bioenergy Association. Register of solid biofuel suppliers. BANZ Information Sheet 53.
Available at https://www.usewoodfuel.org.nz/documents/resource/Information-Sheets/
IS53-BANZ-solid-biofuel-suppliers-register.pdf (accessed 23 November 2020).
Ministry  for  the  Environment.  An  everyday  guide:  Applying  for  a  resource  consent.
Available at https://www.mfe.govt.nz/publications/fresh-water/everyday-guide-applying-
resource-consent/everyday-guide-applying-resource (accessed 27 November 2020).
Ministry  for  the  Environment.  Measuring  emissions:  Summary  of  emission  factors
2020.  Available  at  https://www.mfe.govt.nz/publications/climate-change/measuring-
emissions-summary-of-emission-factors-2020 (accessed 1 March 2021).
Ministry  for  the  Environment.  Measuring,  reporting  and  offsetting  greenhouse  gas
emissions. Available at https://www.mfe.govt.nz/climate-change/guidance-measuring-
emissions (accessed 27 November 2020).
Scion. ‘Energy from wood is good for New Zealand and the climate’. 2018. Available at
https://www.scionresearch.com/__data/assets/pdf_file/0008/64367/Carbon_cycling_
infosheet.pdf (accessed 27 November 2020).
Copyright in SNZ PAS 5311 is Crown copyright, administered by the New Zealand Standards Executive. Access to this standard has been sponsored by the Energy
Efficiency and Conservation Authority under copyright license LN001390. You are permitted to view and print this standard free of charge (subject to printing costs) for your
unless your actions are covered by Part 3 of the Copyright Act 1994. For queries about copyright, please contact Standards New Zealand at [email address]
own use. You are not permitted to reproduce any part of it without prior written permission from Standards New Zealand, on behalf of the New Zealand Standards Executive,
Wood  Energy  website.  Registered  wood  energy  advisers.  Available  at  https://www.
Copyright Standards New Zealand
usewoodfuel.org.nz/registered-wood-energy-advisors (accessed 27 November 2020).
WorkSafe. Working safely with boilers and other pressure equipment. Available at https://
worksafe.govt.nz/topic-and-industry/machinery/working-safely-with-boilers (accessed
19 November 2020).
vi
COPYRIGHT © Standards New Zealand

SNZ PAS 5311:2021
New Zealand legislation
Climate Change Response Act 2002
Climate Change Response (Zero Carbon) Amendment Act 2019

Health and Safety at Work Act 2015
Health and Safety in Employment (Pressure Equipment, Cranes, and Passenger
Ropeways) Regulations 1999
Resource Management Act 1991
Websites
www�bioenergy�org�nz
www�eeca�govt�nz
www�forestresearch�gov�uk
www�legislation�govt�nz
www�mfe�govt�nz
www�scionresearch�com
www�usewoodfuel�org�nz
worksafe�govt�nz
LATEST REVISIONS
The users of this specification should ensure that their copies of the above-mentioned
New Zealand standards are the latest revisions� Amendments to referenced New Zealand
and joint Australian/New Zealand standards can be found on www�standards�govt�nz�
REVIEW
Suggestions for improvement of this specification wil be welcomed. They should be
sent to the Manager, Standards New Zealand, PO Box 1473, Wel ington 6140�
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Efficiency and Conservation Authority under copyright license LN001390. You are permitted to view and print this standard free of charge (subject to printing costs) for your
unless your actions are covered by Part 3 of the Copyright Act 1994. For queries about copyright, please contact Standards New Zealand at [email address]
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COPYRIGHT © Standards New Zealand
vii

SNZ PAS 5311:2021
FOREWORD
This document has been prepared as a guidance document and published as a publicly
available specification (PAS). A PAS is an ISO-recognised category for documents that
are not national standards, but are produced by a national standards body to respond

to a market need, representing either consensus in an organisation or industry, or

consensus of the experts within a working group�
This guidance document has been prepared by representatives of the biomass energy
sector as a col ation of best practice advice for potential new owners of biomass boiler
systems and their advisers�
Biomass boiler systems are not complex or new but there are many new entrants to the
sector who are seeking guidance� This document provides that guidance in a single place�
The objective of this publicly available specification (SNZ PAS 5311:2021 Biomass boiler
systems for small and medium heat loads) is to provide best practice guidance to support
the adoption of low-emission biomass boiler systems in commercial, institutional, and
industrial heat applications� Small to medium heat loads are those between 50 kW and
2 MW, providing hot water below 100°C�
Biomass provides a safe, environmentally friendly, clean, reliable, and economic
alternative to other sources of energy� A biomass boiler system typical y heats water,
which heats buildings via radiators� However, biomass boiler systems are also suitable
for many other higher-temperature heating applications�
The New Zealand Government is setting ambitious targets under the Climate Change
Response (Zero Carbon) Amendment Act 2019 to achieve net zero carbon emissions
by 2050� Reducing fossil fuel use across New Zealand is an obvious step towards these
targets� Fossil fuels continue to be used in many hot-water heating applications in schools,
hospitals, prisons, and much of industry� Biomass boiler systems have excel ent potential
to replace fossil fuels and mitigate climate impact in a cost-effective way� Biomass
systems are also increasingly cost competitive compared to fossil fuels, as the price of
carbon and gas increases, and as sustainability becomes an increasingly important factor�
Biomass boiler systems have been available for many years� However, advances in
technology have made them ideally suited to a wide range of heating applications�
Biomass energy has numerous benefits including:
(a)  Biomass fuel is renewable, sourced as wood from residual plantation forests,
agricultural operations, processing wood, and other biomass applications, and is
therefore environmental y friendly in comparison to fossil fuel options;
(b)  Solid biofuels can be produced to meet any biomass boiler specification;
(c)  Solid biofuels are not subject to carbon taxes like fossil fuels;
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(d)  Biomass boiler systems use proven technology and as a result, are cost effective;
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(e)  Biomass fuel long-term availability is managed by accredited solid biofuel suppliers
and is in no threat of running out;
(f)
Accredited solid biofuel suppliers have third-party auditing and monitoring of their
quality assurance processes so that fuel is reliably and consistently supplied;
(g)  Use of biomass energy supports community employment and wel -being, because
fuel and engineering support is sourced local y�
viii
COPYRIGHT © Standards New Zealand

Section
SNZ PAS 5311:2021
Publicly Available Specification
Biomass boiler systems for

small and medium heat loads

1  GENERAL
1.1
Scope
1.1.1
Inclusions
This publicly available specification (PAS) provides advice and information on biomass
boiler systems for smal to medium heat loads (50 kW to 2 MW) providing hot water
below 100°C� A biomass boiler system includes all primary and ancil ary equipment for
fuel reception and storage, through to the point of delivering hot water to the application
reception point� Within this document, a biomass boiler system is one fuel ed by wood
chip, wood briquettes, wood pel ets, or other biomass�
This PAS includes both technical and non-technical guidance on the fol owing:
(a)  Evaluating heat demand and energy efficiency;
(b)  Generic site requirements;
(c)  Greenhouse gas and local particulate emissions;
(d)  Fuel quality, supply, reception, storage, and handling;
(e)  Operation and maintenance;
(f)
System efficiency;
(g)  Seasonal efficiency;
(h)  Regulatory and non-regulatory health and safety aspects;
(i)
Consenting�
1.1.2
Exclusions
Excluded from this document are the fol owing:
(a)  Biomass boiler systems larger than 2 MW;
(b)  Steam boilers;
(c)  High temperature hot water boilers (over 100°C);
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(d)  Systems that are intended to supply potable water;
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(e)  Co-firing coal boilers;
(f)
Use of industrial effluents, municipal biosolids, anaerobic digestion, and algae as
biomass fuel�
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1

link to page 29 SNZ PAS 5311:2021
Much of the best practice advice included in this guidance document will be equal y
applicable to the excluded biomass boiler systems but expert advice specific to those
technologies should be sought if an excluded application is being considered�

1.2
Objective

The intended audience for this PAS includes potential owners, evaluators, instal ers,
maintenance and operations staff, purchasers, consultants, designers, equipment and
service suppliers, and any others wanting to make an informed choice around biomass
boiler system options�
Sections 1 and 2 are written to be broadly accessible to a non-technical audience who
are making decisions about the purchase and use of biomass boiler systems. Section 2
also includes a checklist of key questions to ask and elements to consider�
Section 3 of this document is a specification and is written primarily for a technical
audience�
The guidance in this document covers New Zealand safety requirements� It refers
to regulatory requirements as well as providing non-regulatory best practice
recommendations�
Much of the guidance provided assumes that the biomass boiler system will be used
to heat hot water, but where applicable the advice provided is also valid for other
applications�
1.3
Definitions
For the purposes of this specification the fol owing definitions apply:
Ash content
Mineral content of biomass left after combustion
Ash
Ash produced by a boiler may contain unburnt carbon as
well as the non-combustible minerals�
Auger
Screw type device for moving fuel from the bunker into the
combustion zone and taking ash out of the combustion
zone into a bin
Basic energy density
Measured in gigajoules per tonne (as opposed to bulk or
volumetric energy density, see below, which is measured in
gigajoules per cubic metre)
Biomass
Wood or herbaceous material derived from living, or
recently living plants
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Biomass boiler system Heating plant designed to produce hot water fuelled by
Copyright Standards New Zealand
combusting biomass, including associated fuel handling
and storage equipment up to the point of connection with
the applications receptor of the hot water�
Briquettes
A densified form of wood fuel, where small particles (such
as sawdust) are squeezed into a larger, dryer, denser form
2
COPYRIGHT © Standards New Zealand

link to page 49 SNZ PAS 5311:2021
Bulk or volumetric
Measured in gigajoules per cubic metre (as opposed to
energy density
basic energy density, see above, which is measured in
gigajoules per tonne)
Calorific value
Energy content of fuel per weight, usually expressed in

megajoules per kilogram (MJ/kg) or gigajoules per tonne

(GJ/t). The calorific value of a fuel can be described as
either net calorific value (NCV) – lower heating value – or
gross calorific value (GCV) – higher heating value. The lower
heating value accounts for the impact of moisture content
in the fuel� GCV assumes that the moisture content of the
fuel that is driven off in the flue gas can be recovered by
condensing the evaporated water on a heat exchanger� The
values for NCV and GCV by moisture content are shown in
Appendix A, Table A1
Carbon dioxide
A metric measure used to compare the emissions from
equivalent (CO2-e)
various greenhouse gases based on their global-warming
potential, by converting amounts of other gases to the
equivalent amount of carbon dioxide with the same global
warming potential
Clinker
Ash that has partially melted and formed into hard lumps
Combustion
A chemical process in which a substance reacts rapidly with
oxygen and gives off heat
Copper-chrome-
A wood preservative
arsenate (CCA)
Design working life
Assumed period for which a structure or a structural
or economic life
element is to be used for its intended purpose without
major repair being necessary� Includes for periodic
replacement of some equipment with less than the overall
expected operational life of the facility� Usually taken as 20
to 30 years
Energy storage tank
An energy storage tank is a water tank that stores energy in
the form of heat (hot water)� An energy storage tank allows
a small boiler to operate at a steady load with fluctuations
or peaks in heat demand being able to be met by extraction
of heat stored in the tank
Escalation clause
A provision in a contract allowing for an increase in prices
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Financial life
The term of facility operation used to calculate the levelised
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cost of energy� Usually taken as a minimum of 15 years
Fuel oil
Liquid fossil fuel suitable for burning in a boiler
Gas
(Natural) gas, LPG, biogas and hydrogen
Grate
Part of a boiler that supports the fuel during combustion
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SNZ PAS 5311:2021
Hog fuel
Biomass, usually wood that has been through a hogger (a
large hammer mill) in order to reduce the particle size of the
biomass
Kilogram of carbon
The amount of carbon dioxide emitted for every gigajoule of

dioxide equivalent
energy produced

per gigajoule
Levelised cost of
Calculates the present value of the total cost of the energy
energy (LCOE)
plant and operating of the plant over an assumed lifetime
Lignocellulosic
Biomass that is made from lignin and cellulose (herbaceous
as well as wood)
Miscanthus
A giant fast-growing grass that can be used as a biomass
energy crop
Moisture (or water)
Wood fuels can have moisture contents that vary a lot� This
content
affects their fuel value and their weight� There are two ways
of expressing the moisture content of the wood� These are
on a wet or dry basis�
When referring to wood fuels, typically moisture content
on a wet basis is used; that is the amount of moisture on
the wood is expressed as a percentage of the as-delivered
weight� Wood fuels are likely to be between 8% and 55%
moisture content wet basis�
The wood processing industry produces kiln-dried wood
products, and they often use moisture content on a dry
basis as a measure of the moisture content of the wood�
This is where the moisture content is expressed as a
percentage of the dry weight of the wood (this can result in
numbers of over 100% for freshly cut material)�
It is important to be clear about which method has been
used or is to be used when determining wood fuel supply
contracts
Particle size
The dimensions of the fuel particles: the target size and the
distribution of sizes around this
Particulates
Very small pieces of ash and unburnt fuel than can exit a
solid fuel boiler in the flue gas stream. These emissions
must meet National Air Quality standards and local resource
consents� These particulates are generally referred to
measured and assessed as PM 10 (particulate matter less
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than 10 microns) and PM 2�5 (less than 2�5 microns)� A
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micron is 1000th of a millimetre
Biomass residues
A by-product of forest harvesting and sawmill and wood
processing that will otherwise go to waste and has limited
financially viable use
4
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SNZ PAS 5311:2021
Soil amendment
Material added to a soil to improve its physical properties,
such as water retention, permeability, drainage, aeration
and structure
Stoker
A device for moving fuel into the combustion zone

Term sheet
A written document the parties exchange, containing
the important terms and conditions of the project� The
document summarises the main points of the agreement
and sorts out the differences before actually executing the
legal agreements and starting with time-consuming due
diligence. The term sheet is non-binding as it reflects only
the key and broad points between parties under which the
project will go ahead� It also acts as a template for the in-
house or external legal teams to draft definitive agreements.
The contents and clauses of the term sheet vary from
transaction to transaction
Turndown
A boiler’s combustion unit will vary its fuel feed and output
or ‘turn down’ as the demand for heat decreases, in attempt
to meet only the required load� The turndown ratio tells you
the minimum output the boiler can achieve before turning
off and then cycling on and off frequently
Wood chip
Wood (pulp logs or offcuts from timber production) that has
been processed by a chipper into small pieces for further
processing or to be used as a fuel
Wood pellet
Densified form of wood fuel, made from compressed
sawdust� Pellets are denser than the original wood and
have standardised size and fuel content characteristics
1.4
Abbreviations
For the purposes of this specification the fol owing abbreviations apply:
CHP
Combined heat and power
CO2-e
Carbon dioxide equivalent
Cubic metre
Measurement of volume; a unit that is a cube with all sides
being 1 m
GHG
Greenhouse gas
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GJ
Gigajoule (unit of energy – for context 1 green tonne of
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wood at 58% moisture content = ~6�9 GJ nett basis)
J
Joule
kWh
Kilowatt hour
LCOE
Levelised cost of energy
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SNZ PAS 5311:2021
LPG
Liquid petroleum gas
m3
Cubic metre
MC
Moisture content

MJ
Megajoule
MW
Megawatt
MWe
Megawatt electric
MWth
Megawatt thermal
MWW
Municipal wood waste
MSW
Municipal solid waste
NCV
Net calorific value
NPV
Net present value
Odt
Oven-dry tonne
pa
Per annum
Wh
Watt hour
wb
Wet basis
Conversions:
1 MW = 1000 kW
1 kWh = 3.6 MJ
1 MWh = 3.6 GJ
1 GJ = 277.778 kWh
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2 OVERVIEW
2.1
What is a biomass boiler system?
A biomass boiler system (see Figure 1) is a renewable energy heat plant specifical y

designed to combust fuels derived from biomass such as wood chip (see Figure 2),

wood pel ets (see Figure 3) or hog fuel (see Figure 4).
Oxygen/
lambda probe
Emission
Induced
control
draft fan
O2
Flue gas
Chimney/
T
temperature
stack
Return
Ash
Hot water
Flow
boiler
T Furnace temperature
P Furnace pressure
Fuel
Sprinkler
conveyor(s)
system
Combustion
Secondary/
Fuel storage
chamber/
over ﬁ re air
Back ﬁ re
furnace
Auto-ignition (optional)
protection
Fuel
feeder
Grate/hearth
Flue gas recirculation (optional)
Primary/under ﬁ re air
Ash
Figure 1 – Stoker biomass boiler system
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SNZ PAS 5311:2021

Figure 2 – Wood chips
Figure 3 – Wood pellets
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Figure 4 – Hog fuel
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SNZ PAS 5311:2021
Biomass boilers do not combust fuel in the same manner as a fossil fuel boiler and are
very different in design and operation to a gas or fuel oil boiler� A biomass boiler system
has ancil ary equipment for fuel reception, storage, and handling, and ash removal�
Together the boiler and ancil ary equipment make up a biomass boiler system�

A modern biomass boiler system also has remote monitoring capability and controls,

which automates the majority of the facility’s operation� It can be easily monitored and
control ed on or off site, providing high operating efficiency and safety.
2.2  Where to start? Evaluation of options
2.2.1  Energy efficiency and emission reduction
When considering an upgrade or change to your heat plant, energy efficiency and
emission reduction should be some of the first things reviewed. In its simplest form,
energy efficiency is obtaining the same level of energy service (for example, delivered
hot water) for the lowest resource input (for example, fuel quantity and financial cost).
Optimising energy efficiency and meeting applicable safety and compliance codes, while
simultaneously mitigating climate impact is the ideal balance for heating applications,
and biomass boiler systems are a potential solution�
2.2.2  Sizing
To suitably size a biomass boiler system it is recommended to calculate existing heat
demand on an hourly basis and adjust for seasonal, weekly, and peak demand� Peak
demand determines the capacity of the system� To meet peak demand the biomass
boiler system can either be sized to the existing demand profile, or a smal er biomass
boiler can be used along with an energy storage tank� An energy storage tank is a
backup storage tank designed to help meet peak demand, maintain a more even boiler
output and thus increase efficiency, reduce on/off cycling, and increase longevity due
to reduced expansion and contraction� Energy storage tanks should al ow the biomass
boiler to be sized more efficiently and also might lower the overal economic cost of the
system and help at morning start-ups�
2.2.3  Heat demand
When a fossil-fuelled boiler is being replaced by a biomass boiler system, it is
recommended to reassess the site’s overall site heating demand rather than attempt to
match the hot water demand of the existing system� The possibility of future changes
in the site should also be considered�
2.2.4  Improving current efficiency
However, all evaluations start with assessing the overall efficiency of the existing
heating system� Even if this evaluation leads to a decision to upgrade the existing
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heating system, the process wil  help inform the investment decisions ultimately made�
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Organisations such as the Energy Efficiency and Conservation Authority have in-depth
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information and advice available to assist with this initial evaluation� (See their website:
www�eeca�govt�nz�)
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link to page 29 SNZ PAS 5311:2021
2.2.5  How to evaluation options
The fol owing sections explore in detail the content of biomass boiler systems and the
critical points to consider when assessing the potential for this technology� Section 2 is
designed to be accessible to a non-technical reader and concludes with a checklist of

questions� Each checklist question links to information supplied in section 2�

2.3  Biomass fuel
2.3.1  Fuel availability
Identification and analysis of the likely supply of biomass fuel suitable for the equipment
proposed is the most important element in a biomass heating proposal� When
considering the economic life of a biomass boiler system, it is important that the owner
or operator of the heating equipment has a good understanding of the fuel supply risks
for the lifetime of the equipment�
The biomass boiler system wil be designed for a specific fuel type or a range of fuel
types� Biomass fuel comes from two primary sources: forest and wood processing
biomass residues� The long-term availability of fuel is directly related to fuel suppliers
having access to one or both of these primary sources� Fuel availability should be
checked with local suppliers. To find local fuel suitable to the needs of your site, see the
Bioenergy Association’s information sheet, ‘Register of solid biofuel suppliers’ online�
The biofuel supplier will provide information on what long-term fuel sources are available
local y, how wel these fit with your site and existing infrastructure, and the delivered
cost of fuel�
Over the expected economic life of a heating system, the sources of biomass fuel can
change and, as a result, fuel characteristics can alter� Combustion and storage equipment
should be chosen or designed to handle variations in fuel characteristics�
2.3.2  Fuel characteristics
Biomass fuel characteristics are different from other fuel types such as coal� Biomass
fuel is defined by characteristics such as ash content, particle size and moisture content.
These characteristics are available from the Bioenergy Association’s technical guide
‘Solid Biofuel Classification Guidelines’ (Technical Guide 01) available online (see the
‘Referenced documents’ section at the front of this specification).
Particle size and moisture content determine the energy content of the fuel, types of
storage, delivery mechanism, and the consistency of optimal fuel supply impacting
boiler system performance�
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2.4  Fuel quality characteristics that effect boiler performance
2.4.1  Moisture content
The amount of moisture in a biomass fuel has a direct effect on the combustion
performance of the fuel; the higher the moisture content, the less energy will be derived

from the fuel per tonne (see Appendix A)� Biomass boiler systems will not run well on

fuels that are too wet� Typical y, chip used as fuel in smal er boilers should be between
25% and 40% moisture content wet basis, depending on the boiler design� Green wood
fuels with moisture contents of 55% or higher should not be used� Wood pel ets will
have a delivered moisture content of around 8-10%�
2.4.2  Particle size distribution
The particle size of the fuel and the distribution of particle sizes around the target size
will affect the performance of the biomass boiler system and its emissions� Too many
very fine particles can lead to particulate emissions and fouling issues, while oversize
material can cause issues with fuel feeding and handling� Biomass boiler systems are
typical y designed to take a particular size or type of fuel�
2.4.3  Ash
The amount of ash in a fuel directly and proportionately affects its energy content and
other aspects of boiler performance, such as particulate emissions and the frequency
of ash removal and disposal�
2.4.4  Fuel energy density
Energy density of a fuel can be measured by weight (gigajoules per tonne)� Another
important metric when matching a fuel to a boiler is the energy by unit of volume
(gigajoules per cubic metre)� Bulk density is the weight of the fuel for a given volume
(kilograms per cubic metre)�
Compared to fossil fuels, biomass fuels have lower volumetric energy densities� The
lower volumetric energy density effects the amount of storage required and the size of
the handling equipment� For example, the volumetric energy density of woodchip (30%
moisture content) is only 30% that of coal� For the same energy storage, a woodchip
plant requires more than three times the fuel storage volume� Wood pel ets, however,
have a much higher energy density than woodchip so require very little additional storage
space� The need for increased fuel storage space can be mitigated by scheduling more
frequent fuel deliveries. The costs and benefits of both approaches requires evaluation
as part of the overall project�
2.4.5  Fuel purchase
Biomass fuel is normal y sold on an energy basis based on net calorific value, ideal y
with reference to a moisture content� A fuel supply contract will specify the characteristic
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of the fuel to be delivered and the payment mechanism� The contract may include an
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escalation clause (a provision al owing for an increase in prices) for contracts with a term
longer than 1 year� The contract will set out the respective responsibilities of the buyer
and the sel er� More information can be found in the Bioenergy Association’s technical
guide ‘Contracting to deliver quality solid biofuel to customers’ (Technical Guide 06),
available online (see the ‘Referenced documents’ section at the front of this specification).
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SNZ PAS 5311:2021
The quality of the delivered fuel should be checked from time to time, as part of the
supplier’s legal obligation, to ensure it is meeting the specification set out in the contract.
Moisture, ash, and fine particle content should be the focus. If the biomass boiler system’s
performance reduces, a check on the fuel quality should be a priority�

2.5  Fuel management and storage
2.5.1  General
The way that a biomass fuel is delivered, handled, and stored needs to be considered�
Biomass fuels can have quite different requirements from other fuels� In particular,
biomass fuels (especial y densified fuels such as wood pel ets) need to be kept dry at
all times, including during delivery�
2.5.2  Fuel deliveries
Fuel handling and storage must be designed to avoid the introduction of water and
contaminants such as dirt, stones, and waste materials� Delivery of wood fuels can be
done by either bulk tipping or walking floor trucks, by auger conveyer, or pneumatical y.
Access to the fuel bunker wil  determine how delivery is made�
Verification that the fuel delivered meets the contract fuel specification is critical for
ensuring fuel is always fit for purpose. An accredited wood fuel supplier is required to
have a sampling and testing regime in place to ensure that the fuel delivered meets
the fuel contract specification. The buyer would normal y undertake a check on the
characteristics of the fuel delivered as it is delivered to a storage bunker�
2.5.3  Fuel storage
Biomass fuels should be kept as dry as possible during storage and should not be stored
outside where they are exposed to rain� This is critical in the case of pel ets and briquettes,
which are densified fuels made of smal compressed particles that disintegrate very
quickly if they get wet� Biomass fuel is also vulnerable to deterioration when exposed
to high humidity� Damp wood fuel can develop fungal growth and exposure to spores
is a health risk�
Handling and storage of biomass fuel can create dust, which can be hazardous to
operators and create a potential explosion and fire hazard. This is most likely to occur
when bunker doors are opened and dust is stirred up. If the fuel is correctly specified
and delivered this risk is minimised�
2.6  Biomass boilers
A biomass boiler works in a very similar way to conventional fossil-fuel ed boilers,
combusting fuel to produce heat that is then used to heat water for space or water
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heating� An enclosed storage area is required to store biomass fuel so that the boiler
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only needs to be refuel ed based on demand�
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2.7  Operation, maintenance, and safety
2.7.1  Operation
Owners of new biomass boiler systems should expect the equipment supplier to
provide manuals and other documentation that offer guidance for the safe operation

and maintenance of the equipment as part of the handover or induction process� This
should also include operational training or familiarisation�
Many modern biomass boiler systems are now largely automated, with software available
to operate and monitor boilers remotely� However, some aspects still require manual
checks and operation� Most important is the real-time monitoring of alarms and safety
devices�
Owners of small and medium-sized biomass boiler systems will general y outsource
the maintenance to professional maintenance service providers� Where operation or
maintenance services are provided by a third party, the contract for such services should
make clear the activities and responsibilities of the respective parties�
2.7.2  Operator training
It is essential that all staff, including on-site or temporary operating staff, have the relevant
competence to ensure the equipment is operated safely, and also that it is maintained
to maximise the life of the facility, and that the facility is operating at optimum efficiency.
The facility owner or operator should ensure that staff training (by the equipment
supplier), and any qualifications or licences, are up to date to ensure safety of the plant
and personnel and operating efficiently.
Staff refresher training should be a scheduled activity� Best practice is that staff training
dates are posted in the boiler house so that the activities importance is recognised by
staff�
This training regime, once established, should be auditable�
2.7.3  System reliability, safety, maintainability, and after-sales support
System reliability and safe operation is dependent on facility owners ensuring that proper
maintenance and operation procedures are established and appropriately known to all
personnel with responsibility relating to the facility� These should be easily available
within the facilities for personnel to reference when necessary� Audits to ensure that the
actual maintenance and operation activities are being correctly implemented should be
undertaken at least annually�
Owners and operators of facilities have obligations under the Health and Safety at
Work Act 2015 to ensure safety of workers and the public� Obligations include, but are
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not limited to, the safe operation of the biomass boiler system� This requires that all
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personnel with responsibilities relating to the facility operation should be appropriately
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trained, with regular refreshers as appropriate�
To ensure safe and efficient operation, and the longevity of the system, a routine
maintenance schedule shall be established and fol owed� This should be provided by the
equipment supplier� It should include tasks that need to be completed at regular intervals�
For example de-ashing, greasing, leak checking, and cleaning the heat exchanger�
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SNZ PAS 5311:2021
Dust is required to be cleaned from the fuel handling sections of the facility on a regular
basis to ensure there is no dust build-up and to reduce the potential for explosion�
Regular inspection of all equipment in a biomass boiler system is recommended
according to the operating manual�

The manual from the equipment suppliers wil  include a multi-year schedule for equipment
maintenance and inspections� It wil  advise whether an inspection should be carried
out by a qualified expert or can be carried out by suitably trained personnel. Backup
or external technical support capability should be identified and kept up to date.
Operational and maintenance personnel should be aware of the availability, or how to
access spare parts at short notice�
Reliable continuous facility operation requires that contingency plans are prepared
and easily available in case of a natural disaster� Plans should also cover planned and
unplanned equipment outages�
2.8  Attributes of biomass boiler systems
2.8.1  Greenhouse gas emissions and particulates
Moving from fossil fuels to renewable biomass residues sourced from sustainably
managed tree planting will substantial y reduce the greenhouse gas emissions from
your boiler system�
Based on Ministry for the Environment figures, emissions from a range of fuels are:
Coal
~100 kg of carbon dioxide equivalent per gigajoule
Gas
54 kg of carbon dioxide equivalent per gigajoule
Fuel oil
91 kg of carbon dioxide equivalent per gigajoule
Biomass
2 kg of carbon dioxide equivalent per gigajoule
Wood fuels are assumed to be largely carbon neutral, with the fuel used in the supply
chain (harvesting and transport) offset by the low emissions of biomass fuels�
Particulate emission control systems can be designed to meet any required emission
limits�
2.8.2  Environmental, social, and economic benefits
There are numerous environmental and social benefits from the instal ation and operation
of biomass boilers� These include the reduction in reliance on fossil fuels, as well as
providing additional renewable energy fuel offerings, thereby contributing to a diversified
fuel market� Biomass boiler systems create value out of what is often a forestry and
sawmil  residue by-product� Using this residue by-product reduces the need for additional
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trees to be planted as fuel supply�
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Biomass fuel and their supply systems provide a variety of regional economic benefits
including in fuel harvesting, processing, delivery, system planning, installation, and
maintenance� With increasing demand for biomass boiler systems, the economic value
of recovering more forestry and sawmill residue grows�
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SNZ PAS 5311:2021
Biomass fuels often come from local fuel suppliers, who provide regional economic
benefits to forestry owners, sawmil s, and delivery channels. Using local wood fuels
also increases the attractiveness of forestry as a land-use option� Local y sourced
fuels reduce the cost of transport and associated greenhouse gas emissions created
by transport of fuels�

Changing the heating system in a school from fossil fuel to biomass provides real-life
learning opportunities about energy and climate change for students and the wider
community� For example, students can be involved in learning about climate change
impacts, school energy audits, researching the properties of different fuels and their
effect on climate change, and identifying changes in school practices to reduce
greenhouse gas emissions and energy use�
Increasing the local knowledge of biomass boiler systems provides a competitive
advantage in a rapidly growing biomass fuel market� This contributes to growing the
innovation potential of a region, through research and development and knowledge
capacity in renewable energy uptake�
While the initial capital cost of new biomass boiler systems may be higher than for some
other technologies, it is important that the comparison of financial costs be taken over
the equipment’s financial lifetime and to include al maintenance and operating costs,
including equipment replacement and future cost of fuel, so that the evaluation of each
option is fair and accurate�
2.8.3 Limitations of biomass boiler systems
Although biomass boiler systems have many benefits, like any system, if not properly
designed, managed, and operated they can have limitations� Biomass boiler systems
require careful design that integrates combustion equipment, fuel reception, storage,
and handling�
The supply chain of local biomass fuel is often more complex than other renewable
energy sources because of the number of parties involved in the supply process (for
example, the supply chain can include landowners, forest owners, forest harvesters,
wood processors, and biomass resource aggregators)� However, using an experienced,
accredited solid biofuel supplier can mitigate the risk of supply failure�
Some biomass boiler system owners express concern over long-term biomass fuel
availability, but like any market, supply increases to meet demand� New Zealand has
large areas of unused biomass resource that could be col ected and processed into fuel�
There are also large areas of marginal land where additional biomass could be grown
when demand increases� Furthermore, over a mil ion tonnes of wood chip and raw logs
are exported from New Zealand monthly, much of which has a value if used as fuel�
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2.9 Scoping and conceptual assessment
When scoping a biomass boiler system, the checklist in 2�11 is recommended� It
summarises critical elements from the previous sections� Developing a new biomass
boiler system requires a site assessment and specialist knowledge� Choosing the right

biomass specialist, someone who has experience, knowledge, or training in operating

biomass boiler systems, and understands their fuel storage requirements and fuel supply,
is an important element in ensuring you can efficiently and cost-effectively manage
your heating requirements� A list of advisors and suppliers can be found on the Wood
Energy website�
2.10 Consenting
Any new biomass boiler system will require resource and building consents as required
by the Resource Management Act 1991� These consents are provided by the regional
and territorial authorities according to the rules set out in the respective regional and
district plans� The rules cover building safety, land use, and discharges to land, water,
and air. It should be noted that while the principles may be similar the specific rules may
differ significantly between each consent authority.
New facility owners (or their agents) are required to make application for consents that
provide for the consenting authority to easily access the application and in particular
identify the likely effects on the environment or people� When issued, a consent may
come with conditions that form part of the consent� These conditions will likely put limits
on the potential effects from the facility� When the facility is operating it is required to
meet these conditions or the consent can be withdrawn and the facility will be unable
to operate�
Applicants for consents for a new biomass boiler system should check with the local
consent authorities on the rules applying to their proposed facility, in the location where
the facility will be built� Early discussion with consenting staff will identify aspects that
must be addressed in the design and operation of the facility� Most consenting staff
want to assist new projects and can provide suggestions on how the facility may meet
any likely conditions�
Successful y and easily obtaining a consent occurs when applicants work with the
consenting authority as ‘partners’ and not ‘adversaries’� Essential y the facility obtains
a social licence to operate from the community in which it is to be located� This will
general y result in a facility operating without complaint or issues being raised by the
community�
Preparing a conceptual plan of the proposed facility and taking this to the consent
authorities near the beginning of a project will reduce risk of unnecessary costs later,
or even not obtaining a consent� The conceptual plan assists consenting staff to see
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what is proposed and provide guidance on how the facility will meet the regional and
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district rules�
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2.11  Checklist for biomass boiler systems
2.11.1  Biomass boiler system selection (see 2.2)
The main points to consider in relation to the selection of a biomass boiler system are:

(a)  Evaluation of existing plant efficiency before purchasing new equipment;

(b)  Determining current and future heat demand and options to improve efficiency;
(c)  Connection to existing or future heat distribution systems;
(d)  The range of system options, including boiler, fuel, and hot water storage;
(e)  Attributes and costs over the economic life of the biomass boiler system�
2.11.2  Fuel checklist (see 2.3, 2.4, 2.5)
The main points to consider in relation to fuel are:
(a)  Fuel selection – determined by type and availability over the life of the plant;
(b)  Fuel quality – moisture, energy, size, and ash content;
(c)  Fuel purchase – contracting agreements;
(d)  Fuel management and storage – delivery, storage, space availability, and
accessibility�
2.11.3  Operations, maintenance, and safety (see 2.7)
The main points to consider in relation to operations, maintenance, and safety are:
(a)  Proper training of operations staff;
(b)  Availability of maintenance and cleaning labour;
(c)  Inspection requirements;
(d)  System reliability, maintainability, spares, and after-sales support�
2.11.4  Consenting (see 2.10)
Local consenting process needs to be engaged with as early as practicable�
2.11.5  Benefits (see 2.8.2)
The main points to consider in relation to the benefits of a biomass boiler system are:
(a)  Reduction in greenhouse gas emissions and particulates;
(b)  Social and environmental benefits;
(c)  Regional benefits;
(d)  Financial benefits.
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2.11.6  Limitations (see 2.8.3)
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The main points to consider in relation to the limitations of a biomass boiler system are:
(a)  The importance of good design for an efficient system;
(b)  The relative complexity of the fuel supply chain�
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link to page 50 SNZ PAS 5311:2021
3  TECHNICAL SPECIFICATION
3.1
General
This section provides more in-depth technical guidance on the components and

specifications of biomass boiler systems. There are a range of documents with more

details in the ‘Referenced documents’ section and in Appendix B�
A biomass boiler system is a renewable energy heat plant specifical y designed to
combust fuels derived from biomass such as wood chip or wood pel ets�
3.2
Biomass fuel
3.2.1  Fuel availability
Fuel availability should be checked with local suppliers� There is a difference between
a potential fuel resource (such as forest harvest residues) and that material being made
available as a fuel� Long-term availability should also be considered as supplies of some
materials will vary over time and possibly by season�
Because biomass-fuel ed heating equipment has a long economic life, it is important
that the owner and operator of the heating equipment has a good understanding of the
fuel supply risks for the lifetime of the equipment� For more information see the Wood
Energy website�
Wood chip, pel ets, and briquettes are likely to be the most common fuel types used in
the size of system covered by this PAS, because of their fuel handling and combustion
attributes�
3.2.2  Fuel type
Biomass fuel is defined by specific characteristics such as particle size and moisture
content. The main fuel types for heating systems covered by this specification, as shown
in Table 1�
Table 1 – Fuel type features for heating systems covered by this specification
Fuel type
Features
Wood chips
Chipped woody biomass in the form of pieces, with a defined particle size produced by
mechanical treatment with disc or drum chippers with sharp knives.
Hog fuel
Fuel wood in pieces of varying size and shape produced by crushing with blunt tools such
as rollers, hammers, or flails.The wood pieces are more splintered as opposed to cut.
Wood pellets
Wood that has been hammer-milled to less than 3 mm particle size and then pelletised
under heat (~100°C) and high pressure to produce a cylindrical wood-derived fuel of
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consistent size. Pellets are typically 6 mm to 8 mm diameter and 8 mm to 15 mm long.
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Compressed
A briquette is made up of small particle-sized wood compressed into medium or large
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fire logs
dimension pieces� Common types of briquettes are fuel logs, charcoal briquettes, and
and briquettes
biomass briquettes� Made from woody biomass and compressed into large dimension
pieces (40 mm to 60 mm diameter and 300 mm long).
Herbaceous
These are lignocellulosic biomass derived fuels sourced from miscanthus, switchgrass,
biomass fuels
other grasses, and straw and may be shredded, pelletised, or baled� These fuels require
specialist expertise to ensure they are effectively stored, handled, and combusted�
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3.2.3  Treated wood (including construction and demolition waste)
Wood that has been chemical y treated with copper chrome arsenate (CCA) is not
suitable for use as a fuel due to potential toxic emissions and ash contamination� Biomass
with high levels of coatings, paints, and glues such as demolition waste will likely be
problematic due to the presence of chemicals in the glues, coatings, and additives in

paints� While some of these materials can be used for fuel under some circumstances (at
high operating temperatures and/or with a long residence time or as a small percentage
of the total fuel), a resource consent is required that specifical y al ows the combustion
of those materials� The amount of the treated or contaminated wood that is al owed as a
proportion of the fuel being fed into the boiler wil be limited and specified in the consent.
Typical y, these materials are only used in larger process heat systems�
3.2.4  Moisture content
Biomass has inherent moisture content� Green wood can be 56% to 58% moisture by
weight, but moisture at this level makes it a low energy content fuel, which requires
higher loads and special y designed plants� Biomass can be air-dried or force-dried
to lower moisture contents (20% to 40%) to improve energy content� At 20% moisture
content biomass fuel is likely to reabsorb some moisture from humidity in the air� Air-dried
wood will have an equilibrium moisture content of 20% to 25% wet basis, depending
on the ambient temperature and humidity. The moisture content affects the net calorific
value of the wood or any other biomass� Dried wood, at 30% moisture content, has a
net calorific value of around 12.5 GJ per tonne (GJ/t), but if harvested at 58% moisture
content it will be reduced to around 6�5 GJ/t� (See Table A1 in Appendix A for energy
content by moisture content�)
An example of moisture content (wet basis) is as fol ows� For fresh radiata pine log, if the
log weighs 960 kg/m3, of this, approximately 400 kg wil  be wood and 560 kg wil  be water�
(
) × 100 = 58�3% moisture content wet basis�
It is important that the moisture content of biomass be below 55% at a minimum�
However, the moisture content required by specific boiler systems or wood fuel standards
is often much lower than this. Densified wood fuels such as pel ets and briquettes
have moisture contents of 8% to 10% (± 2%)� Most small wood chip boiler systems are
designed to run on fuel between 25% and 40% moisture content�
Moisture content of delivered fuel should be checked on a regular basis to ensure that
the required level is maintained� If fuel is below the required level, then the boiler output
wil  reduce and fuel consumption wil  increase�
The contract for purchase of fuel should clearly specify the fuel characteristics, including
moisture content, which the fuel is required to meet� The contract should specify
delivered fuel sampling and testing requirements� Purchasing fuel from an accredited
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solid biofuel supplier will ensure that there is third-party monitoring of the supplier’s
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quality assurance system�
It is also important that all biomass fuels be kept as dry as possible� Biomass fuels should
not be stored outside where they are exposed to rain because water absorbed into the fuel
wil lower its calorific value. This is critical in the case of pel ets and briquettes as these
densified fuels are made of smal compressed particles that disintegrate very quickly if
they get wet� They are also vulnerable to deterioration when exposed to high humidity�
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SNZ PAS 5311:2021
Wet fuels can also cause problems with emissions as they might not completely combust,
leaving particulates to be carried out in the flue gases. Wet fuels can also cause fouling
of the flue.
3.2.5 Particle size distribution

The distribution of particle size around the target size will affect the performance of a
biomass boiler system and its emissions. Too many very fine particles in the fuel can
lead to excessive particulate emissions, while oversize material can cause issues with
fuel feeding� Particulates are very small pieces of ash and unburnt fuel that can exit a
solid fuel boiler in the flue gas stream.
Most biomass boiler systems are designed to run on a fuel with a specified particle size
range� It is important that the particle size of the fuel be matched to the boiler design and
that the fuel does not contain much material outside the specified particle size. A high
amount of fines is likely to cause a high level of particulate emissions, however, this can
be mitigated with an appropriate system design (which may include emissions testing)�
The fuel supply contract should specify the fuel particle size, as agreed to by the boiler
system manufacturer�
3.2.6 Ash
Ash is the non-combustible mineral part of lignocel ulosic biomass� Ash varies with
biomass type� Clean wood has an ash content of 0�2% to 0�4% on a dry basis� Bark has
an inherent ash content of 1% to 2%� Most biomass fuels have ash contents as delivered
slightly higher than the levels inherent in a clean sample due to minor contamination
that can occur at various points through the supply chain� The level of contamination
should be minimal and can be managed by good handling and screening� The ash levels
in wood and bark are lower than most coals burnt in New Zealand, which tend to have
ash contents of 3% to 8% depending on the source mine� Unlike ash from coal, biomass
ash may be used as a soil amendment under certain circumstances�
Ash contents of herbaceous fuels (such as miscanthus and straw) are typical y higher
than that of wood or bark and can be problematic unless the system is well designed
and managed� Many biomass fuels have ash contents higher than the numbers quoted
above, due to contamination during fuel processing and handling.
Fuel handling and storage shall be designed to avoid the introduction of contaminants
such as dirt, stones, and waste materials that contain ash� A higher ash content reduces
the calorific value of the fuel, increases the amount of ash to be disposed of, and,
depending on the nature of the contaminants, can lead to lower ash fusion temperatures
and increased sintering in the boiler, with associated issues due to clinker build-up�
Ash fusion temperatures (particularly the softening temperature) of the proposed fuel
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should be provided to the boiler manufacturer after testing in a laboratory as it will
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influence design and operating parameters.
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3.2.7  Fuel energy density
Fuel energy density is commonly measured by weight, for example in gigajoules per
tonne� However, when it comes to specifying a fuel for the biomass boiler system, it is
important to consider the volumetric energy density (gigajoules per cubic metre)� If the
fuel material is either wetter than it should be or has lower bulk density than it should,

the boiler may not run at its rated output� While some biomass fuels have low volumetric
energy densities, this is not a major issue as long as the boiler is designed to run on
that type of fuel� Volumetric fuel energy density has an important impact on supply and
fuel storage� See Table 2 for a comparison of energy densities and moisture content�
Table 2 – Fuel specifications
Fuel
Moisture content
Basic energy
Conversion from
Volumetric energy
(%)
density (GJ/t)
GJ/t to GJ/m3
density (GJ/m3)
Wood chip
25 to 50
13�6 to 8�2
2�50
5�4 to 3�3
Wood pellets
8 to 10
17�2 to 16�7
1�35
12�7 to 12�4
Hog fuel
25 to 50
13�6 to 8�2
2�80
4�8 to 3�0
Briquettes and
8 to 10
17�2 to 16�7
1�13
15�2 to 14�8
fire logs
Herbaceous fuels
15 to 25
15�6 to 13�5
3�00
5�2 to 4�5
3.2.8  Fuel specification knowledge
It is important that the fuel being used in the biomass boiler system meets the
specifications agreed with the manufacturer. These specifications should be kept in a
place known by all those involved in operating the boiler and ordering fuel to ensure that
correctly specified fuel is ordered and delivered. If there are changes in personnel within
an organisation, this information is an important part of the handover of responsibilities�
A critical step when specifying a fuel is to understand what fuel the biomass boiler
system was designed for� To check the applicable standards for wood fuels, refer to
the Bioenergy Association’s technical guide ‘Solid Biofuel Classification Guidelines’
(Technical Guide 01) available online (see the ‘Referenced documents’ section at the
front of this specification).
3.3
Chip
3.3.1  General
The origin and source of wood chip material varies with the grade of chip� Sources
typically include whole trees, stems, logging residues, and chemically untreated
processed or post-consumer untreated wood residues (for example, old shipping pal ets)�
The measures for chip are:
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(a)  Particle size – target size, and percentage outside of target size, plus minimum
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and maximum size;
(b)  Net calorific value – minimum must be stated (on a mass basis, for example gigajoule
per tonne or megawatt per tonne);
(c)  Ash – limit varies with grade;
(d)  Moisture content – limit varies with grade�
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3.3.2  Bulk density
Bulk density will vary based on the particle size of the chip produced� Underlying
assumptions are that the basic density of wood (based on the resource being largely
softwoods in New Zealand) is around 400 kg/m3, and that 1�0 solid cubic metre of wood
converts to between 2�5 m3 and 3�0 m3 of chip (~2�7 m3 is typical for pulp grade chip)�

Moisture content also affects the bulk density, with dryer material having a lower bulk
density, but with slightly increased energy content on a volume basis�
3.3.3  Elemental composition (trace and mineral elements)
The principal elemental components of dry wood are carbon (50% to 51%), oxygen
(42% to 43%) and hydrogen (~6%)� Other elements are usual y only present in trace
amounts, with ash being mostly silica� For international (ISO) standards for wood fuels,
see Appendix B�
3.4  Hog fuel
Hog fuel is typical y an industrial fuel for larger boiler systems, and has the same measures
as chip (see 3�3), but different limits� Ash contents and elemental component limits are
general y higher than for chip� Suppliers of hog fuel are expected to state the minimum
calorific value and the bulk density.
3.5  Pellets
Wood or biomass pellets have additional measures in their specifications, their
mechanical durability, and the percentage of fines that are allowed� The pellets
themselves can be made in either 6 mm or 8 mm diameters and lengths are expected
to be above 3.15 mm and less than 40 mm. The upper limit on length is to avoid binding
and bridging during feeding�
The net calorific value of a pel et fuel must be above 16.5 GJ/t, with moisture content
of 8% to 10%�
The bulk density of the pel ets is expected to be above 600 kg/m3�
Unlike chip or hog fuel, wood and biomass pel ets are manufactured to specified limits
set out in the ISO standards (see Appendix B)� Manufacturers of pel et fuel have very
stringent quality assurance systems as pel ets are a consistently manufactured fuel with
tight tolerances on the product�
3.6  Briquettes
Briquettes are densified wood or biomass material, typical y in the form of cylinders
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20  mm to 80  mm in diameter and 200  mm to 300  mm in length. They can also be
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produced as pil ow briquettes, although these are less common� Fine material is likely
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to be limited� Briquettes typical y have a high basic energy density (similar to pel ets)
and volumetric density� They have low moisture content (around 6% to 8% wet basis)�
They can be used for boiler fuel, but their most common application is in log fires.
Briquette manufacture is similar to that of wood and biomass pel et manufacture in that
they are a consistently manufactured fuel�
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3.7
Herbaceous fuels
Herbaceous fuels are comprised of materials such as straw, corn stover, and giant
grasses such as miscanthus. New Zealand has a significant straw resource in Canterbury.
Straw has a moisture content at harvest of around 15% and an ash content of 3% to

5%� It can be used as a boiler fuel either as chopped but loose material in bales, or

densified into pel ets. Specialist straw boilers are required for this material as the ash
has a fusion temperature lower than wood� A special design is required to lower the
combustion temperature in order to avoid ash forming clinker�
3.8  Specifying the right fuel
Specifying and using the right fuel for your biomass boiler system maximises the
efficiency and lifetime of your boiler. Boiler systems are general y designed for a specific
type of fuel (typical y pel ets, chip, or briquettes). They do not run as efficiently, if at al ,
on a fuel that they are not designed for. Further, if a fuel is outside of the specification
the boiler was designed for, there wil be a drop in energy conversion efficiency and a
loss in output from the boiler� In extreme cases a boiler can be damaged when run on
an inappropriate fuel�
Typical issues are with:
(a)  Particle size – If there are too many fine particles there may be a loss of energy as
some particles exit the combustion chamber unburnt, contributing to inefficient
use of fuel� Excessive dust can also be an explosion risk and health hazard;
(b)  Ash content – If the ash content is too high then the calorific value of the fuel
is reduced� Minor variations that occur in biomass may not be noticeable or
substantial, but if a fuel is particularly dirty the drop in calorific value and rise in
ash can have a significant effect. The deposition of fly ash on boiler tubes and heat
exchanger surfaces can cause a drop in the conversion of fuel energy into heat
output� It may also mean that more frequent removal of ash is required, with more
frequent shutdowns leading to reduced availability and use of the boiler;
(c)  Ash contamination – Any contaminants causing ash can have a critical effect on
the ash fusion temperature� A lower than normal ash fusion temperature can cause
sintering, slagging, and fouling of the grate and in the combustion system� This
can lead to a partial y blocked grate and flue gas path, and compromised boiler
performance� Contaminants can also lead to an increase in maintenance and repair�
There are laboratories in New Zealand that perform tests on a fuel to determine
its ash content, elemental composition of the ash, and ash fusion temperature� It
is worth getting fuel tested at the start of any fuel supply contract, or if there is a
noticeable change in ash production;
(d)  Moisture content – The fuel specification should refer to a target moisture content
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and acceptable range limits around that target� This will ensure the right moisture
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content fuel is delivered�
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SNZ PAS 5311:2021
3.9  Fuel supply contracts
Contracting for fuel is a critical aspect for any biomass-fuel ed facility, as the availability
and cost of fuel may change over the life of the biomass boiler system�

Fuel should be purchased on a delivered price per gigajoule basis (with reference to

the net calorific value) rather than price per tonne or price per cubic metre because the
weight of the fuel can be increased by higher moisture content, which reduces energy
content� In addition, this price can be impacted by the number and size of deliveries�
The contract for purchase of fuel must set out the important aspects of fuel supply
including escalation of fuel price for contract terms of over one year� A model contract
and other guidance on best practice for the supply and purchase of biomass fuel is
set out in the Bioenergy Association’s technical guide ‘Contracting to deliver quality
solid biofuel to customers’ (Technical Guide 06), available online (see the ‘Referenced
documents’ section at the front of this specification).
3.10  Fuel management and storage
3.10.1  Fuel management and handling
Management and handling of fuel to keep it clean and free of moisture is an important
aspect of efficient operation and will avoid plant stoppages� The design of the
management and handling system should be such that these issues are minimised�
3.10.2  Fuel deliveries
Fuel deliveries need to be planned around the size and loading of the biomass boiler
system, its rate of fuel consumption, and the size of the fuel storage bunker (including
contingency requirements)� These are relatively simple calculations and should be part
of the design process. The ability to deliver a reasonable volume to a specific bunker
needs to be considered, particularly if the plant is in a remote or difficult-to-access
location� That is, can a large tipper truck access it, or does the site require the use of
smal er trucks, or specialist trucks that can auger, blow, or convey fuel into a raised or
otherwise difficult-to-access bunker?
3.10.3  Fuel storage
The storage of solid biomass fuels can be critical to the success of a biomass boiler
system operation. This is particularly so for densified solid fuels such as pel ets and
briquettes� These fuels must be stored in covered, dry, and low humidity (not damp)
environments� Pel ets have no resistance to water exposure (rainfall or puddles) and
will deteriorate in high humidity or damp environments� This deterioration can be either
complete disintegration (water exposure) or reduced resistance to handling or movement
by augering (high humidity exposure)�
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Storage conditions for chip and hog fuel are not so stringent� Individual pieces will not
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disintegrate under wet or humid conditions, but they will absorb water from rainfall or
puddles so should be kept under cover and on a dry floor.
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SNZ PAS 5311:2021
Wet chip or hog fuel in very large piles, or stored in moist circumstances, can provide
conditions suitable for biological activity that may lead to fungal growth, resulting in
degradation of fuel and health risks� It can also lead to pile heating and associated
mass loss�

Any fuel bunkering should ensure that there are no ‘dead’ spots or bridging, so that all

the fuel in the bunker flows cleanly to the boiler feed. It is important for wood chip, but
for wood pel ets it is critical�
Of equal criticality for wood chip is that the fuel store design ensures there are adequate
means to periodical y agitate the chip in the store to break or prevent bridging�
3.10.4 Space requirements
The space required to store the fuel will depend on the type of fuel, its volumetric energy
density and whether the fuel is to be delivered in small or large quantities� The likely
daily consumption of fuel should be calculated� This can be converted into a volume of
fuel� Then delivery options should be considered�
Some indicative figures for fuel densities are given in Table 3.
Table 3 – Indicative fuel densities
Fuel type
Bulk density; t/m3
Moisture content;
Volumetric energy
wet basis percentage
density GJ/m3
Green chip
0�32
50
2�63
Dry chip
0�21
25
2�87
Green hog
0�30
50
2�44
Dry hog
0�20
25
2�67
Wood pellets
0�65
8
11�0
3.10.5 Fuel verification
Once a facility is operational, it is essential that a method of fuel verification is established
by the facility operator� The methodology should include receiving documentation from
the supplier that includes reports on testing the supplier has completed to confirm that
the fuel supplied fits the fuel contract specification.
As moisture content is the most critical fuel characteristic affecting fuel cost and plant
performance, the facility owner shall also undertake their own simple checking of the
moisture content of fuel as delivered� This check would normal y be done with a bin
meter (backed up by regular in depth checking)�
Guidance on methods for verification of delivered fuel is set out in in the Bioenergy
Association’s technical guide ‘Standard methods for verifying the quality of solid biofuels’
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(Technical Guide 05)�
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3.11  Equipment selection
3.11.1  Biomass boiler systems
Biomass fuels burn in quite a different way to many coal fuels, and in three different
(overlapping) stages:

(a)  Firstly, moisture is driven off (for a high-moisture fuel, this step is very important
and may require specific boiler design features);
(b)  As the particles are dried, combustible volatiles are progressively driven off, so
need to be wel -mixed with correct proportions of over-fire air for good combustion.
Failure to design this aspect correctly will lead to the deposit of tars and other
volatiles on gas-side boiler surfaces;
(c)  Final y, carbon is burned out, primarily relying on under-fire air, and residual ash
is discharged down through or off the grate�
Wood chip, depending upon its delivered moisture content wil first absorb a certain
amount of energy from the combustion process in drying� Coal will also do this, but
general y to a lesser extent, depending upon the particular coal type�
When combustion starts, coals require more air supplied beneath the fuel bed to initiate
combustion, drive off the volatiles, and complete the combustion of the carbon fraction
of the fuel, and relatively less air supplied into the space immediately above the fuel
bed to complete the combustion of the volatiles� Due to the high amount of volatiles in
biomass fuels, biomass boiler systems typical y require larger furnaces and less heat
absorption near the combustion zone�
With wood fuels, the proportions are reversed, with relatively less air supplied beneath
the fuel bed and more supplied into the space above the bed�
3.11.2  Biomass combustors
Biomass combustors require specialised design (which is the responsibility of boiler
suppliers) and can be general y characterised as:
(a)  Pile burners – Biomass is either dropped onto a pile or fed vertical y upwards into
a pile;
(b)  Inclined grates (static, vibrating, or reciprocating grates, with or without water
cooling) – Biomass is fed onto the top of an inclined grate and moves down the
grate as it burns� If refractory surfaces are arranged above these grates, they are
capable of handling high-moisture-content fuel;
(c)  Horizontal grates (moving chain grates, ’vibrating‘ or ’dumping‘ grates) – Biomass
is distributed by a feeder so that a relatively thin, even layer is maintained across
the grate� This type of combustor is suitable for larger capacity units;
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(d)  Fluidised bed – Biomass is fed into a shal ow bed of inert material that is fluidised by
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a control ed upwards air flow. This type has somewhat higher parasitic energy use
(that is, power used when on standby) than other types, but is more tolerant of fuel
specification changes. This type of combustor is suitable for larger capacity units.
This list is not exhaustive, some manufacturers have wel -developed proprietary designs� The
plant specifier wil need to consider track record and ongoing service and spares support
– as wel as the capability to use the identified fuel – when selecting a combustor type.
26
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link to page 13 SNZ PAS 5311:2021
3.11.3  Biomass boiler system construction type.
Noting the exceptions (see 1�1�2), several types of boiler commonly fall within the scope
of this specification. Noting the fol owing:
(a)  One such system is the sectional hot water heater, which contains modular heating

sections (for hot water) that enclose the combustion chamber, and contains ash

removal systems;
(b)  Some biomass boiler system designs have the combustion chamber incorporated
within an enclosure formed by heat transfer surfaces;
(c)  Often, a separate refractory-lined combustion chamber is used, and flue gases
are passed into the heat transfer portion of the boiler�
3.11.4  Boiler selection:
Factors to be established prior to boiler selection are:
(a)  The boiler’s capability to burn the selected type of fuel� Note that boilers are
general y designed to only burn fuel that is within a certain specification band
(which may not be a wide band);
(b)  The detailed and signed-off heat demand profile;
(c)  The fuel type and specification;
(d)  The high-level system design;
(e)  Compliance with relevant New Zealand safety regulations�
3.11.5  Technical factors in boiler selection
Technical factors to be established prior to boiler selection are:
(a)  Any highly project specific requirements (for example, site prohibitions on storage
of particular chemicals, particularly stringent specifications regarding dust, noise,
and vehicle movements);
(b)  Boiler attendance level required;
(c)  Boiler turndown and response times;
(d)  Number of start-ups and shutdowns;
(e)  Security of fuel supply specific to the boiler;
(f)
Local availability of skil ed operators for particular boiler types;
(g)  Local availability of service and repair facilities;
(h)  Flue gas clean-up requirement to achieve required air emission standards;
(i)
Availability of automated cleaning systems;
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(j)
Compatibility of control systems with other client systems�
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A guide to the technical aspects to be considered when developing a biomass boiler
system is provided in ‘Consultant/specifier practice paper for wood fuel industrial and
commercial heating systems’ (Bioenergy Association Technical Guide 10), available
online (see the ‘Referenced documents’ section at the front of this specification).
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SNZ PAS 5311:2021
3.12  Capacity ratings
3.12.1  General
Biomass boiler system capacity rating is commonly specified in terms of thermal output
(for example, ‘2 MW’). However, more detailed definitions of output should be used in

the design process� The consultant should note that smal er package boilers may only
be available in nominated capacities, whereas larger designs are adjusted for specific
output requirements. Turndown ratio should be specified and sufficient to meet the
overall heat demand�
Refer to Bioenergy Association Technical Guide 10�
3.12.2  Heat demand
The magnitude and characteristics of the proposed heat demand must be defined in
detail as an authoritative basis for the design or selection of the biomass fuel ed system�
Failure to accurately clarify the patterns and quanta of heat demand is one of the more
common causes of biomass boiler system project problems�
If the existing system is poorly maintained or has obvious inefficiencies, such as poorly
insulated pipework, leaking valves, or inadequate fan and vent controls, these should be
corrected before heat demand is assessed� Failure to correct pre-existing faults will waste
time and may result in an oversized heat-generating system and ongoing economic loss�
3.12.3  Existing design revision
Careful consideration should also be given to the possibility of revising the design,
configuration, and operation of the existing system. It may be possible to reduce the
size of a new boiler (or even avoid the need for one) if significant energy savings can
be made at the site�
When converting an existing boiler, or fitting a new boiler to an existing system, the
existing controls are likely to be inadequate and obsolete� Consideration of effective
‘zoning’ in systems to ensure that heat is only supplied to those areas which require it,
when they require, is important� The combination of effective zoning and control can
often have a significant impact on the sizing of a biomass boiler system.
3.12.4  Energy audit
Once maintenance and system improvements are complete, an energy audit of the
existing plant should be carried out, preferably to the requirements of the latest edition
of AS/NZS 3598�2�
In a situation where heat load does not currently exist (that is, a new plant is planned), an
energy audit is impossible� However, future heat demand must be characterised careful y
and at the same level of scope and detail as for an existing heat load� This is likely to
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be done by using data from the designers of the new plant, or from the performance
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of a similar plant instal ed elsewhere� Suitable margins of tolerance should be applied�
3.12.5  Proposals
Proposals (including scope, timing, and contingencies) for business expansion, change,
or retraction should have been established in the course of preparing the ‘basis of design’
documents. System design and plant selection is difficult when business changes are
28
COPYRIGHT © Standards New Zealand

SNZ PAS 5311:2021
likely� A boiler selected for a future major load may not be capable of stable operation
at a current load, and it may not be economic to specify a boiler plant for current load if
the business intends to expand by 100% in the next few years (or, conversely, if it intends
to downsize or move away from existing markets)� Contingency options may also be
required, in the event that planned changes to business do not materialise�

Changes to existing systems that ‘smooth’ heat demand should also be considered�
Such options may be significantly less costly than design and selection of a system for
very ‘peaky’ heat demand� Options could include the continued or part operation of an
older existing boiler system for peak loads, and the use of various energy storage options�
Following investigation of the above issues, an ‘agreed heat demand’ description should
be drawn up� This document should address:
(a)  Absolute maximum project heat demand;
NOTE – If this demand only occurs over short periods or infrequently, then plant design
options might al ow this to be met without incurring the cost of an oversized boiler�
(b)  The detailed pattern of demand (calculated hourly and adjusted weekly, seasonal y,
and during peak demand)� Variability of the heat demand will be a key consideration
in the selection of the boiler and related equipment;
(c)  Business expansion provisions� Any heat project should include a careful
consideration of likely future changes, such as:
(i)
Expansions or contractions of the plant
(i )  Likely adoption of new processing technologies
(iii)  The retirement of a plant that will reach end of life;
(d)  Specific issues that wil affect plant design, for example the number of start-ups
and shutdowns and the possibility of periodic significant reduction in temperature
of returning circulating water;
(e)  Appropriate margins of uncertainty, based upon the quality of data available�
Refer to Bioenergy Association Technical Guide 10�
3.12.6  Energy efficiency aspects of biomass boiler systems
The efficiency of a biomass boiler system is based on its ability to convert the net
calorific value in the fuel into energy in the form of heat. Modern wel -designed and
specified biomass boilers should have a net efficiency of greater than 85% at ful load.
This efficiency may be reduced by the use of an off-specification fuel, or poor tuning of
the boiler system. Different biomass boiler system designs have different efficiencies,
and some are designed to use particular fuels�
3.12.7  Inclusion of energy storage tanks
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and economic efficiency of the system. If a site has a fluctuating demand over a 24-hour
period, and a temperature difference between flow and return temperature of at least
30˚C, a correctly designed energy storage tank can al ow a smal er biomass boiler system
to operate at higher loads more continuously, at high efficiency, and not waste heat by
being in turndown mode for long periods� The heat generated outside of the peak load
time is stored in the tank and used when it is required� This issue needs careful analysis
to determine its merits for a specific site.
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SNZ PAS 5311:2021
3.12.8  Combustion efficiency
Combustion efficiency can be affected by a number of issues, including changes in
fuel quality. Combustion efficiency can be checked by testing the flue gas composition.
An excessive level of carbon monoxide (CO) in the flue gas (> 2000 mg/m3) indicates

incomplete combustion� Tuning of the boiler to reduce CO emissions can be done by

adjusting under and over-fire air inputs.
3.13  Operation, maintenance, and safety
3.13.1  Operation
The biomass boiler system should be operated as per the manufacturer’s manual and
instructions� Making alterations to these operating parameters can lead to unsafe
equipment operation, excess fuel consumption, boiler fouling, high emissions, and
damage to the boiler in extreme cases�
3.13.2  Maintenance and cleaning
It is recommended that the system design includes flue gas clean-up to reduce particulate
emissions� Options include baghouse, and electrostatic precipitators� Cyclone separators
are often fitted to boilers. However, these have a lower efficiency than the other options.
If the system has filters instal ed, these should be kept clean in order to function
effectively. Cleaning fuel dust out of the storage area is also important to avoid fires
and explosions�
Good system design, and matching of the fuel type to that design, can al ow applications
as covered by this specification to avoid the need for expensive flue gas clean-up
equipment to be instal ed�
3.13.3  Site inspection
It is recommended that biomass boiler systems be inspected regularly according to the
equipment manufacturer’s, or the system designer’s, instructions� These inspections
should include a review of:
(a)  Erosion of fuel feed components;
(b)  Missing parts;
(c)  Corrosion;
(d)  Adhesive deposits;
(e)  Non-combustible rubbish;
(f)
Tar deposits;
(g)  Water deposits;
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(h)  Water leaks;
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(i)
Water ingress to insulation;
(j)
Functionality of backfire protection and sprinkler systems;
(k)  Functionality of automatic cleaning systems;
(l)
Functionality of important instruments and probes (such as the lambda probe)�
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SNZ PAS 5311:2021
3.13.4  Safety and training
For a biomass boiler system, safety considerations shall be made during design,
construction, operation, and end of life of the system� These include:
(a)  Consideration around safety during construction and operation stages of the

biomass boiler system;

(b)  The safety of personnel operating the biomass boiler system (including access to
the equipment);
(c)  Providing training to operation and maintenance personnel�
3.14  Consenting, financial life cycle, and environmental and
social assessment
3.14.1   Scoping and conceptual assessment
The choice of biomass boiler system type will be largely dictated by the preferred fuel
type and the heating application�
Overall biomass boiler system design is an important consideration� For a new boiler
instal ation, the heating demand of the site should be assessed holistical y rather than
simply trying to meet the heat demand of the old boiler� Biomass-based heating is often
the least expensive method of heating, so as much space and water heating as possible
should be included in the new instal ation� This can require an upgrade of the piping
network but such an upgrade wil provide long-term benefits.
The possibility of future changes in the site should also be taken into account when
assessing heat demand� For example, if the heat network might be extended in the future,
the boiler should be sized with this in mind� In addition, the inclusion of energy storage
tanks can enable a smal er biomass boiler system than the old one, as discussed above�
Fuel storage and site access are also important considerations in biomass boiler system
design� The size of the fuel storage dictates the frequency of fuel delivery, and easy
access to a fuel bunker can significantly reduce costs of fuel delivery.
When scoping a potential commercial biomass boiler system it is important, at the start
of a project, that a term sheet be prepared on the proposal so that every party has a
clear understanding of what the project is to achieve and the range of options al owed�
A clear project scope avoids key aspects being missed and decisions being locked in
without due evaluation of the options�
3.14.2  Consenting
As part of investigating the feasibility of a new biomass boiler system, a check sheet
should be prepared for all the required consents and permits that will be necessary for
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the system to be instal ed and operated� Details of likely consent conditions should be
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obtained as these will provide boundary conditions in which the facility will be al owed
to be constructed and operated�
A project plan should be prepared setting out who is responsible for obtaining the
necessary consents� In many situations the equipment supplier is providing a turnkey
solution and is often best placed to obtain the necessary consents, acting in the capacity
as agent to the system owner, because they understand the performance characteristics
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SNZ PAS 5311:2021
of their equipment and fuels and under specific conditions. The owner is required to
obtain consent, while the equipment supplier contracts to supply equipment which
meets consent limits� For larger systems, the primary site contractor may undertake
these responsibilities�

Clarity of the responsibility of each party is critical to mitigate the risk of future issues�

Issues that are likely to be part of a resource consent process are:
(a)  Flue emissions – Particulates and smel ;
(b)  Deliveries – Timing, type and number of vehicle movements;
(c)  Noise;
(d)  Greenhouse gas emissions�
Building consents will also be required relating to:
(e)  Building structural performance;
(f)
Fire safety systems;
(g)  Safety of operators;
(h)  Safe movement of people�
More information can be found by contacting the appropriate regional council for resource
consents and the local territorial authority for building consents�
3.14.3  Fuel costs
The overal long-term financial implications of a choice around biomass boiler systems
and fuels needs to be considered� What looks inexpensive today (a low capital cost,
low fuel cost coal boiler) might not be cheaper in the long run as maintenance costs
can be high, and ash disposal costs and the cost of carbon emissions associated with
fossil fuel combustion could increase over time� Careful examination of these costs is
necessary to ensure that the best decision around the long-term costs of the system,
and the fuel chosen, are optimised for the site� Gas boilers typical y have a low capital
cost and take up comparatively very little space, but the cost of gas is expected to rise
(unrelated to the cost of carbon) as supply constraints occur over the next 10 to 20 years�
The cost of carbon and its trajectory also needs to be considered�
Decisions on the fuel type chosen should be clearly recorded and posted in the boiler
building to assist future operators� The most common problem relating to future operation
of wel -designed and constructed biomass boiler systems arise when future facility
operators change to a different fuel from what the system was designed for because of
the then-cost of the original y specified fuel.
3.14.4  Tendering
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Tender requests should include all ancil ary equipment and services necessary for the
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facility to be successful y operated and maintained for the assumed economic life� This
includes fuel reception, handling, and storage�
A summary, including diagrams and photos of the site showing fuel reception, handling,
and storage areas should be provided so that when tenders are received all parties have
good information on which to base a tender�
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SNZ PAS 5311:2021
The request should seek information and data that shows that tendered equipment is
suitable for the fuels likely to be available for the assumed economic life of the facility�
Available monitored performance data of the proposed equipment and fuel used in other
similar facilities should be requested� This should include fuel consumption, operating

characteristics, and heat outputs�

References to other similar facilities with the same equipment and fuel type should be
sought�
Information should be sought that outlines why the equipment and fuel is proposed,
with comparisons to alternative solid biofuel options provided�
3.14.5 Financial lifecycle
A ful financial life-cycle assessment of the proposed project should be undertaken,
including assessment of the tangible and intangible costs and benefits over the economic
life of the project� Guidance on how this should be done is set out in the Bioenergy
Association guide ‘Best practice guideline for life cycle analysis of heat plant projects’
(Technical Guide 14), available online (see the ‘Referenced documents’ section at the
front of this specification).
To determine the cost-effectiveness of biomass boiler systems compared to other boilers
or other types of energy solutions, it is recommended to undertake a financial life-cycle
analysis of the boiler. A financial life-cycle analysis determines the cost-effective option,
which includes the cost of use� AS/NZS 4536 provides a good overview of the principles
for life-cycle costing�
To compare the cost of running different technologies or to make a decision around
replacement of a new technology, apply the levelised cost of energy (LCOE) metric
for guidance on the average net present cost of energy production over the assumed
lifetime. LCOE also provides guidance on whether the project wil be profitable, cover
cost, or be unprofitable.
LCOE can be derived by using the net present value (NPV) of the total plant and operation
cost (including initial cost of investment, maintenance, operations, and fuel) divided by
energy production over the assumed lifetime� LCOE al ows the comparison of different
technologies (for example, wind, solar, natural gas) of unequal life spans, project size,
different capital cost, risk, return, and capacities as well as comparison to replacement
cost with new technologies� LCOE is critical to making an informed decision to proceed
with development of a facility, community, or commercial-scale energy project�
NOTE – All options should be evaluated for operation over the same period, that is, number of
years. Where a technology might need significant equipment replacement to achieve that economic
life such expenses should be included in the assumptions�
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A financial example comparison is set out in Table 4.
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link to page 28 SNZ PAS 5311:2021
Table 4 – Financial example comparison
Reticulated gas hot water
Electric hot water
Biomass hot water
Capital cost ($M)
1�0
0�5
2�0
Financial life
15 years
15 years
15 years

Capital cost
106,667
53,333
213,333

($ per annum)
Operating, repair, and
100,000
5,000
200,000
maintenance cost
($ per annum)
Output (MWh)
5000
5000
5000
Fuel cost ($/MWh)
50
170
40
Fuel ($ per annum)
250,000
850,000
200,000
Levelised energy cost
91
184
123a
($/MWh)
a
Includes residual value�
It is recommended to integrate risk analysis into your evaluation� Scenario analysis
incorporates different risks, including finance, technological, fuel, operational, and
economic risks� This informs the management of risks, which can be included in different
scenarios over the financial lifetime of the boiler. Ancil ary electricity costs should be
included in the operating cost calculation�
3.14.6  Environmental and social assessment
The operation of a heating facility is no different from many other similar manufacturing
operations where the activity has to exist and operate in harmony with the neighbouring
community� Environmental and social impacts assessment and consideration are integral
to the successful operation of a biomass boiler system� These include consideration of
the effects of discharge of emissions to land, water, and air, greenhouse gas emissions,
noise, smel s, traffic, and general environment and biodiversity impacts.
To obtain a consent to install and operate a biomass boiler system there are a range
of requirements to adhere to, which include discharges to land, air, and water, covered
under the regional plan; and noise and traffic, covered under the district plan. These
can be obtained from your regional council (see the page ‘An everyday guide: Applying
for a resource consent’ on the Ministry for the Environment website), or your territorial
authority�
As set out in 2�10, it is recommended that requirements for a consent are investigated
early in the facility development process� This should also establish whether ongoing
monitoring may be stipulated as a condition of your consent�
An environmental impact report might be required for larger projects� Environmental
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Environmental impact should consider the travel distance of fuel, even though this is
likely to change over the economic life of the facility� Local or carbon-neutral wood-fuel
suppliers should be utilised where possible�
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SNZ PAS 5311:2021
To reduce climate change impacts, mitigation of greenhouse gas emissions may be
available� Biomass boiler systems are considered carbon neutral during their operation
(see the Scion info sheet ‘Energy from wood is good for New Zealand and the climate’,
available online)�

For more information on how to assess the carbon neutrality of your biomass boiler

system operation, see the page ‘Measuring, reporting and offsetting greenhouse gas
emissions’ on the Ministry for the Environment website�
Consideration should be given to the likelihood that the project wil be affected by
increasing climate change impacts such as flooding and inundation. This information
can be provided by your council�
Social impacts of projects should be considered during construction and operation�
Adverse social impacts can include traffic noise traffic affecting neighbours.
It is too late if social impacts are considered during construction� Possible social impacts
should be identified and addressed prior to the project being made public. Opposition
from neighbours and others is probably the second biggest risk (after fuel supply) that
will stop a project proceeding� Best practice is that engagement with neighbours and
providing good information on possible effects should be addressed at the start of a
project�
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35

Appendix
SNZ PAS 5311:2021
APPENDIX A – WOOD FUEL VALUE BY MOISTURE CONTENT
(Informative)
The net calorific value is determined by the fol owing equation:

𝑤𝑤
𝑤𝑤
ℎ
𝑤𝑤

NCV = GCV �1 − 100� − 2.447100 − 2.4471009.01�1 − 100�
Where:
NCV = net calorific value in MJ/kg fuel (wet basis)
GCV = gross calorific value in MJ/kg fuel (dry basis)
w = water content of fuel as percentage of weight
h = concentration of hydrogen as percentage of weight (dry basis)�
The first term simply converts the gross calorific value to the wet basis. The second term
is due to the latent heat of vaporisation of the water contained in the wood. The specific
latent heat of vaporisation of water at 25°C and constant pressure is 2�447 MJ/kg� The
third term is due to the vaporisation of the water produced when the hydrogen in the
wood is combusted� The concentration of hydrogen in woody biomass is typical y about
6% (dry basis)�
Table A1 itemises the net calorific value (NCV) for wood fuel by moisture content.
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SNZ PAS 5311:2021
Table A1 – Indicative moisture content and energy
Moisture content;
GCV;
NCV;
Moisture content;
GCV;
NCV;
% wet basis
GJ/t
GJ/t
% wet basis
GJ/t
GJ/t
1
19�99
18�66
36
12�92
11�20

2
19�79
18�45
37
12�72
10�99

3
19�59
18�24
38
12�51
10�77
4
19�39
18�02
39
12�31
10�56
5
19�18
17�81
40
12�11
10�35
6
18�98
17�60
41
11�91
10�13
7
18�78
17�38
42
11�71
9�92
8
18�58
17�17
43
11�50
9�71
9
18�37
16�96
44
11�30
9�49
10
18�17
16�74
45
11�10
9�28
11
17�97
16�53
46
10�90
9�07
12
17�77
16�32
47
10�70
8�85
13
17�57
16�11
48
10�49
8�64
14
17�36
15�89
49
10�29
8�43
15
17�16
15�68
50
10�09
8�22
16
16�96
15�47
51
9�89
8�00
17
16�76
15�25
52
9�69
7�79
18
16�56
15�04
53
9�48
7�58
19
16�35
14�83
54
9�28
7�36
20
16�15
14�61
55
9�08
7�15
21
15�95
14�40
56
8�88
6�94
22
15�75
14�19
57
8�67
6�72
23
15�55
13�97
58
8�47
6�51
24
15�34
13�76
59
8�27
6�30
25
15�14
13�55
60
8�07
6�08
26
14�94
13�33
61
7�87
5�87
27
14�74
13�12
62
7�66
5�66
28
14�54
12�91
63
7�46
5�44
29
14�33
12�69
64
7�26
5�23
30
14�13
12�48
65
7�06
5�02
31
13�93
12�27
66
6�86
4�80
32
13�73
12�05
67
6�65
4�59
33
13�52
11�84
68
6�45
4�38
34
13�32
11�63
69
6�25
4�16
35
13�12
11�41
70
6�05
3�95
NOTE –
Copyright in SNZ PAS 5311 is Crown copyright, administered by the New Zealand Standards Executive. Access to this standard has been sponsored by the Energy
(1)
Moisture content wet basis = (total weight − dry weight) / total weight
Efficiency and Conservation Authority under copyright license LN001390. You are permitted to view and print this standard free of charge (subject to printing costs) for your
unless your actions are covered by Part 3 of the Copyright Act 1994. For queries about copyright, please contact Standards New Zealand at [email address]
own use. You are not permitted to reproduce any part of it without prior written permission from Standards New Zealand, on behalf of the New Zealand Standards Executive,
Copyright Standards New Zealand
(2)
Moisture content dry basis = (total weight − dry weight) / dry weight
COPYRIGHT © Standards New Zealand
37

SNZ PAS 5311:2021
APPENDIX B – OTHER RESOURCES
(Informative)
B1
International fuel standards

The fol owing international biofuel standards provide a thorough specification of the
solid biofuels field. These standards cover international y accepted specifications for
a wide range of possible wood and biomass fuels� These standards can be used as a
guide to setting the specifications for the boiler fuel.
ISO 17225:----
Solid biofuels – fuel specifications and classes

Part 1:2014
General requirements

Part 2:2014
Graded wood pel ets

Part 3:2014
Graded wood briquettes

Part 4:2014
Graded wood chips

Part 5:2014
Graded firewood

Part 6:2014
Graded non-woody pel ets

Part 7:2014
Graded non-woody briquettes (new draft standard 2020)

Part 8:2016.
Graded thermal y treated and densified biomass fuels

Part 9:2020
Graded wood hog fuel and wood chips for industrial use
ISO 17831:----
Solid biofuels – Determination of mechanical durability of
pel ets and briquettes

Part 1:2015
Pel ets

Part 2:2015
Briquettes
ISO 17827:----
Solid biofuels – Determination of particle size distribution
for uncompressed fuels

Part 1:2016
Oscil ating screen method using sieves with apertures of
3�15mm and above

Part 2:2016
Oscil ating screen method using sieves with apertures of
3�15mm and below
B2
National guidance
The following regulations and standards set out national guidance on biomass boiler
systems in New Zealand�
Health and Safety in Employment (Pressure Equipment, Cranes, and Passenger
Ropeways) Regulations 1999� https://www�worksafe�govt�nz/dmsdocument/419-health-
Copyright in SNZ PAS 5311 is Crown copyright, administered by the New Zealand Standards Executive. Access to this standard has been sponsored by the Energy
and-safety-in-employment-pressure-equipment-cranes-and-passenger-ropeways-
Efficiency and Conservation Authority under copyright license LN001390. You are permitted to view and print this standard free of charge (subject to printing costs) for your
unless your actions are covered by Part 3 of the Copyright Act 1994. For queries about copyright, please contact Standards New Zealand at [email address]
own use. You are not permitted to reproduce any part of it without prior written permission from Standards New Zealand, on behalf of the New Zealand Standards Executive,
Copyright Standards New Zealand
regulations-1999
AS/NZS 1170:----
Structural design actions

Part 2:2011
Wind actions
NZS 1170:----
Structural design actions

Part 5:2004
Earthquake actions – New Zealand
38
COPYRIGHT © Standards New Zealand

SNZ PAS 5311:2021
B3
Publications and websites
The fol owing websites and the publications available from them have more information
on biomass boiler systems, their fuel, and related considerations� They are additional to
the publications referred to in this specification, which can be found in the ‘Referenced

documents’ section at the front�

Wood Energy� Wood Energy Knowledge Centre� Available at https://www�usewoodfuel�
org�nz/wood-energy-knowledge-centre (accessed 27 November 2020)�
Bioenergy Association� Bioenergy Knowledge Centre� Available at https://www�
bioenergy�org�nz/bioenergy-knowledge-centre (accessed 27 November 2020)�
Forest Research� Publications on woodfuel� 2009� Available at https://www�forestresearch�
gov�uk/research/publications-on-woodfuel/ (accessed 27 November 2020)�
Copyright in SNZ PAS 5311 is Crown copyright, administered by the New Zealand Standards Executive. Access to this standard has been sponsored by the Energy
Efficiency and Conservation Authority under copyright license LN001390. You are permitted to view and print this standard free of charge (subject to printing costs) for your
unless your actions are covered by Part 3 of the Copyright Act 1994. For queries about copyright, please contact Standards New Zealand at [email address]
own use. You are not permitted to reproduce any part of it without prior written permission from Standards New Zealand, on behalf of the New Zealand Standards Executive,
Copyright Standards New Zealand
COPYRIGHT © Standards New Zealand
39

NOTES

Copyright in SNZ PAS 5311 is Crown copyright, administered by the New Zealand Standards Executive. Access to this standard has been sponsored by the Energy
Efficiency and Conservation Authority under copyright license LN001390. You are permitted to view and print this standard free of charge (subject to printing costs) for your
unless your actions are covered by Part 3 of the Copyright Act 1994. For queries about copyright, please contact Standards New Zealand at [email address]
own use. You are not permitted to reproduce any part of it without prior written permission from Standards New Zealand, on behalf of the New Zealand Standards Executive,
Copyright Standards New Zealand

SNZ PAS 5311:2021

© 2021 CROWN COPYRIGHT ADMINISTERED BY THE NEW ZEALAND
STANDARDS EXECUTIVE
Approved by the New Zealand Standards Executive on 3 March 2021 to be
Copyright in SNZ PAS 5311 is Crown copyright, administered by the New Zealand Standards Executive. Access to this standard has been sponsored by the Energy
a Standards New Zealand publicly available specification.
Efficiency and Conservation Authority under copyright license LN001390. You are permitted to view and print this standard free of charge (subject to printing costs) for your
unless your actions are covered by Part 3 of the Copyright Act 1994. For queries about copyright, please contact Standards New Zealand at [email address]
own use. You are not permitted to reproduce any part of it without prior written permission from Standards New Zealand, on behalf of the New Zealand Standards Executive,
Copyright Standards New Zealand
First published: 8 March 2021
The following references relate to this standard:
Project No. P5311
Draft for comment No. DZ PAS 5311
Typeset by: Standards New Zealand

Document Outline