Laurie Gibbons Energy Reduction Predictions.pdf

Heat Pump Domestic Hot Water
Energy Consumption Prediction Report
- Summary
22-038 Weymouth Rugby Football Club at Laurie Gibbons
Memorial Park

Date: 23/03/2023

1. Summary
This  energy  consumption  analysis  was  conducted  for  the  proposed  DHW  system  for  the
Weymouth  RFC  at  Laurie  Gibbons  Memorial  Park.  The  analysis  considered  the  following
scenarios:
•  GAME days in warmer months
•  GAME days in colder months
•  PRACTICE/OTHER days in warmer months
•  PRACTICE/OTHER days in colder months
These scenarios covered the differences in heat pump heating efficiency due to the weather,
and  the  different  usage  patterns  at  Weymouth  FRC.  The  energy  analysis  considered  the
heating energy required by shower usage, standing heat losses, and disinfection. The analysis
also  applied  conservative  assumptions  and  realistic  usage  patterns  to  minimise  the
uncertainties in the final results.
Overall, the annual DHW energy estimates produced the following results:
•  Heating energy required: 24,793 kWh
•  Electricity consumption: 10,353 kWh
•  Heating efficiency: 2.39
•  Running cost: 1,984 NZD
•  Emissions: 1242 kgCO2e
The comparison to a gas DHW heating system yields the following results:
•  Estimated gas energy required: 29,169 kWh
•  Estimated gas running cost: 2,526 NZD
•  Estimated gas emissions: 5,688 kgCO2e
•  Electricity cost reduction: 21.4%
•  Electricity emissions reduction: 78.1%
Thus, the conservative annual energy estimates indicate that the new heat pump DHW system
achieves approximately  21.4%  lower  operating cost, and 78.1% lower  carbon emissions. In
addition, the cost of electricity is projected to fall over the lifecycle of the system, thereby further
decreasing its’ operating cost. Most importantly, the new system will help Auckland Council to
achieve the emissions goal.

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Page 1

2. Introduction
This report summarises the energy consumption predictions for the Performance Plus Heat
Pump Domestic Hot Water (DHW) system for the Weymouth Rugby and Football Club (RFC)
at  the  Laurie  Gibbons  Memorial  Park.  This  summary  report  provides  the  estimated  annual
energy consumption and carbon emissions of the heat pump DHW system. The system is also
compared to a gas DHW system.
The Weymouth RFC heat pump DHW system has two hot water cylinders (HWC) with a total
storage capacity of 1600L. The HWCs are heated with 2 Performance Plus 7GD10E-1 heat
pumps, one 6kW electric element, and two 3 kW electric elements. One 3 kW electric element
is  also  added for  backup,  but  it  is  not  in  use  normally.  The  energy  analysis  was  conducted
based on the operations of this system.
2.1. Domestic Hot Water Production
The 2 heat pumps heat cold water from the incoming feedwater temperature (from 5 to 25°C)
up to 60°C. The heat pump will also heat the tanks to account for residual losses in the system.
To assist the heat pumps during high-demand game days, and if either of the two heat pumps
fails, four electric elements are provided and described below:
•
EL1 is a 6kW element located at the top of Tank A. This runs only on game day to heat
water from 60 to 65°C to reduce water draw-off with peak loading. Outside of game day, it runs
only for the disinfection cycle, which is for a maximum of two hours per week, or when a heat
pump fails.
•
EL2 is a 3kW element located at the bottom of Tank A. This runs when there is less
than  600L  of  hot  water  available.  In  practice,  based  on  modelling,  this  element  would  only
come on for the disinfection cycle and a heat pump failure.
•
EL3 is a 3kW element located at the top of Tank B. This runs when there is less than
1000L  of  hot  water  available.  In  practice,  based on  modelling, this  element  would  come  on
during the game day. It will also turn on for the disinfection cycle or a heat pump failure.
•
EL4 is a 3kW element located at the bottom of Tank B. This only runs when there is a
failure of a heat pump and for the disinfection cycle.
The  disinfection  cycle  only  runs  for  2  hours  a  week  to  maintain  the  DHW tank  at  60  °C  as
required by Building Code G12. This is sufficient to kill all bacteria in the pressurised HWCs.
Refer to the Design Package for more details.

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3. Analysis Methodology
The  energy  consumption  analysis  was  conducted  using  a  conservative  approach  and
considered  multiple  scenarios.  Generally,  the  energy  consumption  analysis  was  conducted
considering the following factors:
1)  The energy consumed to heat the DHW for showers.
2)  The energy consumed due to heat losses.
3)  The energy consumed due to disinfection.
To determine the energy consumed to heat the DHW for showers, four types of operations
are considered:
1)  GAME Day in warmer months
2)  GAME Day in colder months
3)  PRACTICE/OTHER Day in warmer months
4)  PRACTICE/OTHER Day in colder months
This  is  to  consider  both  the  different  ambient  conditions  and  the  difference  in  operations
between  Game  Day  and  PRACTICE/OTHER  days.  Refer  to  the  Design  Package  and
assumptions below for more details.
3.1. Key Formulas
This section lists the key formulas used in this analysis.
3.1.1. Hot Water Consumption Formula
During the day when games are played, the system undergoes four distinct periods of
operation. The amount of water available at time sample “n” is determined as follows:
𝑉ℎ𝑜𝑡 𝑤𝑎𝑡𝑒𝑟,𝑛 =   𝑉ℎ𝑜𝑡 𝑤𝑎𝑡𝑒𝑟,𝑛−1 − (𝑉̇𝑆ℎ𝑜𝑤𝑒𝑟𝑠 ∗ (𝑡𝑛 − 𝑡𝑛−1)) + (𝑉̇𝐸𝐿1 ∗ (𝑡𝑛 − 𝑡𝑛−1))
+ (𝑉̇𝐻𝑃 ∗ (𝑡𝑛 − 𝑡𝑛−1)) + (𝑉̇𝐸𝐿3 ∗ (𝑡𝑛 − 𝑡𝑛−1)) + (𝑉̇𝐸𝐿2 ∗ (𝑡𝑛 − 𝑡𝑛−1))
+ (𝑉̇𝐸𝐿4 ∗ (𝑡𝑛 − 𝑡𝑛−1))
Where:
V hot water, n = Available Hot Water at time of sample “n” in Litres
V hot water, n-1 = Available Hot Water at time of sample “n-1” in Litres
tn= no. of minutes since the start of the period at sample “n”
tn-1= no. of minutes since the start of the period at sample “n-1”
VShowers= Rate of water draw off to showers in L/min
VEL1= Rate of water recovery from Element EL1 in L/min
VEL2= Rate of water recovery from Element EL2 in L/min
VEL3= Rate of water recovery from Element EL3 in L/min
VEL4= Rate of water recovery from Element EL4 in L/min
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VHP= Rate of water recovery from heat pumps HP1 and HP2 in L/min
For the summer scenarios, these are the following values:
•  VEL2= 0 for Game Day, 8.61 when conditions are met
•  VEL4=0 for both Game Day and outside of Game Day
•  VShowers =60.32 when in use, 0 otherwise
•  VEL1 = 17.22 for game day when available HW is less than 1600L, 0 otherwise
•  VEL3 = 8.61 for game day when the conditions are met, 0 otherwise
•  VHP = 6.8 when operating, 0 otherwise
•  During winter, VHP = 5.21 L/min when operating, 0 otherwise

3.1.2. Overal  Heating Efficiency Formula
𝐻𝑒𝑎𝑡 𝐺𝑒𝑛𝑒𝑟𝑎𝑡𝑒𝑑 (𝑘𝑊ℎ)
𝐸𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑐𝑦 =

𝐸𝑛𝑒𝑟𝑔𝑦 𝐶𝑜𝑛𝑠𝑢𝑚𝑒𝑑(𝑘𝑊ℎ)

4. Analysis Assumptions and Inputs
The Analysis uses the following assumptions:
•  The majority of the players finish their showers 20 minutes after games/practices
(peak shower period). During this period, all showers are used, resulting in a peak
DHW flow rate of 60.63 L/min draw-off from the tanks when Mains water is at 15°C.
This is 66.78 L/min draw-off from the tanks when the Mains water is at 5°C.
•  While the practices and games are going on, 15% of the peak DHW flow rates are
used. This accounts for showers outside of the peak 20 minutes period.
•  When there are no practices and games, no DHW is used.
•  The number of GAME days in a year is 40 days.
•  The number of PRACTICE/OTHER days in a year is 100 days.
•  50% of the operating days are in the warmer months, and 50% of them are in the
colder months.
•  The GAME day hours are 9 am to 5 pm. 4 peak shower periods were considered for
each day. In practice, only 3 peak shower periods occur.
•  The PRACTICE/OTHER day hours are from 4 pm to 8 pm. 1 peak shower period was
considered for each day.
•  On GAME days only, EL1 is always used to heat the water to 65 °C.
•  Each tank losses heat at a rate of 0.106 kW. This was used to determine the standing
heat losses.
•  The tank heat losses were multiplied by 2.5 to account for hot water piping and
connection heat losses.
•  The electric elements raise the water temperature by 5 °C.
•  The disinfection cycle(where EL1 to 4 all turn on for two hours) occurs once a week
after the heat pumps will have completed a heating cycle. The elements will be on for
50% of the disinfection period.
•  The mains water temperature is 15 °C in the warmer months, and 5 °C in the colder
months.
The analysis has the following inputs:
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•  The energy prices and emission factors are taken from Auckland Council, the MBIE
energy report and Ministry for the Environment report. They are as follows:
o  Commercial electricity price: 0.1916 NZD/kWh (Auckland Council)
o  Commercial gas price: 0.0866 NZD/kWh (MBIE December 2022)
o  Electricity emission factor: 0.12 kgCO2e/kWh
o  Gas emission factor: 0.20 kgCO2e/kWh
•  The electrical element heating efficiency is estimated to be 95%.
•  The gas heating efficiency is estimated to be 85 %.
•  The average hourly temperature of the warmer months was determined using the
TMY file from NIWA. The temperature data from December, January, February, and
March were used.
•  The average hourly temperature of the colder months was determined using the TMY
file from NIWA. The temperature data from June, July, August and September were
used.

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5. Results
The  results  of  the  analysis  are  presented  in  this  section.  Firstly,  the  daily  estimates  are
presented  for  clarity.  After  that,  the  annual  estimates  are  presented.  The  annual  estimates
were determined using the daily estimates and the operating assumptions above.
Note: The running cost is conducted using 5 minutes intervals.
5.1. Daily Energy Consumption Estimates
Table 1 and Table 2 below show the daily energy consumption estimates and comparisons
to a gas heating system.
Table 1: Daily Heating Energy Estimates
Electric
Electric Heating
Heating
Estimated
Energy
Overall
Scenario
Required
Gas Input
Required
Efficiency
(kWh)
(kWh)
(kWh)
(W/W)
GAME Day (warmer
238
105
2.27
280
months)
GAME Day (colder
202
110
1.85
238
months)
PRACTICE/OTHER
126
41
3.10
149
(warmer months)
PRACTICE/OTHER
126
48
2.64
149
Day (colder months)

Table 2: Daily Heating Comparisons to Gas Systems
Electricit
DHW
DHW
Gas
Gas
Electricit
y
Emission
Running
Cost
Emission
Scenario
y Cost
Emission
s
Cost
(NZD
s
(NZD)
s
Reductio
Reductio
)
(kgCO
(kgCO
2e)
2e)
n (%)
n (%)
GAME Day
20.12
24.27
12.60
54.66
76.9
17.1
(warmer months)
GAME Day (colder
20.90
20.58
13.09
46.35
71.8
-1.5
months)
PRACTICE/OTHE
R (warmer
7.81
12.89
4.89
29.02
83.1
39.3
months)
PRACTICE/OTHE
R Day (colder
9.19
12.88
5.75
17.11
80.2
28.6
months)
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Thus,  the  result  shows  that  the  new  heat  pump  DHW  system  reduces  daily  emissions
significantly. It reduced emissions by 71% to 83%. Generally, it also reduces the operating
cost except for GAME Days in the colder months. The annual estimates in the next section will
provide a clearer picture of the analysis.
5.2. Annual Energy consumption Estimates
The annual energy estimates were produced based on the daily energy estimates and the
assumptions. For clarity, the annual operation has the following assumptions:
•  The number of GAME days in a year is 40 days.
•  The number of PRACTICE/OTHER days in a year is 100 days.
•  50% of the operating days are in the warmer months, and 50% of them are in the
colder months.
The annual DHW energy consumption estimate is as follows:
•  Heating energy required: 24,793 kWh
•  Electricity consumption: 10,353 kWh
•  Heating efficiency: 2.39
•  Running cost: 1,984 NZD
•  Emissions: 1242 kgCO2e
The comparison to a gas DHW heating system yields the following results:
•  Estimated gas energy required: 29,169 kWh
•  Estimated gas running cost: 2,526 NZD
•  Estimated gas emissions: 5,688 kgCO2e
•  Electricity cost reduction: 21.4%
•  Electricity emissions reduction: 78.1%

Thus, the conservative annual energy estimates indicate that the new heat pump DHW system
achieves approximately 21.4% lower operating cost, and 78.1% lower carbon emissions.

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Page 7

6. Conclusion
This  energy  consumption  analysis  was  conducted  for  the  proposed  DHW  system  for  the
Weymouth  RFC  at  Laurie  Gibbons  Memorial  Park.  The  analysis  considered  the  four  daily
operating scenarios and included the effects of the usage patterns and the ambient weather.
Generally, the assumptions and inputs in the analysis were conservative, thus, the results have
lower uncertainties.
Overall, the annual DHW energy estimates produced the following results:
•  Heating energy required: 24,793 kWh
•  Electricity consumption: 10,353 kWh
•  Heating efficiency: 2.39
•  Running cost: 1,984 NZD
•  Emissions: 1,242 kgCO2e
The comparison to a gas DHW heating system yields the following results:
•  Estimated gas energy required: 29,169 kWh
•  Estimated gas running cost: 2,526 NZD
•  Estimated gas emissions: 5,688 kgCO2e
•  Electricity cost reduction: 21.4%
•  Electricity emissions reduction: 78.1%
Thus, the conservative annual energy estimates indicate that the new heat pump DHW system
achieves approximately  21.4% lower  operating cost, and 78.1% lower  carbon emissions. In
addition, the cost of electricity is projected to fall over the lifecycle of the system, thereby further
decreasing its’ operating cost. Most importantly, the new system will help Auckland Council to
achieve the emissions goal.
[email address]
Page 8