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www.hoarelea.comNovember 2010
Ground Source Heat Pump AssociationTechnical Seminar 2nd November 2010
M&E design and modelling of large systemsKeith Horsley – Associate, Hoare Lea
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One New Change
32,000m2 high grade office
20,500m2 high grade retail
2 open loop wells
Over 200 energy piles
13 ground source heat pumps
1.7 MW capacity
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Introduction
Overview of building energy modelling and load estimation
One New Change:Energy strategy and energy modellingSpecification of the ground source energy systemDeveloping the operating strategy for the ground source energy system
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Modelling building loads
CIBSE Guide A, section 5 - cyclic calculation over 24 hours.
“Rules of thumb”W/m2 heating and cooling loads in the early stages of design
Results used to size boilers and chillers.But of limited use for designing ground source energy systems.
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Modelling building loads
To correctly size LZC energy systems such as GSES, and to estimate their contribution, annual energy consumption and annual heating and cooling loads are needed.
The energy benchmarks in CIBSE Guide F and TM46 are useful... but not perfect!
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Modelling building loads
Increasingly, the driver for LZC energy systems is a planning requirement for a “renewable energy contribution”, usually as a percentage of the building’s energy demand or carbon emissions.But what is the “renewable contribution” of a ground source heat pump?
0.5MWh elec in
2.0MWh gas in
Boilers
Air-cooled chillers
“Renewable contribution” = 2.0+0.5-1.0 = 1.5 MWh
1.0MWh elec in
1.8MWh heat out
2.0MWh cooling out
GSES
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Modelling building loads
To refine the analysis of LZC energy systems, heating and cooling load profiles are needed.
Degree days give an approximation for heating.
The NCM activity database gives part of the picture.
But more research is required to provide better data.
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Modelling building loads
Building geometryBuilding fabric propertiesGlazing / shading propertiesInfiltrationOccupancyEquipment heat gainsLighting heat gainsVentilation ratesPlant efficienciesControls
Dynamic simulation models
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One New Change
Client – Land SecuritiesConcept architect – Jean NouvelDelivery architect – Sidell GibsonConstruction Manager – Bovis LendLease
M&E engineer – Hoare LeaStructural engineer – ArupGSES specialist – Geothermal International
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One New Change
32,000m2 high grade office20,500m2 high grade retail55,000m2 total over 11 storeys
Start on site mid-2007Completion October 2010
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One New Change
Planning requirement for 10% of the development’s energy usage to be from renewable or low carbon technologies
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One New Change
Hoare Lea Energy Strategy Report – May 2005
Energy consumption at One New Change
(Baseline scenario - without contribution from renewable or low carbon energy sources)
0
1,000,000
2,000,000
3,000,000
4,000,000
5,000,000
6,000,000
7,000,000
8,000,000
Offices Retail
Estimated annual
electricity consumption
Estimated annual gas
consumption
Es
tim
ate
d e
nerg
y c
on
su
mp
tio
n (
kW
h/y
r)
Energy consumption estimated based on benchmarksGSES yield and efficiencies estimatedGSES “renewable contribution” = 14%
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One New Change
Hoare Lea Energy Strategy November 2006
Energy consumption and heating & cooling loads from IES modelHydrogeology input from ArupHeat pump efficiencies from manufacturersInitial design for 5 borehole pairs + energy piles to meet 10.17% of energy demand
0
1000
2000
3000
4000
5000
6000
7000
8000
Annual energy
consumption, MWh
Annual heating load,
MWh
Annual cooling load,
MWh
Retail
Office
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One New Change
Heating and cooling loads
RETAIL OFFICE
Retail condenser loopOffice LTHW system
Office CHW system
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One New Change
Final energy strategy submission – January 2008
0
200
400
600
800
1000
1200
1400
Retail heating Office heating Office cooling
Annual load, MWh
Annual load met by GSES,
MWh
Energy input, conventional
plant, MWh
Energy input, GSES, MWh
"Renewable contribution",
MWh
Energy consumption and heating & cooling loads from IES modelGSES input from Geothermal International – number of boreholes reduced; number of energy piles increasedGSES meets 10.93% of energy demand
0
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
Office Retail
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One New Change
How the GSES was specified
“Renewable energy contribution” (kWh per year) the key performance requirementSpreadsheet included in specification to show how this was calculatedAcknowledgement of difference in performance between initial period and future yearsRequirement for GSES contractor to model the system performance based on the heating and cooling load profiles generated by IESMinimum annual COPs for each load connection pointStandalone control system for GSES with open protocol interface to CNS & BMSEmphasis on metering and monitoring to allow control strategy to be optimizedDesign responsibilities itemised for all parties (Hoare Lea, Loopmaster, Geothermal International and Arup)
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One New Change
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One New Change
The output of the GSES is restricted by:
Peak heating and cooling capacitiesTotal kWh heating or cooling from the ground per dayYield of the open loop wells per dayAvailability of the dry coolers
Also affected by:
External temperature (Can directly cool condenser loop? Cool ground loop?)Condenser loop set point temperature (varies with external temperature)Ground water temperature (Can directly cool condenser loop?)
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One New Change
The control system takes into account:
Total condenser system kWh cooling load the previous dayTotal condenser system kWh heating load the previous dayTotal Office CHW kWh cooling load during the previous dayTotal Office LTHW kWh heating load during the previous dayCurrent outside air temperatureMet office weather data (forecast of min and max temps for next 2 days)The total kWh available today from the open loop (based on open loop temperature and maximum daily yield)Variation with outside air temperature of the efficiency of each heating and cooling generator (from factory and site test data) so the available heating or cooling capacity of the ground loop system is used to displace the least efficient device.
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Conclusion
Estimation of annual building energy loads and load profiles are important for the appropriate application and design of ground source energy systems
Important to revisit as the design of the building, and the GSES, develops
Dynamic simulation modelling essential for complex buildings, but choice of appropriate assumptions and interpretation of results not straightforward
Consultants’ specifications need to be clear on what is required from whom.
The control and operation strategy is important to ensure the contribution of the ground source energy system is maximised
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