Optimised Heat and Power
for maximised CHP % share
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Issue 47
How to Optimise SAP/SBEM
CHP Heat Share with Heat Pumps
The ‘fraction of heat’ value for CHP is an important component
in SAP/SBEM calculations. The larger the heat share from the CHP,
the greater the carbon and cost savings.
Combining electric heat pumps with CHP can significantly increase the share
of low carbon heat, particularly when the project has a comparatively low
electrical demand for the CHP. This is often the case in schools and ‘landlord’
areas within multi-residential developments.
As electricity consumers, heat pumps create additional electrical load for
on-site CHP generation. Heat pumps can be activated during periods of
reduced power consumption; for example, by topping-up low night-time
electrical loads.
Combining CHPs
and Heat Pumps in district
heating schemes is standard
practice in Denmark
This combination of low carbon and renewable energy can offer a powerful
solution and the concept is tried and tested in many Danish installations.
Beata Blachut
Technical Manager CHP / LoadTracker
SAV Systems
Energy, Cost & CO2 Emission Reduction
Energy Cost Saving*
The Sankey diagram compares the energy cost and CO2 emissions from a single
XRGI 15 LoadTracker CHP + ASHP combination with ‘traditional’ grid supplied
electricity and heat from boilers.
39%
10.3 kW lost due to
boiler losses (15%)
CO2 Reduction*
8.9 kW lost due to CHP
losses (16%)
33.4%
54.5 kW
58.6
kW
83.7kW
30.6 kW
9.6 kW
Heat
pumps
Heat
load
58.6 kW
Power
load
5.4 kW
82.4 kW
28
kW
45kW
5.4 kW
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8.1 kW lost due to
power station losses
(60%)
*compared with conventional
gas boiler & grid electricity
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Case Study – The King’s School, Witney
The Project
A school campus expansion project, providing additional space to accommodate
both upper and lower school pupils at the same campus.
The Challenge
To achieve CO2 reduction through on-site energy generation, Satisfying ‘Part L’
and SBEM while minimising project costs and payback time.
The Solution
• One 15 kWe/30 kWth LoadTracker CHP
• Two Mitsubishi ‘Ecodan’ 4.8 kWe ASHP
• Together supplying 83% of space heating & DHW demand.
Features
• Combining low carbon and renewables
• Power generation at point of use
• LoadTracker CHP with real-time automatic modulation
to match site power demand
• Minimal use of high CO2 grid electricity
• Low noise levels of 49 dB(A)
• Long service intervals (8,500 hours)
• Simple control strategy to enable ASHP when required
Benefits
• Carbon footprint savings
• Operational cost savings
• RHI compliant ASHP installation
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High and Low Temperature Circuits
CHP and Air Source Heat Pumps combine to supply the high
and low temperature circuits in the school.
The Heat Pump is located on the lower temperature return from
the underfloor circuit (35˚C), and provides 5˚C of pre-heating.
The CHP supplies a stable and controlled 80˚C to the DHW
circuits and the FlowMaster pump and valve precisely mixes this
high grade heat with the heat pump return to achieve the target
underfloor flow temperature of 45˚C.
Balancing CHP Demands
Combining CHP and Heat Pump can be an ideal way to balance
the loads in multi-residential developments, where the ‘landlord’
electrical demand is comparatively low and heat demand is high.
The Heat Pump provides a steady electric load for the CHP,
increasing the available operating hours, maximising the heat
share and reducing electricity export.
The low carbon site-generated electricity also reduces the
carbon footprint of the ‘renewable’ heat pump!
Summary of Site Demand
71,789 kWh
21,563 kWh
13.19 p/kWh
246,445 kWh
3.48 p/kWh
Annual site electricity
Heat pump electricity
Electricity price
Annual site heat and DHW
Gas price
Carbon Footprint Savings
17 tonnes of CO2 emissions could be reduced by installing
a CHP system relative to a conventional mains supply/gas
boiler system.
CO2 (conv)
99,885 kg CO2 pa
CO2 (CHP)
82,728 kg CO2 pa
Net reduction
17,156 kg CO2 pa
This is an equivalent to 17% reduction of CO2 emissions.
Cost Savings
The use of LoadTracker CHP would result in annual savings of
£4,292 relative to a conventional mains supply/boiler system.
Conv.
CHP
Electricity
£9,469
£5,295
Gas (boiler)
£10,090
£1,695
Gas (CHP)
0
£8,277
Total
£19,559
£15,267
This is equivalent to saving 22% on energy bills
Boiler
41,404
17%
Heat pump
62,749
25%
Heat balance
CHP
142,291
58%
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Thermal Store or Just a Buffer?
The arrangement and management of stored heat is critical when designing
CHP systems.
In a basic system, a “buffer vessel” acts as an oversized header to avoid short-cycling
of the CHP unit.
In a sophisticated, optimised CHP system, a real “Thermal Store” meets specific
objectives and brings significant operational and economic benefits to the system.
Thermal Store Objectives
• To provide a substantial displacement
between the time of heat production
and heat usage
• To enable the CHP unit to meet peak
heating loads greater than the CHP
heat output
• To allow heat demands lower than the
minimum output of the CHP to be met
• To optimise CHP operating time
CHP Thermal Store Management
Download the Technical Bulletin from our website:
www.sav-systems.com
For further information contact:
SAV Systems, Scandia House, Boundary Road, Woking, Surrey GU21 5BX
Tel: +44 (0)1483 771910 Web: www.sav-systems.com E-mail: [email protected]