Energy, Cost & CO2 Emission Reduction
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.
Energy Cost Saving*
*compared with conventional gas boiler & grid electricity
Case Study – The King’s School, Witney
A school campus expansion project, providing additional space to accommodate both upper and lower school pupils at the same campus.
To achieve CO2 reduction through on-site energy generation, Satisfying ‘Part L’ and SBEM while minimising project costs and payback time.
- One 15 kWe/30 kWth LoadTracker CHP
- Two Mitsubishi ‘Ecodan’ 4.8 kWe ASHP
- Together supplying 83% of space heating & DHW demand.
- 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
- Carbon footprint savings
- Operational cost savings
- RHI compliant ASHP installation
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
Annual site electricity 71,789 kWh
Heat pump electricity 21,563 kWh
Electricity price 13.19 p/kWh
Annual site heat and DHW 246,445 kWh
Gas price 3.48 p/kWh
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.
This is an equivalent to 17% reduction of CO2 emissions.
The use of LoadTracker CHP would result in annual savings of £4,292 relative to a conventional mains supply/boiler system.
This is equivalent to saving 22% on energy bills
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
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