HEAT PUMPS PUMPING UP THE HEAT
the same, natural gas is typically around a third the price of electricity. As a result, operating costs from GAHPs are correspondingly lower.
The carbon factor
Using gas as the primary energy source directly at the point of use, rather than grid-supplied electricity, means that GAHPs use energy extremely efficiently, enabling them to provide 98% of usable heat energy compared with the 45% of usable electrical energy from ASHPs. As a result, they have a significantly smaller carbon footprint.
Improved environmental ratings GAHPs use an ammonia/water
A
s gas-driven heat pumps are increasingly specified to provide low-carbon heating and hot water for both new build and
refurbishment projects, Mike Hefford, Head of Renewable Technologies at Remeha Commercial, throws the spotlight on the proven carbon and energy saving benefits of this lesser known heat pump technology. For public-sector organisations juggling tighter budgets alongside challenging environmental targets and steep fuel bills, it is good to know that there is one area at least that offers huge scope for affordable, rapid energy efficiency improvements. Heating and hot water generation accounts for around half the total energy use of a building and its associated carbon emissions, making it a prime starting point for efficiency measures. As we move towards a low-carbon future the choice of renewable technologies may be growing, but when it comes to selecting the appropriate solution,
practicality and high performance must remain the key considerations. It’s for this reason that gas absorption heat pumps (GAHPs), until recently the lesser known of the heat pumps, are growing in popularity as a low-carbon heating alternative: quite simply, by matching versatility with proven outstanding efficiencies they help us use energy more cleanly and effectively.
How do GAHPs work?
Gas Absorption Heat Pumps fall into the air source heat pumps (ASHPs) category, a term historically used to refer uniquely to electric-driven ASHPs. Both work by capturing energy from the surrounding air, which converts to higher temperatures with the aid of refrigerants for space heating and hot water generation. Where GAHPs differ from electric ASHPs is their use of a gas-driven low-NOx condensing heat generator containing an ammonia/water working fluid to draw useful heat from the air. By combining this renewable energy with the gas input and using the gas condensing heat generator to maintain high operational efficiencies, GAHPs are able to increase the thermal output to offer exceptionally high achievable seasonal efficiencies of between 120 and 130%. The high performance of GAHPs means that they deliver reliable operation even at low sub-zero outside temperatures and continuous heating even in defrost phase.
Reduced running costs
One of the key advantages of GAHPs is their use of gas rather than electricity for operation. While the purchase price for electric ASHPs and GAHPs is approximately
22 ENERGY MANAGER MAGAZINE • MARCH 2016
solution with zero global warming potential and ozone depletion potential rather than Hydrofluorocarbons (HFC) refrigerants. This more environmentally-friendly operation, together with their ability to achieve Class 5 NOx levels by using a condensing heat generator with a premixed modulating gas burner, means that they can significantly improve the environmental ratings of a building. GAHPs qualify for five BREEAM credits in total.
Easily retrofitted
A key benefit of GAHPs is their suitability for use in both new build and refurbishment projects. After all, if we are to achieve our steep carbon reduction target of 80% by 2050, it is important that we address the efficiency of our existing building stock as well as designing properties that require less energy to operate. Hugely versatile, GAHPs can be installed as a single unit or in cascade, and are easily retrofitted within an existing heating system either as a ‘bolt-on’ to serviceable boilers, or in a hybrid system in conjunction with gas condensing boilers. Importantly, they require only an extremely low electrical running current to operate - just 1.09 kW for a 35kW GAHP compared to 12.9kW for an equivalent-sized electric ASHP. This makes them a straightforward and affordable retrofit option as there is no need to increase the electrical incoming supply.
Proven high performance
A common general criticism of heat pumps is that their efficiency level drops off as the outside temperatures fall. Yet in our experience, GAHPs can and do deliver reliably high efficiencies all year round in a well-designed system. Perhaps the reason
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