Gas absorption heat pumps raise the efficiency bar

Remeha Commercial, absorption heat pump, space heating, energy efficiency
Proven environmental benefits — Mike Hefford.

The cheapest and cleanest energy choice is inevitably the one you do not use. Mike Hefford of Remeha Commercial looks at how practical, sustainable gas-driven heat pumps are raising the efficiency bar on refurbishment projects for substantial energy and carbon savings and rapid financial payback.

Faced with the triple whammy of stringent legislation, steep environmental targets and high fuel bills, organisations are keen to adopt efficiency measures wherever possible. When it comes to our existing buildings, improving thermal efficiency is a key priority — given that space heating and hot-water generation account for around half the energy demand and total carbon emissions of a building.

As we engineer for a more energy-efficient and sustainable future, compatible renewable technologies are increasingly specified on heating refurbishment projects, often alongside condensing boilers, to maximise carbon and energy savings.

One flexible heating alternative that is growing in popularity due to its high performance and versatility is the gas absorption heat pump. Whether used as a single unit or cascade, installed as a ‘bolt-on’ to serviceable boilers or at the heart of a refurbished hybrid system, gas absorption heat pumps (GAHPs) are proving a practical, sustainable solution to high performance heating and hot-water delivery.

Heat pumps work by exploiting lower-temperature sources like the surrounding air and then transferring this useful heat at higher temperatures with the aid of a refrigeration cycle. Gas absorption heat pumps use gas-driven heat pump technology and a low-NOx thermodynamic condensing heat generator containing an ammonia/water working fluid to draw up to 65% renewable energy from the air.

This absorption cycle is based on hot, high-pressure ammonia vapour delivering heat to the heating system as it condenses to a liquid. The cold liquid passes through an expansion valve to change it to a low-pressure vapour so that it can absorb heat from the ambient air and contribute to the heating process.

By combining this energy with the gas input and employing a highly efficient gas-fired condensing heat generator to maintain high operational efficiencies, they are able to increase the thermal output to offer exceptionally high achievable seasonal efficiencies of between 120 and 130%. Their high performance means that they deliver reliable operation even at sub-zero outside temperatures and continuous heat even through the defrosting cycle.

Far from being the ‘new heat pump on the block’, GAHPs use established, proven technology to deliver a range of financial and environmental benefits to building operators. Key to their particular suitability for retrofit and refurbishment projects is their use of gas rather than electricity for operation.

Whilst energy and carbon savings are high on the list of priorities for building owners and operators, minimising disruption and costs follow close behind. The additional electrical requirement of electric heat pumps can pose problems on retrofit projects if the incoming supply is insufficient to meet the additional demand. As GAHPs run on natural gas. They require an extremely low electrical power of just 1.09 kW compared to 12.9 kW for an equivalent-sized electric heat pump. For this reason, GAHPs reduce and simplify installation on retrofit and refurbishment projects, making them a practical and affordable solution.

Their use of gas also brings financial and carbon savings. Although the initial outlay for an electric and gas-driven heat pump is about the same, the operating costs associated with GAHPs are considerably lower as natural gas is typically a third of the price of electricity.

Then there is the carbon factor. Using gas as the primary energy source directly at the point of use, rather than grid-supplied electricity, means that GAHPs have a significantly smaller carbon footprint due to their superior primary energy ratio.

The green credentials of GAHPs are further enhanced by the use of ammonia/water as the refrigerant, as it has zero global-warming potential and zero ozone-depletion potential, improving the environmental rating of the buildings with additional BREEAM points awarded. Further green credit comes from the Class 5 NOx levels achieved by the condensing heat generator with a premixed modulating gas burner (typically 25 ppm).

A criticism sometimes aimed at electric air-source heat pumps is that they do not provide the high efficiencies when required. Yet possibly the most important benefit offered by gas absorption heat pumps is their ability to achieve continuously high seasonal efficiencies, even at lower outside temperatures.

Supporting this capability is a detailed performance table that we at have compiled for our own Fusion GAHP range. It lists the achievable efficiencies and heating capacity at various temperatures to help facilitate accurate calculations and also help prevent an energy performance gap where buildings fail to deliver the predicted energy savings.

Table 1: Average temperatures in the south east of England and across Scotland during the last heating season (source: Met Office) with the achievable efficiencies of the Remeha Fusion GAHP range.
South east England                            Temperature                            Efficiency at 50°C water delivery temperature Efficiency at 65°C water delivery temperature
Autumn 2014 12.7°C 157% 133%
Winter 2015 4.9°C 149% 120%
Spring 2015 9.4°C 153% 127%
Scotland Temperature Efficiency at 50°C water delivery temperature Efficiency at 65°C water delivery temperature
Autumn 2014 9.3°C 157% 127%
Winter 2015 2.9°C 146% 117%
Spring 2015 6.1°C 150% 122%

Table 1 matches average temperatures in the south east of England and across Scotland during the last heating season (source: Met Office) with the achievable efficiencies of the Remeha Fusion GAHP range.

The figures show that even when the temperatures drop, the GAHPs continue to offer high-performance operation with outstanding efficiencies that lead to carbon reductions of up to 40% compared to traditional heating equipment.

A well-designed and installed GAHP offers low maintenance and operation with a lifecycle of around 18 years — making it a practical, effective solution to high-performance, low-carbon heating and hot water.

However, as with all renewable technologies, there is a caveat. When opting for GAHPs it pays to work with the experts who have the specialist knowledge to achieve the maximum potential from this sophisticated equipment.

Alongside impressive energy and carbon savings, energy data from recent Remeha installations shows that GAHPs offer a full return on investment in just five years, with the prospect of further savings in future years

In a time of unclear energy policies and Government subsidies, what more attractive heating option could there be for organisations looking to raise thermal efficiency than this environmentally and financially sustainable commercial solution.

Mike Hefford is head of renewable technologies at Remeha Commercial.

Related links:
Related articles:

modbs tv logo

Wellbeing and building services

Building services have a significant part to play in improving the wellbeing of occupants in offices. 

Part 2: Holding onto specifications

Alan Jamieson discusses how to keep specifications intact from the design to the completion, a common challenge in M&E engineering.