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HEAT PUMPS The hunt for sustainability


Relatively new to the UK market, gas absorption heat pumps deliver a highly efficient, renewable heating solution for commercial and industrial applications. Stefan Gautsch, Commercial Technology Consultant for Buderus explains how the technology operates and why it is an ideal solution for both the new build and refurbishment sectors.


W


ithin the heating industry, the advantages of both ground source and air source heat


pumps have been well documented over recent years for their ability to provide sustainable heating and hot water. Gas absorption heat pumps are a comparatively newer concept as far as industry discussion is concerned, but offer an established technology with many benefits. Notably, the reduction of carbon emissions and running costs (the overarching benefit of the gas absorption heat pump technology) makes it an attractive addition to commercial and industrial applications, particularly those looking to capitalise on the positive incentive offered by the Carbon Reduction Commitment (CRC) Energy Efficiency scheme. To summarise, gas absorption heat pumps operate by drawing energy from the air using heat pump technology and a highly efficient, gas condensing burner to achieve gas utilisation efficiencies of up to 164%. As suggested by the name, this type of heat pump uses gas as the primary energy source directly at the point of use, rather than electricity which is generated largely in coal or gas-fired power stations. By using this technology the gas absorption heat pump has a significantly smaller carbon footprint than comparable heating appliances such as conventional gas-fired boilers. As well as being able to maximise efficiency via the technology used to provide heating, a gas absorption heat pump can also help to significantly reduce running costs. With fuel prices as they are at present, gas is typically only around a third of the price of electricity, which offers direct savings on the fuel source used to generate the heat required. These savings are further enhanced as the system takes advantage of the free energy available in the surrounding air, which can provide up to 65% additional heat for the building or its hot water demand. Like their electric counterparts, gas


absorption heat pumps are able to extract heat from the air. However, unlike electric heat pumps, there is no requirement for an electrical compressor. Instead, the system uses a generator-absorber heat exchange cycle powered by natural gas or LPG. Whilst


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all heat pumps require a refrigeration cycle, the gas absorption heat pump uses an ammonia/water solution with the ammonia acting as the refrigerant and the water the absorber.


Key operating principles


The basic operating principles of a gas absorption heat pump can be explained in seven easy steps (figure 1). 1. Generator. Within the generator the low NOx gas-fired burner heats the ammonia/water solution via a heat exchanger, increasing the temperature and pressure. This causes it to separate into a strong ammonia vapour and a weak


boiling point and the liquid changes back to a vapour. This vapour passes on to the Evaporator (4) 4. Evaporator. A fan draws ambient air through the fins of the Evaporator. The ambient air contains a high amount of free, renewable energy from the air. This energy is captured by the ammonia vapour. The now heated, low pressure vapour passes on to the Absorber (5). 5. Absorber. In the Absorber, the weak ammonia solution from the Generator (1) recombines with the heated vapour from the Evaporator (4), having first passed through a second expansion valve (6). As the vapour and weak ammonia solution recombine, the


emissions qualifying for the upper levels of the BREEAM assessment for sustainable buildings, a gas absorption heat pump can help to achieve targets for renewable technologies required for new build planning permission. In addition, a further benefit is that both operating and installation costs are low.


In contrast with many comparable


alternatives available for commercial and industrial heating installations, the gas absorption heat pump units are designed for external installation, meaning there is no requirement for them to take up valuable space in plant rooms, whilst flue gas systems and bulky fuel storage outlets are not required either.


With regard to retrofit or refurbishment projects, a gas absorption heat pump can add extra value to a building by reducing its running costs and improve the building’s energy rating through Energy Performance Certificates (EPCs) and Display Energy Certificates (DECs). As commitments to energy efficiencies such as these become more visible, so will the demand for low carbon technologies, of which the gas absorption heat pump is one.


High efficiencies Figure 1


ammonia solution. The strong ammonia vapour travels to the Condenser (2) whilst the weak ammonia solution is circulated to the Absorber (5). 2. Condenser. The now high temperature, high pressure ammonia vapour releases its heat into the heating system in the condenser. In doing so, the vapour changes state becoming a liquid. This liquid travels to the Expansion Valve (3) on its way to the Evaporator (4). 3. Expansion Valve. The ammonia liquid, still at high pressure, passes through the Expansion Valve where the pressure falls. At this low pressure, ammonia has a reduced


vapour changes state into a liquid, releasing further heat into the heating system. The now recombined ammonia solution is pumped (7) back to the Generator (1). 6. Second Expansion Valve. As described


above, this second valve controls the flow of weak ammonia between the Generator (1) and Absorber (5). 7. Pump. The pump moves the ammonia solution from the Absorber (5) back to the Generator (1) where the whole process starts again.


The ideal choice As a renewable technology with low NOx


As a low carbon technology, a gas absorption heat pump can offer high efficiencies and carbon saving even when operating at higher temperatures. Maximum flow temperatures of up to around 65°C can be achieved for heating, whilst the potential for hot water temperature is even higher. This increases the value of the heat pump itself, allowing an application’s heating to be updated without the need to upgrade associated pipework and associated infrastructure around the building. Adaptability further enhances the gas


absorption heat pump’s offering, as it can be easily integrated into an established heating system – taking the place of a condensing boiler, but with the benefits of higher carbon savings, reduced environmental impact and lower running costs. The heat pumps can be supplied as pre-fabricated cascades of up to five units, making them suitable for a range of outputs and limiting the requirement for extended on-site installation. The systems can also be integrated with other heating sources such as solar thermal panels and boilers.


OCTOBER 2011 BUILDING SERVICES & ENVIRONMENTAL ENGINEER 35


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