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Renewables: Tried and tested kit cuts carbon and running costs

Gas absorption heat pump technology has a great future, according to Stefan Gautsch. He explains how these low carbon appliances work efficiently to provide both heating and hot water.
Renewables: Tried and tested kit cuts carbon and running costs
The advantages of ground and air source heat pumps have been well documented over the years for their ability to deliver sustainable heating and hot water; gas absorption heat pumps are a newer concept in industry circles, but a tried and tested technology that has many benefits, especially for the reduction of carbon emissions and running costs associated with commercial, industrial and residential applications.

Gas absorption heat pumps use heat pump technology driven by an efficient gas condensing burner to draw energy from the air. As the name suggests, 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 doing so gas absorption heat pumps have a significantly smaller carbon footprint than other heating appliances such as gas-fired condensing boilers.

As well as being a sound lowcarbon solution for heating installations, gas absorption heat pumps can also help cut running costs. By taking advantage of free energy available in the surrounding air, a gas absorption heat pump can also provide up to 65 per cent additional heat for warming buildings or providing hot water.

Taking heat from the air

Gas absorption heat pumps are designed to take heat from the air in the same way as their electric counterparts.

However, unlike electric heat pumps, there is no requirement for an electrical compressor. In its place, the system uses a generator-absorber refrigerant cycle, which is powered by natural gas or LPG burner. Unlike conventional heat pumps, the gas absorption heat pump uses an ammonia/water solution as an agent for absorbing heat from the environment.

The ammonia refrigerant used in the GWPL 38 has zero global warming potential (GWP) and zero ozone depletion potential (ODP).

The basic operating principles of a gas absorption heat pump can be explained in seven steps, as shown left.

Strong ammonia vapour

· 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 ammonia solution. The strong ammonia vapour travels to the Condenser (2) while the weak ammonia solution is circulated to the absorber (5).
· 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).
· 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 boiling point and the liquid changes back to a vapour. This vapour passes on to the evaporator (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).

Heated vapour from evaporator

· 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 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).
· Second expansion valve. As described above, this second valve controls the flow of weak ammonia between the generator (1) and absorber (5).
· Pump. The pump moves the ammonia solution from the absorber (5) back to the generator (1) where the whole process starts again.

GWPL 38 gas absorption heat pump

Buderus has introduced the GWPL 38 gas absorption heat pump for use as a single heat source or installation with any of its existing range of high efficiency condensing boilers, as well as solar thermal system. The Gas absorption heat pump is available as a single unit or in preconfigured, factory fitted cascade kits of up to five individual units.

The heat pumps have been designed for properties with heating systems controlled by building management systems (BMS) and are suitable for installation outside, with no need for a plant room or requirement for a chimney, as flues are included. With its maximum flow temperature of 65 degrees for heating and 70 deg for DHW the GWPL 38 is suitable for applications in the new built and replacement sector.

Outputs up to 38kW for the single unit and 190kW for cascades make it the ideal choice to provide sustainable heating in larger buildings.

As well as being suitable for new build projects, as a renewable technology with NOx emissions qualifying for BREEAM 5, Buderus' GWPL 38 is perfect for replacement and refurbishment projects, not to mention integration with existing heating systems.

In fact, gas absorption heat pumps are just as easy to install as condensing boilers, but with the additional benefits of higher carbon savings, lower environmental impact and reduced running costs. Installer training courses will soon be available for anyone interested in adding gas absorption heat pumps to their product portfolio. These training courses will enable the installer to train on fully operational gas absorption heat pumps.

• Stefan Gautsch is commercial technology consultant for Buderus
6 December 2011


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