Don’t ignore gas absorption
Gas absorption heat pumps are ideal for replacing or integrating with traditional boilers for retrofit applications, and a highly attractive option for new builds – meeting part L2A and L2B Building Regulations and achieving BREEAM 5. They will also improve building performance in retrofit applications, helping to achieve higher DEC and EPC ratings.
The heat pumps combine the advantages of the two most common heating technologies: gas boilers and electric heat pumps. They extract energy from the air using heat pump technology and a highly efficient gas condensing burner.
By using gas instead of electricity as the primary energy source directly at the point of use, a significantly lower carbon footprint is achieved by avoiding the wastage incurred in converting gas to electricity. The heat pump also provides up to 65 per cent additional heat by drawing in 'free renewable energy' from the surrounding air. This outperforms conventional methods of heating buildings.
In addition, gas absorption heat pumps reduce running costs since gas is typically a third of the price of electricity. The technology will typically reduce energy costs by up to 50 per cent, with payback achieved within two to six years.
Gas absorption heat pumps work by extracting heat from the air, using a generator-absorber heat exchange cycle. This can be powered by natural gas or LPG. In common with other heat pump applications, the process uses a refrigeration cycle, although the working fluid is an ammonia/water solution. The ammonia acts as the refrigerant and the water acts as an absorber.
The heat pumps work using a six step process:
• the gas burner heats the ammonia and water solution;
• the ammonia gas enters the condenser, condenses and releases heat;
• the high pressure ammonia liquid is converted into a low pressure ammonia liquid;
• the ammonia liquid evaporates and draws in heat from the ambient air;
• the ammonia gas absorbs into an ammonia water solution; and
• the solution pump powers the process.
Gas absorption heat pumps can be used as a direct replacement for gas-fired traditional condensing boilers due to their ability to reach temperatures as high as 65oC and up to 70oC to produce domestic hot water. They can also supply chilled water and cooling if a reversible unit is utilised."
The potential energy savings when converting from traditional boiler technology exceed 100 per cent. Additional benefits include ease of installation and low noise levels. They are also advantageous where internal plant room space is limited since they are designed for external installation, also negating the need for complex flue gas equipment.
There is good potential for fusing gas absorption heat pumps with renewable technologies, such as solar thermal and ground source heat pump loops. This further enhances the carbon reduction benefits and provides other benefits, such as reducing the installation space of ground source projects by up to 60 per cent.
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www.energ.co.uk/heatpumps
University reduces carbon emissions and running costs
The UK’s largest closed loop ground source gas absorption heat pump installation is providing low carbon heat to The Open University in Milton Keynes.
Building 12 at the university has achieved a BREEAM Outstanding rating. Along with the gas absorption heat pumps, the 2000 square metre building incorporates natural ventilation, night cooling, solar chimneys, automatic lighting controls, a green roof, solar water heating and photovoltaic panels.
ENER-G Sustainable Technologies drilled 13 boreholes to a depth of 100+ metres to install a ground loop system that feeds four gas absorption heat pumps, with a combined capacity of 140kW heat output. This is supplying the building’s heating requirements and will achieve carbon dioxide savings of approximately 45 per cent in comparison to a system heater via a condensing boiler. This will equate to 125 tonnes of CO2 saved per annum.
Paul Burley, managing director of ENER-G Sustainable Technologies, said: “This project demonstrates the effectiveness of gas absorption heat pump technology in supplying reliable, affordable low carbon heat. The education sector is championing the uptake of heat pumps in the UK, providing an important showcase for this fast growing sector.”
Most of the UK’s gas absorption heat pump installations are air-sourced, using a gas burner to drive the refrigeration cycle, which draws energy from the surrounding ambient air to significantly boost the thermal output of the gas. The energy can then be used to supply hot water up to 65oC for space heating and 70oC for the production of hot water via an indirect cylinder. Being able to reach these temperatures (which a normal electric heat pump cannot) means that they are ideal for the replacement of traditional boilers.
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Mark Wilson is national product manager, ENER-G Sustainable Technologies
