BSEE HEAT PUMPS
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THE PERFECT PARTNER: Gas absorpon heat pumps
It is oen claimed that renewables will play a big part in the UK’s future heang and hot water provision, yet the comprehensive coverage of the gas network suggests it is very unlikely that boilers will be replaced enrely. With this in mind, Richard Davies, Commercial Technologies Consultant at Bosch Commercial and Industrial, reveals one underused technology that could prove to be the perfect partner for commercial gas boilers.
W
ith such a far- reaching gas network, the UK’s transition to ‘greener’
technologies has
been less straightforward than that of our continental counterparts up to now. In spite of this however, the Carbon Trust’s claim that ‘an estimated 35 per cent CO2 reduction could be achieved by 2020 through cost-effective measures’ is promising and encourages stakeholders to assess the potential energy savings that can be made in non-domestic buildings.
A sudden migration towards a comprehensive reliance on renewables is unlikely, but there is opportunity for us to look at how we can make better – or more efficient – use of the gas network. One of these opportunities lies with the use of a renewable technology alongside a gas boiler plant to maximise efficiency.
Absorbing energy eciency
The advantages of both ground source and air source heat pumps have been well documented in the domestic sector, yet gas absorption heat pumps (GAHP) are a comparatively new concept as far as industry discussion is concerned.
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 in some instances.
Whilst 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. These characteristics combine to give rise to a technology capable of achieving very high gas utilisation efficiencies of up to 164 per cent under ideal conditions. Additionally, the option for external installation means there is no requirement for an interior plant room, flue gas system, or fuel storage outlet. The strengths of a GAHP are indisputable, however it is important
that investors consider the manner in which efficiency can vary slightly depending on outside influences. Due to the fact that the technology collects a large amount of its heat output from the surrounding air, the air temperature can create a slight variation in the efficiency of each unit. That said, in the UK it is unusual to see very low air temperatures so air source heat pumps normally operate consistently at high efficiency levels.
The other factor affecting its performance is the flow and return temperature. Heat pumps work most efficiently at low flow temperatures so maintaining this temperature will ensure the heat pump is performing at its peak.
Using modern, intelligent control systems that allow for a comprehensive control strategy over boilers and GAHPs, it has become possible to combine these two technologies and allow them to work efficiently and reliably in tandem.
In this arrangement, it is now becoming increasingly common for a buffer tank to act as a thermal store – known as a buffer bypass system. The benefit of this system is that in times of limited or zero need for domestic hot water (DHW), the GAHP can provide the low water temperatures required for space heating whilst operating at a very high efficiency.
In the event that higher water temperatures are needed to provide for DHW or a particularly large space heating load, the conventional boiler can be started and the system diverted so the GAHP can now pre- heat the return and reduce the load on a conventional boiler. When the system load reduces again, the GAHP can then go back to providing heat for the whole system.
Peak loads
This arrangement also allows for a fast reaction time to high temperature or high peak loads by enabling the conventional boiler to assist the GAHP in generating heat. The fast warm-up characteristics of a modern high- efficiency condensing boiler lend themselves well to providing a backup for high temperature and high demand situations. A set-up like this allows two separate heat generating technologies to work in tandem, resulting in fast reaction times, high
efficiency, reliable operation and a backup heat source during any service or downtime.
Ideal applicaons
Applications for this type of system are wide and varied however this system works especially well in environments where a constant space heating load is required, such as in nursing homes, hospitals or sheltered accommodation. This case is strengthened even further when the technology is used in conjunction with low temperature heat emitters such as underfloor heating. With the GAHP being predominantly fuelled via natural gas, it is particularly well-suited to buildings where a limited electrical supply capacity means that an electrically-driven heat pump is not viable.
As commitments to key legislation such as the Building Regulations Part L, the Carbon Reduction Commitment (CRC), favourable BREEAM assessments, and visible energy efficiency ratings such as Energy Performance Certificates (EPCs) and Display Energy Certificates (DECs) become greater, so will the demand for low carbon technologies. By investing in a ‘best of both’ arrangement comprising of a gas absorption heat pump alongside a condensing boiler, investors can achieve ambitious emissions targets whilst still utilising the existing gas network.
www.bosch-
industrial.co.uk
uInstalling a gas absorpon heat pump.
uBosch gas absorpon heat pump in situ.
uLe: Closeup of a gas absorpon heat pump. GAHPs are well suited to buildings with a limited electrical supply, meaning electricdriven heat pumps are not viable.
20 BUILDING SERVICES & ENVIRONMENTAL ENGINEER MARCH 2016 VISIT OUR WEBSITE:
www.bsee.co.uk
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