heating & plumbing

series of linked ground source heat pump units, efficiencies of over 300 per cent can be expected. The system is flexible and will modulate depending on the heat demand – either caused by occupancy or outside temperature. This means that the number of heat pump units will be switched on or off depending on these factors. This way of operation also provides reliability, so that if one of the heat pump units fails, other units will continue to operate until the problem is resolved. Another positive aspect of district heating, particularly with regards to the social housing sector, is the low cost of maintenance. This is due to the fact that there are no individual boilers in each property that would normally require annual servicing.

Potential drawbacks

A district heat network is excellent at providing space heating. The provision of hot water for bathing and washing up has very different requirements in technical terms. By its very nature a district heating system plant room will be a distance away from the property and this creates significant issues with loss of temperature that is critical for domestic hot water supply. The temperature of water for showering is usually 38 degrees or slightly higher and hot water must be brought up to a higher temperature at regular intervals to kill legionella bacteria. A practical solution is for each property to have individual electrical water heating, either an electric shower and instantaneous water heaters or a hot water cylinder with an immersion heater. Usually there would be scope to install PV on the roof of a new development, which could contribute renewable electricity towards heating the hot water. One other factor that could become an issue with a district heating

system is the periods when the heating needs to be switched off centrally. While it would be wasteful to keep the system running all year round, the

“Pipes feeding the HIU flow and return from the central point. If run by a series of linked ground source heat pump units, efficiencies of over 300 per cent can be expected”

parameters of what external temperature the system should be turned off is a delicate issue – particularly with regards to residential housing for vulnerable or elderly people with more complex requirements. On the plus side, it should be possible to schedule routine maintenance when the system isn’t operating, such as in the summer, thus lessening disruption during the colder months.


The economies of scale of these type of District Heat Networks are obvious. It will be a breakthrough if the Government can achieve the joined-up approach required to deliver on its aims: affordable heating that can lower carbon emissions and is efficient and sustainable. There are obvious challenges in gaining investment but hopefully once these systems become more widely used across the UK, this barrier will also be brought down.

Louise Howlett is commercial director of air and ground source heat pump specialists RA Brown.

38 | HMM March 2017 |

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