District heating schemes have gained popularity across Europe, but the UK is still trailing in the adoption of this energy-efficient heating method. Louise Howlett of RA Brown explains the benefits.
While district heating is widely adopted in Northern Europe, it remains underutilised in the UK, providing less than two per cent of the energy. However, the benefits of district heat networks, such as the fact they can use a variety of heat sources and power off-grid developments or multiple properties from one centralised location, have made them an increasingly popular option for the residential sector, particularly for large-scale refurbishments or new build developments.
A growing sector
In the Government’s fifth carbon budget, it was projected that by 2050 heat networks would be serving 18 per cent of the total heat demand. To address the challenges which local authorities identified as barriers to heat network deployment in the UK, the Heat Network Delivery Unit was formed in 2003. Since then, it has supported over 100 local authorities in England and Wales, and there are now over 200 projects at development stage.
A pilot scheme open to local authorities and other public sector bodies has been launched, with the first payments of the £39m funding to be made by April. However, investment in these schemes is a big challenge for the Government as typically returns are slow, and while district heating systems work well with an owner/operator model, the Government will want to regulate charges as it is committed to lowering heating bills for consumers.
Technical benefits
One of the great benefits of district heating is that a wide range of heat sources can be used to run district heat networks – from gas, burning of waste or bio fuels. Renewable technology such as ground source heat pumps, which extract heat from the ground to reduce emissions, can also be utilised with these systems.
District heating is also scalable – a number of units can be linked together and housed in a large plant room. From that centralised location, the heat is then distributed to individual apartments, for example, via a Heat Interface Unit (HIU). This can be installed inside or outside each home (very much like a gas meter) and that way heat usage can be metered for individual billing. Like with other heating systems, householders are able regulate the amount of heat that they use as the warm water is transferred into the radiators or through the underfloor heating system in each property.
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. 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 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.
Conclusion
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.
This feature was published in the March 2017 issue of Housing Management & Maintenance magazine.
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