While district heating may have had something of a chequered history in the UK in the past, the last few years have seen a considerable resurgence in the popularity of such systems, often ‘re-styled’ as heat networks. This is in line with the move to central energy centres, which make it easier to deploy both traditional and low carbon heat sources together.
As a result, district heating is set to play a key role in the UK’s carbon reduction strategy and is also central to the European heating and cooling plan. The UK government is also making funding available to help local authorities explore the feasibility of district heating systems in their areas.
There have been concerns regarding the overall efficiency of district heating. When the situation is examined carefully, however, it is clear that where district heating systems have delivered disappointing performance this has usually been the result of non-optimal system design.
The key point here is that achieving optimum efficiency requires a whole system approach. Specifying plant that is inherently efficient is certainly one part of the equation but the rest of the system needs to be designed to exploit that inherent efficiency.
In the majority of cases this will also involve integrating different heating technologies and ensuring they work in harmony. So it is essential that the various types of heating plant are controlled to take advantage of the performance characteristics of each.
Beyond the plant room, the management of hot water flow rates and flow and return temperatures is also critical.
In the case of individual multi-occupancy buildings, space heating and domestic hot water are typically controlled, and possibly metered, by heat interface units (HIUs) within each of the spaces.
Where more than one building is involved there can be considerable variation between the temperatures and pressures required by each building. This is especially the case with schemes that incorporate a number of different building types - an approach that is generally desirable because mixed demand patterns spread heat loads more evenly.
In such cases, each building needs to be fitted with a sub-station that is capable of converting the hot water temperatures and pressures provided by the energy centre to the operating conditions required by the building. Each sub-station will typically comprise a plate heat exchanger, control valve, heat meter and necessary valves – ideally in a compact packaged configuration to minimise plant room space requirements.
The important thing is that with any district heating system served by a multi-source energy centre, it is essential to ensure that all of the systems work efficiently together and that hot water temperatures and pressures are properly controlled at each building. A holistic approach to system design and the use of compatible components within the system is the way to deliver the best solution for the end client.
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