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Overestimating peak dwelling heat loads and therefore the dwelling heat interface unit output, combined with poor commissioning will lead to an overpriced and inefficient network. This will be reflected in high heating bills for consumers, high ongoing maintenance costs, and higher heat losses in communal areas.

The dwelling heat interface unit (HIU) is one of the key components of a heat network, providing hot water and heating for each dwelling. It should be selected in line with design requirements and independent performance test results must be available. The first independent UK test standard proving the performance of HIUs under typical UK operating conditions has been launched by BESA (Building Engineering Services Association). The independent test will give a HIU performance benchmark to specifiers and will allow designers to see the impact of a specific HIU on the heat network.

Historically, commissioning is often poor or not existent. This will lead to an unbalanced system, with high return temperatures and therefore high heat losses and a reduced overall efficiency of the heat network. This will often have a major impact on consumer energy bills.

We have seen on sites many oversized HIUs (in the range of 50-100kW), however based on operational data the peak heat interface unit demand is rarely over 35kW/dwelling. Even with some safety margin in mind during the design, the loads for different dwelling types would not exceed the following values:

  • Studio: 30kW
  • 1Bed 1Bath: 44kW
  • 2Bed 2Bath: 50kW

Our District Heating Specialists provide advice to ensure that the heat network has been designed to achieve the highest possible efficiency and in accordance with CP1:2015 (Heat Networks: Code of Practice for the UK) and other relevant standards.