HEAT INTERFACE UNITS | BESA HIU TEST STANDARD TOUGH NEW STANDARDS PUT HIUs TO THE TEST Heat interface units that do not meet minimum performance standards will be deemed to have failed under a major revision of the BESA HIU Test Standard. BESA technical committee chair Gareth Jones highlights the key changes Modutherms MTA Plus HIU T he BESA HIU Test Standard is going through a major revision. As part of this, every parameter (and underlying assumptions) within the test standard (there are more than 100) has been reviewed and either justified or changed. Most require the production of a supporting technical note. The changes include the introduction of minimum performance standards, which means those HIUs that do not meet these requirements will be deemed to have failed. First published in 2018, the standard was developed to assess UK heat network operating parameters. This revision has been carried out by the Technical Committee for the BESA HIU Test Standard, which has been meeting monthly for more than two years. It has generated a vast body of evidence as a supporting reference to the decisions made. Some of this work has already had a wider impact in the market. For instance, the technical note produced by the committee was the genesis for the CIBSE Guidance Note Domestic hot-water temperatures from instantaneous heat interface units (bit.ly/CJAUG22DHW). The test was referenced extensively in the CP1 Heat networks: Code of Practice for the UK (2020). Additionally, the HIU heat loss data from the test is to be entered into the Product Characteristic Database (PCDB), which is used in the SAP 10.2 calculation methodology. All this work was published as part of a market consultation exercise that was completed at the end of June. Off the back of this, all parameters for the test regime have now been finalised. A last exercise is being carried out to review what changes are needed to the design of the test rig, given the new parameters of the standard. Once complete, the current three test houses will make changes to the rigs, before beginning a series of round-robin testing to ensure consistency across them all. Testing to the new standard is set to begin at the end of 2022. There are two key changes to approach that represent a step change for the regime. These are: 1. A change to a modular approach, which, together with various new tests, will allow an expansion of the regime to include different HIU types. These include non-keepwarm HIUs, to be used on heat networks with multiple risers, along with HIUs that have direct space heating. A non-keepwarm HIU does not include the integral keep warm function where the integral keep warm function allows a trickle flow across the HIU plate. Instead, a thermostatic bypass valve is fitted to the top of each riser. This approach is suitable for a multi-riser approach with minimal lateral runs. 2. Introduction of minimum performance requirements, with a pass or fail. Until now, the test standard has only shown comparative HIU performance. However, HIUs will now be required to pass to have results published. There have also been some changes to test approach: n Differential pressure (dP) is being varied, including on a dynamic basis within domestic hot water (DHW) tests. This is to better reflect real-world conditions. n A test has been introduced to assess maximum DHW load. Finally, there have been some key changes to test parameters, to mirror the direction of the industry. These include: n A reduction of primary flow temperatures to 55C for the low temperature regime, to acknowledge a shift to heat pump-based heat networks n A reduction in DHW delivery temperature to 50C, in line with both CP1 (2020) and the CIBSE Guidance Note Domestic hot-water temperatures from instantaneous heat interface units n A reduction in space-heating temperatures to 55C for the high temperature regime, in line with the change in Building Regulations n More stringent requirements on DHW temperature fluctuations, particularly in respect of maximum temperatures, to reduce the risk of scalding. CJ G ARETH JONES is chair of the BESA HIU Standard steering group and technical committee, and managing director at FairHeat www.cibsejournal.com August 2022 33