HEAT NETWORKS | REGULATION Lowering temperatures With the decarbonisation of electricity, heat networks are being designed with heat pumps as the energy source, rather than gas-fired CHP. For heat pumps to be truly effective, says Jones, the flow and return temperatures should be lower than for a traditional CHP district network. Heat pumps are affected by changes in temperatures, both in terms of the efficiency of the refrigeration cycle and the system complexity required to reach high temperatures from cold sources. The coefficient of performance of heat pumps drops quite dramatically at higher temperatures; 5K can make a really big difference, says Jones. A review of three heat pump manufacturers, for example, showed an increase in seasonal coefficient of performance of 13%-21% when generating and distributing at 60C as opposed to 65C. Where heating systems serve DHW and space heating, it will be the DHW supply temperature that defines system temperatures, as the space heating can be a lower temperature. So, a 5K reduction in DHW allows a 5K reduction in generation and distribution temperatures. One barrier to lower temperatures has recently These Telford Homes apartments near London Docklands had acceptance testing TESTING EVERY HOME A consultant is like a GP, says Chris Savoy, head of services at Telford Homes. They know a lot about heat networks, but theyre not specialists. Telford Homes has been acceptance testing new dwellings on heat networks to ensure that performance is in line with the design intention. It has been using FairHeat to check consultant designs for heat networks, and uses the specialist to carry out checks at design, installation and commissioning stage. It also uses FairHeat to ensure water quality and that the BMS controls are implemented properly. Savoy says checks allow him to identify competent designers and contractors, which helps him select the supply chain. The good ones are those that are prepared to be educated and follow British Standards and the ADE CIBSE Heat Network Code of Practice, he says. The focus for Savoy is now on gathering performance evidence including water quality from the first year of operation to ensure that the maintenance contractor is running the system properly. You have to have evidence. You have to prove performance, he says. been overcome after the HSE clarified that HIUs with instantaneous hot water generation are deemed a low legionella risk. Heating systems with hot-water storage have typically had to maintain water at a high enough temperature to prevent the growth of legionella bacteria. However, this is not necessary for low-volume systems where, for example, hot water is supplied instantaneously through a heat exchanger. The HSE says that, under HSG274, Part 2, HIUs should be able to achieve a peak temperature of 50C to 60C. Jones says that network temperatures should be 55C at the HIU, with 50C from the HIU to the tap. Many designers have used a 55C minimum to the tap. This requires a minimum 60C network temperature. The new version of CP1: Heat Networks: Code of Practice for the UK will include far more performance metrics and introduces the concept of acceptance testing. Acceptance testing allows validation of whether heat networks meet specified performance requirements and, as such, is well aligned with the move toward technical certification, as proposed by BEIS. Effectively, acceptance testing will be one of the core mechanisms for any future heat network assurance scheme, says Jones. Our experience is that acceptance testing has a significant positive impact on network performance, with many networks performing better than design because of rigorous commissioning he adds. Telford Homes is using acceptance testing to check its heat networks before handover (see Site test, CIBSE Journal, August 2018), and now also uses FairHeat to test the design, installation and commissioning. (See panel, Testing every home.) Jones says the experience of acceptance testing out in the field will form the basis of an assurance scheme that aims to make sure developers build low carbon heat networks that offer comfort for consumers without the expense. CJ 3803,1*6(/(&7,216)25 38%/,&+($/7+(1*,1((56 6SHFLDOLVWLQZDVWHZDWHUDQGVHZDJHSXPSLQJ 5DSLGUHVSRQVHSXPSDGYLFHVHOHFWLRQVGDWDVKHHWV %HVWWHFKQLFDODQGFRPPHUFLDOSXPSVROXWLRQV &DOORXUH[SHULHQFHGWHDPWRVSHFLI\\RXUSXPSLQJVROXWLRQ )ORRU0RXQWHG/LIWLQJ6WDWLRQV 32:(5( %< ZZZMXQJSXPSVFRXN