HEAT PUMPS | STAR RENEWABLE ENERGY heating without burning gas and biomass and thats where large heat pump solutions come into their own, he says. Although not originally a strategic driver, we have observed the growing emphasis on air quality. Drammen still shows us a fantastic outcome in this regard, with 85% lower nitrogen oxide (NOx) emissions, the gases now attributed to lung, heart and brain disorders, but largely invisible. Although largely attributed to transport in cities, some studies have suggested 40% is actually from gas boilers and other gas devices, such as CHP. Pearson adds: The problem with replacing gas boilers with heat pumps on a piecemeal basis is that gas heating systems are, generally, designed to operate at 82C ow, 71C return temperature. If you want to replace that system with a heat pump, you cannot turn up with a domestic unit that only provides heat at 45C, he says. Star has three systems nearing completion in 2019. The Clydebank river-source scheme will provide heat at 80C, the Hillpark air source heat pump scheme at 62C, while the ground source heat pump serving the renovated old Post Ofce at Islington Square provides heat at 65C. The residents wont be aware of the heat pumps, but they will enjoy cleaner local air with less gas being burnt. Does he see a time when cities will have both district heating and cooling? If you want district cooling and heating systems, you could have four-pipes going into the buildings or a two-pipe ambient loop system and a heat pump in each building, he says. A heat pump in each building would be tricky if aiming for close to 80C and, if youve got dozens of buildings on a network, they will each require a heat pump sized for their individual max demand whereas, if youve got district heating and separate cooling systems, the central heat pump will be sized for the aggregate demand, which could be 50-60% smaller. And, because they are centralised, theyll be easy to turn off very quickly if the grid gets stressed a very valuable technique, far preferable to running auxiliary diesel peaking plant. We can also force-run and store heat, which is far more sensible than curtailment of wind farms, and turns the surplus electricity into three or more units of heat. Pearson has taken his xation with heat pumps home. As part of renovations to my house, Ill probably deploy a ground source heat pump but its a monstrous amount of money when a gas boiler would work ne, he says. But gas will eventually fade and any provision of hydrogen is predicted to be three or more Water-source heat pump scheme in Drammen, Norway times the cost of gas currently. The late Professor Sir David MacKay, the governments chief scientic ofcer, was a huge inuence on Pearsons thinking, encouraging critical thought of populist ideas in his book Sustainability without hot air. Hed question where hydrogen was going to come from, how much it would cost, whether it would require additional methane imports, and how dependent it would be on as yet unproven at-scale solutions, such as carbon capture, says Pearson. If Ive heard anything from the upsurge in thinking from [Swedish schoolgirl] Greta Thunberg who initiated the school strike for climate change movement in November 2018 it is act faster, and that, to me, means deploy what we know works: dont dream of unicorns. I hope they start encouraging a move forward from what we know is the major component of the problem burning gas for the rather simplistic need of heat. CJ HILLPARK, GLASGOW A HIGH-TEMPERATURE AIR SOURCE HEAT PUMP Client: GHA Wheatley Group Refrigerant: R134a Capacity: 400kW Temperature: 62C/40C Supported by the Scottish government Wooden building adjacent to Hillpark high-rise blocks housing Stars air source heat pump An air source heat pump providing heat at 62C (40C return) is being used to provide 351 homes with low carbon heat. The relatively high water temperatures enable conventional radiators to be used to heat the homes. The Hillpark Drive estate in south Glasgow comprises eight apartment blocks, built in the 1970s, and is operated by Glasgow Housing Association, part of the GHA Wheatley Group. It secured a 2.5m grant from the Scottish governments Local Energy Challenge Fund, plus money from Glasgow City Council, to carry out a 5m project to: upgrade the estates heating system; replace the inefcient and impractical electric storage heaters to provide affordable heating; and reduce carbon emissions. The solution, developed by project consultants WSP/Parsons Brinckerhoff, is based on an air source heat pump providing heat for a new district heating system. Gas is used as a top-up/back-up energy source. The linear layout of the eight blocks lent itself to a district heating solution. A piped central ow and return spine was formed from Rehaus Rauthermex polymer pre-insulated pipework, with heat taken off for individual blocks. The heat pump has in-built control systems for remote monitoring, to ensure optimum efciency is maintained. A single energy centre houses the 8m-long heat pump which means only one device has to be maintained and it is expected to have a service life of more than 20 years. 20 May 2019 www.cibsejournal.com CIBSE May19 pp16-18, 20 Dave Pearson Supp.indd 20 26/04/2019 16:15