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HEAT NETWORKS | AMBIENT LOOP AMBIENT LOOP COSTS A feasibility study using waste heat from a supermarket chiller to heat housing via an ambient loop heat network has revealed higher costs than expected as a result of the use of ground source heat pumps in the design. The analysis, by Martin Crane, director at Carbon Alternatives, found that the ambient loop had been designed more like a heat pump ground loop, because the available heat pumps are primarily designed for ground-source applications. As a consequence, the heat network design required larger pipes and more pumping energy to maintain the constant circulating flow required. Crane says most of the source pumps in GSHP are either on or off, so when the heat pump is operating part load the source flow rates are as per peak demand, reducing flow diversity on the ambient loop. The analysis found ambient loop network costs were higher because of the requirement for larger pipes, leading to the need for larger trenches. A longer article based on this research will appear in Septembers CIBSE Journal. The analysis is part of a feasibility study funded by the Heat Networks Delivery Unit and research funding from OxFutures. Biomass boilers Ice store Ground source heat pump Low-temperature network (image courtesy of Dimplex) insulation added easily for required sections. As such, network infrastructure costs are lower than the installation of high-temperature DHN systems. The network also experiences much lower system losses, as the temperature gradient between the network and ambient is very close. This is in comparison to high-temperature networks, where an ongoing issue for many buildings is the standing loss from the distribution network into shared spaces, creating summer overheating. Having individual plant but a common fuel source is more in line with most residents experience, with individual control and responsibility for the domestic boiler. Each recipient is free to change their electricity provider. One of the key limitations to the implementation of shared-loop networks is capital costs. At present, the capex for shared-loop infrastructure is a lot higher than corresponding gas or direct electric alternatives. The Renewable Heat Incentive offers support, but will stop accepting commercial applications in March 2021 and domestic applications a year later. The Clean Heat Grant consultation, launched in April 2020, indicated that shared-loop networks would be eligible for a 4,000 grant per heat pump (below 45kW). However, funding for this scheme is currently only described for 2022-24. DHW is also an issue, as heat pump systems require a local hotwater cylinder, unlike combi-boiler or DHN direct plate installations. Only 11 of the 26 million UK residences are believed to still have a hotwater vessel. Implementing heat pump solutions would require their reintroduction, with corresponding space implications. The higher delivery temperatures to generate DHW also reduce heat pump efficiencies. Until recently, most multi-occupancy developments in London were delivered with gas CHP-driven, high-temperature networks but the decision to implement SAP10 carbon weightings as a consideration to planning has resulted in a significant shift to lowtemperature and ambient shared-loop networks. This shows the effect of a small policy change where there is a competitive market for development. It is to be seen if similar policy changes can give the same impetus across the UK. The integration of heat pumps into smart energy networks, where they respond more flexibly to demand signals within the grid system, offers potential operational savings and a useful grid service, but research on these impacts once heat pumps are adopted at scale is still to be tested outside a few isolated trials. CJ DAVID LINSLEY-HOOD is consultancy director at Locogen The CIBSE ASHRAE Technical Symposium will be held online on 14-15 September. Register at cibse.org/symposium PARASOL Zenith Ready for change SITE D ON OLVE S High performance 4-way distribution comfort module with cooling, heating and ventilation. PARASOL Zenith offers all the benefits of active chilled beam technology with added flexibly throughout your project. With the options of constant, variable or demand control air flow, PARASOL Zenith provides the perfect indoor climate. Parasol Zenith Ad Folder CIBSE.indd 1 36 August 2020 www.cibsejournal.com CIBSE Aug2020 p35-36 Tech symp networks.indd 36 13/02/2020 15:45:45 24/07/2020 17:34