Techno-economic assessment of Bi-directional Low Temperature Networks

This work presents an approach to determine the optimal design configuration and circulation temperature for a given Bi-directional Low Temperature Network (BLTN) using scenario analysis. BLTNs are capable of supplying both heating and cooling via a bi-directional network of 'warm' and 'cool' pipes. They feature decentralised network circulation pumps and building integrated heat pumps, permitting low pipe circulation temperatures and thereby enabling low-grade heat to be rejected into the network. As a case study, a BLTN layout was conceived for a small section of a university campus, currently served by a high temperature heating network with gas-based CHP and boiler plant heat sources. The proposed BLTN utilises a horizontal ground source array and considers future estimated cooling loads which must be served by the network, in addition to existing heating loads. After analysing different design configurations at various heating to cooling load ratios, the headline result from this study is that an ambient temperature design, without centralised ground source heat pumps to control the network temperature, represents the most cost effective option. This result, based on the levelised cost of heating and cooling (LCOHC) over a 50 year period, is consistent regardless of the heating to cooling load ratio for the system. Moreover, as cooling loads are increased, the ambient temperature design becomes increasingly cost-effective relative to other options.