Abstract
Heat exchangers are vital to any geothermal system looking to use direct heat supplied via a district heat network. Attention on geothermal schemes in the UK has been growing, with minimal attention on the performance of heat exchangers. In this study, different types of heat exchangers are analysed for the Cheshire Basin as a case study, specifically the Crewe area, to establish their effectiveness and optimal heat transfer area. The results indicate that counter-current flow heat exchangers have a higher effectiveness than co-current heat exchangers. Optimisation of the heat exchange area can produce total savings of £43.06 million and £71.5 million, over a 25-year lifetime, in comparison with a fossil-fuelled district heat network using geothermal fluid input temperatures of 67 °C and 86 °C, respectively.
Highlights
For deep geothermal schemes that target conventional resources in the UK relatively little work has been undertaken analysing the effectiveness of heat exchangers for district heating schemes
When analysing the higher geothermal fluid input temperature, counter-flow heat exchangers showed an exponential decrease in geothermal fluid output temperature with increasing transfer area, until it reached the circulating fluid input temperature of 30 ◦C (Figure 4a)
This shows that the counter-current flow exchanger is working efficiently, with most of the heat transferring to the circulatory fluid with larger surface areas
Summary
For deep geothermal schemes that target conventional resources in the UK relatively little work has been undertaken analysing the effectiveness of heat exchangers for district heating schemes. Heat exchangers are important to any geothermal scheme as they ensure that the extracted heat is useable, supplying the demand directly. Low-enthalpy or lowtemperature geothermal schemes usually exploit resources under 100 ◦C, and heat is transferred from a doublet (two-well) system through a heat exchanger which feeds a district heat network (DHN) (Figure 1). A heat exchanger operates by transferring heat between two fluids over a given surface area, preventing corrosion and scaling caused by the geothermal fluid in the DHN [1]. It is important to calculate the outlet temperature of the geothermal fluid to assess further use in a cascade scheme or for geothermal modelling of the subsurface during re-injection
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