Development of new ground loop sizing tools for domestic GSHP installations in the UK

Abstract

Commercially available software packages for designing closed-loop GSHP systems, such as Earth Energy Designer (EED), Ground loop designer (GLD) and GLHEPRO have been available in the UK for some time. However, these are rarely used by domestic ground-source heat pump installers owing to their complexity and availability. Until recently, installers were therefore dependent on specialist thermogeologists, manufacturers, or rules of thumb learned through experience or other sources. Consequently, when a UK field trial of domestic ground-source heat pumps showed that several systems were operating with excessively cold ground loops within four years of being installed, the UK Government and the GSHP industry identified a need to develop conservative design tools that were simple to use and readily available. A paper-based design methodology for closed-loop GSHP systems of less than 45kW heating capacity has now been brought into service through the UK Microgeneration Certification Scheme's Microgeneration Installer Standard for heat pumps MIS3005 (MCS 2012). The sizing methods for boreholes, horizontal loops and Slinkies encompasses the diverse geologies, and full extent of both ambient and ground temperatures encountered throughout the UK, over a range of domestic load factors. Supplementary guidance has also been provided on the hydraulic design of these closed-loop systems. This paper describes the underlying philosophy behind the new design tools and how the multi-dimensional task of sizing a ground loop was reduced to 3-dimensional set of tables that UK ground source heat pump installers could begin using with minimal training. With domestic GSHPs designed to these guidelines, or better, the intention is that future installations will meet the performance requirements of both the UK's Renewable Heat Incentive (RHI) scheme and the EU RES directive for renewable energy from heat pumps