What Is “Average Ground Temperature”?
In MCS heat pump system design (MIS 3005), the “average ground temperature” (in °C) refers to the mean annual temperature of the ground at the depth of the ground heat exchanger. This value is essential for correctly sizing and designing closed‑loop ground-source systems.
Section: Why It’s Important
It limits the maximum heat extraction rate to ensure the thermal transfer fluid entering the heat pump remains above 0 °C, meeting MCS requirements for system longevity and performance.
Ensures the design supports ground thermal equilibrium over the system’s lifetime.
If a site-specific measurement isn’t available, the annual mean air temperature based on Met Office data must be used as a conservative proxy
Section: Practical Guidance for Installers
Always aim to determine site-specific average ground temperature using:
Borehole data,
BGS (British Geological Survey) logs,
Thermal response testing,
Or thermo-geological assessments.
If none of the above is available, use the annual mean air temperature for the region (from Met Office tables, based on 1981–2010 data) as the default value.
Document the source of your value and how it was determined—this is critical for MCS auditing and subsidy eligibility.