Ground Source

Ground Source Heat Pumps (GSHP) utilise the recovery of energy as low grade heat from the ground or a body of water, or the rejection of heat from a building into the ground, usually utilising ground source heat pumps (GSHP).

To meet Renewable Heating targets, the UK Government policy is to pursue a massive increase in the electrification of the nation’s heating, primarily through the use of heat pumps. The ‘carbon intensity’ of electricity will reduce radically over coming years as renewable and nuclear sources replace fossil fuel power stations. Many heat pumps will use heat from air, but perhaps 20% will use heat from the ground or bodies of water.

Carbon Zero Consulting firmly believes, based on many years experience, that ground source heating and cooling provides the most efficient and robust renewable heating and cooling technology. The advent of the Renewable Heat Incentive (RHI) for GSHC systems greatly improves affordability of the technology.

The temperature of the soil and upper few metres of rock are at a remarkably constant temperature, equal to the average annual air temperature. For example in southern England this average is about 12°C and in northern Scotland the average is about 9°C. The sun provides the majority of this heat energy with only a very small amount coming from the Earth’s interior. Of course, the ground temperature is not enough to heat a building directly. That’s where a ground source heat pump comes into the picture…see our explanation of how a heat pump works below. But first a brief explanation of the most common methods for a heat pump to take heat from the ground: For a detailed step by step guide to installation see here

Closed Loop Heat Pump

Ground Source Heat Pump Closed Loop

Heat is absorbed from the ground (initially at about 12°C) via plastic pipes filled with a thermal transfer fluid. The pipes can be installed horizontally in trenches, in boreholes or in a lake or river. The length of pipe required to provide sufficient ‘ground-source’ depends on the building’s seasonal heating/cooling characteristics and the properties of the rock or water body. The temperature of the fluid in the pipework, and in the ground, decreases during a heating season. Careful design is required to ensure the ground source is of sufficient capacity to prevent the temperature dropping too low.

As there is no pumping of groundwater in a closed loop system, there are no requirements for a system to be located on a productive aquifer – and (normally) no involvement from a Regulator.

Open Loop Heat Pump

Open Loop Ground Source Heat Pump

In areas of suitable geology, water is pumped from a borehole to a heat exchanger – linked to a heat pump. Water from a borehole is at a near-constant temperature (about 12°C in southern England). Thermal energy is extracted from the water within the heat pump cycle. The resulting cooled water is then re-injected to the ground or returned to the environment.

Ground source heating and cooling systems can be designed to provide heating for a small house requiring just a few kilowatts (kW), up to very large commercial buildings requiring many megawatts (MW) of heat and cool. Closed and open loop systems can provide cooling as well (or instead) of heating. Open loop ground source is particularly well suited for passive cooling as groundwater is already at a perfect temperature.

The fundamental science behind heat transport in the ground, is directly analogous to groundwater flow. Design and assessment of GSHC systems is therefore an extension of our long standing expertise in hydrogeology. This extension is often referred to as “Thermogeology”.

Carbon Zero Consulting has specific, unrivalled experience of the thermogeological properties of the UK, with detailed involvement in many of the UK’s larger and most successful systems. John Findlay is the Vice Chairman of the Ground Source Heat Pump Association (GSHPA, http://www.gshp.org.uk/). He is closely involved with the development of industry standards for closed and open loop systems.

Open loop systems require the project to be located on suitable geology (an aquifer). The project will also require compliance with water resource laws as regulated by the Environment Agency, Natural Resources Wales or the Scottish Environmental Protection Agency. Together with our specialist associates, we provide support to your GSHC project from concept development to design, project management, installation and regulatory permitting.

How A Heat Pump Works

How Ground Source Heating Works

A heat pump ‘moves’ heat from a low-temperature external source (the ground) to a higher-temperature interior space (e.g. your house or business).

Anyone who has a refrigerator has witnessed the operation of a heat pump. A refrigerator extracts heat from your bottle(s) of wine and ‘pumps’ the heat into your kitchen via a heat exchanger (the condenser) located on the back surface of the fridge. The heat flows from the inside of the fridge to your kitchen until the contents of the fridge are at the desired, lower, temperature.

A heat pump’s job of elevating low-grade heat to 35°C or higher involves a cycle of evaporation, compression, condensation and expansion. A refrigerant is used as the heat-transfer medium that circulates within the heat pump.

  1. The cycle starts as the cold, liquid refrigerant passes through a heat exchanger (evaporator) and absorbs heat from the low-temperature source (liquid from the ground loop). The refrigerant evaporates into a gas as heat is absorbed.
  2. The gaseous refrigerant then passes through a compressor where the refrigerant is pressurised, raising its temperature
  3. The hot gas then circulates through a second heat exchanger (condensor) where heat is removed and pumped into the building at up to 55°C, although 35 – 40°C provides the greatest level of efficiency and is sufficient for underfloor and specialist radiator heating applications.
  4. Following transfer of some heat within the condenser, the refrigerant changes back to a liquid. The liquid is rapidly cooled as it passes through an expansion valve and begins the process again.