Heat sources

What Heat Source can I use for a Heat Pump?

Ground source heat pumps can extract heat from three types of renewable sources: soil, rock and water. They do this by using buried collectors called ground arrays.

Heat source

Surface soil

Surface soil is usually an ideal source for properties in rural areas, or any building with a fair amount of surrounding land (40m x 12m). This allows room for long and shallow trenches.

Ground array for soil: Slinky pipes or straight pipe

To extract the heat from surface soil, a network of ground collectors, consisting of a series of pipes, is buried in the ground in trenches to a depth of 1 – 2m. Typically consisting of coiled pipe, collectors of this nature are referred to as ‘slinkies’.

Heat source

Rock

Rock is a perfect conductor for heat energy, particularly for properties with minimal land such as tower blocks, flats, businesses or homes with limited garden space.

Ground array for rock: Boreholes

Boreholes are the collectors used to extract heat energy from rock for ground source heat pumps. To extract heat from the rock, a U-tube pipe is installed into a drilled hole measuring 60-200m deep by 150mm wide. Boreholes are a very discreet and compact solution when saving space and minimal ground disruption is a priority.

Heat source

Water

Water is the most efficient source of heat transfer and is suitable for any property within 100m. Water sources include lakes, ponds, rivers, the sea, and even aquifers – all of which are successfully used by Kensa to provide heating and hot water to residents on the shoreline (or in boats)!

Ground array for water: Pond mats

Pond mats are typically used to extract heat from water sources, but methods such as boreholes and submerged open-loop pipework are also used to great success.

Heat source

Surface soil

Surface soil is usually an ideal source for properties in rural areas, or any building with a fair amount of surrounding land (40m x 12m). This allows room for long and shallow trenches.

Ground array for soil: Slinky pipes or straight pipe

To extract the heat from surface soil, a network of ground collectors, consisting of a series of pipes, is buried in the ground in trenches to a depth of 1 – 2m. Typically consisting of coiled pipe, collectors of this nature are referred to as ‘slinkies’.

Heat source

Rock

Rock is a perfect conductor for heat energy, particularly for properties with minimal land such as tower blocks, flats, businesses or homes with limited garden space.

Ground array for rock: Boreholes

Boreholes are the collectors used to extract heat energy from rock for ground source heat pumps. To extract heat from the rock, a U-tube pipe is installed into a drilled hole measuring 60-200m deep by 150mm wide. Boreholes are a very discreet and compact solution when saving space and minimal ground disruption is a priority.

Heat source

Water

Water is the most efficient source of heat transfer and is suitable for any property within 100m. Water sources include lakes, ponds, rivers, the sea, and even aquifers – all of which are successfully used by Kensa to provide heating and hot water to residents on the shoreline (or in boats)!

Ground array for water: Pond mats

Pond mats are typically used to extract heat from water sources, but methods such as boreholes and submerged open-loop pipework are also used to great success.

Factors that could influence

Your choice of heat source

There are many things to consider when it comes to choosing a heat source and collector. Remember that Kensa can help you with anything from finding an installer, to design or commissioning support. If you’re an installer yourself, you can even use our MCS Umbrella Service.

Nearby water

If you are within reasonable reach (100m) of a water source such as lake, stream, or the sea, this should be your first option for a heat source. Water has exceptional thermal conductivity and cheaper installation costs.

Cost

Borehole drilling is the most expensive of the ground array options, but it’s the quickest and least invasive option.

Geology

The ground conditions and conductivity of the underlying geology will influence the cost of any ground array.

Heat loss calculation

An accurate heat loss calculation for the building is absolutely essential when designing any ground array for a ground source heat pump system. If you need help with this, Kensa conducts calculations as part of our MCS service.

Heating distribution system

The water temperature at which the heating distribution system runs will change the efficiency (CoP) of the heat pump system. So a system using underfloor heating will normally need a slightly larger ground array than one using radiators in an identical building.

Efficiency of the heat pump

One of the ironies of using an ultra-efficient heat pump like the Kensa Evo model is that the ground array size needs to increase slightly. If less energy for a given heat output is coming from electricity, then more has to come from the ground array.

Land area

As a general rule, you need a garden area of at least 40m x 12m to install horizontal heat collectors in the soil.

Reducing the heat load

Calculations for a horizontal array often reveal the garden area is too small to meet the heat load, leading to the costly alternative of using boreholes. Investing in insulation to reduce the heat load could make the garden area a viable heat source and allow for a smaller, more cost-effective heat pump.

Number of buildings

Ground arrays can be shared between multiple properties in a similar fashion to district heating. Each property will have its own heat pump, and the system won’t need any metering or billing arrangements – this is known as Networked Heat Pumps.

Other possible heat sources

Less commonly, other sources of free energy can be found in existing water wells, old mines, natural springs, river water and even seawater. While these projects aren’t so mainstream, the best ones can make highly efficient and low-cost energy sources.