How do ground source heat pumps work?

A ground source heat pump is a highly efficient low-carbon heating system that extracts renewable heat from the ground to provide heating and hot water for buildings.

What is the refrigerant cycle?

The refrigerant cycle is at the heart of how a heat pump operates, continuously moving heat from one place to another. It has four main stages.

1. First, the refrigerant absorbs heat from the ground via a heat exchanger and evaporates into a low-pressure gas.
2. Next, a compressor squeezes this gas, increasing its pressure and temperature. The hot, high-pressure refrigerant then passes through a heat exchanger (the condenser), where it transfers heat to the home's heating system and condenses back into a liquid.
3. Finally, an expansion valve reduces the pressure and temperature of the liquid refrigerant, preparing it to absorb more heat and restart the cycle. This continuous process delivers significantly more heat energy than the electrical energy it consumes.

What is a refrigerant?

Refrigerants are chemical substances that change easily between liquid and gas states, making them ideal for transferring heat. Refrigerants used in heat pumps include R407c, R134a and R290 (which is propane), but there are others.

Do heat pumps work in cold weather?

Absolutely. Ground source heat pumps perform incredibly well in cold weather. The temperature of the ground stays at about 8-12°C all year, meaning ground source heat pumps work efficiently throughout the coldest spells, with no compromise on efficiency.

That is one of the things that sets ground source heat pumps apart from air source heat pumps, which become much less efficient and require much more energy input when the weather is cold. The typical example of this is at night, when it gets much colder, ground source heat pumps maintain the same level of efficiency. This gives more choice to households, enabling them to run their heating and hot water on cheaper overnight tariffs.

Can I use a ground source heat pump with underfloor heating?

Absolutely. In fact, underfloor heating is recommended. Underfloor distribution systems work especially well with ground source heat pumps because they operate at lower flow temperatures. The large surface area of underfloor heating means the heat pump can deliver flow temperatures of just 35°C. This makes for superb efficiency, leaving you with lower heating bills.

Do ground source heat pumps work with radiators?

Absolutely. As with any heat pump, radiators need to be sized to offset the heat loss in a given room. As the flow temperature is decreased, the surface area of the radiator needs to be increased to achieve the same heat output.

Can I use a combination of underfloor heating & radiators with a heat pump?

Yes. Combining underfloor heating and radiators with a ground source heat pump is a very common and effective solution. This hybrid approach allows you to tailor the heating to different areas of your home. For example, you might prefer the consistent, gentle warmth of underfloor heating in living areas and bathrooms, while using radiators in bedrooms.

Modern heat pump systems can be designed with different zones, allowing them to supply water at the appropriate, efficient temperatures for both underfloor heating and radiators simultaneously. This offers flexibility and optimised comfort throughout your property.

How do I calculate the heat loss of my home?

Calculating your home's heat loss is crucial for sizing a heat pump system correctly. In simple terms, heat loss is determined by how well your home's structure – walls, windows, roof, floor – insulates against the cold, combined with the temperature difference between inside and out.

A basic formula involves multiplying what is called the U-value of each building element – how well a material conducts heat – by its area, and the temperature difference. But for the accurate assessment required for heat pump installation, a professional heat loss survey. This detailed room-by-room calculation will need to be compliant with British  BS EN 12831 standard.

Can I use a ground source heat pump for hot water?

Kensa ground source heat pumps can be run at flow temperatures up to 65°C,  and produce DHW to 60°C.

How do ground source heat pumps produce hot water?

When the domestic hot water timeclock calls for the production of hot water, a three-port valve diverts flow from the heating distribution circuit into an indirect coil within the hot water cylinder. The temperature gradually builds up within the cylinder..

When the hot water production ends, the three-port valve switches back to the heating distribution system and the temperature drops back to its space heating design temperature. The heat pump then reverts to space heating mode or switches off if no zones are calling for heat.

The only thing to note is that due to the lower flow temperatures generated by the heat pump, the hot water tank must have an oversized coil to provide the correct heat transfer. The larger the size of the coil within the tank, the better the heat transfer area and the better the domestic hot water performance will be.

Can a heat pump be used for cooling?

Yes.  Ground source heat pumps and ground arrays can be used for passive cooling that protects from overheating. Kensa offers optional passive cooling for ultra-low-cost comfort in the summer, whilst recharging the ground for a more energy-efficient ground source heating system.