Skip to Content
Cooling systems

Heating and cooling from one ground source system.

A ground source heat pump can run in reverse: the same boreholes that warm a building in winter carry its excess heat back into the ground in summer. Passive or active, it replaces standalone air conditioning with one coordinated system.

Request a consultation Compare passive and active
20+ years' experience 4,000+ systems installed In-house design and delivery
20+
Years designing heat-pump systems
4,000+
Systems installed since 2006
In-house
Design, drilling and installation
MCS
Certified contractor
Two routes

Passive and active cooling solve different problems.

Neither route is universally better — the right choice depends on how hot the building gets and how tightly it must be controlled.

Passive cooling

Also called free cooling. The brine circulates through the ground collectors, where the naturally cooler earth chills it before a heat exchanger turns it into chilled water for the building. The compressor never runs — only the circulation pump — so the energy use is minimal.

  • Very low running cost — only circulates fluid
  • Recharges the ground with heat for more efficient winter heating
  • Simple integration with an existing ground source system
  • Gentler than active cooling — best for buildings that do not overheat severely

Active cooling

The heat pump's evaporator and condenser circuits are reversed, so the compressor actively extracts heat from the building and transfers it into the ground through the boreholes or collectors. The result is performance comparable to conventional air conditioning, held at a set temperature.

  • Maintains a set cooling temperature
  • Performance comparable to traditional air conditioning
  • Higher running cost than passive, still below standalone AC
  • Capacity is bounded by the ground array's ability to absorb heat — a design-stage calculation
The same flat cross-section as the heating illustration, showing the summer mode of the same system. Two boreholes run deep into bedrock - typically 100 to 150 metres - drawn at true scale near the surface and near the toe, with a labelled break where most of the depth is not drawn. The sealed ground loop now leaves the heat pump carrying warmth from the house, goes DOWN one side of each borehole where short arrows show that warmth passing out into the rock, and comes back up cooler. Inside the house the underfloor circuit sends cool water out to the floor and receives it back warmer, so the colours of the two pipes are the reverse of the heating picture: colour follows the water's temperature. The radiator branch is drawn grey and still, because radiators cannot cool. The hot-water cylinder and its coil are drawn in the hot-water colour but dashed and without moving speckles, because the cylinder is still heated by this machine all summer - the machine simply pauses cooling and runs its compressor for a while to do it, rather than doing both at once. During cooling itself the compressor is off and only the two circulation pumps run. The three circuits still never mix.

Scroll the picture sideways to see all of it. Every label is written out below.

How a ground-source heat pump cools the same house in summer - passive cooling

What is in the picture

  • Ground loop: warmed fluid down the boreholes, cooled fluid back Borehole, drilled and grouted; Header trench back to the house; A single loop of pipe goes down and comes back; The loop turns round at the bottom; Cooler fluid going back down; Warmed fluid coming up
  • Floor circuit: cool water out to the floor, warmer water back Underfloor manifold; Hot-water cylinder; Heating coil - heating water never mixes with your tap water; Underfloor heating in the screed; Radiator; Warm water out; Cooler water back
  • Electricity from the grid, running the pumps Electricity from the grid; Fuse board
  • Tap water, kept completely separate from the heating water Your shower and taps; Cold water mains
  • Refrigerant sealed inside the heat pump, resting

The four steps inside the heat pump

  1. 1 Collect evaporator Environmental energy warms the refrigerant until it boils. It leaves as a warm gas at low pressure.
  2. 2 Squeeze compressor Electricity drives the compressor, squeezing that gas into a much smaller space. It leaves hot and at high pressure.
  3. 3 Release condenser The hot gas hands its heat to your heating water and condenses. It leaves as a hot liquid, still at high pressure.
  4. 4 Reset expansion valve A valve drops the pressure and the liquid flashes cold. It leaves as a cold mist, ready to collect more.
The same flat cross-section as the air-source heating illustration, showing the summer mode of the same machine. A reversing valve inside the outdoor unit swaps the roles of its two heat exchangers, so the plate exchanger against the heating water becomes the evaporator and the finned coil outside becomes the condenser. Warmth is taken out of the underfloor circuit - short orange arrows show it leaving the rooms and passing down into the screed - carried through the sealed refrigerant circuit, which is running at full speed with the compressor turning, and pushed out across the finned coil into the outside air. The air still travels the same way, in at the top of the coil and out low across the lawn away from the house, but it now arrives as the paler, cooler blue and leaves as the darker, warmer one, because colour follows temperature. The two heating pipes swap tones for the same reason: the pipe leaving the machine is now the cooler of the pair. The radiator branch and the hot-water cylinder coil are drawn grey and still, because radiators cannot cool. Electricity is drawn at full strength, because active cooling of this kind really does cost electricity to run.

Scroll the picture sideways to see all of it. Every label is written out below.

How an air-source heat pump cools the same house in summer

What is in the picture

  • Floor circuit: cool water out to the floor, warmer water back Insulated pipes through the wall; Hot-water cylinder; Heating coil - heating water never mixes with your tap water; Underfloor heating in the screed; Underfloor manifold; Radiator; Warm water out; Cooler water back
  • Electricity from the grid, running the compressor Electricity meter; Fuse board; Electricity from the grid
  • Tap water, kept completely separate from the heating water Your shower and taps; Cold water mains
  • Outdoor air: in at the coil cooler, out again a few degrees warmer Outdoor air is drawn in here; The same air is blown out here, a few degrees cooler; Finned coil - the air gives up its warmth here
  • Refrigerant sealed inside the outdoor unit, running in reverse

The four steps inside the heat pump

  1. 1 Collect evaporator Environmental energy warms the refrigerant until it boils. It leaves as a warm gas at low pressure.
  2. 2 Squeeze compressor Electricity drives the compressor, squeezing that gas into a much smaller space. It leaves hot and at high pressure.
  3. 3 Release condenser The hot gas hands its heat to your heating water and condenses. It leaves as a hot liquid, still at high pressure.
  4. 4 Reset expansion valve A valve drops the pressure and the liquid flashes cold. It leaves as a cold mist, ready to collect more.
Diagram of a ground source heat pump moving building heat into the ground in cooling mode
Why it works

The ground is a natural coolant.

Below around 15 metres the earth holds a near-constant 10–12°C all year — far cooler than summer air. That difference is what a ground source system uses to cool a building without fighting the weather.

There is a second benefit: every kilowatt of heat moved into the ground in summer pre-charges it for winter, so the heating season starts from a warmer source and runs more efficiently. Boreholes and water-source collectors perform best on cooling duty, because they typically interface with groundwater and transfer heat at much higher rates.

Delivery

How the cooling reaches the rooms.

Fan coil units

Compact room units blow air over a coil carrying chilled water — rapid, controllable cooling similar to a conventional air-conditioning terminal, powered by the heat-pump system.

Underfloor cooling

Chilled water circulated through underfloor heating pipes provides gentle, even cooling. A dew-point controller manages the water temperature so the floor never falls below the condensation threshold.

Specified at design stage

Not every heat pump has cooling capability built in. Cooling must be specified early so the right equipment, emitters and controls are included from the first drawing.

Versus air conditioning

One system instead of two.

Heating, cooling and hot water from a single plant — not a heating system plus a separate air-conditioning installation.

One plant, three duties

Heating, cooling and hot water from the same system — saving plant space, capital cost and maintenance overhead.

Lower running costs

Passive cooling uses barely any electricity; even active cooling runs below a standalone air-conditioning system doing the same job.

Summer pays for winter

Heat rejected in summer is stored in the ground and extracted back in winter — a seasonal cycle that improves year-round performance.

Quiet and discreet

No banks of outdoor condenser units. Ground source plant sits inside or underground and operates near-silently, with zero on-site emissions.

Cooling at scale: data centres

Server halls need resilient, efficient cooling around the clock — and reject heat that can be recovered. Data centres get their own dedicated page.

Explore data centres

Planning a ground source installation?

Cooling capability starts with the ground array. See how we design and install ground source heat pump systems end to end.

Explore GSHP installation
Questions

Cooling with a heat pump, answered.

Most modern ground source heat pumps can provide passive cooling, and many models also support active cooling — but it must be specified at the design stage so the correct equipment and controls are included. Raise cooling requirements early in the conversation.

If the building does not get excessively hot, passive cooling is the most energy-efficient choice — it uses virtually no electricity. If summer temperatures climb uncomfortably and you want air-conditioning-level control, active cooling is the better route. Both use less energy than standalone air conditioning.

Yes — chilled water through underfloor pipes gives gentle, even cooling across the floor. Condensation is the design constraint: if the floor surface drops below the dew point, moisture forms. A dew-point measurement controller manages the cooling water temperature to prevent it.

The ground array's capacity to absorb heat. If the brine returns too warm, compressor efficiency drops — so borehole sizing, spacing and long-term ground temperatures are modelled at design stage rather than assumed.

One system for heating and cooling? Start with the load.

Tell us what needs cooling, when it runs and the conditions it must hold. We will tell you whether passive, active or a mix fits your site.

Request a consultation Call 01269 833100