Quiet, consistent heat from the ground beneath your home.

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

1. 

   A house, and two holes in the garden

   The house is drawn straight on. Under the lawn, two narrow shafts go straight down - you can see the top of one of them on the left, and the trench that carries the pipes back to the house.

2. 

   

   Down the borehole

   Each borehole is a single sealed loop: one pipe goes down, turns round at the bottom, and comes back up. Most of the depth is not drawn here - the torn band is where the drawing admits it. They are typically 100 to 150 metres.

   • Borehole, drilled and grouted
   • A single loop of pipe goes down and comes back
3. 

   

   The turn at the bottom

   Below the torn band the drawing is at true scale again - that is what the dimension down there is for. This is the U-bend at the toe of the bore. Nothing is taken out of the ground and nothing is put into it.

   • The loop turns round at the bottom
4. 

   

   Back to the house in one shallow trench

   Two pipes run side by side in a single trench: the cooler one on its way back down to the boreholes, the warmed one on its way in. The cooler pipe is deliberately drawn shallower, which is why nothing has to cross anything.

   • Header trench back to the house
   • Cooler fluid going back down
   • Warmed fluid coming up
   • Underfloor heating in the screed
5. 

   

   Where the loop meets the machine

   The warmed fluid comes up into the base of the heat pump and the cooled fluid goes straight back down. It never meets the water in your radiators - the two circuits only ever touch through a metal wall.

   • Underfloor manifold
   • Fuse board
   • Hot-water cylinder
   • Heating coil - heating water never mixes with your tap water
   • Cold water mains
6. 

   

   Inside the machine: four steps, over and over

   This is the only part of the whole picture that uses electricity. A sealed refrigerant goes round and round, and at each of the four stations it visibly changes.

   • Electricity from the grid
   1. 1 CollectevaporatorEnvironmental energy warms the refrigerant until it boils. It leaves as a warm gas at low pressure.
   2. 2 SqueezecompressorElectricity drives the compressor, squeezing that gas into a much smaller space. It leaves hot and at high pressure.
   3. 3 ReleasecondenserThe hot gas hands its heat to your heating water and condenses. It leaves as a hot liquid, still at high pressure.
   4. 4 Resetexpansion valveA valve drops the pressure and the liquid flashes cold. It leaves as a cold mist, ready to collect more.
7. 

   

   Where the heat actually goes

   Warm water runs to the pipes buried in the ground-floor screed, up to the radiator, and through a sealed coil inside the hot-water cylinder. Your tap water never touches it.

   • Radiator
   • Warm water out
   • Cooler water back
   • Your shower and taps

8. Three separate circuits. Heat passes between them; the fluids never mix.

   Ground loop heat crosses here Refrigerant heat crosses here Heating water

   The loop in the ground is sealed, and so is the refrigerant inside the machine. Nothing from the borehole ever reaches a radiator or a tap.