Ground Source Heat Pumps: 4 Options
Ground source heat pumps require little maintenance once installed, but installation is a distruptive process. However, before you dismiss this renewable technology because of the inevitable upheaval created, have a look at the various methods and systems that can be used: they don’t all require large amounts of digging! Instead there are a variety of ways to harvest energy from the ground in order to feed a ground source heat pump system with valuable natural energy, here we cover the spectrum of options.
Ground Source Heat Pump Collectors
The most traditional of collector type, the horizontal collector, consists of continuous lengths of plastic pipe between (25mm – 40mm diameter) being laid out in the bottom of an excavated hole or trench separated by a fixed distance. The pipes are often made from polyethylene plastic, laid around 1.2-1.5m below ground level and are either 100m or 200m in length. Depending on the ground conditions and heat pump size the amount of buried pipe will vary.
The collector loops all gather in a sunken plastic or masonry inspection chamber in which they are connected to a main flow and return manifold. This allows low grade heat to be gathered from a large area and yet only two pipes return from the manifold location to the plant room location where the heat pump is located.
As a rule of thumb in average ground conditions occupy an area twice the size of the total floor area of the home would be required to gather energy for the home all year round.
Slinkies are made from a similar material to standard horizontal collectors and are often 20mm-25mm in diameter. Unlike standard collectors they come in a continuous coil that is placed in a 1.2m-1.5m deep trench, stretched out and then laid down (a bit like a flat slinky) and pinned in place. Instead of having equally spaced pipework there are many intersections in a single loop and for this reason are not preferred by some installers due to likelihood of premature ground freezing during winter.
The main advantages of slinkies are that they are quicker and easier to install than standard collectors. They also reduce ground works and take up less land space.
For those with limited land available a borehole solution could be beneficial. Boreholes use specialist drilling equipment to bore vertically down to depths of around 100m. Into the 150mm diameter hole created by the drilling rig a loop of pipe is inserted and backfilled with a bentonite clay material that helps conduct heat from the surrounding earth to the pipework.
Energy is absorbed from the surrounding ground but predominantly from water flowing through the rock strata providing excellent year round performance.
Because the boreholes go down vertically and only need to be spaced apart by around 6m they consume very little space in order to harvest enough energy to heat the home.
The final solution is a technological hybrid between horizontal collectors and boreholes in the form of the Helix Probe from Rehau. This system uses pre-packaged pipe coils with a total coil diameter of around 500mm. An array of holes is drilled using an auger to about 3m deep and the coils inserted and backfilled with earth. The tails are connected together and brought back to a manifold similar to that used by horizontal collectors. This system needs approximately 25-33% of the ground area required for horizontal collectors.
So there you have it. A quick whirlwind tour of your ground collector options if you are thinking of harvesting energy from the ground. Please do read some more of our related GSHP blogs for more useful info.