Uncoiling The Facts About Ground Source Heat Pumps

by Nicola Temple on June 6, 2012

Though ground source heat pumps (GSHPs) have been around for over 50 years, they have only truly come into mainstream popularity very recently. As the name implies, they work on the principle of transferring heat that is stored in the ground to your home and/or domestic water.

GSHP systems have three components: a collector, a heat pump and a distribution system.

The collector is a series of insulated pipes that are buried in the ground anywhere from 5 feet to 6.5 feet deep (1.5-2m).  The pipes can generally be laid in a configuration that fits with the landscape, so either in a large perimeter-type loop, or zig-zagging back and forth.

The length of the ground pipes, also known as the ground loop, depends on the size of the home to be heated and the amount of heat needed; the longer the loop, the more heat is drawn out of the ground. A good rule of thumb is 2 – 2.5 times the floor space of the home.

The ground loop pipes are filled with a mixture of water and antifreeze as the water returning from the house is usually below freezing due to the efficiency with which the heat is extracted.

Heat is transferred from the ground into the pipes and the heated mixture of water and antifreeze is piped into the house. Here, the heat is then transferred from the liquid mixture into the heat pump through a heat exchanger.

This heat is then distributed throughout the house through highly efficient radiators or underfloor heating. It can also be used to heat domestic water in the house.

ground source heat pumps

Ground source heat pumps, such as this one being displayed by the US Army Corps of Engineers, convert 1 unit of electricity into 4 units of heat. CC image courtesy of the US Army Corps of Engineers on Flickr.

What are the benefits of ground source heat pumps?

First and foremost, ground heat is a renewable source of energy. The sun’s rays heat the earth whether rain or shine and this heat is a wonderful source of clean energy that we can take advantage of. Also, it’s a fantastic way to lower your personal carbon footprint as it reduces your dependence on fossil fuels.

The heat pump is highly efficient so even though it requires electricity to run, it converts every unit of electricity into 4 units of heat. This improved efficiency means a noticeable difference in your heating bill compared with using direct electric heating.

Generally, GSHPs have very low maintenance costs and long life expectancies of between 20 and 25 years for the pump and up to 50 for the ground loop.

What are the drawbacks?

Since electricity is required to power the heat pump, a reliable electricity supply is required. Depending on where you live, this electricity supply may (and is likely to) come from a non-renewable energy source and will be subject to fluctuations in electricity costs. So, GSHPs are not ideally suited for remote areas that may not have constant power.

Also, the installation is undoubtedly disruptive to your yard. This makes GSHPs ideally suited for new builds where the landscape is already dug up for foundations etc and the landscaping is far from complete.

Is a ground source heat pump for you?

This sort of system isn’t ideal for everyone, but there are certain circumstances where it should be given consideration as an economical and eco friendly heating source. A GSHP is…

…great for new builds or major renovations: Not unexpectedly, it is always easier to incorporate a system like this right from the planning stage. Particularly as installation of GSHPs require considerable disturbance of the garden.

…most effective with energy efficient homes: GSHPs only produce circulating temperatures of around 95-104oF (35-40oC), therefore they are most effective in well insulated homes that prevent any loss of that produced heat.

most economical if your home isn’t already supplied by gas. As ground heat is free, GSHP systems are very economical. However, they do require electricity to run the pump. The annual savings for switching to a GSHP varies depending on what your current heating source is. It could be more than 50% if you use straight electricity, but it could be very little if natural gas is your heat source. For this reason, you may want to consider other ways to cut your energy bill and lower your carbon footprint if your house is supplied by gas.

worth considering if you have the space for the collector. You will need collector piping that covers 2-2.5 times the floor area of your home. This obviously limits many people as their yards simply aren’t big enough even for a vertical bore hole. It’s also not an option for apartment or condominium owners unless it’s a project the entire building undertakes, which would be a very major project indeed.

However, if a ground source heat pump is for you, it’s a wonderful way to take advantage of a free and completely renewable energy source. The video below (in two parts) is made in the UK and is obviously produced by a manufacturer, but it really is an amazing overview of how ground source heat pumps work and it shows an installation from beginning to end.

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