A curious installation is emerging at Bell House. After solar panels; eco bulbs; insulated ceilings and an overall reduction of plastic, the Ground Source Heat Pump (GSHP) was thought as the logical next (big) step to make the Bell House property on the way to carbon neutral.
So, if you are curious about this unique energy provider and want to know more about how it functions beyond just making several deep holes in our back garden, you are in the right place.
1. What is a ground source heat pump?
If we had to explain what GSHP is in one sentence, it would probably be something like: the GSHP system harnesses natural heat from underground providing Bell House heating or hot water thanks to underground pipes. However, it is a little bit more complex than that.
Unlike geothermal, GSHP doesn't use energy from the centre of the earth; the heat that we will be using comes from the warming of the earth's surface by the sun. When radiations from the sun heat the earth, the ground stores and maintains this warmth just two metres or so down (and event below that), at a temperature of around 10°C, summer like winter.
The GSHP uses a ground heat exchange loop to tap into this constantly replenished heat store. To harbour the loop, we are currently making ten holes of 175 metres (574 feet!) deep and 12.5 cm (5 inches) in diameter, which are go through several layers of soil, clay, sand and gravel, and chalk.
A special liquid to collect warmth underneath all these layers circulates in the « closed-loop ». The warmth is then concentrated by a compressor and transferred to the water that in turn is pumped around Bell House. The ground loop fluid, now cooler, is then pumped back down the holes to heat up again. The whole process takes quite a lot of electricity so that the effect is that it is 3-4 times as efficient as just using electric heating.
2. The issues encountered during the installation
The contractors finished three holes before Christmas, but the work was slower than they had hoped because the holes kept collapsing at the sand layers. The drillers - Paul and Mark - found a way of overcoming this by using a sleeve for the sandy sections to hold open the sides of the hole until after they had put in the plastic pipe for the closed-loop. It's also occasionally been slowed down because at the beginning of each hole the drillers have to get an expert on unexploded bombs to use a special detector to make sure that there isn't any unexploded ordnance nearby.
Drilling holes under the snow…
3. The reasons to install a GSHP
The system has a wide range of benefits for the planet. At Bell House, we primarily focus on reducing our carbon footprint so that we burn much less gas but still stay warm in the winter. The installation of a GSHP was making sense for us. We want to do that for two reasons:
(a) to reduce the amount of carbon that gets released by us which, together with the emissions of others, is having catastrophic effects on our planet. According to our calculations, we will cut about 39 tonnes of CO2 emissions every year.
(b) to inspire others to explore similar options for their own homes and organisations. We hope to use Bell House's system as a model of what can be done and the architect and parties involved are planning to use it as a demonstration site for people considering changing their heating systems. To help explain it we are making a short film and plan to have some display boards outlining the logic and practicalities of such installations. We may well host occasional talks on the subject and will welcome the Ground Source Heat Pump Association, which is London-based, to meet up at Bell House.
For those who are interested about the other benefits that a GSHP provides; lowering your fuel bills or providing you with an income through the government's Renewable Heat Incentive (RHI) is part of the advantages. The system we have installed will cost just under £200,000 and the government's RHI (Renewable Heat Incentive) means that we should be getting back about £10,000 each year for 20 years in payments for generating and using green energy. GSHP is also more energy efficient as it distributes heat at lower temperatures over longer periods requiring minimal maintenance, which is not negligible.