[PeterT_EONNext]

Let's talk a little about Ground Source Heat Pumps (or GSHP's for short, as it's a bit of a mouthful)

So what are Ground Source Heat Pumps?

They're a sustainable way to heat both your water and home and a replacement for your standard gas boiler (or other alternative fuel you may be using) as they produce zero emissions.








Well how do they work exactly?

They work by taking in the natural heat which sits underground (this usually sits at a steady 10-12 degrees Celsius all year round)

You would have a unit installed inside the home, around the size of a fridge, however, there are some smaller options too for smaller homes. The unit is connected to what are called 'ground collectors' outside, and situated below the ground, either in horizontal trenches around 1.5 - 2m, deep or in vertical boreholes.

A water/refrigerant fluid (similar to antifreeze) is circulated through the ground collectors, taking in thermal energy from the ground and circulating it back to the heat pump within the home. A compressor inside the heat pump increases the temperature and it's then passed to a heat exchanger, which in-turn transfers the heat to hot water cylinders, radiators and underfloor heating to provide space heating and hot water.

Once the fluid has delivered heat to your distribution system, it's then passed through an expansion valve which cools it before the entire process starts all over again.

What are the running costs?

For every 1kW of electricity used, ground source heat pumps produce around 4kWh of usable heat energy which is an efficiency increase of 400%.

This excellent efficiency reduces your carbon footprint and delivers significant savings on your monthly energy bills when compared to Oil/LPG, so the cost of a Ground Source Heat pump and installation would more than likely be beneficial to you if you live in a more remote area, where you may not have mains gas.

[DebF_EONNext]

Fantastic thread @PeterT_EONNext 😊 I don't think I know anyone who has these installed, it would be interesting to see how they compare to air source!

[meldrewreborn]

@PeterT_EONNext

Since @retrotecchie advises us that his oil is cheaper than gas at the moment, I don't think a GSHP is likely to deliver savings against oil. Which is one of the intractable problems when making big decisions on heating systems - what is the current and predicted prices of potential fuels.

As to producing zero emissions I suspect you mean zero additional ongoing emissions over those already emitted in the generation process.

These obviously are only suitable for those on the ground floor of a building with control over the adjacent land. Air source heat pumps are similar but extract heat from the air rather than the ground.

I think absolute zero is -273 degrees centigrade so there is still lots of heat extractable from the air at what humans consider low temperatures.. Heat pumps are a mature technology , used around the world and probably the future for many of us, but the public have yet to embrace them in a big way.

[retrotecchie]

The Coefficient of Performance (CoP) of a heat pump may push 4 in very rare and specific conditions, but the absolute best you are going to get out of one across the whole year is nearer to 2.7. So for every 1kWh of energy put in, you get 2.7kWh of heat out on average.

With gas around 10p a unit and electricity at around 35p a unit, the heat pump would need an average CoP of 3.5 all year round just to break even against gas and, trust me, that isn't possible in our climate!

Oil is running at about 8p per kWh right now, with no daily standing charges. The majority of rural housing stock in my part of the world that currently uses oil is simply not suitable for conversion to a heat pump. Unless you have an EPC rating of a good C or better, they simply aren't cost effective, viable or even practical.

[retrotecchie]

Running a 20kW oil boiler for two hours a day in winter is 40kWh of energy, or roughly 3.9 litres of kerosene. At 80p a litre, that works out at £3.12 a day.

Gas would be about 40 x 10.5p or £4.20 a day, plus standing charge of around 28p a day. So almost £4.50 a day.

For the six or so months of the year when the boiler isn't used other for the occasional bowl of hot water in the kitchen, the daily consumption is about quarter of a litre of kerosene a day, or 20p.

So, in winter running the heating, it costs much less than gas and in the summer the energy consumption is even less than the daily standing charge for gas.

I was quoted for a heat pump by E.On Next, sight unseen and no survey of the property. One look at our solid stone cottage and any heating engineer will tell you our property is just not suitable for a heat pump. Even after the government grant of £5000, we were looking at around £12k for a system.

So a £12k expenditure, for a system just not suited to our property, running on 34p per kWh electricity at a CoP averaging 2.7...

Compare that to the cost of installing a complete oil-fired system from scratch (completely plumbing the house and fitting rads, thermostatic rad valves, the boiler itself, multizone thermostat and digital controller as well as building a concrete pad in the garden and fitting a 2000 litre oil tank and supply pipework) which came in at a few pounds short of £4k and only costs about 70% of the price of mains gas to run.

If you are starting from scratch, oil is the clear winner. If you have mains gas, you still win over a heat pump. If your only choice of fuel is electricity AND your property is already EPC C or better, then they are an option, but they do have a very long payback time before you start actually saving any money on your heating costs as the up-front investment is very expensive.

If it's just about emissions, oil is broadly similar to mains gas as a fuel, both being hydrocarbons. Electricity is actually not that much better in extreme rural areas due to distance from generation, distribution losses over longer distances and a significant amount of the UK generation being fossil-powered anyway.

I like to be as green and environmentally friendly as I can, but in my book that means just not using so much energy in the first place. With the cost of living and the energy market being what it is, eco has to mean both 'economical' and 'ecological' right now. Heat pumps are not much of either for my circumstances.

[meldrewreborn]

@retrotecchie

Can I ask an idiot question? Why is the energy efficiency of the home a factor in whether a heat pump is cost effective?

I would have thought that its about producing a certain amount of heat using two different technologies. What does the type of building you put it into make any difference?

[retrotecchie]

@meldrewreborn

Heat pumps produce heat at a much lower temperature than conventional hydronic systems. They tend to produce a moderate amount of heat over a longer period of time, but at a significantly lower operating temperature. Radiators for heat pumps are a very different design and more often than not, if you replace a boiler with a heat pump, you also need to completely replace all the rads.

Because the systems generally have a much lower operating temperature, the property has to have a better level of insulation and energy efficiency in order to reduce heat loss. Properties with solid stone walls are particularly unsuitable.

You can run them at hotter outputs, but the hotter you run them, the worse the Coefficient of Performance and thus the more they cost to run.

[meldrewreborn]

@retrotecchie

Thanks for that explanation.

Yet more reasons not to listen to the hype.

[meldrewreborn]

@meldrewreborn

Have you noticed that the front bedroom in the picture doesn't have a door into it? Is this another aspect of GSHP that needs to be explained? 😂

[retrotecchie]

@meldrewreborn

I hadn't noticed that but did think that a garage just about big enough to fit a Fiat 500 touching the back wall isn't much use to most people. Plus all thermal capture pipe should always be black, never blue, and needs to be buried about five times deeper than that.