[Closed] Ground Source Heat Pumps

do i need to bump my post?

Is it not irrelevant what the ambient air temp is (unless you were dealing with an air source heat pump) and the thing works on temperature differential and is a closed system like a fridge?

It's like a backwards fridge. A fridge takes the heat out of the things inside it (even though they are only at 4 degrees or something) and moves it into your kitchen.

A GSHP takes the heat from the ground and moves it into your house. Even though the ground may only be 10 degrees it can still make the radiators 45 degrees so they warm your room.

It's not a heat exchanger, it's a heat pump. It is similar in principle to a fridge. Think of the water in the ground loops as akin to the air inside the fridge. The water in the heating circuits in the house are akin to the air outside the back of the fridge.

The heat pump itself is a closed circuit containing coolant. Part of it uses a pump to increase pressure in the coolant, which therefore emits heat. It emits that heat into the house heating circuit, as the fridge does to the air behind it, where all the cobwebs are. At the other side of the circuit is something that releases pressure, a bit like an aerosol. That gets cold, ie taking in heat. In this case it does that to/from the ground loop. The fridge does it inside the fridge behind the milk.

there was literally a guy on R2 this afternoon explaining how air-source heat pumps work! I assume a ground-source is largely the same. It's filled with a refrigerant which is always going to be colder than the air/ground, so it will warm it, like a fridge but in reverse.

If you want to look at it that way I guess the answer is that the mean annual air temp around your heat pump will be slightly lower than you imagine because you will be using your heat pump to cool it.

Thanks. that makes sense. it’s still early where i live

Another way of thinking about is as a heat concentrator.

The ground might only be 10C but that's still plenty of heat energy, no heat energy is -273C. So the pump takes that heat energy and applies a little bit of additional energy / work to concentrate the heat up to useful levels for heating.

That's how they achieve energy efficiency higher than 100%, they are "borrowing" heat from the Earth

the guy on R2 also said it's absolutely crucial your walls/loft etc are well insulated as the heat pump provides a gentle amount of heat at all times to heat the entire house to the same temp. It's not like a gas boiler where you can have it on low or even off but then crank it up to nuclear temps as required 🤣! Which I didn't realise (but then I'd never looked into it!)

there was literally a guy on R2 this afternoon explaining how air-source heat pumps work! I assume a ground-source is largely the same.

It's exactly the same principal just that the ground temperature is more consistent.

Heat normally flows from hot to cold, these systems move heat from cold to hot

It’s filled with a refrigerant which is always going to be colder than the air/ground, so it will warm it, like a fridge but in reverse.

It's not the reverse of a fridge, it's exactly the same as a fridge (or freezer for that matter)

It’s not like a gas boiler where you can have it on low or even off but then crank it up to nuclear temps as required

To be fair neither do many of the folk who either start looking into it or many of the folk who suggest them seriously on here as a general retro fit inplace of a boiler.

They have a specific usecase and aged housing stock isn't generally one of them unless you have very deep pockets

As Trail_rat says, you need to look at the house and heating as a whole system. You need good insulation and ideally underfloor heating. We totally renovated a cottage in Scotland 14 years ago. We stripped out the inside completely back to stone walls, then dry lined with full insulation, new double glazed windows and doors and new concrete floor with underfloor heat pipes installed. The ground loop is a borehole 110m deep.

We run the heating full time, relying on individual room thermostats to switch the heat pump on and off to maintain the floor temperature; the concrete floor is effectively a large heat store. It has been working well but I suspect is quite expensive to run - I don't have anything to compare it to. The alternative where we are would be oil or LPG which are also expensive.

Later, 7 years ago we also installed an air-source heat pump in a new extension. This is also working well, although it is not as efficient as the ground source.

That's what gets me about announcements like the IEA today telling us the we shouldn't buy gas boilers after 2025. Ground or air source heat pumps could operate at temperatures equivalent to what you get from a gas boiler but you'd need a cascade system (basically twice as much equipment). As a result, you really need something with highly insulated underfloor heating ... not something that is achievable in 90% of timber frame houses. How are we going to change that before 2025? I'd love to have a ground source heat pump for my house but it isn't a single storey bungalow with a concrete pad plus insulation for the floor. Hmmm.

I've gone Air Source Heat Pump in our new house - GSHP would have been about £10k more expensive and you'd only get the extra payback after about 20 years. Both systems rely on high levels of insulation - putting one in a poorly insulated, non-airtight house will just result in huge bills.