Air heat exchanger’s

Oh absolutely it is. But given the massive increase in the market price of gas (5 fold since January), I'd thought there may be some sort of payback on a very significant capital outlay. You consider the increases in cost of living and inflation and the houses that need insulating and modernising are largely not going to be able to afford it. And without much savings in energy costs, the reasoning to buy is likely to be within those who can already afford it without subsidy.

 

Combine it with solar panels and a correctly sized battery storage system, and although the outlay will be closer to 20k, you'll have covered the cost in 15 years. You're unlikely to ever cover the cost of an ASHP on your bills. Especially as the cost of electricity doubles every 8 years.

 

We've got a ground source heat pump, so here's my contribution on this.

To start off, the temperature of the ground deeper than about 10m is roughly 10 to 12 degrees C, all over the world and regardless of which season we are in. That's the basic source of the heat we are after.

Our system was installed in 2017 as part of a new build. Our garden is not that big so we had to have a shaft drilled, vertically 100m deep, believe it or not. It was great watching Red Adair and his mates drilling, especially when they hit rock and the whole rig bounced around like a space hopper. Sadly, no oil was discovered, although that would have negated the environmental advantages of fitting the heat pump in the first place. The system works (as others have said) like a freezer in reverse. It tries to cool the ground by removing heat from it, in the same way that a freezer removes heat from a left over curry that you put in it. The difference is that the freezer eventually succeeds in removing the heat from the curry, so it freezes, but the mass of the earth means that it's (almost) impossible to cool it. The heat pump doesn't realise this of course, and works frantically trying to cool the ground around the drilled shaft by extracting heat from it. This heat is used to warm water in a storage tank in the house, which is then pumped around radiators and/or underfloor heating pipes to warm the house. It's also used to warm water that I use when I have my weekly shower. An air source heat pump works in a similar way, except obviously the air temperature varies, so the system is operating at lower efficiency just when you need it most, in the middle of winter.

In terms of energy usage, it's highly efficient. Electricity is used to operate the pump which circulates brine down and back up the shaft, picking up the heat, but the actual heat source is the earth. The actual heat energy gained is a multiple of the electrical energy used, by a factor of about 4 which is called the COP (coefficient of performance). This means that, for example, to produce 4kW of heat energy we need 1kW of electricity. That's where the big saving comes. However, the COP reduces if we attempt to get too high a temperature from the system, so the output water temperature is usually set much lower than that for a gas system. This means that radiators need to be far bigger, and underfloor heating pipes need to be more closely spaced and longer. So installation costs are higher. It's also difficult to get really hot water (above about 50 C) unless you top it up with an immersion heater, which of course negates some of the energy savings.

Financially, we had to pay the full cost of the installation up front, but we're receiving a subsidy (RHI or Renewable Heat Initiative) quarterly for 7 years. When that finishes in 2024, the system will have cost us about the same as an equivalent gas boiler. However, that's only half the story. To make it work efficiently, we needed to install underfloor heating and (upstairs) bigger radiators, which cost more than those for an equivalent gas system. So there's no doubt that a heat pump system is more expensive to install, and it also takes up much more space, which may not be available in a retrofit situation. An air source system is fitted outside, as it needs a supply of fresh air, so space is not normally a problem. However, they can be noisy in operation and could annoy neighbours. In terms of running costs, we don't need a gas supply so we save on the standing charge for it, as we only use electricity. The system costs us nothing to run from about mid April to mid September, as we have solar panels which generate (on average) enough power to run the heat pump just for my weekly shower, when we don't actually need the heating on. In winter we have electricity bills of about £150 per month, but that includes cooking, lighting etc too.

In summary, it's a great system which is highly efficient and produces no pollution at all in the summer, and only indirectly (depending on where our electricity comes from) in the winter. However, it's big, expensive up-front to install, and requires changes to the heating radiators etc. It's not suitable for everyone.

As a footnote, I often wonder what would happen if every house in the world was fitted with a ground source heat pump? That would be a phenomenal amount of heat being drawn out of the ground, which could well freeze it in densely populated areas, so the heat pump would no longer work. I suppose it's a bit like asking what would happen if everyone in the world breathed in at the same time........?

 

There was a bit on Radio 4's PM program yesterday, well worth a listen (BBC Sounds). I think the bloke ended up paying about £15K. You might need bigger radiators as well?

 

Great feedback.

 

No gas boilers in new build from 2025, not clear yet on if sale of new gas boilers will be stopped, the government dodging that question. It will have to happen but it’s announced now for the climate summit rather than in detail and thought through.

Enjoyed reading the posts and learning more

 

Ask our CEO in the Q&A session.
He may have to ask Conway if he can answer it but whatever, you'll be just as feckin baffled afterwards.

 

Fascinating input - best in depth real use explanation I have seen. Thanks for that.

 

That was going to be my question with regards when they will stop Combi boilers. While ever you can still have on installed I can't see many people swapping over.

 

It wouldn't surprise me if hydrogen doesn't have a big impact to play in future heating requirements, after all there's a massive gas supply infrastructure already, can't see this being scrapped within the next 30 years. Probably start with adding a %age of hydrogen to supplies and eventually phasing natural gas out (my newish boiler already is quoted as being "hydrogen ready").
Edit - just found this article. https://www.siemens-energy.com/glob...-natural-gas-infrastructure-for-hydrogen.html

 

Spot on. We have an ground source heat pump but we built the house from scratch so had the ability to put in underfloor heating all around the house which is what it works best with, and insulated well. They wouldn’t work as well with radiators and therefore retro fitting isn’t ideal. They work better with a constant steadier lower heat (hence underfloor not radiators), which in turns needs better insulation

Also I’m sure the deal under the rhi scheme is a lot more generous than the one they’re proposing.

 

There is heat (vibrational) energy in anything that is above 0K (-273C).

Zero Centigrade is only the freezing point of water (or melting point of ice) it has no great significance otherwise. Zero Kelvin IS a significant thing, it's impossible to have a temperature below 0K, it is the absolute minimum since it is the point at which molecular/atomic vibrations (and therefore, heat) cease to exist.

Physics lesson endeth here.

Edit; 0K has never never been achieved artificially, we've got very close, much modern technology relies on it like superconductors (although some superconductors have been made which operate at much higher temperatures).

 

Or we could give up the car and flying. Or that as well as home changes.

 

I am probably also missing something. But if it works like a fridge why not combine the two?

 

Quite. If you feel the grille on the back of your fridge or freezer it will usually be warm. There's an urban myth that you can cool your kitchen by leaving the fridge door open, sadly all this does is make the compressor work harder and release more heat....

 

I'm in a similar position whereby my house isn't particularly suited. It's victorian, and while we've done a good chunk of work to it to make it more efficient and less wasteful, there is only so far we can go. If a heat pump has to be based on concrete and need room for airflow, there is literally nowhere it can go, front or back.

We changed the boiler as the first thing we did a good while back, changed radiators etc. So if bigger radiators are required, again, we just don't have the room for them in most rooms. We've underfloor heating in the bathroom (electric) but thats all, and thats more than adequate.

We've had the loft insulated, but there are no cavity walls and I'm mindful of not ruining the character of the house. I've put features back in and aimed to match the extension with the outer house, and I really don't want to take them away.

I've read and heard a few things the last day or so, and I suspect a more robust plan is going to have to be made for towns and cities with considerable levels of old terracing.

 

The hydrogen idea certainly works, JCB produce diggers etc which are powered by hydrogen-fuelled internal combustion engines and you could certainly run a domestic heating system with hydrogen as the fuel. The big problem with it is how to make the hydrogen. Hydrogen gas is not found on earth in any abundance (Earth's gravity can't stop it escaping into space, same as helium) it has to be made by electrolysis of water which requires huge amounts of electrical energy much of which is currently still generated from fossil fuels.

 

Not going to happen while we have this government, they are positively encouraging people to swap from IC cars to EVs which will do nothing to reduce the volume of traffic with all the downsides that come with it. Not to mention the massive environmental damage caused by mining some of the metals required for EV batteries. If the planet is to survive in something like the state it is in now (let alone pre industrial) we will all have to get used to less traveling.