Heat pump

[Seeker]

Anyone got one?

I like the concept and I understand the need to stop burning gas but there seems to be obstacles...

The gov are offering a £5k grant but the installation may cost £10k.
You need a hot water tank or space for one. I currently have a combi gas boiler in my (smallish) kitchen and I'm unsure where a tank could be fitted. If it means putting it in the attic there would need to be some considerable pipework alterations. I'm in a dormer bungalow, I don't know whether that helps or hinders.

Your current radiators may not be big enough.
Your property must have excellent insulation. I would describe my house as "cold" - personally I think dormers are a bad idea, my heat drifts upstairs and then through the poorly constructed dormer itself - so that would need fixing. This government had a grant scheme for insulation that was poorly organised and collapsed with few people taking up the offer, so the heat pump scheme already looks shaky.

I have new upvc windows but the cavity wall insulation was done many years ago, I'm sure it's more efficient now but getting the old stuff out, err no, I can't see that happening.

I don't understand the statements about running costs - they say it's comparable to gas because the pumps are very efficient yet gas is much cheaper than electricity although there is going to be a green levy added to gas imminently. On the other hand they can't produce heat at the drop of a hat so have to run continuously.

The pump itself is outside but must not be sited too close to your neighbour because of noise issues although they are supposed to be as quiet as a fridge. I lived in San Antonio, Texas briefly and our a/c used a heat pump which was much noisier than a fridge but maybe cooling needs a bigger fan.

[Sir Trev]

I might be able to put one at first floor level above my garage roof, but as it's a pitched roof the access is poor for fitting and maintenance. Cannot put one one the other side as the neighbours built their garage to the boundary line (years ago when allowed) and I cannot get two metres away. That leaves back elevation, but would be under my bedroom window, so no, or very visible on the front wall, which would look rubbish...

[Bibio]

is a heat pump just a fancy name for air con..

[Seeker]

I think a better plan would have been to mandate heat pumps for all new buildings. Older buildings (my house was built in the late 1960s) are going to need some thought. The grant scheme is for 90,000 homes but I think it said 2.5 million houses need to be changed, I hope there's a back up plan.

Wasn't Tesla selling a "power wall" in conjunction with solar panels that look like roofing tiles?

[ethariel]

For a new well insulated build with under floor heating a ground sourced heat pump is a no brainer, air sourced (air to air or air to water) is a different prospect, once the temperatures fall the efficiency of the unit falls off a cliff so running them as a hybrid system with a backup boiler is prudent.

All comes down to how much are you prepared to spend, the most efficient systems cost more (as usual).

However pushing the additional load over to electricity while adding in EV charging, just means the gas power stations need to run more to keep up with demand so it has it's downsides.

Originally Posted by Bibio

is a heat pump just a fancy name for air con..

Pretty much, just runs in reverse (most systems, especially the air to air 'heat pumps' can provide AC in the summer too)

[Sir Trev]

Ideally I'd go for solar tiles or panels with a power wall of some kind for night time or poor weather. But it probably means ripping out a lot of the current services, pipes, rads etc. and replacing most of it, plus finding space for things in line with planning regs. Not a problem if designed in from scratch but not great for those of us with 60's houses that have already been knocked about a bit.

I'd love to have a well designed/insulated house with ground/air source, solar PV and power storage with appropriate room and water heating to be as independent as possible, especially ahead of the inevitable move to electric cars/bikes, but that really needs ground up planning as Seeker mentioned.

[embee]

OK, here's my take on the numbers, make what you will of it.

An A rated domestic gas boiler around 90% efficiency emits about 220gmCO2(eq)/kWh heat supplied to the house.
If you use electricity in your house, it all (yes, all) comes from a gas fired power station which runs around 550gmCO2(eq)/kWh.
Why do I say all? Because all the renewable/low carbon/nuclear generation is used up by the base load, and then the remainder (somewhere round 45% of the electricity generated) comes from gas, and that is what supplies your house. If you switch on a kettle do they start up a new wind turbine? No, the marginal generation is all gas, they turn up and down the gas fired power stations to supply the variable domestic load. Do not use the "average" figures bandies about for electricity generation, the marginal source is gas.

So a heat pump needs to have a coefficient of performance (COP) of at least 2.5 to equal the CO2 emissions of a gas boiler, which they might just about manage, ground sourced generally better than air sourced. CO2 emissions are thus not much different for a domestic gas boiler and a gas fired power station supplying a decent air sourced heat pump.

The kicker? A gas boiler will cost you around 5p/kWh, an air sourced heat pump will cost you around 8p/kWh if it's maintaining a COP of 2.5
If you want to get 60C hot water from a heat pump the COP falls off a lot, so you'll probably want either instantaneous water heater or a cylinder with immersion, using resistive heating, which will cost you north of 20p/kWh compared to your gas boiler at 5p/kWh.

Have I got the numbers wrong? I'm happy to be corrected.

I won't be looking at a heat pump just yet. Better house insulation and thermal underwear is the way forward for me.

[Bibio]

Originally Posted by embee

Better house insulation.

this is what i'm doing just now. the back bedroom is all done and the difference is around 4c from the rest of the house.

at the end of all the house renovations i'm hoping that the ambient temp in winter will be around 14-18c.

[johnnyrod]

Yes, a heat pump is a fridge/aircon. I've started thinking about it was well but as pointed out above, gathering hear from cold air is difficult, and for good efficiency the warm side needs to be as cool as possible. They work much better with underfloor heating AFAIK so again as said, for a new house it should be easy, as a retrofit I fail to see if being really viable, and then there's the cost. Embee your figures look close enough I would say, not being an expert but knowing a few things. Unless electricity can be made with less CO2 impact then what's the point of not having a good gas boiler at home? Am thinking of solar/PV to heat the water tank but not looked into it yet (don't want to derail so don't follow that one, sorry), it would take a chunk off the work the boiler does.

[embee]

Originally Posted by johnnyrod

....Am thinking of solar/PV to heat the water tank but not looked into it yet ...... it would take a chunk off the work the boiler does.

I think that's a very worthwhile study exercise, you can install stuff for not a huge outlay (solar hot water cylinders pre-heat the lower cool part of the water). Let us know what you conclude about the viability. It's a bit of an 80/20 type rule, you can get a significant benefit from a relatively small investment, we mustn't let the pursuit of the perfect become the enemy of the good.