heat pumps anyone ?

Yes.

Nope, none of that at all.

Nope, that doesn't happen.

The immersion is primarily to get the water above 60C for legionella. You only have to do that once a week, and you can set a timer in the HP to do it for you.

-10C kind of weather) as the maximum output drops ~10-20% - you can have a slightly chillier house or you can add the resistance heat as a boost, but this is on a handful of days per year. Or you can rely on other sources (eg woodburner).

Theo

There's a physical limit of course, but many of the issues are with things being slightly less mature and pushing the boundaries may get them over the line. For example there's new higher temperature refrigerants - if you can run the output at 50-60C with an acceptable COP rather than 45C then you can get away with less work replacing radiators, and no worries about legionella. A better design of evaporator may improve the COP a bit, as might a better design of fan. These aren't groundbreaking laws-of-physics changes, but just squeezing 5% here and there.

A bit like batteries have got a lot better without fundamentally changing the chemistry, but plenty of optimisation in implementation and in manufacturing. There's no intrinsic reason when a monobloc ASHP unit can't be in the same ballpark as a gas boiler - they're just a motor, some pipework and some electronics. Sell them in large enough quantity and economies of scale will kick in. You can buy basically the same thing as an air conditioning unit for £350 [1], just using a refrigerant loop instead of a water loop. In places where they have central air rather than wet heating systems, they're well established.

Theo

Greta thinks? You astinish me.

They wouldn't.

They'll pump heat from the streets into the houses, from where it will leak back into the streets.

The loss of the carbon fuelled heat would likely result in a small drop in city temperatures, but no lower than it is in the countryside.

Getting the electricity to run the things in one of those winter blocking highs is more of a challenge. As is retrofitting a tepid water system to an existing house that was designed with hot water heating.

Andy

The grant is basically a bung to the installer to allay their training costs, and a bung to the distribution network to bring up the economies of scale.

I think it's inevitable that gas costs will go up, just a question of how and when.

That is a problem, particularly for flats where there's no cylinder. (Some flats have communal heat, but there's then the question of where that comes from. Maybe host servers in the plantroom ;-)

It makes more sense at replacement time than ripping out existing, agreed. It's why it's a bit frustrating that boilers are still being fitted to new builds.

Aircon units are used for heating in many countries. It's just the air to water that's less well developed.

Heat pump plus woodburner is actually the ideal combination. Heat pump does most of the work, especially in times of medium demand like spring and autumn. Woodburner will dump a lot of heat into the house rapidly but is hard to modulate - that's good for really cold weather when the heat pump is less efficient. And by using the heat pump most of the time you avoid the emissions of woodburning and having a big wood consumption. Essentially your woodpile is the energy store to shave peak load in the really cold times.

(main tricky time is in winter when you get a temperature inversion and smoke gets trapped)

True. That could be good for places like schools and commercial buildings where you know where the people are most of the time they're sitting down, and when they're standing up they're moving around so generating their own heat.

Theo

I've been wondering what makes these heat pumps so different from, as you note, well-established split air-conditioning systems working to heat in winter rather than cool. John Rumm's article in the DIYWiki is interesting in that he reports how the unit he installed performed at different times of the year:

It seems to me that it was working well enough for heating. Perhaps the problem with the heat pump installations covered in the video is that we are making the system too complicated and trying to follow what we do with gas (or other) boilers. Why have an intermediate hot water tank and all the underfloor heating pipes and larger radiators? Why not just use the warm air it produces directly from that side of the system? True, that would turn it into a warm air heating system which just about everybody apart from me seems to dislike intensely, but would a heat pump produce enough warm air at the right temperature to heat a house that way?

Depending on the size of the heat pump you might need a separate immersion heater for hot water, but that technology has been around for years, and is basically 100% efficient.

Theo pretended :

The wood burners they are banning?

Next door neighbour has had the salesman treatment. Chuffing great heat pump outside his back door but no mods to his wet radiator system so they are only heating rads to 50-60 degrees and so are cold in winter. Salesman has also cover the roof in solar panels and obtained dispensation for over 4kW from the DNO and failed to mention that the sun don't shine during the periods they need the heat pump. He is an intelligent man in his field - a medical professor but has no idea when he is being conned. I even gave him graphs of the relative output variation from my solar PV system during the year but he ignored that. Bob

But the cost of heating water by eletricity is about 3 to 4 times the cost of heating the same volume of water by gas......

at the moment...

Not with a heat pump, which produces 2-4x the amount of heat as the electricity that goes in, so that brings to about parity with gas. And the relation between electricity and gas prices may change in future. Plus you can generate your own electricity if you have solar.

In the US it's common to have ducted air heating, with a central heat pump unit that can both cool and heat air depending on season (due to the greater swings of temperature, in many places they need both heating in the winter and cooling in the summer). Often that unit is on the roof, which avoids having to find space inside for it, and fans can be directed upwards. There's no reason why we can't do that, except the problem is we need to run air ducts and most UK houses aren't set up for that - they're quite large to retrofit. In the US it's easier with houses that are mostly timber and often single storey so there's a loft and a crawlspace underneath.

The alternative is a multisplit with an external fan, refrigerant pipework and a fan coil in every room. Which might be a way to go as you're pumping refrigerant rather than water. The fan coils can be more noisy than radiators, although that's mostly a matter of size. One thing to be said for water-based heating is the radiators are (mostly) silent.

Theo

Exactly! I thought that had been made clear in the video. And if there's no gas anyway, there isn't much choice!

Why should that change?

Currently the cheapest electrical energy is generated from gas and fossil fuels. Green energy costs more, either from windmills or solar panels. Nuclear certainly costs more than gas and other fossil fuels.

If the gas price does go up, then so will electricity in precisely the same percentage.

Because the government will tax it as heavily as is necessary to persuade domestic customers to abandon it.

Not if the revenue raised by taxing gas is used to subsidise green electricity.

It's all in the interests of 'saving the planet', and it will reduce the UK to penury for no good reason, because CO2 will continue to rise unabated.

I thought the video had made clear that it wasn't possible to get water hot enough using a heat pump, and was suggesting an auxiliary immersion heater.

I considered changing our bungalow's pipes and radiator central heating to a ducted air system (heating and cooling), but The Management was not keen at all. It may be opportune to change to split a/c in specific rooms ahead of the time when we need to change the gas boiler (it's coming up to 3 years old, so should last another 7 at least). I guess it depends on whether or not we'll get hotter and more humid summers.

I cannot stand radiators, and would be happy to see them go tomorrow, but it's not going to happen. :-(

It will be ten times once they have made gas 'illegal'

knee jerk!

In Sweden air heat pump systems are fairly standard technology. They don't heat water to pump round to carry the heat, they pump around heated air, with their houses having built in air ducting, with exhaust ducts to keep an air flow. My son had one in northern Sweden, with winter temps down to -20C and it worked very well. Yes they are big and the electricity bill is hefty - but at those temps any heating is going to cost. It helps that insulation standards are far superior to ours.

I can't see that happening when the gas lobby will say it's green to burn gas in the home than burn loads more to generate the electricity.

Then for many we might as well heat by electric directly and throw out the heat pump.

When the gas lobby point out that burning electricity is not green, minds will change, especially when the generating industry realise the supply can't charge all the new EV cars.

I'm not going to worry, I'll be burning gas until it becomes economic to change.