Heat pump experiences

[chris-suffolk]

Are you sure? I've just seen the Channel 5 programme about heat pumps, and the tanks on there were so large they go from floor to ceiling. That's my problem, I have a convenient place to build an airing cupboard, but it's not that tall.

So, let me get this right? You need a hot water tank with a ASHP system? I'm guessing yes else you have no hot water to the kitchen or cloarkroom / bathroom for washing your hands / washing up. The alternative is an on demand electric heater (which won't be cheap to run)

What about the large number of houses that have been built around on-demand gas boilers. They will likely have nowhere to put a hot water tank.

 

[icowden]

So, let me get this right? You need a hot water tank with a ASHP system? I'm guessing yes else you have no hot water to the kitchen or cloarkroom / bathroom for washing your hands / washing up. The alternative is an on demand electric heater (which won't be cheap to run)

Yes. And it's pretty big too. I looked at moving to ASHP and was told that our current airing cupboard wasn't big enough. It needed to be something like 1m x 80cm and 1.5m in height. Our existing cupboard has the height (although we would lose the towel storage) but not the width as it's only 60cm wide.

 

[mjr]

Hence - you could not fill a bath from one tank

That's a choice. We chose to keep roughly the same size tank as the oil system used, which fills a bath and a bit, but the extra insulation on a modern tank meant it had to be relocated to the loft, which is possible now because of the extra insulation... this had benefits that the back of the airing cupboard was used for some of the ASHP equipment and then boxed in (with removable panels for servicing, and using the old backup immersion heater power feed), and the pipe run from the tank to some hot taps is shorter than before.

PLUS - as soon as you start running a bath then the tank start topping itself up with water - which is obviously cold
Hence the hot water you are using become cooler.
So if you are in the bath - and it is getting cold - then if you try to top it up with hot - it comes out as luke warm

Again, that's a choice. Ours draws the hot water from the top of the tank while cold is added to the bottom. Eventually it will homogenise to be colder and then be reheated, but not in the time it takes to have even a long bath. Also, when the reheat kicks in, it heats the bottom (cold) part of the tank and heat rises, so it doesn't stay lukewarm long. Of course, it is possible to end up with lukewarm tap water if the settings are wrong, but it's not inevitable unless you try running two very full baths inside an hour. There are also a couple of thermometers in the tank and a display by the bathroom door, so you at least have some warning that pressing "force reheat" and waiting a few minutes might be a good idea, which we never had with the old tank.

and the heat pump does not have the thermal welly of a gas boiler and so will warm it up much slower

Slower, but the extra insulation on a modern tank means it isn't that much slower. It is true that it can't lift the temperature from cold mains water to hot tap in one go like a combi boiler does, but those tend to be horribly inefficient at either water or heating or both. You can't design the same heater to do both temperatures well.

same would apply for a shower - I presume - if two people had one back to back and took their time

It's less of a problem with a shower because you (or the mixer control, if thermostatic) tend to react to the gradually reducing temperature by changing the balance of hot and cold.

On top of which there is the "needing bigger radiators" problem
plus we have no idea how good the insulation is here but there are horror stories about the builders and insulation - from people who have lived her a very long time

so we won;t be heading in that direction without written guarantees

If I'd done something different, it would have been to have an insulation surveyor check the insulation first with cameras and not trust the old-fashioned surveys, even though Ofgem trust the pathetic EPCs for grants. Some will check it for free, in the hope that you'll buy from them if an upgrade is needed or possible. The one who checked ours was great but they didn't sell the insulation type we needed (due to restricted access for installation). So we got Aran Group from Suffolk in, who also seem great.

I think some suppliers do now offer guarantees, including Octopus and Heat Geeks, but so far they are either pretty conservative about where they'll install (so horror stories about builders might deter them) or charge quite a bit extra to fund the stronger guarantee. I think you also surrender some control over the installed system settings, else the guarantee is voided, but that's probably OK for most people who don't want to innovate much with their heating.

 

[mjr]

Are ASHPs hermetically sealed like fridges & freezers, or do they need re-gassing like a car aircon?

I think both are available. Our Mitsubishi is a sealed unit, which meant it could be installed by a plumber who doesn't have refrigeration certification. I think the service engineer checks it isn't losing any, but doesn't normally re-gas it.

The heat from a fridge condenser isn't contributing to heating the room because the heat pumped came from the room in the first place.

Let's take that to absurdity: do you think a fridge half the size of the room would leave the rest of the room no warmer than it would be with a 1 cubic-meter fridge?

The room outside the fridge is still slightly hotter than it would be without the fridge keeping a subset of its volume cooler. Therefore, the condenser is heating the room slightly.

 

[mjr]

What about the large number of houses that have been built around on-demand gas boilers. They will likely have nowhere to put a hot water tank.

1. They're shoot. Just one of the problems with great British housing developers and their "build it as cheap as we're allowed and to hell with the running costs, the pollution, the health of the inhabitants, ..." approach of at least the last 50 years. There are some good homes, including some that are so well-insulated that they don't use much energy overall and it won't be ruinous if they use solar-thermal+electric hot water, but there's a lot of paper-thin crap out there too.
2. At least some of them will have lofts or backs of garages that can be used for modern well-insulated tanks. I've no idea how many. I would hope that Ofgem and friends were actually researching this, but I've interacted with Ofgem and they've not only been cut to the bone, but some of the bones seem to have been cut too.

If I'd bought a home in the last 5 years, I would definitely have been looking for how easy it would be to get away from gas once the boiler dies, or the gas starts running out.

 

[chris-suffolk]

Yes. And it's pretty big too. I looked at moving to ASHP and was told that our current airing cupboard wasn't big enough. It needed to be something like 1m x 80cm and 1.5m in height. Our existing cupboard has the height (although we would lose the towel storage) but not the width as it's only 60cm wide.

So, we encourage people to get rid of their hot water tanks, because on-demand boilers are more efficient. Then (potentially) build houses giving no space for a hot water tank, and then finally tell people they need a huge tank and must buy ASHP. That's progress then!!

 

[presta]

Let's take that to absurdity: do you think a fridge half the size of the room would leave the rest of the room no warmer than it would be with a 1 cubic-meter fridge?

Of course it will, because a bigger fridge has a bigger motor that consumes more electricity.

Therefore, the condenser is heating the room slightly.

No, it's the electricity consumed by the motor that contributes to room heat, the heat pumped out of the fridge contributes nothing because it got into the fridge from the room in the first place.

Fairly confident it'll do similar because I've had other refrigeration units last longer, like @Tenkaykev mentions, and they work 24x7 all year, unlike the ASHP which only does 30 minutes a day for half the year.

Fridges don't run non-stop, they have thermostats, and they're ultra-reliable because the motor and compressor are all in one hermetically sealed unit.

To deliver a whole day's heating energy in the space of half an hour you'd need an output in excess of 100kW, not to mention some huge great thermal mass somewhere to smooth out the temperature variations.

For example, in a typical winter month my house consumes about 70kWh/day, which averaged over the whole 24 hours is 2.9kW. To deliver all that in 30 minutes would need 140kW.

 

[mjr]

So, we encourage people to get rid of their hot water tanks, because on-demand boilers are more efficient.

That was never the reason, was it? People were encouraged to get rid of hot water tanks because on-demand burners are more convenient (effectively infinite hot water), less efficient (so more gas sold = economic "growth") and have a shorter life span (because of the higher temperature and fiercer burn, so more replacement boilers sold = economic "growth").

 

[mjr]

Of course it will, because a bigger fridge has a bigger motor that consumes more electricity.

Let's pretend the motor heat could be dumped to the outside. Do you still think that lowering the temperature of half the room volume would not raise the temperature of the other half?

Fridges don't run non-stop, they have thermostats, and they're ultra-reliable because the motor and compressor are all in one hermetically sealed unit.

I said work, not run. Our monobloc ASHP is also a sealed unit, so I hope your reasoning for "ultra-reliable" is correct!

To deliver a whole day's heating energy in the space of half an hour you'd need an output in excess of 100kW, not to mention some huge great thermal mass somewhere to smooth out the temperature variations.

For example, in a typical winter month my house consumes about 70kWh/day, which averaged over the whole 24 hours is 2.9kW. To deliver all that in 30 minutes would need 140kW.

The half of the year where the ASHP only runs about 30 minutes a day is summer plus a bit either side, where the heating isn't on at all and it's only reheating the water tank and at crazy efficency due to the warm air outside. Of course it's on longer the other half of the year. Sorry if that wasn't clear to you.

 

[presta]

we encourage people to get rid of their hot water tanks, because on-demand boilers are more efficient

Have they been doing that? I'm not sure it's necessarily correct.

A well insulated tank isn't losing much heat, and in winter the 'lost' heat isn't really lost at all, it's just contributing to heating the house.

Set against that, the waste heat and water from running the tap long enough for the water to run hot, which doesn't even contribute to room heat, as it goes down the plughole. I wasn't particularly fazed by the warnings of the tap being slow to run hot when I got my combi boiler because I previously had a multipoint which also heats on demand and takes time to warm up. However, what I hadn't appreciated is that they're constructed very differently, and the combi is a lot slower to warm up than the multipoint was.

 

[presta]

Let's pretend the motor heat could be dumped to the outside. Do you still think that lowering the temperature of half the room volume would not raise the temperature of the other half?

The only source of energy that the fridge has is the electricity supply, it you remove all that runs from it, you have nothing left to generate heat.

The half of the year where the ASHP only runs about 30 minutes a day is summer plus a bit either side, where the heating isn't on at all and it's only reheating the water tank and at crazy efficency due to the warm air outside. Of course it's on longer the other half of the year. Sorry if that wasn't clear to you.

Summer isn't the half of the year that's causing most of the wear and tear you were arguing about. My gas consumption is split about 14%-86% summer-winter.

 

[presta]

So, let me get this right? You need a hot water tank with a ASHP system? I'm guessing yes else you have no hot water to the kitchen or cloarkroom / bathroom for washing your hands / washing up. The alternative is an on demand electric heater (which won't be cheap to run)

What about the large number of houses that have been built around on-demand gas boilers. They will likely have nowhere to put a hot water tank.

I don't understand what you're getting at, you seem to be trying to contradict me with my own argument.

Yes, of course you need a water tank, and as I said above, the ones they showed on Channel 5 recently were effin' enormous, too big to fit in the space I have for one without eating into living space. This contrary to the post I quoted which claims that they're smaller.

 

[mjr]

The only source of energy that the fridge has is the electricity supply, it you remove all that runs from it, you have nothing left to generate heat.

I don't disagree that there's no generation, but there is still heating of the rest of the room, unless you can explain how the energy extracted to lower the temperature inside the fridge doesn't heat the space outside it.

Summer isn't the half of the year that's causing most of the wear and tear you were arguing about. My gas consumption is split about 14%-86% summer-winter.

Sure, but it's still half the year where an ASHP doesn't do much, unlike a fridge that works all year.

Interestingly, my heating electric consumption is split 18%-82% summer-winter.

 

[MrGrumpy]

There are quite a few people in the village who have had the lot curtesy of the government scheme, insulation everywhere, solar panels, heat pumps. Within 2 months they had the heat pumps taken out as they were so expensive to run and gave out so little heat that they just couldn't afford them.

They may be fine in brand new houses with tons of insulation but no thanks. Everyone who had them here have gone back to using their wood burners and just have the solar panels.

I read somewhere that the boss of one of the energy companies had a wood burner installed as the heat pump was rubbish and just didn't cut it.

I’m wary of those spouting how great ASHP , solar panels have an immediate effect , not so much the heat pumps . Coupled with the fact you need to benefit from special tariffs to keep costs down . I’ll keep plugging away with the gas boiler until it makes financial sense to replace .

 

[ebikeerwidnes]

Are you sure? I've just seen the Channel 5 programme about heat pumps, and the tanks on there were so large they go from floor to ceiling. That's my problem, I have a convenient place to build an airing cupboard, but it's not that tall.

This was just a short new piece - probably a different person

nice to know there are different sizes and they work better than in "the old days"