High temp heat pumps??

[martyc]

Hi there.
Will be replacing boiler in the next year or so.
Wondering if anyone has experience with the higher temperature air to water boilers?
Curious if they are genuinely a good alternative- 1950s semi D - not the warmest.

 

[omph]

Heatpumps are not a good idea if you don't have an insulated, warm house. Primarily because they need to run below 55c - usually 30-40c to gain maximum efficiency and keep the COP above 3.5. Why 3.5 ? because electricity costs that much more than gas. If you run it at higher temps you will end up spending a crap load more than gas.
The are also designed to run 24/7 and not like normal gas boilers. Its a different beast.

 

[martyc]

Thanks Omph.
So the ones advertised to run at higher temps do so at a reduced COP?

Here’s one I see advertised:

Monoblock R290 Heatpumps - Axe Biotech - Biomass Boilers & Stokers

Monoblock R290 Heatpumps. A heat pump can be defined as a universal solution for a space comfort achieving.

axebiotech.ie

Too good to be true I guess!

 

[omph]

75c is too hot and will be very expensive to run. Anything below ~3.5 (350% efficiency) is not a good idea. HPs are more than 100% efficient, they can go up to 600-700%. What that means is 1kW in -> 7kW out. The lower you can get the water temp, the higher your COP. So you can save a lot if done right, and cost you an arm and leg if done wrong.

Not sure if you can control the heating flow temp on your boiler, but if you can, lower it to 35c and let it run for 2-3days and see how that goes. If it is comfortable then you may be okay.

 

[robinbanks]

Here’s one I see advertised:
[

Have you found anyone willing to state what the COP is at 75*C? I haven't..

 

[vulcancontinental]

Have you found anyone willing to state what the COP is at 75*C? I haven't..

That would rather depend on the OAT the COP was calculated at

 

[martyc]

Thanks both- bit if food for thought as they say!
I might just try running the house boiler at 35- that’s a smart idea- pretty sure it wouldn’t cut the mustard but I might be pleasantly surprised too.
I’m no where near even considering investing in one of these.

 

[Why Not Indeed]

Here’s one I see advertised:

That's a particularly poor site. The manufacturer's own site says "heat pumps are intended for low-temperature heating / cooling systems" and 75°C is nowhere near "low temperature". Note that the manufacturer's spec tops out at 60°C flow:

Heat pumps - Centrometal | HEATING TECHNIQUE

Heat pumps are devices that use the environment to meet the demands for space heating and cooling and DHW preparation at very high efficiency level. In its portfolio, Centrometal has air/water type heat pumps in monobloc and split version, with nominal heating capacities from 4 to 16kW. There is...

www.centrometal.hr

 

[fixitflav]

I might just try running the house boiler at 35

Unless you have an untypically big rad area for the size of house, that's unlikely to keep you warm enough.

 

[drives]

If it helps, we have an averagely (at best) insulated 1970s house. To give you an idea, full width dormers across the first floor. 12mm plasterboard and 100mm loft roll type insulation crudely taped to the reverse- then cladding tiles. In places around the eaves we actually have no insulation- just the plasterboard. No insulation under floorboards. 100mm loft insulation.

Max flow temp on ASHP currently set at 46. For the really cold days that we had in Nov that was easily sufficient. This is with heat set at 20 degrees C and might drop to around 19 to 19.5 at night.

I remember trialling our boiler at 55 a couple of year back and even in milder weather it got cold, so I was sceptical, with less than a quarter of our radiators being upgraded, how the ASHP would cope. Well it is certainly toasty enough....I guess by just keeping the building fabric warm so if you do test it out dont use any drastic set backs. That is what I mistakenly did and the house could never get back up to temp in the morning. 60 was the lowest I could get away with through the winter with a setback of 15/16 at night or when we were out.

I agree with the above in terms of steering clear of high temp ASHPs- defeats the object. The Vaillant arotherm seems to be a very popular choice for installers but that goes up to 70 and it seemed to us that we were paying a premium for something we'd never use. We went for a Clivet Edge Evo which was over 2k cheaper and a more modest 60.

Anyway no complaints, both cost and comfort wise, from us. In fact, quite the opposite and this was coming from a decent Vaillant condensing boiler.

 

[robinbanks]

That would rather depend on the OAT the COP was calculated at

I don't mind; pick the most favourable. The others in their datasheet are A7 - that'll do

I ask my ASHP to produce CH water at 27. If I was throwing thousands at heating I'd start with the insulation detailing, not thousands at a high temp heat pump in the hopes that it could be a drop in boiler replacement

I might just try running the house boiler at 35- that’s a smart idea

It doesn't really emulate the rest of the setup though

 

[vulcancontinental]

It's the refrigerant that gives the higher temps, R290 (propane) up to 75C but at that temp it'll have a COP OAT 7C of 2-ish. R32 will give 65C OAT10, 60C OAT -5deg.

The highest temperatures are not the target, the lowest that maintain com fortare the best because the COP improves so if your machine can give 75 the last thing you want it to do is run at that (anti legionnaires can be run at 60deg).

The Riello NXHM R32 shows as best efficiency A2W HP on heatpumpmonitor.org past 90 days, a listing of enthusiasts who compare their installations but will not go above 65degrees and you definately don't want it to.

 

[ericmark]

Some good info given, the problem as I see it, is to get the energy out of the radiators either they need to be very big, or fan assisted, with fan assisted you can use some heat pumps in reverse, to cool the home in summer, clearly what we want if we are getting gobble warming, but you can't get a grant if it cools as well, and all the pipes need lagging to stop condensate forming on them and the radiator needs a reservoir and pump to get rid of condensate. It also often needs a large bore pipe work, and as already said, home maintained 24/7 not each room heated as and when required, I use oil fired boiler with programmable TRV heads so work on the just in time idea. And likely half the rooms in the house not heated.

I would say, even with the best heat pump, my heating bill would double. Mother's house used gas and modulating boiler, the TRV's could allow a room to move from 17ºC to 20ºC within an hour, so rooms only heated when required. OK I cheated, I would set to 22ºC at 7 am and back to 20ºC at 8 am, as the anti hysteresis software was OTT, but TRV heads have improved, with Drayton Wiser you set time and temp you want to use the room, and it works out when it needs to switch on.

 

[drives]

Some good info given, the problem as I see it, is to get the energy out of the radiators either they need to be very big, or fan assisted, with fan assisted you can use some heat pumps in reverse, to cool the home in summer, clearly what we want if we are getting gobble warming, but you can't get a grant if it cools as well, and all the pipes need lagging to stop condensate forming on them and the radiator needs a reservoir and pump to get rid of condensate. It also often needs a large bore pipe work, and as already said, home maintained 24/7 not each room heated as and when required, I use oil fired boiler with programmable TRV heads so work on the just in time idea. And likely half the rooms in the house not heated.

I would say, even with the best heat pump, my heating bill would double. Mother's house used gas and modulating boiler, the TRV's could allow a room to move from 17ºC to 20ºC within an hour, so rooms only heated when required. OK I cheated, I would set to 22ºC at 7 am and back to 20ºC at 8 am, as the anti hysteresis software was OTT, but TRV heads have improved, with Drayton Wiser you set time and temp you want to use the room, and it works out when it needs to switch on.

Not convinced zoning and set backs are any cheaper to run long term. Even with the gas boiler and nest thermostat geo fencing to switch off when away from 0700 until 1700 (when at work) the difference in our gas usage versus weekends was negligible. I then tried smart TRVs and zoning areas of the house, and that definitely wasn't cheaper and made the house far less comfortable. In fact coming home from work wasn't fun, waiting for the house to warm up again.

 

[vulcancontinental]

Some good info given, the problem as I see it, is to get the energy out of the radiators either they need to be very big, or fan assisted, with fan assisted you can use some heat pumps in reverse, to cool the home in summer, clearly what we want if we are getting gobble warming, but you can't get a grant if it cools as well, and all the pipes need lagging to stop condensate forming on them and the radiator needs a reservoir and pump to get rid of condensate. It also often needs a large bore pipe work, and as already said, home maintained 24/7 not each room heated as and when required, I use oil fired boiler with programmable TRV heads so work on the just in time idea. And likely half the rooms in the house not heated.

I would say, even with the best heat pump, my heating bill would double. Mother's house used gas and modulating boiler, the TRV's could allow a room to move from 17ºC to 20ºC within an hour, so rooms only heated when required. OK I cheated, I would set to 22ºC at 7 am and back to 20ºC at 8 am, as the anti hysteresis software was OTT, but TRV heads have improved, with Drayton Wiser you set time and temp you want to use the room, and it works out when it needs to switch on.

Forget cooling, for that go AC.

Your bills will definitely be higher if you changed to HP and run the system the way you do but if the system ran continuously with possible increase in radiator sizes (not always necessary as many are oversized) it would be cheaper but that statement has the same credence as your own regarding doubling cost.

Oil is around 11p/kW so at 22p/kW electricity the HP has only to achieve a COP of 2 to break even. It's straightforward to achieve 3-5 COP so there'd be a saving and you'd have a £7500 Boiler Upgrade Scheme grant to offset the cost.

To achieve the higher SCOPs stay away from the energy suppliers installers, they only have to achieve a SCOP of 2.8 under the terms of the grant. An experienced independant installer would be the way to go but they'll charge for their expertise whereas an energy company will be selling you power.