Air Source Heat Pumps

[mcbook]

Guys, help me out here... I'm trying to work up a cost model for ASHP vs Oil. Here's my current thinking, please let me know your feedback on assumptions, anything I've missed, or anything else you can think of. Thanks.

[Jambo85]

Lemming Train said:

Right. Got my wires crossed then. I thought that they also "recycled" the residual heat from inside the house but on further reading apparently they don't and only get it from outside. So that makes them even less efficient as they are solely dependent on the outside ambient temperature.

Aye but there is still a muliplier eg. something like 3 kWh of heat energy from 1 kWh of electrical energy. Storage heaters are 1:1.

[Jambo85]

mcbook said:

Guys, help me out here... I'm trying to work up a cost model for ASHP vs Oil. Here's my current thinking, please let me know your feedback on assumptions, anything I've missed, or anything else you can think of. Thanks.

Your assumptions seem reasonable to a fellow layman, although you could consider likely future costs of oil and electricity if you have a crystal ball. And throw 0% finance on the ASHP into the equation too.

PS are you aware that you can get oil/ASHP hybrids? Grant make one. The RHI is more complex because you need a meter to measure heat consumed from the ASHP side (standard RHI is just based on assumptions), and I think the HES loan will only pay for the ASHP "half" of the system, if anything.

[caziques]

mcbook said:

Guys, help me out here... I'm trying to work up a cost model for ASHP vs Oil. Here's my current thinking, please let me know your feedback on assumptions, anything I've missed, or anything else you can think of. Thanks.

Someone is taking the piss with the price of the heat pump - and the price of "maintenance"

Need more details about your proposal to comment further.

I charge £3500 for a 12kW air sourced hot water heat pump (NZ underfloor heating), you may need two of these for a radiator system.

Bigger heat pumps need three phase.

Generally maintenance of an air source hot water heat pump is a con, (much like servicing of an EV)

With underfloor systems, (closed loop), I use zero ferrous materials, hence no water changes, ever.

The outdoor unit needs as much servicing as a fridge, ie none. (OK, perhaps the drains need clearing on occasion).

(I left the UK soon after Voldermort/Blair became PM)

[Evanivitch]

Your heat pump cost is huge.

Also, wouldn't you go underfloor heating on a new build regardless of heating method?

[mcbook]

Evanivitch said:

Your heat pump cost is huge.

Also, wouldn't you go underfloor heating on a new build regardless of heating method?

Thanks. Heat pump cost was based on what a previous poster had said... also some websites gave £10k as a ballpark firgure so I added a bit onto that to be conservative. I'll do some proper research and revise.

As for underfloor heating, I'm not 100% sure about it. I don't have a problem with traditional radiators and they're cheaper to install and repair.

[mcbook]

caziques said:

Someone is taking the piss with the price of the heat pump - and the price of "maintenance"

Need more details about your proposal to comment further.

I charge £3500 for a 12kW air sourced hot water heat pump (NZ underfloor heating), you may need two of these for a radiator system.

Bigger heat pumps need three phase.

Generally maintenance of an air source hot water heat pump is a con, (much like servicing of an EV)

With underfloor systems, (closed loop), I use zero ferrous materials, hence no water changes, ever.

The outdoor unit needs as much servicing as a fridge, ie none. (OK, perhaps the drains need clearing on occasion).

(I left the UK soon after Voldermort/Blair became PM)

For maintenance I just Googled the price of a maintenance contract for both ASHP and Oil boiler. Trying to be consistent in the comparison.

Heat pump cost is a 'finger in the air' so I'll look into that in more detail.

Thanks for your comments.

[mcbook]

Jambo85 said:

Your assumptions seem reasonable to a fellow layman, although you could consider likely future costs of oil and electricity if you have a crystal ball. And throw 0% finance on the ASHP into the equation too.

PS are you aware that you can get oil/ASHP hybrids? Grant make one. The RHI is more complex because you need a meter to measure heat consumed from the ASHP side (standard RHI is just based on assumptions), and I think the HES loan will only pay for the ASHP "half" of the system, if anything.

Hybrid seems like an interesting option but the potential complexity scares me... I'll look into it. Thanks.

[anonymous-user]

mcbook said:

Evanivitch said:

Your heat pump cost is huge.

Also, wouldn't you go underfloor heating on a new build regardless of heating method?

Thanks. Heat pump cost was based on what a previous poster had said... also some websites gave £10k as a ballpark firgure so I added a bit onto that to be conservative. I'll do some proper research and revise.

As for underfloor heating, I'm not 100% sure about it. I don't have a problem with traditional radiators and they're cheaper to install and repair.

Go for ufh every time if you can. I cannot see any reason not to.

[mcbook]

garyhun said:

Go for ufh every time if you can. I cannot see any reason not to.

Cost is the main reason - looks like it will cost about twice as much to install UFH versus radiators.

[Equus]

Jambo85 said:

Aye but there is still a muliplier eg. something like 3 kWh of heat energy from 1 kWh of electrical energy. Storage heaters are 1:1.

But of course storage heaters use cheap, off-peak electricity.

ASHP's use electricity whenever they happen to be running, which includes peak rate.

There is an argument - particularly with increased use of renewables like wind and solar, which can be producing electricity whether we need it or not - that intelligent use of systems like storage heaters or heat stores that 'soak up' excess electricity that would otherwise go to waste can be more sensible than systems that increase overall demand at peak times (when we're having to burn gas to generate the electricity, anyway).

The other big unknown in McBook's calculation is the number for that multiplier... he's assumed a COP of 3.0, but this can vary according to numerous factors - I've seen figures ranging from manufacturer's fantasies of anything up to 6.0 (which I've never seen achieved in practice), down to barely better than 1.0

[anonymous-user]

mcbook said:

garyhun said:

Go for ufh every time if you can. I cannot see any reason not to.

Cost is the main reason - looks like it will cost about twice as much to install UFH versus radiators.

Lower water temp alone would be the key for me if running a heat pump.

[mcbook]

garyhun said:

Lower water temp alone would be the key for me if running a heat pump.

A poster further up in the thread said his ASHP maintains 55 degrees (with help from immersion heater)... is that not hot enough? Serious question... I don't know. I think my current combi is set around that level, but maybe a little higher.

[Jambo85]

mcbook said:

garyhun said:

Lower water temp alone would be the key for me if running a heat pump.

A poster further up in the thread said his ASHP maintains 55 degrees (with help from immersion heater)... is that not hot enough? Serious question... I don't know. I think my current combi is set around that level, but maybe a little higher.

That temperature is in the water cylinder though, the heating loop could be lower potentially (I don't know if they are, just highlighting the possibility).

[Equus]

mcbook said:

his ASHP maintains 55 degrees (with help from immersion heater)

You can make a block of concrete fly, if you attach a big enough aero engine to it... it doesn't mean that it's much COP (you see what I did there?) at doing the job on its own.

Serious answer is that yes, 55 degrees is adequate:
a) if the heat pump is sized sufficiently to maintain that temperature under all (or all but genuinely the most extreme) conditions and;
b) if the heat emitters - be they radiators or UFH - are sized sufficiently to transfer that reduced level of heat to the house fast enough to keep pace with the rate it's being lost through the thermal envelope.

Those can be pretty big 'ifs', though.

Edited by Equus on Thursday 18th April 10:32

[mcbook]

I think things are becoming clearer here... in that there's clearly no easy answer.

Financials seem quite evenly balanced (new build, ASHP vs Oil) so it appears more and more like a lifestyle or life-philosophy choice.

If you're really into renewables and want to do your bit to save the planet, seems like an ASHP will do the job.

If you care more about adjustability, known reliability, having a boiling hot bath/shower, maybe want to keep capital costs down, seems like oil is the way to go .

[rdjohn]

mcbook said:

A poster further up in the thread said his ASHP maintains 55 degrees (with help from immersion heater)... is that not hot enough? Serious question... I don't know. I think my current combi is set around that level, but maybe a little higher.

My current Vaillant combi works quite happily at 50degC most of the time. If I have been away, I will lift the temp to 65degC for a while. It has a separate temperature setting for hot water.

Would adding a Honeywell EvoHome system help? Progressively heating bedroom / bathroom - kitchen / dining room before lounge in the morning should help with the load, particularly with a higher minimum temperature overnight, during winter.

[Wilts_jeff]

mcbook said:

I think things are becoming clearer here... in that there's clearly no easy answer.

Financials seem quite evenly balanced (new build, ASHP vs Oil) so it appears more and more like a lifestyle or life-philosophy choice.

If you're really into renewables and want to do your bit to save the planet, seems like an ASHP will do the job.

If you care more about adjustability, known reliability, having a boiling hot bath/shower, maybe want to keep capital costs down, seems like oil is the way to go .

Having lived with an ASHP for 12 years I think you have pretty much nailed it on the head here. There is no right or wrong answer, it comes down to costs, your view on 'renewable' energy, and the fabric of your house. We are very happy with our setup but I know that it would not suit everyone. The latest heat pumps are miles ahead of the models from 10 years ago, as you would expect, so noise is minimal, we have plenty of hot water all the time and the house is always comfortable. Does not mean that it would work for everyone so I do appreciate your predicament.

Would be happy to have a further chat about our experiences if it would help.

Cheers,

Jeff

[mcbook]

Wilts_jeff said:

Having lived with an ASHP for 12 years I think you have pretty much nailed it on the head here. There is no right or wrong answer, it comes down to costs, your view on 'renewable' energy, and the fabric of your house. We are very happy with our setup but I know that it would not suit everyone. The latest heat pumps are miles ahead of the models from 10 years ago, as you would expect, so noise is minimal, we have plenty of hot water all the time and the house is always comfortable. Does not mean that it would work for everyone so I do appreciate your predicament.

Would be happy to have a further chat about our experiences if it would help.

Cheers,

Jeff

Thanks for the offer, Jeff. I'm still in the very early stages (planning app) but I might take you up on your offer as we move further through the process.

[gareth h]

For those that don't want to upgrade radiators Daikin do (or were it's some time since I spoke to them) a heat pump that produces water at upto 75 deg c, it uses 2 refrigerant circuits in a cascade system, one on r410 and the other r134a, decent COPs, I seem to remember that it qualified for RHI too.