Air Source Heat Pumps

richardc1983 · 15 February 2010 at 2:14PM

MHI are brilliant pieces of kit, you wont be dissapointed! Literally fit and forget.

Very very good that you have oversized slightly you will benefit from this.

Cardew · 15 February 2010 at 2:43PM

lomb wrote: »

i wouldnt worry about defrost on air source .

With respect, this is exactly the sort of comment that is unhelpful in that it provides no 'evidence'.

There are loads of quotes(like the professor above) that state exactly the opposite i.e.The energy used has a big impact on economic performance. but again no 'evidence'.

I read, on a refrigeration engineer's forum, that it was absolutely pointless in looking at the manufacturer's quoted COP data at xC etc as the defrosting was the killer of COPs at low temperatures.

The Ecodan manager talks of an average 3 min defrost cycle.

We want 'evidence'!!!

lomb · 15 February 2010 at 3:22PM

Why are you so worried about defrosts and efficiency? Heat pumps are currently competitive with gas. Probably gas has the edge as the boilers are 700 or 800 quid and simple to fix(yes even condensers) parts are cheap relatively and rads at 80 degrees heat quickly as well as one can heat their whole house.
However splits have the advantage of heat and cool as well as a digital thermostat as well as fairly instant heat. The ideal is probably a combination of heat pump splits and traditional rads.
In the future nuclear electricity and very expensive liquid and gas fossil fuels will ensure that heat pumps be they wet system or air are widespread as they make back the losses on grid transmission.

richardc1983 · 15 February 2010 at 3:22PM

Not sure how you can provide the evidence.

I have said a few times how long the defrost lasts on my air to air system.

It will be similar for all inverter units.

Its about 3-5 minutes. Below 0C ur looking at about 5 minutes before the air is blowing warm again.

The system controls when and for how long, based on air temps and coil temps etc, but it will stretch it out so defrosts are less, being inverter they will not be running flat out all the time so defrosts are less.

lomb · 15 February 2010 at 3:25PM

richardc1983 wrote: »

MHI are brilliant pieces of kit, you wont be dissapointed! Literally fit and forget.

Very very good that you have oversized slightly you will benefit from this.

I got a mix of their cassettes and their hyperinverters. A 3.5kw units for a 5.5x4 room for example. I prefer to have too much capacity than too little. I think they ramp down to 500 watts minimum. The cassettes have cops of 4.1 and the hyperinverters 4.6 -5.5 i think. I will let know how comfortable it feels there in due course. I think the 3.5kw is a cooling figure in reality they can put out 6kw of heat for a short time or 4+ indefinately. This should be more than enough even when its subzero i should still have 3kw.

richardc1983 · 15 February 2010 at 3:30PM

paceinternet wrote: »

Yes it would be really useful if albyota and others could post real data for defrosting.
2 or 3 mins?
Can you confirm that the system can be heating on full load, go into a defrost cycle for 2 mins, and is then immediately running on full heat output again?
If so, it may be reasonable to say:
At 0 deg C, a 3kw in / 6kw out unit would cost what?
(I am assuming an 8-10 kw heat pump would be outputting 6 kw at 0 deg C.)

2 mins x 3kw of electricity to run the defrost + another 2 mins x 3kw to recover the lost heat in the defrost. Costs about 4 pence an hour.

But I doubt it is that quick, so some real numbers would be good.

lomb wrote: »

I got a mix of their cassettes and their hyperinverters. A 3.5kw units for a 5.5x4 room for example. I prefer to have too much capacity than too little. I think they ramp down to 500 watts minimum. The cassettes have cops of 4.1 and the hyperinverters 4.6 -5.5 i think. I will let know how comfortable it feels there in due course. I think the 3.5kw is a cooling figure in reality they can put out 6kw of heat for a short time or 4+ indefinately. This should be more than enough even when its subzero i should still have 3kw.

This is how I think! They all ramp down to next to nothing anyway and you have the extra capacity there should you need it!

YOur prob looking at about 4.2 maxed out for a short period of time.

It also means you can run them in low fan speed because the stated duty is only on high fan speed. So at lower speeds = less noise and also the unit will be probably running at the actual output required for that room.

Cardew · 15 February 2010 at 3:41PM

lomb wrote: »

Why are you so worried about defrosts and efficiency? Heat pumps are currently competitive with gas. Probably gas has the edge as the boilers are 700 or 800 quid and simple to fix(yes even condensers) parts are cheap relatively and rads at 80 degrees heat quickly as well as one can heat their whole house.
However splits have the advantage of heat and cool as well as a digital thermostat as well as fairly instant heat. The ideal is probably a combination of heat pump splits and traditional rads.
In the future nuclear electricity and very expensive liquid and gas fossil fuels will ensure that heat pumps be they wet system or air are widespread as they make back the losses on grid transmission.

I am not worried, merely trying to discuss the relative advantages and disadvantages of ASHPs

There is plenty of evidence all over the web, and indeed on this forum, that some customers have been dissapointed in the performance of their ASHP systems over this cold winter.

Now given that the quoted COP figures for most systems are still high at temperatures well below freezing, I am surmising that other factors such as defrosting have been a significant factor in lowering the output.

As I posted earlier in this thread, for days when the ASHP system is not coping, it isn't a disaster to have suplementary heating(a £20 fan heater) used for a while.

richardc1983 · 15 February 2010 at 3:58PM

Cardew wrote: »

I am not worried, merely trying to discuss the relative advantages and disadvantages of ASHPs

There is plenty of evidence all over the web, and indeed on this forum, that some customers have been dissapointed in the performance of their ASHP systems over this cold winter.

Now given that the quoted COP figures for most systems are still high at temperatures well below freezing, I am surmising that other factors such as defrosting have been a significant factor in lowering the output.

As I posted earlier in this thread, for days when the ASHP system is not coping, it isn't a disaster to have suplementary heating(a £20 fan heater) used for a while.

the people who haven't been happy most probably have an undersized system or not designed for temps below 5c. Sized correctly and a little over and they work very well even at sub zero and I can back that up.

littletiger82 · 15 February 2010 at 4:30PM

Hi,

I've just moved in to a two bed ground floor maisonette with an Ecodan/Mitsubishi heating/hot water system.

In all honesty I'm pretty clueless about how and when I should be using it to maximise the efficiency. I've had the place since 28th Jan and used 463 units of electricity at a cost of £53 in that time. This seemed very high to me and the man at EDF!

I've had the heating on 24/7 at 22C as the house seems to get really cold very quickly when it's off. I'll find it difficult to put it on a timer as I work shifts so am in and out at different times every day. As I have an electric shower the hot water has only been on for an hour or two every few days, but I've just programmed it to come on for an hour every morning.

Does anyone have any tips or tricks on how to best use the system? Should I be leaving the heating on 24/7 to keep a constant temperature?

Thanks.

lomb · 15 February 2010 at 7:25PM

The ecodan is what 8kw? How can this unit heat a house unless it is superinsulated and the temps are well above freezing. Otherwise the output will drop to 6kw probably ,can one heat their house with 3 fan heaters?
The thing is a standard 3 bed house has something like a 24kw gas boiler fitted! Thats why i went for about 21kws in 1440 well insulated sq foot, i reakon that should give me about 16kw when the ambients drop still hopefully enough.
I dont think ashp heating a wet system are really suitable unless one has two of them in tandem or something that can put out 20-25kw peak. Even then one needs underfloor heating to take advantage of the low output temps. I have heard the diakin altherma is significantly better than the ecodan but know no more than that.

Air Source Heat Pumps

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