So if all households did this, total UK residential space heating carbon emissions would fall by at least 40%, greatly helping to reach carbon reduction targets. The 25% lower running costs would pay for the investment, without subsidy, and would reduce energy poverty. Ignore one or two extremely minor problems with this reasoning (cough, cough) and I’ll take my knighthood now thank you…

And while I’m in dreamland: Use the gas previously employed for space heating to generate electricity instead, reducing grid carbon intensity and electricity costs. Makes the results of the Great A2A Revolution even better.

Conversely, provide marginal electricity with coal (i.e. cheaply), and assume A2A pumps in the UK achieve the 4.9 SPFs needed to turn this into heat with the same carbon intensity as gas boilers (not utterly crazy). No carbon savings, but far cheaper heating costs. Not sure how much?

Back in the real world… my home will be a pain to insulate too (cost, hassle and worry), and that’s not uncommon. However, A2A will be better with good insulation as heat will circulate rather than escaping and COPs will be higher. So I will insulate, but when the insulation cost(£ and faff)/benefit becomes questionable (EWI anyone?), A2A could be a way to green further easily/cheaply.

Posted By: ferdinand2000Housing Associations are not dummies

Not so sure about that. Friend of mine had to do an audit for a local HA after they fitted heat pumps. It covered running costs, CO2 savings, suitability and easy of use. It was done with a combination of utility bills and user surveys plus a lot of temperature logging.
What was missing was an initial baseline to work from. When he brought this up and pointed out that you could not say if there was any benefit for definite, they just said 'well we have fitted the HPs so there has to be a saving', meaning he had to show that there was. All he found out was that newer housing had better thermal properties than older ones.

A2A's a doddle to use (from experience in Japan). Each comes with its own remote with on/off, desired temp and fully programmable timer. Mike7, what's your experience?

For costs, a gentleman here suggested £65pa, and think that was for more complicated A2W:

http://www.greenbuildingforum.co.uk/forum114/comments.php?DiscussionID=11285

Specifying a pain, until I found the Swedish data. Now I can work out what will give enough oomph at low temps (wish I could find more on their testing methodology though...).

Installation seems -very- straightforward compared to A2W and GSHP. Apart from evacuating the system properly, doesn't appear to be many things an installer can easily get wrong. Daserra, is that fair?

As for it not being suitable for mass adoption, these are already the most popular heat pump type by far! Millions in place in Japan and other countries (especially those needing both cooling and heating).

Posted By: daserra.................Quite easy to fit yes, you need a large 63mm SDS bit,

Why 63mm daserra? I'm interested for myself and the split units I'd looked at only seem to be connected, external HP to internal fan/emitter by microbore,- I think. Is the 63mm to allow for insulating the microbore all the way through the wall.

Thanks for that.

Some units need topping off with gas every now and again which is easy enough if you have a set of manifolds and a bottle of gas. Harder with an inverter unit though as the pressure varies. The modern gases are blends and can evap at different rates so if you're topping off a lot it's best to find out where the leak is as the blend will end up with altered proportions.

The pipes ice up in cooling mode when there's not enough gas, or the interior unit ices up. I've not seen a glass sight on a HP, just on manifolds and vacuum pumps.

SteamyTea Oct 13th 2013 states :-

1: It is all to do with how close to the Carnot Cycle it can get. So the less temperature difference between input and the output the less 'extra' energy is needed.
[Exactly]

2: Not sure how hot an A2A heat pump gets the output temperature to, but probably no more than 55°C and possibly only 45°C, so that may only be a rise of 30 to 40°C.
[When starting, I have seen peak temperatures of about 43C but these settle down gradually to the 30-33C range when running continuously in economy mode.]

3: When they are used to heat water then they try and get the temp to 60°C, so needs more work done. There is also the amount of time they will run for. About 4.2 times longer to heat the same mass of water as air
[Ed Davies Oct 13th 2013 addressed this one]

4: Why I asked the question a while back somewhere as to just how important is the ambient air temperature really is (knowing that it very rare that it goes below 0°C in the UK (even accounting for the last two cold winters, even went below that down here)
[The start of the answer to this is supplied by Carnot's Law (websearch on 'wikipedia carnots law'). Pick your hot and cold refrigerant temperatures and extract the maximum theoretical Carnot Efficiency from the Table below. The realistic efficiency is the next step.] :-

The theoretical maximum Coefficient of Performance (CoP) of a heat pump is calculated exactly, in accordance with Carnot's Law [http://en.wikipedia.org/wiki/Carnot%27s_theorem_%28thermodynamics%29] by :-
CoP (TC /TH) = (273+TH )/ (TH-TC) where TH and TC are stated in degrees Centigrade

Table 1: Maximum Theoretical Carnot Efficiencies at Stated Tc and Th Temperatures
80 75 70 65 60 55 50 45 40 35 30 Th
20 5.88 6.33 6.86 7.51 8.33 9.37 10.77 12.72
15 5.43 5.80 6.24 6.76 7.40 8.20 9.23 10.60 12.52
10 5.04 5.35 5.72 6.15 6.66 7.29 8.08 9.09 10.43 12.32
5 4.71 4.97 5.28 5.63 6.05 6.56 7.18 7.95 8.94 10.27 12.12
2 4.53 4.77 5.04 5.37 5.74 6.19 6.73 7.40 *8.24* 9.33 10.82
0 4.41 4.64 4.90 5.20 5.55 5.96 6.46 7.07 7.83 8.80 10.10
-5 4.15 4.35 4.57 4.83 5.12 5.47 5.87 6.36 6.96 7.70 8.66
-10 3.92 4.09 4.29 4.51 4.76 5.05 5.38 5.78 6.26 6.84 7.58
-15 3.72 3.87 4.04 4.23 4.44 4.69 4.97 5.30 5.69 6.16 6.73
Tc
Notes:
1: The values in the table are refrigerant temperatures in the evaporating and condensing sections of the heat exchangers of a running heat pump. These temperatures can be inferred from pressure readings and reference to the pressure/saturation table for the refrigerant in question.
2: Exact value from Carnot's Law CoP(2/40)=8.24
3: The CoP at (-15/70) is almost exactly half that at (2/40) (cf 4.04 and 8.24)
4: If each heat exchange is assumed to have a 5C inefficiency then for an A2W pump the CoP(2/40) refers to A7/W35 as the pump conditions (the normal rating temperatures).
5: At the theoretical level, a cool-running A2A at CoP(5/30)=12.12 would use half the electricity of a high temperature retrofit A2W running at CoP(5/60)=6.05 because 12.12/6.05=2, in order to pump the same amount of heat.
Conclusion: Pumping unnecessarily to high temperature wastes serious money.

Paul, you will notice from my posts that I see a lot of advantages to A2A. A residual concern is how often the defrost cycle will kick in in the damp, low single digit temperatures we see quite often in the UK, and the impact this might have on COPs. Do you a a view, or any evidence, on this issue?

The UK A2W field trial results, which showed median SPFs of 2.8 for those, provide a baseline. I. E. Since these will have been achieved despite potentially 'suffering' from frequent defrosts, then A2A should achieve significantly more due to their inherent efficiency advantages. But it's a shame there's no field data to confirm whether UK A2As match or exceed south Sweden (a lot colder than most of the UK, but perhaps drier) actual SPFs of about 4.0.

Well, for me, 20% lower running costs than my gas boiler (sub 10 year unsubsidised payback), and even more so a 40% reduction in space heating CO2 emissions given current grid intensity, is worthwhile, so I'll be retrofitting them. There are few other green investments I can make with as good an economic and environmental payback.

If increased electricity demand resulted in higher average grid intensity, despite the push for renewables, then -some- of the benefit might be offset, but I think you could argue the gas I was going to burn directly might end up (fairly greenly) generating the electricity I'll use for my heat pump. And if we do succeed in greening the grid, by using an ASHP the carbon benefits will be multiplied for me (vs. gas etc.).

And on new builds, I kind of get it, but even if your DHW is 50% of your demand, then, with A2A for space heat and direct electricity for DHW, your average SPF is (0.5*4.0+0.5*1.0=) 2.5. i.e. only slightly worse than if you installed a more complicated A2W system (2.8) for three times the price.

Your dislike of forced air is, of course, entirely understandable. Haven't got a response to that one!

<blockquote><cite>Posted By: davidfreeborough</cite>Paul
Personally I dislike any kind of heating which relies on forced air movement, so given the choice I would be installing over-sized radiators or underfloor heating.</blockquote>

Radiators (convectors) are essentially forced air. Compare air exit temperatures and you'll find that they move similar volumes to an A2A unit.

Winter time DHW is the killer. Sharing a gas fired micro CHP over a few properties for winter electricity, hot water, and top up space heat (with solar PV for summer electrical demand, hot water, and top up cooling) wouldn't be madness. The business model to operate such a communal scheme is hard to do though.

GarethC 4 hours ago
1: Defrosts: 'Do you have a view, or any evidence, on this issue?'
The way to deal with the energy loss from defrosts is to stop them happening. To do this with a small A2A, you put the pump in the suitable loft in a house. The pump dries the air in the loft as it endlessly recirculates and sends the condensate down the drain. As the temperature drops progressively into the defrost range (usually +5C to -5C), the air is so dry that no or very little frost forms. I have seen a narrow band of white on the coils but nothing to cause a defrost. To the best of my knowledge my pump has never defrosted whilst running 24/7 through this winter. Worth about 10% on energy according to some manuals that I have read.

2: 'it's a shame there's no field data to confirm whether UK A2As … ':
DECC and the EST have deliberately suppressed all mention, testing or reference to A2A. To take this to ludicrous extremes, the DRHI Regs define 'air-sourced' as having a 'liquid discharge'! Just another attempt to suppress all mention of A2A.

3: A2A data:
Despite DECC's best efforts, I have some A2A data for this winter. For the expenditure of 909kWh of electricity, my year-on-year gas consumption has dropped 11,595kWh. This is an effective CoP of 12.76. This is not just due to Carnot efficiency. The single source of heat in a house is important; the heat demand of my house 'all internal doors open' to 'all internal doors shut' is a factor of two apart. The closed off rooms drop three or four degrees in temperature. Also last winter would have been colder than this one. We were very lazy with the gas heating, all rooms tended to be heated and I can see why the nominal CoP of 5.7 could be easily doubled by this effect (really a halving of the heat demand of the house). My pump has a rated power of 450watts or 0.45*24=10.8kWh(electrical)/day. The average load on the pump over the coldest three months has been 6.4kWh(electrical)/day for a cost of about 6.4*0.1435*30=£27.50 per 30 day month.

davidfreeborough 3 hours ago
1: 'However, if there is already a gas boiler then the benefits are so small that I would question whether it makes sense to increase the load on the electricity network.'
My billing spreadsheet predicts a spend of £127 for the whole of this winter against a mains gas saving of £541. There is a payback period of about six winters in this as the pump cost about £2,000 professionally installed with electrics and instrumentation.

2: I cannot really comment on new build as I have not studied it.

3: 'forced air movement'
I agree with you about this. The blower unit is in the hall and the pump is in the loft where both can do their own thing without disturbing me in other rooms.

GarethC 2 hours ago
The calculations on grid efficiency and 'greening' with wind turbines are complex. What I can say from the demand end of the calculation is that my house was sized for a 10kW(electrical) A2W but runs for space heating on a 0.45kW(electrical) A2A. Lets call that a factor of twenty different on the peak grid demand. Repeat that over 27 million houses and you reduce the potential total grid demand from 27,000,000*10/1,000MW=270GW to about 12GW.

The problem with heat pumps is that they will all be running at maximum load at the same time in the middle of a high pressure weather system with cold temperatures and no wind. The capacity factor of onshore wind is 21% and that of offshore about 30%. 270GW of wind mills needs 270GW of gas turbines to provide backup. That is 540GW of plant; current grid maximum system demand is about 54GW. The grid reinforcement will need to be on a similar scale and that includes digging up all the roads with distribution cabling beneath. The cost of all this approaches the size of the current National Debt.


markocosic 2 hours ago & SteamyTea 1 hour ago edited
'Sharing a gas fired micro CHP over a few properties for …'
Have you looked at Ceres Power (http://en.wikipedia.org/wiki/Ceres_Power)?

Besides the caravan club's "tow car of the year" is the Skoda Superb estate.

James,
The calculation is based on three meters; the gas and electricity billing meters and a meter in the heat pump electricity cable. The only historical record is the energy company's bills which include the kWh consumption numbers.

1: The actual SPF of the pump with a rated CoP of 5.7 is one issue; I think that a heat meter for A2A would be needed.
2: The effect of open/closed internal doors is obvious when living in the house but measuring it accurately is difficult. The doors are in random states during the day but mostly all closed at night. With everyone else out of the house I can test by watching the pump power meter and ambient temperature. A factor of about two for open/closed is right. I have rough pump power/ambient temperature curves for the open/closed states (they are square laws)
3: Accurate degree day data for both winters would be useful. Where do I get it? Met Office perhaps?
4: There is yet another complication. We have a gas fire in the lounge with an atrocious thermal efficiency. My project this summer is to try and find a way to get it taken out of service next winter.

Making sense of all the variables without the instrumentation to separate them is probably impossible. All I have for the moment is the numbers described. Part of the saving is purely technical, part is climate, part is the way the house is used.

Paul, I use this: http://www.degreedays.net/

Djh, I see the car analogy probably doesn't work so well because the cost of buying two cars is so much greater than buying a single less efficient one. But in the case of space heating and DHW, I think the cost of separate systems for each, in terms of both capital and running costs, can be lower than single systems designed to do both.

For example, you can buy an A2W for £6k with an SPF of 2.8, or a GSHP for £10k with an SPF of 4.0. Or a biomass boiler for £8k.

Alternatively, you could get an A2A system for £2k with an SPF of 4.0 for space heating, giving you £4k (vs. A2W), £8k (vs. GSHP) or £6k (vs biomass) to install a DHW system.

I've not actually satisfied myself as to what the best DHW solution is, but that's quite a lot of cash to use finding one. As I think I've mentioned before, if you just use electricity (perhaps cheapest capital cost solution?) for DHW, and assuming that's 50% of your demand (quite high), you're overall "SPF" will still be 2.5 (0.5*4.0+0.5*1.0). i.e. no worse than A2W in running terms, but cheaper and simpler to install.

If instead you install an oil or lpg boiler (off grid) or even natural gas just for DHW (smaller system than if using for space heating, and cheaper due to no need to install rads), you're probably still quids (and carbon emissions) in. That make sense?