Hi Owlman - I haven't used these people but their website is certainly helpful: http://www.saturnsales.co.uk/
They seem set up to help DIY installers, whereas manufacturers often appear a bit reluctant. Mitsubishi Heavy Industry do some high COP models, I see.

Re size - with just one emitter size would be affected by not just the heat demand of your living/dining room but by how much heat would waft out from there to other rooms. Are doors generally left open, and is there an open stairwell to a first floor? Exact output may not be too critical as I believe most will modulate their output according to set temperature ( my Hitachi certainly does, although I notice that if the output is too low (maybe less than a third of maximum) the COP seems to drop off). The higher the output the more likely you will need the emitter somewhere like a hallway so that the warmth has a chance to diffuse before it reaches you.

I've also noticed that higher output units have lower COPs. I think this is because the heat exchangers tend to be similar in size, but just driven harder ie with a bigger pump/higher refrigerant temperatures.

For heating I think the emitter is best mounted at floor level, and many are designed with this in mind. They may however cost more - if so, I can say I have found the usual high level aircon type quite OK at low level, albieit with a bit of adjustment of the set temperature to get the desired result.

Rather a disjointed bunch of comments, but re your sizing question, my guess is that you'd be best off with maybe no more than 3 or 4 kW output. Much more than that and you might want to think about two systems - for the higher COPs and also better distribution from two different places.

I did quite a lot of research into this based on the Swedish data, including looking at £/Kw for different models.

One thing the Swedish tests seem to suggest is that there's not THAT much difference in the performance of similar output models across makes, presumeably because, despite any bells and whistles, they're by nature fairly simple machines and competitors adopt each others' performance improving measures quite quickly.

I'm planning to get an LG Prestige, but part of that was a particularly quiet outdoor unit (neighbours very nearby). I'll dig out my table looking at different models's pros and cons. From memory, I think the Mitsubishi Heavy Industries (as distinct from Mitsubishi Electric, which are also good) units had good £/kW rating, but outside units were a slight noisier.

One thing, Tony, I see your point, but tests suggest that over-sizing these things tends to bump up their COP, so the smallest you can get's not necessarily the best I think, especially if you have open plan areas that can benefit from any extra heat. But I'm fairly sure the more pricey models (e.g. Panasonic and Hitachi from memory), and some of the 'high efficiency' models, while perfectly good, don't really warrant their price premium.

Interestingly, I asked a Japanese friend to look out any Japanese field test results. As these are incredibly popular there (it get both much hotter and much colder than the UK), I thought there should be a good resource. Her old man got back to me (ex Sanyo employee). He said that Japanese firms self-test, and their results are generally accepted. I asked if they were trusted, and he reckoned a Japanese company would never dare to air brush their results!

Ah, yes, quite a major counterexample.

Incidentally, going back to my question in the OP, not only do the Swedish test data suggest that A2A's manage 4.0 SCOPs, they also confirm that A2W only manage in the high 2's. The latter corresponds with the EST's field trials. Agreement of results between the Swedish and British A2W stuff was important to give me more confidence in their A2A figures.

I think that A2A show a higher CoP because the temperature differential is lower than an A2W. This is not the complete picture though as you have to take into account the other efficiencies in the system, mainly how much you need to run it. If an A2A heats your home up quicker, then it is a winner. I also think that you are better of just heating the air and nothing else to keep a home warm.

Give that most oil boilers do not modulate well and hate short cycles more than gas, it is very possible that the A2A stop the oil boiler operating on days that did not need much heat and saved a lot more oil than you would expect for the amount of heat it provided.

The issue I have with A2A and new builds is that as we increase the level of insulation, there are fewer days in the year that needs heating. A2A work least well in the middle of winter, they work best when the outside air is not much below the level you wish to heat to, but we have just removed the need to heat on these days with the additional insulation and waist heat from our computers etc.

Ed,

Is that using day rate electric, or Fan Storage Heaters to get the base cost of £750 a year?

The issue Ed, is that unless you are close to Passive House Levels, a single point of heating in the building is unlikely to be good enough. So more than one A2A will most likely be needed.

The real questions is, in a NEW build that does not have main gas, how much better insulation can you get for the money you save not having A2A?

Clearly adding a A2A to the living room of current “off gas” homes can be of great benefit and allow the current heating system to be left turned off for a lot of the year.

Personally I don’t see “off peat” electricity stopping being an option for long time, I expect that its control will become more dynamic so the heaters can be used for load levelling. I am not expecting electric vehicles to become common for a very long time due to most people in the UK not having their own driveway.

(Even with our own drive way, we will not be able to justify the cost of an electric car until they are at about the price of a normal car, as we don’t drive enough and buy 2nd hand cars. )

I still think that in a build with near passive level of insulation,a heat pump feeding into an oversized MVHR would be sufficient. tony has admitted that his MVHR does shift heat despite others saying it wont.

Fair point djh, but I also think that a house with good levels of insulation the heating season is so short it seems pointless to install a heating system that costs lots in outlay and maintenance/repair when a few panel heaters will cope with the coldest of days.

I am hoping to get my plans finalised soon so will pick all your brains on actual numbers etc.

<blockquote><cite>Posted By: ringi</cite>How long does an A2A last and what are the maintenance costs?

If it return is as much as 6 years without taking maintenance into account, I rather expect that in real life the cost will not be recovered before a replacement is needed.</blockquote>

Not from experience, but from my research, they should last at least ten years, probably around 15 on average, and can last 20 years with regular maintenance. Maintenance of £50-£100 per year including minor replacement parts and renewal. Quite simple systems. Happy to hear of experience on this.

For an average home with moderate insulation (loft and cavity wall insulation and draught-proofed, but still quite leaky), payback based on two units (in principle enough to supply all heat even in coldest weather) costing £1.6k in total (DIY install mind you) vs. high efficiency gas should be about 10 years (much faster if you can then do away with the gas altogether, so no standing charges and boiler maintenance, but that's unlikely due to DHW needs), LPG/oil 7 years and electricity 3.5 years.

For a new build, spending the money on insulation is better. These can be a good option for a retrofit where further insulation is expensive or a major hassle. While the cost and payback is just OK (still a lot better than many alternatives), the real benefit's the ability to cut your heating CO2 emissions vs. even high efficiency gas by 40%, and 80% vs. leccy.

Put it this way, I'd put these far higher up the list of retrofit options than double glazing.

Gareth; you started this thread, did you eventually fit an A2A as a result of your initial soundings. If so how has it fared?

Will the noise barriers not reduce the air floor reaching the pump?

(I never know that planning permission was needed for A2A heat pumps.)

Posted By: ringiWill the noise barriers not reduce the air floor reaching the pump?

Think about noise barriers put up between new motorways et al and nearby houses and baffles in exhausts, weapons and MVHR attenuators....sound doesn't 'do' zig zags that well either.

Posted By: GarethC'slightly flammable'

I just read a few articles, which are generally positive, I think, but the quote that stood out was 'Both are flammable, albeit that one large manufacturer likes to shout about R32 only being slightly flammable which prompted my comment that it is like being "a little bit pregnant"!' There are also seem to be some concerns about storage, handling and recovery of used refrigerant.

Good news about the move away from R410a though, I think ...

Resurrecting this old thread I have a question;

On an A2W system How is the heat transfer, ( eventual refrigerant to water ) effected, and where does it happen e.g. at or near the compressor end, or in some dedicated specially designed indoor thermal store, with a refrigerant link between the two.
Or, for instance, is the heat transfer first done to some other medium e.g. Glycol which could then be used/pumped to a coil in any existing water storage tank.

If the latter then is it possible to simply link a A2W compressor, with incorporated suitable heat exchange facility, to any water storage facility with a spare coil.