I always reckon that the CoP of water to air or even water to water (water source heat pumps are the best in terms of efficiency but you need a water source)

GSHP out perform air source but are more expensive and more reliable.n Also they work in cold weather, ashp often freeze up and cant do the job either

Air to water as you are saying are getting to compete with condensing boilers but they are not quite there yet in either cost or carbon terms. in pure energy they probably are but not if it cold like it has been for the last few years in winter.

Posted By: SeretMost UK homes are fitted with a wet central heating system though. Flats like yours are a minority, houses with multiple floors are going to need ducting or multiple units, which adds hassle and expense.

Mostly I think it's just that people aren't familiar with the technology. And as you say, if you give people something which can work as an air conditioner they'll probably use it as one. I very deliberately didn't mention the cooling mode of our little A2A heat pump to the wife when I fitted it.

Would they really, much? I don't get the impression it gets hot enough for air conditioning more than rarely.

The 145m2 house we rented for the last 3 years was heated almost entirely by an A2A heat pump. There were also oil-filled electric rads in all the rooms but we only ever used the ones in the bathroom and the kitchen (which was furthest away from the HP).

The heat pump was almost always able to keep the house at a reasonable temperature except when it was cold and very windy due to draughts.

Some words of caution though. Stick with the big name far east brands for reliability. The heat pump in our house was an Italian brand and both indoor and outdoor units had to be replaced last spring. The installer reckoned that the outdoor unit was only 5 years old and the indoor unit was 8 years old. By comparison my BIL has an 8 year old Panasonic that has never missed a beat and is still as quiet as when it was new. Our indoor unit had become very loud and there was a huge improvement in noise levels in the house when the new unit was installed.

I suspect that our unit was probably too small for the size of house as although it usually kept the place warm it ran almost continuously throughout the heating season and this probably contributed to it's early demise.

The outdoor unit was pretty exposed to the weather with winds blowing directly into it from the sea 75m away but as it is the Baltic salt isn't a problem.

Posted By: GarethC2. I realise A2A don’t do water, but this is just 25% of heating demand and heat pumps struggle to deal with the required temperatures. I think it’s better to leave hot water to gas. Still whacking a big chunk of your CO2.

Seems a small fraction of your energy usage, how have you calculated it?

Posted By: GaryBMy focus is on whole house systems which currently are around the 3.6 mark for CoP. In a few years' time these should improve to 5.0 or better.

An efficient MVHR unit with a 4-5kW A2A HP built-in would be great.

bit noisy for close neighbours and possible reverberation noise for building it is in

Tony
Less noise than the discharge from a pressure jet oil boiler or biomass, or indeed a larger ASHP unit.

Would be great to hear more details Gary, if you can divulge, I looked at using a Hitachi ducted A2A with my MVHR but the airflow requirements of the two units were considerably different which put me off.

I also looked at other so called "Magic box" solutions but they were all crazy expensive and I wasn't keen on an exhaust air heat pump.

A simple integrated solution with MVHR and heat pump all in one box with an outdoor unit for the heat pump is what I would see as ideal and keep DHW production seperate.

Very interesting points all. To pursue a few.

* I’m most interested in installation of A2A to existing homes with natural gas heating. There are many of these, and they currently have almost no sensible way of further cutting their heating carbon emissions (after insulating and boiler upgrades etc), so this is the big win. None of the ‘green’ options (A2W, GSHP, wood pellet boilers) are worth pursuing, largely because of cost (they’re just –far- too expensive to be mass market without subsidy), and only secondarily because they’re perhaps not green enough. A2A, at a quarter to a third the cost of alternative systems for units that can supply a high proportion of heating demand at COPs likely (though currently not proven) to ensure they are greener and cheaper to run than gas, just seem to be the only option worth one of these homes adding to their mix.

* I take your point that most homes have wet central heatings systems Seret (as does mine), but with the cost and disruption of having to change radiators or install UFH to make wet heat pumps work well, it doesn’t seem to be much of a point in favour of ‘wet’ heat pump systems? Also, if you have a combi boiler (like me, and very popular up here), you also need a hot water tank.

* I think there’s an awful lot of single floor two and three bed flats around, many with open living room-kitchens. Even if you have two floors, you could put two A2A units in, one on each floor (larger on ground floor), which between them should pump out plenty of heat, which in a well insulated house will tend to make it into all rooms, and, importantly, I think it will still only cost at most half as much as lower powered A2W etc. units, and net I think disruption would be lower (or no worse) than A2W given radiator faff. What do you think? I think the key to internal noise is having the units in central areas like halls, but realise this won’t be great for homes with lots of corridors. Will be interested to see how quietly they run. From my time in Japan, my air con unit rarely bothered me once I was used to it.

* COP of A2A vs alternatives. I suspect that the simplicity of A2A once it gets into the house (no transfer to water, storage losses, losses in pipes etc) offsets some of the significant disadvantage caused by the variability and low temperature of using air for the heat source. Certainly the COPs -claimed- for best performing A2A seem to be higher in general than claimed for A2W and even GSHP. This might just be because it is harder to refute manufacturers’ performance claims for A2A than the others. Evidence from my previous question (thanks all for input) on this does seem to suggest that A2A get reasonably near to claims, and that performance doesn’t fall off precipitously enough at the lower temperatures we tend to get (even up here in Scotland) to end up being more expensive or dirtier than gas very often.

There must be more on this. I’m going to ask a Japanese friend to see if she can find some cold weather analysis of A2A performance from there (it does get very cold).

* If the government is worried about use as air con (even here in Scotland), then they really should just ask manufacturers’ to produce versions without cooling functions. Can’t be that hard, but I’m not aware that they’re encouraging the industry to do so. It’s very encouraging to hear from GaryB that work is going on. I assume no cooling function is part of your work Gary?

* I nicked the hot water % of total straight from Energy Saving Trust I think.

* Tony, unit I’m looking at has a stated outdoor unit of 46dB, which is a lot less than older models. I’ve got neighbours immediately above and below, so am keen to comply, and exceed if possible, NR25. In principle this should be easy, but I’m worried that the actual noise characteristics may be worse. The government did a study looking at the noise from air source units, and concluded that noise was a big issue. But oddly, they seemed to look only at large and/or old units. The quietest stated unit was 49dB, and most were above 50. One of the manufacturers promptly responded to the report to point out that many of the recommendations had already been adopted by the industry, rendering the study less useful and frankly unhelpful. I’m thinking of asking Napier University, who are just up the road and did the study for the government, to re-run their methodology for my unit if I get it installed. Should add to the body of evidence.

* Calvinmiddle, that included upgraded (larger) radiators and installation. Once you add that, doesn’t look far off your quote? I’m trying to do this analysis excluding any subsidy. If A2A compares favourably pre-subsidy, the government reallly should look at offering some, even in principle. i.e. if they said “Systems without cooling modes (even if they don’t exist currently) and COPs above 4.2 (to be lowered once data confirming performance is available) would attract RHI of X” that might stimulate the market. Subsidy would go far further given the lower unit cost, and the ability to apply to existing gas fired homes would mean it would make a big contribution. That it could develop into a large market should lower costs, further improving viability.

Posted By: GarethC
* I take your point that most homes have wet central heatings systems Seret (as does mine), but with the cost and disruption of having to change radiators or install UFH to make wet heat pumps work well, it doesn’t seem to be much of a point in favour of ‘wet’ heat pump systems? Also, if you have a combi boiler (like me, and very popular up here), you also need a hot water tank.

Sure, if you consider A2A heat pumps to be competing against A2W ones, but in houses on the gas grid it's going to be heat pump vs gas boiler. If a gas boiler and wet system is in place, anything else does entail a fair bit of extra faff and expense. That'll be a real turnoff for a lot of people.

Of course, it's a one-time expense, and people took a larger hit to fit the central heating in the first place, so they would do it if the comfort or cost incentive was there.

From what I have read, the better performance of A2A is based on the lower temps required for Air heating. The thread that seems to run through all A2W heat pumps is that the performance drops off the higher the water temp. Performance at 35C is respectable, but poor at 55 - 60C. The piece of junk EAHP that I have heats my house by a combination of air warming and wet radiators, sized for low temps. Flow temp at 0C ambient is 33C. Air temp being delivered to rooms at that ambient is around 25C, flow temps dropping around 3 or 4C on return. Purely on the heating side, if A2W / wet heating (radiator or UFH) is only having to produce these kind of low temps, it is going to have similar performance to A2A. It may be cheaper to install but you still have to think about DHW. Back to the same argument about whether to have 2 separate systems for heating and DHW, or integrated systems based on A2W.

My only experience of A2A was in an office, it was either too hot or too cold, could never get the settings right (but that was a poorly built and maintained public building).

A2A heatpumps are the norm over here in North America (though the A/C function is usually required, even in Canada). It is possible to mix A2A and HRV, though not in a single duct system. One way to do it is to use the return air ducting as the supply for the HRV but have a separate set of exhaust ductwork for the HRV. To make it work properly, though, it might be necessary to run the fan on the heatpump, even when not heating/cooling. There's at least a factor of 10 difference in the volume of air required between the two systems.

A properly designed A2A system works well - but one has to use large enough ducts for the supply if noise is to be avoided (otherwise the air velocities end up being too high and this leads to noise). I have a W2A GSHP system and it is quieter than the oil boiler it replaced - there's virtually no air noise in the bedrooms, for example.

Mini-split systems are popular if there's no space for ductwork - though the interior wall units can be ugly - they do work well, though, and have high COPs. The outside units are pretty quiet these days, too - though obviously you need space to put them. The mini-split systems tend to have fairly small outdoor units, though.

Hope this helps,

Paul in Montreal.

Posted By: GarethCAssume it attracted only 1/3rd the level of RHI subsidy

Why would it get any? Your hypothetical propety has a gas main so it doesn't qualify!

And if you decide to change your property so it doesn't have gas, please explain how you are going to heat the water.

Posted By: GarethC40% reduction in heating carbon emissions

And you only save emissions if you believe in the "I pay my electricity bill to a green company so I must be getting green electrons (or making more green electrons breed)" meme. I'm one of those that don't. Unless and until we 'green the grid' we should be trying to reduce electricity consumption, not increase it.

Some Canadian info on heatpumps in a cold climate:

http://oee.nrcan.gc.ca/publications/residential/heating-heat-pump/4608
http://oee.nrcan.gc.ca/sites/oee.nrcan.gc.ca/files/pdf/publications/infosource/pub/home/heating-heat-pump/booklet.pdf


Mitsubishi cold-climate heatpump (works down to below -20C):
http://www.mitsubishielectric.ca/en/hvac/zuba-central/zuba_central_vs_traditional_furnaces.html
http://www.mitsubishielectric.ca/en/hvac/zuba-central/specifications.html

[edit]

Testing cold climate heatpumps: http://www.chba.ca/uploads/TRC/May%202013/Cold%20Climate%20Air%20Source%20Heat%20Pumps%20Presentation%20-%20May%202013.pdf

Summary of the above:

o Dispelling the myth - New cold climate air source heat pumps (CC-ASHPs) do work in Canadian winters
o CC-ASHPs are important in areas where natural gas is not available
o Paybacks under 5 years vs. fuel oil or electric baseboard


Hope these help.

Paul in Montreal

Posted By: Paul in MontrealSome Canadian info on heatpumps in a cold climate:
[SNIP]
o Dispelling the myth - New cold climate air source heat pumps (CC-ASHPs) do work in Canadian winters

I'm sure it can be very cold in Canadian winters, but what's the RH% like? I presume there is less icing up (& thus defrosting) with drier air?