Green Building Forum - Shouldn't A2A heat pumps be receiving more attention?

Shouldn't A2A heat pumps be receiving more attention?

mike7 — Tue, 22 Oct 2013 21:15:00 +0100

Posted By: jamesingram if it's there they'll use it , if not, they wont, degree days or not

As one of They I can report that despite having a2a heatpump for two years now I've never felt the slightest inclination to use it in cooling mode. My middle class guilt was such that I felt I had to do some things to lower my fuel consumption on heating, and the heat pump has been a major success in contributing to a dramatic reduction in my use of LPG and wood. I looked upon it as a short-term low investment thing while I continued to look for what the ideal long-term solution for us would be. Still looking, but the pump has easily paid for itself already in Lsd terms. Carbonwise I am not able to judge.

If the fear of aircon units being used in the cooling mode is a problem, then an easy solution would be, with the cooperation of eager manufacturers, to supply them in non-reversible heating only mode. The kit needed to fiddle with these things makes it too difficult for the average They to reverse the action. It could perhaps also be specified that the indoor units be fitted at floor height, which I find is more suited for heating.

Further on the heating mode only suggestion - I wonder if these aircon units are capable of improvement if they are for heating only. I can imagine there are compromises made when they are to be able to function in either mode. Anyone here know enough to say?

And another thing ... if it's a high COP we're after then what we want is great big heat exchangers to waste as little as possible of the delta T , not 'compact' and 'unobtrusive' ones as manufacturers seem often to aim for. Don't we ?

Shouldn't A2A heat pumps be receiving more attention?

Paul in Montreal — Tue, 22 Oct 2013 21:37:12 +0100

Posted By: mike7Further on the heating mode only suggestion - I wonder if these aircon units are capable of improvement if they are for heating only. I can imagine there are compromises made when they are to be able to function in either mode. Anyone here know enough to say?

The only difference between a heat-only unit and one that does A/C as well as heating is a simple reversing value, to change the flow of refrigerant. Otherwise, the evaporator and condenser heat exchangers are essentially the same - though there's no defrost unit on the indoor coil.

Posted By: mike7And another thing ... if it's a high COP we're after then what we want is great big heat exchangers to waste as little as possible of the delta T , not 'compact' and 'unobtrusive' ones as manufacturers seem often to aim for. Don't we ?

It's not quite that simple - but a big evaporator usually works better at lower outdoor temperatures than a smaller one - but may require more refrigerant and then there's all the other things to consider such as gas flow resistance and so on.

Paul in Montreal.

Shouldn't A2A heat pumps be receiving more attention?

mike7 — Tue, 22 Oct 2013 22:27:59 +0100

Thanks Paul - the temperature ranges they would work over are obviously a bit different. Would that have any effect - say on the ideal amount or composition of the refrigerant?

Shouldn't A2A heat pumps be receiving more attention?

mike7 — Wed, 23 Oct 2013 01:13:17 +0100

There's also the way they are driven or regulated. My Hitachi has to be set to try for 32C before it will run at full pelt. Don't seem right.(Edit: This turns out to be because of where the temperature sensor is located - it is where it is able to receive partially heated air due to the low mounting position. It would be better sited more immediately in the unheated air entering the unit. Not really a problem, though).

The more recent one, a Toshiba/Midea, wont go low enough. If I set it to 16C - the lowest it will go - it continues to deliver heat up to 19C. ..Or it would do if I hadn't tweaked it by adding a resistor across the thermistor doing the measuring. I've a feeling that in both cases more sensitive thermistors would be a good thing to try.

Whatever, my limited knowledge means I'm fiddling with something I don't properly understand, and I don't know how to get more aquainted with the technicalities, short of getting a job with one of the manufacturers, and that would be a bit over the top. I guess there's quite a few people around in the UK feeling the same. Might be different in the US and Canada where aircon has been common for a long time.

Shouldn't A2A heat pumps be receiving more attention?

SteamyTea — Wed, 23 Oct 2013 06:04:40 +0100

Posted By: mike7say on the ideal amount or composition of the refrigerant?

Along the same lines there should be an optimal size for any given temperature range, would 2 or 3 units be better than 1 rather than relying on supplementary resistance heating.

Shouldn't A2A heat pumps be receiving more attention?

jamesingram — Wed, 23 Oct 2013 07:49:05 +0100

Sorry Mike you can't put yourself in the 'they' or 'them' bracket as you post on here
and you tinkering with the units to maximise the efficiency seems to prove to me that 'they' (most) would use them with considerably less care, thus potentially losing the desired benefits .

Shouldn't A2A heat pumps be receiving more attention?

davidfreeborough — Wed, 23 Oct 2013 09:59:27 +0100

We have reversible A2A heat pumps in each office at work & along with radiators fed by remote gas fired boilers controlled by a weather compensator which sets the flow temperature according to the outside temperature. There are no room thermostats or thermostatic radiator valves.

The A2A units are always on & are set to heating when the radiators are not delivering enough heat & cooling when they're delivering too much. Windows may or may not be open depending upon outside air temperature, level of sun, level of wind & whether its raining.

I'm not saying its a good model, but it is typical of what happens in the UK when reversible A2A heat pumps are added to an existing building.

David

Shouldn't A2A heat pumps be receiving more attention?

bella — Wed, 23 Oct 2013 11:31:11 +0100

Posted By: davidfreeboroughit is typical of what happens in the UK when reversible A2A heat pumps are added to an existing building.

I bame the parents.

Shouldn't A2A heat pumps be receiving more attention?

mike7 — Thu, 24 Oct 2013 01:14:48 +0100

Posted By: jamesingramSorry Mike you can't put yourself in the 'they' or 'them' bracket as you post on here" alt="" src="https:///forum114/extensions/Vanillacons/smilies/standard/smile.gif" >

Oh alright then. But can I at least be middle class - I mean I shop at Waitrose and read the Guardian and everything...

Posted By: jamesingram
and you tinkering with the units to maximise the efficiency seems to prove to me that 'they' (most) would use them with considerably less care, thus potentially losing the desired benefits .

Hah! Clutching at straws now. Leaving out the reversing valve not good enough, eh?

Posted By: bella
Posted By: davidfreeboroughit is typical of what happens in the UK when reversible A2A heat pumps are added to an existing building.

I bame the parents.

Nice one -

Shouldn't A2A heat pumps be receiving more attention?

GarethC — Tue, 29 Oct 2013 11:25:16 +0000

Hello all, hope you donâ€™t mind me bringing this one to life again.

SteamyTea â€œYes, if we swapped to HPs of all sorts then out CO2 emissions would go up until we have 60% nuclear generation.â€

I thought we were thinking that HPs might cut CO2 emmissions so long as the -average- mix remained the same? Are you saying that marginal increases in electricity output will almost certainly have worse than average carbon emissions, despite closing coal plants?

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David Freeborough â€œAny benefit in COP from the A2A heat pumps ability to operate at lower flow temperatures need to be balanced against the fact that many people will use them for cooling, significantly increasing energy consumption & carbon emissions.â€

To wade into this one, I canâ€™t understand why people would use it for cooling for two reasons:

1. The climate rarely asks for it, as discussed
2. It costs money. Why use an HP to cool, when you can open the windows for free? The days when itâ€™s worth cooling a UK home AND the heat canâ€™t be alleviated for free by opening windows are very very rare, are they not?

I note your point about your office scenario, but workers donâ€™t pay the office energy bills. In a residential setting, itâ€™s unlikely residents would do the same, so Iâ€™m not sure you can describe it as typical?

Iâ€™m not saying cooling would never happen, but I doubt it would be more than 2% or 3% of the total amount of time HPs were used. I canâ€™t imagine it being even 5% of the time. So this shouldnâ€™t be a significant worry should it? As mentioned, if the govt said they would support only â€˜heat onlyâ€™ A2A heat pumps, manufacturers would supply them in extremely short order as it should be easy.

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David Freeborough: â€œIn a well insulated airtight house,there is a lot to be said for a properly design A2W system which is directly connected to underfloor heating & delivers DHW via a separate cylinder/thermal store. Heat can be delivered where it is needed when it is needed at temperatures just above room air temperature without the horrible sickly smell of warm air from an air conditioning unit.â€

Yes, but the vast majority of houses are not new and millions are difficult to insulate well (solid walls) and/or make appreciably airtight. Even if you can stomach the disruption and cost of insulating your solid wall property, surely retrofitting underfloor heating or large radiators and installing A2W is just too much additional expense and hassle to be a mass market solution.

i.e. A2W in new, well insulated airtight houses are a great, but niche, solution. Whereas I think what weâ€™re talking about is something that works for the mass market. The much much lower installation cost and disruption, and potentially lower running cost and carbon footprint even compared to natural gas, of A2A could make them a good solution for heating existing, even relatively poorly insulated, properties?

Shouldn't A2A heat pumps be receiving more attention?

mike7 — Tue, 29 Oct 2013 13:26:11 +0000

Well said Gareth. Sometimes I think this forum should be clearly divided into 'New Build' and 'Retrofit' sections, both subdivided into 'It works a treat in my (unusual) situation' and 'This is what everyone should be doing'.

Shouldn't A2A heat pumps be receiving more attention?

SteamyTea — Tue, 29 Oct 2013 13:41:59 +0000

"There are 10 types of people, those that understand binary and those that don't"

Shouldn't A2A heat pumps be receiving more attention?

davidfreeborough — Tue, 29 Oct 2013 13:49:38 +0000

Gareth

You make some very good points & I can see why A2A heat pumps appeal to you as a pragmatic solution. However, I'm a big believer in fabric first & I think the benefits are too marginal in the situation where there's an existing gas fired boiler.

There are too many houses in this country that were never designed for central heating & if I had my way they wouldn't be allowed to install/operate central heating until the house is insulated to a given standard, say, current building regulations. When it comes to government subsidies, I certainly don't think the government should be subsidising any heat source before the house is insulated to a given standard.

In addition to this, once a reversible A2A heat pump is installed, it is only human nature that the user will stop thinking about heat sources, outside air temperature, opening windows, cross-ventilation, etc. They will just increase the set point when they are too cold & reduce it when they are too hot.

Most people I know block up all their airbricks/trickle vents, shut-off extractor fans, use their central heating thermostat as an on-off switch & only open windows in extreme overheat situations which could have been avoided by opening a window earlier. They will be no different with an A2A heat pump controller, except they will spend money on cooling as well. Even where the logical solution is to open the window, I predict many people will not until it is too late & as a result will become hooked on air conditioning, as many already have in their cars.

David

Shouldn't A2A heat pumps be receiving more attention?

djh — Tue, 29 Oct 2013 15:47:10 +0000

Posted By: GarethCYes, but the vast majority of houses are not new and millions are difficult to insulate well (solid walls) and/or make appreciably airtight.

Solid walls are not especially difficult to insulate. It's just that some (most) people think that the existing aesthetic is more important than saving energy. I happen to disagree with that.

Even if you can stomach the disruption and cost of insulating your solid wall property, surely retrofitting underfloor heating or large radiators and installing A2W is just too much additional expense and hassle to be a mass market solution.

I'd say the easiest by far would be unfastening radiators and fitting some larger ones (or doubling single panels, or using fan-assisted ones, or skirting ones)

Shouldn't A2A heat pumps be receiving more attention?

daserra — Fri, 08 Nov 2013 23:44:58 +0000

I fit A2A systems here in Portugal, mainly for cooling. Mitsubishi Inverters mainly. The consensus is that the hot air they provide is uncomfortable and stifling. Lots of convection and no radiation does not a comfortable house make.

Shouldn't A2A heat pumps be receiving more attention?

mike7 — Sat, 09 Nov 2013 00:32:30 +0000

Posted By: daserra The consensus is that the hot air they provide is uncomfortable and stifling. Lots of convection and no radiation does not a comfortable house make.

Might that be because they have been used for cooling? - odours may have collected on the heat exchanger. Also the indoor units will have been mounted high. Better at ankle height for heating I find.

Shouldn't A2A heat pumps be receiving more attention?

Seret — Sat, 09 Nov 2013 07:32:38 +0000

Posted By: mike7Better at ankle height for heating I find.

I'd agree with that. I've got one mounted quite low and it warms the room really effectively. The only problem is that unless it's throwing out tons of heat the airflow from it does create an uncomfortable draught for anyone sitting in the line of fire. My wee girl loves the way it blows her hair, but I don't enjoy sitting eating my corn flakes in a draught. You've got to be careful where you site them.

Shouldn't A2A heat pumps be receiving more attention?

mike7 — Tue, 12 Nov 2013 11:47:15 +0000

Have just read the users notes for my Hitachi aircon - it confirms that odours can collect when the unit is used in cooling mode, and then be released when heating mode is used.

So - another good reason to use them for heating only.

Shouldn't A2A heat pumps be receiving more attention?

jamesingram — Tue, 12 Nov 2013 16:04:50 +0000

Mike, do you know of any heat only models currently on the market ? Perfectly fine idea , but tricky if there's not available .

Shouldn't A2A heat pumps be receiving more attention?

mike7 — Wed, 13 Nov 2013 17:18:57 +0000

True, Jim, but the 'more attention' of this thread could include introduction of incentives such as FITs or VAT concessions for heat-only hps. Manufacturers would be able to respond to that in a twinkling.

I suggest any such incentive might only apply to smallish units - up to 4 kW output say. In the average UK home that would lop the bottom off the consumption curve in the heating season without adding greatly to the peak winter electric demand. The winter peaks would be met by the pre-existing system.

Shouldn't A2A heat pumps be receiving more attention?

GarethC — Thu, 09 Jan 2014 16:02:20 +0000

Swedish tests (http://tinyurl.com/ouev7es and copy to Google Translate) suggest that latest air to air heat pumps achieve seasonal performance factors of about 4.0 in Malmo. FINALLY some A2A field data â€“ thanks Chris P Bacon!

Malmoâ€™s average temp is 8.1 degrees. Edinburghâ€™s is 9.3. Malmo has 14% more heating degree days at 15.5 degrees base temperature and 41% more HDDs at ten degrees base.

i.e. if A2As manage 4.0 SPF in Malmo, they should achieve at least this in Edinburgh.

At this SPF, A2A space heating would emit 40% less carbon at current grid carbon intensity, and be 25% cheaper given current relative costs, than a 90% efficient gas boiler (2.4 SPF needed to be greener, and 3.0 to be cheaper).

Two LG A2A units with combined output of 8.6kW at -7 degrees (10.8kW at +7 degrees) â€“ according to the tests, not the manufacturer â€“ would cost Â£2k. With annual gas heating costs of Â£800, so Â£200 savings per year, they would pay for themselves in 10 years, unsubsidised.

I reckon thatâ€™s a worthwhile reduction in carbon emissions, and better finances than I can find for other renewable heating technologies. I may well buy a couple unless Iâ€™m missing something.

Shouldn't A2A heat pumps be receiving more attention?

daserra — Thu, 09 Jan 2014 18:19:12 +0000

Posted By: mike7
Posted By: daserraThe consensus is that the hot air they provide is uncomfortable and stifling. Lots of convection and no radiation does not a comfortable house make.

Might that be because they have been used for cooling? - odours may have collected on the heat exchanger. Also the indoor units will have been mounted high. Better at ankle height for heating I find.

The Mitsi's we fit have a mode where they go into heat mode for 1min or so after a cooling cycle to dry off the internal unit. Part of the maintenance we do is to spray disinfectant into the blowers.
I agree low units are better for cooling; they do exist but are quite rare here.

Shouldn't A2A heat pumps be receiving more attention?

Triassic — Thu, 09 Jan 2014 18:30:14 +0000

Posted By: GarethCi.e. if A2As manage 4.0 SPF in Malmo, they should achieve at least this in Edinburgh.

I bet the man fitting it in Malmo knows what he's doing and the man in Edinburgh, well I'm not so sure.

Shouldn't A2A heat pumps be receiving more attention?

mike7 — Thu, 09 Jan 2014 19:21:42 +0000

Posted By: Triassic:- " I bet the man fitting it in Malmo knows what he's doing and the man in Edinburgh, well I'm not so sure."

That's one of the advantages of smallish A2As - there's not nearly so much that the installer has to get right as compared to a full stand-alone HP system. I regard it as the low hanging fruit that can be plucked on a large scale immediately to give lower carbon and fuel cost. Against this is the argument that if you can reduce fuel cost by such means, you reduce the potential savings (and thus weaken the justification for investing in the real long-term ideal) of --- ta- da --- Better Insulation.

Shouldn't A2A heat pumps be receiving more attention?

jamesingram — Thu, 09 Jan 2014 19:28:45 +0000

I guess the question then is , how much for the A2A and what would you get in terms of energy saved if similar was invested in reducing heat loss ?

Shouldn't A2A heat pumps be receiving more attention?

SteamyTea — Thu, 09 Jan 2014 19:32:23 +0000

An A2A would be a lot less hassle to fit I would have thought. Though airtighness may be more important than insulation when you are heating the air first (which is the way it should be).

Shouldn't A2A heat pumps be receiving more attention?

mike7 — Thu, 09 Jan 2014 20:22:49 +0000

Posted By: SteamyTeaAn A2A would be a lot less hassle to fit I would have thought.

I think so too. Having avidly read on GBF about the many potential snags insulation can entail, I am now like a frightened rabbit when the prospect of doing any such to my house comes to mind. Never mind the planning and the cost.

Shouldn't A2A heat pumps be receiving more attention?

mike7 — Thu, 09 Jan 2014 20:27:33 +0000

Posted By: SteamyTeaThough airtighness may be more important than insulation when you are heating the air first (which is the way it should be).

I think you're just splitting airs.

Shouldn't A2A heat pumps be receiving more attention?

SteamyTea — Thu, 09 Jan 2014 20:30:07 +0000

Posted By: mike7I think you're just splitting airs.

Mike
I shall wait till yours is fitted before I have a go at one then

Shouldn't A2A heat pumps be receiving more attention?

Paul in Montreal — Thu, 09 Jan 2014 21:26:13 +0000

Posted By: SteamyTeaThough airtighness may be more important than insulation when you are heating the air first (which is the way it should be).

It doesn't make a difference. The air is being recirculated anyway - just as it is with radiators (through convection). Air tightness is important to reduce heat loss, irrespective of the heating method. Arguably the only time it doesn't make a difference is with high-temperature radiant heating. In frigid Montreal, there are places with quartz-halogen radiant heaters outside where people have to queue for things like taxis at the airport - even when it's cold, they work well - and there's no air tightness at all then!

As for the earlier comment about A2A heating being draughty and uncomfortable, that's just a sign of a poorly designed system. I live in a house with a forced air heating system heated by a GSHP and everyone always comments on how comfortable the house is - the temperature is very even as there's next to no stratification - despite the vents at floor level (on one floor) there are really no areas that feel draughty. Even candles don't flicker (much to my surprise, to be honest).

Paul in Montreal.