[Closed] Air to air heat pump - anyone got one?

All over Australia if it's what I think you mean - reverse cycle air conditioning. Blows warm air around the place while making the leccy meter spin. Best left set to an ambient temp as they are inefficient at heating the space up but better at keeping it warm - like the oil filled rads.

Yep, that's the jobby. Getting 2.5 x the heat per Kw has got to be better than nothing.

Don't they have minimal operating temps at something like 5ºC? Then they need an internal heater for the incoming air.

depends how do you like having warm dry air blown around...
Of the choices here in Oz I went for the oil rad over the heat pump, was much quieter. How is the office insulation?

[quote=captainsasquatch ]Don't they have minimal operating temps at something like 5ºC? Then they need an internal heater for the incoming air.

I know nothing about this myself, but I was just checking out how these things work on Wikipedia and it says:

A "standard" domestic air source heat pump can extract useful heat down to about ?15 °C (5 °F)

From experience in a commercial facilities setting, 5 deg is more accurate. They are not good as the primary heating source if outdoor temps start to head towards zero.

A "standard" domestic air source heat pump can extract useful heat down to about ?15 °C (5 °F)

They work best when air is warm. Cold, wet winter = nowhere near the stated performance.
My old boss had two on houses - it's an aircon in reverse, with all the power usage that entails.

Remember to factor cost (financial and carbon) of gas/oil/wood/fuel of choice vs electricity

Insulation is average (it's a converted double garage with 30mm insulated plasterboard on the 9" walls and an insulated vaulted ceiling. Floor in not insulated.
House is heated by oil which is fine (especially at the moment) but the cost of running the pipework to the office would be daft.
I can get a brand new split system with external compressor and wall mounted indoor unit for about £5-600 quid (or about £150 for a used one on ebay).
I'm looking at this as a bit of a test really as we also have a holiday house that is heated purely by electric panel heaters and I'm quite keen to reduce the amount it costs to run. We have PV there and I'd really like the ability to use the spare PV production to power an air to air heat pump thus giving a bit of background heat all year.

I think air source heat pump is the technical term?
Noisy too ime

I would be highly suspicious of any claim to be able to extract useful heat out of external ambient air of -15 deg C.

They work by use of an internal heater (i.e. just like your resistive oil filled rads really) when it gets cold.

I believe there is a history of this...

http://www.bbc.co.uk/news/business-19511637

I personally wouldn't be looking at such a system... (and I design heating systems as part of my employment).

I'm looking at this as a bit of a test really as we also have a holiday house that is heated purely by

They are generally crap at getting heat round a house, you either need a lot of ducting and that or leave all the doors open around the house and having it running 24/7.

Get it sized correctly by a knowledgeable professional and it'll deliver sufficient heat year round. Lots and lots and lots of commercial buildings use VRF (air/air heat pumps) as it's only source of heating and they manage. COP's of 3-4, so they are actually more efficient than electrical resistance/storage heating and gas heating.

I can get a brand new split system with external compressor and wall mounted indoor unit for about £5-600 quid (or about £150 for a used one on ebay).

I would be highly suspicious of any claim to be able to extract useful heat out of external ambient air of -15 deg C.

They work by use of an internal heater (i.e. just like your resistive oil filled rads really) when it gets cold.

No they don't.

So we're back to the question of colder outdoor temps, let's say 0ºC. How does this heat the occupied space?

We had a succession of ASHP in houses in NZ where they are common. Last one was a Tosh ducted system with a mahoosive double inverter.
Rubbish frankly, but efficient, very efficient - not sure where the other comparisons on leccy usage came from but ours all seemed to be really cheap to run.
The type of heat is weird and as said before when it got to -5 the inverter froze and had to deforst which was when you needed heat ! This was a proper bells and whistles system as well. The whole house never really felt warm and this was a new build triple glazed well insulated sunny house. I can't imagine how they would work in the UK for heating like that on a domestic setting.

We have one. It's very noisy and I certainly wouldn't want one in the same room as I'm using (think noisy fan). It causes draughts from one room to the next as it sucks cold air around the building. We can't use it at night as, if we do, we wake up feeling totally dehydrated (mouth, eyes and nose all incredibly dry). Hate it!

We have one. It's very noisy and I certainly wouldn't want one in the same room as I'm using (think noisy fan). It causes draughts from one room to the next as it sucks cold air around the building. We can't use it at night as, if we do, we wake up feeling totally dehydrated (mouth, eyes and nose all incredibly dry). Hate it!

We have one. It's very noisy and I certainly wouldn't want one in the same room as I'm using (think noisy fan). It causes draughts from one room to the next as it sucks cold air around the building. We can't use it at night as, if we do, we wake up feeling totally dehydrated (mouth, eyes and nose all incredibly dry). Hate it!

No they don't.

There is useful heat in anything above -273degC.

I have a work colleague who did his final year thesis on his degree course on air-to-air in NE Scotland (day release as a working services design engineer). His conclusion was 'dinna...'.

Sorry for the triple post. Don't know why that happened and cant seem to edit it. I don't hate it enough to type the same message 3 times 😉

vapour compression refrigeration cycle. Refrigerant R410a boils at -48.5degC.

you've already decided to give it a go haven't you and your just asking permission

How do 'Mitsubishi, Toshiba or Daikin' do it? Usually direct resistive electric element from memory. Happy to be proved wrong like.

Toshiba’s light commercial line-up, which now spans from 1hp through to 10hp and offers models across the spectrum in this important sector. Boasting exceptional efficiency and fully compliant with the ErP Directive (Lot10) threshold for 2015, the new models have a sector-leading operating range, delivering cooling from -15 up to 46deg C and can provide heating in ambient conditions as low as -15deg C

I'd still get a wood burner though.

The air/water systems usually have a top up heater in the calorifier/water cylinder.

Hmm, maybe I'm getting my systems mixed up... 😳

I know from 'real world' experience that ASHP's are expensive to run in the North of Scotland. We can regularly get temps in the region of -15 deg C, in winter '09/10 it stayed approx. this for 6 weeks!

I'd still get a wood burner though.

No argument about that

[url= http://www.coolingpost.com/features/what-future-for-r410a/ ]http://www.coolingpost.com/features/what-future-for-r410a/[/url]
Sounds like lovely stuff. 😐

And now in a way that this idiot will understand, please?

Quite a lot to cover!

Sounds like lovely stuff.

Quite a lot to cover!

That's nothing. Google R12 and R22. The whole refrigerant debate is a very wide one!

Metalheart, you might have seen a cheap or poorly sized system that needed supplementary electric heating, I had the misfortune to be asked to troubleshoot a system like this in Vancouver with such heavy frost build-up on the coils it had buckled the outer casing of the unit!

I always think of the system as taking the huge amount of low grade i.e. <21C heat from the air and compressing it to give a smaller amount of high grade heat instead. Find it easier to visualise than refrigerant boiling points!

Interesting that R410a isn't banned simply because a safer alternative can't be found rather than it being deemed OK.

Go on, try me.

I honestly thought we'd be seeing the natural gases such as isobutane etc more widespread by now. Co2 and Ammonia will only ever be suitable for large applications.

You will need to understand heat transfer, types of heat (sensible and latent), and gas laws (Boyles, Daltons and law of combined gases) for starters.

I'd be happier seeing PCMs being used more widely for cooling and getting rid of full on mechanical systems altogether.

I also figure that if an elevator pitch can't be done, then there's an element of skulduggery going on.

It normally starts with "can you put up with 28degC for two days a year?" or other such bollocks and ends with a very pissed off building operator.

If you say so! I am not going to be giving a lesson on the principles of refrigeration (which I am very well versed in thanks) on a thread on STW!

We used them as our only source of heat for many years in Japan (a/c in the summer, reverse in winter). A bit noisy as others have said, but that depends on the model and the installation, so it may be fine for you. Also v dry, but that's probably a good thing in the UK. Might not be so great in a cold wet winter as they can ice up - ours had an automatic cycle of shutting down, like defrosting a fridge.

A paraffin burner would probably be a cheaper alternative.

For those wondering how they work, fundamentally it's just a refrigerator turned inside out, heating element on the inside, cooling on the outside.. (actually reversible, so you can do heating or cooling).

Also v dry, but that's probably a good thing in the UK.

Or possibly not. If you have 100% saturated air at -15 deg C and heat it up to 21 deg C the relative humidity is only ~10%. The recommended is somewhere between 40-70%. Too low RH has problems like too much (static electricity, shrinkage, etc.).

13thfloor: nah, I was just getting it wrong. Wrecker had it, air to water HP's tend to have electric resistive heaters to cope with the sub zero external ambients. But thanks for trying to dig me out of a hole (of my own making). I don't like it when mistruths surface, happy to stand corrected!

My theoretical air con knowledge is (obviously) not as good as wreckers. In my defence, I've not had to revert to theory since sitting air conditioning exams back in the 90's. I thought I'd better check my RH was right (there being people who would call me on it if I was out) so I dug out some text books. Turns out it was dated 1990 and doesn't even cover R140a... So no, I'm not going to try and explain reverse cycle heat pumps neither...

In mechanical building services design, air con (& refrigeration especially) is probably as difficult as it gets. We leave that to the specialists... Just thinking about refrigerant pressure-enthalpy diagrams makes me break out in a (cold) sweat!

I work in building services engineering (non-design) nowadays too. My trade training was in the 90's also! I haven't used a Mollier chart in anger for a long time, even the lecturer on the building services engineering degree wouldn't mess with them.
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Air conditioning (proprietary) design is actually very simple, it's about understanding the product and load. Refrigeration design is far more interesting. Flooded evaps, compressor packs, heat recovery. Lovely.

Yeah air con isn't too bad, I can navigate around a psychrometric chart and designed operating theatre vent and for a burns unit amongst other things in a previous incarnation.

I have an easy design and a difficult design. The easy way is using the electricity councils design guide from (probably) the 70's 🙂 KISS.

Had to resort to the specialist for the ice rink plant mind...

ETA: btu/lb! Jeez, was it the 1890s? KJ/kg puhlease.

OP it may have been mentioned above but the CoP figure varies with temperature, the lower the temp the lower the efficiency rating, if too cold you are using £ for electric just like electric heating anyway. So check actual figures not just headline marketing stuff and see if it's worth it. A new system may well be £thousands...anyway let us know how you get on, we all like a bit of science:)
Can you run it off PV panels...or just get better insulation and a space heater.

metalheart, it's a rare house that is -15C inside! Do you not realise that these systems don't actually take in air from outside, it's just the heat that is transported? Try starting with 100% saturated at 10C instead and you may be pleasantly surprised.

As you are a heating system designer, I'm surprised at several of your posts. Certainly our heat exchangers (we had 3 in all) did not have direct resistive heaters, and the air temp was frequently below zero though I don't think we ever saw -15C. Bits of Japan certainly get that though. Humidifiers were also comonly used in Japan (we had one too) but I really can't see that being needed in the UK in winter!

thecaptain: I'm assuming that they are like other ASHP's and there's an external unit that sits outside? That's where you can regularly find temps of -15 deg C in Scotland. The 'outside' air is the heat source. On air-to-water they don't work very well at those temperatures and have electric resistive heaters to make up the shortfall as the CoP drops away. Air-to-air I already admitted I didn't know enough offhand and accepted wrecker's correction.

Ok, I see where you're coming from now. No, it's not outside air being heated through the internal unit but where does the inside air come from in the first place? You need some fresh air inside. Relative humidity in summer is higher than in winter. You're highly unlikely to have 100% RH at 10 deg C inside (unless you're continually boiling the kettle) in winter either. I was coming at it from that angle. Your source air has low RH, unless you're generating water vapour inside where's it coming from?

I've come across at least two office blocks in Scotland with (electrically generated steam) humidification presumably to overcome static electricity issues (seems a bit of overkill to me personally considering the running costs)

Some light reading:

https://en.m.wikipedia.org/wiki/Air_source_heat_pumps

Seems you can get units to operate as low as -35 deg C (albeit at CoP's considerably less than, er, ideal).

Guess I better apologise to the OP for derailing the thread. sorry!

metalheart, your argument on humidity applies equally to any more common soure of heating, be it resistive electric or water-filled central heating radiators. The only additional effect from the heat exchanger system is the fan blowing wamr air around which does probably add to the discomfort in dry conditions, but doesn't actually dry the air per se. Don't forget normal human life generates significant amounts of indoor humidity, which is often the cause of damp problems over and above the ambient climate. Maybe less so in an office with no cooking, bathing, laundry.

Don't worry MH ..... it's all good stuff!

cvilla: Yes the COP value can be a little misleading so a number of manufacturers are now quoting the SCOP which is the performance figure averaged across all the seasons.
As the [other] house is only occupied sporadically during winter I'm just looking to convert some spare PV output to heat in the house just to keep it above 11c!
I'd use the raspberry pi that monitors the PV production to switch the heat pump on for x amount of time if the power being generated was over a set threshold. Cloudy/dark = no heat pump. The place isn't heated at all if we're not there so anything would be a bonus.
During the shoulder months though (spring/autumn) the PV production could inject a reasonable amount of background heat.

Lots of info on GreenBuildingForum.
http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=11248&page=1

If you can pick one up as cheap as you say it sounds like it's worth a try. I'd try to find some way of tracking the power consumption to see how much it's actually costing you to run.

The other question is whether you can improve insulation and airtightness.

OP - we have them in the offices at work, which are basically extensions or partitioned off sections of an agricultural barn. They are many times more efficient than the storage heaters they replaced and can provide heat in the afternoon.

Basic observations are that the coldest place is next to one, which is also the noisiest place when a bit of casing isn't sitting right. The opposite side of the room is far warmer and quieter. Mount the external unit high if you get snow, have had to dig ours out that are on the floor. Equally the one next to the outside toilet has made it a chilly place for a quiet sit down, but it's off the ground, under a deck, so wins on that front.
The external units can drop a fair bit of water, which hasn't been great for the ones over concrete.

There are days when we would far rather have a wood burner as the thing seems to have a mind of its own, a different temperature scale to us and a million running options on the controller. We just want heat NOW.