Green Building Forum - Air-to-air with DHW

Air-to-air with DHW

GreenPaddy — Fri, 10 Feb 2023 12:21:15 +0000

I'm re-posting this comment by "bogal2", as it was sort of bypassed in the middle of another thread.

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Hereâ€™s a new air to air heat pump with a HW cylinder. Not got a lot of info about itâ€™s efficiency. Sounds good in theory!

https://www.daikin.eu/en_us/product-group/air-to-air-heat-pumps/multiplus.html

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It seems to me to be an excellent solution for certain situations, and develops on the experience of "owlman", and others, whereby not a lot of space heating is required, but direct electric immersion is used for DHW generation.

I've seen a number of questions about simple air-to-air for space heating, but if only there were a way to get DHW too.

Not sure about the price, as like bogal2, there doesn't seem to be that much info on it on Google, but perhaps worth discussing, following up on?

Air-to-air with DHW

owlman — Fri, 10 Feb 2023 21:05:30 +0000

I'd not seen this before but it doesn't surprise me, I guess other manufacturers will follow. As far as I can see the plate heat exchanger/water heater bit is simply another spur off a multi split system and like A/A itself is well tried and tested but would require an " F " gas fitter to install; no harm in that.
I think I once heard that remote plate heat exchangers have always been possible as part of a heat pump set and it surprises me that the concept isn't more widely adopted, better in many ways than monobloc IMO.

Air-to-air with DHW

WillInAberdeen — Fri, 10 Feb 2023 23:26:49 +0000

Curiously difficult to find any data for this on the mfr's website or anywhere else - eg CoP ratings, water heater power rating, heat losses, noise etc. Or prices.

A Spanish website thinks the outside unit is rated 8kW but doesn't say if the water tank can absorb all the 8kW by itself, or if the outdoor unit has to modulate down.

The tank is quite small 120l, but if it is actually 8kW it could reheat fairly fast, or you could circulate hot water off into a separate store.

The heat pump apparently heats the hot water to 55â°C, with optional immersion heater to top it up to high temperature if required.

The idea is good, of moving heat round the home in the form of refrigerant vapour rather than warm water. Smaller pipes and lower refrigerant temperature.

On the back of any fridge or freezer is a radiator grid, which transfers heat from the refrigerant directly to the air. I'd like to see similar-but-bigger radiator grids become available, which could be hung on walls or be sunk into floor screeds, so that air-air heatpumps could operate without fan units. Still don't seem to be any about!

Air-to-air with DHW

fostertom — Sat, 11 Feb 2023 10:41:02 +0000

Interesting, but ... in a poor-to-averagely insulated house, requiring a lot of heat input relative to available heat-emitter area, hence heat emitters running at higher temp, hence higher air-to-water heat pump output temp, hence degraded CoP, the latest type of heat pump using CO2 as refrigerant can apparently maintain better CoP under such conditions. Alternatively an air-to-air heat pump can deliver its output at exactly target room-air temp, just a lot of it, i.e. cooler than any air-to-water heat pump, whether in a well-insulated or a poor-to-averagely insulated house, hence potentially best-of-all CoP. That depends upon delivering its output as warm air, not as warmer (or hot) water.

So, getting to the point, I don't see Will's idea of using refrigerant-filled heat emitters, whether as exposed radiant-plus-convective emitters (like an ordinary 'radiator'), or embedded in floor (or wall?) screed (like UFH). Either way, HP's output wd have to be at (a little or a lot) higher temp than an air-to-air setup, so back to degraded CoP - innit?

Or is it that the stage that causes the degradation of CoP is the heat transfer between refrigerant and intermediate emitter-thermofluid (water) or via fan-coil to air? In which case using the refigerant directly as emitter-thermofluid could be advantageous enough to overcome the CoP degradation due to required higher HP output temp? Or reduce the required HP output temp?

Air-to-air with DHW

owlman — Sat, 11 Feb 2023 10:57:54 +0000

' @ Will:
I agree, transferring heat from outside unit to remote PHx? with a split A/A unit, with refrigerant, is more efficient than monobloc with its relatively large bore water pipes; also practically speaking much easier and less disruptive. I guess its big limitation is the refrigerant pipe lengths that are possible, same goes for your wall hung/ UF refrigerant emitter idea.

Air-to-air with DHW

WillInAberdeen — Sat, 11 Feb 2023 13:38:05 +0000

Hi Tom, as your last paragraph. The issue with Air-water heat pumps is the heat needs to get transferred twice, once from the refrigerant to the CH water, then again from the CH water to the air or DHW. Whereas air-air heatpumps only have one heat transfer step.

Each transfer needs some delta T, twice as much for the A-W as the A-A, so the refrigerant needs to run hotter in an A-W than it does in an A-A. Hence the generally poorer CoP.

An air-air hp directly heating a big radiator or UFH or DHW cylinder, would be as efficient as an air-air heating a fan unit (a fan unit is basically a little radiator with a fan).

As you know the advantage of radiant heating is it makes people feel warmer even at lower temperatures, so is more economical than the purely convective heat transfer you get out of an a-a fan unit.

Hi Owlman, the radiator can have lots of flow loops in parallel (like a conventional UFH) to limit the pipe length, if required.

Air-to-air with DHW

fostertom — Sat, 11 Feb 2023 14:00:45 +0000

V interesting, thanks Will. It's an ongoing conversation with at least three clients! New insights helpful.

Air-to-air with DHW

owlman — Sat, 11 Feb 2023 14:49:56 +0000

Posted By: WillInAberdeen

Hi Owlman, the radiator can have lots of flow loops in parallel (like a conventional UFH) to limit the pipe length, if required.

Hi Will,
Multi split units are governed by their initial design and therefore the number of splits they can accommodate, each with their total design length. That I can assume is governed by compressor pump size and capacity. I can also imagine that any form of radiant heat emitter will quickly exceed that design criterion. it may be possible to have bigger and bigger units to facilitate the many " refrigerant flow loops " you envisage, but in reality more industrial than domestic, no?
Even then one sees commercial units racked up in rows, rather than one large unit.

Air-to-air with DHW

djh — Sat, 11 Feb 2023 17:14:02 +0000

I too was interested by that Daikin Multiplus system, and frustrated by the lack of information. So I suppose I will wait a while and then have another look to see if more info is available.

The Multiplus seems to be quite clever as it can run air-handling indoor units in heating or cooling mode whilst running the water heating in heating mode at a different temperature, IIUC. On the downside, it uses R-32 rather than propane or CO2 as the refrigrant, so not absolutely ideal.

It struck me that my original plan of just having a single indoor unit in one room (living room, probably) would likely not work well because the output temperature would not allow enough heat to be transferred. So I'm back to considering a ducted indoor unit that heats the supply from the MVHR.

I don't think refrigerant-filled radiators for space heating are likely to become a thing. Too many problems with the volume of refrigerant needed and with protection against damage and subsequent leaks.

I just replaced a radiant heater in our shower with a fan heater of marginally lower power. We both find the fan is better (more comfortable) although the noise is a bit annoying against the near total silence of the radiant heater.

Air-to-air with DHW

fostertom — Sat, 11 Feb 2023 17:20:08 +0000

Posted By: djhI just replaced a radiant heater in our shower with a fan heater of marginally lower power. We both find the fan is better (more comfortable)

That goes against all that I've understood - and experienced! How come?

Air-to-air with DHW

djh — Sat, 11 Feb 2023 20:45:39 +0000

The radiant heater heats the walls slowly but leaves the air cool. It doesn't heat a body in the shower because the glass stops it. So the end result is a wet body in cool air.

The fan heater heats the air, also slowly but quite noticeably. The warmish air can get inside the shower, driven by the same forces that cause a cold draught in the case of the radiant heater. So the end result is a wet body in warm air.

Air-to-air with DHW

fostertom — Sat, 11 Feb 2023 21:20:18 +0000

Ah - so the solution might be to place the radiant heater so it can 'see' the body in the shower - toasty!

Air-to-air with DHW

bogal2 — Sat, 11 Feb 2023 22:10:14 +0000

Thanks for reposting Green Paddy. According to the latest email from the installer who told me about it itâ€™s not available in the UK yetâ€¦

Air-to-air with DHW

GarethC — Sun, 12 Feb 2023 10:06:31 +0000

A wonderful system. And if I installed it, my EPC would worsen. Madness.

Air-to-air with DHW

djh — Sun, 12 Feb 2023 13:08:29 +0000

Posted By: fostertomAh - so the solution might be to place the radiant heater so it can 'see' the body in the shower - toasty!

Not possible in our room, unfortunately, and more tricky in any room owing to the area definitions in bathrooms.

Air-to-air with DHW

owlman — Sun, 12 Feb 2023 13:44:05 +0000

Re: OP & Bogal2 here is a similar thing from Toshiba.

https://www.toshiba-aircon.co.uk/product/r410a-estia-5-series-air-to-water-split-heat-pump-system/

Air-to-air with DHW

djh — Sun, 12 Feb 2023 17:06:01 +0000

That's an air-to-water HP though isn't it?

Air-to-air with DHW

owlman — Sun, 12 Feb 2023 19:36:08 +0000

Apologies, I got it wrong.

I wrongly thought that because the indoor and outdoor units are refrigerant connected, ( not water as in monobloc ), I assumed the fan coil emitters for both heating and cooling were refrigerant types. They do come off a water space heating circuit though.
I'm not sure if Toshiba twin R32 units have two sets of refrigerant outlets where maybe you could run one with the ESTIA water heater and the other as A/A. Alternatively just an independent stacked double.

Air-to-air with DHW

djh — Sun, 12 Feb 2023 20:23:25 +0000

There was an article in the Sunday Times this week about a village in Cambridgeshire that has a communal heatpump system. What struck me was that the two 750 kW GSHP output is at 75Â°C which struck me as quite impressive. There's an apparently free version of the story at https://www.thetimes.co.uk/article/heat-pump-uk-village-energy-homes-cost-z2m83sqjd

Air-to-air with DHW

WillInAberdeen — Sun, 12 Feb 2023 21:11:44 +0000

Nice project!

https://www.cibsejournal.com/case-studies/digging-for-britain-swaffham-priors-heat-network/ (no paywall)

"The heat network is designed to supply heat at around 72Â°C, in line with that generated by oil-fired central heating.The high temperature will enable residents to dispense with conventional oil-fired boilers... without having to upgrade radiators or insulation."

"heat pumps with ammonia as the refrigerant [are] able to generate higher temperatures while maintaining a reasonably good COP"

"connected to a 28MW (AC)/39MW (DC) solar farm"

"two 0.75MW GSHPs and one 0.5MW ASHP.... using the ASHP in the summer, as the warmer air gives a higher coefficient of performance... gives the GSHPsâ€™ ground loops a chance to replenish"

"1.5MW ... immersion heaters as the back-up heat source... 4x50mÂ³ thermal stores"

"Â£11.9m capital cost.... 300 homes â€“ as well as two churches, a pub and school"
[IE Â£40k capital cost per house served]

Air-to-air with DHW

GarethC — Mon, 13 Feb 2023 13:31:34 +0000

Isn't ammonia fairly toxic stuff??

Air-to-air with DHW

djh — Mon, 13 Feb 2023 18:17:49 +0000

Posted By: GarethCIsn't ammonia fairly toxic stuff??

Yes, and can also explode in the right conditions But the article Will linked to explains the precautions in the energy centre. What I'm not clear about is what fluid is distributed in the heat mains to the individual units at the houses. Is that just plain water? A hot water main?

Apart from the two individuals in the village who drove the idea, they seem to have been very lucky with the local councils who had the spare land and nearby solar farm that make the whole thing economically viable.

I'm not sure how many of the 300 houses the project can serve. 1.5 MW / 300 houses = 5 kW per house. Given that the houses haven't been adapted, is that likely to be enough power on a cold day? If it was half that number then the capital cost would double per house of course.

Air-to-air with DHW

Peter_in_Hungary — Mon, 13 Feb 2023 18:36:38 +0000

Posted By: WillInAberdeen"Â£11.9m capital cost.... 300 homes â€“ as well as two churches, a pub and school"
[IE Â£40k capital cost per house served]

Â£40k is an awful lot of money to swap out a gas boiler !

Posted By: djhI'm not sure how many of the 300 houses the project can serve. 1.5 MW / 300 houses = 5 kW per house. Given that the houses haven't been adapted, is that likely to be enough power on a cold day? If it was half that number then the capital cost would double per house of course.

And yes on the face of it those numbers don't seem to stack up.

Air-to-air with DHW

djh — Mon, 13 Feb 2023 20:25:03 +0000

Posted By: Peter_in_HungaryÂ£40k is an awful lot of money to swap out a gas boiler !

Good point. It would pay for a good amount of insulation instead.

Air-to-air with DHW

Victorianeco — Tue, 14 Feb 2023 23:25:43 +0000

We have air to air in our office and my wife's shop. Don't think we'd like to use it in a house.

I don't think it would handle multiple rooms and areas very well.

Our own house is run off an ASHP and oversized rads, we've run the flow at 35c all winter and has been more than ample.

I think rads give better control. UFH even better again.

Something about air to air heating that just doesn't feel comfortable to me. Particularly when the outside unit has to defrost, I bet they don't put that in the adverts!! We get 2mins of freezing cold air almost every hour

Air-to-air with DHW

owlman — Sat, 18 Feb 2023 13:26:30 +0000

Posted By: VictorianecoWe have air to air in our office and my wife's shop. Don't think we'd like to use it in a house.

We get 2mins of freezing cold air almost every hour

I'm curious to know who is the manufacturer of the units.

Air-to-air with DHW

Victorianeco — Sat, 18 Feb 2023 22:00:24 +0000

We've used the ones on appliances direct, they use a Panasonic inverter

Air-to-air with DHW

owlman — Sun, 19 Feb 2023 10:53:52 +0000

They'll be the electriQ ones I guess.

Air-to-air with DHW

PeterStarck — Mon, 20 Feb 2023 08:08:44 +0000

What happens with say a Daikin or Toshiba unit when in defrost mode? Do they turn everything off so there is no warm air being blown into the rooms. How long does a typical defost session last?

Air-to-air with DHW

owlman — Mon, 20 Feb 2023 13:36:56 +0000

I mentioned Victorianeco's comments to my "F " Gas fitter ( 30 years experience ), fitting commercial, industrial, and domestic Aircon, and still doing so.
It was something he had never experienced. He can only think it's defective equipment, or controls, assuming of course that the install was correct, and done by an experienced fitter.

1. The indoor unit temperature settings may be incorrect.
2. The indoor unit temperature sensor may be defective
3. The indoor unit fan may be defective
4. The outdoor unit defrost cycle is not operating correctly, or it may be badly sited, causing it to do so.

The installer needs calling to rectify the problem. Reverse Cycle heat-pumps are generally problem free, and it may only require the controls tweaking.
As a rule my fitter only fits branded equipment from the major manufacturers with good service and spares backup, and good control systems.