Air to air split heat pumps for UK spring and autumn heating

[apesort]

Anyone here using split A2A heat pumps for heating? Or in combination with an existing gas boiler or air to water heat pump.

 

They seem tempting as a relatively simple solution, especially for Spring and Autumn heating loads. With the added benefit of cooling being an option for scorching weather.

 

For example we've a 3 storey - 200m2 house. My non-detailed calcs would put the total winter heat demand around 13kW max.

 

Our front hall, stairs and landing are all quite open plan up to the loft landing. The existing radiator in the hall does a lot of the work in heating the whole house. 

 

I've been looking at single  5kW to 7kW A2A systems, to install in just the hall (without considering other rooms at this stage). This would be 4-5 times the output of the hall radiator.

 

My theory is that the hot air may circulate enough from this one device to sufficiently warm the whole house on Spring and Autumn days  (or even cold June days like this morning!). We tend to have our bedrooms fairly cool anyway.

 

For example this 6.0kW Daikin unit is about £1k - Even with "F-Gas" installation I'd imagine around £2k fully installed - Probably less than a days work for the installer and no need to touch the existing boiler or pipework.  

 

https://www.airconditioningworld.co.uk/daikin-ftxf60c-rxf60b-6-0kw-

 

A full A2W upgrade of an existing hydronic system would of course be much more expensive and more disruptive as most of our radiators would have to be changed.

 

I'm leaning towards getting a single A2A unit this year and testing how it performs this Autumn (and winter alongside gas). Then next year either go A2W heat pump or add additional A2A units to phase out gas.

 

If we ended up with  an air to water heat pump the Daikin in the hall could be additional, backup or just there in case we ever needed cooling.

 

Am I missing any serious down-sides to my plan?

[SteamyTea]

7 hours ago, apesort said:

I'm leaning towards getting a single A2A unit this year and testing how it performs this Autumn (and winter alongside gas). Then next year either go A2W heat pump or add additional A2A units to phase out gas.

Have you thought of buying a cheap one to see how it works?

https://www.appliancesdirect.co.uk/p/tf-12000ch/telefunken-tf12000ch-air-conditioner-air-conditioner

 

If it is successful, I will take if off your hands when you are done for free (saves getting an F-Gasser in).

 

[MrMagic]

Yes I use A2A units in the bedrooms - originally fitted as A/C but I used them for heating over the past winter, works fine. Few items to consider - 

 

1) It's a different kind of heat - not everyone likes warm air being blown on them so consider the position (or use the vane/flap adjustment) to direct the airflow in to the middle of the room

2) During the winter you may notice the defrost cycle - some units are smart and close down the internal unit whilst the external unit is defrosting to avoid blowing cold air about, but not all

3) Aircon remotes/programmers suck - it's like going back to programming a VCR sometimes. I found the wired wall mounted controllers seem to fare better in the wife acceptance factor department

 

...otherwise they 'just work'. Cheaper overall than an air2water heat pump. I'd highly recommend getting them fitted properly by an Fgasser - it's worth the money. I also have a no-name "easy fit" unit which worked fine for a year or two but has repeatedly broken down since Vs my 'proper' Mitsubishi units which are purring along fine. Strictly speaking that Telefunken unit above should be fitted by an FGas registered bod as it involves vac'ing down the lines and working with refrigerant.

[apesort]

13 hours ago, SteamyTea said:

Have you thought of buying a cheap one to see how it works?

https://www.appliancesdirect.co.uk/p/tf-12000ch/telefunken-tf12000ch-air-conditioner-air-conditioner

 

If it is successful, I will take if off your hands when you are done for free (saves getting an F-Gasser in).

 

Thanks for the suggestion. I'd go for one of the main brands if I were to get one. 

[apesort]

1 hour ago, MrMagic said:

Yes I use A2A units in the bedrooms - originally fitted as A/C but I used them for heating over the past winter, works fine. Few items to consider - 

 

1) It's a different kind of heat - not everyone likes warm air being blown on them so consider the position (or use the vane/flap adjustment) to direct the airflow in to the middle of the room

2) During the winter you may notice the defrost cycle - some units are smart and close down the internal unit whilst the external unit is defrosting to avoid blowing cold air about, but not all

3) Aircon remotes/programmers suck - it's like going back to programming a VCR sometimes. I found the wired wall mounted controllers seem to fare better in the wife acceptance factor department

 

...otherwise they 'just work'. Cheaper overall than an air2water heat pump. I'd highly recommend getting them fitted properly by an Fgasser - it's worth the money. I also have a no-name "easy fit" unit which worked fine for a year or two but has repeatedly broken down since Vs my 'proper' Mitsubishi units which are purring along fine. Strictly speaking that Telefunken unit above should be fitted by an FGas registered bod as it involves vac'ing down the lines and working with refrigerant.

Thanks for the reply, very useful points. Can I assume you don't find noise a big issue with them in bedrooms? 

[SteamyTea]

16 minutes ago, apesort said:

Thanks for the suggestion. I'd go for one of the main brands if I were to get one. 

Happy to take that away as well. Magpie me.

[MrMagic]

On 07/06/2022 at 10:33, apesort said:

Thanks for the reply, very useful points. Can I assume you don't find noise a big issue with them in bedrooms? 

 

No issue for me personally - they are quiet but not silent. I like the kind of 'white noise' it gives off, helps me sleep. The only thing we had to do is choose fan speed 1 rather than 'auto' - we found if we left it to auto the fan would spool up whenever it was heating, using the fixed fan speed solved this.

[JohnMo]

We lived overseas for a while and had Aircon in all rooms.  Wife didn't like the air being blown, drove her nuts.

 

Noise gets blanked into the background.

[markocosic]

They're lousy for heating.

 

Anything less than 37C feels cool to humans. The air leaving these will be at more than say 21C setpoint but less than 37C (for efficiency reasons). It'll make you feel cold. It will annoy you.

 

 

They're great for cooling.

 

Anything less than 37C feels cool to humans. The air leaving these will be at less than 21C setpoint. It'll make you feel cold. It will please you. it will still not please you as much as still air at 21C would please you.

 

 

There is a MATERIAL variation in performance between units. It is DIFFICULT to work out what it is.

 

Explore here:

https://www.eurovent-certification.com/en/advancedsearch/result?program=AC&product_type=AC1%2FA%2FS%2FR&keyword=&champ_23=3-4#access-results

 

 

Or look at the attached spreadsheet where I compare five units.

 

Row9 = standard bracket Midea, €650 for the 3.5 kW / 12000 BTU kit.

Row11 = basic bracket Panasonic, €650 for the 3.5 kW / 12000 BTU kit.

Row12 = standard bracket Panasonic, €1300 for the 3.5 kW / 12000 BTU kit.

Row13 = premium bracket Panasonic, €2600 for the 3.5 kW / 12000 BTU kit.

 

Row15 = premium bracket Panasonic, €2200 for the 2.5 kW / 9000 BTU kit.

 

 

The ratings are built around cooling mode.

 

The 3.5 kW class units provide ~2.5 kW of cooing at 30C ambient. COP4.75 for a basic one, 6-6.25 for a standard one, 7.5 for a premium one. Not much difference you might think.

In the more common condition we see 1.6 kW of cooling at 25C ambient. COP7.25 for a basic one, but 10.5-11 for the standard one, and 12.25 for the premium one. That's a material efficiency bump.

 

 

The differences get even more spectacular in heating mode.

 

When it's 2 degC out the premium unit manages 2.25 kW at COP 5.75, but the standard unit only do 1.5 kW at COP 4.5-5.25 (that COP falling off a cliff if you push them harder), and the basic unit just 1.25 kW at COP. The premium units also come with more defrost / snow / ice type equipment protection than the standard units. That premium unit will still be giving you 4.2 kW at -10 degC with a COP of 2.75+ which is damn impressive for heating. You definitely want these units if it's your only source of heat. Standard class units will probably do if you're only cooling or only operating in the shoulder seasons.

 

 

2.5 kW class units work even better. 2 kW at COP 6 when it's +2C out, 1.25 kW at COP 8 when it's +7C out, 3.6 kW @ COP 3 when it's -10C out. You're better off with two of those than a single larger unit. One upstairs one downstairs. Downstairs takes more of the heating load than upstairs but both are available in limit conditions. Vice versa for cooling.

 

 

Multisplits don't work as efficiently unless you ONLY use the one head at a time and you undersize the outdoor unit. (i.e. you have the 2.5 kW outdoor units with two 2.5 kW heads) That's due to the operating range limitations of the outdoor units. It only has one sweetspot if you're going for the ultimate performance.

 

 

I threw in a standard range 3.5 kW Panasonic unit in the UK in a fit of heat induced insomnia rage a couple of years ago. Works adequately for shoulder season use. Not worth paying double for the premium unit. I wouldn't use it in preference to the gas boiler in winter for comfort reasons though.

 

The XtremeSave Midea performs decently for the money. (standard panasonic performance for the basic Panasonic price) Don't buy the Midea Blanc etc for €50-100 less. That extra €50-100 makes an enormous difference to the performance. For ~€999 fitted we're going to pop one in the apartment to take the edge off in summer and the edge off in spring/autumn when it's the odd cool day but the district heating hasn't started up yet.

 

You won't justify the step up to premium if it isn't the main source of heating / cooling. The basic range is never worth it for cost of ownership reasons. 

 

 

I am still seriously tempted to use an air to air unit in the cabin build instead of a ground source heat pump. COP 3 ish at -10C is approaching what the ground source unit does anyway. Heat distribution and comfort from a lack of drafts swings me back to wet heating systems though.

 

 

MoreDetailPerformance.xlsx

[Radian]

1 hour ago, markocosic said:

Anything less than 37C feels cool to humans.

Agreed when touching a surface (or in water) but if a space is otherwise going to be unheated and the air temperature is, say, only 5C then I'm struggling to "visualise" the difference in feeling. I know what sitting in an room at 5C is like but not at, say, 20C when only heated by A2A. Funny that. I guess this is what you mean by directing the airflow away from you? Was I dreaming or was there a Mitsubishi A2A that had a thermal occupancy sensor that would do this automatically?

[JamesPa]

We have a Mitsubishi A2A unit in a domestic-sized office at work.  Nice warm air in winter, nice cool air (if you switch it on) in summer, and well distributed throughout the office.  Far superior in feel to the previous heating (night storage) heating.  I cant really comment on the noise, the work environment is obviously inherently a bit noiser than a quite domestic one, but I certainly wouldn't rule out A2A on the grounds of comfort.   

[markocosic]

Air movement makes you feel cold.

 

IME:

 

Insulated wall / triple glaze / UFH / 18C - feels a bit like - less insulated wall / double glaze / radiator / 21C - feels a bit like - less insulated wall / double glaze / A2A / 23C. 

 

Not as comfortable for a given air temperature; even if you are not in the direct stream; but being in the direct stream makes it worse.

 

 

Shoving it downstairs and relying on it running up the stairs and through the bedroom doors during the day does work. You wouldn't want to sit downstairs as the air is running past you and up the staircase though. You wouldn't want to walk around downstairs with it wafting past your face either. 

 

Better insulation and higher ceilings and more open spaces all help. A ceiling plenum would be interesting but adds fan power and question marks on dust etc. A landing could function well as a plenum for reducing airspeeds and letting the cool air into landing / hot air into rooms. Our layout doesn't suit this - unit currently blows across an open plan space before shooting up the staircase.

 

 

Noticeably warmer air and no draughts probably means a unit operating with a hotercondenser and lower fan speed. Comfortable but not as efficient. The unit we have offers decidedly lukewarm air at quite the rate of knots if operating at any meaningful output.

[Radian]

50 minutes ago, markocosic said:

Insulated wall / triple glaze / UFH / 18C - feels a bit like - less insulated wall / double glaze / radiator / 21C - feels a bit like - less insulated wall / double glaze / A2A / 23C. 

Nicely observed.

 

One thing I've discovered recently is that being in proximity to large expanses of glass in cold weather can make you feel cold despite what would otherwise be comfortable air temperatures. Emissivity apparently (fairly obviously really) works in both directions so radiating personal heat outwards has a very noticeable effect.

[SteamyTea]

2 hours ago, Radian said:

Emissivity apparently (fairly obviously really) works in both directions so radiating personal heat outwards has a very noticeable effect.

I am not sold on this idea that we loose body heat though the window panes.

Just got to do the numbers, remembering that it is only the surface parts of the body that are exposed to the window area that count, so quite a small area, and most of that area is clothed.

We like to think that the body is at 38°C or so, but that is core temperature, not exposed skin temperature.

Then there is the window.  Most are at least double glazed, and a bit dirty, and often filled with a gas that blocks radiation, not to mention the IR, one way, coatings.  And that is before we look out of it and see what it faces.  Not many people have windows that look up into the darkness, and vastness, of the universe.  At best, it looks up at cloud, a lot warmer than the 4K that the CMB generates.  Most windows look onto another building, so pretty close to OAT, some may look out onto woodlands, so slightly higher than OAT, and others out onto an ocean, very often higher than the OAT.

So we may loose a little power though windows, but in reality, way to small an amount to bother with.

 

[Radian]

I hear what you say, but it's really been quite a noticeable effect in our garden room on the colder winter nights - stuck out into the garden a fair way from anything else. With the UFH being so effective and heating through radiation I wonder if that's what makes the difference? I mostly felt the cold from the glass on the tops of my wrists and on neck/cheeks. That's what comes of sitting round in T-shirts when jumpers would be more sensible. The room has three fully glazed sides (two 3.8m sides split into three equal panels with the central one sliding, and the 5m rear split into four equal panels with the middle two sliding). The roof is a warm-roof construction and the glazing is all low-E but only double, not triple. Insulated floor etc. Overall it's pretty good energy loss wise.

[RichardL]

Interesting topic!
All things being equal - i.e. insulation state on the building etc.
Currently I'm heating from Oil and Hot water from Solar/oil backup.

Air to water brings with it the infrastructure changes with radiator increase in size + its an all or nothing jump onto a marginal untested/trust the installer (for my building) investment.
 

Air to air - taking on the points previously in the thread  about moving air feeling cold etc - seems like a way to install in stages & do away with the water approach entirely for some parts of the house.


Experimenting with Air to Air in the main living space might provide a transition away from oil heating over time - i.e. install in one space , see how it goes cooling/heating but keep the oil boiler in place for the medium term as a backup and topup. Added to that my living space is double height so might be just right for an air-air/con heating to avoid those draughts?

I have a house of two halves -  1800's 2' thick stone walls - kitchen/bedrooms, and 1960s timber+EWI - living spaces/bathroom etc.
The timber end is ~15m from the boiler with the 2x 22mm central heating pipes to/from it down the middle of the house.
 

[JohnMo]

Air to air may put you off also.  I lived with Aircon for a few years, and found it blowing at you all the time, even though it was supposed to blow in any other direction instead of you.  Not sure hot heating would be much better.

[RichardL]

Installed this week Multisplit with 2x inside units for my living room and home office.
I'm not minding the air flow so far - granted its not anywhere near extreme weather.

Front room unit is a good 8' high, office one more like 7'

Control - with the stock remotes will need some work - the concept right now is more like a plug in heater than the usual central heating single timeclock etc. one remote per unit (no supprise) but all timers are in the remotes - the inside air-con units have no 'brain' for timers.

 

I'll live with it for a while then intend to hook into the house main heating timeclock  - so theres a single winter/summer on/off switch & a daily on/off to heat during at-home/waking hours etc.  (overridable in the summer for air-con cooling) - but obv. leave each inside unit's own thermostat for the local room, but perhaps a wired remote so it feels more like central heating control.


Interesting experiment so far - inside units are quiet - not silent, but certainly not obtrusive.
Outside unit completely silent (the other side of a double glazed window)

Better than increasing rad sizes for a wet heat pump.

Kit: Mitsubishi Zen
(Zero VAT on air heat pumps too right now too)

Edited September 23, 2022 by RichardL

[Radian]

22 minutes ago, RichardL said:

(Zero VAT on air heat pumps too right now too)

Took the plunge myself today, gone for a couple of Daikin Emura 3's. The UFH loop we put in to heat the ground floor room  will just have to twiddle its thumbs for the time being. Maybe when the cost of air to water systems falls into line with A2A I might put yet another compressor unit on the back wall.

[gregh]

On 23/09/2022 at 18:55, RichardL said:

Installed this week Multisplit with 2x inside units for my living room and home office.
I'm not minding the air flow so far - granted its not anywhere near extreme weather.

Front room unit is a good 8' high, office one more like 7'

Control - with the stock remotes will need some work - the concept right now is more like a plug in heater than the usual central heating single timeclock etc. one remote per unit (no supprise) but all timers are in the remotes - the inside air-con units have no 'brain' for timers.

 

I'll live with it for a while then intend to hook into the house main heating timeclock  - so theres a single winter/summer on/off switch & a daily on/off to heat during at-home/waking hours etc.  (overridable in the summer for air-con cooling) - but obv. leave each inside unit's own thermostat for the local room, but perhaps a wired remote so it feels more like central heating control.


Interesting experiment so far - inside units are quiet - not silent, but certainly not obtrusive.
Outside unit completely silent (the other side of a double glazed window)

Better than increasing rad sizes for a wet heat pump.

Kit: Mitsubishi Zen
(Zero VAT on air heat pumps too right now too)

@RichardL (and anyone else!) curious to hear how your experience with these is going as we head into colder months.

[markocosic]

I have a single "3.5 kW" Panasonic Etherea unit downstairs in an averagely crap house. (70 m2 1970s council terrace with "filled" cavity, double glazing, and an awful attic conversion)

 

https://www.saturnsales.co.uk/Panasonic-Etherea-CS-Z35XKEW-Wall-Mounted-System.html

 

It's a little undercharged as it has 15 m of pipework rather than the 7.5 m precharge.

 

 

Turned it on for the first time on Wednesday.

 

It's set to "17C" which translates to the open plan downstairs at 20C - go figure - and bedrooms upstairs at about 17C.

 

It's set to run from 06:00 to 22:00. The overshoot on Saturday was me cooking.

 

It cycles a lot at this low output. It uses about 4 kWh/day. That feels eminently reasonable for 2C overnight / 10C daytime. 

 

 

 

 

 

The COP ought to be of the order 5 (at 2C) to 8 (at 12C) at low outputs - hence running it during the daytime - but there's no way to check.

 

The "heating biased" CU-VZ12SKE / CS-VZ12SKE unit would be a much better choice. (look at the power numbers for what's nominally the same capacity unit)

 

https://www.aircon.panasonic.eu/MT_en/model/kit-vz12-ske-cs-vz12ske-cu-vz12ske/

 

The "heat charge" is just for defrost; to avoid cooling the indoor air to defrost the coils.

 

 

 

Edited November 20, 2022 by markocosic

[RichardL]

Update re the cold snap in Nov/Dec - Mitsubishi Electric units in two rooms/end of house with radiators off in those rooms.

Normal consumption on my 2x rooms - living room 3.5kw unit, office 2.5kw unit is around 500w
During the cold snap that rose to anywhere near double consumption - 1.2kw - with outdoor temps down to -3 to -5ºC

The A2A still heated the rooms although the air seemed to stratify more easily when it was colder and I needed to manually turn up the fan to stop the top half of the room getting all the benefit. That was only really a problem in the front room which has a double height ceiling which also has the indoor unit mounted about 3m high.

It does become a balance of moving the air vs creating a breeze + a little more fan noise inside. The outside unit - outside the front room double glazed window is silent - I don't think its ever really working that hard 5kW (I think) capacity.

Changes
I upgraded the front room to a wired remote - on the wall - so it feels more oldschool/expected themostat type control - i.e. to pass the wife (and me TBH) test on ease of use. That needed an interface box and PAR41A(or similar code) off ebay and a little work with some cat5 cable.

Costs
I don't have detailed stats, the water/radiators in the two rooms are still off so I can get a feel for oil use reduction vs the approx £10/month electric increase. I'm intending to make a pretty coarse assessment based on monthly bills in the spring.

My crude overall OIL house + hot water bill is around £110 / month averaged out, so +£10 on the electric for the aircon for 2 rooms is promising - or at least order of magnitude workable.

Next...
Still planning out possibilities for the rest of the house - bedrooms I think - perhaps a single unit above the landing with ducting; I don't heat the bedrooms at night when sleeping - just warm them up in the evening and mornings - to turn in and get up & tick over during the day.

-or- perhaps wall/floor mounted inside units (look like radiators) so heat rises rather than having to be forced down?

That would mean another external unit at the other end of the house too.


Jury is out on hot water in the winter when there's no solar for the immersion. Perhaps a small oil boiler in the medium long term just for that job?

Edited December 19, 2022 by RichardL

[George]

I think it was on Heat Geeks where they said you should point the fins downwards when heating .... don't quote me on that though. 

[Radian]

On 20/11/2022 at 22:11, markocosic said:

The COP ought to be of the order 5 (at 2C) to 8 (at 12C) at low outputs - hence running it during the daytime - but there's no way to check.

 

I see you're using Tasmota to monitor the power draw using MQTT I imagine. I have yet to insert some smart sockets to measure my A/C units. I bought a pack for this purpose but they've all been nabbed for the x-mass deccies. 🙄

 

But I think I might have made a mistake by scheduling the heating to be running all night set back to 16^oC - I only have the crude energy report in the Daikin App to go on but it shows an average of 12kWh per day to maintain 16oC/20oC inside for two 3.5kW units heating 60m² throughout last week when it barely got above freezing all day.

 

On the other hand, by comparison, that's pretty good compared to the 160kWh/day average for my gas CH serving 190m² 😧

[RichardL]

FWIW - I tried 16º setback overnight for a bit -  but the AC units heat the rooms up so quickly I reverted to a nominal 18º during waking hours increasing for the evening then off overnight (similar to how I have central heating setup for the rest of the house).

Normally rooms drop to 15º min overnight with no heat, but in the cold snap I had one morning where they went down to 12 inside!

IMHO Just need enough heat to avoid condensation or cold soak in the building for long periods.