A2A Heat Pump minimum working temperature?

[Ferdinand]

Can anyone give me a quick summary, or link, as to the minimum practical external temperature for A2A heat pump installs to function?

 

Background is that I am currently using GFCH underfloor downstairs / rads upstairs, and I have been experimenting with a portable A2A heat pump heater / cooler for about 18 months in the kitchen diner. 

 

I am satisfied that it puts off any need for GFCH use by a few weeks either end, a boost to the house via air flow, and gives me a nice cooling facility in high summer.

 

But my unit says it is not practical below 7C external temperature.

 

Were I to look to install A2A units as an eventual replacement for the GFCH would that limit be about the same ie not much use below 7C?

 

Hence my question.

 

Thanks in advance for any replies.

 

[Gill]

Hi @Ferdinand - I had A2A installed earlier this year.  4 indoor Mitsubishi LN models and 2 outdoor.   In my limited experience, the operating temperature range was ridiculously hard to find for various manufacturers / models.   

Here's a doc link that covers my units : https://les.mitsubishielectric.gr/uploads/document/full-product-2022_air-conditioner_5045.pdf.  Hidden in those 143 pages is the Guaranteed Operating Range range of -15 to + 24 for heating of my units.  I recall looking into Daikin as well as a few other bigger names and only discarded them in favor of better COP /SCOP of the Mitsubishi models so I think most of the big players were in the similar operating range. 

Temperatures where I am in the last week have barely topped 10C and last few days we're not going above 2C daytime and dropping to -4C overnight.  The units are heating the place nicely - noticed a few more defrost cycles last night but that's not had any adverse impact.  Would be nice to find the time to rig up some energy monitoring to see how the drop in temperatures is impacting energy use but that's low down on a long todo list.    

[Ferdinand]

14 minutes ago, Gill said:

Would be nice to find the time to rig up some energy monitoring to see how the drop in temperatures is impacting energy use but that's low down on a long todo list.    

 

Thanks, Gill.

Won't a normal Smart Meter give you a good shot at this last requirement?

 

I'm will Octopus. and I can just download a whole lot of data as a spreadsheet, or look at various charts in my account online.

[Gill]

To some extent my smart meter data gives me a rough idea and comfort that the usage hasn't increased much at all with the temperature dips.  Don't have a fixed heating schedule as routines are constantly changing.  There was a channel on youtube did a decent dig into temperature vs energy consumption  - Tim & Kat https://www.youtube.com/watch?v=mkSPS-scLMA if you're interested.  

[HughF]

My cheap as chips r290 mini split really struggles when it’s below 5 outside. Put it on last night and it was defrosting within 20 mins…

[Gone West]

2 hours ago, Gill said:

The units are heating the place nicely - noticed a few more defrost cycles last night but that's not had any adverse impact.

When your A2A is defrosting, does it just turn off the indoor units.

[Gill]

1 hour ago, Gone West said:

When your A2A is defrosting, does it just turn off the indoor units.

Yes. The indoor and outdoor fans stop until the cycle competes. 

[Ferdinand]

So there is cause for caution at lower temperatures,. and probably a need for some sort of Plan B.

 

Mine 'defrosts' - or I assume it is defrosting when it stops and starts draining water into the bucket on the drainage pipe - from time to time.

[Gill]

1 hour ago, Ferdinand said:

So there is cause for caution at lower temperatures,. and probably a need for some sort of Plan B.

 

Mine 'defrosts' - or I assume it is defrosting when it stops and starts draining water into the bucket on the drainage pipe - from time to time.

 

That sounds like the defrost cycle. It should lead to water coming from the outdoor unit as the compressor is still running to defrost any ice build up. 

 

We're not planning a backup system although we did undersize our living room setup which may or may not turn out to be the correct decision. We wanted to avoid short cycling, we have plenty of heat loss issues to address along with some remodeling which hopefully reduces heat loss. If not we'll get another unit in our semi open plan living area. This is winter should give me a baseline to go from. 

[Ferdinand]

4 hours ago, Gill said:

 

That sounds like the defrost cycle. It should lead to water coming from the outdoor unit as the compressor is still running to defrost any ice build up. 

 

We're not planning a backup system although we did undersize our living room setup which may or may not turn out to be the correct decision. We wanted to avoid short cycling, we have plenty of heat loss issues to address along with some remodeling which hopefully reduces heat loss. If not we'll get another unit in our semi open plan living area. This is winter should give me a baseline to go from. 

 

My current one is a portable thing I'm experimenting with, which can be installed in all sorts of ways.

One of these:

https://www.appliancesdirect.co.uk/p/airflex15/electriq-airflex15

[Iceverge]

1 hour ago, Ferdinand said:

 

My current one is a portable thing I'm experimenting with, which can be installed in all sorts of ways.

One of these:

https://www.appliancesdirect.co.uk/p/airflex15/electriq-airflex15

 

Very interesting. 

 

I'm currently installing a Daikin FTXM25R. It's going at a snails pace mind you. 

 

Keep us posted. 

[Redbeard]

@Ferdinand, I was wondering about one of those. Presumably you have to get the optional hose kit and either dangle it out of a window or drill a hole of the requisite size? Any 'learning from experience' gratefully received. Thanks.

[Gill]

3 hours ago, Redbeard said:

@Ferdinand, I was wondering about one of those. Presumably you have to get the optional hose kit and either dangle it out of a window or drill a hole of the requisite size? Any 'learning from experience' gratefully received. Thanks.

Also curious having discounted full A2a install in our garage convertion and now wondering if that was the right call.  Thanks 

[Ferdinand]

I did a thread starting in summer 2022 about this, with some background (including a rude joke about Boris Johnson.)

 

I will add a few more recent notes on this thread.

 

TL:DR - at under £400 it's imo a bit of a steal, even if you just use it as a portable dehumidifier / heater / cooler. Remember that there is a Wi-Fi controllable version.

If you install it with a direct external outlet, you are looking at a 200mm hole in your wall - which is BIG.

 

Here:

 

[SteamyTea]

Generally, a air source heat pump will work down to pretty close to the expanded refrigerant gas temperature, which could be -27°C or more.

Practicality is a different issue.

The defrosting is not caused by the external air temperature, you get air conditioning units frosting up in the tropics.  Your fridge/freezer also frosts up.

The frosting is more to do with the absolute humidity, the greater the mass of air in a given volume, the more there is to settle on the external unit's heat exchanger.

Liquid water has its greatest density at 4°C.

It is a quirk of the UK weather that we have high humidity at temperatures below 8 or 9°C, this makes for a relatively high dew point.

Once below 0°C, the humidity drops as liquid water precipitates out of the air.  This is not instant, it can take a few days of sub zero temperatures, which we seldom have in England.

Because of this quirk, we have to be careful about judging the performance of an ASHP.

It really comes down to how often the outside air temperature is between 7°C and 0°C, and what the humidity is during those times (and the associated air pressure).

 

 

[Ferdinand]

1 hour ago, SteamyTea said:

Generally, a air source heat pump will work down to pretty close to the expanded refrigerant gas temperature, which could be -27°C or more.

Practicality is a different issue.

The defrosting is not caused by the external air temperature, you get air conditioning units frosting up in the tropics.  Your fridge/freezer also frosts up.

The frosting is more to do with the absolute humidity, the greater the mass of air in a given volume, the more there is to settle on the external unit's heat exchanger.

Liquid water has its greatest density at 4°C.

It is a quirk of the UK weather that we have high humidity at temperatures below 8 or 9°C, this makes for a relatively high dew point.

Once below 0°C, the humidity drops as liquid water precipitates out of the air.  This is not instant, it can take a few days of sub zero temperatures, which we seldom have in England.

Because of this quirk, we have to be careful about judging the performance of an ASHP.

It really comes down to how often the outside air temperature is between 7°C and 0°C, and what the humidity is during those times (and the associated air pressure).

 

 

 

I wonder how much having the external air feed from a conservatory (with an external conservatory window) helps?

AFAICS the warmer-than-outside air initially in the conservatory should provide a short-term performance buffer until the conservatory has been cooled down. That will afaics help the initial boost, but has benefit only for an initial period, and then needs the conservatory to heat up again as outside air hopefully heats up.

So potentially helpful on eg a cold morning where it heats up to a degree later.

[SteamyTea]

Just now, Ferdinand said:

 

I wonder how much having the external air feed from a conservatory (with an external conservatory window) helps?

AFAICS the warmer-than-outside air initially in the conservatory should provide a short-term performance buffer until the conservatory has been cooled down. That will afaics help the initial boost, but has benefit only for an initial period, and then needs the conservatory to heat up again as outside air hopefully heats up.

So potentially helpful on eg a cold morning where it heats up to a degree later.

It really depends on how large the conservatory is, and what the mass air flow is.

 

It is really just a modification of a Trombe Wall, and they are brilliant, so brilliant we all have them in every house in the country, and no heating bill what so ever.

[Ferdinand]

31 minutes ago, SteamyTea said:

It really depends on how large the conservatory is, and what the mass air flow is.

 

It is really just a modification of a Trombe Wall, and they are brilliant, so brilliant we all have them in every house in the country, and no heating bill what so ever.

 

Heh.

 

I have a conservatory with double glazed "external" doors to inside and outside, since the previous house-adaptor ran out of getting his money back and did not built it. So he turned it into a patio and put external doors on the kitchen and lounge. We finished it.

 

I'd say it's a useful buffer for a boost for the kitchen in the morning, but that is about the extent of it. I also get solar in the morning as it is mainly East Facing, so that helps boost the CoP.

 

Conservatory: 12 sqm. Kitchen: 30sqm ish.

As I sit here in my blogging pants in my kitchen-diner dispensing my wisdom (don't get excited - I am talking about Yankee-Doodle blogging 'pants') the temperature is about 15-16C, which is a little below my comfort zone, so I hope my Trombe-Conservatory will give me a couple of degrees extra over an hour or so.

 

F

[Wil]

Could I put one of those units in a fireplace and reject the cool/ heat up the chimney? I have multiple 200mm holes in my roof which are currently blocked at the room I could use…

 

And are they too noisy for a bedroom?

[Beelbeebub]

1 hour ago, Wil said:

Could I put one of those units in a fireplace and reject the cool/ heat up the chimney? I have multiple 200mm holes in my roof which are currently blocked at the room I could use…

 

And are they too noisy for a bedroom?

Ideally you would need a duct for inlet and exhaust for those portable units to work well.

[Ferdinand]

1 hour ago, Wil said:

Could I put one of those units in a fireplace and reject the cool/ heat up the chimney? I have multiple 200mm holes in my roof which are currently blocked at the room I could use…

 

And are they too noisy for a bedroom?

 

I would not put one in a bedroom, and want it to work whilst I was asleep. But you can arrange it so that the unit is outside eg on a balcony.

 

The thread I linked has a copy of the manual linked, which tells you a lot more. I am not sure that it would be able to drive the flow up the height of a chimney.

My view is that I would probably not make one a permanent installation but would go for a minisplit, or one of those where there is a single unit inside the room and a 70mm hole carry the connections. If eg I had a summer office it would be useful as tactical heating. / cooling.

For me, it is also a spare powerful dehumidifier which I might ultimately use as another lend-to-tenants or dry-the-washing device.

 

[Ferdinand]

28 minutes ago, Beelbeebub said:

Ideally you would need a duct for inlet and exhaust for those portable units to work well.

 

I'd point you to the manual, but of course one of the two (inlet or outlet) is in the room, and the other exits through a window or a hole in the wall.

 

I have to think about it again every half year when I reverse the unit to change it from heating to cooling by plugging it in the other way round, to keep my brain straight.

[SteamyTea]

If you pumped the cold air up a chimney, you would cool the brickwork, that may cause problems.

[Ferdinand]

7 minutes ago, SteamyTea said:

If you pumped the cold air up a chimney, you would cool the brickwork, that may cause problems.

 

It would have to be done in an insulated duct.

[SteamyTea]

2 minutes ago, Ferdinand said:

 

It would have to be done in an insulated duct.

Think you would get too much back pressure.

I am still umming and ahhing about one of the though the wall ASHPs.  Only the noise that worries me at 56 dB.  Having said that, my old fan heater is 62 dB.