Help sizing an air-to-air heat pump

2nd_time_buyer

I am on the point of ordering an air-to-air heat pump (air conditioning unit). I would be grateful for advive on what size unit to go for.

The room is North-West facing kitchen/diner/living room around 35m2. It is well insulated and currently heated by a 7000 BTU radiator (the second radiator is returned off).

I have been looking at this 3.5kw Panasonic unit.

https://www.airconcentre.co.uk/products/panasonic-3-5kw-wi-fi-wall-mounted-inverter-r32-kit-tz35-wke

Any thoughts on whether that will be sufficient or should I go for a bigger 5kw unit:

https://www.airconcentre.co.uk/products/panasonic-5kw-wi-fi-wall-mounted-inverter-r32-kit-tz50-wke

What puts me off the bigger unit is the efficiency is not quite as good and the noise levels are higher and it costs a bit more. The lower power input of the 3.5kw (around 1kw) might also be a slightly better match to my solar panels.

The typical sizing guidelines don't seem to account for orientation or insulation. And they don't seem to change depending on location I.e. the same whether it is for Australia or the UK. It makes me think they are generally over specced - but I am probably missing something(?).

I am suffering from analysis paralysis. Any thoughts welcome!

Thanks

JKenH

I have a Mitsubishi Heavy Industries SRK35ZS-S 3500w unit in my 38sqm lounge (2.4m ceiling height with 8am of double glazing) and it does an excellent job. Installed cost in January 2019 was £1100.

One of the reasons I went for the unit was how quiet it is. (My installer runs the same units in his house). Unless we come home to a cold house and need rapid heat (which it does provide very effectively) it is barely noticeable in use. It does have a Wi-Fi option but we didn’t bother with that as we are at home most of the time. 

It was relatively easy to install, powered by a 3pin plug into an existing socket with a hole through the outer wall and that gives me the facility to monitor its consumption using a plug in meter.

I also have a smaller MHI 2kw unit in the kitchen which is only around 18sqm.

2nd_time_buyer

Thanks JKenH. That sounds reasuring.

The price I have been quoted is £1420 installed for the 3.5kw unit. Which I think feels about right. It is a few quid cheaper for the non WiFi model. But that is an older slightly less efficient model, so although I don't think I would use the WiFi it is a nice to have.

My feeling is that they are unlikely to get complaints if a system is over specified. So that installers err on the side of caution. I have also been surprised at the lack of understanding with regards to power consumption. A couple of installers quoted the heat output as the power input requirements. Even though the electricity consumption is typically 3-4 times lower.

2nd_time_buyer

JKenH - have you had any problem with icing up when heating in the winter?. One installer said that if you need to use it for heating then you need to over spec significantly. It seem strange to me as air-to-air are used extensively in Scandinavia where they have much colder winters.

1961Nick

I had a 5.2kWh unit installed in a large 'P' shaped conservatory which has a suspended floor with air bricks & had the usual plastic sheet roof. The room was basically as energy inefficient as it's possible to get & the HP had no problem heating it in the middle of winter with capacity to spare.

I've now had a proper roof installed with several inches of Kingspan & the HP can heat the conservatory, kitchen, hall, landing & a bedroom if I leave a door open... & that's in January!

I don't think you'll have any problem heating 32m2 with a 3.5kWh HP.

The physical size of the indoor unit usually changes above 3.5kWh & it can look less aesthetically pleasing.

1961Nick

The outdoor unit runs a defrost cycle if it detects freezing. The only inconvenience is that there's sometimes a 5 minute delay before it starts heating.

2nd_time_buyer

Thanks both. I have just ordered the 3.5kwh. Fingers crossed!

JKenH

2nd_time_buyer said:

JKenH - have you had any problem with icing up when heating in the winter?. One installer said that if you need to use it for heating then you need to over spec significantly. It seem strange to me as air-to-air are used extensively in Scandinavia where they have much colder winters.

None that I am aware of.

Martyn1981

2nd_time_buyer said:

I am on the point of ordering an air-to-air heat pump (air conditioning unit). I would be grateful for advive on what size unit to go for.

The room is North-West facing kitchen/diner/living room around 35m2. It is well insulated and currently heated by a 7000 BTU radiator (the second radiator is returned off).

I have been looking at this 3.5kw Panasonic unit.

https://www.airconcentre.co.uk/products/panasonic-3-5kw-wi-fi-wall-mounted-inverter-r32-kit-tz35-wke

Any thoughts on whether that will be sufficient or should I go for a bigger 5kw unit:

https://www.airconcentre.co.uk/products/panasonic-5kw-wi-fi-wall-mounted-inverter-r32-kit-tz50-wke

What puts me off the bigger unit is the efficiency is not quite as good and the noise levels are higher and it costs a bit more. The lower power input of the 3.5kw (around 1kw) might also be a slightly better match to my solar panels.

The typical sizing guidelines don't seem to account for orientation or insulation. And they don't seem to change depending on location I.e. the same whether it is for Australia or the UK. It makes me think they are generally over specced - but I am probably missing something(?).

I am suffering from analysis paralysis. Any thoughts welcome!

Thanks

We've got two 3.5kW units, and tbh they are oversized for normal sized rooms, but the idea is to leave doors open and help warm the house off PV generation, or E7, which works well.

I think you'll find that enough even for 35m2, especially if well insulated.

Just looked up 7,000btu radiator and it seems to equate roughly to a double panel, double finned rad of 600mm by 1,000mm, smaller than I'd expected for 35m2, so if that works fine, then the HP will be great.

Just to add, same here regarding icing, the system corrects for that when necessary. And noise wise, the outside units are pretty quiet, and the inside ones are really only as loud as you choose to run the fan speed. Ours have speeds of 0 to 6, and upto 4 is barely noticeable.

Swan_Valley

We have an A2A ASHP in the lounge & another in the kitchen. They provide the majority of our heating. Have not used any gas for the Central Heating system since February last year (apart from checking that the frost protection still works).

They are both quiet, inside & out. The only maintenance needed has been to clean the internal filters every month to remove collected dust.

If it does get very cold they do sometimes get ice on the outside unit. However, they automatically run a de-icing cycle , which basically runs them in reverse for about 5 minutes to remove it.

2nd_time_buyer

Thank you both. Install of the 3.5kw booked for next Saturday. 

We don't really need it as we have GCH. But we have excess solar and it seems to be the right thing to do to reduce gas consumption.