Air Source Heat Pumps

Swipe

18 degrees isn't so bad for a household ambient temperature, considering the extremely low temps this week. I'd just supplement the living room with that oil radiator.

Cardew

Swipe wrote: »

18 degrees isn't so bad for a household ambient temperature, considering the extremely low temps this week. I'd just supplement the living room with that oil radiator.

The point is that these systems are designed to work in Scandinavia and places where the temperature drops to -20C regularly.

They should be able to cope with colder weather than we are currently getting - which is around 0C during the day.

Frankly 18C is cold in a house!!

Swipe

Cardew wrote: »

The point is that these systems are designed to work in Scandinavia and places where the temperature drops to -20C regularly.

Most don't work below -15C (and at that temp they'd be defrost cycling every 30 min) so not sure how that figures.

Cardew

Swipe wrote: »

Most don't work below -15C (and at that temp they'd be defrost cycling every 30 min) so not sure how that figures.

They actually give specifications including down to -20C see here:

http://uk.sanyo.com/aircon/products/CO2-ECO-Heating-System/90kW-Single--Three-Phase/

I agree they won't work well,(and I have mentioned the effect of defrost cycles several times) but at the sort of temperatures we are having -0C during the day and perhaps as low as -5C at night a properly designed system should be able to get rooms up to 21C at least.

paceinternet

I think the point to recognise and accept is that it should be a "system".
It is not just the heat pump item that provides the kw output in all temperature conditions. "Auxiliary" heaters are included in a system.
If a heat pump has an output of 8 kw at 7 degC outdoor air temperature and 45 degC inlet water temperature (about 50 degC outlet), if you increase the inlet water temperature setting, or the outside air temperature goes below 7, it will not produce 8 kw on its own..........
And as Swipe says, defrost cycles wll further reduce the output.

But if all of that is taken care of, the "system" can provide a heating solution.

Consider it another way. If your building heating design calcs show you need 8 kw at outside air temperature of 7 degC, and 10 kw at -15 degC, and you want a heat pump to work with no auxiliary heating, it may well have to be sized at 20+ kw at 7 degC outside air temperature to provide that 10 kw at -15 degC. So, in most cases you have the 8 kw at 7 degC model, and some auxiliary heating to run for x hours a year.

I have just been reading back on some of Andy_WSM posts, and have to believe he has a very well insulated building and is very fortunate that his Activair system provides a solution for him. It wouldn't work on it's own for most other buildings of a similar size in other parts of the country.
See the "heating performance" here:
http://www.trianco.co.uk/pdf/activair_s300_s500.pdf
Page 12 shows his 5 kw unit.
It is rated at 5 kw at 20 degC ambient air temperature, COP 4.
At 0 degC it is rated at 2.7 kw, COP 2.7
At - 5 degC it is rated at 2.25 kw
It doesn't say what water temperature these figures are for, but it is likely that they are at the minimum outlet of 40 degC. If so, it would be very difficult to make a radiator heating system work because for a room temperature of 20 degC you would only have a delta T of 20 deg which would mean you only get 30% of the output from a radiator compared with delta T of 50 when the water temperature is 70 degC and you get 100%.
Which means you would need radiators with 3 times the normal sizing output.
If you increase the temperature the system runs at to example 50, then the heat pump kw outputs will be lower.

It is very efficient, but it would struggle to heat one 25 sq m room for many people with average insulation in sub zero ambient conditons.

I am just using this example to show that what works for Andy is not the answer for the next person. And unfortunately ASHP's can get a bad reputation when they do not provide the heat the house expected in winter conditions.
But a "system" could if designed corectly.

clockworks_2

Swipe wrote: »

18 degrees isn't so bad for a household ambient temperature, considering the extremely low temps this week. I'd just supplement the living room with that oil radiator.

I think that's what i am going to do. An oil rad is cheaper than a new system and as it works fine during the rest of the year it's not too bad.

richardc1983

My system is working fine -5 and 22c inside. A lot of you are mentioning defrost cycles... Mines defrosted twice in 11 hours, the system is over sized by 4kws so that it is not running flat out all the time d when we have cold like this we can have nice temperatures inside as we ave taken worse case scenario into consideration when we installed.

greendwarf

clockworks wrote: »

Thanks for that Richard, Problem i have about leaving it on 24/7 is the system also extracts air from the ensuite. Which is pretty noisy and it keeps me awake so i have to turn it off at night and use and oil heater in the bedroom. Will try and get used to the noise and leave it 24/7 but even now its been on for 8 hours and its still struggling to get over 18 degrees.

This is very like my experience with the Airforce unit (see above) apart from yours being ducted around your flat whilst I just leave the doors open. Mine set at 30c and I'm getting a similar 18c at the moment as we've now lost the day's solar gain on the house. Noise from the internal unit seems to be one of the drawbacks they never mention in the publicity.

richardc1983

greendwarf wrote: »

This is very like my experience with the Airforce unit (see above) apart from yours being ducted around your flat whilst I just leave the doors open. Mine set at 30c and I'm getting a similar 18c at the moment as we've now lost the day's solar gain on the house. Noise from the internal unit seems to be one of the drawbacks they never mention in the publicity.

Not bragging here but I class LG as budget equipment in the commercial side, and this weather is proving they are good as its -3.5 now and we are still at 22.8C inside.

I think the problems with the b&q systems is they are not meant to work below freezing and this is the problem with them, I also suspect that the defrost cycles are regular, you would notice these by how many times the unit stops heating for 5mins at a time.

Setting the unit to 30C will make no difference.

While there is a 3C difference from your target temperature and the actual temperature the compressor will be running flat out anyway.

30C may just give you the impression it is working harder, ensure the outlet is pointning to the floor and bump up the fan speed if you can handle the noise.

Perhaps maybe close internal doors to other rooms and you may find that you can keep that one room nice and warm... do you really need to heat the other rooms if your not in them?

Andy_WSM

paceinternet wrote: »

I have just been reading back on some of Andy_WSM posts, and have to believe he has a very well insulated building and is very fortunate that his Activair system provides a solution for him. It wouldn't work on it's own for most other buildings of a similar size in other parts of the country.
See the "heating performance" here:
http://www.trianco.co.uk/pdf/activair_s300_s500.pdf
Page 12 shows his 5 kw unit.
It is rated at 5 kw at 20 degC ambient air temperature, COP 4.
At 0 degC it is rated at 2.7 kw, COP 2.7
At - 5 degC it is rated at 2.25 kw
It doesn't say what water temperature these figures are for, but it is likely that they are at the minimum outlet of 40 degC. If so, it would be very difficult to make a radiator heating system work because for a room temperature of 20 degC you would only have a delta T of 20 deg which would mean you only get 30% of the output from a radiator compared with delta T of 50 when the water temperature is 70 degC and you get 100%.
Which means you would need radiators with 3 times the normal sizing output.
If you increase the temperature the system runs at to example 50, then the heat pump kw outputs will be lower.

It is very efficient, but it would struggle to heat one 25 sq m room for many people with average insulation in sub zero ambient conditons.

I am just using this example to show that what works for Andy is not the answer for the next person. And unfortunately ASHP's can get a bad reputation when they do not provide the heat the house expected in winter conditions.
But a "system" could if designed corectly.

The key to my system - and I have said this before, is that I run it at low temperature (45C) ALL THE TIME. Yes, the insulation is good, loft insulated to 9", walls insulated and polystyrene beneath the tiles floors, but it's still a detatched house.

I never resized the radiators, at all. Gas boiler out, ASHP in.

It's below -6C here now and I'll hold my hand up and say the system is on it's knees right now - I have heard it defrost twice in the last hour and the temps inside are not up to usual. In fact, my hot water is only at 39C this morning so I'll have to pop the immersion on for half an hour before I can shower. In all fairness though, I never spec'd the system for such cold conditions living on the SW coast. We can go entire winters without a sub zero temperature.

I've had to put the gas fire on in the living room too for extra heat this morning, something I rarely HAVE to do, but do like the comfort glow some evenings!

Still, despite one or two days a year when the system doesn't give me everything I need of it, my low heating bills and 24/7 warmth more than make it all good.