Air Source Heat Pumps

richardc1983

Yeh.... its actually better for the compressor to leave it running rather than it having to heat the house up from cold.

Hows ur system going Andy... -3C here now in Leeds.

Andy_WSM

richardc1983 wrote: »

Yeh.... its actually better for the compressor to leave it running rather than it having to heat the house up from cold.

Hows ur system going Andy... -3C here now in Leeds.

Only -1C here at the moment, but gale force winds, so feeling much colder. Fine indoors though Am leaving the system on tonight, for precisely the reasons discussed above!

richardc1983

Will you turn the set point down or leave at normal temp... im not sure whether to turn it down to 18C?

richardc1983

clockworks wrote: »

Appreciate your efforts. I fear they may have shut down as their number doesn't connect. I may be screwed as if the unit is broken and they have shut down i won't be able to replace it as it seems a pretty bespoke one box unit i haven't seen anywhere else.

Lets hope the weather improves for my sake!

If you needed to replace it there are other systems available that are similar to what you have now, whether they perform better at freezing temperature you would have to ask them...

http://www.unicosystem.co.uk/

greendwarf

richardc1983 wrote: »

Perhaps that is just how your system works... in this weather your best off leaving it on all the time so it doesnt have to work as hard to raise internal temperatures. I would ensure as well that it has full access to outside air, check that any return air grilles/filters are not blocked. Assuming the unit gets its air from the outside?

I only found this thread yesterday but couldn't agree more with this reply. I've got a B&Q 18000 BTU Airforce Inverter which I run 24/7 during the winter on the basis that the open plan (plus leaving doors open) house fabric acts as a heat store. But even so, set at 30c it is still only managing 18c tonight in London despite the addition of an oil-filled electic radiator on full. Probably ought to go to bed instead of reading these!
BTW anybody have any experience of using an air pump to just heat DHW? Can I just connect to the old gas CH heat exchanger in the hot water tank?

richardc1983

My LG system is working great, indoors were at 22.6C and otudoors is -3! So unless I open the curtains its business as usual..

YOu need much more equipment than that, you need to find a way to transfer the heat, then you need to get controls etc... you really need to get the proper equipment....

Google Daikin Altherma

greendwarf

Sorry I didn't mean literally just directly connect it - I'm planning to go to full overlay underfloor heating with an air pump but wondered if I could start with it just providing DHW (and so quckly cut running costs to pay for the rest) and whether the old disused CH heat exchanger could be used or will I need a new HW tank?

mech_2

stevehead wrote: »

The COP value stated by reputable manufacturers is not taken from a spot measurement, it is taken over time but with a constant outdoor temp of 7C.
No, I can't find you a link to a test that shows a COP of over 4, and that's because I can't find a test of any unit which claims to have a COP of >4 in the first place.

The interesting figures are seasonaly corrected vs stated COP (@ 7C).
For example, the Ecodan has a COP of 3.85 'in the lab' whereas UK field trials show it gives a seasonally ajusted COP of 3.25. This means that we can use a formula of COP X 0.84 to get the likely UK performance.

Fair enough. My apologies. It seems we have moved on since the time when you were assuming an overall COP of 5.45. I find 3.25 perfectly believable.

This is the same method as the beloved SEDBUK; take manufacturers lab claim and crunch it through a UK Seasonal Ajustment formula.
Oh, and not forgetting that SEDBUK does not take into account DHW, whereas the Ecodan field trial does.

SEDBUK does not list hot water efficiency seperately from central heating efficiency. That's not that same as not taking it into account. It just means an assumed proportion of energy used for each. For an energy assessment of a property it would be more useful to weight hot water usage according to the number of bedrooms etc. Clearly the same problem exists for a single COP figure for a heat pump that provides DHW. When making generalisations across all households I don't think this is a problem.

"From data provided by BRE testing (the UK's leading centre for independent advice for the built environment) and from case study analysis running costs can be reduced over a conventional gas boiler by approximately 35%. These saving are achieved using standard tariff electricity."

Well unsurprisingly that comes stright from Mitsubishi's advertising blurb, and they give no detail on the assumptions used to arrive at that figure. I cannot draw any conclusions as to its applicability without more information. Presumably they mean a boiler of average efficiency rather than a new one.

A back of envelope calculation suggests a COP of 3.25 and a cost ratio of 3 between electricity and gas would offer a 17% cost benefit over a 90% efficient boiler, which is pretty good if acheivable. The thing is, with a less efficient source of hot water heating you could well be wiping out the cost benefit. We don't know.

Andy_WSM

richardc1983 wrote: »

Will you turn the set point down or leave at normal temp... im not sure whether to turn it down to 18C?

Sorry Richard, I had already crashed out by the time you replied! No, I don't adjust mine. I leave alone. It has run through the night happily. Well below freezing here now with gale force winds (-3C, Wind chill taking it to -12C), but still 21C indoors. the ASHP has used a grand total of 60pence worth of electricity through the night.

clockworks_2

richardc1983 wrote: »

If you needed to replace it there are other systems available that are similar to what you have now, whether they perform better at freezing temperature you would have to ask them...

http://www.unicosystem.co.uk/

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.