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Air Source Heat Pumps/Air Con - Full Info & Guide - Page 2

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Air Source Heat Pumps/Air Con - Full Info & Guide

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  • richardc1983richardc1983 Forumite
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    The cop will fall as temperature drops below 5C but at -15C the unit will stll have 85% capacity in most instances. The cop is based on normal uk temps. MHI are not the same company as MITSUBISHI ElECTRIC. Both are different products with diff spec so make sure you are researching the right brand!

    Cop is much talked about on the heat pump posts. The most important part is how much capacity you have in the unit at -15C, cops of around 3.5 are good and the figure of 85% capacity is good at -15C. At -5C your still going to have full capacity. They are rated down to -15C and how often does it get to that in england during the day or evening?

    Daikin is excellent, mitsubishi electric is excellent, MHI is also good but Mitsubishi Electric comes before MHI or Daikin on the COP figures and efficiency.
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  • CardewCardew Forumite
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    TeeKay63 wrote: »
    What I'm trying to find out is whether the Mitsubishi really does deliver a COP of 5, how that changes with loading (if at all) and how the COP falls as o/s temperature drops to around freezing. Or is this the A/C world's equivalent of the car fuel consumption figures?

    Welcome to the forum.

    I really don't think you are going to find out a realistic overall COP.

    I suspect, rather like you, that a COP of 5 will not be realistic in practical situations, and most of the independent publications talk of 3 to 3.5 as achievable.

    Even then a heat pump needs to be working all day in cold weather as it simply does not have the 'muscle' to warm up quickly a house that has been empty all day.

    That said, IMO any system the will give an overall COP of, say, 3 is excellent and will be competing with gas.

    I also think that there is too much emphasis on performance at low temperatures of -5C etc. If you have an ASHP and on the very few occasions it cannot cope with the low outside temperatures, you won't freeze to death - you simply turn on a £10 fan heater for a few hours.
  • richardc1983richardc1983 Forumite
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    Cardew wrote: »
    Welcome to the forum.

    Even then a heat pump needs to be working all day in cold weather as it simply does not have the 'muscle' to warm up quickly a house that has been empty all day.

    Or you could do as I do and just set the set points to about 18C when your not in or in bed during very cold weather so that when you get up you can just put it back up again and it will not have a struggle to get back upto temp.

    Cardew I have to point out that our huge central heating system took longer to heat the house up from 13C than the air con did. The air con took about 2.5hrs whereas the central heating 5hrs later the house was still cold!
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  • CardewCardew Forumite
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    Or you could do as I do and just set the set points to about 18C when your not in or in bed during very cold weather so that when you get up you can just put it back up again and it will not have a struggle to get back upto temp.

    Cardew I have to point out that our huge central heating system took longer to heat the house up from 13C than the air con did. The air con took about 2.5hrs whereas the central heating 5hrs later the house was still cold!

    I can only suggest that there is something wrong with your house insulation or your previous CH system and/or you have 40ft ceilings!!

    From 13C my gas CH will take less than 30 minutes to bring some large rooms up to temperature.

    An ASHP system capable of a 9kW output should not take 2.5 hours to raise a flat to an acceptable temperature from 13C.
  • richardc1983richardc1983 Forumite
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    As pointed out previously Cardew, the house has no insulation, we have 12ft high ceilings and an open cellar beneath the floors. Thick solid walls and no insulation at all in the walls or the floors, or the attic. Its a victorian house built in 1900 The house can drop to about 8c in about 5 hours if its been very cold. The central heating in winter is set on 80C and the radiators are large double ones and correctly sized.

    We have doulbe glazing but it is very draughty. As its a rented flat theres not much I can do about it!
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  • Andy_WSMAndy_WSM Forumite
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    Hi Richard!

    I posted in the other A/C thread that I have been using my Fujitsu heat pump system to warm the house this Winter after my boiler failed.

    Well...I took the plunge and replaced the old gas boiler - with an Air to Water Heat Pump!

    Best investment ever! It is only a 5KW pump, but is maintaining the temperatures in my 2 bed bungalow with no problems at all. I leave it running 24/7 and let it do it's thing. It is costing £1.50 - £2 a day to run which compares very favourably (cheaper to run!) with my Gas bills of approx £200 a Quarter. And I now have heat and hot water 24/7 which suits my chaotic (due to work) lifestyle.

    The unit is one of the cheaper ones - a Trianco, Activair and it's in the loft! It is only just audible is you stand beneath where it is mounted (above the bathroom).

    I plumbed it so that it heats the hot water tank as priority, then the return continues around the heating system before going back to the unit for reheating.

    The hot water tank is always hot and each room has it's own thermostatic valve.

    Living room set at 22C
    Master bedroom 21C
    Second bedroom 18C (not currently in use)
    Kitchen 21C
    Hallway 20C
    Bathroom 23C

    The unit cost £925 which is comparable to a boiler, but I now don't have servicing costs, didn't have to pay a CORGI engineer to fit it and will benefit from much lower bills going forward.

  • albyotaalbyota Forumite
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    Hi Andy, who advised putting it in the loft?, how did you drain the condense? and when it has pulled all the heat from your loft, how does it perform?
    There are three types of people in this world...those that can count ...and those that can't! ;)

    * The Bitterness of Low Quality is Long Remembered after the Sweetness of Low Price is Forgotten!
  • Andy_WSMAndy_WSM Forumite
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    albyota wrote: »
    Hi Andy, who advised putting it in the loft?, how did you drain the condense? and when it has pulled all the heat from your loft, how does it perform?

    The manufacturer recommends this can be done. The advantage is that the loft is ALWAYS warmer than the outside temperature, more so in the Summer, so plenty of very cheap hot water coming up. The other night it was -4C outside and the loft never dropped below -1C (I fitted a remote thermometer so I can check this). Right now it's 2C out and 5C in the loft. On the other side of the coin, despite an outdoor temp of just 7C yesterday the Sun was warming the tiles meaning the loft was 15C, so the unit ran even more efficiently yesterday than it would have done if it was outdoors.

    You will never pull ALL of the heat out of the loft as the loft is ventilated (as it should be) and you can feel a draft up there.

    If at the very worst case the temp in the loft drops below -5C (very unlikely here) then the unit will shut down and I'll have to run the immersion for hot water and plug a fan heater in. I can't imagine that ever happening though as I am near the sea...

    Draining of the condense is easy as the unit has a tray built in to catch the condense and it's simply a case of connecting this to a drain, which I have up there anyway as I also have whole house ducted A/C. The other bonus is that the condense goes into my rain water harvesting system, which in turn is used to flush the toilet and run the washing machine!

    (You can tell I'm impressed with it, can't you?!)

  • richardc1983richardc1983 Forumite
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    Andy very good what you have done but all manufacters i know advise the outdoor unit to be installed in open air. For instance most peoples lofts are not big enough to have a unit installed in them. Lofts are draughty but they are not fully open to the outside air. YOu say your loft is always warmer than outside thats crazy... (not that i dont believe you) but I have heard customers have had those self install units and put them in the loft. In heating the loft starts of at 5C but then quickly after about an hour the loft is at -10C and the unit is unable to remove any more heat and over working.

    Lofts are ventilated but not enough airflow for a unit. However you must have a large loft if you have proved the air temp doesnt drop. You may find yoou have to clean your coil more as dust in lofts is quite fine and may clog the coils.
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  • Andy_WSMAndy_WSM Forumite
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    Andy very good what you have done but all manufacters i know advise the outdoor unit to be installed in open air. For instance most peoples lofts are not big enough to have a unit installed in them. Lofts are draughty but they are not fully open to the outside air. YOu say your loft is always warmer than outside thats crazy... (not that i dont believe you) but I have heard customers have had those self install units and put them in the loft. In heating the loft starts of at 5C but then quickly after about an hour the loft is at -10C and the unit is unable to remove any more heat and over working.

    Lofts are ventilated but not enough airflow for a unit. However you must have a large loft if you have proved the air temp doesnt drop. You may find yoou have to clean your coil more as dust in lofts is quite fine and may clog the coils.

    It's all there in the manufacturers literature and on their website (units up to 5KW can be mounted indoors or outdoors, bigger units, outdoors only). It's been running up there now for over a week and despite the sub zero nights continues to work very well. The manufacturer recommends this unit for DHW, but other literature suggests it can be used for low level heating and it does this very well.

    Outside right now 8.8C, loft 12.5C, Lounge, 22C.

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