Air Source Heat Pumps



  • Chrislincs wrote: »
    Hi again,
    Just back from the Build and renovate show at NEC armed with many brochures, I've had many questions answered but now have new ones. Above E7 usage is mentioned, and was brought up by a salesman of pumps (Trianco, I think) but he waffled rather than clarified how and what for. He used the word storage of heat produced but didn't elucidate the point.

    I didnt' go for the Trianco system because IIRC it doesn't operate below -5degC and thus, whilst ok for 99% of the year, I just felt that I didn't want it operating at near it's minimum range during winter when the temperature hovers around freezing. The Mitsubishi system I got operates down to -20degC.
    Other displays stated that pumps could be sited in the loft - why is this not generally considered when it would elminate the problems of distance from the tank, and the air always warmer?
    I was also told this when I bought my system, but it doesn't work. We had to temporairly install ours in our conservatory for a few weeks for various reasons and the reason it won't work in a conservatory or loft is this:

    A heat pump draws warm air in the back, extracts the warmth out (and directs it into your house) and blows cold air out the front. It is assumed that you have access to an unlimited supply of warm air, which you only get outside as the fan in the heat pump blows the cold air away from the HP so new warm air can be drawn in. If you install it in your loft, you are effectively putting you HP in a big box. Whilst it is initially warmer in your loft, your HP will rather quickly remove all that warm air and replace it with cold air. As a loft doesn't have many drafts, that cold air then stays in your loft and just gets recirculated through your HP, whilst the tempeature in your loft will get lower and lower...

    We found that our single glazed conservatory is normally around a few degrees warmer than outside, after about an hour of HP operation, it droped to many degrees colder than outside, thus making it less efficient, caused water pipes to freeze, massive amounts of condensation and created a higher temperature differential between inside the house and the conservatory.

    So when a salesman tells you that it is warmer in a loft and thus the HP will work better, that is only true for about the first hour of operation. (Unless you have a highly ventilated loft).

    Imagine what would happen if you put a fridge in a box, the box would get warmer and warmer, and the fridge would have to work harder and harder to keep the inside of the fridge cold, thus causing the box to get even warmer, thus causing the fridge to work even harder etc...
  • Chrislincs
    Chrislincs Posts: 17 Forumite
    Thanks Samtheman1k for info. My windfall is looking more possible for mid winter 08/09 so will continue genning up and watching this site. Almost 100% set on airflow system so all info being stored for right choices. Need to make home more saleable as market slumps put storage rads off most folks radar, despite agreeing with above re:management of electricity usage. Hope this will make more attractive than competitors. However it will need to payback cost in value rise. fingers crossed.
  • OK I've now roughly worked out in my head what I would ideally like to do but need your comments on how mad I am or how feasable the plan is. For various reasons I want to use an ASHP to supply 35/40C water via a thermal store just to underfloor heating. No DHW or rads involved. A quite large thermal store to be heated indirectly from the HP and UF taking heat, again indirectly, from the thermal store. Backup heat into the thermal store by electric; either immersion or small boiler. The thermal store to be heated up normally by the HP at offpeak electric times on tariff 7 or 10. Also, as the house is already fitted with an air management system which uses extraction warm stale air to preheat incoming cold fresh air I plan to duct the extraction air, which is still relatively warm, into the intake of the HP so that it is working off air thats above ambient air temperature as a start point. The aim is to buy heat at offpeak rates and then use the COP multiplier to gain further cost advantage. In particular the 10 tariff would seem to allow the store to be topped up at off peak rates and the stored heat would bridge the gap at peak times until the next cheap rate came round. Bearing in mind that I already have 25 tons of concrete storage under the floor I think that such a system would produce a fairly stable even temperature. What do you you think guys? Particularly about the use of extraction warm air as the intake for the ASHP. Any useful comments would be appreciated.
  • knightstyle
    knightstyle Posts: 6,988 Forumite
    First Post First Anniversary
    Another great thread. Just wanted to say there is a system here in France which draws warm air from the loft and expels cold air to the outside. I can't see if they put vents into the loft or rely on air getting in round tiles etc. They have a site
  • amtrakuk
    amtrakuk Posts: 630 Forumite
    Is this what a air source heat pump is?

    At £600 you can use a lot of e7 or standard rate electric to heat
  • samtheman1k
    samtheman1k Posts: 473 Forumite
    First Anniversary Combo Breaker
    Yes, though that is an air-to-air heat pump where warm air is taken from outside and blown inside. It will only heat one room. To heat a house, you'd normaly get an air-to-water heat pump that takes the warmth from the outside air and transfers it to heat up water for distribution through a conventional water based radiator central heating system.
  • amtrakuk
    amtrakuk Posts: 630 Forumite
    I guess its down to the BTU required. I've got a week off in a couple of weeks and will see if i can get a quote for installation
  • flygti
    flygti Posts: 8 Forumite
    If you don't already have radiators installed in the house - why not consider an ASHP with inverter/aircon units in the house? We are looking at 8 aircon units in the house and one ashp unit outside. Cost approx £8500 installed. Can heat and cool the house with the benefit of filtering the air etc. The electricity consumption is expected to be 1/2 to 1/3 of the cost of our storage heaters but obviously still need to factor in peak rate electricity instead of economy 7. However if running costs are similar to my storage heaters I will be happy due to the convenience and control they offer.

    My worries currently are:
    Noise. I am assured the outside unit is very quiet.
    Running Cost. Can't be sure until all is installed and running.
    Cosmetics: We will have floor standing units downstairs which are much smaller than the storage heaters so probably OK. Upstairs though are wall mounted. Not sure what they will look like!

    Can't find anyone else who has a similar install and very little documentation on the web.

    My alternative is an oil install which will cost similar when I include radiators etc but am pretty sure that it will cost more to run at current oil prices and of course won't offer cooling (not that we will need it this summer!).
  • Cardew
    Cardew Posts: 29,036 Forumite
    Name Dropper First Anniversary First Post Rampant Recycler
    flygti wrote: »
    The electricity consumption is expected to be 1/2 to 1/3 of the cost of our storage heaters but obviously still need to factor in peak rate electricity instead of economy 7. However if running costs are similar to my storage heaters I will be happy due to the convenience and control they offer.

    As these are air to air heat pumps, how do you 'expect' to have costs 1/2 to 1/3 of your storge heaters?

    Whilst(in winter) a COP of 2 or 3 would be a reasonable expectation virtually all this use will be at 'daytime' electricity rates. Thus even at a COP of 3(giving one third of the cost) your electricity price will be roughly the same as Economy 7.

    To be honest I would think your proposed system of 9 units would be impractical.
  • Rabiddog_2
    Rabiddog_2 Posts: 418 Forumite
    Earlier reply noted.. Guess I'll just go for the most efficient condenser boiler £1k (to replace a 15+yr old Gas Boiler)
    tribuo veneratio ut alius quod they mos veneratio vos
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