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Ducted Air to Air Heat Pumps

  • 03-01-2021 2:03pm
    #1
    Registered Users Posts: 1,627 ✭✭✭ quentingargan


    Does anyone have experience of these? Because you are only bringing the exhaust air up to 20 to 23 degrees, the claimed COP is 6. I have ducting for heat exchange ventiliation, and I was considering abandoning this system and using the ducting for an air to air heat pump.

    18 year old straw bale house - well enough insulated, though modern houses now would have a better BER rating.

    Any thoughts on this would be appreciated. :)


Comments

  • Registered Users Posts: 337 ✭✭ handpref


    Does anyone have experience of these? Because you are only bringing the exhaust air up to 20 to 23 degrees, the claimed COP is 6. I have ducting for heat exchange ventiliation, and I was considering abandoning this system and using the ducting for an air to air heat pump.

    18 year old straw bale house - well enough insulated, though modern houses now would have a better BER rating.

    Any thoughts on this would be appreciated. :)


    It will work differently to ‘heat exchange ventilation’ as it’s your primary heating system.

    You will need a suitable size void to hang the indoor unit and allow for the pipe run to your outdoor unit.

    The flexible and insulated ducting would be roughly 8” in size, your current set up may not allow for that.

    You will also need the same for the return air ducts from each room.

    The cop will depend on the type of unit you buy and the relationship between the corresponding refrigerant and inverter driven compressor.

    The void unit should ideally be in an extremely well insulated area, otherwise the heat losses will kill off any benefits from good cop efficiencies.

    After putting in 82.5mm internal insulation here, spray foaming the attic, triple glazing and ensuring supreme air tightness my units run very little, you can have an extremely efficient heat pump but if the bugger is running it will still add up. Think I’m down to about €300 to heat and cool the whole house at 21 deg winter, 20deg summer all year round.

    You are on the right track with the air to air, it’s how to execute it is the issue.

    I’ve looked at a lot of new so called A rated houses that are draughty- several didn’t even have the attics spray foamed..
    12.5mm of plasterboard and a bit of rock wool between the upstairs bedrooms and the 0deg outside air in the attic. Wind blowing from one eve to the other, and then down the wall plate to all the rooms. Just because it says BER A rated doesn’t mean that it is....


  • Registered Users Posts: 1,627 ✭✭✭ quentingargan


    Thanks @handpref. I have good space for both indoor and outdoor units, but with a grass roof, I am stuck with what ducting I have, unless I want my house looking like a submarine with pipes everywhere. So all I have for the air flow is 4" pipe going along each side of the house with Ts dropping into bedrooms. The returns would have to come from the hall and bathroom. So it may require additional fans to push the warm air flow and return through the system.

    The house isn't air tight, but isn't draughty either. The present heating system is a range that only burns wood - usually sitka from my own forestry. I let it go out at night and don't light it until the following evening and the house stays warm enough at that, so I don't think it requires a huge amount of heat.

    If 4" wavin won't do the trick, the other option would be air to water using existing radiators, or higher spec ones where necessary.


  • Registered Users Posts: 337 ✭✭ handpref


    "quentingargan-
    I had a quick check there and for a 2.5kw unit you would get away with 4”, however only two outlets or rooms could be supplied with air.

    Your idea for the return air in the hall would work, providing doors were left open during the day or an air gap was left under the door.

    At present if your happy with your stove set up and home grown supply of timber why mess with it.

    If you go air to water your current rads would probably need to be spec’d up as you said, Your probably looking at the best part of €10k for an 8.5kw system with domestic hot water and buffer vessel. A mono block would come in a bit cheaper again.

    The new builds with these air to water units are not always performing well, most probably are set up incorrectly as it’s highly unlikely the fridge guy, plumber and electrician have all been on site commissioning at the same time.

    They are often done on price work and each lad does the minimum and flies off to the next job. Seldom jobs are labelled or tested/commissioned correctly.

    They take time to set up right particularly in relation to flow rates. Also they end up running for longer or harder than initially designed because the house build quality isn’t what it should be despite the A rated label.

    Food for thought- the low hanging fruit may yield greater returns 6-10k is a lot of money, I added 82.5mm warm board to my internal walls for about 1k and probably another grand for plastering. The results were outstanding- going triple glazed then really sealed the deal. But the 2k outlay and my time for the warm boarding was well worth it.

    Keep the faith -


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