Advertisement
If you have a new account but are having problems posting or verifying your account, please email Niamh on [email protected] for help. Thanks :)
New AMA with a US police officer (he's back!). You can ask your questions here

Air-2-air in semi-d retrofit

  • 09-10-2019 12:54pm
    #1
    Registered Users Posts: 460 ✭✭ mcbert


    Hi,

    I'm trying to research cost of a retrofit to houses I might buy, but it's hard to find info on A2A units as searches just return air-2-water results.

    I'm asking because installing UFH and/or larger radiators is an additional expense on top of the other insulation and sealing costs that I would rather spend on other things.

    I understand they are really just an air conditioner.

    But why is there so little information about them in domestic retrofits? Are they not that good?

    I see people suggesting they are more suited to smaller houses or apartments, but would installing 2+ units not work in a typical 3/4-bed semi-D ? Unless I'm mistaken, 2 units would still be cheaper than a single A2W unit.

    Are they cheap to run, comparable to A2W? I assume that comes down to COP at different temperatures? Hows does the COP compare to air-2-water?

    They look easier/cheaper to install than A2W, especially given MHRV or DCV will be needed anyway, with ducting etc, and it avoids having to put in UFH or larger/any radiators?

    Are they noisy indoors?

    Thanks!


Comments

  • Registered Users Posts: 2,820 ✭✭✭ air


    It just comes down to convention and tradition really.
    Since we never had a requirement for domestic air conditioning in this country they were never installed so people aren't familiar with them as an option.

    I would imagine that the efficiency would be a little less than UFH all right but they could be a good option for upstairs IMO.

    It would probably be prudent to use 2 multi splits so you still have some heating if one fails.

    The primary disadvantages are that they're point heat sources and would create even more air circulation than radiators.
    Also you're limited in the number of heat outlets - around 4 max for most multi splits, which could be an issue if you have a lot of rooms.


  • Registered Users Posts: 18,889 ✭✭✭✭ murphaph


    One advantage of a2w (with UFH with traditional thicker concrete screed) is that you can "charge up" the screed during the day when cop is much better. If PV is being considered this is a double benefit as you can use the afternoon sun to heat the house during the night effectively. You can also generate your hot water during the afternoon as well. Just something to consider.


  • Registered Users Posts: 10,929 ✭✭✭✭ Calahonda52


    What about a heating coil in the MHRV
    In addition the A2A may fall foul of the new Regs from 1st Nov re renovations


  • Registered Users Posts: 460 ✭✭ mcbert


    In addition the A2A may fall foul of the new Regs from 1st Nov re renovations

    Really? How so?


  • Registered Users Posts: 979 ✭✭✭ Gardner


    Sorry to hijack your thread but have a question in regards to A2A.

    i'm in the middle of designing my own house and it is basically a single story flat roof house. approx 2500 sq feet.

    Can i use A2A system with basically a split system ducted air con unit to heat the house with a MVHR running parallel to it?

    don't want to install radiators or underfloor heating and would rather a ducted heating system.


  • Advertisement
  • Registered Users Posts: 460 ✭✭ mcbert


    Gardner wrote: »
    Sorry to hijack your thread but have a question in regards to A2A.

    i'm in the middle of designing my own house and it is basically a single story flat roof house. approx 2500 sq feet.

    Can i use A2A system with basically a split system ducted air con unit to heat the house with a MVHR running parallel to it?

    don't want to install radiators or underfloor heating and would rather a ducted heating system.

    No problem, I'd like any answer to your question too. I cant help much except to point at these: https://www.nibe.eu/en-eu/products/heat-pumps/exhaust-air-heat-pumps

    ... combining ventilation and ducting, they seem to take their heat from the indoor air that is exhausted, recycle it.


  • Registered Users Posts: 2,820 ✭✭✭ air


    You'd be mad not to use UFH in a new build that's going to be heated with a heat pump IMHO.
    Do you know the design heat load of your new house and the volume of air per minute that would be required to deliver it?
    Not a fan of using air to deliver heat at all and it's likely to be even worse in a bungalow with distribution (presumably) in the unheated area.


  • Registered Users Posts: 3,292 ✭✭✭ 0lddog


    Do a search and you will find a few threads where A2A is mentioned e.g.

    https://www.boards.ie/vbulletin/showthread.php?t=2057984494

    Most have just put in simple split units. Some years ago I put in a multisplit.

    Ducted systems can work very well. A great writeup of one in NZ https://www.jethrocarr.com/2018/07/07/the-heating-project/

    There are pros and cons to A2W, A2A splits and A2A ducted

    Splits have background noise due to the fan to move the air. Ducted units are usually quiet. A2W wont be much good if you need cooling as well as heating. Woe betide you if the under floor pipes leak.I have the impression that many A2W units have abysmal low temp performance. If you are thinking A2W dig into the performance from +5C to -15C before deciding what to buy.


  • Registered Users Posts: 2,820 ✭✭✭ air


    0lddog wrote: »
    A2W dig into the performance from +5C to -15C before deciding what to buy.

    All else being equal, the COP of an A2W unit feeding UFH should always be superior to A2A as the condenser temperature can be as low as high 20s with dense pipe spacing.
    It needs to be higher for air to air in order to transfer the heat effectively.

    You also have a major advantage of having a large amount of thermal storage in the floor slab which is helpful if you want to build up heat during night rate electricity hours.

    The NZ project linked looks poor from a number of perspectives.
    The ducting is very poorly insulated and of a poor standard, it's located in the cold attic space where it's likely to lose heat impacting efficiency.

    It looks to be drawing in cold air from the attic, heating this and blowing heated air into the occupied rooms.

    This open loop design would lead me to believe there's a constant loss of heated air from the home at the flow rate of the air distribution fan.

    Finally it doesn't look like the contractor is doing the vacuum evacuation correctly (via the manifold) and there's no sign of a micron gauge, which doesn't bode well for the lifetime of the unit.
    Poor standards like this are rife in HVAC in Ireland in my experience which is why I would prefer a factory sealed monobloc where possible.


  • Registered Users Posts: 2,820 ✭✭✭ air


    air wrote: »
    A.

    It looks to be drawing in cold air from the attic, heating this and blowing heated air into the occupied rooms.

    This open loop design would lead me to believe there's a constant loss of heated air from the home at the flow rate of the air distribution fan.

    I was incorrect there, I had only looked at the Mitsubishi diagram included.
    I see now the intake is in the hallway.

    This still begs the question of how air recirculates to the hall from the rooms with doors closed. In practice the hallway is likely to have slightly lower pressure and draw in external air with the opposite for the supplied rooms, so long as internal doors are closed.


  • Advertisement
  • Registered Users Posts: 19,025 ✭✭✭✭ Water John


    A2A was never grant aided by SEAI, not efficient enough I presume. UFH pipes don't leak unless some idiot put joints on the pipe.
    Replacing the rads with alu rads shouldn't be very costly, but you would need a good idea of the house heat demand, to size the whole thing correctly.


  • Registered Users Posts: 460 ✭✭ mcbert


    Water John wrote: »
    A2A was never grant aided by SEAI, not efficient enough I presume. UFH pipes don't leak unless some idiot put joints on the pipe.
    Replacing the rads with alu rads shouldn't be very costly, but you would need a good idea of the house heat demand, to size the whole thing correctly.

    There is a grant for A2A - €600. Much less than A2W, but still, it is still included.


  • Registered Users Posts: 3,292 ✭✭✭ 0lddog


    @Air : Me2 :eek:

    I had to read the thing three times to believe what he got up to. I muttered many WTFs and 'I dont believe it' s

    Not only that but so far as I could make out the windows are not even double glazed.

    It took me a few days to standback and understand that (a) it seems to work and (b) the guy seems happy with what he has.

    When it comes to heating a house with a heat pump there is more than one way to skin the cat ! :D

    WRT

    "All else being equal, the COP of an A2W unit feeding UFH should always be superior to A2A as the condenser temperature can be as low as high 20s with dense pipe spacing.
    It needs to be higher for air to air in order to transfer the heat effectively."

    Thats right, but in the real world I wonder how A2W low temp performance compares to for instance the A2A that I mentioned in the linked thread ? (Mitsi MSZ-LN35VGHZ )


  • Registered Users Posts: 3,292 ✭✭✭ 0lddog


    mcbert wrote: »
    There is a grant for A2A - €600. Much less than A2W, but still, it is still included.




    A2A units tend to be much less expensive than A2W - so need for any grant could be debated


  • Closed Accounts Posts: 40,086 ✭✭✭✭ Harry Palmr


    A2A needs proper branding and marketing for Ireland, as mentioned Air-Con doesn't really work as a selling point here.

    For the OP you can get in touch with https://www.rosstechnical.ie/daikin-air-conditioning who specialise in Daikin heat pumps.


  • Registered Users Posts: 19,025 ✭✭✭✭ Water John


    The climate in NZ is much milder than here. Most houses have single glazing and small A2A heat boosters.


  • Closed Accounts Posts: 40,086 ✭✭✭✭ Harry Palmr


    Depends where you are, it's 1600 Kms from top to bottom.


  • Registered Users Posts: 19,025 ✭✭✭✭ Water John


    I accept that the bottom half of the South Island would be similar. The top half, where they grow grapes and a wide range of fruit, along with North Island, no.


  • Registered Users Posts: 177 ✭✭ ercork


    mcbert wrote: »
    There is a grant for A2A - €600. Much less than A2W, but still, it is still included.

    That's true. However, to claim the grant you need to get an inspection carried out which costs about €700!


Advertisement