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General Heat pump questions

  • 27-03-2023 3:05pm
    Registered Users Posts: 2,623 ✭✭✭

    I'm looking at the idea of moving to an A2W heat pump, to be more env friendly and eventually, hopefully, reduce costs.

    One issue I'm trying to wrap my head around is will I need more heat output from a heatpump?

    My house is reasonably well insulated, some draughts which will require fixing either way, and I reckon on the coldest winter days I'd having a 20kwh oil boiler on for about 4 hours. So max 80kwh of heat output.

    If I switch to a A2W system will I need more output because of the lower temp?

    I'm looking at matching the system with solar panels. So I'm trying to get an idea of how many panels I might need to run the heating system or how much I'd have to make up by buying electricity directly.

    If my house requires 80kwh on the coldest days, with a heat pump at just 2 times efficiency, means I'd need to supply 40kwh of power to it. Could I have it running on daylight hours and night rate only?


  • Registered Users Posts: 388 ✭✭Biker1

    A heat pump must be sized based on the actual heat loss from each individual house. Throwing a spurious figure of x Watts per m2 may be ok for an oil boiler but not for a heat pump. Firstly you need to determine if your house is suitable for a heat pump to be cost effective. Also PV will not run a heat pump regardless of the size of the array as the highest demand for power is when there is the least output from the PV.

  • Registered Users Posts: 5,202 ✭✭✭Padre_Pio

    The heatpump is most efficient running 24/7.

    The water out of my heatpump is rarely above 30C and it keeps the house plenty warm. Pulls maybe 10kW to heat the house and 3kW to heat the water tank to 45C. My underfloor and rads are barely lukewarm at the best of times.

    Imagine if your boiler was doing the same, would your house be warm or cold?

  • Registered Users Posts: 5,202 ✭✭✭Padre_Pio

    You may need to upgrade your rads and put in bigger ones too. more surface area.

  • Registered Users Posts: 2,623 ✭✭✭MegamanBoo

    So 13k in total per day?

    I'm guessing your house is very well insulated?

  • Registered Users Posts: 2,623 ✭✭✭MegamanBoo

    Thanks, I appreciate that and I wouldn't proceed without getting a full independent survey.

    I know though that in my older house there's only so much insulation I can put in without it getting very expensive.

    I'm trying to figure out at what point it would be better to invest in PV above insulation.

    It must be possible at some point to run the heat pump from solar, even mid winter it seems they'll generate 20% of what they're rated for. It seems a 15k system would generate 24kwh per day at 8 hours of poor daylight. Or am I missing something?

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  • Registered Users Posts: 5,202 ✭✭✭Padre_Pio

    A2 rated, with mechanical ventilation. I spent some time learning the controls and have a COP over about 4, which is very good for the house.

  • Registered Users Posts: 2,623 ✭✭✭MegamanBoo

    So it seems I am missing something, it looks like these solar figures wouldn't be typical. Going by the solar thread it looks like solar output typically comes in on average at about 10-15 of output rating during the coldest winter months.

    What looks useful to me though is how a solar battery can be used to capture night rate electricity, so the system could still reduce heating costs in winter.