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Upgrade Oil Boiler to Heat Pump - Worthwhile Investment?

  • 12-01-2021 8:59pm
    #1
    Registered Users Posts: 349 ✭✭ fitzie79


    Hi, I've been browsing here for a while looking at various threads on heat pumps...

    My oil boiler is working fine but I am considering upgrading heating system to a heat pump now both for long term cost savings and also environmental reasons.

    The house is dormer bungalow, 11 years old and is B3 rated. I have a HRV system (A/C was ~3 from memory at time of installation) and drylined external walls. I also have solar panels on a south facing roof as well.

    Would a heat pump system require existing steel rads to be replaced with alu rads or would this payback on this not be worthwhile.

    Can the existing solar panels be integrated with a buffer tank from the heat pump for DHW and approx. how large would such a tank be for a 2500 sq ft house?

    Finally, any recommendations (by PM) on suppliers in cork area for this type of retrofit?


Comments

  • Registered Users Posts: 11,177 ✭✭✭✭ KCross


    fitzie79 wrote: »
    My oil boiler is working fine but I am considering upgrading heating system to a heat pump now both for long term cost savings and also environmental reasons.

    Cant see how it would be worth it in that case.
    A HP system is likely to cost you a small 5 figure sum. You wont get any long term savings from that when your existing system is working fine.

    If you have money to burn add a bunch more Solar panels. That will give you a better return on your money and give you the envionmental benefits you are after as you will reduce your reliance on the grid and can also heat water (instead of your oil burner) for a few months of the year.


  • Registered Users Posts: 308 ✭✭ idc


    fitzie79 wrote: »
    I also have solar panels on a south facing roof as well.


    Can the existing solar panels be integrated with a buffer tank from the heat pump for DHW and approx. how large would such a tank be for a 2500 sq ft house?



    Just to be clear which kind of solar panels are you talking about? Are you talking about panels that generate electricity or heat water?


  • Registered Users Posts: 349 ✭✭ fitzie79


    idc wrote: »
    Just to be clear which kind of solar panels are you talking about? Are you talking about panels that generate electricity or heat water?

    heating water


  • Registered Users Posts: 11,177 ✭✭✭✭ KCross


    Good question/clarification @idc.

    @fitzie79, when I said add more Solar I meant add Solar PV panels. They generate electricity and can be used to reduce your electricity consumption from the grid and can also be used to generate hot water.


  • Registered Users Posts: 132 ✭✭ Birka


    I've a BER of B2, condensing oil boiler and steel rads and can't get the numbers to work for changing from oil to A2W heat pump. I'd really like to but it makes no sense to spend that much (between €12k and €15k) for a saving in my case of around €400 a year.


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  • Registered Users Posts: 349 ✭✭ fitzie79


    Birka wrote: »
    I've a BER of B2, condensing oil boiler and steel rads and can't get the numbers to work for changing from oil to A2W heat pump. I'd really like to but it makes no sense to spend that much (between €12k and €15k) for a saving in my case of around €400 a year.

    That's interesting. What are you spending per year at the moment on oil? How did you calculate the expected savings?

    I have hoped that a heat pump would cose more like 8k before any grants but is this overly optimistic?


  • Registered Users Posts: 349 ✭✭ fitzie79


    KCross wrote: »
    Good question/clarification @idc.

    @fitzie79, when I said add more Solar I meant add Solar PV panels. They generate electricity and can be used to reduce your electricity consumption from the grid and can also be used to generate hot water.

    I had thought about solar pv but thought they would come at a later stage. I haven't been overly impressed with the solar thermal panels for hot water but the draw is quite long from my attic roof to hot water tank.

    I must read up a bit more on solar pv options as well.


  • Registered Users Posts: 132 ✭✭ Birka


    fitzie79 wrote: »
    That's interesting. What are you spending per year at the moment on oil? How did you calculate the expected savings?

    I have hoped that a heat pump would cose more like 8k before any grants but is this overly optimistic?


    The best quote (of three) that I got for an A2W heat pump was €12k before grant. I've all rads, no underfloor heating unfortunately. If I needed to replace my rads with aluminium/higher output ones, it'd add another €3k. My technical assessor was of the opinion that while I might get away with my existing steel rads, the numbers were marginal and because the SEAI process was very strict, I'd probably have to replace them before it could all be signed off for the grant.

    When I last crunched the numbers, my oil bill was coming in at €970 a year with my estimation of the heat pump running costs coming in at around €504.


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


    You can add radiator fans to existing rads in order to maintain the same heat output with the lower flow temperature of a heat pump.

    Aluminium rads are a con in my opinion, the thermal conductivity through the steel of a radiator is not a significant limiting factor in the heat output of a radiator.

    Aluminium rads may heat up a fraction faster but this is completely negligible and irrelevant in the real world, even more so for a heat pump system that will run for much longer.

    Oil prices are incredibly low at present so a heat pump system could rapidly become more attractive as that changes.


  • Registered Users Posts: 626 ✭✭✭ conor_mc


    I thought it was the larger surface area of new alu rads that was the advantage over old-skool steel rads, no?


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


    It is for sure, but you can buy bigger steel rads or replace singles with doubles to achieve the same effect.


  • Registered Users Posts: 74 ✭✭ monkeycork


    air wrote: »
    It is for sure, but you can buy bigger steel rads or replace singles with doubles to achieve the same effect.

    Air2water systems do not work efficiently at temperatures above 50c. So the radiators wil not get hotter than 50c

    For example a stelrad compact radiator 600mm high x 1000mm long double radiator on a heating circuit reaching 70c typical gas/oil(delta 50) room temperature to 20c: the output is 1732watts

    That same radiator on an Air2water system reaching 50c (delta 30) the output is 892watts

    To correctly size a steel radiator for that rooms heating requirements for an Air2water system, radiator would need to be a 600 x 2000mm double. 2 meter long steel radiator on a stud Plasterboard wall ;-)

    Underfloor heating and Air2water work extremely well because of the low temperature requirements


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


    I agree with you on all of that monkey, the point I was making was around the performance difference between aluminium and steel radiators, which is going to be negligible assuming similar surface area.

    As an aside 50C is too hot to be running a heat pump for optimal performance.


  • Registered Users Posts: 74 ✭✭ monkeycork


    air wrote: »
    I agree with you on all of that monkey, the point I was making was around the performance difference between aluminium and steel radiators, which is going to be negligible assuming similar surface area.

    As an aside 50C is too hot to be running a heat pump for optimal performance.


    Ture about the 50c underfloor is ideal.


    Talk to Grant in Offaly, that will advise on the suitably of your existing system as they manufacturer oil boilers and sell heat pumps and both aluminium / steel radiators.


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


    50C is ideal if you have a typical Irish underfloor heating system installed by contractors that don't understand what they're doing with regard to pipe layout and spacing.
    This is the kind of incompetence that has given UFH and heat pumps a bad name in this country.

    A good rule of thumb is that every degree of flow temp costs 1% in system efficiency.
    A flow temp of 35C is more typical in other countries where installs are properly designed by people who know what they are doing.


  • Registered Users Posts: 507 ✭✭✭ G-Man


    air wrote: »
    A good rule of thumb is that every degree of flow temp costs 1% in system efficiency.
    A flow temp of 35C is more typical in other countries where installs are properly designed by people who know what they are doing.

    Does that mean for every 1C increase in heating water temperature, you loose 1 percent of efficiency.... So you would design your heat budget with an eye to keep water temp as low as possible and perhaps then having a cheaper or more optimally sized system.


  • Moderators, Category Moderators, Motoring & Transport Moderators, Regional East Moderators Posts: 58,818 CMod ✭✭✭✭ unkel


    air wrote: »
    A flow temp of 35C is more typical in other countries where installs are properly designed by people who know what they are doing.

    Surely your water for baths / showers would need to be at least 50C and regularly over 60C, or am I missing something here? I know nothing about heat pump systems - apologies if question is stupid.

    "Wind is Ireland's oil" - An Taoiseach, 25/05/2022



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


    Exactly, by reducing your pipe spacing you increase the total pipe surface area exposed within the slab so you can achieve the same heat output with a lower flow temperature.

    The power consumption of the heat pump is directly proportional to the lift in temperature it has to achieve.
    If it's 5C outside and you're lifting it to 50C flow temperature that's a 45C lift. However if you are only lifting to 35C, that's 30C of a lift (33% reduction), so you should see far better system efficiency, probably 20% or more.
    The heat pump will also work at a lower condensing pressure so should last longer all else being equal.
    For this reason it's generally better not to use a heat pump for DHW if it can be easily avoided.

    You can look up proper pipe layouts online also, these dissipate the most heat at the room perimeter where losses are greatest and keep the flow and return pipes near one another to help achieve an even floor temperature.
    This will ensure better comfort at lower air temperature by helping eliminate any air movement due to temperature differentials, again further improving efficiency.


  • Registered Users Posts: 60 ✭✭ Gamma1


    I have a B3 bungalow with PV, electric car condensing oil boiler, wood stoves and pellet burner. Have looked extensively at air to water HPs and not for me for these reasons
    Have a mix of different pipes - gunbarrel, Cu, plastic.
    Efficiency falls with reducing outside temp and increased water temp
    No real savings.
    The only type of system I am considering is air to air HP based on one outdoor unit and multiple indoor units (3 for me is fine). Efficiency here will be higher overall as there is no intermediate water.
    There will be minor savings - mostly against wood but I will probably do it for the sake of convenience.


  • Registered Users Posts: 11,177 ✭✭✭✭ KCross


    unkel wrote: »
    Surely your water for baths / showers would need to be at least 50C and regularly over 60C, or am I missing something here? I know nothing about heat pump systems - apologies if question is stupid.

    Separate "zones" for that.

    The UFH should optimally be running at ~30°C (what @air called flow temp) and will be the largest energy consumer by a long way.

    The DHW will, of course, be at ~50°C and will run a boost every few weeks for legionella which takes it up to ~60+°C.


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  • Registered Users Posts: 3,911 ✭✭✭ mp3guy


    KCross wrote: »
    Separate "zones" for that.

    The UFH should optimally be running at ~30°C (what @air called flow temp) and will be the largest energy consumer by a long way.

    The DHW will, of course, be at ~50°C and will run a boost every few weeks for legionella which takes it up to ~60+°C.

    How does the HP split that temperature? Does it just mix with 50c water, or can you only heat the UFH at different times to the DHW?


  • Registered Users Posts: 11,177 ✭✭✭✭ KCross


    mp3guy wrote: »
    How does the HP split that temperature? Does it just mix with 50c water, or can you only heat the UFH at different times to the DHW?

    The HP manages it itself. I'm sure there are different implementations but I suspect a series of valves to heat one or the other. Heating DHW would be a very small proprtion of the overall time it spends doing space heating.


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