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New House - A2 Rated - Heatpump, no Solar or Underfloor

  • 06-08-2021 12:36pm
    Registered Users Posts: 3,901 ✭✭✭

    Hi all,

    There are tonnes of information on this forum, and I am slowly getting up to speed on it but I hope a dedicated thread is not too repetitive as I get a handle on what I can do on the renewable front.

    I am moving into a new build house in the next couple of months. Here are the main points:

    • A2 rated, semi-detatched
    • Central balanced, demand control mechanical ventilation system
    • No solar panels
    • No underfloor heating
    • Air source heat pump (Samsung of some sort, it looks like)

    My Notes:

    To my surprise, there are no solar panels on the houses in this estate.

    There is no underfloor heating, so the heat pump is dealing with radiators up and down stairs.

    The demand controlled ventilation system looks to simply mean that there is a central extractor fan in the attic taking air out of the toilet, shower rooms and the kitchen. Each room has one of those humidity strip controlled vents.

    My Ideas (as a numpty of a newbie!!)

    • Underfloor Heating: We are getting cheap flooring in downstairs to allow us to settle into the house and save up for better flooring down the line when we are more sure of what we want. I was thinking of taking the opportunity to retrofit some kind of underfloor system downstairs. I have seen a system which cuts channels into the existing concrete base for the pipes or low profile options. I do not think we would miss raising the floor up a couple of CM if needed. From my reading, underfloor will take the pressure off the heat pump as lower water temperatures are required. I do not think anything is possible for upstairs though.
    • Heat Recovery: I lived in an apartment with a Vent-Axia heat recovery system and I really liked it. I got quite nerdy with it and monitored air temps pre and post the heat exchanger and I was quite pleased to see it take the edge off cold temps in winter. I suppose the downside was that I could hear it operate slightly. Since the house will have a central extractor fan anyway, it seems like a no brainer to swap that for a Vent-Axia style unit. I wont be able to route many inlet pipes around the house, but I can get one into the downstairs living room and into the upstairs bedrooms. My thinking is, since air is getting centrally extracted anyway, let's try and use that exhaust heat.
    • Solar Panels with a Battery: In my ignorance, I just thought this was a no-brainer for all new builds along with underfloor heating. The house will be A2, so maybe there was no need for the builder to do anything too fancy. I have read some posts saying that the battery is just not cost effective. I have a PHEV and at some stage, we will both have EVs. I like the idea of at least charging a battery using the night rate for use during the day. Some solar panels on top of that, and it looks attractive.

    With all that said, it sounds great but is there actually going to be a significant cost benefit to us? The upside of my situation compared to some of the threads I have read here, is that we are starting with an A2 rated house so any changes we make are not to make the house warmer or more efficient in heat loss, but just to save money in the long run.

    From what reading I can get my head around so far:

    • Underfloor heating will be a cost benefit, especially with a heat pump
    • Heat recovery as I describe probably won't do much for us cost wise.
    • Solar panels must be of some benefit to us
    • Hooking up a battery, I do not really know.
    • I have seen what I think are alternative battery approaches where users here have sourced components and completed a DIY build of sorts. For the sake of this thread, I will stick to supplied and fitted options, at least until I get more experience.

    I am looking forward to getting up to speed thanks to the forum, but the mean time I appreciate any introductory information you have.


  • Moderators, Sports Moderators Posts: 18,430 Mod ✭✭✭✭slave1

    I stayed in an AirBnB similar to what you are moving into few weeks back, chatting to owner about their HRV and underfloor heating and they said they used the UFH twice in 10 years.

    On PV, you will not be able to avail of any grants as house too new, this will impact cost recovery...

  • Registered Users Posts: 3,901 ✭✭✭GTE

    Thanks for that, it's interesting. So would they have used their radiators primarily?

    In that scenario, I've read a lot saying that heat pumps work better with underfloor systems due to the lower operating temperature.

    Since I can not build the heat recovery system into the house from scratch, I could get one inlet into the sitting room and then perhaps one per bedroom upstairs. There is an extractor in the master ensuite, so an inlet on the far side of the bedroom would work best.

  • Posts: 864 ✭✭✭[Deleted User]

    What exactly are you trying to achieve? An A2 house isn't going to be cold in the winter even with the heat off...

  • Registered Users Posts: 3,901 ✭✭✭GTE

    It's very simple really, lower running costs over the next 30 years.

    The underfloor question relates directly to that.

    The heat recovery is based off experience in an A2 rated apartment which had that system, which by the way, was cold enough when the heating was off that you'd miss the heating. I know that from when the central heating was broken.

    The solar side may make the above redundant if I'm in a position to store electricity and just run the heat pump in what looks to be the less efficient configuration by driving radiators.

  • Posts: 864 ✭✭✭[Deleted User]

    But you'll never get your outlay back, the house is already extremely efficient. You'll looking to spend a fortune to get pennies back.

    Are you sure you lived in an A2 apartment? A2 has only been a requirement since September last year or so.

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  • Registered Users Posts: 3,901 ✭✭✭GTE

    Thanks for that, yes I am sure it was an A2 apartment. Fantastically cheap on heating and hot water.

    If its at the stage that the initial outlay wouldn't be recouped, then we are getting somewhere with the thread.

    Do you mean specifically underfloor heating and heat recovery in your experience?

    Would solar and battery still be a runner? That would at least be the easiest to quantify.

  • Registered Users Posts: 3,901 ✭✭✭GTE

    25% saving on running costs is interesting, if accurate. We will have a full winter with the radiators before we do anything with the flooring and the potential underfloor installation. That should give a baseline cost, as long as I get the hang of the system, settle in and hit a comfortable level.

  • Registered Users Posts: 11,997 ✭✭✭✭KCross

    As you’ve suggested get at least a years worth of data first and then decide but I’d also doubt you’d save anything on retrofitting UFH. That’s very disruptive to retrofit.

    Solar PV panels are your best bet for saving money as the value they generate isn’t tied to heating or one particular device. The power generated can be used for heating water, running heat pump, charging an EV and general house consumption.

    Note: It won’t run the heat pump during winter months so don’t count on that. Get yourself a cheap energy monitor and record your electricity usage and then run the numbers for a Solar PV system.

  • Registered Users Posts: 3,901 ✭✭✭GTE

    Thanks for the info there.

    The upside about a underfloor retrofit is that we are getting very cheap flooring down stairs to start off with while we settle into the house. We were thinking of doing the retrofit when the final flooring goes down in a year or two.

    Interesting point on running the heatpump; do you mean solar PV on its own wont be able to run the heatpump, which I'd expect, or do you mean solar PV in combination with a battery?

  • Registered Users Posts: 1,095 ✭✭✭kabakuyu

    Have you priced an underfloor retrofit? it might be an expensive fix for little savings if that is your reason for doing it.

    One other thing,all the new build houses that I see around here with heat pumps have underfloor heating, was there a reason for using rads in your new build.

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  • Moderators, Home & Garden Moderators Posts: 5,467 Mod ✭✭✭✭graememk

    Simply put, the days that you need heat, Its not gonna be sunny, or short days. - Heat pumps when running can use quite a lot of power, (think of along the lines of 3-4kw).

    I have 8kwp of panels, It was sunny - ish about 30 mins ago and was generating 4 kw, dark clouds rolled in, only generating 400w now!

    As its A2 rated, - without solar panels too bear in mind, (they are a cheap way of raising the BER) It wont need much heat. Maybe the Radiators are more than enough and expensive underfloor heating isnt needed? Especially to retrotfit... The dust would be brutal.

    The idea of charging on night rate and discharging during the day is nice, but to be anyway noticeable on payback you need a decent battery.

    I have a 10kwh battery, which i use 20%-100%, Total round trip losses ive measured at the consumer unit is about 20% so say i put in 9kwh, i get 7.2 out.

    Im on energia's EV plan which is now 20c day 5.8c night. Daily saving is about 90c/day

  • Registered Users Posts: 3,901 ✭✭✭GTE

    I've not priced it yet as I'm waiting to get into the house, but I was expecting a hefty initial investment. The key will be data (either mine or others) about potential cost savings.

    The housing estate developer has chosen to put radiators in which is a surprise after reading a bit about heat pumps working better with underfloor. It's a good house, but I doubt the developer really cares in this market.

    Thanks for the data and good point about not needing underfloor. In the A2 apartment, we used the heating a fair bit but it was not expensive at all (and radiator based) . 25% reduction on not a lot is the way I'm looking at it. A night rate charged battery running the heatpump during the day sounds more financially efficient.

    I'd be up for a good sized battery if I were to go down that route. Solar and a battery seems to be the no brainer of the ideas I have.

    With exhaust venting already in place, the heat recovery seems to be along the no brainer route too. Seems to be, anyway.

    Post edited by GTE on

  • Registered Users Posts: 1,095 ✭✭✭kabakuyu

    Good luck with whatever you decide to do.My son moved into an A2 new build in January , he finds the electricity very economical.The house has heat pump and u/f heating but no solar.

  • Registered Users Posts: 11,997 ✭✭✭✭KCross

    It would still be very disruptive to retrofit UFH. Losing the cheap flooring would be the least of your worries. It would mean laying out a network of pipes, laying down a new concrete base on top of that and them plumbing all that back to the heat pump. Technically possible but very messy while continuing to live in the house. And assuming you have an upstairs you would probably end up leaving rads up there anyway.

    It would only really be viable, imo, if it was a house renovation where everything was going to be stripped back anyway and part of a larger project.

    In addition you would only gain the difference in running costs from UFH to rads. It would be different if you were going from, say, oil to a heat pump+UFH. You already have the heat pump so you have already "banked" that saving so you are only getting the efficiency difference from rads-->UFH which would likely never justify the upheavel and cost involved in retrofitting UFH to an already A2 rated house.

    An energy monitor and a years worth of data will definitively answer all this for you. That needs to be your first step. The sooner you get that the sooner you get to your 1 years worth of data.

    On Solar PV... the heat pump runs the most (winter and at night) at exactly the time that the sun shines least! There will be some days that it will be sunny and cold and the heat pump will run and can utilise the Solar PV electricity but its only for a few hours for a few months of the year... it wouldnt add up to much.

    In the summer, your heat pump will run to heat hot water and you can use excess Solar PV energy to heat the water which in turn will then save the heat pump from having to turn on at all the following day. That means less wear/tear on your heat pump, which is a good thing, but the overall money gain to you will be marginal as you have to pay for the hot water diverter.

  • Registered Users Posts: 11,997 ✭✭✭✭KCross

    NOTE: A battery may not be able to drive your heat pump on its own. Its not a simple case of "the battery is full so I can turn everything on".

    The battery will have amp limits on its discharge rate and that would likely exceed the amps required to drive your heat pump (unless you have a very low rated heat pump). The shortfall would then have to come from the grid.

    Battery systems are also quite expensive if going the traditional off-the-shelf route with grant approval and I think your primary goal here is to save money.... a battery might never save you money so get your facts/figures straight before signing any cheques when it comes to battery systems... they have a finite life.

    Solar PV on its own is a good investment if you purchase right and it has no serviceable parts and will last decades (apart from the inverter, which is relatively cheap to replace).

  • Registered Users Posts: 3,901 ✭✭✭GTE

    Aha! I suppose you'd not be able to split the battery output so once the house as a whole reached the 21amp limit of a Tesla Powerwall, to take and example, the battery is bypassed. So a 20amp heat pump in the winter would deactivate the battery if a hefty toaster was enough to max the Powerwall.

    Thanks for the rest of the info, that's all making sense with respect to how the components relate to eachother. I'm looking forward to the data even more now.

  • Moderators, Home & Garden Moderators Posts: 5,467 Mod ✭✭✭✭graememk

    No it wont deactivate the battery,

    In that scenario, say the load is 5kw, battery can supply 3kw, 2kw will come from the grid.

  • Registered Users Posts: 45,144 ✭✭✭✭Bobeagleburger

    Best bet is to do a full year in the house and see how the electricity bills work out.

  • Registered Users Posts: 1,868 ✭✭✭garo

    You also have to realise that depending on the orientation and slope your panels could produce one-tenth of what they produce in May in December. So even with a battery total production over a week may never produce enough electricity to drive the heat pump. DO NOT think of Solar PV as a way to cut heat pump electricity costs.

    In your situation the most effective thing for you to do most likely is to get a 6kW PV install without a battery and forget about battery or UFH.

  • Registered Users Posts: 1 Oneek

    I am curious to hear back from your experience living in the house, and if you managed to upgrade the house ?

    we are moving in in a similar new build (A2, no UFH, central ventilation , but no heatRecovery, no PV)

    would be great if you could share your thought and experience on this .


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  • Registered Users Posts: 802 ✭✭✭keno-daytrader

    Another thing to consider is the amount of insulation on top the the concrete foundation. Builders are notoriously cheap when it comes to building estate housing, hence the decision to put rads in. How to verify what level of insulation is there..... is a tricky thing. I certainly wouldn't take the builders word for it.