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Heating and cooling: Passive-ish house - ASHP Vs Infrared

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1 to 19 of 19

  1.  
    • CommentAuthorMorven
    • CommentTimeJun 25th 2020
     
    Hi everyone, I've read various overlapping threads on this forum, but I'm hoping for some specific advice for my own case. My energy consultant has estimated our average daily heating load from October to March to be 19kWh for our new build, so about 3500kWh for the heating season (Wall U-values 0.11, triple glazing 0.79, air permeability max. 3ac/h, MVHR system). Advised heating system output of 1.6kW upwards. All DHW will be point of use electric heating, so no HW cylinder (DHW requirements are low). The house is 169m2, 1.5 storeys, basically a bungalow layout but with a second lounge and guest room upstairs. Weighing up my heating system options, my thoughts are as follows:

    1. Infrared heating panels. We'll have solar PVs, though obviously they won't help us due to the seasonal misalignment, so I'm calculating all electricity units at full price, so around £525/y at current prices. System outlay costs look to be around £4000 for 10y warranty German panels. I like this option due to its simplicity and lack of maintenance, plus it can be done post-completion, so saves a big CH system expense during build budgeting. My concerns are the risks of big bills if electricity bills go up and I'm unsure about their expected lifespan.

    2. 5kW ASHP + wet UFH ground floor slab. Quotes for this are around £12000 (Ecodan 5kW). We're not competent DIY-ers so wouldn't be happy putting in the system ourselves. RHI payment estimates vary between £2500-£4500 over the 7 years. It seems questionable whether the ASHP CoP (I'm guessing 3) electricity savings plus RHI will make this option pay-off, even if the ASHP lives 20-25y. I'm not enough of an UFH convert to go for this option for the feel alone.

    3. Nilan MVHR with integrated air-to-air HP. I've pretty much ruled this out as though it's a nice compromise in being affordable but still offering the CoP electricity savings, I'd be nervous of relying on air heating.

    Questions, which I'd really appreciate your help on:
    Does anyone know the average lifespan of infrared panels?
    Is it a bad idea to go for a direct electric heating option in a house with this heating input requirement?
    Is there a more affordable small ASHP option?
    Does anyone know which end of the scale (£2500-£4500) is most likely for our RHI? I believe it will be based on our final EPC certificate which may well overestimate heat requirements, am I right?
    ASHP lifespans seem to vary between 10y and 25y, depending who you ask. What are the opinions on here?
    Do those of you with ASHPs recommend annual servicing? If so, what's the cost?
    Is there a way of doing an ASHP + wet UFH system without a thermal store/HW cylinder or would I need to allocate the space for a tank?
    Plus, correct me if I'm wrong to rule-out the air heating HP option.

    Any advice will be greatly welcomed. I'm new on here, so go easy on me!
    •  
      CommentAuthordjh
    • CommentTimeJun 25th 2020
     
    Posted By: Morven(Wall U-values 0.11, triple glazing 0.79, air permeability max. 3ac/h, MVHR system)

    Welcome to GBF. :bigsmile:

    It all looks PH-ish as you say apart from the airtightness. Is there a particular reason you're aiming at such an unambitious target? It should be pretty easy to reach 1.0 ACH and the PH limit of 0.6 ACH is doable with care and attention. It will make a noticeable difference to your heating load.

    Does anyone know the average lifespan of infrared panels?

    I don't but I'd look at the length of warranty and the availability and costs of spares (elements and switches chiefly). I have some Stiebel-Eltron units that seem to be OK so far (five years). I've had to shorten the pullcord switch on one where it frayed through, but that's all so far.

    I'll leave your other questions to others with more knowledge of heat pumps, except that I will say I am watching the performance and costs of air-air units myself. We currently use a post-heater in the MVHR and a radiant panel, both overnight on E7 and I wonder if at some point I might consider it worthwhile from a cost or carbon point of view to switch to an air-air HP.
    • CommentAuthorgoodevans
    • CommentTimeJun 25th 2020
     
    If you are not keen on UFH, and you don't need or want a DHW cylinder I would look again at heating with a A2A heat pump.

    This has 2 benefits - a) The COP should give you a return and b) it can be used for Air conditioning in weather like this.

    I looked at RHI for my house and it wasn't worth it - you will use so little energy that the renewable element of the payments won't cover the cost of using the registered installers - particularly as you are only claiming for space heating. If you don't use RHI it is much easier get the right price for the components and installation.

    You will find that the heat moves between rooms quite easily - especially if the doors are left open so you should not need to heat the air in every room.
    • CommentAuthorMorven
    • CommentTimeJun 25th 2020 edited
     
    Posted By: djhIs there a particular reason you're aiming at such an unambitious target? It should be pretty easy to reach 1.0 ACH and the PH limit of 0.6 ACH is doable with care and attention. It will make a noticeable difference to your heating load.


    3.0 ACH is just what I've been told to expect by my timber frame company, and because we don't have a project manager and I'm a novice, I'd rather base my heat calculations on worst case scenario. Hopefully we'll be more in line with your suggestions in real-life. Is there a rough guide as to how much of a reduction in heat load to expect from a reduction from 3.0 to 1.0 ACH? And how early in the build process can you test air permeability and get a meaningful indication of what your final value will be? If early enough, I'll do that and then recalculate my heating requirements to decide whether ASHP & UFH will be worthwhile or not. But obviously that plan doesn't work if the screed would have to be done before worthwhile testing.
    The Nilan MVHR + HP was surprisingly affordable btw. Although not so much if you've already got MVHR!
    • CommentAuthorMorven
    • CommentTimeJun 25th 2020 edited
     
    Posted By: djhIs there a particular reason you're aiming at such an unambitious target? It should be pretty easy to reach 1.0 ACH and the PH limit of 0.6 ACH is doable with care and attention. It will make a noticeable difference to your heating load.


    I'm attempting that again in the hope it works this time!
    • CommentAuthorMorven
    • CommentTimeJun 25th 2020 edited
     
    Posted By: goodevansI looked at RHI for my house and it wasn't worth it - you will use so little energy that the renewable element of the payments won't cover the cost of using the registered installers - particularly as you are only claiming for space heating. If you don't use RHI it is much easier get the right price for the components and installation.


    Great to know. Thank you. That's the feeling I was starting to get. I've been shocked at the cost of ASHPs. Plus most providers are hugely oversizing the unit compared to what I need. I'll try my local plumber instead and see what he says. No need for AC in our house. We're building on top of a windy hill in Scotland, so leaving a window open on the two sunny days a year should be more than adequate :)
    • CommentAuthorEd Davies
    • CommentTimeJun 25th 2020
     
    Welcome Big Hill. If you want blockquotes, etc, to format nicely then choose “Format comment as” HTML just below the comment entry form. Unfortunately, if you choose that links don't work. If you want links to work choose Text. Weird trade off, it's just an odd quirk of this forum's software, which otherwise seems pretty straightforward.
  8.  
    Hello Morven,
    I believe it will be based on our final EPC certificate which may well overestimate heat requirements, am I right?
    ASHP lifespans seem to vary between 10y and 25y, depending who you ask. What are the opinions on here?
    Do those of you with ASHPs recommend annual servicing? If so, what's the cost?
    Is there a way of doing an ASHP + wet UFH system without a thermal store/HW cylinder or would I need to allocate the space for a tank?
    Our first ASHP failed after 7 years. Despite this we were pleased with it overall, it saved a huge amount of carbon and with RHI and fuel savings it paid for itself vs the previous oil boiler.

    The annual service contract was expensive £200/y iirc but it was a condition of the ashp's manufacturer's warranty that we had it serviced. It didn't appear to have extended the lifetime and it was out of warranty by the time it failed.

    Ours had no thermal store and didn't heat the DHW. ASHPs are less effective at the higher temperatures which you'd need to store meaningful amounts of heat. However for our next house we would consider storing heat in either a thermal store or a floor slab because off-peak electricity is likely to be greener and cheaper than peak-time. There was a thread on this by Goodevans I think who found the ashp was still more efficient than an immersion heater for heating hot water.

    Our RHI payment was based on EPC and CoP, but check the new rules about heat metering. The RHI scheme rules are proposed to change. As mentioned it may be cheaper to get a non-MCS installation and not bother with RHI.


    Couple of other thoughts:
    - have you looked at electric UFH? To store heat in the floor slab during off peak periods.

    -have you looked at good-quality electric convection panel heaters ('radiators') - the good ones don't click or smell and have individual timers/thermostats and smartphone controls etc. They are cheaper than you mentioned for the IR panels. We had a couple of adax neo we liked but others available.
    • CommentAuthortony
    • CommentTimeJun 25th 2020
     
    I think DIY small ASHP, forget the ir as only 100% efficient compared to 350 to 450% On the ASHP

    Air tightness will be difficult and I would write it into the contract
    •  
      CommentAuthordjh
    • CommentTimeJun 25th 2020 edited
     
    Posted By: Morven3.0 ACH is just what I've been told to expect by my timber frame company, and because we don't have a project manager and I'm a novice, I'd rather base my heat calculations on worst case scenario.

    Hmm. You're the client - tell the timber frame what you want and if they object find another company! Oh and try to get the airtightness number in the contract. It's wise to plan for the worst case as well the best though - have alternatives in mind. We didn't have a project manager (I did it out of necessity) and I was a novice when I started too. It is wise to plan to be on site as much as you can, I have learned through the experience. Even with the best will in the world and experienced tradesmen, it's amazing how fast things can go off track. Not a big problem if caught quickly.

    Is there a rough guide as to how much of a reduction in heat load to expect from a reduction from 3.0 to 1.0 ACH? And how early in the build process can you test air permeability and get a meaningful indication of what your final value will be?


    Over in Cranbrook's MVHR thread I posted a link to a guide produced by Paul that includes the following statement as well as some other info on the topic of airtightness: "Approximately 30% of the heating energy can be saved in airtight buildings with highly efficient MVHR systems compared to naturally (uncontrolled) ventilated buildings".

    To some extent you can decide how early you can do an airtightness test, by design and work scheduling. Key things on a build that is intended to be airtight are:
    - make sure the airtightness layer is clearly marked on drawings, and is continuous (a red line is usual). That way both you and everybody involved can understand where they must not make holes etc.
    - nominate an 'airtightness champion' who is on site all the time and make sure they know what they're doing and that they have the authority to stop work or get things redone if necessary. It might typically be you, or the project manager/site supervisor.

    To do an airtightness test, you need to make the building airtight! So you'll need external walls, ground floor, roof, doors & windows. But the doors and windows could just be sheets of plywood, and in practice you'll probably also have the first floor in place. You'll probably also want a load of sealing material - tapes & membranes etc in place. In our build we deliberately did the first test before putting in any internal walls. You also always have to do a test at the very end when everything is pretty much finished, to get the certificate.

    PS You can go back to your existing posts, choose to edit them and then select HTML format.

    PPS I just noticed the cost of the electrical heaters you're looking at. I have a duct heater and a radiant wall heater that together probably cost a tenth of those.
  11.  
    Hi Morven, welcome to the forum. We have built our timber frame house to PH standards and achieved an airtightness of 0.47ACH without any membranes or tapes, so I would aim to reach at least 1.0ACH. We have roof and wall U values of 0.095 and ground floor 0.1 and heat our house to 23C. We don't have any central heating and use electric towel rails as our main heating which is supplemented by warm air heating from our Genvex Combi 185LS which also provides DHW and MVHR. In a less well insulated house I would seriously consider air to air heat pumps.
    • CommentAuthorMorven
    • CommentTimeJun 26th 2020
     
    Posted By: WillInAberdeen- have you looked at electric UFH? To store heat in the floor slab during off peak periods.

    -have you looked at good-quality electric convection panel heaters ('radiators') - the good ones don't click or smell and have individual timers/thermostats and smartphone controls etc. They are cheaper than you mentioned for the IR panels. We had a couple of adax neo we liked but others available.


    Thanks Will. I'd thought about electric UFH, but was going with the infrared panels just because there's not flooring disruption if they go wrong. Hadn't thought about the benefit of the off-peak rate though. And good point about the electric radiators. I like the infrared panels because you can fit them high on the walls or on the ceilings, saving valuable wall space, but that won't be a priority in every room. I will look again at the electric UFH or radiators for the rooms with easily lift-able flooring/ample wall space.
    • CommentAuthorMorven
    • CommentTimeJun 26th 2020
     
    Posted By: djhSo you'll need external walls, ground floor, roof, doors & windows.


    Perfect - thanks. It's a kit house so the superstructure goes up in a one-er, so I'll do it as soon as it's wind and watertight. That should help guide my decision making. Do you just Google airtightness testing and pick someone local to do the test? I'm not sure who offers that service.
    • CommentAuthorMorven
    • CommentTimeJun 26th 2020
     
    Posted By: PeterStarckWe don't have any central heating and use electric towel rails as our main heating which is supplemented by warm air heating from our Genvex Combi 185LS which also provides DHW and MVHR.


    Hi Peter, it was actually based on your Genvex-related posts that I started looking into MVHR + HP and came across the Nilan ones! Do you rely on the air heating day-to-day throughout your heating season or is it just when it's particularly cold outside? Where in the country are you? And so because the heat is supplied through the MVHR ducts, it's only supplying heat into your dry rooms, is that right? And then you have the towel rails providing the heat to the bathrooms.
    • CommentAuthorMorven
    • CommentTimeJun 26th 2020
     
    Posted By: Ed DaviesWelcome Big Hill
    :bigsmile:
    • CommentAuthorMorven
    • CommentTimeJun 26th 2020
     
    Posted By: djhWe didn't have a project manager (I did it out of necessity) and I was a novice when I started too.


    Any good practical resources to help guide the novice project manager on airtightness monitoring on site?
    • CommentAuthorPeterStarck
    • CommentTimeJun 26th 2020 edited
     
    Posted By: MorvenHi Peter, it was actually based on your Genvex-related posts that I started looking into MVHR + HP and came across the Nilan ones! Do you rely on the air heating day-to-day throughout your heating season or is it just when it's particularly cold outside? Where in the country are you? And so because the heat is supplied through the MVHR ducts, it's only supplying heat into your dry rooms, is that right? And then you have the towel rails providing the heat to the bathrooms.


    We only have air heating which mostly comes from the three electric towel rails via the MVHR extracts in the bathrooms, which is supplemented with heat from the EASHP in the Genvex if required which isn't very often. Using the MVHR to move warm air around only works when very small amounts of heat are required. We are near the coast in East Kent so although we sometimes get cold east winds we don't get a lot of frosts.
    •  
      CommentAuthordjh
    • CommentTimeJun 26th 2020 edited
     
    Morven asked: "Do you just Google airtightness testing and pick someone local to do the test? I'm not sure who offers that service."

    Well I was aiming for PH certification, so the first thing I needed was somebody who conducts airtightness tests to that standard rather than the looser Building Regs requirements. I'd heard a lot of good things about Paul Jennings, so I contracted him. There's a bit about the process and him at https://www.aecb.net/event/the-airtightness-process-aecb-expert-advisor-paul-jennings/ and more at https://carbonlite.net/wp-content/uploads/2017/04/Aldas-12-Steps-to-Airtightness-revised-June-2019.pdf including contact details.
    • CommentAuthorMorven
    • CommentTimeJul 1st 2020
     
    Great. Thanks very much for all the help everyone. I feel better prepared to make a decision. Now I'm off to swat up on Airtightness supervision...

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