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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
These two books are the perfect starting place to help you get to grips with one of the most vitally important aspects of our society - our homes and living environment.

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    • CommentAuthorLittleJim
    • CommentTimeAug 16th 2017

    We are currently renovating a 2-bed, 2 lounge, one kitchen, one bathroom, very old stone cottage. At the moment the heating is by a solitary 5kw stove in one downstairs room. We intend to install an 8kw stove in the other downstairs room and attach a back boiler (3kw). Could anyone suggest what tank would be suitable? I'm not clued up about all the different sorts on the market - vented, thermal store etc...

    We are thinking a smallish tank (there are only 2 of us) in the bedroom above the stove with the back boiler.

    Eventually we hope to have solar PV that should go some way to helping with the hot water and also help run an electric Everhot cooker in the kitchen.

    Any advice would be very much appreciated.

    • CommentAuthorowlman
    • CommentTimeAug 16th 2017
    Hi James, Welcome. That's a small question with lots and lots of potential answers. The first is possibly the wisdom of installing a WBS with boiler, with all it's implications, fuel supply, efficiency etc. etc.. If that decision is already made then you need to also factor in the plumbing schematic with radiators, header tank/ F&E etc. and not just the DHW supply.
    The basic problem with relying on a WBS for space heating and DHW is that you may find you are roasting in the room where the WBS is located which out of necessity you need to keep going just the have a reliable DHW supply and/or heating elsewhere in the house.
    If I could suggest that you expand on your overall plan for space heating and DHW in order to get the best forum advice.
    • CommentAuthorLittleJim
    • CommentTimeAug 16th 2017 edited
    Thanks for the reply. We don't necessarily need to install the WBS with boiler - we could just install the WBS. At the moment we don't have any hot water (apart from an electric shower), so we are just using a kettle.

    Overall plan for space heating was to have a WBS in both downstairs rooms and an electric Everhot in the kitchen. Electric underfloor heating the the small bathroom. We've had electric underfloor heating installed in both downstairs rooms, but it wasn't meant as a proper means of heating the rooms to a comfortable temperature - just as a back up to keep the house getting too cold if we are not at home for a period of time. No heating in either upstairs rooms was planned.

    We don't have gas and we don't particularly want oil, so were a bit stuck for how to get DHW, hence we were thinking of the WBS with boiler, with an electric immersion for when the WBS isn't running. And then solar PV when money is available.

    Anything further information that would be helpful to know, just ask.
    I'd look into an ASHP... Ideal time to upgrade the rads, and can add PV at a later date
    • CommentAuthortony
    • CommentTimeAug 16th 2017
    Yes, with an ashp you get 3.5kW of heat from each kW of electricity for heating not quite as much for hot water.
    What owlman said above about combining DHW with space heating +1 - don't, its not a good idea.

    For DHW consider a standard DHW tank with an immersion heater running on what ever night rate / cheap rate electricity you can get. Once you have the DHW tank double or triple the insulation that the manufactures provided.

    Cost this option against the costs and maintenance of an ASHP, factor in the when you will get PV and don't forget that ASHP make a noise when running.

    The cheap instant fix is a standard DHW tank with an immersion heater, but the insulation provided by the manufactures is inadequate. For extra luxury and good showers especially if you have limited loft height for a header tank consider a mains pressure DHW
    • CommentTimeAug 16th 2017
    Instantaneous electric water heaters are another possibility. No storage losses but full price electricity.
    To separate DHW and space heating you could consider a Sunamp for the DHW and an ASHP or air to air HP for the space heating which would allow you to be all electric.
    • CommentTimeAug 17th 2017
    First thing you need to know is your heat load for both the space heating and the DHW.
    Without that information you are really just guessing.
    • CommentAuthorowlman
    • CommentTimeAug 17th 2017
    As you can see James there are numerous solutions to your situation so time to take stock. Here are a few questions to throw back at you, sorry to sound as if I'm prying.
    1. Is this a forever ( almost? ) home for you, a holiday let, or just a turn around to sell on, i.e., how much do you want to throw at it.
    2. If the former then logically think long term, it's worth the investment.
    3. The knock on effect of that decision will first be to INSULATE and draught proof.
    4. Having done that, or concurrently, work out the heat load as Steamy says. You may be surprised that you don't need as much as you think.
    5. You mentioned not being at home for some time. WBS are labour intensive, more especially in the way you originally envisaged, so any absences may prove problematic. Maybe just have a small one for aesthetic and entertainment purposes and a bit of occasional space heat but rely on one of the other methods others have mentioned for your main DHW and space heat needs.
    6. Think holistically about the solution, and should you decide to go down the electric route for the core needs then maybe PV should move up the priority list.
    • CommentAuthorLittleJim
    • CommentTimeAug 17th 2017
    Thanks so much for your suggestions. It seems that most think that we should not link the WBS and the DHW. Perhaps Peter's suggestion of a mains pressure DHW (but super insulated) with an immersion would be best. And perhaps moving PV up the list would be a good idea, rather than leaving it util later. It could then work for the DHW, the Everhot in the kitchen and the underfloor heating (which we weren't going to switch on if we could help it).

    To answer oilman's questions:

    At the moment we envisage it to be our forever home so are keen to 'do it properly'. It's not being let out or a holiday home.

    We've taken up the concrete onto earth floor and insulated with glapor and hempcrete, then laid reclaimed slate. Windows are now mostly double glazed and the roof is currently being insulated with homotherm, then sheets wool, then reed and lime plaster. Walls are two foot thick stone which we are lime plastering inside and out (previously it was pebble dashed outside, concrete inside).

    Not sure how we work out our heat load for space and DHW. I will look into that.

    And you're not prying Owlman, it's all very, very helpful. Thanks!
    I am going through same thought process in similar old house, as others said I have separated DHW from space heating ( in my case space heating was solved by insulation+ashp).

    For DHW the 'hidden' costs of storing hot water seem disproportionate. 1) buy and fit cylinder and boiler/wbs/flue/solar/etc 2) build house bigger for cupboard space for cylinder 3) constant heat losses. - add up to many £ks. And new tech like sunamp is lots of fun but very ££. Electric heat is £ and not very green.

    I am looking at instantaneous DHW using LPG cylinders - Google 'rinnai' or similar, seems much lower whole life cost.
    • CommentAuthorLittleJim
    • CommentTimeAug 17th 2017
    Just another thought... nobody has mentioned solar water heating panels. Any thoughts? There will only be two of us at the property, so a smallish 2m2 panel might work?
    • CommentTimeAug 17th 2017
    Posted By: LittleJimWalls are two foot thick stone which we are lime plastering inside and out

    Are you insulating the walls? That will be very beneficial to your fuel bills. I believe insulating them is required if you are replastering, in England anyway, not sure about other places. Since they are rendered outside, you should be able to use external wall insulation (EWI).

    Just another thought... nobody has mentioned solar water heating panels. Any thoughts? There will only be two of us at the property, so a smallish 2m2 panel might work?

    My journey actually started a few years ago by considering fitting solar thermal panels to my then house. I finished by building myself a new house, which does have PV panels but still no solar thermal. PV systems are generally cheaper and simpler these days, with less maintenance to look forward to. The main advantage of solar thermal is that they are more efficient in terms of energy collected per square metre, so they are still useful if your available space for panels is very limited but probably not otherwise.

    moving PV up the list would be a good idea, rather than leaving it util later. It could then work for the DHW, the Everhot in the kitchen and the underfloor heating (which we weren't going to switch on if we could help it).

    PV is useful for making hot water through summer and most of spring and autumn, and it will contribute to cooking in the summer, but don't count on it for anything in the winter.
    • CommentAuthorowlman
    • CommentTimeAug 17th 2017
    I have both PV and Solar Thermal, (ST). Much current thinking is not to bother with the ST and just use PV. Personally I'm not convinced, although I do have a totally different system however and the ST does work remarkably well, even in winter, pre-heating my rising mains DHW before it's final boost to the taps.
    ST I suspect does that more efficiently in winter than PV, unless you have lots of it. Like everything though there are pros and cons.
    • CommentTimeAug 17th 2017
    I heard, over at the other place, that a 'pressurised' i.e. UVC, water heating system not only needs a G3 certificate at installation, but also an annual check. So like any combustion system there are high maintenance costs.

    If you can, look at the advantages of the Sunamp, it has very low standing losses and is a compact unit for the amount of storage offered. This a bit of clever plumbing it can be configured to act as either a primary DHW system or to boost the temperature of an existing system from a heat pump.

    Word of warning about heat pumps, the higher you want the output temperature, the lower the CoP is. Eventually you can end up with a CoP of 1, which is the same as an immersion heater.

    Just to add to comments about WBS, you should also consider the environmental impacts, they are not benign at all, quite the opposite in fact.

    One advantage of PV is that it is much easier to 'plumb in' than ST, just a cable, timer/diverter and immersion heater.

    Are you in a hard water area? This needs to be looked at too.
    • CommentAuthorLittleJim
    • CommentTimeAug 17th 2017
    The Sunamp looks good. I'd not seen those before. Worth looking in to.

    We're soft water.
    • CommentTimeAug 17th 2017
    Soft water saves you a grand to start with.
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