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Heating and cooling: So many options - but which heating/DHW system

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    • CommentAuthorgoodevans
    • CommentTimeApr 8th 2017
     
    So I have made a rough stab at the fabric and ventilation losses for my new build - excluding solar gain and waste heat. - see attached

    Sap calcs for my situation looks like a target value of around 205W per Kelvin for the nominal dwelling, my build shows 145W/K - but approx 30 of that is penalty psi values which won't be there, and perhaps another 10 or more to come off in better windows than the default 1.4 lambda values.

    Leaving approx 105W/K to heat.

    I am not going to go for high solar gain option - my plan is for steady comfortable living in winter (through moderate heating) and in summer (on hot summer days - house sealed up to keep the internal temp lower than outside). Location Cambridgeshire.

    We tend to keep our house on the cool side in winter (18degC), but the house is occupied all day - on average waste heat could be around 500W with cooking, living, appliances etc so I think additional heating would be small (can anyone give me an annual and peak KWH for this situation)

    Starting from the simplest - low capital option....
    Electric only, in line hot water heaters at every sink/shower (no bath), Fan heaters where / when necessary

    to the most complex high capital option...
    Solar PV, Excess PV to HW store, Small regular gas boiler, DHW via heat exchanger on HW store, UFH From HW store.

    Or anything in between.

    To keep this thread focused on the heating/DHW the rules are 500w waste heat heating the house on average, 105W/K loss to outside - Assume the house has MVHR, EWI, medium density solid wall blockwork.

    Is this house efficient enough to go for low capital outlay and on demand electric heating/DHW?
    •  
      CommentAuthordjh
    • CommentTimeApr 8th 2017
     
    Posted By: goodevansSo I have made a rough stab at the fabric and ventilation losses for my new build

    Apologies but this site's search facilities are not very good and neither is my memory. Have you told us about this before somewhere?

    Sap calcs

    SAP is not good for low energy buildings. Better to use PHPP.

    Is this house efficient enough to go for low capital outlay and on demand electric heating/DHW?

    Dunno. It feels like you're being deliberately mysterious. What size is it for starters?
  3.  
    Posted By: djhWhat size is it for starters?

    djh, Nothing mysterious about this:

    internal width 8.7
    internal length 11.5
    ground floor height 2.7
    roof angle 40
    internal ridge height 3.6501
    gross ground wall area 109.08
    gross 1stF wall area 31.756
    gross volume 317.66
    living area 154.1

    From his SAP attachment! :wink:
    • CommentAuthorgoodevans
    • CommentTimeApr 9th 2017 edited
     
    No - not trying to be mysterious - see post above

    I know your are not a fan of SAP you have said so before - however I'm just using the first few sections to get a reasonable estimate of the losses I can expect.

    There are calcs in attached pdf in first post - its just 1 page of PDF with areas, U values etc - should give info required (but in answer to your question 1.5 story house/bungalow at just over 150m2).

    I have talked about tea cosy eaves details etc here, - you recommended I acquire "Details for Passive houses" which I now have (alas it no details help me with the suspended slab I think I'll be stuck with). I have also discussed render options, blockwork wall options - and so far the help has been erm... helpful.

    If possible please look at the PDF - there is nothing special about the calcs - I'm not going for PH standards - just something somewhere between UK Building regs and PH.

    So - to get back on track - I'm looking for guidance on the heating philosophy/approach for best value - I am genuinely torn between a high capital system and a keep it simple system.
    •  
      CommentAuthorSteamyTea
    • CommentTimeApr 9th 2017
     
    Have you looked at the SunAmp for your DHW?
    It is electrically powered, delivers a decent flow, have very little standing losses, is physically small and could probably be used to deliver to an UFH system.
    Not that cheap compared to a basic, self-installed vented system, but about the same as an unvented thermal store.
    • CommentAuthorgoodevans
    • CommentTimeApr 9th 2017
     
    I've checked out the SunAmp - the main advantage is that the phase change fluid allows a more compact storage - but if I went for a thermal store - I would go with regular water storage on popularity and future maintenance reasons.
    • CommentAuthorgyrogear
    • CommentTimeApr 9th 2017 edited
     
    Posted By: goodevansIs this house efficient enough to go for low capital outlay and on demand electric heating/DHW?


    Well, put it this way, your envelope heat losses are 3X less than mine !
    (I checked your suspended slab, it is also 3X better than mine)...
    Of course, I am in a totally different context (trying to eco-renovate an 1980's bioclimatic villa)

    I have still managed to kill the infloor radiant electric; replaced it with a wood burner of the same power (7.5 kW)
    I am now re-investing in electric understair (peanuts, 90 Euros to buy, a bit more for electrician)
    will also be investing in about 5 kW of radiant heaters for cold mornings as woodburner -- muchas I love it; it can still be a PITA...

    MORAL: From an initial (and admittedly psycho...) rigid anti-electric stance that forced me to look at other options (reinforced insulation, better windows, wood stove...) I am now seeing the utility of "leaning" back on electric, I shall still be quids-in (I hope !) and far more comfortable.

    So my feeling is that you could maybe opt for a similar approach - for a start, the initial layout is basically zero, and the installation costs idem, give it a year or two, then install a wood stove if needed [or perhaps a radiant wall from a home-built solar thermal if you have the time/inclination ] !

    gg
    •  
      CommentAuthordjh
    • CommentTimeApr 9th 2017
     
    OK I looked at the PDF. There's lots of number that don't mean much to me and the ones I think I probably do understand don't have units. And then there's things like 'internal ridge height' which I guess has units of metres, and from that presumption and its magnitude and the fact you've said its 1.5 storey, I suppose it must be the height above the first floor, but that's a lot of presumption and I still don't know what the first floor height is (as opposed to the ground floor ceiling). So I'm afraid I'm not going to struggle to work out the rest of the numbers; sorry. What's the heat demand (kWh/m² per year) and/or max heat load (W/m²)?

    The main advantage of the SunAmp is the low standing losses, by the way. I went with a 250 L thermal store just before the SunAmp came out. It works well for the two of us using a storage temp of 60°C in winter when powered by E7 each night and a storage temp of 85°C the other 8 months when powered by PV. The tank needs to be big enough to carry two or three days when PV-powered. The SunAmp does look attractive but would require a complete redesign of the DHW system, which I haven't bothered doing just as a hypothetical exercise. I'll look again when the thermal store needs replacing but it may be simpler to do a like-for-like swap even then. As you say, future maintenance is a major concern.
    • CommentAuthorgoodevans
    • CommentTimeApr 9th 2017 edited
     
    Ok DJH - Fair enough units not clear. - U values in W/(m2 K), heights lengths areas in m & m2. I'm not comparing with anyone else so heat loss is for total wall/total window/total lintels/total house etc in Watts/Kelvin.

    Its a simple 1.5 story house with 2 gable ends. Unlike PH standards I'm using internal dimensions for the wall floor and roof areas (as per SAP) but taking the wall height to 2.7m (where the roof starts), with the the roof ridge being 3.65m above this level.

    I guess peak heating load would be for about a -10degC to 22degC heat rise which gives 105W/K * 32 = 3360Watts assuming no other heat source. So far as annual heat demand I think with the waste heat at 500W (equiv to approx 4.8 degC) I need perhaps 2200 degree days/annum so say 105*2200*24/1000 = 5544 KWh/annum - but the number I'm most unsure of is the number of degree days I should use - much depends on solar gain and waste heat and this number seems high compared to the peak heating requirement.

    If I go for thermal storage I would also go for approx 250l (just 2 of us) but I have the option of either gas or PV + electric.
    • CommentAuthorgyrogear
    • CommentTimeApr 9th 2017
     
    Posted By: goodevansI'm most unsure of is the number of degree days I should use


    this might help:
    https://www.u-cursos.cl/ingenieria/2008/1/ME550/1/material_docente/bajar?id_material=165384

    gg
    •  
      CommentAuthordjh
    • CommentTimeApr 9th 2017
     
    Posted By: goodevansI have the option of either gas or PV + electric

    FWIW, I have the option of gas as well, but I decided that it wasn't worth the added complication and expense, given that PV was a given.

    It's all that guesswork that PHPP takes out of the estimates. You get figures that you can compare with lots of real-world built examples. On the basis of your guesses though, I'd think you do want some kind of heat distribution mechanism.
    • CommentAuthorringi
    • CommentTimeApr 10th 2017
     
    Price up having gas, also consider if you want a gas hob. Personally if gas cost less then a few £K to connect I would have it, just for the benefits when I come to sell the house if nothing else.

    One of the best setup for DWH is a thermal store (or SunAmp) heated by PV, feeding the pre-heated DHW into a gas combi boiler. (Check that the combi can take preheated water, and has a large modulation range.)

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