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Heating and cooling: What to do for space heating outwith winter, when Rayburn is overkill: solar water? ASHP?

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  1.  
    • CommentAuthorjiminyrock
    • CommentTimeSep 7th 2012 edited
     
    Hi, this is my first post here, but I've been reading the forum for a little while and find the advice and knowledge out there very interesting and helpful!

    We have been renovating a 1960's built 70sqm floor space house on the north west coast of Scotland on a tight budget, which is currently 2 bedroom, but with a planned loft conversion will eventually be 3 bedrooms. Nevertheless, we have probably made a lot of bad decisions. We currently have:
    - cavity walls currently uninsulated
    - suspended wooden floor, insulated between joists ~200mm glass wool (breather membrane) floor partially carpeted and elsewhere partially engineered wood
    - loft insulation 200mm glass wool
    - double glazed PVC windows
    - 2nd hand solid multifuel rayburn (355sfw)
    - mcdonalds engineering thermflow vented 250lt tank, mains pressure hot water, direct input from rayburn, direct to heating circuit, oversized radiators, 2x 3kw immersions, one on econ7 and an additional coil I think designed for solar water
    - but we didn't have the cash for solar water panels before

    Generally, this system seems to work ok, and further development has stalled until now due to lack of time and money. The main problem we are having is as follows. The rayburn is great in winter, but is way too hot to run in the summer. I mean my dad likes to sun bathe in front of his wood stove pretty much any time of year with a whisky in his hand, but I've not developed the ability to enjoy this habit... ...yet!!! We expected the Rayburn to be too hot in the summer, but hoped that an insulated house would be warm enough just with people living in it, cooking and the sun coming in whenever it decides to grace us with its presence, but we are jessie's who are finding it can be a little too cold. So we may have made some expensive mistakes, I don't know. We seem to get sufficient DHW from the electric boost / econ 7 +/- Rayburn, but would like to get more economical DHW than using immersions if possible.

    Anyhow, we've surprisingly inherited a little cash, and then just yesterday I got a very surprising indication of a tax rebate.... from back in 2005!!! So all of a sudden I have some money again to put into this project, which prompted me to sign up and get some advice here.

    The question is, what can I do to take this project forward... ...how can I space heat without utilising the Rayburn.. ..would Solar water or an air source heat pump be potentially sufficient? We are 20m from the sea on a spring tide, and don't have enough land for a horizontal GSHP. The cavity (100mm) hasn't been insulated thus far over concerns about potential penetrating damp through the harling and concrete block, and possibly creating a bridge for moisture, but maybe we should do this anyway. Any advice / questions / criticisms / ideas appreciated... ...thanks...

    Jamie
  2.  
    ''The cavity (100mm) hasn't been insulated thus far over concerns about potential penetrating damp through the harling and concrete block, and possibly creating a bridge for moisture, but maybe we should do this anyway''

    But maybe you shouldn't! I share your concerns. Think v carefully before doing it, on the assumptin that you get horizontal rain and soaked walls on occasion.
  3.  
    The North West coast of Scotland is classed as a Very Severe exposure zone with >100 litres/m2 per spell of rain. If the harling is in good condition then it may be possible to fill the cavities, but any problems with cavity trays, cavity bridges, mortar snots, etc are likely to lead to damp penetration.

    David
  4.  
    Thanks guys. I suspected this might be a problem which is why I hadn't done it. The harling is all in one piece, visually fine, but I suspect very porous given that I think it is the original harling from 1967. The harling could look pretty damp for a while after rain. You can see down all the cavities from above, and the space and ties look clean. Are all materials used for cavity filling equal in this respect? I think I'd rather not risk it, but thought it was worth asking.
  5.  
    Not sure if its any use, but I've attached the thermflow tank schematic and forgot to say the house has a south facing roof.
    • CommentAuthortony
    • CommentTimeSep 8th 2012
     
    I would fill the cavities with polystyrene beads, insulate the loft more, do air tightness stuff well, you could consider both solar pv and solar thermal and a water source (sea source ) heat pump

    sounds like a worthwhile project.

    plan is reduce heat requirements first then decide what is needed to fulfil the demands.
  7.  
    As Tony says, if you are ging to fill the cavity with anything, use poly beads.
    • CommentAuthorjiminyrock
    • CommentTimeSep 8th 2012 edited
     
    Interesting points, thanks. Regarding air tightness, there is a tension, is there not, between air tightness and condensation / damp?

    When we first bought the house an expensive survey failed to pick up the extent of damp in the house which hadn't been lived in for 15 years. I removed concrete block by concrete block from the roof down a very large free standing centrally placed chimney with two fireplaces on each side which freed up a huge amount of space internally, but when I got to removing the base at ground floor level, I could see under the suspended wood floor for the first time. There was at least 1 foot of standing water and clearly a few inches above the damp proof course!!! Surprisingly, none of the floor timbers that I personally, and had professionally inspected had any rot (one rather crucial beam in the roof was rotten through though, but that was associated with small hole in the valley lead flashing of the roof, but thats another story!!!). We live right infront of a big munro (see picture), so you can imagine how much water comes down, and looking behind the house revealed that sodden wet earth was up against the house above the damp proof course all the way along. So I got a couple of metres of earth dug out at the back, and put drainage at the back of that to move water away from the house. Touch wood, since then, there has been no evidence of water under the ground floor, even in some pretty protracted periods of heavy rainfall, but the earth/rubble base does still feel damp when its very wet outside.

    When I insulated the floor, I used glass wool, and secured it all in place as leak proof as I could with a breather membrane. So when you say as leak proof as possible, what do you mean. For example, there are quite a few air vents that move air under the suspended wood floor, and these are presumably crucial to maintaining the damp free environment. What / where else should I be thinking air tightness wise?
      house.jpg
    • CommentAuthortony
    • CommentTimeSep 8th 2012 edited
     
    Air tightness is important to reduce heat loss, uncontrollable draughts should not be confused with good ventilation, build tight ventilate right to me means less than 1m^3/m^2?h
    @ 50Pa is a standard way of measuring air tightness and mechanical background ventilation with heat recovery is essental.
  10.  
    Hi tony, and thanks. It may have been the bitter and twisted I was drinking last night, but I don't follow exactly what you're saying. What does "build tioght ventilate right to me means less than 1"?

    And is the idea that mcehanical background ventilation with heat recovery is essential a generally held view amongst those on the greenbuilding forum?

    For what its worth, there is alot of air moving under the suspended floor. To seal up better, I'd probably need to:
    1) Get the membrane under the floor to seal up with the walls to plug that gap.. ..how do you do this?
    2) Our walls are kingspan (50mm)fused with plasterboard (subsequently plastered) fixed on battens fixed onto the concrete block wall. I'd probably need to double check the bottom of the kingspan / plasterboard to plug gaps there with silicon sealant. Is that worth doing?
    3) There is one very deliberate hole coming in to supply sufficient air for the rayburn, and there isn't yet, but there will be an extraction hood for the hob. How does this sit with mechanical ventilation and heat recovery? Can such a system be setup to provide sufficient air to keep the Rayburn happy and safe?

    Also, can such a system also be combined with a heat pump to warm air, or is it better to have a separate air source heat pump or other pump to heat water?

    Lots of questions so sorry about that!
    • CommentAuthortony
    • CommentTimeSep 9th 2012
     
    Air tightness is important to reduce heat loss, uncontrollable draughts should not be confused with good ventilation, build tight ventilate right to me means less than 1m^3/m^2?h
    @ 50Pa is a standard way of measuring air tightness and mechanical background ventilation with heat recovery is essential.

    1) my favourite membrane would sit on the warn side of the insulation and be trapped behind plaster or skirtings, it is them a vapour barrier and air tightness all in one if it is vapour resistant, unkeen on one under the insulation.

    2) It is crucial that outdoor air cant get into the rooms from behind the thermal linings, otherwise they loose their purpose.

    3) a balanced mhrv system is in theory OK and provides ventilation, in practice it is technically difficult and also not fail safe which leads to problems, can you manage without the Rayburn?

    Separate heat pump unless you are insulated to better than Passive house or minergie standards, or can afford monster ducts
  12.  
    I guess there would have to be some internal positive pressure ventilation present to prevent the potential of CO posioning if we removed the air venting for the rayburn. Difficult. Can a mechanical ventilation with heat recovery system provide measured positive pressure and be rendered passive on failure, in which case, if it could normally run at positive pressure then I would of thought that would be okay. I'm paranoid enough to have installed CO detectors already anyway!

    I'm disinclined to do without the Rayburn because of a) sunk cost, b) almost free fuel and c) it works so damn well over the winter d) and synchonously provides sufficient heat for boiling drinking water / cooking needs e) potential for a very irate wife if I removed it.

    If the Rayburn stays, is there any point in sealing up good and proper except for one source of air for the rayburn and installing mechanical ventillation, or would one leak to outside render the whole thing pointless?

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