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Heating and cooling: Solar Facade

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  1.  
    • CommentAuthorgyrogear
    • CommentTimeMay 11th 2016 edited
     
    I am interested in this idea of solar facade -- http://www.waf.at/solar-systems/?lang=en

    and wonder if anybody has ideas regarding this "selective solar varnish" that I'd like to get my paws on...
    The idea is to stack heat up behind the slates, rather than have them radiating it all back out to the cold.

    I looked up "Solkote", but it is not usable for my application (slate cladding)...
    (http://www.solec.org/solkote/solkote-technical-specifications/)

    Otherwise I am "stuck" with straight roof varnish, which seems to be a waterproofing solution, which is not what I need neither...

    Thanks for any help or pointers

    gg
    • CommentAuthorbxman
    • CommentTimeMay 11th 2016
     
    stack heat up behind the slates

    retain / store ?

    what is the objective ?
    •  
      CommentAuthordjh
    • CommentTimeMay 11th 2016
     
    The best known selective coating is Tinox. I doubt you'll find anything intended for slates though.

    You can put silicone tubing or maybe hosepipe behind slates and you might be able to help with warming a pool but that's probably about it. For anything more you probably want to replace the slates.
    • CommentAuthorgyrogear
    • CommentTimeMay 11th 2016
     
    Thanks for the responses, the aim is to increase radiant heating through the wall, into the house.

    Think I'll just paint 'em blacker...

    gg
    •  
      CommentAuthordjh
    • CommentTimeMay 11th 2016
     
    Posted By: gyrogearThanks for the responses, the aim is to increase radiant heating through the wall, into the house.

    Think I'll just paint 'em blacker...

    Probably won't make much difference. So they're hanging tiles on a wall rather than roof tiles? Putting a sheet of glass in front of them will help them retain heat.
    •  
      CommentAuthorfostertom
    • CommentTimeMay 11th 2016
     
    The trick with ultra-lo-grade solar heat collection for space heating when it's needed i.e. cold winter days while the sun's shining, is to collect the heat and move it away, before the sun goes behind a cloud and all the heat you've just collected immediately re-radiates back to the cold surroundings and sky.

    If you can't devise a way to move the heat away to safety, as it comes, forget it!

    Actually, extremely high collection efficiencies are possible if you get this right - far and away higher than the efficiencies quoted for wet solar panels, let alone PV.

    That's thanks to your thermofluid (whether air or water) running at v low temp - say 21C if you want to use it to heat your rooms by big-area radiant (e.g. a whole wall) to say 19C air temp (which is all you need to feel comfortable, given a v high radiant vs convected input component). That low thermofluid temp halves (or better) the simultaneous re-radiation loss to surroundings, which is a big factor in degrading the efficiency of any thermal-collection (i.e. not PV) panel.
    • CommentAuthorEd Davies
    • CommentTimeMay 11th 2016
     
    Posted By: gyrogearThink I'll just paint 'em blacker...
    Which'll also help them radiate outwards better. Means they'll absorb heat better at the times of year when you don't want that and radiate heat better at the other times of year when you don't want that, either. Other than with a selective coating in the heating season (to absorb short-wave radiation but hang on to longer-wave thermal radiation), radiant heat transfer is usually something you're better off without.
    • CommentAuthorgyrogear
    • CommentTimeMay 11th 2016 edited
     
    Posted By: fostertomcollect the heat and move it away


    Yes precisely !

    I'm looking at both air and hydronic on the same cladding, I've done some preliminary tests and it looks like it works!

    Posted By: Ed Davieshelp them radiate outwards better


    Yes, I guessed that'd be the problem !

    Posted By: djhPutting a sheet of glass in front of them will help them retain heat.


    But I cannot glaze them becos town hall (and port...) rules, so was thinking clear varnish, If I can locate some of the Right Stuff...

    (can't go blinding the ships):shocked:
    gg
    •  
      CommentAuthorfostertom
    • CommentTimeMay 11th 2016
     
    Apart from the collection efficiency is much lower, it's so v much easier to skip thermal collection, go to PV instead.

    Then no issues of moving heat away so it's not re-radiated, no expensive/elaborate piping/ducting of thermofluid, just electric trace-tape zigzagged all over the wall that's going to be the heat store/radiator.

    As and when there's PV generation going on, at whatever varying voltage weak to peak, it's dumped straight into the trace-tape as DC, no inverters etc, where it generates heat at varying temp weak to peak, which the wall stores in its mass.

    Best if the wall is say 500thk rubble stone, its outside face zigzagged with trace-tape, EWI applied over that. Then the wall becomes part of the internal environment. Heat input as and when available into the outside face of the wall takes a week or 10 days to trickle through the massive wall, arriving internally with all the peaks and troughs smoothed to steady 24/7 radiant output. Better get the sums right, because there's no way to 'turn down' the heat flow once it's on its way through the wall!

    But all this depends on having
    a) plenty of collector area, as PV is so inefficient at collecting the incoming solar, and
    b) high insulation/airtightness, to reduce demand to what such mid-winter collection can supply
    Or rather, balance those 2 factors against ea other.
    • CommentAuthorgyrogear
    • CommentTimeMay 11th 2016 edited
     
    Posted By: fostertomHeat input as and when available into the outside face of the wall takes a week or 10 days to trickle through the massive wall, arriving internally with all the peaks and troughs smoothed to steady 24/7 radiant output.


    Many thanks for the overview, Tom !

    At the moment, I suspect I *do* already get the trickle you mention, as the wall does not go cold overnight in Winter, after a nice sunny period... It is uninsulated blockwork. The outer cladding is slates, to lathes, on rafters. 2 meters high x 5 meters wide. Airspace of 12 cms between back of slates and blockwork. Fiberglass blanket laid between rafters, latter on 60 cm centers. Been progressively ripping the F/G out... :devil:

    I have experimentally been dragging air out of the bottom of this "cassette", noisy and draughty, but does not matter as I dump it bulk, in the garage. Trying to decide what to do with it next ! Already insulating the garage outer wall (not the roof, it is my lounge floor above !). Will pull the air into the crawlspace next, then dump to outside, via duct.

    Also (one day...) want to put some copper in the airspace, to drive a drainback collector for preparing DHW...

    Phoned a varnish outfit, the sales person will (hopefully) call me back, I want to boost the airspace temp (at the moment it cruises at 35 to 40 in winter, but gets to 60+ in summer). (But in summer I would not be pulling air, and would throttle the copper also).

    Many thanks for your interest !

    I think "aspirated transpired facade is the way to go" for my site, & water could be part of it, I intend to build a partial test platform before too long...

    gg
    • CommentAuthorDBrowne76
    • CommentTimeMay 12th 2016
     
    Hi gyrogear,

    I felt stuck too when first started looking for a solar solution for my slate facade. Then I found this solar system in natural slate that can be used either for roofing, cladding or flooring. (http://www.cupapizarras.com/uk/thermoslate/solar-collectors/solar-floor) I have installed 5 collectors for heating and hot water and I cannot be happier with it!

    Hope this helps
    • CommentAuthorgyrogear
    • CommentTimeMay 12th 2016
     
    Thanks, DBrowne76 !

    Yes, I know that product, there is a similar Spanish one, that is 800 E per square meter !

    I'm actually engaged in a low-cost minimalist retrofit, to an existing bioclimatic house.

    gg
    • CommentAuthorgyrogear
    • CommentTimeMar 16th 2017 edited
     
    just updating with latest ideas and drawing,

    all comments welcomed as usual !

    gg
    • CommentAuthorJohn Walsh
    • CommentTimeMar 17th 2017
     
    My comment is simple - just do it. There will be unknowns (positives and negatives) that you'll only become aware of by doing it. At 48deg N (if that's where you are - saw this on your drawing) you've plenty of sun to play with. The state of our collective knowledge of such systems is at an early stage (despite what 'experts' say). It's only by doing it, that by gaining experience in your context, that you'll be able to develop what you do, find which materials work best and so on.

    Well done for braving the indifference towards / bias against solar thermal that appears again and again on this forum (which has the effect of stifling discussion - I'm careful about what I disclose because of this). It's a baffling attitude and antithetical to the green building tradition and ethos going back to Alternative Technology in the 70s.

    My experience of solar thermal is from moving in to a house with a 20m2 footprint, 4m high dual pitch roof conservatory and being amazed by the solar thermal potential (53N in the UK). We experimented with an old 4 inch fan found in a shed and some aluminium ducting lying around. What we found was that we could easily increase the temperature in living rooms and that running the fan made no difference to the T in the conservatory roof.

    From those observations and from looking around at what others have done, we now harvest solar warmed air from purpose built solar gain spaces. Recently, we've switched on an MVHR installation which, at this time of year, has its air intake from a solar gain space. It works, it's free heat and like DBrowne76 (above) we 'cannot be happier with it'.
    • CommentAuthorgyrogear
    • CommentTimeMar 17th 2017 edited
     
    Great, JW, thanks for your enthusiasm !

    Somebody ought to refurbish that old music hall song:

    "My Old Man says Borrow the San
    and Don't Dilly-Dally on the Way !"

    right, I'm just going to do it !
    (actually, there *IS* some support on here for this kind of stuff, thank dog (they know who they are !)

    Cheers, wash this space...

    gg
  16.  
    I am looking forward to seeing the clean space....
    • CommentAuthorgyrogear
    • CommentTimeMar 18th 2017
     
    sorry, I hadn't got my dentures in :bigsmile:

    gg
    •  
      CommentAuthorjoe90
    • CommentTimeMar 18th 2017
     
    This thread makes me think of this http://www.cherrymortgages.com/sustainable_zero_carbon_housing/solar_conservatory_glengariffe_passive_house_viking_ireland.htm
    which is a few years old now but stirred my imagination.
    • CommentAuthorJohn Walsh
    • CommentTimeMar 19th 2017
     
    Yes, joe90, well said - that project was an early inspiration for us too. Here's a couple more, both of which have 'open' days. Hockerton do charge, but seeing such projects 'in the flesh' and talking to occupants was very worthwhile, gave us confidence.

    http://www.hockertonhousingproject.org.uk/

    http://www.allanjoycearchitects.co.uk/news/516-g-4-s-p-g-h
    • CommentAuthorgyrogear
    • CommentTimeMar 19th 2017
     
    Garden House is very nice - I'd just worry a bit about damage to sunspace glazing from those tall trees behind...

    gg
    •  
      CommentAuthorjoe90
    • CommentTimeMar 19th 2017
     
    Going back to my post above I am having a conservatory ( don't like that name, I would rather call it a sunspace!) along the south elevation ( rear) of my new build and yes I know it will overheat in summer ( when the clouds are not there, which is quite rare in north Devon.) but I can deal with this by shading when I know what the problem is. I am having patio doors into the kitchen diner and the lounge and recon I can let heat into the house by opening these or exclude it by shutting them and pulling curtails/blinds. I am not into lots of gadgets and prefer the kiss approach. I believe(hope) that the advantage of sunshine in the shoulder seasons and even low winter sun will outweigh any overheating for a short time, I will let you know. ( house roof being started next week).
    • CommentAuthorJohn Walsh
    • CommentTimeMar 19th 2017
     
    joe90 - an example of shading used in the Hockerton houses (the conservatory is the full width of the house). From memory, theirs is pretty much a kiss approach - open doors to the house as and when (the low tech approach to shading being another example).
      hockerton-conservatory.jpg
    • CommentAuthorEd Davies
    • CommentTimeMar 19th 2017
     
    At least originally the Hockerton houses had an air-source heat pump which took heat out of exhaust air from the conservatory and used it for DHW. Unfortunately they were installed quite a while ago and were custom made to fit in the space over the entrance door so when they failed it was hard (impossible?) to get replacements. Not quite so KISS.
    • CommentAuthorgyrogear
    • CommentTimeMar 19th 2017 edited
     
    Posted By: joe90recon I can let heat into the house by opening these or exclude it by shutting them and pulling curtails/blinds.


    Nice idea !

    I suspect that the "heat" might need helping along, with a draught of air or two...

    Here is a good vid that U might find useful, if you've not already seen it.
    see "natural-convection airflow path" at cue 5'.45''...

    Unfortunately, Larry is no longer with us, but his thinking will hopefully outlast him...

    https://www.youtube.com/watch?v=lzGaLw__kdk

    Posted By: joe90( house roof being started next week).


    If it's not too late, maybe consider including some means of evacuating hot summer air (cf. cue 6'.24").

    Final word...
    Posted By: joe90I believe(hope) that the advantage of sunshine in the shoulder seasons and even low winter sun will outweigh any overheating for a short time


    I hope so too !
    Know nothing of your design, but if you have got anywhere to shove warm air into, such as cold low northern areas, go for it !

    Enjoy your build !

    gg
    • CommentAuthorJohn Walsh
    • CommentTimeMar 20th 2017
     
    Good to see your comments Ed Davies - it's very useful to have someone provide the role of a nitpicker to help guard against the echo chamber tendency. Thanks. Although, on this occasion, your service isn't up to your usual standard - AFAIK, the heat pumps were replaced by large, very well insulated DHW cylinders running off E7, partly in order to re-align DHW with their predominantly kiss approach.

    Happy equinox to all and please remember: Your Mileage May Vary

    PS well spotted gg - those Garden House trees are close but perhaps not within the plot, so just tough luck and hope the neighbour manages their trees?
    •  
      CommentAuthorSteamyTea
    • CommentTimeMar 20th 2017
     
    I have visited this place
    https://www.foe.co.uk/news/solar_heating_cornwall
    Was interesting but not sure if stacks up financially. Does all depends on how you juggle the numbers.
    • CommentAuthorEd Davies
    • CommentTimeMar 20th 2017
     
    John, yes, that's why I wrote those comments in the past tense prefixed by “at least originally”. The immersion heaters are now powered by renewable energy so not sure about E7.

    https://twitter.com/lizlaineuk/status/807503050793480192
    • CommentAuthorskyewright
    • CommentTimeMar 20th 2017 edited
     
    Posted By: joe90I can let heat into the house by opening these or exclude it by shutting them and pulling curtails/blinds. I am not into lots of gadgets and prefer the kiss approach. I believe(hope) that the advantage of sunshine in the shoulder seasons and even low winter sun will outweigh any overheating for a short time, I will let you know. ( house roof being started next week).

    That sort of approach works for us at 57N. 30m2 long narrow(ish) sunspace along the whole of of the WSW facing 'front' of our bungalow.
    Yesterday it was ~7C outside, high 20's in the sunspace. In such cases we simply open the 'front door' and the windows along the front & leave the internal doors open, that's sufficient to allow warmth to spread throughout the house.
    To keep temps under control in summer (when the place is full of plants) we have lots of ventilation[1] and lightweight white cotton curtains (hangs from on para cord that runs between cleats). Around the end of October we take down the curtains, then they go up again in March (I put them up last week).

    [1] Including several transoms placed at the bottom to aid circulation on hot still days - that was partly inspired by the Irish house and partly inspired by greenhouse "alpine vents".

    Edit to add: I've mentioned this before (:bigsmile:) and recall a comment about curtains degrading in sunshine. They've now served two full summers and they still look & feel like new (being simple they are also simple to put in the washer at the end of the season).
    • CommentAuthorgyrogear
    • CommentTimeJun 12th 2017 edited
     
    Posted By: djhThe best known selective coating is Tinox. I doubt you'll find anything intended for slates though.


    In which case I would like to have a go at making my own !

    I have today found this link:
    https://www.google.com/patents/US4376801

    =====================
    "Vegetable oils, such as castor, corn, tung, soy and palm, have all been found to be suitable coating materials. Likewise, animal materials such as lard, butterfat and beeswax and certainly petroleum hydrocarbons also produce satisfactory solar coatings.

    Synthetic materials, such as vinyl polymers, can also be pyrolyzed to produce solar selective coatings. The coating material could be 100% of the organic compounds or mixtures thereof or could be diluted in a suitable solvent, such as toluene, kerosene or mineral spirits.

    The percentage of the solvent in the coating composition is selected to produce a desired viscosity for coating of the composition onto the solar collector.

    The composition may be coated onto the collector by means such as spraying, roller coating or brush coating, each of which requires a different viscosity for proper application. Thus, the solvent could be present as an amount of from 0-90% by weight of the total composition."
    ==============================
    I am thinking of a mixture such as diesel fuel, linseed oil and white spirit.

    Applied with a paintbrush, then blowlamped for a while to get it all nice and sooty...

    I would test this DIY recipe by painting onto two mock-up slate collectors, rather than try on my real-life
    slate facade (dimensions 2 m high by 5m wide). One collector is doped and the other is left bare.

    Results would be measured using two radio-sensor packages from my weather stations...

    All thoughts welcome...

    (updated for latest layout plan)

    gg

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