Hi all
I hope someone might have experience with this. We are intending to build a straw bale house, with a conventional wooden floor ie not on a slab. Many reasons for this, the main one being that we feel that in a cooler climate (Tasmania) it is important for a house to "feel" warm as well as being warm - and hard floors don't do this. Timber floors can give this warm feeling, and carpet even more so. It's called "higgelig" in Denmark - and they know how to build warm houses there!
We intend to build using passive solar principles, and realise that we need to get some thermal mass into the house somehow. I have been looking at the idea of using a Trombe wall, but know that such walls obviously can block views from windows, and where we are building has a truly sensational view (high up in Collinsvale).
I have found in my research that water is a better heat sink than rock or masonry, but even better is a material called Glauber's salts - meaning that you can have a lot more heat storage in a much smaller volume. So I am hoping to be able to make a Trombe wall that won't be so high as to block the view from the north facing windows. Now I have also found that there are some potential problems with Glauber's salts as a heat sink, well summarised in this article: http://www.extension.purdue.edu/extmedia/ae/AE-89.html
Now what I need to know is if anyone has gone down this road and what are their experiences. Can you get the modified Glauber's salts in Australia, and just as important can you get it in suitable cannisters to be used in a building? Any suggestions as to what sort of structure to put the cannisters in eg a glass case? Or within a wall that could be rendered perhaps? Anyone with any experience here I'd love to hear from you.
Cheers, Graeme
Glauber's salts as "thermal mass"
(14 posts) (6 voices)-
moisiemo
MemberPosted Monday 30 Aug 2010 @ 12:10:40 pm from IP # -
dave lawrence
Membergood for you . never heard of Glaubers salts but they sound interesting .
just a thought... have you considered building a thermal mass wall inside the house that is heated via winter sun through north facing clerestorey windows ?
that can work really well ,but depends on having a particular roof type.Posted Monday 30 Aug 2010 @ 8:48:29 pm from IP # -
Eco
MemberI have only ever read of one house in Australia that used PCMs - that was in Renew many years ago. There are a few other buildings that have trialled their use. Would love to hear of any other housing projects out there.
Because I will be shortly building my house on stumps or piers I am planning to use PCMs to make the house work better thermally - to increase the house's thermal capacity. However I have no practical experience as yet. The quantity of PCM required and the temperature of the phase change to be used relies on thermal analysis of the house.
This thread relates to PCMs: http://www.ata.org.au/forums/topic/phase-change-materials-pcm
Posted Wednesday 1 Sep 2010 @ 10:39:30 am from IP # -
I presume that you know the phase change is what is necessary to store the heat and that this occurs around 32 degrees? To gain the benefits your floor would have to get to 35 degrees or more on the surface. If you do that in a wall it could be more because of the insulation of the outer coating of (say gyprock).
You would also be aware of the expansion coefficient of the material as well and the challenges that would create for you in a building.
The most promising use of this kind of material is for storing excess heat from something like solar hot water systems.
Posted Wednesday 1 Sep 2010 @ 11:58:55 am from IP # -
moisiemo
MemberThanks for the responses and the links - these could be very helpful. In answer to a couple of the questions, yes I am aware of the phase change of Glauber's salts at 32 degrees - but I didn't know about other PCMs that have lower phase change temps, so I will do some more research. I also have no idea as to how much these things cost, so I will need to find out this too.
I was thinking of using cylinders containing the salts, put behind windows at the north of the house. I think in this situation it would be quite easy for them to heat up to the phase change temperature. I have seen a picture of just such a setup in a glasshouse, and it looked much like a hot water radiator as is common in most colder countries. I have considered possibly containing them within a glass or perspex cabinet, thinking more of keeping them clean as anything else - I figure cylinders mounted next to each other could be a good dust collector. But I still need to find out a lot more before deciding just which way to go.
Cheers, GraemePosted Monday 6 Sep 2010 @ 11:38:50 pm from IP # -
dymonite69
MemberSpec data suggests anhydrous Glauber's salts have lower volumetric heat capacity:
Water
4.18 J/cm3/K
Glaubers (anhy)
142 g/mol (MWt)
2.664 g/cm3 (Density)
128 J/mol/K (Heat capacity)Therefore
128 J/ 142 g/K
=128 J/53 cm3/K
=2.4 J/cm3/KAre you sure it isn't the water in the hydrated from actually giving the additional heat capacity.
Posted Tuesday 7 Sep 2010 @ 3:16:28 am from IP # -
Benny
MemberI think I saw the same house plans you did moisiemo - the US professor with several house retrofits including the cylinders with glaubers. I was thinking that an alternative use of the gyprock sheet material would be to make a box with multiple layers of the sheet, separated by say 10mm spacing, so that warm air could flow through easily and the volumetric heat capacity would be quite high. If 10mm of sheet is like 100mm of concrete then a 200mm wide box at 50% fill capacity would be like 1m of concrete. Still this would need active air flow unlike your "cylinders sitting in the sun" idea.
The stacked gyprock idea might be a nice clean easy to make alternative to rock piles and water tanks as heat storage.Posted Wednesday 8 Sep 2010 @ 2:23:17 am from IP # -
Eco
MemberThe latent heat of fusion of Glauber's Salt is about 254 kJ/kg with a phase change temperature of around 32 degrees C - http://www.cibse.org/pdfs/Latent%20heat%20storage.pdf. This is the energy storage as the material changes phase from solid to liquid. This heat can then be released as the material changes back to solid. So potentially a lot more heat storage than water over a limited temperature range - provided the phase change temperature is included in the range.
Posted Wednesday 8 Sep 2010 @ 10:28:12 am from IP # -
moisiemo
MemberIndeed you would need to keep it out of the sun in summer dymonite - which is part of a passive solar design. The house we are building will have eaves wide enough to block out the summer sun. Thanks for your input btw - this is a very steep learning curve for me!
Cheers, GraemePosted Wednesday 8 Sep 2010 @ 11:07:20 pm from IP #
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