[Greenbuilding] Hydronic Radiant Underfloor Heating

[Chris Green]

Gary Viljoen wrote:
> Thank you all for the quick response.
>
> To clarify:  
>
> By 'polystyrene' I mean compressed foam boards used for insulation.  Is that
> what you are referring to as 'rigid insulation'?
>   
Yes.
> And does your 'poly' refer to thin plastic waterproof sheeting instead?
>   
Yes. Short for polyethylene.
> So, if I'm correct and working from bottom to top, I start with:
>
> 1. Well compacted and level base, then
> 2. Compressed foam/rigid insulation layer on top (with an additional strip
> running along the foundation walls), then
> 3. Plastic waterproof sheeting on top of this, then
> 4. Steel mesh positioned at approx 40mm above this waterproofing layer
> 5. Hydronics piping tied directly onto the mesh, then
> 6. Concrete surface bed poured over this, then
> 7. Screed to follow
>
> Please let me know if that sounds right.
>   
Yes.
> Any ideas for a 'greener' product to use for the under-slab insulation
> (greener than the compressed foam - polystyrene - insulation)? 
I can't think of any at this time.
Some people will suggest you can leave the insulation out and use the 
earth under the slab as  thermal mass storage. Others will argue against 
this because the heat will flow out beyond the building and you just  
wind up heating up a lot of ground around the house ( and any water 
flowing by) and you will end up using more energy in the long run than 
what it takes to make the insulation.
My instinct would be to use the insulation.
> Also I would like some input on how to lay the pex piping.  What is the
> optimum length per square meter? Meandering pipes or tight turns??
>   
I'll defer on answering that other than to suggest that one shouldn't 
run the tubes under the fridge or deep freeze. There are some list 
members who work with this stuff for a living and can better answer that.
There are probably some guidelines to study and might even be some 
software you can download to help plan the layouts and keep the runs 
about the same length, but I haven't gone looking for it.

The hydronics links I have in my files are:
http://www.radiantandhydronics.com/CDA/
http://www.healthyheating.com/
http://www.radiantdesigninstitute.com/page32.html
I haven't poked around this one much, but the above page has some 
illustrations. Note the one showing the insulation on the outside of the 
foundation ( a practice sometimes called exulation.).
> Gary
>
> Ps: By the way, life in Cape Town is magnificent this morning!!
>   
You must be getting into Spring down there. Someone sent me photos of 
when your bay froze a few months ago. Impressive. The bay looked like a 
really big Slushy...


Cheers,

Chris Green.