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More thermal system questions.

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Posted by john on July 23, 2008, 2:36 am
Thanks to all that responded to my last post (Heating a green house at

I'm still fishing for info although I have started ground breaking;

Is a thermostatically controlled diverting valve optimal or overkill for
controlling supply temp from the collector; is a manual diverting valve
or even just a circuit setter sufficient?  My thoughts lean toward the
controlled diverting valve.

Should the target be a larger volume of lower temp water or a lower
volume of higher temp?  My thoughts lead me toward generating the most,
hottest water the system is capable of, but I do see trade-offs.  The
panels should have more capacity at lower delta T.

Debating forced warm air vs under floor radiant delivery system (good
understanding of forced air; know little or nothing about underfloor
radiant.)  From what little I do think I know, I like the simplicity of
the radiant... I'm just warming plants.

Considering building an oversize tank (from build it solar) and filling
with the amount of water I need.  (could help off-set really bad
roundoff error...)  Drafting from and returning to the tank below the
water line should help offset pump load.

Got any good leads on designing and building an underfloor radiant heater?

Know a good nontoxic (food grade) antifreeze?

BTW, what typical flows and delta T are to be expected from typical
thermal panels?  I was getting an estimated 10k BTU/h each the other day
just sitting flat on saw horses in the back yard (two panels parallel at
1+ gpm yielding 40+ delta T.)  But in Dallas, TX in July on a Sunny day,
  you can fry an egg on a rock...


Posted by Tommy on July 25, 2008, 3:19 pm


Propylene glycol heat transfer fuild.
Non-toxic - 60*f protection
food grade corrosion inhibitors.

I'm  a maint. mech. working with industrial machinery, and most
everything used has to be food grade.

Hope this helps with one of your questions.


Posted by john on August 3, 2008, 3:22 pm

Thanks for the info.


Tommy wrote:

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