# Low Thermal Mass Sunspaces for Space Heating and Other Stuff



## GaryGary (Jan 20, 2013)

Hi,
I've been working on low thermal mass sunspaces for the last couple months and have become a real fan of them.  I think they might be the real gem of solar heating with lots of other side advantages.

http://www.builditsolar.com/Projects/Sunspace/sunspaces.htm#LowMassSS

It looks like they are as efficient at space heating as good commercial solar collectors while at the same time offering some additional space for all kinds of other activities.  They also can look really nice and might be an answer for people with picky HOAs.

Any thoughts on this?   

Gary


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## begreen (Jan 20, 2013)

If you have an opportunity to utilize the heat from a space like this that would be awesome. Looks pretty easy to construct. Just be sure to think about operation when it gets warmed outside of even hot.


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## Ehouse (Jan 21, 2013)

My home (under construction) has radiant floor (in concrete) extending into the sun space.  I anticipate being able to distribute the heat generated to the rest of the floor by simply running the circulators.  Not technically a low mass set up but an alternative to air distribution, sort of like an opened Trombe wall.  Insulated drapes for nightime.

Ehouse


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## GaryGary (Jan 21, 2013)

begreen said:


> If you have an opportunity to utilize the heat from a space like this that would be awesome. Looks pretty easy to construct. Just be sure to think about operation when it gets warmed outside of even hot.


 
I guess what really impressed me is that it did as well on heat production per sqft of glazing as very good commercial collectors -- and you can be sitting inside your collector having a cup of coffee while its collecting 

It does take off like a rocket when the sun is on it and the fan is off -- about 10F rise per minute.  It definitely needs good ventilation -- kind of like a greenhouse in the summer, but even more.

Gary


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## GaryGary (Jan 21, 2013)

Ehouse said:


> My home (under construction) has radiant floor (in concrete) extending into the sun space. I anticipate being able to distribute the heat generated to the rest of the floor by simply running the circulators. Not technically a low mass set up but an alternative to air distribution, sort of like an opened Trombe wall. Insulated drapes for nightime.
> 
> Ehouse


 
That's and interesting idea -- had not heard of that before -- seems it should work to me.
I guess you have it set up so you can run that loop independently of the rest?

Gary


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## Seasoned Oak (Jan 21, 2013)

Ehouse said:


> My home (under construction) has radiant floor (in concrete) extending into the sun space. I anticipate being able to distribute the heat generated to the rest of the floor by simply running the circulators. Not technically a low mass set up but an alternative to air distribution, sort of like an opened Trombe wall. Insulated drapes for nightime.
> 
> Ehouse


Wont ypu be giving back some heat when the sun goes down?


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## Seasoned Oak (Jan 21, 2013)

GaryGary said:


> Hi,
> I've been working on low thermal mass sunspaces for the last couple months and have become a real fan of them. I think they might be the real gem of solar heating with lots of other side advantages.
> 
> Any thoughts on this?
> ...


I achieved this very concept just by enclosing a south facing porch. I have 150SQ ft of south facing glazing ,floor to ceiling 6 windows 3x8Ft i bought at an auction for $360.  The space goes from outside temp to about 75 by 10 AM and if i dont open the door to the house it will go up to 100 Deg no matter the outside temps. It keeps the whole first floor about 80 degrees with no other heat source on a cold winter day. It usually takes until 9-11 PM before the temp goes down to 75 and the central heat kick on(we keep t warm)


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## Ehouse (Jan 21, 2013)

GaryGary said:


> That's and interesting idea -- had not heard of that before -- seems it should work to me.
> I guess you have it set up so you can run that loop independently of the rest?
> 
> Gary


It's a high mass house (ICF) with each floor a single zone.  There are 2 loops in the first floor however, splitting the kitchen/dining/sun space from the great room, so I can split the zone if need be.  The great room will have a recycled Tulikivi so this setup may work very well.  I can't take credit for designing it this way, it's just serendipity.  I'm one of those maniacs that reads a lot and does most things by dead reckoning, sometimes with interesting results.  The house is designed for heating with a (closed) pond loop GHP, but I'll certainly try it with the Tuli and solar before I hook it up.  Might get lucky!

Of course,  you wouldn't need a high mass floor in the sun space, maybe Gypcrete with a dark surface transitioning to something like Warmboard if you wanted a system with faster response.


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## Ehouse (Jan 21, 2013)

Seasoned Oak said:


> Wont ypu be giving back some heat when the sun goes down?


 
Sure, but my sun space isn't all that large ( about 12' across if I remember), and by closing the drapes and turning the circulator(s) off, I should have a net heat gain. Also, I had intended to use a light colored, tight to the edge, throw rug on the floor of the SS to help prevent over heating.  That should help a lot with heat loss also.


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## Seasoned Oak (Jan 21, 2013)

If you have some roof overhang ( i have about 18") you should get little to no sun in summer ,when you dont need it. I have grey/black floor tile over cementboard over T&G porch flooring. It heats up fairly fast and holds the temps above 70 for about 3-6 hours after sundown. I save the equivalent of 1 tank of heating oil per season just from this sunspace.


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## woodgeek (Jan 21, 2013)

A wacky idea....can I use a lightweight radiant floor product as the business part of a solar collector??  Anyone tried it?


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## Ehouse (Jan 21, 2013)

woodgeek said:


> A wacky idea....can I use a lightweight radiant floor product as the business part of a solar collector?? Anyone tried it?


 

If you mean a panel pre-routed for tubing you would probably want tighter tube spacing which would require sharper bends which would require smaller dia. tubing or fab'd joints.  You could pour a light-weight gypcrete type panel over a spiral/return spiral and eliminate that problem.  I don't know enough to say if such a mini Trombe would be better than a hot box collector, but it seems to me a bit of thermal mass in direct contact would help.


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## Ehouse (Jan 21, 2013)

Seasoned Oak said:


> Wont ypu be giving back some heat when the sun goes down?


 

After thinking about it, I probably wouldn't turn off the circ..  In a high mass situation like mine, you need to maintain constant temps.  The floor design temp is only 81 degrees and the house is superinsulated and tight so I expect the drapes and rug should handle it.  If I had designed for this I could have put the SS on it's own zone.  Do you have any insulation under your space?


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## Seasoned Oak (Jan 21, 2013)

I have  tool room under the space. Part of a finished basement.


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## mole (Jan 22, 2013)

woodgeek said:


> A wacky idea....can I use a lightweight radiant floor product as the business part of a solar collector?? Anyone tried it?


 
Not wacky at all.  Gary has a collector design based on pex tubing at Builitsolar.com with a lot of performance data.


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## woodgeek (Jan 22, 2013)

mole said:


> Not wacky at all. Gary has a collector design based on pex tubing at Builitsolar.com with a lot of performance data.


 
Yup. A few minutes googling found a lot of 'heat transfer plates' for sale for $1-3/sq ft, including at local big box stores, intended for 'staple up' radiant floor heat.  I've read through Gary's projects, but always hung up in folks making their own HTPs on a brake or with a hammer, seemed like a PITA.  At a couple bucks per square foot, I'll just go get them at Lowe's!


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## Seasoned Oak (Jan 22, 2013)

woodgeek said:


> Yup. A few minutes googling found a lot of 'heat transfer plates' for sale for $1-3/sq ft, including at local big box stores, intended for 'staple up' radiant floor heat. I've read through Gary's projects, but always hung up in folks making their own HTPs on a brake or with a hammer, seemed like a PITA. At a couple bucks per square foot, I'll just go get them at Lowe's!


Can you clarify? Heat transfer plates?are you talking about ceramic tiles?


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## GaryGary (Jan 22, 2013)

woodgeek said:


> Yup. A few minutes googling found a lot of 'heat transfer plates' for sale for $1-3/sq ft, including at local big box stores, intended for 'staple up' radiant floor heat. I've read through Gary's projects, but always hung up in folks making their own HTPs on a brake or with a hammer, seemed like a PITA. At a couple bucks per square foot, I'll just go get them at Lowe's!


 
Some info on the heat transfer fins for homemade collectors: http://www.builditsolar.com/Projects/WaterHeating/Fins/Fins.htm

I like the heat transfer plates that Tom makes -- they have nice, well formed grooves that fit the collector tubes well, and they 0.018 gage is also good for 6 inch wide fins, and they are competitive just buying the bare alum and putting the grooves in yourself.  Tom is a DIY solar guy who just took up building the fins out of the truck center he runs in Michigan UP.  His website is interesting and has some good DIY solar projects -- not to mention a world class wind turbine project.   He is listed at the link above along with a lot of other methods for making fins.

---
On the embedding tubing in the floor of a sunspace to collect heat for the house.  Kind of an unusual way to go -- a bit like a Trombe wall in that it can delay the transfer of the heat into the house a few hours -- on a really well insulated house that already has some passive solar gain, this delay might be a plus.   The embedded tubes would probably give you more control over how much and when the heat gets transferred into the house.  The down side of Trombe walls is that they lose quite a bit of heat to the outdoors, so they don't have a very good collection efficiency -- in the low twenty percents on the ones I've seen numbers on.   In the context of the low thermal mass sunspace, I think that another way one could go is to have mass in the sunspace that directly picks up heat during the day from the sun shining on it, and then has some type of movable insulation curtain that insulates it when the sun goes down and makes the heat available to the house.  Actually, a Trombe wall at the back of the LTM sunspace with an insulating curtain in front of it would work and would be pretty simple.

--
Got a note from Mike who did the nice LTM sunspace in CO that his kids are insisting that he add an elevated play platform in the sunspace with ladder -- he drew the line at adding a zip line 
Gary


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## woodgeek (Jan 23, 2013)

Seasoned Oak said:


> Can you clarify? Heat transfer plates?are you talking about ceramic tiles?


 
Gary's link shows em near the middle.  For a solar hydronic panel, folks use a Al plate wrapped around the tube.  I never realized there were commercial solutions....I thought I had to DIY the plates.


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## begreen (Jan 23, 2013)

precaud has added a couple of these low mass sun collectors to his house in NM. He gets a nice return from the system.


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