I post a question here for those vastly more knowledgeable than myself about thermal gain, loss and transfer.
A pal has a barn with a small 1 room living studio at the end. Barn faces south, has a metal roof and the interior is not yet complete. We ran pex in the slab before the pour and insulated w/ 2″ styro below.
Question? Can he expect to reasonably increase the performance of his radiant slab system by running copper piping or thin fin style diffusers beneath the s. facing metal roof and insulating below to try to capture that heat and transfer it in to his gas fired hot water tank fueled radiant system.
I am sceptical but he feels that he is missing a good opportunity to capture a good free heat source. Cold climate area around Albany NY.
Any one care to chime in ??
Thanks
Jim
Replies
I suppose it could be done, but you'd need controls to cut the loop out overnight, on sunless days or when the temp of the rest of the system is higher than the temp in the roof loop - otherwise, you'll just wind up heating the roof, not vice versa.
If he wants heat from the roof, probably better to use a conventional collector.
Mike Hennessy
Pittsburgh, PA
Everything fits, until you put glue on it.
I assume you mean one mounted on the outside collecting solar ?
Lets say that although this structure was dutifully inspected and is legit, at one time it looked like a 4 stall carriage barn it now resmbles a 3 stall barn with a cute little apartment on the end that does not wish to draw the attention of anyone. Needless to say I had suggested that but he wants it to be inconspicuos.
Thanks Mike.
Yep. Store-bought.
Don't forget that you will probably want/need to ventilate under the roof to deal with condensation, so that'll further erode the minimal heat gain you might get from this setup.Mike HennessyPittsburgh, PAEverything fits, until you put glue on it.
You describe a solar collector ... which if not in a box w/ a cover (glass), will not do very well for your purpose. Mounted inside behind the window, maybe. But you would also have to coat it w/ a low-e black coating (like they do on solar collectors).
While your concept idea holds water (nyuk), it really won't work very well in your application w/out some significant modifications/improvements to your idea. If you feel the need to push the idea, you need to work on details.
Me -- I didn't describe anything. I think you meant to send that to the OP.Mike HennessyPittsburgh, PAEverything fits, until you put glue on it.
woody.
freezing? In cold weather the risk of freezing offsets possible thermal gains.. Now you can minimise freezing problems with antifreeze but that adds further complicationsIncluding the fact that antifreeze reduces heat transferance.
You'd have a very narrow window on bright sunny days in the winter when the thermal gains would offset the thermal losses. No advantage during cloudy or at night..
I suspect the net would be a loss not a gain.. Calculations are available..
Description of the set up as imagined by he in question.
Thanks, I am planing to put a circuit of copper pipes between the Green metal roof and the purlins on which that roof rests( there are 8 "bays" made by the 2X4's, if you will, about 2' apart). The insulation below the 2X's will trap a relatively hot cavity of air and radiate to the tubes, fins from a radiator arraignment will augment the pipes, then collect in a manifold to go to the PEC tube embedded floor when it is hot enough and the furnace( your old hot water heater) is not on. The roof faces South by south-east and in the winter gets about 4 hours of direct sun, more in the fall and spring(trees and sun angle). The space is about 18 ' wide and ridged 20" tube can be run into the purlins easily. The manifold can be constructed in the heated space or the garage and insulated as needed. I had thought of using PEC tubing but I don't think the heat transfer rate is great enough in a tube to air configuration.
He states it more clearly than I originally did.
these guys do that:http://www.dawnsolar.com/this is not an endorsement, I am skeptical myself, but if anyone knows what it does, they have more direct experience with it than most I imagine.-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
Rob
Thanks for the link.
There's a better way.
Make a duct or two, using the metal roof as one side of the duct. have openings to the room on both the 'uphill' and 'downhill' ends of the duct. Add dampers, and a thermostst-controlled fan at the exhaust end. Insulate around these ducts so they are outside the building's conditioned space.
The hot roof will heat the air within the ducts; when the ducts are hot enough, the fan kicks on and delivers hot air to the room. You can add a second thermostat to the room to keep this from happening if the room is already warm enough.
How well this works depends, in part, on how much higher one end of the duct is from the other. When you have this mounted in the wall, you often don't need a fan; it's amazing just how much heat you can capture this way.
I mis posted/directed this, I guess .... so in case you didn't read it ...
You describe a solar collector ... which if not in a box w/ a cover (glass), will not do very well for your purpose. Mounted inside behind the window, maybe. But you would also have to coat it w/ a low-e black coating (like they do on solar collectors).
While your concept idea holds water (nyuk), it really won't work very well in your application w/out some significant modifications/improvements to your idea. If you feel the need to push the idea, you need to work on details.