EcoRenovator - View Single Post - DIY heat pipe (evacuated tube type solar collector)

strider3700 · 01-13-11, 11:16 AM

true but you now need the collectors, tank, heat exchanger and all plumbing to be able to survive 350 degrees. That's going to force you into everything being copper and/or stainless steel. It might even require special valves for the turn offs.

Then there is the question of what to do with that heat?

You'll need some sort of control system that only pumps the oil into a heat exchanger only for short bursts to gradually heat whatever you want up since you can't just directly pump water through a heat exchanger in 350 degree oil. It would boil at first and if it did cool the exchanger enough to not be boiling it would still be amazingly hot and I'm not sure regular "inexpensive" tempering valves can handle beyond 160F or so.

If you where pumping the oil directly into radiators for space heating you have serious safety and fire risks if the rads are hitting 350.

you also have the issue of insulation on the tank and all plumbing. I had to track down polyisocyanurate for the back of my collectors and for around the tank since regular pink rigid insulation melts below 200. poyiso is only good to 300 or so is my understanding. If you can find insulation that will hold up due to the deltaT being so high compared to a 140F tank you're going to need a ton of insulation to make it effective.

Basically my point here is the cost of the materials will be insane vs a homebrew system using conventional materials like pex, off the shelf plumbing and the pond liner tanks. If you want to increase BTU storage go with a bigger tank...

Now if you where using that heat to turn a generator or something then oil is probably the way to go. Thats what the big solar heat power plants do. for space heating though you want about 180F for radiators, 90F for radiant and for domestic water 140F is just fine...

01-13-11, 11:16 AM	#10
strider3700 Master EcoRenovator Join Date: Dec 2008 Location: Vancouver Island BC Posts: 745 Thanks: 23 Thanked 37 Times in 30 Posts	true but you now need the collectors, tank, heat exchanger and all plumbing to be able to survive 350 degrees. That's going to force you into everything being copper and/or stainless steel. It might even require special valves for the turn offs. Then there is the question of what to do with that heat? You'll need some sort of control system that only pumps the oil into a heat exchanger only for short bursts to gradually heat whatever you want up since you can't just directly pump water through a heat exchanger in 350 degree oil. It would boil at first and if it did cool the exchanger enough to not be boiling it would still be amazingly hot and I'm not sure regular "inexpensive" tempering valves can handle beyond 160F or so. If you where pumping the oil directly into radiators for space heating you have serious safety and fire risks if the rads are hitting 350. you also have the issue of insulation on the tank and all plumbing. I had to track down polyisocyanurate for the back of my collectors and for around the tank since regular pink rigid insulation melts below 200. poyiso is only good to 300 or so is my understanding. If you can find insulation that will hold up due to the deltaT being so high compared to a 140F tank you're going to need a ton of insulation to make it effective. Basically my point here is the cost of the materials will be insane vs a homebrew system using conventional materials like pex, off the shelf plumbing and the pond liner tanks. If you want to increase BTU storage go with a bigger tank... Now if you where using that heat to turn a generator or something then oil is probably the way to go. Thats what the big solar heat power plants do. for space heating though you want about 180F for radiators, 90F for radiant and for domestic water 140F is just fine...