Our solar shop heating collector built back in 2003 has worked well, but, as always, there are a few things we might do differently -- this page lists changes I'd consider if starting over.
Back to the shop heating collector main page...
The picture to the right (from the Home Power article) shows a cross section of the collector. The absorber is the black dotted line. It actually consists of two layers of black aluminum insect screen. I would make these two changes:
I would tilt the absorber screen so that it starts out
further away from the glazing at the bottom and ends closer to the glazing at
the top. The idea here is that all of the air is on the glazing side
of the screen at the bottom of the collector, so the flow path should be deeper,
and at the top its just the opposite.
I would move the bottom of the screen to about 1 inch from the back wall, and move the top of the screen to about 1 inch from the glazing -- these are just guesses.
On the current version the two layers of screen are not separated -- they are in direct contact with each other. I would space the two layers of screen a bit (3/8 inch?) apart from each other. The idea is that this would allow easier airflow around the screens and improve the heat transfer.
I don't have any real data that says either of these two changes will actually improve performance, but they seem sensible, and they don't really add much work. I may change one bay to use this new construction later this winter and actually compare.
I would consider using the twinwall polycarbnate glazing instead of the SunTuf glazing. This is by no means necessary, as the SunTuf performs quite well.
The reasons I would consider making this change are:
I would consider adding an inlet filter on each inlet vent if your collector is in a dusty area. From this testing, it appears that a relatively open inlet filter will not affect performance by very much.
My collector is 9 winters old, has no inlet filters, and this does not appear to be a problem. There is a bit of dust accumulation on the bottom of the collector, but the screens appear to be relatively free of dust.
The top sill of the collector should have metal flashing that starts under the siding just above the top sill, and then extends out onto the sill a couple inches. This would insure that rain does not get into the collector or rot the top sill.
I don't have this flashing and its not been a problem, but our climate is very dry.
The horizontal glazing supports that run horizontally just behind the glazing at the 1/3rd and 2/3rds points were made from 1 by 1's on the original collector. I have since found that half inch EMT galvanized electrical conduit works better for these supports. The EMT is very cheap, straight, and comes galvanized -- its available at any big box (or little box) hardware in the electrical section.
I would work out a way to incorporate some additional glazed area in the back wall of the collector that would let more daylight into the shop.
My other shop (everybody has two?) uses this collector setup... A set of glazed doors was added outside the regular panel garage door, so that when the door is up, the added set of glazed doors make a large solar collector. They not only let in solar for heating, but the lighting is really nice. I like this lighting so much that I'm planning to add some glazed panels to the thermosyphon collector to improve the light levels in the barn/shop.
If anyone has ideas on how best to incorporate more glazing in the collector back for daylighting, I'd really like to hear them.
The collector outlet vents are up near the ceiling, and the hot air coming out them tends to stay up near the ceiling. Its good to have some way to mix up the air in order to make better use of this hot air near the ceiling.
I'm currently using a PV power attic ventilation fan that I bought for another project to do this, and it works pretty well. A low power ceiling fan would likely also work well. Anything that keeps the air a bit stirred up should work fine.
Paul House, who is now offering a commercial version of this collector, has suggested that a large hole saw might be used to cut the inlet and outlet vent holes. This would save some time and probably look better. I did some testing on this, and while there is some performance hit, and 8 inch round vent hole could be used with an about 19% drop in heat output. I don't know if larger hole saws are available, but a 9 inch hole saw would probably reduce the performance hit to zero.
January 5, 2012