TOOLS, CONSTRUCTION, ALTERNATIVE ENERGY > Alternative Energy
Passive Solar Collector
moto123:
A couple suggestions:
1. You need to be able to seal off the solar unit from the room at night time. Otherwise all your heat gained during daytime will be lost at night time when it gets cold outside and the process reverses.
2. This system was designed to work with an existing double hung window. For better performance, the cold return duct would be connected at the bottom of your conditioned room to pull the coldest air off the floor. It would then be routed flat to the bottom of the solar heater. This would require an additional floor or wall penetration.
Flyin6:
--- Quote from: moto123 on December 13, 2016, 02:23:53 PM ---A couple suggestions:
1. You need to be able to seal off the solar unit from the room at night time. Otherwise all your heat gained during daytime will be lost at night time when it gets cold outside and the process reverses.
2. This system was designed to work with an existing double hung window. For better performance, the cold return duct would be connected at the bottom of your conditioned room to pull the coldest air off the floor. It would then be routed flat to the bottom of the solar heater. This would require an additional floor or wall penetration.
--- End quote ---
OK, based on the little I have read so far: Responses in red
1. You need to be able to seal off the solar unit from the room at night time. Otherwise all your heat gained during daytime will be lost at night time when it gets cold outside and the process reverses.
This is true. However there are more factors to consider here. The first being the principal of therman mass. Big thick, dense things collect and store long wave radiation like sunlight and collect ambient heat or cold. Basically they work to egual the temp. So if a bit of warm air is circulating about the cooler thermal mas pulls in that heat.
Know what a good thermal mass collector is? A big tank of water is a great one. So the working theory in my unstable brain says that if I can use a big delta of heat over ambient during the day, to warm up the big thing which is a 330 gal tank of water, then that big thing will radiate the heat in short wave radiation for much longer...i.e. over the night. So open or close the clod would have a harder time making a big mass cooler, that the effort of collecting heat during the day that occurred.
2. This system was designed to work with an existing double hung window. For better performance, the cold return duct would be connected at the bottom of your conditioned room to pull the coldest air off the floor. It would then be routed flat to the bottom of the solar heater. This would require an additional floor or wall penetration.
I think I'll build mine a bit differently. I was thinking I'd have a port at the top which connected to the water tank box, and on the bottom of the unit run a few air duct lines which originates from the bottom of the water containment box. So, yes it requires openings in the top and bottom to work properly, with the lower inlet connected to the heated space to be most efficient
Wilbur:
I think some of those pics are the exact ones I modeled mine after....got it from Mother Earth News.
I used one of those corrugated Plexiglas panels for the clear stuff, and plywood for the rest. I didn't have it all the way up into the window so I ran two small 4" stove pipes as the input and output. that went into a box I made for the window. I then just used louvered round vents for input and output and had them turned away from each other. The thing I found was that the air didn't move fast enough on its own so I put a small fan in (a small computer fan would work) for the output side (inside the box) to blow the hot air out, that also created the suction to pull in cold air.
Like I said it would raise the temp of the air 70 degrees even with the fan on it which was pretty good. I was really proud of my invention and if my house didn't face directly south I would still be using it. But the wife thought it looked ridiculous and made me get rid of it. No sense of humor in some people.... ::)
I was going to move it to the side of the deck (I had originally built it to be turned on its side) but that's right by the furnace output blower so I decided that potentially killing my family probably wasn't worth it. I will likely install it in/on my shed which I want to use for some projects.
moto123:
Yes a large thermal storage (water tank) will hold heat. But it will also hold cold, or lack of heat. The same amount of heat energy that allows it to stay warm all night is equal to the amount of "lack of heat" that it also holds during the morning hours of the day. The storage volume does not create heat, it only acts as a flywheel on the system, slowing down the rate of change.
None of this is related to closing off the solar collector at night. That was just a suggestion to make it more efficient. You would have to run a calculation to compare heat gained from radiation versus heat lost from conduction and convection to determine how much closing and then opening the ducts daily would help. If you don't want to close off the solar collector, then make the collector bigger and insulate it very well. The increase in size will output additional heat during the daytime to offset the loss of heat at night time. This has nothing to do with storage volume, it is purely the difference between heat gained and heat lost. We need to make sure the net result is positive heat gain.
moto123:
--- Quote from: Wilbur on December 13, 2016, 04:06:19 PM ---The thing I found was that the air didn't move fast enough on its own
--- End quote ---
This is caused by the fact that the supply duct at the top of the collector is short. If you were able to increase the length of this duct upward before the air outlet, you would see an increase in air flow. This is due to the stack effect, also known as draft. The same principle is applied to fireplaces and other appliances that heat air. The farther the flue or chimney extends above the heat source, the greater the air flow.
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