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Intro
I've gleaned a lot of info off this board. Now it's my turn to share.
My system circulates crawl space air. I insulated my crawl space walls, put 6 mil plastic on the floor and have over half of it covered in 6”-thick faced fiberglass insulation.
Site
I live in Fort Collins, CO. Collector location is on back of house and is within a few degrees of due SE.
I added attic insulation to R-60.
Two Big Mistakes
One big mistake was using vinyl screen. Don't do it. I had to rip it out and replace it with aluminum screen. The vinyl out-gasses when it gets hot and stinks strongly. It had the appearance of condensation on the inside of the glazing. Bad news.
The second big mistake was using polycarbonate for glazing. My panel goes to at least 270F on stagnate. So if your fan shuts off for any reason while the sun is shining then you're in big trouble. The max long-term temp rating on Suntuf is 212F. Even in operation the panel temperature can approach this. Damage caused by overtemp looks to me like UV damage---cracking and breaching. With much hassle I replaced the polycarbonate with single pane tempered glass. Three sheets are textured solar glass re-purposed from hot water panels that I found on Craigslist. The rest are standard tempered glass sheets. The solar glass is cooler to the touch than the standard glass.
Lessor Mistake
I used 2x6s for the frame ripped to 60 degrees on both long sides. This was a waste and 2x4s non-ripped would have been better.
Paint
One poster mentioned that if you purchase charcoal aluminum screen then you won't have to paint it. I found this to be incorrect as the flat black grill paint is blacker than the charcoal aluminum screen. I had to disassemble half of the panel to paint my charcoal screen flat black.
Collector Size
Just over 100 sq ft. and my house is 1056 sq ft. I use a 424 cu ft fan rated at 284F and 6” ductwork. The 6” ductwork was necessary to fit inside a bedroom closet. I'm certain that 8” ductwork would have worked better had I had the room for it. I have dampers on both ports and the ductwork is insulated in the closet, as through the wall.
Cost
Probably around $500.
Performance
I am thrilled by the performance of this system. Even on the coldest days, as long as the sun is shining, my crawlspace, joists and flooring material become a thermal battery releasing heat long after the sun goes down. My forced air furnace does not run as long as the sun is shining no matter how cold it is outside and often not until early morning hours.
The temperature gain in the panel is 70--130F depending on how cold it is outside. It's easy for the working temperature in the panel to be 200F.
Energy Savings
My gas co. tells me both my current usage and usage over the same period a year earlier.
I've had a couple bills indicating a colder average temperature for the month yet I'm still saving 25% on therms used.
Fabrication
Build the frame according to the sizing of the glass you procured.
1” poly iso inside the frame against the house.
2 layers of screen carefully spaced, painted flat black on both sides. This is important as I understand it, since not only is heat absorbed best into flat black, but heat is released best on a flat black surface as well.
I run my fan at 110V as at 120V I had a thermal shutdown on a warmer Spring day (if you're using polycarbonate it just got trashed).
90/110 snap switch is working well but I might consider a warmer one like 95/115 or whatever so cooler air is terminated sooner at the end of the solar day.
I'm using a thermal snap switch, variac, relay (RIB relays are excellent) and 24VDC transformer.
On cloudy days I can turn the fan speed down to keep the heat up inside the collector so it doesn't shut off.
K-type thermocouples x 4. One on the collectors inlet and one on the collectors outlet. These are connected to a dual thermocouple unit so I can easily T1-T2 to find the temperature gain in the collector.
Then two different places in the crawlspace.
The fan is on the collector's supply, sets in the crawlspace and sucks air through the collector providing a negative pressure.
Future Improvements
I'm considering replacing the thermal snap switch, variac, relay and transformer with the Nimbus Smart Fan Controller. We'll see if I get there as I'm getting pretty tired of this project. I'm not certain it will control this fan either.
Covering For Summer
I don't want this hot air collector to stagnate at 270 degrees or greater. I think the polyiso has a limit of 300 degrees before it starts breaking down. After a lot of soul searching I decided to use 1/2” polyiso sheets to cover the panel in Summer. The polyiso is more rigid than plywood and is light. I'm planning on using 3/4” sticky white Velcro to attach the polyiso perimeter to the glass. I'm thinking of adding a thin bead of silicon caulk to the Velcro attached to the glass since the silicon should hold up to the temperature extremes a whole lot better.
Pointers
Get an idea of where your collector will go and find the glass first. Check craigslist and like sources.
Once you have the glass, build the collector accordingly.
IMG_0006_1000.jpgIMG_0004_1000.jpgIMG_0003_1000.jpgIMG_0008_1000.jpgIMG_0007_1000.jpg
I've gleaned a lot of info off this board. Now it's my turn to share.
My system circulates crawl space air. I insulated my crawl space walls, put 6 mil plastic on the floor and have over half of it covered in 6”-thick faced fiberglass insulation.
Site
I live in Fort Collins, CO. Collector location is on back of house and is within a few degrees of due SE.
I added attic insulation to R-60.
Two Big Mistakes
One big mistake was using vinyl screen. Don't do it. I had to rip it out and replace it with aluminum screen. The vinyl out-gasses when it gets hot and stinks strongly. It had the appearance of condensation on the inside of the glazing. Bad news.
The second big mistake was using polycarbonate for glazing. My panel goes to at least 270F on stagnate. So if your fan shuts off for any reason while the sun is shining then you're in big trouble. The max long-term temp rating on Suntuf is 212F. Even in operation the panel temperature can approach this. Damage caused by overtemp looks to me like UV damage---cracking and breaching. With much hassle I replaced the polycarbonate with single pane tempered glass. Three sheets are textured solar glass re-purposed from hot water panels that I found on Craigslist. The rest are standard tempered glass sheets. The solar glass is cooler to the touch than the standard glass.
Lessor Mistake
I used 2x6s for the frame ripped to 60 degrees on both long sides. This was a waste and 2x4s non-ripped would have been better.
Paint
One poster mentioned that if you purchase charcoal aluminum screen then you won't have to paint it. I found this to be incorrect as the flat black grill paint is blacker than the charcoal aluminum screen. I had to disassemble half of the panel to paint my charcoal screen flat black.
Collector Size
Just over 100 sq ft. and my house is 1056 sq ft. I use a 424 cu ft fan rated at 284F and 6” ductwork. The 6” ductwork was necessary to fit inside a bedroom closet. I'm certain that 8” ductwork would have worked better had I had the room for it. I have dampers on both ports and the ductwork is insulated in the closet, as through the wall.
Cost
Probably around $500.
Performance
I am thrilled by the performance of this system. Even on the coldest days, as long as the sun is shining, my crawlspace, joists and flooring material become a thermal battery releasing heat long after the sun goes down. My forced air furnace does not run as long as the sun is shining no matter how cold it is outside and often not until early morning hours.
The temperature gain in the panel is 70--130F depending on how cold it is outside. It's easy for the working temperature in the panel to be 200F.
Energy Savings
My gas co. tells me both my current usage and usage over the same period a year earlier.
I've had a couple bills indicating a colder average temperature for the month yet I'm still saving 25% on therms used.
Fabrication
Build the frame according to the sizing of the glass you procured.
1” poly iso inside the frame against the house.
2 layers of screen carefully spaced, painted flat black on both sides. This is important as I understand it, since not only is heat absorbed best into flat black, but heat is released best on a flat black surface as well.
I run my fan at 110V as at 120V I had a thermal shutdown on a warmer Spring day (if you're using polycarbonate it just got trashed).
90/110 snap switch is working well but I might consider a warmer one like 95/115 or whatever so cooler air is terminated sooner at the end of the solar day.
I'm using a thermal snap switch, variac, relay (RIB relays are excellent) and 24VDC transformer.
On cloudy days I can turn the fan speed down to keep the heat up inside the collector so it doesn't shut off.
K-type thermocouples x 4. One on the collectors inlet and one on the collectors outlet. These are connected to a dual thermocouple unit so I can easily T1-T2 to find the temperature gain in the collector.
Then two different places in the crawlspace.
The fan is on the collector's supply, sets in the crawlspace and sucks air through the collector providing a negative pressure.
Future Improvements
I'm considering replacing the thermal snap switch, variac, relay and transformer with the Nimbus Smart Fan Controller. We'll see if I get there as I'm getting pretty tired of this project. I'm not certain it will control this fan either.
Covering For Summer
I don't want this hot air collector to stagnate at 270 degrees or greater. I think the polyiso has a limit of 300 degrees before it starts breaking down. After a lot of soul searching I decided to use 1/2” polyiso sheets to cover the panel in Summer. The polyiso is more rigid than plywood and is light. I'm planning on using 3/4” sticky white Velcro to attach the polyiso perimeter to the glass. I'm thinking of adding a thin bead of silicon caulk to the Velcro attached to the glass since the silicon should hold up to the temperature extremes a whole lot better.
Pointers
Get an idea of where your collector will go and find the glass first. Check craigslist and like sources.
Once you have the glass, build the collector accordingly.
IMG_0006_1000.jpgIMG_0004_1000.jpgIMG_0003_1000.jpgIMG_0008_1000.jpgIMG_0007_1000.jpg
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