9/ 11/13 Construction of a sol ar ai r heating c ol l ect or using a f l ow through screen absorber www. buil ditsolar.com/Ex periment al/ Ai rColTesting/ScreenColl ect or/Buildi ng.htm 1/6 Building the Aluminum Window Screen Solar Air Heating Collector This is part of a program to test several solar air heating collector designs for performance... This collector desi gn uses three layers of ordinary aluminu m window (insect) screen l as the ab sorber. The air enters at the center bottom of the collector, where an aluminu m baffle spread s the flow across the width of t he collector on th e glazing sid e of the screen absorber. The air rises up between the glazing and the abso rber, and eventually finds i ts way throu gh the three layers of screen ab sorber a nd flows to th e back si de of the collector. The air then f lows up th e back si de of the collector to the exit vent l ocated a t the top of the collector. The design is similar to the vented aluminu m soffit absorb er collector, and uses pretty much th e sa me collector geo metry, but su bstitutes the three layers of wind ow screen for the vented aluminum soffit as the absorber. NOTE: Some of the testing was d one with this collector that has an absorbe r made from 3 layers of screen, but the screen collector used as th e "reference" collector i n the later part of the testing seas on used only 2 layers of screen. Back to the Solar Air Heating Collector test program home.. The test collector was derived from the aluminu m soffit collector. The changes made were to: - Remove the aluminum soffit absorber, and substitute the 3 layers of scree n that were spaced about 0.4 inches apart from each other. - Add about 1 inch to the collector depth to accommodate the thicker screen absorber. The screen absorber sits on the same supports that the soffit absorber was installed on -- so, the flow passages above and below the absorbe r are the same depth on the soffit collector and the screen collector. The Collector Box The first part of the construct ion is the same as the Reference collector-- I basically built a box with an insulation board ba ck, 1 by 6 si des, and 2 b y 6's for the top and bottom si lls as shown ju st below. Home Getting Started Projects References Half Program Experimental Site Map Search The Renewable Energy site for Do-It-Yourselfers
Transcript
7/29/2019 Construction of a Solar Air Heating Collector Using a Flow Through Screen Absorber
Building the Aluminum Window Screen Solar Air Heating Collector
This is part of a program to test several solar air heating collector designs for performance...
This collector design uses three layers of ordinary aluminum window (insect) screen l as the absorber.
The air enters at the center bottom of the collector, where an aluminum baffle spreads the flow acrossthe width of the collector on the glazing side of the screen absorber. The air rises up between the
glazing and the absorber, and eventually finds its way through the three layers of screen absorber and
flows to the back side of the collector. The air then flows up the back side of the collector to the exit
vent located at the top of the collector.
The design is similar to the vented aluminum soffit absorber collector , and uses pretty much the same
collector geometry, but substitutes the three layers of window screen f or the vented aluminum soffit as
the absorber.
NOTE: Some of the testing was done with this collector that has an absorber made from 3
layers of screen, but the screen collector used as the "reference" collector in the later part of the
testing season used only 2 layers of screen.
Back to the Solar Air Heating Collector test program home..
The test collector was derived from the aluminum soffit collector . The changes made were to:
- Remove the aluminum soffit absorber, and substitute the 3 layers of screen that were
spaced about 0.4 inches apart from each other.
- Add about 1 inch to the collector depth to accommodate the thicker screen absorber.
The screen absorber sits on the same supports that the soffit absorber was installed on --
so, the flow passages above and below the absorbe r are the same depth on the soffit
collector and the screen collector.
The Collector Box
The first part of the construction is the same as the Reference collector -- I basically built a box with an insulation board back, 1 by 6 sides, and 2 by 6's for the
top and bottom si lls as shown just below.
Home Getting Started Projects References Half Program Experimental Site Map
SearchThe Renewable Energy site for Do-It-Yourselfers
For the screen collector, you need the dimension from the back of the glazing to the bottom of the box to be about 5 inches. Since I was starting from the Soff
Collector collector, which was only about 4 inches deep, I added an inch of depth by gluing on one inch wide strips to the sides and top and ends. This extra
inch just accommodates the thicker screen absorber -- the screen absorber sits on exactly the same absorber edge supports as the soffit absorber did.
VentsYou can also see that the collector I started with had i ts vents on opposite corners, and since the screen and soffit collectors want vents on the centerline, I filled
the old vent holes in with insulation plugs and Great Stuff, and cut new vent openings on the centerline.
This is one of the new 6 inch diameter centerline vents.
Shows the two new centerline vents and the two old vents before they were
plugged.
All the vents are foamed in place with Great Stuff to avoid leaks.
Absorber The screen absorber is far from the glazing at the bottom of the collector (where air enters), and is close to the glazing at the top of the collector where air exits
The idea is that most of the flow is on the glazing side near the inlet end of the collector, and most of the flow is on the back side of the absorber near the outlet
end of the collector, so sloping the absorber allows the depth of the flow path to match the flow rate.
Absorber AssemblyThree pieces of Charcoal aluminum insect screen for windows are cut out to just fit inside the box. The three pieces are spaced 3/8 inch from each other by
wood spacers that make a sort of picture frame around the screen. So, the stack up from the bottom is: 1) window screen layer 1, 2) 3/8 inch spacer board, 3
window screen layer 2, 4) 3/8 inch spacer board, and 5) window screen layer 3 on top. Total thickness of the absorber assembly is close to an inch. (Note tha
for the two screen version, the stackup is the same except that the 3rd layer of screen is omitted).
Corner of the frame for the 3 layer screen Cutting the screen to size.
The screen is then just stapled to the edge frame.
The finished 3 layer screen
I supported all edges of the screen absorber with wooden strips as shown in the next pictures. These are the same strips that supported the soffit absorber.
The absorber support strips being attached to the collector box sides.
The depth from the top of the strip to the back of the box is 3 inches on the outlet end of collector, and half an inch near the bottom end of the collector. This
means tapering the support strip down to half and inch on the inlet end.
These pictures are from building the collector that uses aluminum soffit for the absorber, so you see pieces of soffit in the picture, but installing the vents is the
same for the screen absorber collector.
Inlet Vent Detail
This half inch plywood spaces the bottom of the screen a bit off the bottom of the collector box, and provides a base to staple the screen to where the screen is
penetrated by the inlet vent (see below). It is just held in place with Great Stuff foam.
The screen absorber assembly has been set in place, and
a knife is used to cut a hole in the screen for the inlet vent
to come through.
The inlet vent is cut to make tabs that are then folded
down on top of the screen.The inlet vent tabs screwed down i
absorber support strips.Push the frame outward to put tension
on the screen, and then nail or screw the
absorber frame to the absorber support strips.The absorber assembly installed in
Install the baffle plate that spreads the flow from the inlet across the width of the collector. This is the same baffle plate that was used in the soffit collector. The
purpose of the baffle is to spread the incoming air out over the full width of the collector and to keep the inlet air from impinging directly on the glazing (which
would result in a lot of heat loss).
Install the Glazing
Install the SunTuf glazing. Suntuf glazing is corrugated polycarbonate. It transmits 90% of sunlight, has a high temperature capabili ty, and is very tough. Home
Depot is one of the retailers that carry it.
Be sure to install at least one glazing support bar to keep the glazing from buckling excessively as it heats. I used scrap copper pipe for the support in this case
but half inch galvanized EMT conduit is fine.
A bead of silicone under the corrugation close out
In this case, I used half inch EMT metal conduit to clamp the edges
of the glazing panels to the collector box. This was mainly to make it
easier to quickly take the glazing on and off the box, and at thesame time insure a good tight seal between the glazing and the box.
There is a strip of EPDM rubber roofing membrane between
the glazing and the collector box.
This shows the PVC "wood" compression bar used to press the
corrugations tightly into the foam closeout strips.
I should point out that these are collectors I'm building only for test purposes. For permanent collectors, I'd give more thought to the life of the collector.
Some people feel that wood should not be used in collectors as i t may limit the life of the collector. I'm not so sure about this as my 6 year old large wood
collector looks as good inside and out as the day it went up. It probably depends on your local climate, and the details of how the collector is mounted. I do
think that using deck "wood" or PVC "wood" for the external batten strips that hold the glazing down is a good idea as the glazing batten strips take a lot of
weather -- the 6 year old deck wood batten strips on my Solar shed collector are still like new.
If you do use wood construction be sure to think about the details, don't let water penetrate the collector, be certain to prime and then follow with two coats of
good exterior paint, and keep an eye on the collector for signs of needing maintenance over the years -- take care of it like you do your house. If you feel more
comfortable with metal construction, then by all means build the collector from metal.
Gary January 12, 2011
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