Aluminum Hybrid Collector

An Experimental Copper/Aluminum Solar Water Heating Collector

These pages cover an experimental solar collector for heating water that usesaluminum heat absorbing fins and copper pipes for conveying the heat transferfluid. The key to good performance in this design is a good thermal connectionbetween the aluminum fin and the copper pipe -- a lot of attention is given toproviding this good thermal bond. The aims of the collector are to: 1) performance that is very close to commercialcollectors, 2) low cost - perhaps a quarter of commercial collectors, 3) long life,and 4) easy construction using readily available materials.

Directory

Copper/Aluminum Collector Concept Construction Details Performance Cost of Collector Overheating Protection Drainback Conclusions Additional Possibilities A Solar Water Heating System using this Collector Galvanic corrosion...

Copper/Aluminum Collector Concept Solar water heating collectors are used to heat water for domestic use and also to provide hot water for space heating. The most commoncommercial collectors consist of copper fins that are soldered or welded to copper pipes. In operation, the sun heats the fins, which in turntransfer their heat to the copper pipes and then to the water flowing through the pipes. This is a good design that works efficiently and has along track record. But, the design, does have some drawbacks from a build-it-yourself viewpoint: 1) the materials have become veryexpensive, 2) soldering or welding the copper pipes to the fins is time consuming and not a common DIY skill.

Note that the recent drop in copper prices have made thecopper collector more attractive.The copper collector now costs about $5 per sqft compared to the$6 per sqft when this was first written.April 4, 2009

This design uses aluminum fins instead of copper fins over a grid of copper pipes. Since the thermal bonding of the aluminum fin to the copperpipe is a potential thermal bottleneck, every attempt is made to provide a good thermal bond.

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The finished, full size, prototype collector using copper tubes andaluminum fins.

Some overview pictures -- see the Construction section for much more detail.

The copper grid -- using copper pipe.

The aluminum heat transfer finsthat transfer absorbed solar heat

to the copper tubes.

The key to good performance withoutsoldered or welded fins is lots ofheat transfer area, and very good

thermal contact.

The potential advantages of this construction:

The collector is easy to build using ordinary tools and skills -- its a fairly easy DIY project.

1.

The collector is about 1/4 th the cost of commercial collectors (a saving of about $700 on a 4X8 collector)

2.

Materials to build the collector are locally available -- the cost and hassle of shipping large assembled collectors is avoided.3.


For one case I looked at, shipping on a commercial collector was nearly as much as the total cost of materials from the collector. Compared to the PEX collector, this collector offers better performance, and is more resistant to the effects of high stagnationtemperatures, but the materials cost more. The build time is about the same.

4.

Prototype Construction DetailsThe construction is very simple.

The frame is made with 2 by 4's and a 2X6 for the top plate. The glazing is corrugated SunTuf polycarbonate ($1 per sqft at HD) The absorber is built on a sheet of plywood. The copper pipe grid secured to the plywood, and then the aluminum fins are applied overthe copper pipe grid and stapled tightly in place using silicone to fill any tiny gaps and provide better heat transfer. A sheet of polyiso insulation is set into the back of the frame to insulate the back.

Much much more on the construction here ... Prototype PerformanceSome day long performance tests of the full size prototype copper/aluminum collector are here ... These small panel tests of the copper/aluminum collector as well as the PEX/aluminum collector and the traditional all copper commercialcollector construction give a better idea of how the performance of the copper/aluminum collector compares to other collector designs. Cost of PrototypeNote that the reduction in cost of collectors is the result of a number of factors:

- Aluminum is cheaper than copper- Polycarbonate glazing is cheaper than glass- The cost of truck shipping is avoided.- You don't have to pay yourself any wages.

Cost for the 4X8 ft prototype -- using all new materials:

Item Quantity Unit SizeUnitCost

Total Cost

SunTuf Corrugated polycarbonate glazing 2 2X8 ft $18 $36

Framing 2 by lumber (studs) $10

Plywood or OSB absorber backing 1 4X8 ft $10 $10

Atlas R-Board polyisocyanurate insulation 1 4X8 ft $16 $16

Aluminum absorber fins 32 sf $1 $32

Copper pipe 60 ft $1.00/ft $60

Copper fittings (mainly T's) $14

Silicone 3 tubes $3/tube $9

Screws, paint, wiggle strips, ... $10

Total $197

A bit over $6 per sqft.

All of this adds up to a 4X8 ft collector that cost about $200 rather than $600 to $900 plus shipping that may run $150 ish.

Note that the recent drop in copper prices have made thecopper collector more attractive.The copper collector now costs about $5 per sqft compared to the$6 per sqft when this was first written.April 4, 2009

Protecting the Collector From OverheatingThis collector uses all high temperature materials and does not need any special protection for stagnation conditions. I still think that is a goodthing to not leave collectors stagnated for extended periods (as do commercial collector manufacturers). So, try to protect your collector insome way if you can -- shade cloth, high tilt, use the heat for something... Stagnation Test ... (for PEX collector, but should be very similar)


Drainback TestOn the PEX collector, I did a drain back test with clear tubing just to make sure that its serpentine tubing layout would drain well. This copper/aluminum collector should have no drain back issues, and with the half inch risers should drain back very reliably. When I did theleak test in the shop, at the end of the test I opened the valve at the bottom to let the fluid in the collector drain into a bucket, and it drained withgreat gusto. As with all drain back systems, the collectors and the collector plumbing should slope toward the storage tank. Tentative Conclusions and Remaining IssuesCompared to the PEX collector, this version that uses copper instead of PEX tubing offers better performance, and more resistance tostagnation temperatures at an additional cost of about $50. For most people I think this is probably the better choice between the two. Additional PossibilitiesWhile I have talked mostly about using this collector for domestic solar water heating, it would also be fine for things like winter space heating,hot tub heating, and even pool heating into fall and winter in cold climates. One space heating possibility would be to integrate the collector into your south facing wall. This would reduce the cost and material use forboth, and (I think) should save some money and be a good use materials. Bear in mind that this collector could be built in just about any shape you want to. It could be used to fit odd spaces you may have available. Isuppose that even triangular, trapezoids, and circles might be possible -- collector art :)I suppose you could even go around obstacles with it, just leaving a hole in the collector for the obstacle (e.g. roof vent pipes). I think that large collectors might be a good way to go (e.g. build a single 64 sqft collector rather than two 32 sqft collectors. But, the largersizes do get heavy and awkward to handle, so make sure you have a way to move it into position when you are done (or build it in position). Example Solar Water Heating System using this CollectorFor an example of a simple solar water heating system that could use this collector, go here...This is my solar water heating system, and it uses the PEX versions of the collector, but the copper versions described here would work evenbetter.While this system uses a collector of about 48 sqft, a copper/aluminum collector would only require about 40 sqft to achieve the sameperformance.The system was put in place in September of 2008 -- full details on how its is performing are at the link listed above. Gary September 23, 2008, September 29, 2008, October 4, 2008

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Copper Tube/Aluminum Fin Collector -- Construction DetailsThe pictures below detail the construction used on this prototype collector usingcopper tubing to with aluminum fins. OverviewThis is how it goes together:

The copper pipe grid is built with the traditional top and bottom manifoldswith vertical riser tubes spaced about every 6.5 inches. The absorber is made from 6.5 inch wide aluminum strips with groovesthat snuggly fit over the copper pipe. The absorber is fit into a frame made from 2 by lumber. An insulation panel is fitted behind the absorber. The SunTuf corrugated polycarbonate glazing is installed.

As always, comments are welcome Gary...

This is nothing fancy, and is easy to build with ordinary tools and skills, and it looks pretty good (at least to me :). Most people will find all thematerials are available locally. Building the Copper Pipe GridThe size of the absorber is 46 inches wide by 94 inches high. This size basically comes from working backwards from what two sheets ofSunTuf polycarbonate glazing will cover and adjusting fro the width of the frame.

Within reason, you can make the collector any size you like -- that's one of the advantages of building it yourself. Cut a sheet of half inch plywood to the size of the absorber. This plywood can then be used to lay out the top and bottom manifolds and thecopper riser tubes. The plywood will act as a base to tightly secure the aluminum fins over the copper pipes.

This is what the finished copper grid will look like. Water will flow in at the lower right corner, and make its way upall 7 of the riser tubes, and exit at the upper left corner.

The copper grid is made from half inch copper pipe and abunch of T fittings. All available at your local hardware.

Since the copper is the most expensive single element ofthe collector, you might want to think about picking thecollector height to reduce waste of copper? I did not dothat, and ended up with some scrap.

The usual approach is to use 3/4 or 1 inch pipe for thecollector upper and lower manifolds. I did not do that forthe primarily due to the high cost of the reducing T's ordifficulty in braising the half inch pipe into the larger pipe. One consequence of the half inch manifolds is that itwould not be a good idea to string several of thesecollectors together -- if you want to do that, you probablyneed the larger manifolds. But, two large collectors feedfrom bottom center with returns from the outer uppercorners would be fine.

Cut the risers to length:

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Click on the pictures for full size versions.

Layout one of the vertical risers withits top and bottom manifold T

to get the length of the riser pipes.Allow a little spacing from the topof the plywood to the T as shown.

Mark and cut all of the riser tubes to thesame length.

Tube may be cut with this kind of tube cutter, or with an

electric saber saw ora hacksaw.

In hind site, cutting the wholebunch of tubes to the left

at once with the electric sabersaw would have been faster.

After cutting, clean up any burs left inside the tube -- the tubing cutter leaves a ridge inside the tube all the way around that must be cleanedout with the blade that is included on the back of most cutters. Work out the riser spacing:

Using some of the aluminum fins placed over the riser pipes to getthe spacing of the risers.

See the "Make Fins" step below to make a few fins for this.You should to have as much of the available area

covered by the aluminum as possible -- leaving gapsjust reduces the efficiency of the collector.

Place T's on the end of the risers, andcut the short pieces between the T'sthat make up the supply manifold.

When assembling the copper pipe grid, bear in mind that:

The spacing between the risers should be equal to the width of the aluminum fins. The fins edges should ideally just touch the nextfin edge.

Note that the first riser gets a T fitting (this will be the where water flows into the collector), and the last riser gets an elbow fitting.


On the other end of the collector, the elbow goes on the first riser, and the T goes on the last riser (where water will exit thecollector). By arranging the grid such that it is feed on one corner, and water exits via the opposite corner, the flow path lengthfrom inlet, through riser, and to exit is the same for all risers, so they will all have about equal flow.

Solder the grid together:If you have not soldered copper pipe before, it is mainly a question of getting all the pipe ends and fittings very clean with emery paper or wirebrushes, then fluxing all the pipes and fittings thoroughly. When heating the joint, bring the torch against the opposite side from where youintend to apply the solder. Make sure that the torch heats up both the fitting and the pipe to above the the solder melting point -- since thefitting is more massive than the pipe end, put more of the torch flame on in. When you apply the solder, it should flow by itself around the fulljoint, and the capillary action should suck it right into the joint. Once the solder has been applied, get the torch off the joint. Wipe anyremaining flux off the joint with a cloth, as it can cause corrosion later. There are lots of DIY plumbing books that cover this in great detail. Here is a YouTube video on soldering...

You will need tools equivalent to theseto clean all the copper fittings, and

then flux and solder them.The hand copper cleaning brushes

can be adapted to an electricdrill with a little thought.

Cleaning all the pipe ends withthis special wire brush, or

with emery paper.

Clean all the female fittings witha wire brush or emery paper.

Apply flux to all the cleaned endsboth male and female.

Push the fittings together, makingsure they are fully mated.

Prop the manifold up off the floorand solder all the connections.

This is one of the manifolds aftersoldering. Do the other manifold

in the same way, except thatthe feed points are at opposite

corners.After cooling, wash off the remaining goo

with soap and water.

Test copper grid for leaks:This is one way to leak test the grid -- there are probably better ways, but this seems to work OK.


Stand the grid up, and plug up the outleton the low end.

Poor water into the high end until thegrid is completely full.

Let it set for a good while and then check allthe joints for leaks, also check forany drop in fluid level in the pipe

at the top.

Better to find any bad solder joints now than after you get the absorber all nailed together -- so do a leak test now. Joints can look quite spiffyfrom the outside, but still leak. The pictures show a simple way to do a leak test. A better method would allow you to apply a little pressure. Setup the Copper Grid on the Absorber Backer, and add Inlet and Outlet:

Center and clamp the grid to theabsorber backup plywood, and

clamp in place.

Add the fittings that will connect to thesupply and return pipes.

Here the fitting exit the back of thecollector, but they could alsoexit the sides of the collector.

You could actually solder the inlet and outlet fittings back when you did the rest of the manifold, which would save some time and probably be abetter way to go. Make the Aluminum Fins:

The material just below shows you a fairly simple way to make the absorber fins that go around the copper tubes. For more options on making or buying absorber fins, including some nice pre-formed fins from Tom...

I start with aluminum soffit material (Rollex System 3) that my local lumber yard sells. It runs about $1 per sqft, and is about 0.018 thick (abouttwice the thickness of hardware store aluminum flashing). It also has some shallow grooves in the right places so that they can be poundedout (see below) into a groove that will fit over the copper pipe. You could also buy premade heat spreader plates that are used for radiantfloors -- these already have the groove formed in them. The premade heat spreaders come in an extruded form that is very nice, but also verypricey, and in a stamped sheet metal form which are only a little pricey.


The first step is to cut the soffit material so that the grooves that you want to expand out to fit over the copper pipe are centered in about 6.5inch widths of aluminum. The soffit material can be cut with just about any kind of wood working tool -- table saw, electric saber saw .... Wearsafety glasses.

This is the "tool" used toexpand out the grooves to fit the

copper pipe snugly.

Drive the steel rod intothe groove with the flat

top of the sledge.

The finished groove.

Good exercise.

After you get the fins cut to the right width, then use a tool like the one shown above to expand out the shallow groove already in the fin to agroove that fits snugly over copper pipe. the steel rod is 5/8ths inch diameter. The groove tool is made by screwing and gluing two pieces of5/8 inch plywood to a base piece of plywood. The two 5/8th pieces should be spaced 5/8s apart (you can use the steel rod to space them). Make sure they are securely attached with screws and glue. You might have to experiment around with this a bit to get the groove right. Itsimportant that it fit around the copper pipe snugly. I use some paste wax on the groove, which (I think) makes it easier to drive the steel rodinto the groove. The fins shown here are 2 ft long -- they could be longer. But, it may be a good idea to not make them too long, as the aluminum and copperexpand at different rates, so short fins can probably handle this better. In addition to the grooved fins, you will also need some about 3 inch wide flat strips of the same soffit material to go under each copper tube. Note that if you are going to make many collectors, you might want to look at some of the tools that Tom fabricated to make lots of finsaccurately and quickly... Install the Aluminum Fins Over the Copper Pipes:Clean off the plywood absorber backer board. First install the 3 inch wide flat aluminum strips under the copper tube.

Just slip the 3 inch wide strip underthe copper tube.

Run a bead of silicone caulk on eachside of the copper tube that fills the

area between the copper tube and thealuminum strip.

Then run a very light bead of caulk furtherout the aluminum strip on each side of the

copper pipe.

The idea of adding the flat strip under the copper pipe is that it provides an additional heat transfer path from the aluminum fin into the bottomof the copper pipe. Since the transfer of heat from the fin to the copper pipe is the biggest thermal "bottleneck" for this collector, it is importantto use every path from the fin to the tube.


The bead of caulk that runs along the outer area of the flat aluminum strip is intended to enhance conduction of solar energy absorbed by thefin into the flat aluminum sheet and then into the bottom of the copper tube. It is important to use silicone caulk. It will handle high temperatures, and it remains flexible. Some have suggested using heat transfer greaseor the like -- this may work, but I would try to test it under high temperatures first to make sure it stays in place. Richard H. has suggestedusing the aluminum filled gutter sealant that comes in caulking tubes, and this may be a good option, but I have not had a chance to try it yet.

I've done some further testing, thinking, and analysis on siliconecaulk vs other things in the gap between the aluminum fin and thecopper tubes. I believe that the silicone caulk is the best way to go,but all the details on Optimizing the Thermal Conductivity of the Finto Riser Tube Joint are here...

You will need about one tube of silicone caulk per 12 sqft of collector. I find that using a colored caulk makes it easier to see the size of the bead you are laying out. There are some silicone caulks available that have a filler to increase thermal conductivity -- this would be a good thing to use if you can findthem. Install the Grooved Top Fin:

Apply a bead of silicone caulk into thegroove of the fin to be installed.

Push the fin firmly down onto the copperpipe. Now very firmly push the stapleragainst the fin right next to the copper

pipe, and staple it.Be sure to press hard -- it is important that

the gap between the aluminum andthe copper be paper thin.

You should first check to make sure that the groove in the aluminum fin fits snugly over the copper pipe. The silicone bead is put in the fin so that silicone fills any tiny gap remaining between the fin and the copper -- silicone is about 10 times moreconductive than air. Ideally the amount of caulk you use should be just enough to fill the very thin air gap -- using too little won't fill the gap,and using too much may make the gap thicker (which is bad). Staple the fin firmly along one side of the copper pipe. Then move the other side of the pipe and staple it -- really lean into it.

When you put a staple in on the nearside of the copper pipe, the fins should

pop up a little on the far side.This means that when you put the staple in

on the far side it will pull the find rightdown onto the pipe.

Another close up view.

Fin stapled in place --not that the gap isnearly invisibly small.


The staples should be stainless steel. These are available at Home Depot for Arrow staplers -- a box costs about $10 for a 1000 box, but willdo about 110 sqft of collector.

All fins stapled and sealed in place.

The method shown above works just fine, and nothing fancier is really needed. But, I didhave a go at a gadget to clamp the alum fin more tightly to the tube. The better fin totube clamp looks like this...

This is modeled after Tom's clamp (see above) that is based on a pair of modifiedvice-grips. Tom's version is probably better, but I don't have a welder.

Paint the Absorber:The absorber needs to be painted flat black.I use flat black high temperature barbeque paint -- lots of collector builders seem to use this.

There is a somewhat selective spray on coating that could be used -- Thermalox Solar Collector Coating This improves performance byreducing radiation of heat from the absorber. Start by cleaning an silicone or other gunk off the absorber with Acetone or whatever. Set the absorber up outside, and spray away. It will likely take two light coats and some touchup to get it. The absorber wants to be thoroughly dry before the glazing goes over it. You don't want the volatiles from the paint coating the inside of theglazing. Leaving the bare absorber in the sun will heat it up and dry it well.


It takes a couple coats goes to getto full black.

Pretty close.

The paint.

Building the FrameConstruction of the frame is very simple. The sides and bottom of the frame are 2X4's, and top of the frame is a 2X6. Running around the inside the frame at the back is a 1X1 that the absorber board will be screwed to.

This picture shows the relationship ofthe frame members. The top 2X6 sill

overlaps the two side frames, andthe lower frame member fitsinside the two side frames.

The frame is sized so that the plywood thatbacks up the absorber fits inside the frame

with about 1/8 inch of play all the way around.Note the 1X1 all the way around theinside of the frame that the absorber

board sits on.

Closeup of the top sill where it attachesto the side frame.

Note the 1X1 that is nailed and gluedto the inside of the frame all the wayaround. The absorber will sit on this

1X1 ledger board.

The pictures show the frame. The corners are secured with glue and screws. For steeply tilted collectors, the upper 2X6 sill provides some rain protection for the top glazing joint. This is a good time to prime and paint the frame.NZ Mike reports very good results using a "two pot" epoxy paint for this, but I have not been able to find a US source for this as yet.


A cross section through the collector. (thanks to Mike for this)

Installing the Absorber BoardThe absorber board that you built earlier just plops into the frame. It rests on the 1X1 that goes around the inside of the frame.

This is the absorber board installedinside the collector outer frame.The absorber board should bescrewed to the underlying 1X1

at about 12 inch intervals.The absorber board lends a lot

of stiffness to the collector whenscrewed in place. Glue is probably

unnecessary , and would make removalof the absorber board difficult.

Closeup of absorber board sitting in theframe. Be sure to allow or cut clearance

for the collector inlet and outlet if thethey go through the back of the

collector.

NOTE -- from here on out, the steps are the same as for the PEX Collector, so I just copied the material in below. So, you will see somepictures with the PEX absorber below, but it works exactly the same for the copper absorber. Back InsulationThe insulation behind the absorber is 1 inch thick Atlas R-Board polyisocyanurate rigid insulation board. Due to the potentially hightemperatures at the back of the absorber, it is probably best to use the polyiso insulation and not use something like polystyrene. If you check around, many lumber yards carry the polyisocyanurate insulation, but they may not know it as polyisocyanurate. If in doubt ask togo out and look at what they have. If its polyiso insulation, it will say so on the sheet. It is often tan colored and almost always has some typeof foil or fiber face sheet.Its only slightly more expensive than polystyrene, and has a much higher temperature capability. To install the insulation:

Trim the sheet so it fits into the back of the frame.

1.

To hold the insulation in place, spray some of the polyurethane foam in a can insulation onto the back of the plywood, and press theinsulation board down into the foam. One brand of the PU foam is "Great Stuff". Be careful -- if you get any on yourself, you will bewearing it for a week.

2.

Weight the insulation board down until the foam in can sets -- it will want to expand.3.


The foam board ready to be loweredonto the polyurethane foam that acts

as glue to hold it in place.

Weight down the board to keepthe foam from pushing it up.

Note that if your collector has its fluid inlet and outlet going out the back of the collector, you will have to make holes in the insulation board forthe inlet and outlet pipe. GlazingThe glazing material I used is SunTuf corrugated polycarbonate glazing. It has a high temperature capability, good transmission, is very tough,and has a layer to filter out UV. This is all good for a solar collector. It costs a little over $1 per sqft. Many Home Depots carry it. Step 1: Join two sheets of 2X8 ft polycarbonate sheet into a single 4X8 sheet. This is done by overlapping thetwo sheets by one corrugation. To bond the sheets together, I used a bead of clear silicone -- I weighted thisuntil the silicone set. I then screwed the two sheets together at three places using small blocks of wood behindthe corrugations at the screw locations. Use a strip of wood under the two overlapped corrugations to support the back side of the corrugations whilethe silicone is setting and there are weights on it. Step 2: Install the two intermediate horizontal glazing supports. I used half inch EMT electrical conduit for these intermediate supports. TheEMT is good for this, it is straight, galvanized, and cheap. To anchor each end of the EMT, drill a 3/4 inch hole in the edge frame that the EMTcan slip into (see picture).Note that these last few pictures showing the glazing supports and glazing going in were taken when the PEX/aluminum Collector was beingbuilt, but this copper/aluminum collector is done in exactly the same way.


Frame with the two intermediateEMT glazing supports installed.

Notch for the EMT intermediateglazing support.

EMT intermediate blazing supportinstalled.

Step 3: Buy or cut some 3/4 by 3/4 inch strips of wood. Mount one of these strips along each of the two side frame members. Before securingthem with glue and screws, make sure that when you place the glazing panel of over the strips that each strip is centered in the glazing paneledge corrugations.

3/4 inch edge strip installed along rightedge frame member.

The last corrugation of the glazing sheetwill sit over this 3/4 inch strip.

3/4 inch edge strip where it runsover the intermediate glazing support.

The bead of silicone on the EMT isto keep the glazing from rubbing

on the metal

Step 4: Mount another 3/4 by 3/4 strip of wood to the bottom of the top sill so that it will support the "wiggle strip" used along the top of theglazing (see picture). Install the foam wiggle strip on the 3/4 by 3/4 strip using a bead of silicone. The top wiggle strip seals the corrugationopenings on the top edge of the glazing.

The top "wiggle strip" which sits on a3/4 by 3/4 wood strip that is attached to

the bottom of the top sill.


The wood cap strip that is on top ofthe glazing holds the glazing in place

against the wiggle strip

Step 4: Install the lower "wiggle strip" on the lower still. this will seal the corrugation openings on the lower edge of the glazing.

Lower foam "wiggle strip" inplace

Step 5: Using screws with EPDM washers, secure the vertical edges of the corrugated glazing to the 3/4 by 3/4 vertical strips you installed instep 3. For each screw, with the glazing in place, drill a small pilot hole through the glazing and into the wood. The with a larger drill, enlargethe hole through the glazing material so that it is oversized for the screw. When you tighten the screw, the EPDM washer should be just barelycompressed -- not flattened into a doughnut shape. If your drill has a torque clutch, try finding a setting that just barely compresses thewasher.All of this care with the holes is supposed to allow the polycarbonate glazing to move a little with thermal expansion -- otherwise cracks maydevelop at the screw locations. Step 6: To hold the glazing against the wiggle strips at the top and the bottom, cut strips the width of the collector. Place one strip over theglazing at the top edge of the collector, and screw it to the underlying frame in several places. This strip will uniformly press the glazing into thefoam wiggle strips. Do the same for the bottom wiggle strip. In the past, I have secured the glazing at the top and bottom with a bunch of the washer screws. This works OK, but it takes a lot of screwsand does not achieve the uniform pressure that using the external strips as described above does.

Top of collector showing thetop "wiggle strip" with the external

wood strip pressing theglazing into the wiggle strip.

Bottom of collector showing thelower wiggle strip with the external

wood strip pressing the glazinginto the wiggle strip.

The 3/4 by 3/4 edge strip witha couple of the EPDM washerscrews if visible on the right. All the glazing in place

and secured.

If you live in a windy area, you may want to carefully screw the glazing to the EMT horizontal glazing supports. Use the same kind of washerscrews that you used to anchor the edges of the glazing. I think that a couple screws in each horizontal support should resist any tendency ofthe glazing to bow in and out in high winds. How Long Does It Take?I did not time everything, but here are some actual timings and some estimates:


Cutting, cleaning, and soldering the manifold -- about 2 hours.Pounding out the 28 2 ft long fins took 15 minutes.Attaching all the fins to the absorber board, including caulking and stapling took 1 hour and 45 minutes.Painting -- half an hour.Building the frame -- half an hourInstalling the insulation panel -- 15 minutesGlazing the collector -- 45 minutes for all steps. This adds up to 6 hours -- probably closer to 7 with some think time -- probably closer to 8 with some coffee breaks --but you maybe faster.

A group of people could put a bunch of these together assembly line style very efficiently. Gary September 23, 2008

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