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DIY Solar Collector Hot Water

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DIY SOLAR HOT WATER by John Canivan All rights reserved. No part of this e-book may be reproduced or transmitted in any form or by any means electronic or mechanical for the purpose of selling or making profit without the express permission of the publisher.
Transcript

DIY SOLAR HOT WATER by

John Canivan

All rights reserved. No part of this e-book may be reproduced or

transmitted in any form or by any means electronic or mechanical for

the purpose of selling or making profit without the express permission

of the publisher.

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DIY Solar In 1970 a friend of mine left the civilized comforts of a New Jersey home to seek out and experience the free, wild wilderness of an Adirondack hilltop in upstate New York. Jack loved the country life and swore that he’d never leave his mountain retreat. He endured the cold winters without electricity and baseboard heating, but Jack still missed running hot water. When spring came he took a 300-foot coil of black plastic tubing and connected one end to a spring high up on the mountain. He draped the remainder of the 300-foot coil on his roof and spread it out to cover as much surface area as possible. For a $50 investment and one hour’s worth of labor Jack had himself a bona fide hot water shower. He made good use of it whenever the sun was high on the mountain. I used it a few times myself. It worked. The roof might look a little funny and the hot water would run out sooner than you’d like, but it did work when the sun was shining. When the sun disappeared the shower would get very cold. By the end of September water would freeze inside the exposed plastic tubing. You might be interested in a simple system like this if you enjoy taking showers when the sun shines. BUT If you’re looking for a more sophisticated hot water system you’ll need to invest more time and more money. This article introduces the basic DIY concepts of active closed loop serpentine collectors and active open loop Modified Trickle Down solar collectors. Details are available at www.jc-solarhomes.com . My first serpentine collector was first built in 1980 and my first MTD collector was built in 2006. BUT before we begin let’s take a quick look at a direct connect passive, batch heater. This may be all you need if you live in a warm sunny climate.

PASSIVE HOT WATER

BATCH HEATERS In mild climates like coastal California or almost any place in Florida where freezing is a rare occurrence a simple passive batch heating system is all that’s necessary. The batch heater could

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be as simple as a water tank painted black. A more efficient system would enclose this black tank in an insulated box. Glass or some form of glazing would be installed at an angle perpendicular to the sun’s rays. This is a practical, cost effective passive solar hot water system, ideal for mild climates. For more information about batch heaters check out www.solarnet.org.

ACTIVE HOT WATER Active solar hot water systems are designed for colder climates. Although they are a bit more complicated and require electricity to run a circulator pump, active solar hot water systems harvest a thousand times more energy than they consume.

What is the difference between parallel flow flat plate collectors and

serpentine flat plate collectors?

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This parallel collector is designed to transport collector fluid from the bottom of the collector to the top via a network of parallel pipes. Notice that the top and bottom pipes are larger than the vertical pipes. There is a reason for this. Fluid mechanics favors an increased flow rate for the end pipes. This is because incoming fluid pressure is greatest at the base of the first pipe and outgoing fluid pressure is smallest at the top of last pipe. If the top and bottom pipes are large the pressure difference is moderated and the flow rate in each of the parallel pipes is more uniform. These collectors may be connected in series because the top and bottom distribution tubes are so large. It is unfortunate that the flow rate is minimal at the center of the collector where most of the heat is concentrated. Other problems associated with the parallel flow include cost and leaks. Half inch and two inch copper tubes are expensive; also there is a leak risk t the solder junctions.. One small, undetected leak on one T fittings could become a catastrophic mess.

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SERPENTINE FLOW DYNAMICS

The serpentine collector consists of one long continuous flexible tube so there is no problem with uniform flow rate. The size of this flexible tubing is an important consideration. Quarter inch copper tubing is inexpensive, however it restricts the flow rate too much. Half inch flexible tubing is difficult to bend and fairly expensive. 3/8 inch tubing is just right for the money. It has a reasonable flow capacity, low cost, and ease of fabrication. What more could one ask for? The main problem with a serpentine collector is flow rate restriction. Even the larger half inch copper tubing restricts flow rate too much and puts an unnecessary burden on the circulator pump. Connecting the serpentine collectors in parallel alleviates this problem. A two-collector system works fine. A four-collector system works even better. It is very important to bend this 3/8 copper tubing carefully to avoid kinks. This will insure that the flow rate is uniform throughout serpentine collectors hooked in parallel.

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Absorber Plate Construction Solar Collectors would not be very practical without absorber plates. Absorber plates increase the surface area exposed to sunlight. More than 700 linear feet of copper tubing would be required to cover the same surface area that could be covered with 60 linear feet bonded to a well-constructed absorber plate.

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Copper absorber plates facilitate the soldering of copper tubes, but they are expensive, heavy, difficult to fabricate and unnecessary. Aluminum absorber plates are less expensive, lighter, and easy to fabricate. You should be relieved to know that my design calls for aluminum absorber plates. Did you know that aluminum is a superior conductor of heat? That’s nice to know but how do you expect me to solder That’s nice to know but how do you expect me to solder That’s nice to know but how do you expect me to solder That’s nice to know but how do you expect me to solder a copper tube to an aluminum plate?a copper tube to an aluminum plate?a copper tube to an aluminum plate?a copper tube to an aluminum plate? I don’t. A metallic bond of copper to aluminum requires a special helium arc set up. The process is time consuming and expensive. We’ll be using tar and a support lip. Sounds a little sticky to me. Sounds a little sticky to me. Sounds a little sticky to me. Sounds a little sticky to me. It is sticky. That’s the point. Tar also provides a conducting medium. If you have ever walked on a hot tar roof you’ll know what I mean. OK tar sounds good. How large should this absorber OK tar sounds good. How large should this absorber OK tar sounds good. How large should this absorber OK tar sounds good. How large should this absorber plateplateplateplate be? be? be? be? The aluminum plate should cover the largest possible area inside the collector. The inside dimension of a 4X8 collector would be 46½” X 94½ “. The width of the absorber plate should be less than 46½ ” to accommodate the semicircle bends of the copper tube.

So… the width of the absorber plate should be about 40 inches. The starting length of the plate should be 100 inches. After 16 grooves are pounded into the aluminum sheet the length should shrink about 6 inches. So … the finished absorber plate should measure about 40 X 94 inches. You may have difficulty finding sheets of aluminum that are 40 X 100 inches. Two 20 X 100 inch sheets work fine. If you purchase a 50-foot roll of 20-inch aluminum flashing you will have enough for three collectors. A 67-foot roll would be just right for four collectors, but I doubt that such an animal is commercially available. You’ll need two 50-foot rolls for a four collectors, or three 50-foot rolls for eight collectors. A fifty-foot roll of 20-inch aluminum flashing costs about $40.

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What else will I need?What else will I need?What else will I need?What else will I need? Good question. Might as well get everything you need in one trip.

Tools and Materials for Absorber Plate Construction

1. Two 50-foot rolls of 20-inch aluminum flashing for four collectors. 2. Four 1X6X8’s common pine. (Actual size ¾” X5½” X8’) 3. Two 7/16 inch steel rods. 4. Heavy hammer. 5. Tin snips. 6. One pound of 1 ¼ - inch drywall screws. 7. Hacksaw. 8. One gallon of roofing tar and a throw away brush.

Are we ready?

Let’s go.

I recommend that you work on a level concrete floor. First you’ll need to build what I call a pounding jig. This jig will be used to pound 16 grooves into each 20 X 100 inch sheet of aluminum. Pounding Jig Construction Instructions

1. From the wood that you purchased make four 1X6X4’s and seven 1X6’s 20 inches long.

2. Take the remaining piece of 1X6 and cut off a ½ inch strip. The width of this strip should be precisely ½ inch. It will be used as a reference spacer.

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3. Rip the remaining piece in half to make two 1X2’s 20 inches long 4. Place the eight 1X6X4’s in a row on top of the concrete floor with half-inch spaces between them. This will be the base of the pounding platform. The base platform should measure 24 inches by 48 inches.

5. Screw a 1x2 onto one end of the base platform with drywall screws perpendicular to the base platform. Now secure a 20-inch 1X6 ½ inch from the 1X2. Use the reference spacer between the 1X2 and the 1X6 to get accurate spacing. Be sure all the 1X6 boards are also perpendicular to the base platform and spaced ½ inch apart.

6. Fasten the top layer of boards to the base platform with 1¼-inch drywall screws. The most important consideration in the construction of this jig is the spacing between the boards. The ½ inch spaces should be centered 6 inches apart, and the pounding jig should look something like this when you’re done. I will now refer to the spaces between the boards as slots.

Now for the pounding

1. First cut some aluminum sheets 100 inches long. You will need eight 20X100 inch strips for four collectors.

2. Cut a 7/16” steel rods in half so that you have two rods 24 inches long. 3. Lay the aluminum sheet on top of the pounding jig so that one end of the sheet extends 3 inches beyond the center of the first space. It is important to get off to a good start so I recommend that you center the aluminum sheet on the pounding jig. The edge of the aluminum should be parallel with the edge of the pounding jig platform. When the sheet of aluminum is properly centered with

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one end protruding 3 inches from the center of the first space place your knee on the aluminum to hold it in place and carefully press the rod into the first ½ inch slot like this:

The absorber plate should look something like this when you’re done.

Guess it might seem a bit crude, but believe me it works. Once the serpentine tube is bonded to the groove with tar and the absorber plate is coated with a lampblack tar coating it will look something like this close up. Notice how the absorber plate wraps around the copper tubing.

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VIDEO http://www.youtube.com/watch?v=QdHQpzbk0MI

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Building a Serpentine Collector Find a nice hard level surface and assemble the frame like this. Be sure the length is eight feet between the outside corners and the width is four feet between corners. You could attempt to screw the corners together if you like, but you may find it difficult to hold them in place while driving a screw. I like to gently throw the 4X8 CDX plywood on top of the 1X4’s. One or two of the 1X4 may fall down, but they can easily be put back in place. The important thing is to line up the 1X4’s under the plywood one at a time. Make sure the outside edge of the 1X4 is flush with the plywood and the corners of the plywood line up with the outside tips of the 1X4’s.

Make all your collector frames at once and then paint them inside and out with an oil base paint of your choice. Now take a break. You’ve earned it, and besides you’ll have to let the paint dry for a few days before giving a second coat. If it becomes impossible to wait for paint to dry you could spend some time working on the 3/8 inch copper tube-bending jig.

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Construct tube-bending jig

Take those four 1X6X8’s and cut them in half so that you have eight 1X6X4’s. Cut semicircles on the ends of the 1X6 boards and then make 8 boards like this one.

Now cut each of these boards in half, and flip a collector frame over so that its plywood bottom faces up. Center the bending jig boards on top of the collector bottom in the manner demonstrated below. Use a half-inch reference spacer board to position the bending jig boards so that they have a half-inch gap between them and screw them into the CDX plywood with drywall screws. Two screws in each board should be sufficient. Use a carpenter’s square to trace out guidelines on the collector bottom. This will help you secure these 1X6 boards in this manner demonstrated.

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STEP FIVE Bend copper tubing. If you have carefully laid out the bending jig and have spaced the bending jig boards correctly you should have no difficulty bending the copper tubing. Keep the tubing snug when you press it down into the grooves, but do not put kinks in the tube. Kinks restrict the flow rate and lower collector efficiency. If you do put a few small kinks in the tubing don’t shoot yourself. With a little TLC you can squeeze kinks out with the help of vice grip pliers. You will be bending a sixty-foot coil of 3/8 inch ID copper tubing into the tube bending jig slots from one end of the jig to the other. A friend may prove useful. If you don’t have a friend to help you may wish to hold the start end down with a board and a few screws. Start the tube about a foot from the top of the first loop so that you have enough tube for the entire serpentine bend. The bent tube will look something like this when you are done:

Find a good place to store your serpentine tubes. DON’T KINK THEM. Give all the collector frames at least two good coats of oil enamel paint. After the collector frames have thoroughly dried you can check yourself into a nearby mental hospital. Say hello to my wife while you’re in there. Only kidding. If you have come this far I think you’ll make it. Hang in there you are doing fine. Now go on to step 6.

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STEP SIX. INSTALL INSULATION AND SUPPORT SQUARES

Turn a collector right side up and install a 4X8 sheet of one-inch ridged isocynate insulation with a foil back. Place the insulation inside the collector foil side up and trim off the excess with a drywall knife so that the insulation fits nice and snug. MARK INSULATION: Mark the insulation where the copper tubes will go. The lines should be 6 inches apart. The first line and last line should be 2¼ inches from the inside edge of the collector frame. Now rip 5¼-inch strips of ½- isocynate insulation and glue these pieces (with contact cement to the back of the absorber plate as illustrated below. These squares will help position and support the absorber plate.

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STEP SEVEN Drill inlet, outlet and vent holes The absorber plate grooves will hold the serpentine copper tubing that you bent. Before unrolling these groovy absorber plates I’d like you to drill four ¾-inch holes into the sides of your collector frame. The inlet and outlet holes should be centered to accommodate the inlet and outlet positions of the serpentine tube. Center the inlet and outlet holes 3 inches from the collector corners and about 2 inches down from the top rim of the collector frame. A distance of 90 inches must separate the inlet and outlet holes. You will also need a few vent holes in the bottom side of your collector to vent trapped collector moisture. Vent holes should be centered on the bottom side of the collector one foot from the corners and 1½ inch down from the collector’s top rim. Center the vent holes one inch down from the top and one foot over from the bottom side corners. The ¾-inch holes may seem a bit large but there is a reason for this. Half inch copper union connectors will be inserted into the inlet and outlet holes. The space between the tube and the wood will be filled with clear silicon caulking.

These vent holes are for the right collector. The left collector will have vent holes on the other side. All vent holes should be on the bottom side of the collectors.

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STEP EIGHT Install absorber plate

Now unroll two absorber plates into the collector body, groove side up and overlap them in the center of the collector body. Overlap the absorber plates so that their outside edges are 4 inches from the inside edges of the collector sides. A distance of 90 inches should separate the end grooves. You may wish to trim the ends of the flashing to fit the collector body.

STEP NINE Install serpentine tubing If you did a good job bending the 3/8 inch tubing, installing it into the collector body will be a piece of cake. Handle the tubing with care. You have come this far without a kink; why spoil it now? Gently glide the tubing into position. This serpentine assembly should measure about 94 inches long and be 45½ inches wide.

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Congratulations! Your collector should look something like this after the serpentine tube is inserted. If you examine this three dimensional collector closely you will notice that it has 14 groves instead of 16. This is merely a pictorial representation of the actual collector. Your absorber plate should have sixteen groves and the serpentine tube should fit into these groves, if they don’t, make the necessary adjustments before continuing. Do not press the tubes into the grooves yet.

Join 1/2 ID copper pipes to the 3/8 ID copper tube with adapter sweat fittings and allow the ends to protrude through the predrilled ¾ inch holes. The solid protrusions from the collector represent ½-inch copper tubes. These tubes will later be trimmed to fit sweat unions that will fit snug against the side of the collector.

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Solar Hot Air Alternatives

Passive solar greenhouses and modified, passive Trombe Walls can also supplement some of the heating needs of a home, but air is not a good heat transfer medium and the heat from air is difficult to store. If you decide to stick with a passive solar air heating system and you live in a cold climate with limited sunlight be sure to have a back up heating system.

I prefer water to air when considering heat exchange systems, but a combined air and water system could work. For large solar heating and domestic hot water systems I recommend using water as a heat exchange medium because a cubic foot of water can hold about 2,000 times more heat than a cubic foot of air and heat is exchanged through water at a faster rate than through air. As a mater of fact the direct heating and storage of solar heated water is perhaps the most practical method of collecting and storing the sun’s energy. So rather than use copper flow tubes and aluminum absorber plates and heat exchange coils to transfer heat indirectly consider the advantages of transferring heat directly into water. This is what Harry E Thompson did in 1960 and this is what Richard Heiliger and I have been doing since 2007. http://www.jc-solarhomes.com/trickle-down%20solar.htm

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Trickle-Down Solar Heating

Harry E Thompson

In the 1960’s an engineer from North Carolina by the name of Harry E Thompson invented a simple method of collecting solar heat without using copper flow tubes bonded to metallic absorber plates. Conventional collectors use copper flow tubes to harvest the sun’s trapped heat from a blackened absorber plate. Commercial

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parallel flow tubes are soldered to a copper absorber plate and serpentine flow tubes may be pressure bonded to an aluminum absorber plate. Although the serpentine collector uses less Copper than the parallel flow system they both rely on Copper to isolate collector fluid from the glazing.

Harry Thompson felt that flow tubes and copper absorber plates were an unnecessary expense. Instead of using flow tubes Harry decided to pump water from a storage tank to the ridge of a roof and allow it to dribble down across a corrugated aluminum absorber plate. Thus heat transfer occurred directly from the absorber plate into the water.

At the bottom of the corrugated aluminum roof a trough was placed to catch the heated water which was channeled back into a huge heat storage tank in the basement. This tank was buried in a pit of stones which picked up heat from the tank. A thermostat on the first floor was used to turn on a fan that forced cold house air across the heated stones. The

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heated air from the stones in the basement entered the living area through grates in the first floor. As you know hot air is lighter than cold air so it has a natural tendency to seek a higher elevation and spread throughout the house. A fan is often used to extract heat in a more controllable fashion. There are still houses along the Canadian border that use Harry Thompson’s trickle-down solar heating system and I have for some time been interested in the concept. Concerns about heat losses through the glazing material and the necessity of using a corrugated metal roof have prevented me from investigating this solar heating option until March 2006. At this time I became aware of the increasing cost of copper and decided to build some experimental collectors without copper flow tubes that trickled water under a plastic film to prevent heat loss. I call this kind of collector a Modified Trickle Down collector or MTD. MODIFIED SOLAR THERMAL ROOF

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My first experiment with MTD was a disaster. On the positive side I discovered that the plastic trapped plenty of heat but it soon melted without water flowing. Leaks through the absorber plates and through the underlayment developed and I was forced to dismantle the entire roof. Since no provision had been made for modular trouble shooting all five sheets of Kalwall and all ten absorber plates had to be removed. After dismantling was complete I noticed that the polyethylene underlayment had fused with the nylon netting, and there were areas near the ends of the trickle down tube that had melted clear through to the TYVEK.

MELTED POLYETHYLENE UNDERLAYMENT HOT SPOT

Modular Modified Trickle Down

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After my first experience with an MTD roof I developed modular MTD collectors with the help of Richard Heiliger. A modular design facilitates the construction, installation and maintenance of MTD systems. I learned to use heat resistant Mylar and polypropylene as inner glazings and polyester felt as an absorber plate. A modular array of MTD collectors might look something like this:

Richard Heiliger’s house in Richmond Utah

To collect water from your Modified Trickle Down collectors you’ll need to make a PVC gutter that looks may look like this:

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To distribute water to the tops of your MTD collectors you’ll need a Trickle Down Distribution System that looks something like. I use a modified heater hose:

This trickle down tube is one method of bringing water to the top of the collectors, but if the tube is too long water will never reach the holes near the ends of the tube. Here is another view of the gutter and gutter support. Notice how the bib tab is bent up and over the bib. The bib is actually the first layer to be bent into the gutter. After the collector is installed on the roof the gutter may be slid into position from one end of the collector array.

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The Installation Modified Trickle Down Collector Installation as well as any other solar installation works best when flush mounted on a roof. The MTD collector has been specially designed for easy mounting. The protruding lip on the gutter support makes this possible, but in order to work properly a stop support must first be installed.

This stop support is simply a 1x2 screwed into the roof rafters with 3” drywall screws.

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As you can see the collector rests on the stop support and facilitates the mounting process. Top support and central supports prevent the collector from warping.

Here is a close up side view of the stop support and a collector resting on it. Notice the 1x1 finish support on the edge of the gutter support. This may be installed before or after mounting the collector.

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TDD Installation

After the collectors are secured into position press the two TDDs into the TDD supports. The TDDs for this eight collector system will each be about 106 inches long. For more information about DIY solar heating systems go to: www.JC-Solarhomes.com This is the MTD shed that I’ve been experimenting with for the last 2 years. The shed has already paid for itself in the heat collected and the products made from the collected heat. From the data collected I have estimated that the efficiency of converting sunlight into heat is about 50%

http://www.jc-solarhomes.com/MTD/MTD%20Data/mtd_data.htm

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A full MTD solar heated workshop will be my next project…

VIDEO http://www.youtube.com/watch?v=xsDViPYnk7U For more information about serpentine and MTD solar collectors as well as MTD collector kits visit www.jc-solarhomes.com and get your fair share of sunlight. John Canivan


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