Solar Dehydrator

Solar Dehydrator Illustrated Plans

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Solar Dehydrator Illustrated Plans Post by WCE on Oct 31, 2004, 7:41pm

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Copyright Walnut Creek Enterprises 1998-2004

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Solar Dehydrator Introduction Post by WCE on Nov 3, 2004, 10:44am

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The WCE Portable Solar Dehydrator

Design, Plans and Illustrations by Dan Jincks Copyright Walnut Creek Enterprises 1998-2004 Introduction The Walnut Creek Enterprises Solar Dehydrator is a unique innovation in dehydrator designs. It uses the power of the sun to dry large loads of herb, seed and foods. The drying is accomplished in the shade without sunlight burning the vitality out of your herb or food. Sunlight is converted to circulating hot dry air to accomplish the dehydration. A typical full load is about 100 square ft. of drying space. About 10 times that of “home dehydrators”. Its solar efficiency is unusually high due to a number of interrelated innovations. Though large in capacity, the efficiency allows a wonderful portability to be built into the design. A reality of solar powered devices are those not-so-solar days and of course the nights. Slower static drying is designed in to continue without any sun and a simple electric heater interface allows rapid drying without respect to the sun. In December 1999 a new section was added about adapting the dehydrator for winter use. Not only can you effectively dry herb and food during sub-freezing sunny weather, you can do it indoors and heat the room as well. Its convection air flow requires absolutely no electric or other energy to bring in hot air. Probably the most amazing aspect is that it doesn’t cost hundreds of dollars - and you can build it yourself. A practical piece of



equipment that’s practical to build and use.

Solar Dehydrator Frame Post by WCE on Nov 3, 2004, 10:46am Building the Frame The shape of the dryer base may at first seem complex and require fancy carpentry. This is not the case. You’ll need a crosscut saw, electric hand held circular is recommended, though a manual saw will do. The recommended joining technique is deck (or drywall) screws driven with a variable speed reversible electric drill, with a Phillips magnetic driver bit. This technique is fast and creates solid joining. Drilling holes for screws isn’t even necessary with softer woods like pine. Nails are not recommended unless you clamp and glue the joints as well. This would add considerable time to the construction since the glue must set up between steps. You’ll also need a framing square, combination square, tape measure and long straight edge. The lumber used in these plans is 1 x 3 (3/4 x 2 1/2) firing strips. 1 x 4 or high quality 1 x 2 can also be used. We tried to specify dimensions so any of these can be used. 20 - 8 foot boards should build the frame, screen lid and probably a few drying screens - if you plan your cutting carefully. The paneling over the frame will require most of 3 - four by eight foot sheets. We chose 1/8” Masonite as the best compromise between weight, strength, durability and thermal characteristics. Plywood and flake board can be used, but keep in mind that more thickness equals more weight. (Be sure to use exterior grade) Sheet metal is not recommended since it dissipates heat out of the unit in an efficiency defeating manner - unless you add a layer of insulation. If you were to use 2 x 4s and 1/2” plywood, the extra weight would require heavy duty wheels and probably change portability into a 2 man operation. You would about triple the weight! When built as suggested, one person can tote it around on fairly uneven ground - even with 12 loaded screens.





Creating the Side Profile On a flat surface, lay down your 2 slanted horizontals and arrange the two legs on top. See the drawing for details. Take your time and get these 4 boards squared up and spaced properly - they define the shape and results more than any other step! Trimming the ends can be done after assembly. Once they are aligned to your satisfaction, carefully rest a foot on the leg board and drive 3 screws into each lap joint. Trim the ends as shown and the profile is established. Use these boards to mark and cut another set. Turn the assembly over. Lay matching boards on the horizontals and put the legs on top again. Align everything to match the first assembly and screw together. You now have a matching pair of mirrored sides. Now attach the two boards that define the profile of the screen platform. Note that all vertical boards are on the same side of the horizontal boards. The small board at the intake end is shown in the first illustration for clarity, but may be more accurately installed after the cross bars. Installing the Cross Bars Note: We chose 42 inches as our width. This is fairly arbitrary. A 36 inch width may be easier to handle for smaller folks. Build a screen frame first to judge handling. Transparent window material may also be easier to find in 36 inch width, so you may want to acquire that first to determine the width. 48 inches is about the practical maximum width. Now we fill out the frame width by installing 10 cross bars between the sides. Prop the sides upright by leaning against boxes, chairs, etc. or use a helper. The slanting horizontals are to the outside. The four cross bars along the bottom are 40 1/2”, with the other six being 42”. Start with the 42”. Using “C” clamps as an aid is easiest. Install just 1 screw per joint on the first 4 cross bars, then check squareness and spacing. After adjusting, add extra screws and proceed with the remaining. The bottom cross bars are best handled by pulling in the sides with a long bar or pipe clamp. If you don’t have a long clamp, drill pilot holes in the side boards so screw threads don’t grab and prevent the side from pulling in tight. Be gentle when tightening these bottom cross bars since the screws are biting into a weak orientation. The panels will stiffen the structure at these joints later. Copyright WCE 1998-2004

Solar Dehydrator Dew Buster & Diverter Post by WCE on Nov 3, 2004, 10:52am Strengthening the Rear Legs Jump ahead a bit and decide if you will be using large diameter wheels. If so, you will need to coordinate the structuring with this strengthening. If using smaller wheels; glue, screw and clamp a second board inside the rear legs to add strength since most of the weight and transport stress will be carried by them. If you have your wheels handy, mark the axle area and don’t put any screws near there. The electric heater illustration shows the double board legs. Why not just use a single bigger board? Two boards laminated together are more stable and tougher than a single board of their combined size. Filling the Gaps You can put this off until just prior to installing the panels, but we’ll mention it now so you can start saving scraps of wood. Since the verticals are on the inside, there are low spots



on the outside of the frame. Fill these out with scrap wood so that the entire frame has a surface to attach the panels. The rear corners can be done a couple of ways, but which doesn’t matter as long as both side and back panels have a solid corner to screw into.



Low Angle (Dew Buster) Collector The first two morning hours of sun are largely useless to the primary solar collector. This is true for two reasons. One, the angle of the sun is extremely low. Two, dew usually forms on the transparent collector cover and blocks what little light might get through. The last hour or so before sunset isn’t very useful to the main collector either. Those three or four hours of inefficiency are a significant percentage of the average solar day. A simple auxiliary collector significantly boosts drying and automatically helps clear the dew from the inside of the main collector. We’ve estimated an improvement of well over 15% on a 12 hour solar day (equinox). Shorter Fall, Winter and Spring days see even a higher percent boost. Note that if your horizons are blocked by trees etc., the effect of this collector is less significant. The collector consists of two simple parts. A sheet of aluminum, spray painted black on one side, and a piece of transparent plastic mounted as a window. We use 1/8” clear polycarbonate (aka Lexan, Tuffak, etc.). It’s one of the most expensive window glazing plastics, but it will never break from flexing or impact. Nor will it melt or even soften in this application. It’s the original “bullet proof” plastic. See the later collector window section about other plastics. The location of the panel is the flat vertical surface in front under the screen platform. The surface is structurally significant, so this panel needs to be of rigid material. If you opt not to install this collector, cover this surface with Masonite or whatever you are paneling with. If you want this collector, get a piece of plastic at least an inch larger than the opening, in both directions. Drill holes every 3” around the edges and screw down over the frame opening. Paint that area of the frame black first. We also suggest that you paint the plastic black around the overlap to prevent pocketed heat between plastic and frame. The heat exchanger is just a piece of aluminum sheet screwed to the inside of the frame behind the plastic covered window. 2 1/2 inches separate the window and exchanger, and the top and the bottom of this cavity are open to allow convection circulation around the exchanger. Aluminum flashing sheet will work fine. The thickness isn’t at all critical. We use .032. The side facing the window should be lightly spray painted flat black. Leave the back bare to shed heat rapidly. Take notice that the exchanger is in the same area as the diverter panel. If the exchanger extends too low it will prevent the diverter from closing. You will need to adjust the two so that they will not interfere with each other. How does is work as a dew buster? The exchanger heats the air which rises creating a slight vacuum which draws outside air in across the inside face of the main collector window. The air movement dries off the dew allowing the main collector to contribute, which quickly increases air flow and finishes the dew removal. This even works fairly well with the screen lid closed since heavier cold wet air is forced down and out of the bottom of the intake. The dumped saturated air is not drawn back in by nature of the main collector design, so drier outside air helps the process accelerate even faster. Point the unit East in the evening and you don’t have to get up at the crack of dawn to get things started. Electric/Solar Air Flow Diverter Electric heat is input from the back (explained a little later) and solar generated heat is input from the forward collector. They function differently and not at the same time so we



need to switch the air flow. The switch is a piece of Masonite or other sheet material that is attached with hinges to a bottom cross bar. When tilted forward it seals off the main collector so that hot forced air from the electric heater goes only up into the screens. When tilted back for solar use, no seal is required as long as the heater porthole has a cover. We recommend tying down the diverter when back in the solar position, since if it accidently falls forward, collector air flow is stopped. In full sun a blocked collector may get hot to the point of doing damage. The lashing is best accomplished through the heater porthole, that way you do not need to remove the drying screens. The lashing can be as simple as ‘eye’ screws on the upper diverter bar and on the porthole frame, using cord to tie down. The diverter panel has two full width horizontal bars that provide rigidity. The bottom one also acts as a seal. Install two hinges on the bottom cross bar so that their pivot center is in the middle. Once the panel is fitted properly in the forward position, let its bottom edge rest on the cross bar and screw the hinges to it. Now whenever tilted forward, the edge touches and seals against the cross bar. A tight proper fit in the forward (electric heat) position is important so that your costly electric drying heat goes up into the screens rather than out the nose of the collector. The corners will need to be notched in to clear the frame. Don’t cut away any more than is needed for front fit. It will stop against the rear legs when swung back. The upper edge of the cross bar should contact the front upper cross bar in the middle or lower, and clear the low angle collector heat exchanger panel. You may be able to devise a tight corner fit, but we just stuff rags into the corners when we switch to electric. They can be reached through the heater porthole. Once the panel is fitted you may want to screw boards to the vertical outside edges, between corner notches, to prevent warp. Copyright WCE 1998-2004

Solar Dehydrator Electric Heat & Wheels Post by WCE on Nov 3, 2004, 10:57am Auxiliary Electric Heat Many dehydrator plans use complicated, expensive and potentially dangerous methods to generate electric heat. Even if you know about electricity, why make things difficult? Just use your forced air electric space heater! For $30 - $50 you can buy a triple heat output 500/1000/1500 watt heater that is UL tested and approved not to malfunction, set fires or electrocute you. With automatic thermal overload and tip over shut down, they are quite safe. The one potential trouble circumstance is that you don’t want to run them outdoors in the rain. If they suck in water, its difficult to predict what bad things might happen. That’s not a UL tested circumstance. The heater used isn’t real critical except: 1. It should be 1500 watts or less. Up to 1800 watts is acceptable as long as it has lower settings and you monitor temperatures carefully when at the higher settings. 2. It must be a high air movement / low air temperature type of forced air heater. Heaters meeting these requirements are actually the most common cheap heater. Convection or radiant type heaters should never be used as they could cause a fire! Theoretically other heat sources could also be used and resulting hot air be blown into the porthole via ducts. If you get adventurous: Limit peak air temperature to about 150 degrees F. A heat exchanger must be used to isolate combustion exhaust gases outside the



dryer. Fumes from wood, coal, kerosene, etc. would contaminate the herb, seed or food being dried. Adapting an electric heater is quite simple. Frame in an opening for it to fit into and then devise a way to secure it from falling in or out of its opening. We had a number of plastic bodied heaters that we use in the winter, so we just adapted for them. In our case, it was just a matter of utilizing the flex of the plastic bodies. They just press fit into the correct size holes. You may not be so lucky, but while adapting them, remember: 1. You’ll need to get to the controls from time to time. 2. You’ll need to cover up the porthole, probably from the outside, when you switch back to solar. We just stuff rags (carefully) into the gaps and handle hole to seal ours in. We suggest you maintain a flat clean outside face and put any brackets or ledges inward. You will need to cover the porthole for solar use. If the heater sets completely inside you may be able to leave it installed. We remove ours. The cover can be a simple screwed down piece of panel or a more elaborate internal part of the diverter that seals when the diverter is back in solar position. The seal doesn’t need to be super tight since solar mode doesn’t generate much vacuum or pressure, and the diverter panel is a partial blockage. Keeping rain and its runoff out is also a consideration when creating a cover.



Wheels Portability is a considerable asset to this kind of solar device. You can put it where the sun is best. Use it to tote around screens. Take it where you are loading screens. Most importantly, you can aim it at the sun from time to time to get maximum efficiency. We estimate an over 20% boost in efficiency if re-aimed about every 3 hours verses stationary South facing orientation. Fall, Winter and Spring use is even more affected by positioning. Even if you don’t have time to aim, the portability is a joy in itself. All you need is a couple of matching wheels, a 4 foot axle rod and some tubing for an axle spacer. We use new 7 inch all plastic ‘lawn mower’ wheels that cost under $5 each at discount stores. Their axle hole is 1/2”, so a 4’ piece of 1/2” cold rolled steel rod is the axle. The axle spacer between the legs is 1/2” electrical conduit. You may need to hunt for the 1/2” rod since smaller hardware stores may only carry 3’ lengths. Try machine shops, welding shops or farm supply stores. To install wheels, just put a wheel on the floor next to the leg, stick a pencil in the axle hole and mark the axle location (centered on the leg). Drill holes big enough for the axle and cut a couple inches off of each leg. Cut the spacer tube to fit between the legs - minus two washer thicknesses. Install tube with washers against each leg and slide the axle through. Install washer / wheel / washer; and cross drill the axle and put in cotter or hitch pin. Cut off any extra axle length and you have it. Any 6” - 10” pair of wheels should work fine. You’ll just need to adapt axle size etc.. Wheels over about 10” are liable to turn into annoying obstacles unless you fashion a way to move them more under the dryer base. If you fancy (or need) big spoke wheels, you’ll need to construct some extra framing off of the back legs back to the frame bottom. An illustration shows a possible large wheel installation. The extra framing for the inset axle would need to be double or triple laminated boards and should be flush or inside the established outer frame face. Don’t move the axle forward past the middle of the screen platform or balance and stability will get weird. Our 7” wheels work fine on fairly solid ground with 12 loaded screens, and can navigate turf, the occasional small rock and mole tunnels. If you you will be using on soft, rocky or uneven ground; those big spoke wheels may be a good investment.



Copyright WCE 1998-2004

Dehydrator Handle Panels Paint Heat Exchanger Post by WCE on Nov 3, 2004, 11:03am The Handle With wheels, a front handle is a necessity, but may be useful even if wheels aren’t used. The handle is simply a 1 x 3 or 1 x 4 - 42” long that has a hand recess cut into it. You’ll need a sabre or keyhole saw. Be sure to round and sand the outside and hand area edges. Use an extra good piece of wood to make it. Attach from behind with plenty of screws. Glue would be a good idea as well. The hole shown is for the work stand set-up chain to pass through. It can be added later. Installing the Exterior Panels If you are using the recommended 1/8” Masonite, it will have a finished and a rough side. Rough side goes in since the roughness both absorbs light and releases heat better. The sides are made by laying the frame on its side, on a 4’ x 8’ sheet and tracing the outlines. Both sides can be obtained from a single sheet. The bottom and back should be measured and carefully cut square. Start with them and twist and tweak the frame as needed to force it to square up. Then be sure it is properly square in all directions before tracing the sides. We’ve used ‘come-along’ winches, bar (pipe) clamps, jacks, helpers and you name it for truing. It’s best to maintain squareness early on and at each step - but errors and warp can sneak in. The panels should be screwed to the frame about every 6 inches. Anchor to all framing surfaces, not just the outline. It’s best to install your screw lines from their center outward to maintain good pull down without buckled areas. If you didn’t install a low angle collector, you’ll need to panel that surface as well. Once installed, use a wood rasp to pretty up the edges. Then break sharp edges with sandpaper. Paint Before the heat exchanger is installed, at least the collector interior must be painted. We recommend flat black exterior acrylic house paint inside and out. The blacker the better. Most labeled ‘flat black’ is more like dark gray. It will work, but it’s worth a couple of extra dollars to have extra black pigment added if possible. We recommended black outside since when the sun strikes and heats a side, that heat contains and adds to the interior heat. This isn’t a big necessity. Even if the exterior were white, the total efficiency change would probably be on the order of a few percent. If you want to be artistic or colorful on the exterior - go for it. The sun would never strike the outside bottom or back during operation, so anything can be done with these surfaces and it will have no effect at all on efficiency. The interior alone will use up a quart or more of black house paint. The course side of Masonite really soaks up paint. If you’ll only have one quart of flat black, start at the front, paint only the interior and save the area just below the screen platform and behind the diverter panel for last, in case you come up short. The entire base should be sealed inside and out with exterior paint. Color isn’t extremely critical except that the collector interior be flat black.



The Heat Exchanger The plans call for aluminum downspout for the heat exchanger. If buying new, get pre - painted black or brown and lightly spray paint flat black. Up-side-down aluminum guttering should work fairly well, but may be less efficient. Copper is even better than aluminum. Steel is a poor choice since it doesn’t release heat well. Stick with aluminum or copper. If your stock is used, with brushed on paint, it must be stripped and lightly repainted. The thick paint acts as an undesirable insulator. The purpose of the heat exchanger is to convert sunlight to moving hot air. Aluminum or copper lightly painted black, do this quickly and efficiently by rapidly releasing their heat. The air heats up and expands, getting lighter and rising - creating the convection air flow. The hot air inside the tubes flows upward with heat increasing as it continues. By not flowing up against the window surface and partially dissipating, a higher efficiency is maintained. Hot air also peels off of the outside of the tubes as well and travels up the collector. The available air volume in the base increases with the increasing temperature. This expansion chamber affords more room for the volume increased by heating. This aids the rate of convection movement. The stack of drying screens forms a chimney. The more screens stacked the greater the drying load and also the greater the chimney effect to aid convection. It self compensates for drying loads. 12 screens dry at nearly the same rate as 2. At night, with the lid closed, drying continues. Air cooled by evaporation sinks and drains out the collector front. Slightly warmer and dryer air is drawn in through and above the extended collector tubes. This is why the front opening is cut back at the bottom and the tubes are extended. The dumped cold wet air isn’t drawn back in. These little FM (fun & magic) techniques all add up to efficiency gains not realized by typical solar dehydrator designs. These tubes might seem a bit costly - but they don’t wear out or cost you any external energy while operating. They also allow the use of a very inexpensive collector window that more than offsets their cost. Less heat on the window and more moving hot air to the screens. The solar efficiency on a summer afternoon is competitive with that 1500 watt auxiliary electric heater. The tubes illustrated are standard 10’ lengths cut in half. The side mounted tubes are a bit shorter than 60”. Close the diverter panel and use that as a stop reference. If no diverter, the lower tubes should extend out to about the end of the collector nose - not including the handle. They are attached with 2 1/2” decking screws. They must be marked and pre-drilled. The screws go right through the middle of the 3” face. The center group attaches to the two specially spaced cross bars. The 2 side tubes attach to the two frame verticals and at the nose. We show a lot of space between them. A greater density can be used and may improve efficiency, but maintain at least 1/2” gaps to allow heat to dissipate off of the sides. Greater heat exchange surface area means more hot air faster and greater convection. The tubes have far greater surface area inside and out than a single sheet of aluminum would - which is why we didn’t suggest to use one. Copyright WCE 1998-2004

Dehydrator Window, Screens. Lid & Stand Post by WCE on Nov 3, 2004, 11:06am The Collector Window



The first step is to paint the rim on sides and front white. This prevents heat buildup between window material and the rim, which might degrade the window material. The material we use is flexible transparent vinyl. We get it at a store called ‘Fabric Warehouse’. Judging by the three digit store number, there may be one near you. If not, try fabric stores or shops that repair convertible car tops or boat tops, or plastics suppliers. What we get is about .010 thick and costs $2.50 per 4 foot wide yard. You’ll need two yards. The light transmission is quite good, but visually it is about like looking through a rainy day windshield without any wiper. Installation is a breeze. Just staple it to the side rims, stretching moderately as you go. In the front, roll it over the edge and staple to the front face above the handle. In the back, pull it under the cross bar and staple to the back of it. You’ll have to carefully cut in the corners where it changes from over to under. Trim off the surplus material with a razor knife. If you can find stainless steel staples, they are the way to go. You may want to cover the side rims with 1” x 1” ‘L’ wood corner molding to give you edges to set screens on when you are loading them. We paint the molding with white house paint. Other more conventional glazing materials could be used as well. Unless you already own it, they will all cost more than the vinyl. Glass is traditional and has great light transmission, but we would probably break it about 4 times a season around here. If its not hail or rocks from the mower, freak wind gusts blow the lids off - most of the time they land on the collector window! The vinyl can tolerate any of these challenges. There is also sufficient flex in the unit that it could crack untempered glass. Rigid window plastic should work great. If price is not object; hard coated, UV inhibited, 1/8” polycarbonate (aka Lexan, Tuffak etc.) would be the ultimate window material. (It scratches very easily if not hard coated.) You might be able to find the 3 1/2’ x 5’ piece you need for under $150. Acrylic (aka Plexiglass etc.) is cheaper, but it softens at a much lower temperature - boarder line for our use. It is also somewhat brittle, so 3/16” would be about the thickness needed. Avoid styrene unless it is free - melt down is likely if collector air flow was ever stopped in hot sun. The needles on our thermometers were buried by sun hitting the collector with the diverter closed. It was over 160 degrees F. Styrene melts at around 140 F, acrylic softens but recovers at 170 F, polycarbonate is good to over 260 F (and the wood ignites at something over 450 F). We aren’t sure what temperature that this vinyl can take, but we haven’t lost a $5 window yet - to heat or anything else!



Drying Screens



The drying screens start with a simple frame made with 1” x 2”, or larger, wood. Fiberglass screen is then stretched over one side. Cut your frame pieces as square as possible. Drill clearance holes for installing 2 screws through each end of the long boards. Use framing corner clamps, if available and install 1 screw at each corner. Then twist and tweak to square and flatten as you install the second screw in each corner. The flattening can be done for the final 2 screws by standing with frame on edge between legs, pressuring with heels or knees to take out the twist as you drive the screws. Use 30” screen and cut 45” pieces. With frame flat, center it and staple once in each corner, pulling lightly. Stand frame on side and pull the screen around the side and staple once in the center of each side, pulling tight on the second opposing side. From the center out, staple down each side pulling tight. Do one pair of opposing sides, then the other pair. Fold the corners and staple down. Hammer down any high staples. The drying screens are used screen down with the frame being a surrounding lip. For heavy load items, a cross divider bar can be installed with screen stapled to it underneath. We don’t paint our frames, but if used for food, sealing with white paint might help cleanliness and allow easy spotting of possible contamination. Light colored screen is also good for the same reasons. The Screen Stack Lid The lid performs several functions: 1. It keeps direct sunlight off of the load. 2. It protects from rain. 3. It closes the stack and chamber at night to keep out dew and allow static drying. 4. It protects the top loaded screen from being wind blown or insect contaminated. 5. It utilizes wind to accelerate stack air flow. 6. It is used to adjust air flow and temperatures for the different phases of drying. This all sounds complex, but it is amazingly simple to build and use. Use two screen frames. One is screened, the other is not. Fasten them together with two hinges on one long side - the screen surface between them (upside down from normal.) Install an overhang roof on the unscreened frame and you have it. We experimented with various roofing materials and went with corrugated galvanized steel barn/shed roofing sheet. It’s 2 foot wide so we lapped two - 3 foot long pieces to get front and rear overhang, but have none on the sides. We screwed into valleys and silicone caulked the heads, and then painted the tops white so that they wouldn’t be hot to handle. Bend under the corners and file the edges dull to avoid getting cut up. Other materials will of course work - but watch the weight. Heaving a monstrosity off and onto tall stacks is a needless personal abuse. Utilizing the lid is quite basic. We make 2 prop sticks for each - 9” and 4” from 1” x 2”. They prop openings of 9”, 4”, 1 1/2”, 3/4”, plus closed. 9” is for high air flow, lower temp, when first drying the “green and wet” loads. Once the main juiciness is dried, switch to 4” followed by a finishing hot and slow crisp dry with 1 1/2” or 3/4” opening, depending on the temperature tolerance of your load. If cloudy, use smaller openings. If rain is possible, use 4” or less. Close at night or on rainy days for dew protection and static drying. The front/rear edge openings from the corrugations don’t allow dew in but add some overheat safety with the lid closed. They have also turned out to be the ideal restriction for our electric heaters. We run the electric heaters with the lids closed venting only through the corrugation gaps. The rising lid top face also creates a ventri effect on breezy days. By keeping the opening end on the trailing side of the wind, a suction is created, increasing air flow through the



screens. The more opening the more suction (to about 12” max). If the wind goes into the opening, circulation will be impeded or even reversed. Try to keep the opening direction away from the wind. Wind hitting from the side is fairly neutral. Aim the collector for the sun and the lid for the wind. A good gust of wind from behind can flip the lid clean off. One of ours went about 30 yards one time. If there is any chance of gusty or high wind, lash the top down. We put 6 screw ‘eyes’ around the screen platform edge and use bungee shock cords and sash chain to hold things together in wind and during transport. Work Stand This was one of those “gee it would be nice if...” after thoughts that turned out to be a real asset. When drying a bunch of screens you inevitably need to ‘shuffle the deck’, sometimes a couple of times a day. The most dried loads are best on the bottom As loads dry they shrink so you can combine contents of 2 or more screens onto 1. The expansion chamber keeps ‘hot spots’ to a minimum, but once in a while turning screens helps. Where to set all of this? That big collector surface is just the right width to set two stacks of screens --- but it slants too much and they slide off. We made a stand that splits the slant between collector face and screen platform. Not enough slant on either to cause slides. You can shuffle screens, load/unload screens, even wash roots since the collector still slopes and drains. All at a convenient work height. We put some FM in it as well. Pull a ‘T’ handle and it sets itself up! Lift the front and the stand folds itself out of the way and all is back in solar position again! It’s easy to make. Make the ‘H’ leg frame. Attach with 2 hinges. The cord from the middle cross bar is an elastic "bungee" shock cord that folds it up. It is a long stretch medium strength, the type usually cloth covered. The set up ‘cord’ is a light chain that goes through a hole in the handle. Chain is used so a link loop can slip over a nail or screw on the handle to effectively safety lock the stand legs down. A guide/leverage board for the chain is mounted on top and extending out from the front bottom cross bar. You may need to experiment to get the optimum position and length. An over travel stop chain is a good plan. It stabilizes things and prevents accidently ripping out the hinges. We also put a set of eye/hook gate catches between the front legs and the closed stand, to lock the stand up and secure during transport. The handle is a ‘T’ type like on lawn mower pull starters. If everything is balanced and working smoothly, when you pull the handle up it will simultaneously lift the front and set up the legs. At worst you might need to lift a bit on the front handle when there is a heavy load of screens. When the retraction elastic cord is setup correctly, unhook the pull chain, lift up the front and the legs will fold back out of the way. Copyright WCE 1998-2004

How to Use the WCE Solar Dehydrator Post by WCE on Nov 3, 2004, 11:09am How To Use Your Dehydrator First air it out for a day to get paint odors and such out of it. Point it South on a sunny day, put on the lid without screens and prop open 4 inches a couple hours, then close down to 1 1/2” the rest of the day. Wash and dry your new screens. Load your screens, screen down, frame up. Don’t overload. There needs to be openings so air can rise through and exit the top. As loads shrink from drying, contents can be



combined to free up screens for fresh loads. The typical drying cycle is 1 - 4 solar days. This variability is dependent on time of year and the type of load that you are drying. Day 1; Open lid 9 inches all or most of the day to obtain maximum air circulation - this removes a majority of the moisture fast. ALWAYS CLOSE AT NIGHT. Day 2; Set opening to 4” or 1 1/2” all day, if the load is dry, remove before sunset. Day 3; Screen contents can be combined and fresh material loaded. Always shuffle the driest screens to the bottom and wettest to the top. This keeps convection and drying maximized. Set opening to 4” or 1 1/2”. Remove what is dried before sundown. The cycle continues, loading some new on top and finish drying on the bottom screens. Full initial loads dry at 9” opening and mixed loading at 4” to 1 1/2” depending on operating temperatures and how sensitive your load is to temperature. Minimal 3/4” opening is used for cloudy days or cooler weather. It can also boost morning start up. Thermometers and Hygrometers (humidity gauge) These are a big help to see what is going on in the dryer. We mount electronic temperature/humidity meters in the expansion chamber and put in windowed portholes to see them. (Radio Shack sells a similar meter #63-1013 for $24.99 in 1999 cat.) The amount of temperature drop from the expansion chamber to the top of the screen stack tells how much drying is still needed on homogeneous loadings. Evaporation causes a drop in temperature, so the greater the drop, the wetter the load is. Almost no drop means that it’s dry. Knowing the relative humidity in the expansion chamber tells you how effective the drying will be. Ambient temperature rise - the difference between the outside air and the heated air, similarly indicates efficiency. A 7 deg. ambient rise on a cloudy day is 25% as efficient as a 28 deg. rise on a blazing bright day - if the relative humidity is the same. Stack temperature is important for drying live seed (and keeping it alive) and for drying herbs with volatile constituents - such as the mint family. Temperatures over 110 F aren’t good for either. Tips --- If you are loading the screens heavily, you should stir or “toss the salad” once or twice a day. --- If rain shuts you down. You can wait out a day if the load was nearly dry. If the load was fairly wet, use auxiliary heat, or mold or deterioration will occur. --- Cloudy days still provide about 20-25% of the energy of the full sun but cannot crisp dry a load. Use auxiliary heat if cloudy conditions last more than a day or two. A fresh wet load in cloudy times should at least be partly dried with auxiliary heat to avoid deterioration. --- Bringing the loaded screens (or entire dryer) into a closed garage or similar will help avoid problems during wet weather. --- Some succulent difficult to dry foods are probably not suitable for this dryer. Sliced fresh tomatoes, for example, will likely spoil before drying. Obtain a good book on dehydrating and use it as your guide. NEVER consume food that may be moldy or spoiled! --- After fruit and vegetables are dry, 1/2 hour at 150 - 160 deg. F in an oven, can kill any bacteria or insect intrusion. If fully crisp dry, little if any nutrition should be lost. --- Some herbs and vegetables suffer damage if exposed to high temps when they are fresh wet-and-green. Try to keep temps. under 110 deg. F until fairly dry. Open the lid wider or partly cover the collector to reduce temperature.



--- When drying food that has a potential to spoil, it may be best to use solar in daytime and auxiliary heat at night to avoid problems. Particularly on the first night when moisture is still high. --- Bringing into a shelter, such as a garage, at night will help prevent re-hydration from high night humidity. Copyright WCE 1998-2004

Solar Dehydrator Winter Uses Post by WCE on Nov 3, 2004, 3:02pm



Solar Dehydrator Cold Weather Uses Post by WCE on Nov 3, 2004, 3:09pm Using your WCE Solar Dehydrator in Cold Weather Design and text by Dan Jincks There is one very critical limiting factor to dehydrating food, herb or root in cold weather. If it’s frozen it won’t dry. Raising the ambient temperature lowers the relative humidity, which does the actual drying. As surface moisture dries, internal water is wicked out and the inside dries as well. If it is frozen, moisture cannot wick to the surface. So, in the winter, increasing the collector’s ambient temperature rise becomes a new objective. The higher the rise, the lower that the outdoor temperature can go and can still continue drying. The sun is much lower and shorter lived in the winter, but there is still a lot of energy to work with. The available energy depends on how far North that you are located. Our Ozarks are about mid way. We have five months of “wood stove” heating weather, but most of the winter days have temperatures going above freezing and sunlight is usually abundant with 6 or more hours of usable solar output. These days and this solar unit work well together. Up around Canada, the results may sound fairly marginal. But read on Northerners - there still may be something for you. You are not doubt masters at the use of insulation and will see improvements beyond our suggestions. Note: The process known as “Freeze-Drying” is a high tech energy intense process that requires a tight chamber under high atmospheric vacuum. Being frozen and drying efficiently are a contradiction under normal conditions. The normal summer configuration utilizes high air flow to aid drying. The high air flow limits maximum temperature - which is correct in hot weather. Many herbs and foods are damaged by temperatures over 130 degrees. Live seed and fresh wet herb are best held to no more than 110 degrees. Keep these upper limits in mind for winter use as well - they can be exceeded! The first step is to make a cover for the air intake. The opening needs to be fully sealed, but the lower openings of the heat exchanger tubes must not be blocked. Be sure that there is at least 1 1/2 inches of clearance in front of them. They will still need to draw in air to circulate. The cover restricts the intake air to the hotter internal air - which greatly increases its overall temperature rise. The cover is made of four 1x3x42 inch boards and



masonite strips that form an “L” as viewed from the side. End caps of masonite are added to complete the enclosure. Ours are attached with three screws for easy summer removal - two under the handle and one in the work stand chain guide. You will need to remove or refit the work stand pull up chain. Caulk the cover joints, paint and install weather strips at the fit up edges as gasketing. (Don’t use polyethylene foam as it may melt ) This intake cover is the primary winter adaptation. It is something like the covering you will see on some truck radiators in the winter, so they run hotter. Just like the radiator, if it is in place in warm weather - the collector will get very hot! Even with proper upper venting, expect a 60 degree rise over ambient temperature. That’s 140 degrees on a warm 80 degree day. If venting is blocked, the ambient rise could go high enough to ruin a vinyl collector window! To be on the safe side, it would be a good idea to cover the collector window with an opaque tarp until in actual use. We need to establish a controlled source of input air for the heat exchanger tubes. They will create an upward internal air flow as they heat up from the sun, resulting in a suction at the lower openings. The downward slope of the floor directs cooler heavier air from the expansion chamber floor toward the lower input. The heated air rises to be released, but flow is restricted unless an outside source is allowed to replace it. The amount of replacement air determines flow rate and temperature rise, so it needs to be adjustable. You will need more restriction on a cold afternoon, but more flow on a warm one. Direct input of cold outside air into the exchanger tubes would reduce the obtainable ambient rise, so we will buffer the input air by mixing it with warmed air. If you have installed an electric heater porthole and its diverter panel, you have a ready made adjustable buffered air input. Varying an opening at the porthole and/or how far forward the diverter panel opens, will create a controlled source of outside air. Just make a new porthole cover with an adjustable opening up to about 6 inches diameter maximum, and block the diverter about 6 inches from being fully open to the collector. You could also make a control rod that sets the panel opening to experiment with the effects of variations. If you haven’t a diverter and porthole, construct a baffle wall and cut an opening in the back and make an adjustable cover for it. Now we need to consider our hot air exit. Your summer lid may or may not close tight enough to limit air flow. Try it before making anything new. The screen stack itself is probably the more significant consideration. Unless you are a very meticulous and exacting carpenter, there will be gaps and leaks between screens. These leaks were insignificant to the high air flow in the summer, but should be eliminated for winter use. Probably the easiest and most effective solution is an “overcoat”. Establish a maximum screen stack height and use it whether all screens are filled or not. Construct an insulating and sealing wrap-around outside cover. It could be a fabric blanket or a rigid box enclosure, but it must tolerate weather and not create a contamination hazard. Fiberglass or bare wool blankets are a bad plan. A blanket with an outer plastic wrap would resist rain. A rigid outer box is actually one of the best long term solutions, though it will cost more time and money up front. The lid itself should close fairly tight and have fine adjustability to be barely open. A corrogated steel top will need to be sealed to eliminate the corrogation gap leaks and be insulated underneith the metal with at least some plastic film. Metalized mylar like emergency “Space Blankets” are made from, make good thin insulation that is very heat tolerant. The collector body should be insulated as well, so it can retain internal heat as well as practical. All insulation goes on the outside. The bottom and back are the most significant surfaces since they never add heat from the outside by the sun warming them. The sides



are not nearly as important since as the sun strikes them morning or late afternoon, they heat up adding and holding in internal heat on that side. The thin foam board which is installed behind brick walls should work well for insulation. Metalized mylar film seems rather minimal but is significantly better than nothing. (The experimenter with a few dollars to spare, might actually build “side collectors” that add heat in the sun yet insulate fairly well in the shade. Something similar to the low light angle collector on the front. This would create self adjusting early/late boosters eliminating much of the need for aim adjustments! You will need more polycarbonate sheeting and must consider structural compromises. Considering the significance of that little low light angle front collector, it is likely a worthy line of experimentation.) The collector window is very important for serious winter use. The higher the quality, the more heat that gets in. A thicker window traps more heat as well. Vinyl film will work, but 1/8 inch polycarbonate with hard coating is about ideal and will take the weight of snow quite well. Double glazing will let a bit less light in, but traps heat much better. Since the heat exchanger tubes direct much of the heat without relying on the window to hold it, double glazing probably will not yield enough gain to justify the expense. This is particularly true of double polycarbonate, however vinyl over (and protecting) polycarbonate might equate well. A vinyl window costs $5 and may last 2 years. A polycarbonate window costs about $100 and should last 5-10 years. That $5 piece of vinyl on top could well double the life of the polycarbonate since the vinyl takes the dirt, scratches, impacts and absorbs part of the damaging UV radiation. A 3/4 inch separation between double window panels should work well. Polycarbonate handles heat to 270 degrees, which is well above any temperature that this collector could develop - even closed tight in the summer heat. Polycarbonate is the way to go if you want to be care free or experiment with high temperature dehydrating in the summer. Your black interior surfaces effect efficiency. Most flat black paint is more like dark gray - a lot of light is reflected instead of absorbed. Have extra black pigment added to the paint if possible and compare samples for blackness - and heat production in the sun. The paint used on heat exchanger aluminum should be thin and sprayed on. Military or camoflage paint may produce the best black - but compare samples if practicle. Dirt reflects! Remove the collector window, clean and lightly spray paint over black surfaces before winter use. Dirt, debris and bugs mostly accumulate during spring and summer usage. Be sure to install the low light angle collector. It is a necessity to best utilize the low angle of the winter sun. Now an odd twist of caution. An insulated, maximized, collector will be much more efficient than a quick summer version. Great for winter - but watch out for July! Keep an eye on peak temperatures and be prepared to partially cover the collector. Be sure to remove the intake cover before day high temperatures exceed 80 degrees. Copyright WCE 1998-2004

Solar Dehydrator Winter Uses Post by WCE on Nov 3, 2004, 3:14pm The Ultimate Winter Solar Dehydrator No matter how much you adapt the unit to doing winter duty, there are still some significant flaws. One, when the sun sets, the world freezes over. Some things should not be allowed to freeze and precious winter solar time is lost waiting for the thaw so that



drying can begin. Two, taking dryer loads in at night and out in the morning, to protect them, is a lot of extra effort. Three, it’s no fun working out in the cold. About the best you might expect to do, to deal with this situation, is to wheel the entire loaded dehydrator in and out of a garage each day. If you are fortunate enough to have a convenient South facing window, you may be able to build what some would consider the ultimate winter solar dehydrator. You can back the collector under the window and port the output into the comfort and convenience of a sheltered space. Not only does it dry your herbs and food, but it adds FREE heat to the inner space - without any electric or additional energy of any kind. And the adaptation is cheap! The ideal location would be a window facing South to Southwest, with its opening being just higher than the collector top. The inner space would be unheated or minimally heated, but above freezing. The temperature requirement is due to the fact that convection flow only happens when collector high temperature exceeds the inner space temperature. For example: Say it’s a zero degree day outside and the collector produces a 60 degree rise, so 60 degree air is produced. If the inner space is 70 degrees, no convection flow can be produced. If the inner space is 40 degrees, there is a 20 degree rise above the inner space temperature and good convection circulation is produced. The ideal location is likely a garage or outbuilding or unheated room - that needs the extra heat as well. We suggest using a window because it is easy to adapt the opening, but ducts could also be run through a wall. Of course it makes a great deal of sense to run the extra heat into a living space to supliment your heating needs. You just must realize that below a certain outdoor temperature, it will not add heat indoors or circulate. You can expect about a 60 degree rise on a clear day. Cloudy days derate to about 25% on average, yielding only about a 15 degree rise. You need the same intake cover, insulation, and collector window as mentioned above. The input and output is rather different. They become a pair of 6 inch diameter ducts passing into the inner space. The lower duct is the input and feeds in cool air behind the diverter panel or a similar barrier. The output from the solar collector vents into the upper duct. They are pictured as over/under, but they can be side by side. They can be situated right, left, or centered. They can extend up as needed, but the output should not drop down unless it remains a tight unreleased flow, and then rises well above the collector output height before it vents free. The more twists and turns in the ducts, the more that flow is impeded. If the sun strikes and heats the cool air input duct, it may backflow and stall circulation - especially if heated inside the collector. Ducts can be insulated metal, but plastic is better since it won’t conduct cold into the inner space at night. Installing tight cutoff dampers in both ducts will allow you to close out any possible cold air that might back flow at night or during cloudy periods. Under ideal conditions, back drafting cold air shouldn’t happen even if the ducts are open. Fireplaces, furnaces, wood stoves, exhaust fans, etc, can create back drafting from leaks in the collector or air ducts. When you fully close the dampers, it’s a good plan to cover the collector window with an opaque tarp to avoid accidental overheating. Covering the collector window at night also keeps frost off and allows the earliest start. White reflective frost is slow to clear and it prevents the collector from warming and defrosting itself. Do not try to scrape frost from the collector window - you will damage the plastic. Partially closing down a damper on either duct reduces flow and should create more temperature rise to maximize use with colder exterior weather conditions. The output can



simply pour heated air into the inner space or be directed into a simple cabinet containing dehydrator screens. The dehydrator “cabinet” can be a stack of summer screens on an enclosed box base or be an actual cabinet of other size. The dehydrator cabinet should be above the output duct height to maintain best convection flow. The output is quite impressive. Our original test setup utilized a “summer dirtied”, uncaulked, uninsulated collector with leaky steel ducts, and a 2 year old patched vinyl window - into a loose window adapter. (About the worst efficiency likely.) It connected into a 9 x 12 utility building with a 6 1/2 foot ceiling - R11 insulation all six sides, but it has some noteable thermal leaks. The collector ambient rise was still 55 degrees at 2 pm in early December and it maintained at least a 20 degree rise in the building for over 12 hours. (This included latent heat held and released by the enclosed mass after sundown.) The solar powered convection flow blew its heated air for over a foot horizontally out of the end of the output duct. This ambient rise brought the collector output air down to 15% relative humidity - which was a new record in low relative humidity here in our moist Ozarks. There were no other sources of heat or even unshuttered window openings. Another similar unit heats an office used primarily in the afternoon and evening - where it has very noticeably reduced the need and cost of other heating. The versatility of this simple solar device is quite amazing. All summer long it quietly sits out by itself drying herb and food, and then it docks into a building to do more drying and provide warmth. All this without a single watt of synthetic energy or any moving parts! Copyright WCE 1998-2004


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