Category: Making

Projects that make or build something.

Post #1858: Indirect solar food dryer, Part 2: Building a roll-up solar air heater.

In a nutshell:  In an afternoon, I made a roll-up solar air heater using plastic sheeting, a pile of green mesh vegetable sacks, some tape, and a fan.  At solar 3PM, that’s now putting out a nice stream of air at just under 130F.  That should be adequate to serve as the hot air source for drying food.

See the just-prior post for the theory.  In particular, why a mesh-filled tube is a pretty good choice for a solar collector.

When I’m done with it, I can just roll the whole thing up and store it in a nice, compact package.

Background

I want to make a solar air heater, to use for drying my garden produce.  Mainly, for making dried tomatoes.  Solar-powered, because otherwise, in the humid climate of Virginia, my only reliable option is to use an ungodly amount of electricity to make those dried tomatoes..

Source: Post G22-010.

At this point, I’ve exhausted all of the simplest solar-drying options.

Even in Virginia, if you get perfect drying weather for four days in a row, you can dry tomatoes using old-fashioned open-air drying (Post G23-056).  The problem is, you can rarely count on a stretch of weather like that, around here, when you need it.

I also tried making a simple power-ventilated direct solar food dryer.  (That is, a clear-topped, ventilated box in which sunlight shines directly onto the food to be dried.)  My conclusion is that direct solar dryers just don’t have enough power to dry tomatoes reliably in my humid climate (Post G23-058, Post G23-057).

My aha! moment came when I realized that direct solar food dryers are simple flat-plate solar air heaters.  The food sits on or above that flat plate.  Simple flat-plate solar collectors are the least efficient way to convert sunlight into heat energy.

So here I am.  My late-season tomatoes are (finally!) ripening, so it’s time to get this done.  I’m upping my game by making an indirect solar food dryer.   This is a dedicated solar air heater, hooked up to a box that contains the food to be dried.  That arrangement allows you to increase the power input, both by increasing the efficiency of the solar energy capture, and increasing the ratio of solar energy capture area to area of food to be dried.

Celebrating the cheap and flimsy design.

Source:  Government of New Zealand.

Funny thing about the word “cheap”.  Once upon a time, it had no negative connotations.  It was used as we might use “inexpensive” today.  Goods were advertised for their exceptional cheapness.  Which, back in (say) Colonial American times, meant low price, not shoddy construction.

My point being that as long as I’m making a cheap and flimsy solar air heater, I might as well celebrate that.  No sense in trying to make a high-quality cheap and flimsy device.  Might as well make it as cheap and flimsy as possible.

Construction overview.

Solar air heater.
  • Make a big plastic tube out of a single sheet of clear plastic.  When flattened, roughly 4′ across by 16’+ feet long.
  • Place a 4′ wide piece of black or reflective plastic inside the tube, to form the inside bottom of the collector.
  • Stuff the tube, between the black/reflective plastic bottom and the clear plastic top, to a few inches depth, with a loose layer of dark, porous material.  I’m using mesh produce sacks, see below for other suggestions.
  • Leave 2′ empty, at either end of the tube, for attaching it to fan and duct.
  • “Quilt” the stuffed portion of the tube.  That is,  stitch through it with twine, or otherwise tack top to bottom, just enough that the top of the tube cannot “balloon” when the fan is turned on.  (The point of this is to force the air through the porous filler, not above it.)
  • OR, simply weigh down the top of the tube, with pieces of wood, to achieve the same end of keeping the top of the tube sitting firmly on the stuffing.
  • Tape the fan to one end, oriented to blow air into the tube.
  • Tape a piece of flexible dryer duct to the other end.

In pictures:

Plastic, about 8′ wide by about 20′ long.

Plastic sheet folded in half to make a long 4′ wide tube, then taped (see tape seam at left), with a 4′ wide piece of radiant barrier inside the tube to serve as the bottom.  I’m not even sure that radiant barrier (or equivalent piece of black plastic) is necessary.  FWIW I used Gorilla (r) duct tape, and that seems to be sticking well to the plastic sheet.

A bunch of mesh vegetable sacks drying in the sun, after being hosed off.  Why do I own these?  Long story.  But because I already owned them, I’m using this as my solar collector material, rather than black screening.

The plastic tube, now stuffed with those mesh sacks, balled up.  Try to pack it loosely, but with no voids that would let air flow around the mesh, rather than through the mesh.  You want to force the air to flow through the mesh so that it will pick up heat from the sun-exposed mesh.

Ready to run.  Fan is clipped into the near end, a piece of flex duct is clipped into the far end, and chunks of wood weigh down the top.  You can see that the top still balloons up a bit, between the pieces of wood, from the force of the fan.

The fan is an ancient twin-bladed window fan.  I’m guessing that with no resistance, it moves 250 CFM on low, and draws maybe 30 watts.  With the resistance imposed by passing through the mesh, I have no idea how many CFM it moves.

Same, side view.

Same, end view.

A nice stream of 129F air, at solar 3 PM, on an 80F day, with no adjustments?  That’ll do.

Total assembly time was around two hours.  And I now have a roll-up solar air heater that is adequate for the task of drying tomatoes.

Food dryer (TBD).

I am greatly simplifying my task by using Nesco food dryer trays.  With the addition of a bit of tape, these can be stacked to form an air-tight cylinder, with the food to be dried neatly laid out within that cylinder.  All I need to do is place that cylinder above an appropriately-sized hole in a cardboard box.  Run the flexible duct from the solar air heater into that box, and that will serve as the food dryer unit.

Note that with this design, the cardboard box itself doesn’t get wet.  All the humid air from the food goes up the stack of trays, and out.

 

Materials/tools list for the solar collector:

  • Pair of scissors.
  • Clear plastic sheet, approximately 8′ x 16′, or longer as desired.
  • Black or reflective plastic sheet, 4′ x 12′, or ditto.
  • Optional:  Additional clear plastic sheet 4′ x 16′, or ditto.
  • Dark, porous material to fill the tube (e.g., plastic screening, see below).
  • Tape (packing tape, duct tape, or whatnot).
  • Twine and something to use as a needle for “sewing” with that twine,
    • OR, double-stick tape.
    • OR four 8′ 2x4s.
  • Window fan or standard 20″ box fan.
    • Cardboard (e.g., 20″x20″ square) for modulating air flow from box fan.
  • Small length of flexible dryer duct.

Materials for the food dryer unit

  • Cardboard box
  • Nesco round drying trays (or substitute what you have).
  • Tape.
  • Cardboard sheet to cover the top of the stack of trays.
  • Instant-read thermometer.

Details

Step 0:  How big?

I’d like this to to produce around 900 watts of heat, on average, over an eight-hour sunny summer day, at 40 degrees north latitude.  Assuming this is 30% efficient at capturing sunlight, then, based on my prior calculations, this should capture an average of 18 watts per square foot.  So I’m shooting for about 50 square feet of collector.

I have no intuition as to the right shape.  I’m guessing that depends on a lot of factors.  The material I’m starting from is almost 20′ wide, so I’m tentatively planning on a tube about 4′ wide and 20′ long.  That’s a bit larger than necessary, but it matches what I have on hand.  Of that 20′, a couple of feet on either end will be used to connect to fan and duct, and so will not contribute much, if anything, to solar energy collection.

I’m guessing that one 8′ x 16′ piece of clear plastic sheet should be adequate to form the tube.  I’ll need a further 4′ x 16′ piece of black or reflective plastic to line the bottom of the tube.  And, optionally, one more piece of clear plastic, 4′ x 16′, to add to the top for “double glazing” of the finished, quilted tube.

Step 1:  Obtain a large amount of dark, porous, lightweight material.

In my case, that’s a box of mesh produce sacks that I’ve had on hand for years.  (These were part of a failed attempt to simplify the handling of my firewood.)

Plastic window screening should work fine, but is an expensive solution if you are using new materials, due to the amount of material required.

Or, you might try doing this with no filler.  Just blow air down a hollow clear-topped tube.  That should make this much less efficient at capturing sunlight.  So make the tube bigger than you would otherwise.

Beyond that, if you use something that isn’t compressible, you lose the ability to roll this up when you are done with it.  If you don’t value that, you could consider:

  • Styrofoam packing peanuts, painted black.
  • Coarse, dark, shredded wood mulch.
  • Possibly, lava rock.
Step 2:  Make a large plastic tube with a clear top and a black or reflective bottom.

This couldn’t be easier.  Get some clear plastic sheeting, e.g., the stuff they sell as dropcloths at the hardware store.  (In my case, I’m using greenhouse plastic, which is more UV-resistant than garden-variety hardware-store plastic sheeting.clear-topped plastic tube.)  Fold it in half, and tape the edges together.

I’m going for a reflective bottom because I own a roll of house-construction radiant barrier material.  The idea is that any light penetrating the layer of loose fill will get reflected back up into that loose fill.  And, where the fill is at least a half-inch away from the radiant barrier, the barrier will act as insulation against radiation heat loss through the back of the tube.

Step 3:  Stuff the tube — but NOT the last 2′ on either end — with a few inches’ thickness of dark, porous material.

For me, this was as simple as temporarily closing off one end of the tube, scrunching up the mesh sacks, chucking them inside, and using a stick to arrange them into a single, packed mass.

This isn’t precision work.  The air is going to flow through all 16′ of the tube.  As long as there’s no continuous channel through which the air can flow from end to end and bypass your porous material, you should be fine.

Step 4:  Keep the top of the tube from ballooning up.

You want air to pass through the porous filling, not above it.  So you want to keep the plastic top sheet right down on top of the filling, in some fashion.

I was originally going to “sew” or tape the top and bottom together in places, to do this.  But on reflection, the easiest thing to do is weight the top down, while obstructing as little light as possible.

I’m just going to toss some 2×4’s onto the top of the sheet, and, if necessary, weigh them down with (e.g.) bricks.

Optionally, add a second layer of “glazing” by tossing another clear plastic sheet on top of this.  That will trap insulating air where the top of the tube is depressed by the quilting or the 2x4s.  I’m guessing this isn’t worth it, but I make try adding it and taking it off to see what happens to the resulting air temperature.

Step 5:  Attach fan and duct.

Attach a window fan or 20″ box fan to one end, and a short length of flexible dryer vent to the other.

I want to be able to take this apart at the end of the season, to store it, so I’m doing these attachments with lengths of bungee cord.  You could just as easily make the attachments with tape, and peel back the tape at the end of the season.

Step 6:  Make and attach air distributor for food drying (TBD).

Because I’m using round Nesco trays, my air distributor will just be a box, somewhat larger than the trays, with holes for the dryer duct and the trays.  Run the dryer duct into the box.  Place a piece of cardboard on top of the uppermost tray, to make sure the hot air hits all the food as evenly as possible.  That’s it.

Step 7:  Operation.

Place the tube on the ground, in the sun.  Place weighs on top of the flat solar-collector tube, to keep the top from ballooning up.  Attach duct, fan, and (eventually) food drying box.  Turn on the fan.

Summary

It works.  And it’ll roll up at the end of the season.  So that’s a success.

This could use a bit of tweaking.

I probably used way more mesh “stuffing” than I really needed.  I can’t even see the reflective bottom of the solar air heater, through the green mesh bags stuffed inside.

I’m sure this would get hotter if I could tilt it so that it was perpendicular to the sun’s rays.  As one would do with a solar panel.

But … it works well enough as-is.  So I don’t see any need to modify it.  I can unroll it in the sun, attach small fan and duct, and produce a nice stream of hot air as long as the sun shines.  That’s really all I need it to do.

Arguably the most mickey-mouse aspect of this right now is the weights for the top.  Without those, the plastic sheeting simply balloons up, and the air passes over the mesh, not through the mesh.  Tossing some sticks on top makes it work, for now, but I’d like to get a more elegant solution at some point.

I’m now going to roll this up and put it away until my final crop of late-season tomatoes starts ripening in earnest.  Then I’m going to use this for a last batch or two of dried tomatoes.  Weather permitting.

Addendum:  Oh for duh!

Turn the fan around and stick it in the other end of the tube.

After I put this together, I went looking for a better fan.  Window fans of the sort I’m using really shouldn’t be used to push against considerable resistance. 

That’s when I realized that if I sucked air out of the tube, instead of blowing air into the tube, the entire problem of having the surface of the tube balloon up simply goes away.  All the wood and metal pieces on top of the solar air heater are unnecessary.  And I end up with a simpler and more elegant design.  If such a word can be applied to this cheap and flimsy roll-up solar air heater..

Post #1855: An example of why you should do Swedish death cleaning as you age.

 

My recent foray into furniture repair has turned into a lesson on why you should do you own Swedish death cleaning as you age.

To recap, this is what is left of a pair of chairs that got tossed to the curb, across the street from me, here in the middle-class suburbs of DC.  They were in great shape when I picked them off the curb, but years of use by my kids took their toll on the half-century-old fabric and foam.

These were discarded, in excellent condition, alongside heaps of other household goods, by the children of an elderly, recently-widowed woman.  Her kids were clearing out her house, as they prepared to move their mother down to Texas to be near them.

At that time, I couldn’t find any images of these on the internet.  I assumed they were 1970s Sears knockoffs of a mid-century-modern design.  Or similar.  Middle-class couple, middle-class house.  Surely these were nothing special.

Yesterday I started putting these back together, as shown in the just-prior post.  At that time, I didn’t even know what to call them.  But they’re pretty nice, and it would be a shame to see them end up in the dumpster.  So why not.

On a whim — now two decades after my first attempt to ID them — I did another Google search.

I have now gotten a certification, from the son of the designer, that this is (or was) what’s left of a pair of Adrian Pearsall Craft Associates chairs.  

Adrian Pearsall is now something of a legend in U.S. mid-century-modern furniture design.  Properly restored, this pair of chairs would be worth thousands of dollars.

Worse, improperly restoring them is something of a sacrilege.  Not for the money lost, but for taking a valued piece of Americana and destroying it.

This is suddenly a different and more complex task.  All my woodworking plans go out the window.  And now I have to figure out how to proceed, now that I know what they are.  I don’t collect antique furniture, so it’s not clear these have any business staying with me.

I guess the real take-away is that these never should have ended up in the trash.  But they did so, because the prior owner left it up to her kids.  I only discovered the chairs’ secret identity because they became part of my own Swedish death cleaning.  I still have no idea what to do with them, but at least I’m making the decision, with an understanding of what they are.

Post #1854: Can this furniture be saved? Part 2, diving right into it.

 

Today I started restoring the two chairs pictured above.  I glued up one frame, and started a Tom-Johnson-style repair (below) of the other.

The sad circumstances under which I acquired these are given in Post #1697.

I’ll be writing up the progress, a bit at a time.  The idea is both to make notes, and to present an un-edited version of how this restoration actually played out.  Cuts and all.

Edit:  I may have goofed, big-time.  I picked these off the curb years ago, as described in Post #1697.  Last time I looked into it, I could not figure out who made them.  I assumed they were run-of-the-mill furniture, likely Sears Best or similar.  But now, the internet shows me that these are identical to Adrian Pearsall Craft Associates 932-C Sling Lounge Chairs.  Like these, on Ebay.  If so, these are (or were) valuable antiques.  Unless I can show that these are knockoffs, there will be no followup to this post on repairs.

 

Getting reacquainted with hand tools, or Today I Learned That Wood Chisels are Sharp!

Today I sliced the side of my thumb with a wood chisel.

‘Tsall good.

I’m now more mindful of where the sharp edge of the chisel may go if it slips.  And I take pains to hold the work and tool accordingly.

Let’s do Q and A about this incident.

Q:  Was I being a dumbass?  A:  Yes

Q:  Did it hurt like hell?  A:  Yes, eventually.

Q:  Deep cut?  Did I bleed on stuff?  A:  Yes and yes.

Q:  Gonna try not to do that again?  A:  You got it.

Summary of today’s progress.

There are two walnut frames, and two cloth-covered rigid foam seats, that must be restored.

One of the walnut frames is now glued back together.  That frame needs to have a corner block made and glued into place.  At that point, it will be complete except for cleaning, and having a finished seat installed.

This part was mostly boring and/or complicated by my lack of tools.  In particular, the nylon-rope-as-clamp was a bit of a clown show.  It took a couple of tries, but I think I got it adequately tight.

Above, left, is the wooden internal support for the rigid-foam seat.  When done, that will fit within the frame, with most of the occupant’s weight resting on two curved cleats screwed to the frame, as shown below.  Just four non-weight-bearing wood screws (two in the top bar, two in the bottom bar) hold the seat to the frame.

I don’t even know what to call this thing.  TV chair?  Lounger?  Even though it’s seems 1970s vintage (owing to the burnt orange fabric), the frame just says mid-century modern to me.  Whatever it is.

On the other frame, I have started a  repair patterned after those of Tom Johnson, of Gorham, Maine.  He’s a fine furniture restorer on YouTube.  In a situation like the one I’m facing, where the end of one leg is broken, he typically cuts the wood back to what’s sound.

Then he glues in an oversized block of matching wood.  Then he carves it to shape by hand.  That last part makes this fairly risky, for an amateur.  But after looking at my options, this seemed at least potentially feasible for me.

I think I can get that into shape.  For a no-talent like me, some combination of rasps and sandpaper (and lots of time) should allow me to get close. We’ll see tomorrow.

For the walnut piece that I glued in, I went to my local thrift shop and bought an ugly little piece of walnut bric-a-brac, from which I cut the block of walnut I used.  It was cheaper than buying a walnut board, and I could see how the wood would look when finished.

At this point, the only difficult task was drilling out the broken dowels.  FWIW, I drill a little pilot hole, hoping that it’s centered and square.  The drill a hole just smaller than the diameter of the dowel, hoping the drill bit stays entirely within the dowel, and doesn’t drill out into the walnut.  Then I scrape out any remaining wood that I can reach.  Then I clean out the hole using a drill bit that’s the full diameter of the dowel.

The whole game plan is to avoid wallowing out the hole, while cleaning out all the wood and glue in the hole.  I came close.  Mostly.

Dealing with loose but intact joints.  I’ll probably spend time in Purgatory for doing this, but I did not knock all the loose joints apart and re-glue them.  Two joints in the side frames were loose, but I feared taking the sides of the chairs apart entirely.  So instead of knocking the sides apart, I used clamps to spread those joints, exposing the loose (un-glued) dowels.  I liberally applied glue to those dowels before clamping the joints back together.

Arguably, the other sin I committed was gluing the dowled joints using Titebond (yellow aliphatic) glue.  I think the experts say to use hide glue on the joints, so that the furniture can be knocked apart as needed at a later date.  But having saved these from the trash once, I think that if I can get them back together at all, even once, that’s good enough.  So regular Titebond it is.  Plus, I already own it and know how to use it.

Next post will outline the overall plan.

Post G23-057: Solar food drying, a better understanding

 

Upshot:  Direct solar food drying — putting your food out in the sun (with or without some clear cover) — is an inherently low-powered and slow way to dry food.

By contrast, indirect solar food drying — connecting a solar heat collector to a box full of food to be dried — can be much, much faster.  That’s because you can increase the power of the device.  Mostly, you can greatly increase the efficiency of the solar collector, relative to direct solar drying.  Secondarily, you can also make it larger, if you choose — there’s no necessary relationship between solar collection area and the area covered by food.

And faster drying means lower taxes!!!  Uh, no, I meant, faster drying means fewer days-in-a-row at the mercy of the weather.

The key, to all this new-found wisdom?  Figuring out that a “box-with-clear-lid” food dryer is, technically speaking, a flat-plate solar collector.  Then realizing that flat-plate is really inefficient, relative to other things I could make.

I need to make an indirect solar food dehydrator.  And it only took me two or three years to figure this out.

In the interest of reducing TL;DR, I’m breaking this into two posts. This post is just the setup.  Next post should be the actual construction and use, if any. Continue reading Post G23-057: Solar food drying, a better understanding

Post #1842: … and the voice of the chihuahua is heard in our land, …

With apologies to Song of Solomon, 2:12.  But surely the blog title makes at least as much sense as ” .. the voice of the turtle … “.  Whatever.  This post isn’t about Bible specifics.

The background here is that a friend, has a little kid, who really likes a stuffed toy, that has a broken electronic voice-box.

The catch is that the toy in question is a 25-year-old plush chihuahua dog.  It was a promotional giveaway from Taco Bell.  It was never meant to be repaired.

There are probably a lot of these exact Taco Bell chihuahua dogs still in existence.  You can buy one on Etsy (below).  But at this point, it’s a fair bet that the 25-year-old batteries in the device either have died, or will soon die, if the toy is actually used as a toy. So if you want one that talks — and the little girl in question definitely wanted that — you’d best be prepared to replace the batteries, at least.

Source:  Etsy (link to page). 

 

So, would I mind trying to fix it?  Needless to say, replacement parts may be an issue.  And in terms of helpful instructions on the internet, I found none.

In the end, I tried to fix four broken Taco Bell chihuahua voice boxes.  You never know who might want to read about fixing a mute Taco Bell chihuahua plush toy.  So I thought I’d document the fix.  It’s not as if hordes of folks read this blog, even on my best days.  Bottom line, three out of four now work. Continue reading Post #1842: … and the voice of the chihuahua is heard in our land, …

Post G23-010: No-dig potatoes, using leaf mulch

Today is St. Patrick’s day.

That’s the traditional day for planting potatoes, in this climate.

But my new raised beds aren’t ready yet.  And the old ones are a weedy mess.  Which I didn’t much feel like hoeing out of the way, this rainy St. Patrick’s day morning.

So I planted this year’s potatoes as no-dig (no-till) potatoes.  I placed them on top of an existing weedy garden bed, and buried them under half-a-foot of free leaf mulch.

Edit 7/23/2023:  Near-total failure.  See Post G23-041. Continue reading Post G23-010: No-dig potatoes, using leaf mulch

Post G23-009: New garden beds. Working harder, not smarter.

 

At the start of the pandemic, I recycled some political yard signs and bamboo into a set of raised garden beds (Post G05).   After three years of intensive use, a) those are now in disrepair, and b) I know a whole lot more about gardening.

My plan is to replace those beds with something better.  With St. Patrick’s day just one week away — the traditional day for planting potatoes — I can’t procrastinate much longer.   Time to finish pondering and start shoveling.

This post documents the final design.  The next post will show the construction.

Continue reading Post G23-009: New garden beds. Working harder, not smarter.