Post G23-064: Tin-foil-hat gardening success: Radiant barrier over poly sheet.

 

Above, my tomatoes stayed at 50F, despite an overnight low of 43F.

Short answer:  Draping sheets of radiant barrier over an air-tight plastic enclosure keeps the plants underneath warm.  In fact, about 7F warmer than the ambient air.  (That’s the same magnitude I found when I used radiant barrier as frost protection, last spring.).  This protection against low temperatures should be sufficient to allow my remaining green tomatoes to ripen, despite cold nights.  Continue reading Post G23-064: Tin-foil-hat gardening success: Radiant barrier over poly sheet.

Post G23-063: Tin-foil-hat gardening fail, loose-fitting radiant barrier does nothing to keep plants warm.

 

Short answer:  Draping sheets of radiant barrier over my tomatoes did nothing to keep them warm last night.  If I want my remaining tomatoes to begin ripening on the vine, I’m going to have to build a temporary air-tight plastic-sheeting greenhouse around them.  Then put the radiant barrier over that.

Not sure if a couple-dozen tomatoes are worth the effort.

Continue reading Post G23-063: Tin-foil-hat gardening fail, loose-fitting radiant barrier does nothing to keep plants warm.

Post G23-061: Tin-foil-hat gardening, or, yet another garden radiant barrier experiment. Part 1

In a nutshell:  I’m going to try draping radiant barrier material over my tomato plants, to allow them to continue ripening tomatoes despite oncoming low nighttime temperatures.  I’ll use a couple of temperature data loggers to track the results, which I will report tomorrow.

Let the garden wear the tin-foil hat this time, instead of the gardener.

Continue reading Post G23-061: Tin-foil-hat gardening, or, yet another garden radiant barrier experiment. Part 1

Post #1671, reposted: The future belongs to Boaty McBoatface, or, Why it’s time to cash in my I-bonds.

 

Edit:  I originally posted this back in January 2023, as Post #1671.  I didn’t cash in my government bonds at the time.

Yesterday I came across the phrase “the crumbling of the American political system”, and it really resonated. 

I mean, come on, seriously, how many unprecedented events have to occur before you realize that this time, it really is different.  To put it plainly, I think the “red Caesar” totalitarians are going to win, riding on the backs of the ignorant. 

With the House unable to function more-or-less indefinitely, the Supreme Court a corrupt arm of the Republican party, and the propaganda machinery running full-bore, all we need now is a good, stiff economic recession to ignite the flame. Any appeal to “checks and balances” and “free press” to prevent this is just so much whistling in the dark.

I guess what I’m saying is that, right now, it does indeed look as if the U.S.A. has been McBoatfaced.

I think I’ll buy some more gold.  Not a good investment, but it makes me feel better.

Original post follows.

Normally my posts tend to be reality-based and fact-oriented.

Today, by contrast, I’m having a hard time dealing with reality, so I’m going to blather about the current state of affairs in the U.S.A.

I will eventually get around to those I-bonds.  But it’s not exactly a direct route.


Business 101:  Scope of authority should match scope of responsibility.

Your scope of authority is the stuff you have control over. Things you can change.  Decisions that you get to make.  That sort of thing.

Your scope of responsibility is the stuff you’ll be held accountable for.  Financially, legally, morally, socially, or whatever.  It’s all the stuff that, if it goes wrong, you take the blame and/or penalty.  And if it goes right, you get the praise and/or reward.

If you’ve ever taken a class on how to manage a business, you’ve almost certainly heard some version of the maxim above.  In an ideal business — and maybe in an ideal world — each person’s scope of authority and scope of responsibility would coincide.

Where scope of authority exceeds scope of responsibility, you get irresponsible decision-making.  The decision-maker doesn’t have to care about the consequences of the decision.

Where scope of responsibility exceeds scope of authority, you get stress.  A classic case might be where a customer screams at a waiter over the quality of the food.  It’s not as if the waiter cooked it.  But the waiter is held responsible for it.

This is really not much deeper than saying that you should be held accountable for your decisions.  And, conversely, that you shouldn’t be held accountable for things outside your control.


Boaty McBoatface:  This is what happens when you violate Business 101.

Source:  Wikipedia

You can read the full saga on Wikipedia or the New York Times.

Briefly:  About a decade ago, an arm of the British government (the NERC) decided to make a major investment in a nearly $300M polar research ship.  That ship has the serious mission of measuring the effects of climate change in the earth’s polar regions.

As the ship neared completion, it required a name.  And so, to gin up popular support, they decided to choose the name of this new capital vessel via internet poll.

Hijinks ensued, in the form of the most popular name, by a wide margin, being Boaty McBoatface. The name was, in fact, suggested as a joke.  The guy who suggested it eventually sort-of apologized for doing so.  But it won handily.

In the end, the NERC reneged and gave the ship a properly serious name (the RRS Sir David Attenborough).   But they did name one of the autonomous submersibles the Boaty McBoatface.  As shown above, courtesy of Wikipedia.

This was a classic violation of Business 101.  The scope of authority — the right to name the ship — was handed to an anonymous internet crowd who bore no responsibility whatsoever for their actions.  Meanwhile, the people responsible for paying for and running the ship had, in theory, no control whatsoever over the name.

This is hardly the first time that a seemingly serious internet poll led to a frivolous outcome.  But it was such a stunning backfire that “McBoatface” has now become a verb in its own right, per the Wiktionary:

Verb

Boaty McBoatface (third-person singular simple present Boaty McBoatfaces, present participle Boaty McBoatfacing, simple past and past participle Boaty McBoatfaced)
  1. (neologism) To hijack or troll a vote, especially one held online, by supporting a joke option. [from 2016]
    
    

Did we just McBoatface the U.S. House of Representatives?

In the U.S., an election is an anonymous poll in which those casting votes bear no individual responsibility for the consequences.

It’s hard for me to see much difference between that, and a typical internet poll.  Other than the fact that it’s difficult to vote twice.  And that some people actually do take elections seriously.

I guess it’s a bit pejorative to suggest that the current chaos in the House of Representatives has occurred because we McBoatfaced the last election.  Still, you have to wonder about the people who voted for candidates whose sole promise was to be loud and disruptive, and do their darnedest to interrupt the normal business of government.  Did they think that would be fun prank, the same as the McBoatface voters?  Own the libs, or whatever.  Or was that really their serious and thoughtful goal?

At least their candidates seem to be carrying through on their campaign promises.


What people are getting backwards about the current situation.

Here’s one that kind of cracks me up, but kind of doesn’t.  You hear a lot of people saying that the lack of a functioning House is OK, because the Federal government already passed a budget for FY 2023.  They won’t have to face that task until this fall.

I think that’s backwards.

Rephrased:  Senate Republicans saw this predictable train wreck months ago, and so worked with Democrats to pass the current (2023) FY budget.  That’s presumably because they already knew (or strongly suspected) that the House wouldn’t be capable of doing that.

Re-interpreting today’s events:  The predicted chaos has come to pass.  I’d have to bet, then, that there will be no new budget for the next fiscal year, and no increase in the debt ceiling.

The currently-funded fiscal year (2023) ends on 9/30/2023.  So that’s a known.  Even then, I believe that entitlement programs (Social Security, Medicare) remain funded.  It’s only the “discretionary” part of the budget that is not.

But as to when, exactly, we hit the debt ceiling, nobody can quite say.  Consensus seems to be mid-2023.

At that point, the Federal government will continue to make what payments it can.  So, likely, Social Security checks will continue to go out.  (Figuratively speaking — I don’t think they’ve mailed out physical checks in decades.) Other payments will not be made.


On lock-picking, McBoatfacing, and I-bonds

Source:  Covertinstruments.com

Which brings me to my final speculation.  Everybody is working under the assumption that, eventually, this will all get straightened out.  Somebody will figure out some way to rein in the House of Representatives so that they can do their required business.

By contrast, I keep asking myself, what if this is as good as it gets?

What if the house is permanently McBoatfaced? 

Back when I was a kid, we had joke Presidential candidates.  Comedian Pat Paulson was one.   There was a movement to elect the fictional TV character Archie Bunker as U.S. President.  And so on.  But everybody knew they were jokes, or that they were fictional characters.

Enter Representative Santos of New York.  Line, meet blur.  The people of that district definitely elected a fictional character.  They were simply not aware of it at the time.  To which we can add a handful of Republican house members whose sole platform appears to have been being mad as hell, and stating their unequivocal unwillingness to go along with anything required to conduct the business of government.  I guess we all now know they weren’t kidding.

A couple of days back, a friend asked me to see if I could open a couple of old suitcases that had belonged to her grandmother. Luckily, I happened  to own the Covert Companion (r) tool, pictured above.  The version I use has a few tools to help with what are called “low skill” attacks on locks.  (“Low skill” being an accurate description of my lock-picking ability).  Because I happened to own those crude little pieces of steel circled above, I had relatively little problem opening the simple warded locks on those suitcases.

But if I hadn’t had the tools, I’d have been helpless.  The only way to open the suitcase would have been to destroy it.  It’s a case of any tool, no matter how crude, being better than no tool at all.

Right now, I’m not seeing the tools in hand to fix the U.S. House.  Not even the crudest tactic that could possibly resolve the current impasse, let alone get the place functional going forward.  And, unlike those old suitcases, nobody has the power to destroy it, to achieve some end.  The House works the way it works, or doesn’t, until such time as it works well enough to change the way it works.  Which can’t happen.  Because right now, it’s not working.

Which finally brings me to I-bonds.  Is it smart to own I-bonds when the House is broken?

I’ve owned these for decades.  In fact, they are so old that they are going to quit paying interest just a few years from now.  Pre-tax, they pay just a bit more than the rate of inflation.  Most of the decades that I have owned them, they’ve paid little more than zero.  But now, as these things are reckoned, they are paying pretty well, compared to the alternatives.

But that high rate of return means nothing if you can’t spend it.  And of all the people the Federal government could choose to stiff, in the event of a permanent failure to fund the government or raise the debt ceiling, I’d bet that small bondholders would be right at the top of the list.  (N.B., I-bonds are marketed at small savers, with a purchase limit of $5000 per person per year.)

In any case, my conclusion is that if the House is permanently McBoatfaced, I might be wise to cash those I-bonds before we hit the debt limit sometime this summer.  Otherwise, I just get the feeling that the longer this goes on, the longer it’s going to go on.  Combined with the feeling that maybe this is as good as it gets.  That there is no tool for fixing it.

And that if everybody has their hand out, to the Feds, I’m going to end up at the back of the line.

I told you I’d get to I-bonds eventually.  It just took a while.

 

Post G23-060: Gardening’s booby prize.

 

Green tomatoes.  Not exactly inedible, but close. I pickle mine (Post G31).

I have lots of them, in several different varieties.  And it looks like the weather is going to turn cold, around here, just a few days from now.

What to do?

Source:  My garden, this morning.  That’s “Celebrity” on the left, and “Big Momma” on the right.  I have not yet gotten even one ripe tomato off these late-season plants. 

Continue reading Post G23-060: Gardening’s booby prize.

Post #1860: Heard about the big increase in COVID cases recently?

The question is and isn’t serious.  The answer is no.  The reason is that a lack of trend isn’t click-bait.

But the serious point is that sometimes you have to figure out what’s going on by what’s not being said.  Silence on this issue means it probably went away.  Not just because it’s not clickbait any longer, but also because those who flacked the trend never come back to apologize for making a poor prediction.

Not that it isn’t the right time of the year for it.  Right along with flu. So I think it’s newsworth that we’re not seeing a trend, FWIW.  But I realize I’m the outlier there.

In any case, a few weeks back, you could scarcely open a news website without seeing a reminder that COVID-19 cases were rising.  Then I realized I hadn’t been hearing about that lately.

Sure enough, in Virginia, and maybe in the U.S., COVID appears to have peaked in early September.  For now, at least. Continue reading Post #1860: Heard about the big increase in COVID cases recently?

Post #1859: Why all bathroom fans suck. A corollary to Post #1843

 

Answer:  Because they’re small.  That’s it.  It’s just basic physics.  And there’s nothing that can be done about it.


Background

In Post #1843, I figured out and explained why ceiling fans are vastly more efficient that box fans.  Where efficiency is measured by cubic feet of air moved per minute, per watt of power used (CFM/watt).

The answer turned out to be remarkably simple:  To move the same volume of air, a smaller fan blade has to move that air much faster.  That’s just arithmetic.  (If the area swept by a 20″ box fan blade is one-seventh the area swept by a big ceiling fan, the box fan has to move the air seven times faster, to keep up with the volume moved by the ceiling fan.)

Moving air faster takes much more energy than moving it slowly.  Not due to the energy-wasting turbulence that might create ( though that can be a factor), but merely because it takes more pressure to move air faster, and overcoming that pressure takes more energy.

Roughly speaking, CFM/watt should scale inversely with the size of the fan.  Given identical designs and motors, a box fan that is one-seventh the size of a ceiling fan should take seven times the wattage to move the same amount of air.  Roughly.

That’s all laid out in Post #1843.


And now on to bath fans

Today the penny dropped, and I realized that this same phenomenon explains the poor performance of bathroom vent fans.  Seems like bath fans take forever to clear a bathroom.  And I include all bath fans, almost regardless of make or quality.  Where a box fan stuck in a window could clear the air in a bathroom in a couple of minutes, an in-ceiling bath fan might take half an hour.

At best, a bathroom vent fan might have 6″ blades, feeding a 6″ diameter duct.  (Although 4″ duct for bath fans is far more common).  Since the area of a circle goes as the square of the radius, the area swept by the blades of a 6″ bath fan would be about ( 3-squared / 10-squared = ) 9% of the area swept by the blades of a 20″ box fan.  And so, to move the same volume of air as a box fan, a hypothetical 6″ bath fan would require (1 / .09 =) 11 times the wattage.

Let me now put that to the test, via virtual shopping at Home Depot.

And, sure enough, the median bath fan from Home Depot moves about one-tenth as much air per watt, compared to a box fan.

Bottom line:  A bath fan that could clear a bathroom as fast as a box fan would draw ten times the wattage of the box fan.  If you could squeeze that much air, that fast, through the ducts, you’d need to have a 500-watt bath fan*, in order to clear a bathroom as fast as a box fan sitting in the window.  That, before we even consider whether or not you could move that much air through a small duct without undue losses due to turbulence.  That, before we consider how much noise that would make.

* That’s 2/3rds of a horsepower, more or less.  A big electric motor, in this application.

And so, the apparent poor performance of bathroom fans is not a figment of my imagination.  Bath fans move air quite slowly, compared to (e.g.) common box fans.  It’s not a design flaw, or an intentional choice.  It’s just physics.  The smaller the fan, the more power it takes to move a given amount of air.  And bath fans — typically restricted to 4″ ducts — can only move a tenth of the amount of air that box fans can move, per watt of power.

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..