I remember it well. Standing in the last field that was part of SGC up in Bellevue, Washington. It was, gosh, about 1997, or so.
We were demonstrating an HF SSB Manpack to some para-military customers. I was showing off how a single operator with nothing more than a radio (like ours) on his back could talk great distances somewhat reliably.
I called KMI – the high seas station that used to be open to private calls – and no answer.
“Retune the antenna.”
I protested – I had done everything by the book. But, the company president (Pierre, now a silent key) insisted I had goofed. “No, you didn’t get it right – retune – the numbers never lie.”
I did the tuning process again – 12 foot whip antenna on the manpack – and sure enough on the first call I raised KMI – around 800 miles, maybe more.
Later, Pierre shared one of the finest secrets of HF single sideband, electronic troubleshooting, and – as it turned out this week – about fixing greenhouses.
The Numbers Never Lie!
OK – really they do – but that’s on the extremely rare occasion when there’s a “subspace error” and those are infrequent enough glitches in the force that they may be safely ignored.
Just not this week.
As you remember, or maybe don’t, I have been tuning up the lean-to greenhouse because I wanted the tomatoes, peppers, squash, and bok choi growing right next to the house behind a transparent wall the deer can’t nibble through.
The problem I was having? The daytime temperatures, even with the new Vevor evaporative cooler, were not getting consistently cool enough.
At first, I thought maybe it was the Vevor – somewhat smaller than the Hessaire 38 series units we’d used in the past. Which would have made logical sense. The Vevor is a bit smaller, and although handling the same 3,100 CFM of air flow, the Hessaire might have had more evap media surface.
I’d find, though, that the new Vevor is just fine. It was something else.
“Trust Numbers, Not Thinking”
This was a profound lesson coming around again. I have found it true in radio engineering, in 3D printer trouble-shooting, in growing plants, and even in flying airplanes which we’ve done lots of.
Before you remember the saying “Trust the Numbers” you might be tempted – as I was – to solve the wrong problem.
See, I assumed that the reason the room was running on the “hot side” was that the two smaller 10″ fans that I’d stacked, didn’t have anywhere near the swept area and airflow to keep up with 3,100 CFM of cooled air.
So, I promptly set about ripping up the north end of the “grow room” and putting in a serious commercial shuttered fan. It wasn’t a waste, mind you: the small fan bearings were starting to make noise and they wouldn’t have lasted another full summer in the Texas heat.
It took only an hour to toss in this beast and lay a serious bead of high-expansion foam around it, ensuring no air leaks:
It only takes a minute with a sharp serrated “everyday carry” knife to whittle everything down when dry. Which takes under two hours on a warm day. Same on the inside:
That shiny wall on the left is a space blanket – which is about the cheapest high reflectivity radiant barrier you can buy. (Ask your, um, grower.) Again, I’ll spend a bit of time this week trimming down the excess foam.
Great Work! But It Didn’t Help!
Now comes the lesson. There I was, big fan in on a warm day, and realizing that I still was not getting any temperature drop inside. I figured after all this monkey-motion, I would at least be down to break-even. Which would have been the inside air temp being at – or under – the outside air temp with solar gain less my cooling scheme.
Nope. It was still running hot – about 4-5 degrees above outside ambient.
WTF?
That’s when I remembered the day long ago in the field southwest of the SGC building.
I had run the numbers through two AIs – enough to trust them:
“The room has a sloped ceiling, so use the average height to calculate the volume:
Average height = (11.5 ft + 8 ft) / 2 = 9.75 ft
Room Volume
Volume = length × width × average height
= 20 ft × 10 ft × 9.75 ft = 1,950 cubic feet
Air Changes per Minute
With 3,100 CFM (cubic feet per minute) of airflow:
Air changes per minute = CFM ÷ room volume
= 3,100 ÷ 1,950 ? 1.59 air changes per minute
OK, this was nuts. I was forcing 3,100 CFM out of the north end of the room and changing the air completely three times in two minutes. Unless I wasn’t really changing the air…
The “Rule of Pierre”
Or, better known as Conan Doyle’s rule from the Sherlock Holmes series.
“When you have eliminated the impossible, whatever remains, however improbable, must be the truth.”
I went over the whole wall structure on the house side with a fine-toothed comb. Looked fine. Then I got out the ladder and that’s when I found it:
A couple of dozen roof fasteners had been torn up by the local raccoon population.
After an hour with a pilot hole drill and an impact driver plus three dozen fresh fasteners (with larger rubber and steel washers) the roof was again sealed.
I also found that the house-end had been ripped up, again, by the raccoons in a way that wasn’t visually obvious.
More fasteners. Three more cans of spray high-expansion foam and the room was back to pulling all 3,100 CFM of exhaust air in through the house-end (shaded) air intake.
The room was cooling. I may not even need the new sun shade to solve the “heat tunnel” problem on the ceiling side.
Sure, this may seem like a trivial story this weekend except for two things.
First, repairs & modifications like this take time. Maybe 3 hours by the time I get done – four if I count covering the (butt-ugly) foam, with trim.
Second is that it explains why my focus on the roof-side “heat tunnel” had been misplaced/misguided. That energy should have been spent out on the rifle range, zeroing in the .22 LR with a game scope on it.
Yeah – I know – animal lovers and I take no pleasure in reducing their population.
But I’m also of an age where I don’t want to keep redoing the same work, and if the “right answer” is a .22 long-rifle? Sorry. Guns are tools, sometimes, too.
When the hate mail comes – as in today’s world seems likely – I will offer any whiners a reminder about mouse traps and insect killers, sticky traps and more. Not saying any of it is right, but that’s how you roll out here in the woods. You don’t pet the possums or the copperheads, and you steer clear of the cottonmouths down at the creek.
Write when you get rich,
Read the full article here