The Experiment Station

We are nothing if not empirical around here. If you want to know whether or how well something is going to work before you invest largely in it, an experiment is the way to go. Back in March of last year we had a very good time setting up the experimental hydronic floor grid in the craft workshop, and came up with a good plan for even heating. Now we’re trying to decide what kind of glazing will go on the south-side solarium/greenhouse wall of the new house.

We thought glass. Glass is clear. Glass is strong. Glass, given various modern treatments in the way of coatings, has good transmission of the light spectrum we want to the heat-sink masses within the house, and for horticulture inside the greenhouse. Coatings can control the passage of heat into the greenhouse as well as the escape of heat on the way out. And glass, y’know, it has the appeal of  literary references: “He that lives in a glass house must not throw stones.” Also,“glasshouse” to the British means a greenhouse and, our greenhouse was meant to be glass.

Green has become a difficult word these days. How is one to know what a person means when they say, “We have a Green House?” Is it a glasshouse?

Wisley glasshouse

(This one is at  Wisley Garden in Surrey)

Or is it a green house?

The green house at Summit

(The arctic green house at Summit)

Or is it, as we expect ours to be, a Green House?

Green House not green with greenhouse

with a greenhouse.

Try not to think too hard about it.

But I wander.

Monty, our fondly held builder, wants to use polycarbonate plastic. He says it’s safer (it’s half an inch thick, so I suppose he has a point there; if you’re going to throw those stones,  that’s a consideration). We say it’s electrostatically active (We might actually have said “cling,” but just think how much stuff sticks to statically charged surfaces). He says it can be done with larger panels and less framing (OK, another point).  We say, but, it turns yellow. He says, not for years. We say, not enough years! Who wants to replace all the glazing in the greenhouse in 10 years? He says it transmits light and heat just as well as glass. We say: LET’S DO AN EXPERIMENT!

We can’t, obviously, test the yellowing over time before we’d like to move in. Besides, manufacturers provide that kind of information. Here are the labels off samples of glass with different coatings. Almost all you could want to  know about light transmission

The Large Print

except how it performs in the field.

So, let’s build little boxes!

Little boxes, all the same

These little plywood houses covered in insulation and duct-taped over the seams each contain a concrete block for a heat sink and are glazed with [Sta. A] Makrolon® “High-tech plastic from Bayer;” and [Sta. B] glass. It’s more complicated than that, but it’s glass. It’s been several different kinds of glass over several periods of observation, all in comparison with the polycarbonate. The idea is to see how much heat goes in, and how much heat stays in when the outside air cools. We could have built a half dozen little boxes to run simultaneous tests, but we didn’t. Chief Scientist and Mechanic Richard changes out the glazing  in the glass box, leaving the poly box unchanged, and even tries masking the glazing altogether to establish a control condition.

Experiment stations A and B in placeAnd we make notes. Lots of notes on a little yellow pad


kept beneath the thermometers mounted on the boxes.

Science happening live

Science is happening live, daily, at local stations.

Published in: on February 22, 2009 at 3:51 pm  Comments (4)  

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4 CommentsLeave a comment

  1. I look forward to seeing the results!!

    I’ll put you in contact with the Chief Scientist and Mechanic!


  2. Hm. I may have to reconsider my offer to move in if you’re not using real glass.

    Yeah. Me, too.


  3. You all are nothing if not dependable…and thorough! 😉 The whole process has been fascinating. And not really, but IS because you document everything in such an enjoyable and informative way.

    Thanks. I try not to bore you to death!


  4. You may want to consider checking for what plastic allows the closest to full-spectrum light through it.
    Some plants won’t flower or set fruit if the light isn’t right.

    That’s been one of our concerns, and is part of the specifications list for materials. As it happens, it appears glass is winning in the transmissions contest, so the question of coatings on plastic may be moot. Thanks for the comment!


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