A LOAD OF HOT AIR

My better half is impressed with the heading. Says it’s the first time she’s seen any tangible return from something she’s endured for decades…..recons it should be easy to write…..I didn’t quite catch it (she was moving away at the time) but she seemed to mutter something about “expert”……
Sometimes, if I’ve been woken in the wee small hours, I think my way down some problem-solving track. Call it lateral thinking, call it heuristics, call it cussedness, and maybe there’s an article in there, somewhere sometime. Some of the resultant solutions are unique, some are firsts, some are failures, in the light of day most turn out to be a reinvention of somebodys wheel. (I remember once working on a high, steep roof, and that night mentally inventing the back-pack inertia-reel safety harness. Then I googled it……)

Such a thing happened recently. I’d always thought to use our north-facing conservatory to thermosyphon the hot air into the house.
Thermosyphoning is what happens with the wet-back in Granny’s old coal range. Water is heated in the wet-back and rises, piped, to the top of the cylinder, while the cooler water at the bottom is piped into the wet-back. An endless circle, driven by heat. It works with air, same principles exactly, except the medium is about 1000 times thinner.
The plans showed sliding plywood panels (like ‘seventies cupboard doors) up high, and ranch-sliders below. Cold air from the house, goes through the ranch-sliders, up in the conservatory, through the square holes into the house – you get the picture. Somewhere along the way, this morphed into glass which tilts rather than plywood that slides, but it works a treat. We have maxed out at 44ºC in the conservatory, 38ºC in the house.

Anyway, there I was, clock saying 3:48am or some such unrealistic thing, pale moon shining through the glass vents, and the cranial gears in motion (the human equivalent of second cog in a K Bedford – trust me) thinking: wouldn’t it be a good thing to put a conservatory outside the east wall. It would grab all that morning heat we wastefully reflect away. No, darnit, the inside stairs would be in the way of any ranch sliders. How about if we only had vents, top and bottom. Ah – penny drops – (change into third, watch for the double-de-clutch) why have a conservatory, why not just a glass panel up the wall. A 50mm thick conservatory. Vents top and bottom. Close ‘em off when de sun go down. Paint the wall matt black. Maybe that will kill the wall skin, maybe a matt-black second surface then. Galv maybe. Hey, you could make ‘em up and sell ‘em as modular bolt-ons……….. (shift into neutral – hard to spot the difference – and zzzzzz).

So I share this revelation with a builder friend “Yeah, good idea, they’re doing it!” Next, I share it with an old friend who lectures on a completely unrelated subject (money, believe me, we’re unrelated) “Oh yes, there are a couple of them down by the ‘uni’, real ‘seventies!” Worse, I send a draft of this to Nadene Hall, and she points me at a ‘how to build one’ website!

OK, I get the picture. Point is though, that this is probably the cheapest, most effective way to warm up an existing house. Drive through the country, and there are old 1930’s villas and 1950’s brikkies everywhere, with huge masses of wall just blocking out the sun. Sure, solid wall is needed for holding up the roof, for diagonal bracing, for privacy (I’ve almost forgotten why) and for hanging things on. A couple of through-vents won’t affect any of those functions.

The cheapo way would involve a couple of battens up the wall, with plastic stapled over. I’m using a couple of recycled ranch-sliders for ours. I just know she-who-was-walking-away will be delighted. She’ll see it as one more bit of junk not lying around, whereas in reality it’s just created another space for me to store something equally essential. Quite irrational, I know, but I’ve learned to be tolerant over the years……..

That said, it never pays to underestimate your better half. They may have made a fundamental mistake in choosing you as a life partner, but we can all have off-days! Mine has cottoned on to the fact that if I have to write about something, I will need photographs. Presumably of the something in question. Meaning it may actually get done. I sense a list coming.

The fact that I built the thing in no time flat, and that the photographs appear here, is entirely coincidental……..
This panel uses two ranch-slider doors one above the other, because height should create a bigger heat differential and thus a better air flow. They are set out from the wall on ‘T’ section aluminium, and hinged at one side for access. The vents are yachting access ports at the bottom, and standard extractor vents at the top, the kind with a flap which closes. It is interesting to do some rough numbers at this point. Say the materials cost $200. If we work on a kilowatt of sunlight per square metre, there are 3.5Kw hitting the panel. Allowing for conversion and loss, let’s say we get 1.5Kw of that as heat into the house, averaging four hours a morning every second day. (1.5 x 4 x 182.5) x 17c = $186.15, so you have essentially wiped out the up-front cost in the first year.

We’ll report back on performance. Question marks remain about overheating in summer (hinge them open like shutters?) and about the heat-tolerance of the upper plastic vents. Reverse chilling at night may well act as a dehumidifier, which would be a definite bonus. Watch this space!

Meantime, 1.5 kilowatts for free on a frosty morning is not to be sneezed at, if you catch my drift……..

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