Thursday, 22 July 2010

Thoughts On The Glasshouse

Thinking that we'd make better use of the solar radiation around-about we took the shadecloth cover off of the glasshouse last week. Not sure if it was the cover providing a little extra insulation that has saved us to date, or just the strength of the frost, but last night we had something of a disaster in the glasshouse. It looks like most of the cotton plants have been badly hit, and a few of the chilli plants, which we've had growing for about 3 years now, also copped a hiding. The tea plant and avocados seem okay, but they may take a bit longer to show the effects.

At the moment the glasshouse is just, well, a house made of glass. Nothing in the way of thermal mass to store heat, and enough loose joints to make sure it doesn't quite work properly. Over the last few weeks, reading along with John Michael Greer's series of posts about Green Wizardry I've toyed with a few ideas about how to make it more useful, or more correctly, how to make it do what I think it should do.

The first of these plans was a great little home made solar hot water panel along with a series of drums containing water. Excellent thermal mass, and should do a good job, it could even be supplemented with a wood/biomass system if needed. In considering how well it would work I got to thinking about the basic design of the glasshouse itself. It's a prefabricated unit of aluminium framing with thin single layer glazing. It's glazed all around, even the roof.

For a start, this is not the most ideal structure, given that the sun only shines from the east, north and west here, south of the Tropics. Why have glass, which is not the best insulator, on the south side of such a building? Why have it on the south plane of the roof, when it's usually so hot in there by summer time that it needs to be cleared of all plants anyway?

I toyed with the idea of covering the back and top with fibro panel or similar, which would allow for the inclusion of insulation, but that still leaves the front faces to lose heat, not to mention the question of whether the frame would support that extra loading.

Having given it more thought I am leaning towards reconstructing completely. It's current location is next to a four foot and more high rock and earthen wall. With a little planning this could be extended and expanded to form three sides of a new structure. By glazing just the northern facing aspects there would be as much light, and not nearly as much heat loss. If the design is clever enough then the glazing will be removable during summer to allow it to function as a greenhouse, eliminating the need to have plants migrating in and out as the seasons progress. And if I try to be really tricky I could build in water storage to act as thermal mass, and that thermal mass might even be able to double as place to grow up a few water plants and fish, allowing the glasshouse structure to fulfill more than one role, and provide for more than one system.

Obviously heating the water with a solar panel might not be such a good idea if one was growing fish in it, but there's nothing to say we can't have two water storages, one heated, one ambient, or even use a different form of thermal mass for the heat providing side of the equation.

In other news, all is going along in it's wintery fashion here, we've had some beautiful days, and some awfully frosty nights. Half the pruning has been done, and work is progressing (only slowly) on the vege garden renovations, primarily due to a hectic social schedule, including birthdays, lawn bowls, and even a trip to Abercrombie Caves (well worth a visit if you ever get the chance) to fill in those two days that separate work time.

There is also the fact that most jobs I do tend to turn into an experimental or creative endeavour well outside their original scope. Cleaning the chicken house out a couple of weeks back, which would normally take about an hour, if not less, turned into a three hour job. I'd often longed for a long-handled scraper to assist in pulling the muck out from underneath the raised house. This time I succumbed to the urge and built one using the steel sheet from an old computer case, a couple of bits of angle iron and tube and a hoe handle I'd purchased but not yet fitted. It works wonderfully, and the DW only rolled her eyes a little to find that the cleaning operation had taken so long and gotten so sidetracked. I imagine that next time it wont even take 15 minutes to get the whole job done!


The Duck Herder said...

oh no, bad news about the glass house disaster! I suspect you might have lost a layer of insulation.......

if you would like more inspiration and procrastination, there are two books I LOVE by Eliot Coleman - "the winter harvest handbook, year round vegetable production using deep organic techniques and unheated greenhouses" and "Four Season Harvest - Organic Vegetables from your home garden all year long" from the same author.

Our little pre fab greenhouse (weird hard plastic stuff house) has some shade mesh running on hangers on the inside - so I can pull it aside like a curtain during the day but put it back again at night to prevent mishaps just like yours! (knowledge gleaned from similar sad experience) But in practice I end up leaving the cloth on because it is hard to remember to put it back each night....

Hope the avocado is OK. I am pretty attached to mine.....

stay warm!


The Duck Herder said...

And if you really want to go crazy!

Samantha in Oz said...

I will follow your glasshouse progress with interest!

I love the Abercrombie caves. (My grandfather's grandfather, Sam Grosvenor, was the caves' first caretaker).

Geoff said...

Hi Duckie,

Thanks for the book references, and that website, a great looking dome!

I'm reconsidering my first set of results that it was a frost, as some of the plants are coming back with a good watering. It could well be that it just got too hot in there during the day!

Over winter, with the shade up we normally don't need to water for a week, but it seems without the shade we might need to water every couple of days. Still not 100% sure as some of the mushy leaves looked awfully like frost had hit them.

Either way a glasshouse re-design is still on the cards.

You'll be pleased to know the avocados survived just fine. This Spring they'll be planted out in the wattle grove where they'll get protection from frost and hopefully grow tall enough to avoid it's worst effects.

Hi Samantha,

The DW and I both commented on what an amazing job caretaking the caves would be, though I'd imagine that in your grandfather's grandfather's day it would have been incredibly isolated. We can't wait to go back and take some of the tours through the other caves that aren't permanently open to the public.