Ground temperature data.

To check the ground temp for the previously mentioned cooling system I rigged up a simple temperature probe consisting of a meter length of garden hose taped to a stick (to keep it straight) and plugged at the bottom end. I buried this to a depth of about 90 cm (3 feet, as far as my arm can reach into the ground), put in a small amount of water for conductivity, and lowered in a glass thermometer on a thread. I then plugged the open end of the hose to prevent air exchange.
Every so often I pull out the thermometer and record the ground and air temperatures.
The ground is dry sand on a 45 degree incline, shaded throughout the day. Initially I measured a spot beside the house which got direct sun most of the day, and it was about 7 C hotter


Results:

	Ground (C)	Air (C)
January 14th
14.24	22	21.5
22.30	22	22
Jan 15th
10.10	21	26
12.00	21.5	26
14.00	21.5	25
17.15	21.5	24
Jan 16th
8.30	21	25
13.30	21.5	35.5
15.15	21.5	30
16.45	21.5
23.00	21	22
Jan 17th
10.45	21	29.5
Jan 24th
09.00	21.5	18

This shows that even an air temp of 35.5 C (96 F) doesn't affect the ground temperature at that depth at all, making this cooling system potentially quite viable.

Once I get a chance (after the solar device is going) I'll take a crack at piecing this together.


Mild update: overnight temperature went down to 13 at about 3.30 am, but ground temp measured at 9.15 am hadn't budged 0ff 21.5. At this point I'm going to call this conclusive.

Nother update; ground temp is up to a steady 23, so guess there's seasonal variation. February is generally the hottest month round here.

Update the third; I suspect the increase may be due to the sun shifting on to it as it gets lower in the sky. Also have had an air temp of 38 C, ground temp unaffected.

Update IV; had a cloudy day, and the temperature was still 23, so if that's due to increased direct sunlight, it's at least a couple days averaged. In other news the ground temp has now gone up to 24, the maximum air temp has been 39.5, and the probe has been removed to make way for the cooling tank as I actually make this thing.
A 1.5 meter deep hole involves more digging that you'd think...

I've been thinking about ultra simple cooling systems.

The most available source of coolth seems to be ground temperature, which according to the internet deeper than a meter is about 10-16º year round worldwide, maybe up to 25º if it's real hot outside and you're on wet clay.

So, this idea would be to bury a water drum and pump the air through it. The hot air inlet would enter at the base so that the air bubbles up through the water dumping most of its heat and humidity. Cool air is then drawn out of the airspace at the top of the drum and piped into the building.

The pump can be driven by whatever is available, but a wind turbine would be easy enough and keep the whole system non electrical.

The growing space would have insulated walls and skylights with diffusers to bring the light levels down to about 30% of sunlight, which is optimal for most edible plants. Temperature would be regulated by airflow.

According to some quick, probably wrong, calculations on wolfram it looks like water is about 3000 times the thermal sink of air, ie taking 1º C out of 3000 litres of air would raise a litre of water 1º. Therefor a volume of air 2 meters by 3 by 4 would be balanced by 8 litres of water. So a 200 L steel drum would take care of just about anything, depending on the conductivity of the various walls.

This all seems extremely simple, which I guess means it's either already been done or there's something very wrong with the idea.

Here is the first basic design for the greenhouse. The main consideration is extreme ease of construction, and that it cost practically nothing in materials. Secondly that it maximise growable area and be easily customisable to different growing techniques, ie permaculture, hydroponics, aquaponics (combined plant and fish farming), bee hives, etc.

The design pictured has a side length of 16 meters, giving a 110 meter footprint and about 280-320 square meters of growing area, depending on use. The design is very scaleable and can be easily modified to whatever footprint is available.

Materials consist of 9 x 7 meter poles, about 262 meters of clear plastic mulch film, rope, and scrap wood for shelving, floors and stairs. All of this can be realistically recycled for free, or fairly cheap if paid for.

Click for larger view.

The greenhouse in 3d, wrapped and unwrapped. Click to view and install the player when prompted. Verified virus and spyware free.
Check http://www.3dvia.com for more information.