The greenhouse project

It's been rather quiet on the modest manor blog, but that doesn't mean nothing has been happening. Indeed it means that so much has been happening that we haven't had time to write anything. At our previous (rental) house we built a lovely greenhouse against the north wall of the house, we also had a window conveniently located so that we could let air in from the greenhouse into the main house. This worked so well for heating the house in winter that we've decided to build a greenhouse with this goal specifically in mind.

The plan calls for two 3.6m x 2.5m 'rooms. You enter from the west (where the current front path is). The west half will be desert, kept fairly dry, with a table and chairs. The west half has a door into the east half, which will be tropical, with a pond. Summer cooling is performed by drawing air through an inlet covered in a dense tomato or similar vine.

I'm using 1x3 hardwood flat walled frame, and twin-wall poly
as per this sketch:

I resketched this in QCad, which alerted me to a few errors in my floorplan.

There are a number of reasons for going this way:

• The space we have is fairly limited.
• We want multiple use for the space.
• A smaller greenhouse is easier to maintain.
• A smaller greenhouse is cheaper to build,
  
• and if it doesn't work properly, cheaper to rebuild.
  

The south wall will be a solar heater for the house, with fin tube at the top to preheat water for domestic hotwater. Similarly the top of the greenhouse will have a fin tube to heat the fish pond water and keep the greenhouse cool without venting on sunny winter days. The south wall will
be insulated to R1, the collector will be shaded mid-summer.

The south bench has a full length pond made from like plywood and EPDM pond liner for fish and water supply.



There is a trickle water fall with ferns on the west wall of the tropical house. which recirculates into the pond.

Yesterday and today Dad and I put together the water storage/fish tank. The tank itself weighs at least 100kg. I did the engineering calculations for the tank, here are some stats:

dimensions: 3.6m long x 0.9m wide x 1.2m tall, buried in the ground to be 0.8m above greenhouse floor level.
capacity: 3.5kL. Of course we had 30mm of rain the day before I got the tank assembled, but people assure me that it will rain again some day.
average pressure on long walls: 6kPa, i.e. 600kg per metre of tank. This means that the sides will have a sheer force of 2.6 tonnes. If the side walls weren't strengthened with steel straps the wood would bow out nearly 30cm in the middle. The bolts are rated to a shear strength of 12 tonne, the steel strapping 1.2tonne.

With any luck the whole thing will stay together when full. (It's a little scary, but I'm fairly confident of my calculations, if not my construction techniques)

We filled the tank with something like 500L to see if the liner would straighten out. It did, but it drifted off square which means I'll probably have to get into the tank and pull it square again, or alternatively, pump the water back into the rainwater tank it came from.