npub1xfkwp23vm2g6fcq7gwyvf4g796ej9qur8c828gfvaxr9lpxyxqgq03f3v5 (npub1xfk…f3v5) npub1eavnczg44hkruat47xlr463h5hczyqjqduylj7nlyatx4enn0fzqu7g6f3 (npub1eav…g6f3)
For the first experiment, I'm going simple, small, cheap. The design is still tentative.
We're moving a 3x6m polytunnel in the spring, building a brick foundation for it, etc. The tunnel will orient East-West on the long axis.
East is downhill ~50cm from West; pray for my dirt-moving back. There is a layer of gravel at 25-100cm. It carries water (like a flowing river) when we get heavy rains (200mm in two weeks last year). Soil above the gravel is sandy loam, with some light clay and rock chunks.
I'll be using 50~75m of 75mm corrugated, single line perforated tube (french drain stuff), buried with the holes down on a thin layer of sand. Once done, the surface will be covered by ~100mm of woodchip mulch. I am not going to insulate the sides as some people have suggested.
I plan on burying as close to the gravel layer as possible, two layers @ 25 & 50 cm where I can. Each section will be 10-15m, ending just above ground level.
The fan will be a bilge fan rated at 220 m3/hour, about 2.5 changes per hour. If needed I'll add a second and/or a speed controller. The fan will be inside a plywood manifold box running up the side of the polytunnel. Dampers will be controlled by a greenhouse vent lifter: >25C upper damper open, lower closed, <25 the reverse.
There will also be a manually controlled "dump to outside" damper for summer.
Fan on/off signal will be controlled by:
- a programmable timer in-line with a cheap house thermostat
- a switch on the upper damper (open==on)
I'll use automotive relays to turn signal into current.
I'm going to run this one off 12v from a charger until I have a good idea what total daily draw is. Then I may migrate it to solar.
John Timaeus /
npub1vd…9vpmv
2024-01-11 23:21:42
in reply to nevent1q…zapn
Author Public Key
npub1vdj4cuvf2xkqy9qqrwhrdhqe69j4nhgl2da937g66s4gkkyh8v9qm9vpmvPublished at
2024-01-11 23:21:42Event JSON
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