I'd definitely put shutters on your wetwall - otherwise a strong cold wind would blow your heat straight out.

Regarding your relays, it's hard to answer your question without knowing more about the problem. Can you write down rules likes 'if it gets too hot, then turn off the main fan and turn on the evap cooler water and turn on the extractor fan'? If you can write rules in this pedantic form then we can have a bash at designing a relay network for you.

Well I'd like to have my circulation fans on 24/7.

Then if it gets too hot, say 85-90 degrees then I'd have the circulation fans turn off and the exhaust fan + wetwall turn on.

That's about it. Are there shutters that are 10'x3' and are automatic? Where can I buy these at?

Ok, you'll need 1 relay: You need a DPDT relay, capable of switching the largest load (whether it is circ fan or the wetwall stuff) - probably you can get a 120V 15A relay quite cheap. I don't know what you intend to switch it using, perhaps an off the shelf thermostat. Whatever does the switching will have to provide a voltage and current to drive the relay on and off. That is the coil voltage of the relay.

Connect the NC contacts of the relay to the circ fan and the NO contacts to the wetwall and exhaust fan. The commons go to the mains. Make sure everything is well soldered, there are no bridging wires or solder and put the whole thing in a water tight box (I usually use clear kitchen plastics for this, with a blog of silicone on all the wires and good metal wire-clamps attached together to prevent a yank from breaking the device.

Solder all the Earth lines together and insulate - this is the most important step as it will give you some protection against faults, particularly if you also have a GFI/ELD/RCD safety switch.

(* njh wonders about the sensibility of wiring a high voltage relay following instructions off the web...)

Perhaps you should find someone who knows about these things to do it for you? It's quite straightforward, but if you get it wrong you might make the fan become electrified or something.

I don't know about the shutters, perhaps you can just buy 3 lots of 3x3? I'd ask the place you got the wetwall. I don't live in the US, so my advice there would be useless in any case.

When you wire the thermostat remember that a thermostat closes and applies current when it is too cold so you will wire the fans that you want to run all the time to the side of the relay that makes contact when the coil is energized. When the GH gets too hot and the thermostat will cut the current then the spring closes the relay and turns on the wet wall

When dealing with mains voltages - if your expertise is such that you need to ask how to do it - then it is best to get someone else to do it for you. Especially in a situation where there is water involved..........

I'd recommend multiple relays. You don't always want/need to run both the exhaust fan and evaporative cooler. Ideally, cooling would be handled in stages as the temperature increases, something like this:

Stage 1 - Open vents
Stage 2 - Exhaust fan on
Stage 3 - Evaporative Cooler on

The resaon for running the fan after turning off the coooler is to dry out the pads.

Thanks for the help so far guys. I think I like gbrendemuehl's idea of having several thermostats. That way I don't even need relays and all this electrical work since I know nothing about it. My main expertise is orchids. Will post pics in about 2 weeks !!! I'm so excited.

Hi kaylin002,

I was just wondering where you purchased the supplies(exhaust fan, evaporative cooler etc.) I am also looking to build a greenhouse in Southern CA almost the same size as yours.
Good luck with your grenhouse and let us know of the progress!

I bought the exhaust fan/wetwall/and shadecloth at http://www6.mailordercentral.com/igcusastore/products.asp?dept=1034

I bought the twinwall at sundance supply because I only went with 6mm. If you go with 8, you should get it at IGC i think, almost the same price. The structure is going to be wood so that's gonna be HD.

hope this helps.