Control greenhouse temperature

[deneo]

Hiya folks

I'm new here but would like to dive in with a question if I may. I have a 12' x 8' greenhouse and have installed 2 extractor fans (240v) in each gable. I wondered would anybody know of a cheap thermostatic control to start the fans when the temperature gets too high - I don't think normal room stats would work as they switch "off" when a higher temperature is reached. Thats where my knowledge ends!

Thank's in advance for any advice

Dene

[Thomas W]

I would control the fans with a small NSLU2 computer and 1-wire temperature sensors and relays. It would be easy to log the temperature measurements too and see what's really going on in your greenhouse at all times.

[tomate]

Originally Posted by Thomas W

I would control the fans with a small NSLU2 computer and 1-wire temperature sensors and relays. It would be easy to log the temperature measurements too and see what's really going on in your greenhouse at all times.

Yes i use a NSLU2 computer and 1-wire sensors and relays. I find they are the best and ;ike what Thomas said, i can really find out whats going on in my greehouse.

[Thomas W]

Originally Posted by tomate

Yes i use a NSLU2 computer and 1-wire sensors and relays. ...

What type of relays and 1-wire IC's did you use?

[mclarke18]

Primair fan controller are great, you can control either 2 extractors or 1 extractor and 1 intake fan and had its own long thermo probe, so the controller isnt in the way....

You can also control the speeds manually if you wanted setting a minimum speed if needed and it will extract more depending on the temp you set it at...

They are around £80 new on ebay, so you might find a used one cheaper!

[Willonthewall]

Hi everyone.
I'm new on here today and came across the forum when looking for polytunnel temperature control.
I'm in the process of building my first tunnel for growing tobacco next spring so am planning for that purpose.
I have the scaffold poles for the vertical supports and MDPE Water pipe for the hoops.
I was looking for an almost automatic system for this so invested in a 1000 litre IBC Plastic Tank (Ex rapeseed oil) and am about to purchase some kit for automatic watering.
I already have a battery bank and 12v solar panels and am in the process of building a wind generator for trickle charging the batteries as well.
I got a 16" 12volt radiator fan from

16" Radiator Cooling Fan Kenlowe Spal Pacet TypE on eBay (end time 07-Sep-09 16:39:54 BST)

on ebay for £17.99 - it's excellent for greenhouse/polytunnel extraction, surprisingly powerful, and I have a simple thermostat from

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for £2.93. I'll fix it to a metal heatsink near the roof and it will cut in the fan at 60c.

I'm (well my son and his pal with me "helping") digging a trench inside the tunnel for a heatsink. I have some salvaged sheets of polystyrene to line the 2ft x 2ft x 8ft trench which we can fill with broken glass, gravel, rubble and cast iron scraps then concrete over the top to form a central path then paint it matt black.
I'm planning on two crops of 3 varieties in each crop. One crop in the tunnel and one on the patio in 30 litre pots. It'll be interesting to see the difference

Sorry to rabbit on but I thought it might be of interest to know that extraction/cooling can be set up on the cheap and if you already have a 240v supply there, a transformer for 12v DC operation can be picked up very cheap.

We also have an oil fired AGA so have a ready supply of kerosene at a "reasonable" price for my greenhouse heater for both heat and CO2 production.

Any advice on growing tobacco would be appreciated before I go any further with the plans