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Building a greenhouse!

Hey all! I've recently begun working on my greenhouse plans again. It's going to be a custom job, as usual, for highland Nepenthes. I've got a couple of technical questions, though:

1) I am going to purchase an exhaust fan and motorized intake shutter, both to be controlled by a thermostat. Can I control both devices with one thermostat?

2) During some seasons, I will need the heater to attain both day and night temperatures, some the cooling system. Others will be a combination of both systems. I know programmable thermostats will allow me to set two temperatures for one device, but is there a cheaper alternative? (BTW, installing two separate systems probably won't be cheaper!)

Construction probably won't start until this summer, if any time soon at all. Thanks for the help.

-D. Lybrand
 
1. A dual stage thermostat is usually used. The low set point will activate the shutter and then when the temperature rises a few more degrees the fan is activated.

2. Other than manually resetting the thermostat every day and night, a programmable thermostat is probably the cheapest and simplest way to run differential day/night temperatures. Otherwise your talking about two single thermostats and a relay and timer.
 
So a dual stage thermostat will allow me to connect both devices? This shouldn't be too much more expensive. I guess I will need to go with a programmable thermostat, so this changes things a bit. Thanks.

-D. Lybrand
 
Another dilemna: programmable thermostats all seem to be 24v. How will they hook up to a 120v heater? It just doesn't make sense!

-D. Lybrand
 
You need a 24v transformer if your going to use a low voltage thermostat.

On the dual stage if you are using it for cooling then make sure it is labelled for cooling or cooling/heating. You don't want one labelled solely for heating cycles. Yes both the power shutter and the exhaust fan are both wired to the single dual stage thermostat.

Tony
 
Hello D. Lybrand, I am by no means an expert in this field but I did buy some really nice equipment for my greenhouse from charleysgreenhouse.com. They have a great printed catalog you can order (free) and they carry everything you need for heating and cooling including vents, fans, etc., and I know they have a thermostat that controls a heater and a swamp cooler all in one.
 
D. 24 Volts is the max those things can handle. If I am not mistaken they work on 12 volts too. It should have an output of 24 volts when it kicks on. You will take that 24 volts and run it to a contact. Its a 110 or 220 relay that will accualy turn on the power to the heaters and things. So what happens if I have this right. The thermastat will connect to 110 or you may have to get a 24 volt transformer to break down the 110 to 24 volts to go into the thermastat then the output of the thermastat will be 24 volts when it kicks on. That 24 volts will go into the accuator side of the contact. Basicly when it gets charged it pulls the contacts over to let power to the assigned plug. So if there is a power serge from the contacts kicking on it wil not fry the thermastat, but fry the contact instead. I remember looking for them and if I remember corectly they are called contacts in the granger catalague. Relays are for 12 or 24 volts. Although you may be surprised, but I have 2 thermastats made by my grandfather and they use the car relays. You have to get the ones rated for the proper amps you will be running, but they power my 1500 watt heaters one for each heater, and I have two for my fans. It has been working for 2 years now. Although the one for my heaters is using breakers instead of fuses because the fusses were getting to hot, but the breakers are fine. I am using the box that used fuses on my fans since they draw less current. For what I would pay to make a new box though I could spend a little more to get a premade one. OR!!!!!!!!

You can go to MG reptiles and get their johnsons thermastat. It handles up to 1500 watts and does cooling or heating. Its digital with one setpoint though. It is about 80 bucks. I use one for my snakes. In a GH aplication I woudln't think you would want a proportional thermastat so I wouldn't spend the extra money on one. The Johnson's is either on or off. The proportional ones regulate the voltage so sometimes they are not all the way on no all the way off to keep temps more stable for snakes. Just a thought!!
 
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