The greenhouse is semi-automated in that temperature, ventilation, and misters are all controlled, but the plants still need to be watered. At the heart of the system is an Autopilot Eclipse F60. It is a 110V controller that provides four control outputs – Heat, Cooling, Humidity and Cycle Timer. This is how I use them.
Heat is the simplest. This is connected to a small heater. The one I use is the Bio Green PAL 2.0. The reason I chose this one is it is a sturdy free-standing heater that is stainless steel cased. It is one of the few I could find that really is specified for humid environments. At 1500W it is also the largest I can run from the circuit I have installed and well within the abilities of the controller. It is a gentle heat and is enough to hold the greenhouse at 50 degrees when the temps are down around freezing. It can probably handle colder, but we have just never reached there. Don’t expect it to quickly ramp the temperature.
The cooling output basically handles both air re-circulation and external venting. When the temperatures reaches the maximum, the louvers at the bottom of the greenhouse are opened and the exhaust fan turns on. The louvers are powered to ensure that chipmunks and other critters cannot easily get into the greenhouse.
The exhaust shutters are not powered and open as soon as the air starts to flow through. I perhaps went a little overboard with the sizing, using a 20″ fan and two 18″ shutters, but it is certainly effective and turns over the air in the greenhouse in a very short time. Given that our air temperatures never get really high, this is highly effective. This fan is very similar to the exhaust fan I used, and this is similar to the recirc fan.
When the exhaust fan is not running, the re-circulation fan is running. Both are accomplished from the same output of the controller. What I did was to install a double pole, double throw relay. In one position, the re-circulation fan runs and in the other the exhaust fan runs.
Both fans also have speed controllers attached. I have found that most of the time I have them both set to minimum, but it is nice to be able to turn off the recirc fan when I am in there working.
The misters come off the cycle timer. This controls a solenoid in the water line. It can be set for so many seconds every so many minutes. For a more complete description of the mist system see Greenhouse Interior. I do vary this a little between winter and summer. It is set to not operate at night and this is a function provided by the controller. What I found is that I needed to make two modification, using two more relays.
The first is that when the misters are running, the fans need to be turned off – otherwise the mist gets blown to all of the wrong places. The second modification is to turn off the misters when the humidity gets above a certain level. I was beginning to suffer from liverworts growing in the pots and wanted to avoid this.
The system isn’t perfect. One problem with the controller is it thinks it is an error if the temperature and humidity do not change for 2 hours. Huh! We often go days when we are at 100% humidity and absolutely no variation in temperature for many hours – just one of the joys of living on the coast. The blessing is that this error does cause any problems because the only thing that should be running is the recirc fan and that is the default condition of the relay. It does mean that the controller has to be reset before it will do anything again.
The other is that the cage around the recirc fan is not stainless steel and is corroding, even after just a couple of years. I will need to replace it at some point. This kind of wiring may be beyond some people, but it should be possible to find an electrician who would be capable. My setup may not be “to code,” but all the parts are designed for these kinds of environment and the bus-bars being used to connect everything are marine grade, as is all of the wire and the fittings within the greenhouse.