Sounds like a fun project.
I would imagine the first thing you would need is some form of "weather station" both outside and inside the greenhouse. You would need to know what conditions are present on the outside, and what may be coming in the next few hours, especially by way of lighting (sun, clouds, etc.), wind, temperature trends and humidity. Likewise, you would need to be able to measure the conditions inside the greenhouse. A program would be necessary to correlate all of this information and make "adjustments" to the greenhouse "systems" based on what is necessary to maintain the ideal environment in the greenhouse depending on the stage of development for what you are growing.
In other words, each plant has an ideal growing environment that may or may not change during it's life-cycle. You would have to know what that ideal environment is so you could maintain that ideal for optimum growth and production by use of greenhouse systems (more in a moment). Now, a greenhouse is greatly affected by the outside environment; so, you would have to know the outside environment and how that IS affecting and WILL affect the greenhouse environment now and in the immediate future. You could then "adjust" each of your greenhouse systems so they counteract any negative influence from the outside environment.
To maintain the exact ideal has been the goal of greenhouse growers since the dawn of greenhouses. MAYBE we have become more successful in maintaining a close ideal greenhouse environment through technology, but successful greenhouse growing is as much an art as it is a science; don't forget that. People tend to think of a "smart" greenhouse as one that is run on technology based on science, but I would say the science with the art....someone with years of experience, both successes and failures...to observe subtleties and nuances...and make further adjustments is what a true smart greenhouse is all about. So you need a "HAL" to monitor, compute and adjust and you need a "Dr Dave Bowman" to tweak what a computer can't "observe".
OK...the systems that you would need to maintain the ideal environment and counteract any negative outside influence would include (from an article in Novedades Agrícolas entitled "What is an intelligent greenhouse?":
Climate control. Two weather stations, one inside to control the climatic parameters of the cultivation, and another one on the outside to control the external environment in order to make the necessary operations such as closing ventilation in case of rain or strong winds.
Irrigation and nutrient application control. Controls the frequency of irrigation and the application of nutrients through a schedule imposed by the farmer or the farm technician, or from external signals using probes soil water status and / or plant through probes of a climate station. The programming of the application of nutrients is from the irrigation scheduling, scheduling a particular nutritional balance for each physiological stage of the crop.
Temperature control. The temperature control is performed by temperature probes in a weather station installed inside the greenhouse. From the temperature measurement a number of actuators depending on the program herself. Thus we can find between automatism opening and closing mechanisms of zenith and side windows and fans for causing the drop in temperature inside the greenhouse and heating systems to increase the temperature.
Humidity control. The relative humidity is monitored in the weather station inside the greenhouse and acts on the functioning of misting systems (fog system) or cooling system to increase moisture or forced ventilation systems to evacuate the air too humid greenhouse.
Lighting control. The lighting is controlled by the drive mechanisms that extend shade screens normally installed inside the greenhouse to reduce radiation incident on the crop when it is too high, which prevents thermal injury in the leaves of plants. You can also increase radiation in certain periods connecting artificial lighting systems installed in the greenhouse in order to provide a greater number of hours of light acting on the photoperiod of the plants causing changes in physiological stages and increases in production due to increased in photosynthetic rate.
Application Control CO2. Controls the application of CO2 systems, based on measurements of the content inside the greenhouse.
Hope some of this is of help.
