What is VPD? Vapor Pressure Deficit, VPD, is an indicator of the evaporation potential of water into the air. It’s a measurement that’s defined as the difference, or deficit, between pressure exerted by the moisture present in the air currently and the pressure at saturation. It’s one of several different methods that you can use to evaluate crop stress or water stress within a plant.
You need a good digital controller that has the ability to read sensors and actuate equipment, or interact with something that can actuate equipment. If I have to crank all the levers, that doesn’t do me any good.
To name a few manufacturers in order of my experience with them…
- Wadsworth makes several controllers that can track and handle VPD. I am currently using two Wadsworth EnviroSTEP controllers in two of my greenhouse projects.
- Argus makes a very strong system with lots of flexibility. I have used Argus in research and production greenhouses, but it was not quite as user friendly to me when compared to others. A lot of information that I’m reciting today is partially quoted from an Argus control guy that we met a long time ago because he happened to have a really great set of definitions.
- I have recently seen a very nice Hortimax system replace an older outdated controller in a tomato greenhouse locally.
- I believe Link4 makes a control system which is likely appropriate. I have seen a client begin installing a Link4 in his greenhouses, but have not seen them operating yet.
- Hanna Instruments does some controllers, but I think they’re fertigation controllers mainly.
- Another strong greenhouse controller would be Priva for the more professional growers.
- I’ve even used Arduino’s and Raspberry Pi’s successfully to read sensors and actuate equipment.
Be warned though, Priva and Argus systems are very sophisticated controllers that require a smart grower, and sometimes even an engineer… not the guy who just got promoted to be master grower. They require someone who really knows horticulture and the various parameters that the controllers interact with. All of these controllers are appropriate because they are computerized, they have digital displays, they can all read sensors you deploy into your growing conditions, they can all do some level of basic calculations, and they can actuate equipment such as heaters, fans, CO2 generators, evaporative coolers, pumps and so on and so forth.
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