In order to improve temperature control inside of a growing system, we must understand how temperature works inside of a system with plants and the variables involved in determining temperature for our crops.
There are different variables that affect temperature in plants. Some of the most important variables are radiation, metabolic heat, latent heat and sensible heat.
Radiation: This is the heat transfer by photons transporting energy from one object to another. There are two types of radiation that are important in growing systems: solar radiation, also called short-wave radiation, and radiation from earth objects, also called long-wave radiation.
Sensible heat: This is the heat transfer by temperature difference and there are two important types of sensible heat. Conduction and convection. Conduction is the transfer of heat through materials. For example, in growing systems it is very important to know the heat transfer from our glazing material. This can help you to select a good material that can make it easier to maintain the optimum conditions of heat inside your system in conditions where you need to heat or cool down your greenhouse. By the other hand, convection is the heat transfer by movement of liquid or gas. We can control convection by fan ventilation. Air flow is a key variable inside growing systems.
Metabolic heat: This is the heat generated by metabolic activities in any organism including plants. This variable can affect leaf temperature.
Latent heat: This is heat released by change in the water phase. This includes two important definitions: Condensation and evaporation. Condensation is a process where gas change to liquid. This process releases heat. Condensation is something that happens inside greenhouses when humidity is not controlled and can trigger fungi and bacteria growth. Evaporation is the process when a liquid changes to gas. This process consumes heat. Evaporation is the technique we use inside a greenhouse to reduce temperature. In order to reduce temperature in greenhouses we use fogging systems and wet walls.
All variables mentioned are connected and together determine air and leaf temperature. If we understand their behavior we can control our system better. For example, in a condition where plant transpiration is reduced, sensible heat will increase. Why? Latent heat will be reduced because less evaporation will take place. Evaporation consumes heat therefore air temperature will tend to increase.
In growing systems, we should consider how solar radiation, transpiration, wind velocity and relative humidity work together:
Solar radiation can affect leaf temperature, leaf temperature affects transpiration, transpiration affects both humidity and air temperature. Also, air velocity can affect humidity (reduces and transpiration (improves).
The more we understand variables involved in temperature, the more we can control our systems. Addition of fans, exhaust fans to remove humidity. The use of shade cloths to reduce heat from radiation are just examples of all manipulation we can do inside systems.
The advance in technology makes it possible to measure, evaluate and take action inside systems in order to improve the environment. In Hort Americas we can help you to select the best tools, not only to monitor your system but also evaluate variables in a very easy way. Let us help you to succeed!