April 8, 2022

Greenhouse heating and cooling systems

What is a greenhouse heating system?
Greenhouses create a secure and sheltered environment for plants to grow in. they trap solar radiation to increase the heat. The heating systems in a greenhouse try to create an artificial environment for plants to grow in by ensuring the temperature is hot enough for a conducive environment.
For most places, there exists at least one period of time where the climate is too cold for the specific plants to grow where the temperature outside is too low to support crop production. The heat energy provided by the heating systems can be measured in British thermal units, horsepower, calories or joules.

How is heat lost from greenhouses?
In a greenhouse, heat energy must be added to the greenhouse at the rate at which it is lost from the said greenhouse, in order to maintain the required temperature. There are 3 main ways energy is lost from a greenhouse:

  1. Radiation: This refers to the loss of heat energy due to the emission of radiant energy from a warm area (the greenhouse) to a cold area (area outside the greenhouse) with very little warming of air. Compared to greenhouses made out of polythene film, glass walls of a greenhouse do not allow the passage of radiant energy.
  2. Conduction: This refers to the loss of heat energy through the doors, fans, metal purlins, glazing etc. Glazing leads to a major loss of heat energy in a greenhouse and conduction is a major factor of the same.
  3. Infiltration: This refers to the loss of heat energy through any cracks that may exist between and around the panels, doors and fans. No matter how tight and well designed the greenhouse is, there is always up to at least 10% of heat loss due to infiltration.

What is a greenhouse cooling system?
A greenhouse cooling system refers to a system where the greenhouse is cooled in summer or when the external temperature gets too hot and does not facilitate the growth of crops. High temperature outside the greenhouse and solar heating within the greenhouse make it essential to install a cooling system to remove hot air from inside the greenhouse.
Sometimes, when the outside temperature is appropriate, the air inside the greenhouse can simply be replaced by the air outside to maintain the required temperature. In winter, cooling may be required because of the solar input and hence the cooling systems used in summer and winter are often different from each other.

What is a greenhouse fan?
A greenhouse fan helps breaking the air stratification in the greenhouse. Since hot air is lighter than cool air, the greenhouse tends to have the hot air on top and the cold air below. A greenhouse fan helps in mixing the two temperatures of air constantly to maintain the overall temperature inside the greenhouse.

A greenhouse fan affects and improves:
• Air temperature
• Gas Concentrations (Carbon di oxide and oxygen)
• Moisture level
• Plant hardiness
• Dust and pest levels
There are various types of fans that have different purposes such as- exhaust fans, circulation fans, solar powered fans, thermostat fans, and fanjets. The right kind of fan can be chosen based on the size of the greenhouse, plant needs, outdoor climate and energy needs of the greenhouse.

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