Many greenhouses revert to ventilation and evaporative cooling to achieve the desired temperature. However, in warm and humid climates, it is not possible to cool down the greenhouse sufficiently with evaporative cooling. Other technology must be used, namely, active cooling. This cooling technology can be compared with air conditioning, but on a really big scale. It requires a chiller to provide the water and an air handling unit to cool and dehumidify the air.
Active cooling system in a greenhouse can be based on
- Water cooling
This will provide chilled water with a minimal temperature of 4°C - Glycol solution
This solution can be cooled to temperatures far below 0°C!
The choice and the design will be based on the cooling demand and the energy costs.
Advantages of active greenhouse cooling using chillers:
- Precise temperature control
- Precise humidity control, moisture removal from the air
- Suitable for any outdoor climate
- Separate temperature and humidity zones
- Minimal to no introduction of external air
How does a chiller work?
A chilled water cooling installation consists of a chiller and a piping network. Chilled water is transported throughout the greenhouse in a loop to provide cooling. The process during which water is used as the heat-transfer medium is called hydronics, in this case to provide cooling.
Using valves, the piping network can be divided into several groups, so the greenhouse can be segregated in several areas in which the temperature is controlled separately. Individual temperature zones are assigned in the greenhouse. The air handling units together with the chiller provide optimal greenhouse temperature and humidity conditions.
In the air handling unit, a fan draws warm and humid air past a heat exchanger with the chilled water, the cooling coils. The air is cooled and the moisture condenses. Cool and dry air is spread into the greenhouse. The temperature in the cooling coils is regulated with temperature sensors and valves and variable fan power influences the amount of air that is cooled. This allows precise climate control in the greenhouse.