Greenhouse Heating Systems

Heating is essential in winter or cold regions to maintain optimum temperatures for crop growth, flowering, and fruiting. The goal is to maintain both air temperature and root-zone temperature. There are several popular types of heating systems for greenhouses. The most common and least expensive is the unit heater system.

A. Unit heaters:

• Warm air is blown from unit heaters with self-contained fireboxes.
• Heaters are located throughout the greenhouse, each heating a floor area of 180–500 m2.

B. Central heating:

• Steam or hot water is produced, plus a radiating mechanism in the greenhouse to dissipate the heat.

C. Wall pipe coils:

• Perimeter-wall heating can provide part of the additional heat requirement and contribute to a uniform thermal environment in the greenhouse.
• Both bare and finned pipe applications are common.
• Side pipes should have a few centimeters of clearance on all sides to permit the establishment of air currents and should be located low enough to prevent the blockage of light entering through the sidewall.

D. Overhead pipe coils:

• An overhead coil of pipes across the entire greenhouse results in heat loss through the roof and gables.
• The overhead coil is not the most desirable source of heat, as it is located above the plants
• They can also be used to reduce the risk of Botrytis cinerea outbreak

E. In-bed pipe coils:

• When the greenhouse layout allows it, the in-bed coil is preferable.
• By placing the heating pipes near the base of the plants, the roots and crown of the plants receive more heat than in the overhead system. Suitable for plants grown on benches, fixed tables, and rolling or transportable tables.

F. Floor pipe coil:

• Floor heating is more effective than in-bed pipe coil heating.
• In addition to the advantages of in-bed coils, floor heating has the ability to dry the floor quickly.
• Air movement caused by the warmer floor reduces the humidity around the plant. Suitable for plants directly grown on the floor, flooded-floor areas or work areas.

G. Pipe/rail heating systems

• These systems maintain uniform temperatures with a positive effect on the microclimate.
• Air movement caused by the warmer pipe/rail reduces humidity around the plant
• Such systems are suitable for vegetable production

H. Radiant heater systems

• These heaters emit infrared radiation, which travels in straight path at the speed of light.
• The air through which the radiation travels is not heated.
• After objects such as plants, walks and benches have been heated, they will warm the air surrounding them.
• Air temperatures in infrared-radiant-heated greenhouses can be 3–6 °C cooler than in conventionally heated greenhouses with equivalent plant growth
• Grower reports on fuel savings suggest a 30–50 percent fuel reduction with the use of low energy infrared-radiant heaters, as compared with the unit heater system.

I. Thermostats and controls

• Various thermostat and environmental controllers are available for commercial greenhouse production.
• Sensing devices should be placed at plant level in the greenhouse
• Thermostats at eye level are easy to read but do not provide the necessary input for optimum environmental control.
• An appropriate number of sensors are needed throughout the production area
• Environmental conditions can vary significantly within a small distance.

J. Heating for anti-frost protection

• Heating can be used to protect crops from freezing.
• It can also keep the greenhouse air temperature at levels above critical thresholds for condensation control.
• When not equipped with heavy and complicated heating systems, a unit heater is usually enough.