Chapter 2

Greenhouse Heating

Greenhouse Infrared Heating Systems

Greenhouses can be heated using an infrared heating system that supplies radiant energy (See Figure 2.12). Infrared heaters emit infrared radiation, which travels in a straight path at the speed of light. Objects in the path absorb this electromagnetic energy, which is immediately converted to heat. The air through which the infrared radiation travels is not heated. After objects such as plants, walks, and benches have been heated, they will transfer their heat to the surrounding objects and air. As a result, the plants and soil may be 3 degrees F (1.7° C) or more higher than the surrounding air temperature during a heating cycle. This difference between plant temperature and air temperature is not enough to fully stratify warm air in the greenhouse. The air temperature remains nearly the same anywhere in the greenhouse from the floor to the peak. In the conventional system, the air is heated first; the air then heats the plants.

Types of Infrared Heaters

Most infrared radiant heating systems utilized in greenhouses are gas fired, low intensity tube systems. These tubes are installed in tandem or near the peak of the greenhouse, and run the length of the house. Two major types of low-intensity infrared heaters are typically used in greenhouse applications: Unitary and Burners-in-Series. Unitary heaters have a single burner located at one end of the heat exchanger tube. The combustion takes place at the burner end, and the products of combustion are exhausted or vented at the opposite end.

Zone Heating

When designing an infrared heating system for a greenhouse, it’s also important to note that these systems can be zoned to maximize their efficiency. With infrared heaters, it is possible to divide any area into separate smaller zones and maintain a different comfort level in each zone. For example, one zone with a high concentration of plants could maintain a 75 degrees F while at the same time another zone, with no plants, could be kept at 50 degrees F or at a lower temperature.

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