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US: Pointers on greenhouse heating and energy conservation

With increase concerns about global warming, it is very important to use the least amount of fossil fuel for energy to minimize the impact on our fragile environment.

In this article, fossil fuel refers to natural gas, LP gas, coal or fuel oil.

For growers, it can be very difficult in winter months to maintain the greenhouse at ideal temperatures for plants, even during the day. During winter months, the strategies to conserve energy may not be enough to keep the air temperature within an optimum range, therefore, the use of fossil fuel is necessary to heat the growing environment. The method to increase air temperature inside the greenhouse has to be affordable, efficient and safe to use. In other words, the capital invested has to be recoverable, the heat source must be close to the plant, support the entire growing area, maintain temperatures high enough to promote active growth, and finally, the fuel source has to be safe.

Central heating systems:
  • Heat is transferred from the hot water pipe to an object; this type of heat transfer is considered radiant heat.
  • This type of heating systems uses a boiler to heat water or to produce steam.
  • Boilers can burn fuels like natural gas, wood, coal or fuel oil.
  • Hot water systems are more efficient than steam systems.
  • One by-product of the boiler is CO2. This gas can be trapped and delivered into the greenhouse to help the plants in the photosynthesis process.
  • This system is recommended for large operations due to high installation and hardware cost.
  • The warm water or steam has to be transported in pipes throughout the greenhouse.
  • The efficiency can be higher than the use of forced air heater units because the greenhouse is heated uniformly; there is little need for ventilation.
  • The pipes can be placed around the inside perimeter of the greenhouse in the case of a single-span greenhouse. For a gutter connected greenhouse, it is recommended to install pipes close to the gutters (to melt ice) and/or under growing benches.
  • The water temperature for overhead systems can be up to 200˚F (94˚C) while the water under the benches can be up to 104˚F (40˚C).
  • Floor heating is another method to heat the greenhouse with hot water. With this method, pipes are placed in the ground under a layer of concrete, gravel, sand or soil. Heating pipes form loops around the entire surface of the greenhouse. The water temperature can be up to 104˚F (40˚C).
  • These systems require time to reach the desired temperature; similarly, it will take time to decrease the temperature.
  • In greenhouses dedicated to vegetable production, two pipes carrying hot water are placed in the ground, parallel to the rows and between the rows. These pipes serve to heat the greenhouse and look like train rails. Trolleys can be used on these rails to transport produce, support equipment to spray plants or support equipment for people to work on plants.
  • Another option for vegetable production is to place polyethylene pipes with warm water in close proximity to the plants.

Publication date: 11/6/2015



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