Soaring midday temperatures and increasing humidity stress greenhouse plants beyond sustainability. Ventilation is necessary to keep the environment optimal for growth. Supplying heat and light is the main objective of a greenhouse. Passive solar greenhouses rely primarily on the sun, while heated greenhouses are not so dependent. Control of humidity light and temperature is achieved with a combination of opening windows and doors, fans, heat storage devices and sensors.
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Active Climate Control
Large commercial greenhouses rely on fans to remove hot, humid air, heaters to keep the air warm and thermostats to regulate temperature and humidity. Automatic climate control devices can be installed to take over regulation of the greenhouse climate. They are sophisticated enough that they can be controlled with software from your home computer. The software can program specific areas of the greenhouse with different humidity levels and temperatures for growing a variety of plants. Devices like these, although energy-efficient, are expensive and not necessary for home gardeners.
Using Heat Sinks To Control Temperature
Greenhouses are made of plastic or glass, allowing for maximum exposure to the sun. The sun's radiant heat is absorbed by the plants, soil, ground and other things in the greenhouse. Taking advantage of this capability to absorb heat is an easy way to regulate temperature in the greenhouse. The best substance for storing heat is water; it has a high heat capacity. A cheap solution is to fill plastic milk bottles with water and place then between the plants and the greenhouse walls. Painting them black would also increase their ability to absorb heat. At night, as the greenhouse temperature drops, the water slowly releases its heat back into the air, keeping the plants warm.
A more active but expensive heat sink can be made by pumping the hot air up in the roof down into barrels filled with water. During the night, the heat from the barrels is released back into the greenhouse.
Using Windows And Doors To Regulate Heat And Humidity.
Using a thermometer is the best way to decide when to open a window in the greenhouse. The optimal temperature for greenhouse plants is 10 to 29.4 degrees Celsius. Opening a window is the easiest way to get rid of hot, humid greenhouse air. A cross breeze can be achieved by opening the door or another window. Window opening mechanisms, sensitive to heat, can be attached to the windows. As the mechanism heats up in the midday sun, the metal expands, pushing open the window. In the evening as the sun goes down, the temperature falls, the metal contracts and the window closes.
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