Cooling Greenhouse Temperatures
Cooling Systems for Controlling Greenhouse Environments.
Cooling with Shading and Reflection
Automated Retractable Shading
Automatic Shade Curtains - at higher temperatures shade curtains automatically reduce the high heat levels for the greenhouse crop by reflecting incoming radiation.
In addition, roof panes can be opened to allow heated air to be replaced by cooler air.
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Greenhouses
Horizontal Airflow Fans, or HAF fans, are used primarily to distribute heat during the cooler seasons. Automatic shading reduces greenhouse temperatures closer to optimal greenhouse crop growth temperatures.
Greenhouse Shading - Shading greenhouse crops is essential in warm climates or during the summer in temperate climates. In addition to reducing temperatures closer to the optimal growing temperature, shading will reduce water costs.
Note the Horizontal Airflow Fans - HAF fans - used primarily to distribute heat during the cooler seasons.
Automatic Shade Curtains - at higher temperatures shade curtains automatically reduce the high heat levels for the greenhouse crop by reflecting incoming radiation.
In addition, roof panes can be opened to allow heated air to be replaced by cooler air.
Horizontal Airflow Fans, or HAF fans, are used primarily to distribute heat during the cooler seasons. Automatic shading reduces greenhouse temperatures closer to optimal greenhouse crop growth temperatures.
Greenhouse Shading - Shading greenhouse crops is essential in warm climates or during the summer in temperate climates. In addition to reducing temperatures closer to the optimal growing temperature, shading will reduce water costs.
Note the Horizontal Airflow Fans - HAF fans - used primarily to distribute heat during the cooler seasons.
Whitewash applied to greenhouse glass reflects light and shades the crops. There are other commercially available compounds available for shading; and, mud can even be used. Thermal screens can partially reflect and diffuse the incoming light. In Europe, flowing water over the glass is used sometimes to shade and cool the greenhouse. Deciduous trees planted and growing near or in the greenhouse structures can provide seasonal shading.
Cooling with Ventilation
Greenhouse growers utilize natural air movements to assist cooling in greenhouses when greenhouse temperatures are too high. Partial vacuums in roof ventilators can assist in cooling. More importantly, convection currents carry warm air masses upward and out roof ventilators. Greenhouse sidewall ventilators allow cooler air to replace the rising heated air. Side windows can be opened with manual crank and elbow arms or rack and pinion machinery; whereas, a chain fall apparatus is common for opening roof ventilators. In a addition to harnessing natural air movements, many greenhouses have exhaust fans controlled by thermostats to assist with ventilation. Ventilation is very important. In addition to cooling, it can help to increase the carbon dioxide (CO2) supply depleted by the plants and reduce the relative humidity that, in turn, makes the environment less habitable for disease organisms.
Exhaust fans with louvered openings and protective mesh are fitted in greenhouse walls, away from prevailing winds, and play a key role in the ventilation system of a conventional greenhouse. They are rated in terms of the volume of air they move in a minute — Cubic Feet Per Minute (CFM). Thermostats control the fans.
Inlet vents are placed on the windward side, the opposite walls from the exhaust fans. In a evaporative pad cooling system, wet pads are used at the inlet vents to cool the air down that moves into the greenhouse. In some areas, cooling pads are placed inside the greenhouses. This cooler air will absorb heat on its way to the exhaust fan wall. Pad cooling is used in dryer climates and not very effective in humid zones.
Cooling with High-Pressure Fog
Evaporating mist can remove heat from greenhouse air. Ideally, evaporation is quick such that water does not accumulate on the plants. In this system a humidistat activates a high pressure pump (500 to 700 psi) that delivers clean water to nozzles to produce fog in the greenhouse. If the water is dirty or is mineral laden, the nozzles can get clogged. A water softener can be used to treat the water.