Choosing a greenhouse cooling system
Of course, your challenges are going to vary depending on your local climate, but cooling a greenhouse will require a combination of shade, ventilation and humidity that works in your particular growing zone.
Regardless of where you are, plants in an overheated greenhouse will experience a loss of stem strength, reduction of flower size and a delay of flowering.
To lower the temperature in your greenhouse, consider the following cooling systems and the benefits that they offer.
Vents
Traditionally, vents placed in the roof have allowed the warmer air that rises to escape, while drawing in cooler air from side vents. Vent positions can be changed manually or mechanically to naturally maximize benefits from wind direction. Though vents carry lower operational costs, construction costs may be higher. Using natural ventilation alone will not bring the indoor temperature lower than the outdoor temperature. A system that combines exhaust fans with vents helps increase the efficiency of excess heat removal, but may still need to be used in conjunction with another cooling method.
Shading
Paints, blinds or cloths are another low-energy cooling option for your greenhouse. Shade paints are a quick way to filter the sun’s strength and can be applied in more layers in higher heat and washed and brushed off during cooler spells. Internal or external blinds can also help. External blinds are the most effective, but keep in mind they may obstruct efficient vent operation. Shading can help make other types of cooling systems more efficient by reducing the sun’s intensity, as well as retain heat overnight. Take care that light is not reduced to undesirable levels, such as on cloudy days or early mornings or near nightfall when light is not as intense.
Evaporative coolers
Fan-and-pad systems are the most common for summer cooling. Evaporative cooling systems like these use the heat in the air to evaporate water from plants and other wetted surfaces to lower the greenhouse temperature. Pads mounted on a sidewall are supplied with water, and air drawn through the pads by fans on an opposite wall can drop the indoor temperature by 10 to 20 degrees below what’s outside. Evaporative cooling systems are ideal for dryer climates, but can provide cooling anywhere in the U.S.
Misting or fogging
These systems use high pressure water delivery to emit very fine water particles, and the drops evaporate in the air, reducing the temperature. This low-cost solution, when used with fine nozzles, can introduce additional humidity in the greenhouse, and that moisture can help reduce the frequency of watering plants. Some of the benefits of this option include: preventing plants from drying out or wilting, like some vented systems; operating costs are lower than fan-and-pad cooling; achieving nearly 100 percent cooling efficiency; and allowing wet bulb temperatures to be obtained.
For more information:
Gothic Arch Greenhouses
1-800-531-4769
www.GothicArchGreenhouses.com