We can also supply you with all of the Greenhouse Supplies needed to run and maintain your greenhouse for optimal performance. Please feel free to call and talk to Steve about your greenhouse needs!
Greenhouse ventilation is removing air from inside of the greenhouse and replacing the air with fresh air from outside. Ventilation can come from natural air flow produced by the wind and air temperatures or by a mechanical devise such as a fan or evaporative cooler. The purpose for ventilation is to control the high temperature from summer caused by solar radiation and to maintain relative humidity levels during the winter months. Ventilation systems must be taken into considerations when building a greenhouse.
There are many factors to consider when cooling a greenhouse and which system should be used. Things to consider:
· No cooling
· Natural ventilation
· Fans & shutter cooling
· Fan & Shutter using a shade cloth
· Evaporative cooling
No Cooling – Inside temperature of greenhouse can exceed 140º. Plants will die within a short period of time
Natural Ventilation – Greenhouse has a roof vent which opens to allow hot air to escape to outside. The doors or openings must be left open to provide for incoming air from the outside to replace exhausted air. Keep in mind that hot summer days temperatures can rise 20 to 30 degrees above outside temperature inside of a greenhouse. This type of cooling is only recommended for mild climate areas only.
Fans & Shutter Cooling – The outdoor air is introduced through motorized inlet shutters and the hot air is exhausted using exhaust fans. The temperatures inside greenhouse can be maintained within 10º of outdoor temperature with a properly designed system. The fans and shutters are controlled by thermostat.
Fan & Shutter Using a Shade Cloth – In the greenhouse the outdoor air is introduced through motorized inlet shutters. The hot air is exhausted by exhaust fans and the shade cloth is placed over exterior of greenhouse. Temperature inside Greenhouse can be maintained within 3 to 4 degrees of outdoor temperature with a properly designed system. The fans and shutters are controlled by thermostat.
Evaporative Cooling– Outdoor air is cooled using an evaporative cooler which is located on the outside of the greenhouse structure (usually located in the rear of the greenhouse) which vents inside. Hot air is exhausted through outlet shutters which operate automatically on pressure differential. The temperature inside greenhouse can be as much as 10 to 15 degrees cooler than outdoor temperature with properly designed system. Evaporative Coolers are usually and most often controlled by thermostat. System efficiency can be increased with the use of shade system. The fans on the evaporative cooler will not have to work as hard to maintain the desired temperature using the shading.
Circulation of air is required anytime there are plants in a greenhouse. The constant movement of air helps keep temperatures even throughout the greenhouse plus reduces the condensation which reduces mold, fungus and plant disease.
Light is a limiting factor in the production of greenhouse plants. Growers in the South receive high quantities of light and warmer greenhouse temperatures. Many greenhouse owners in the South typically provide shading beginning in April; while in the North often wait until mid to late May.
Shading is installed to limit the rising temperature inside of the greenhouse structure. Most shade-avoiding crops can tolerate high light levels just fine. However, the amount of energy that comes from the sun is high from late spring until early autumn. This energy increases air and plant temperature, and as a result the quality of some plants can decline when temperature is excessively high. Shading also diffuses the light inside a greenhouse, making bright areas dimmer and shaded areas brighter.
Exterior shading is the most effective method of preventing heat build-up. Aluminum Roll Up shade which provides from 63% to 80% shading while Shade cloth, or screening material which provides from 35% to 75% shading. This product has been used by commercial growers for years and is available for hobby greenhouses.
The heat requirements for a greenhouse depend on the type of plants you will be growing, the size of your greenhouse structure, the greenhouse cover material and your climate zone. The type of plants you grown in your greenhouse will also determine whether the greenhouse is a cool, warm or hot-house.
A cool house maintains a night temperature of 40º – 45º degrees.
A warm greenhouse requires a night temperature of 55º for plants that require a warmer environment.
Hothouses require a nigh temperature of 65º for orchids or tropical plants.
Most plants are warm or cool crop plants. Having separate growing areas in a greenhouse can be difficult in smaller types of greenhouse structures. A good heating system is also important in temperamental climates. Greenhouses collect solar heat. On sunny and winter days when the temperature outside is 20 degrees, the temperature inside the greenhouse can reach upwards of 65 degrees.
When designing a greenhouse make sure to include vents to allow air to flow in and out. You can effectively cool greenhouses smaller than 200 square feet of ground area with evaporative cooling. Large greenhouses will cool easier with a wet wall or fan-and-pad system. Greenhouse cooling and heat should be controlled by a thermostat which should be placed in a protected area which can be easily accessed.
It’s a good idea to have a thermometer located inside of the greenhouse. This will allow the gardeners to record daytime high as well as overnight low temperatures ensuring you can correctly control your growing environment.