Goldenscape Greenhouses Kits-Ventilation
Most Kenyan small scale Greenhouses ventilation is usually by leaving some spaces (natural ventilation) on the roof which in turn provides circulation of air into the green houses in order to control temperature, remove moisture, or replenish carbon dioxide (CO2). Several ventilation systems can be used as explained below.
The total volume of air in a medium to large greenhouse can be estimated by multiplying the floor area times 8.0 (the average height of a greenhouse). A small greenhouse (less than 5,000 ft3 in air volume) should have an exhaust-fan capacity estimated by multiplying the floor area by 12.
The capacity of the exhaust fan should be selected at one-eighth of an inch static water pressure. The static pressure rating accounts for air resistance through the louvers, fans, and greenhouse and is usually shown in the fan selection chart.
Ventilation requirements vary with the weather and season. One must decide how much the greenhouse will be used.
One single-speed fan cannot meet this criteria. Two single-speed fans are better. A combination of a single-speed fan and a two-speed fan allows three ventilation rates that best satisfy year round needs. A single-stage and a two-stage thermostat are needed to control the operation.
Refer to the earlier example of a small greenhouse. A 16-foot wide by 24-foot long house would need an estimated ft3 per minute (cubic feet per minute; CFM) total capacity; that is, 16x24x12 ft3 per minute. For use all year, select two fans to deliver 2,300 ft3 per minute each, one fan to have two speeds so that the high speed is 2,300 ft3 per minute. Adding the second fan, the third ventilation rate is the sum of both fans on high speed, or 4,600 ft3 per minute.
Some glass greenhouses are sold with a manual ridge vent, even when a mechanical system is specified. The manual system can be a backup system, but it does not take the place of a motorized louver. Do not take shortcuts in developing an automatic control system.
Most Kenyan small scale Greenhouses ventilation is usually by leaving some spaces (natural ventilation) on the roof which in turn provides circulation of air into the green houses in order to control temperature, remove moisture, or replenish carbon dioxide (CO2). Several ventilation systems can be used as explained below.
- Natural ventilation uses roof vents on the ridge line with side inlet vents (louvers). Warm air rises on convective currents to escape through the top, drawing cool air in through the sides.
- Mechanical ventilation uses an exhaust fan to move air out one end of the greenhouse while outside air enters the other end through motorized inlet louvers. Exhaust fans should be sized to exchange the total volume of air in the greenhouse each minute.
The total volume of air in a medium to large greenhouse can be estimated by multiplying the floor area times 8.0 (the average height of a greenhouse). A small greenhouse (less than 5,000 ft3 in air volume) should have an exhaust-fan capacity estimated by multiplying the floor area by 12.
The capacity of the exhaust fan should be selected at one-eighth of an inch static water pressure. The static pressure rating accounts for air resistance through the louvers, fans, and greenhouse and is usually shown in the fan selection chart.
Ventilation requirements vary with the weather and season. One must decide how much the greenhouse will be used.
One single-speed fan cannot meet this criteria. Two single-speed fans are better. A combination of a single-speed fan and a two-speed fan allows three ventilation rates that best satisfy year round needs. A single-stage and a two-stage thermostat are needed to control the operation.
Refer to the earlier example of a small greenhouse. A 16-foot wide by 24-foot long house would need an estimated ft3 per minute (cubic feet per minute; CFM) total capacity; that is, 16x24x12 ft3 per minute. For use all year, select two fans to deliver 2,300 ft3 per minute each, one fan to have two speeds so that the high speed is 2,300 ft3 per minute. Adding the second fan, the third ventilation rate is the sum of both fans on high speed, or 4,600 ft3 per minute.
Some glass greenhouses are sold with a manual ridge vent, even when a mechanical system is specified. The manual system can be a backup system, but it does not take the place of a motorized louver. Do not take shortcuts in developing an automatic control system.