If you have a greenhouse you will definitely need to think about ventilation. Greenhouse ventilation is a very important function in a greenhouse. When your greenhouse is well ventilated the air movement will help to lower temperatures and distribute the air to remove cold and hot spots.
During the summer you will need greenhouse ventilation to help with cooling and moving stale air. An exhaust fan will help to push hot air out of the greenhouse and draw the cooler air in. On extremely hot days, you may need to use shade cloths and evaporative coolers in addition to exhaust fans.
Winter greenhouse ventilation is needed to help prevent condensation and to distribute the heat evenly in the greenhouse. This is important to make sure all areas of the greenhouse are getting enough heat.
You can provide greenhouse ventilation by making sure your air flow is at the proper level. Circulation fans should stay on 24 hours a day to keep air continually moving in the greenhouse and distribute fresh air to your plants. Exhaust fans with thermostat controls can be set to draw hot air out of the greenhouse when the greenhouse researches the temperature you set. You can use fans, doors, vents, or windows to help aid your greenhouse ventilation.
If your greenhouse uses a plastic poly film covering, you can also control the air flow by removing or gathering up a portion of the covering.
If you decide to use fans for greenhouse ventilation the proper placement is important. You will want the exhaust fans to be as high as possible for more efficient cooling. Intake vents should be low to the ground and opposite your exhaust fans to draw air in from the ground level and to push the hot air up and out the opposite end.
Position circulation fans so they will pull the air across the length of the greenhouse. Exhaust the hot air to the outside and you will be cooling your greenhouse efficiently.