Keeping cool in summer

One of the best aspects of the summer months is the increased temperatures and plenty of sunshine. After the cold winter months and damp spring, summer is a welcoming sight for many. However, in a commercial greenhouse, this can be a double edged sword. Summer has increased daylight and higher temperatures leading to less need for supplemental heat and lighting.

The greenhouse can really soar in temperatures and create an environment that is too extreme for even plants to grow. Higher temperatures bring a myriad of issues to a greenhouse from increased pest and disease risk, reduced yields, and lower crop quality. Cooling is important to keep a greenhouse at an ideal temperature. There are two different types of cooling systems - passive and active cooling.

Active cooling
The most effective method of cooling in a greenhouse, no matter the size, is active ventilation. Increased efficiency also causes an increased energy consumption, cost, and maintenance. However, just using one type of cooling is not an ideal scenario for a greenhouse. Active and passive work together to regulate temperature efficiently.

One of the most commonly used active cooling methods are through HVAC and fans. Fans provide essential air movement and cooling in a greenhouse. Fans draw cooler air into all areas of the greenhouse. There are plenty of different types and brands of fans, exhaust, and shutters available for a greenhouse. A grower needs to take into consideration size, air needs, and spacing of fans for the best selection of fans, louvers, and shutters.

Key points to consider for fans in a greenhouse

Proper size to efficiently circulate air (one air exchange per minute up to a height of 8’)
Fan location: draw should be less than 150’, higher than the plant canopy
Louvers placed on opposing sides of the greenhouse than fans
Proper maintenance and cleaning of fan blades and motors, and removing debris from louvers.
Another form of active cooling that has a lower cost and a relatively easy installation is evaporative cooling pads.

Passive cooling
In comparison to active cooling in a greenhouse, the overall cost of installation, maintenance, and overall costs are much lower. The use of passive ventilation relies on two main factors - the effect of wind and thermal buoyancy. The effect of wind is in reference to the way wind blows around a structure. This blowing effect creates smaller pressure differences on the outside of the structure. The use of wind as a cooling method is very important as it provides the majority of air circulation.

The principal of warm air rising is also used in cooling of a greenhouse through louvers and vents installed at the top or along the ridge of a greenhouse. The usual passive ventilation methods are through roof and wall vents using vents and other passages, and air circulation to maximize the full potential of air flow in a greenhouse. By using these two principals, a grower can lower their operating costs and increase the energy efficiency. A modern greenhouse is designed to offer the maximum ventilation in order to provide ideal growing conditions.