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.
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.
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.
Evaporative cooling pads
In addition to the typical cooling methods of active and passive cooling, there's evaporative cooling pads. These use heat to naturally evaporate water on all structures, equipment, and plants in a growing area, these systems can effectively lower temperatures. An evap system is much more complex than the other cooling methods as they have multiple mechanical parts and will incur a slightly higher operating cost. However, these systems provide excellent cooling capabilities that truly come to the rescue in greenhouses that require serious cooling capacity.
The most preferred evaporative cooling method is through the use of a fan and pad. These systems consist of a water pump, water storage, fans, and cellulose pads. The pad is soaked in water supplied by the pump with the fans installed on the opposite side of the pad pulling the cooler air into the growing area. Evaporative cooling is statistically shown to work better when relative humidity is low and is super effective in arid areas or regions. It is important to select the right size fan and pad system to ensure effective and maximum cooling for a growing area.
For the commercial greenhouse operator that wants to minimize fungal growth and control temperature for plants picky about lighting, a shade cloth install may be the answer. The installment of shade cloth helps to control lighting and provides protection from fungal growth of fungi that love the sunshine. Shade cloth is also commonly used in commercial greenhouses with photosensitive plants to force blooming or mimic natural processes to start seasonal plants earlier. Shade cloth can be installed as a manual roll or on automatic rolling systems. These automatic systems can also have timers integrated to unroll at set times. These automatic systems are sometimes connected to the thermostats to open or close based on temperature.
Another technique to increase relative humidity and control temperatures is through a fogging system. A commercial greenhouse can install automatic foggers through specialized nozzles in the irrigation system or through manual cart foggers. Some carts have the automatic option as well for fogging. The system works best when the water fog or mist is sprayed from the greenhouse ridge. This technique is also ideal for emergency situations where the temperature needs to be lowered quickly. Fogging and mist systems are also good for new seedlings whose roots are not strong enough to stand standard watering. Some tropical plants require a higher humidity with foggers simulating the tropical environments they call home.
Overall cooling during warmer months in a greenhouse holds the same importance as heating in cooler months. Steady temperatures and ideal conditions allow a grower to maximize yields and quality as plants are less stressed. There are many methods to cooling a greenhouse to ensure that temperatures stay in check from active, passive, cooling pads, and installation of equipment and tools to provide areas of shade and quick temperature fixes. A combination of these methods should be used to provide a multi-spectrum approach to cooling a greenhouse or indoor farm. This follows the adage of not keeping all your eggs in the same basket. When one method is not enough for cooling, the grower has another ace up their sleeve to get temperatures in check.
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