Countries with unfavorable weather conditions find a sanctuary in greenhouses. Extreme heat causes dehydration in plants as stomata will not shut down and the transpiration rate increases. Extreme cold reduces the metabolic activity in plants.
Unlike humans and animals, plants are the only creatures that produce their food and also feed the entire ecosystem. But we know that the earth rotates around the sun and is spherical. As a result, the regions in the north and south poles experience sub-zero temperatures. Countries beyond the tropics have short summers and long winters. They have a short harvest cycle, and it’s practically impossible to grow enough food unless greenhouse farming is the local culture.
Greenhouses are spaces where the sunlight and heat are trapped in a contained space where the plants are protected from the outside climate. In hot places, greenhouses with shade nets can be used to protect plants from excessive sunburn. As the temperature rises, humidity also increases in the form of water vapor. Plants will not be able to release their excess water into the atmosphere, and they will rot and die. However, If vents are used to release the excess humidity, plants will continue to thrive well in their contained spaces. Traditional guillotine or rack and pinion greenhouse vent are commonly used in greenhouses. Some greenhouses need to use fans to cool the temperature as and when required.
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Cooling greenhouses is a critical, and time-bound activity. Even a few hours of negligence can damage the entire crop. High temperatures will also cause early flower drops, leading to lower fruit yields. The ideal air circulation rate is 0.5-0.7 meters per second to maintain the air exchange and carbon dioxide levels for plants. Without ventilation, the exchange of air and gasses is impacted, which translates to a rise in pathogenic activity. Greenhouses are meant to safeguard the plants and not cause more stress. By functionally placing vents and ducts greenhouses can operate without distressing plants.
A sauna is good for the human body, but can you take it for an extended time with a temperature rise? The answer is no; Likewise, plants thrive when heat and light are maintained at optimum levels. There has to be a mechanism to let out or absorb the heat whenever it rises beyond the optimal levels. Here are a few ways to cool and vent a greenhouse:
Outlets
Vents can be mechanized or manual. Mechanized vents are automated, and manual labor closes the latter. Vents can be traditional guillotine kinds that are installed at a height. Rack and pinion vents work on the mechanism of rotational and linear motion between the circular and linear actuators. It eases the need for applying pressure when opening a vent. Initial greenhouses were made with simple vents, and this approach is still valid for small-sized contained environments.
Whenever the temperature of a closed place increases, hot air goes up, and cold air moves downward. Cooling the greenhouse with vents placed at the top helps reduce the impact of hot air that goes up due to thermal buoyancy. The vents placed upwards work like chimneys that let out the heat using the external wind. When hot air is pushed out, and cool air comes inside, the temperature stabilizes till the next phase of rise in heat and humidity. On cool days, air exchange within the greenhouse is impactful. On hot days, the thermal buoyancy is less as everything around tends to get hot. Extreme care should be taken, so as not to direct the hot air from upwards to downstream using fans. Placing fans in the right location will solve this issue to some extent.
Exhaust Fans
Much like the exhaust fans that are installed in our kitchen systems that send the hot fumes out to maintain the balance of the atmosphere, greenhouses use them for the same reasons. Hot air is pulled out, and cool air is sent in through fans to evenly cool the internal temperature of the controlled unit. On summer days, these fans work through the day to send out the excessive heat that can be life-threatening for the people working within the place.
Fans and vents are ideally placed opposite of each other. In big greenhouses, fans are often placed on the sideline. Fans that can move as per the wind direction offer maximum benefit in cooling the place faster.
Dehumidifiers
In summer months the best of greenhouses grapple to bring the temperature down as the difference between inside and outside is likely to be 10-20o F. If the humidity level rises, the natural transpiration rate of plants inside the greenhouse reduces. Plants will stop absorbing water from the roots, and their metabolic activity is affected to the extent that they can decay and die. Dehumidifiers can be used to condense water vapor with cool air, pretty much like air conditioners. The hot water vapor is condensed into water droplets. However, it is ideal to match dehumidifiers with not just the transpiration rate of the plants but the total evapotranspiration of plants within a greenhouse.
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Conclusion:
Understanding a plant’s basic needs will solve a lot of issues that a farmer faces. If the plants that you intend to grow transpire more and you are in a relatively hot region, then dehumidifiers will be useful. Whereas if you live in a cold weather place, it’s pointless to use one.
Similarly, all things that go into the functioning of a greenhouse are specific to the plant’s needs, zone, budget, and farming requirements. Fans may not be required in cold places, but climate-controlled heating systems are meaningful tools in maintaining heat alongside grow lights and thermal curtains.
The greenhouse that you design or improve involves capex requirements. This amount will not be offset by revenue of a single year. It has to be spread across for a few years in your business books, to be capitalized. Since the investment will be substantial, it is ideal if one can spend some time on due diligence before committing.
