Misting Fans: A Cheaper Option for Greenhouse Cooling
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One of the biggest challenges for greenhouse owners is find the right way to control heat, humidity, and circulation. Greenhouses trap heat by capturing sunlight and transforming it into infrared heat as it's absorbed by the glass, plants, and soil inside. The absorbed heat is radiated back into the greenhouse at a lower wavelength and is prevented from escaping by the glass walls. In winter, this cycle maintains a healthy temperature for the plants inside. In summer, it can become harmful as temperatures soar and the heat inside builds up past tolerable levels. Excessive heat also lowers humidity. As air heats up, it expands, forcing air and water molecules further apart. In order to control these two factors - heat and humidity - and ensure air circulation for their plants, many growers have begun cooling greenhouses with misting fans. Misting fans offer numerous benefits for growers. Misting fans are considerably less expensive than comparative, high powered misting systems. Less than half as expensive in most cases. Besides cooling greenhouses cheaper, misting fans aid the growing process by providing better humidity and circulation, which makes them the ideal greenhouse cooling solution.
How Misting Fans Cool Greenhouses Cheaper
Misting fans like theLuma MF24B and theLuma MF26B reduce temperatures through evaporative cooling. They pump water through high powered centrifugal misting systems, which breaks up water into micro droplets, and blow it out using strong fan blades. As the water flows into the air, it evaporates. The heat is absorbed by the water and becomes trapped in the water vapor as it transitions from a liquid state into its gaseous form. Because misting fans use micro droplets, only a small amount of energy is required for them to reach their evaporation point. This means they evaporate quickly, and the more quickly evaporation happens, the quicker temperature drops. Under the right conditions - high heat, low humidity - misting fans can lower the temperature by as much as 20-30 degrees over an 800-1000 square foot area.
Not only are misting fans considerably cheaper than other comparative misting systems, they're also self-contained, low maintenance units. The centrifugal systems in the Luma MF26B and Luma MF24B prevent clogged nozzles and hard water mineral buildup. Their only area of concern is there water tanks, which have to be refilled every 4-6 hours. Even this inconvenience is mollified in smaller units like the Luma MF18W, which has a hose attachment that supplies the fan with a continuous water stream, allowing it to run almost indefinitely. Setup is minimal and their low wattage systems means they can be run for long periods at very little cost. Even the most powerful fan uses only 287 watts per hour, which means ten hours of continuous use would only cost growers $0.25-$0.59, depending on their local utility.
Benefits Over Traditional Misting Systems
Traditional greenhouse cooling systems have relied on a great deal of specialized hardware. Evaporative cooling was created by constructing overhead water pipes that released water through specialized misting nozzles that broke water up into micro droplets. Cooling greenhouses with misting fans requires none of the time or technical expertise of these low pressure systems. The fans can be set up and being cooling almost as soon as they're unpacked and upkeep is minimal. Even nozzle fed units like the Luma MF18W can be unclogged with a screwdriver and a little vinegar. Fans with centrifugal systems, like the MF26B and MF24B, only need to be periodically wiped down with soap and water. They have a waterproof coating that prevents rust and oxidation, which means their operational lifespan is quite extensive.High pressure misting systems require less equipment and set up, but cost a great deal more, almost $2000 per unit. A high powered Luma costs less than $750. They require no special attachments, they can be placed wherever convenient, and require nothing more than an electrical outlet, generator, or extension cord.
How Misting Fans Benefit Greenhouses
Misting fans solve three of the greatest difficulties growers face in greenhouses: heat, humidity, and air circulation. Each of these factors has to be carefully balanced for plants to thrive in a sealed environment.
Heat
Plants cool themselves through the process of transpiration. Just like humans, plants excrete water through their pores (called stomata). Stomata are located in the leaves of the plants. Just like in humans, when the water evaporates from the plant's surface, it transfers heat from the body of the plant into the air. In direct sunlight, plant temperatures rise roughly nine degrees every hour. For every 18 degree increase in temperature, their rate of transpiration doubles. Once a plant's temperature reaches 85 degree Fahrenheit, the rate of water loss starts exceeding the rate of water absorption and the plant begins experiencing heat stress. Heat stress is very damaging for a plant because it entails a huge amount of water loss. Plants transpire quickly in an attempt to lower their temperature, compromising many of their internal processes.
| Consequence of Water Loss | Explanation |
| Photosynthesis declines | Water is the primary component of photosynthesis. Without water, plants can't convert sunlight into chemical energy |
| Plant starvation | As photosynthesis slows, plants start consuming food reserves. After extended exposure to high heat, nutrient loss can be catastrophic |
| Leaves and flowers wilt | Turgor pressure, which keeps plants erect, depends on water levels. When water is diverted for cooling, turgor pressure drops |
| New buds die. Stem growth and flower size is reduced | New plant tissue is 80-90 percent water. As water levels drop, plants can't generate new cells and growth becomes unsustainable |
Under prolonged heat stress, plants will actually close their stomata in order to preserve water. When this happens, transpiration ceases and plants over heat until they literally cook inside their skin.
Plant temperature corresponds closely with air temperature. As it increases, so does plant temperature. Evaporation also increases at high temperatures. There is more energy to
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Humidity
Problems caused by excess heat are exacerbated by low humidity. When humidity is low, air accepts water vapor more readily and evaporation occurs more quickly. In normal temperature ranges, humidity below 30 percent can drain water from leaves, causing them to curl or dry out, and kill of flower buds. Humidity levels of 50-60 percent allow plants to exchange water with the air at optimal rates. These levels are often difficult to maintain in greenhouses, which is why misting fans are such valuable tools. They not only reduce heat, they return moisture to the air in order to keep plants healthy and hydrated.
Air Circulation
Transpiration is not only how plants cool themselves, it's also how they excrete waste products like oxygen. Without strong air circulation, these gases accumulate around plants and make it harder for them to draw in fresh CO2 for photosynthesis. Low air circulation also encourages the spread of diseases. Germ bearing particles are often released through transpiration and get absorbed by neighboring plants as they draw in CO2. Air circulation removes these contaminates and draws in fresh, healthy air instead.
Misting fans not only circulate air, they also circulate mist and create temperature differentials that help airflow. As the fan blades blow micro droplets of water through the greenhouse, it cools the air faster, causing it to sink and providing more room for the warm air near the soil to expand. As the cool air heats up, the warm air gets saturated by the mist from the fan and cools in turn, which causes it to sink down and warm air to bubble up again. In this way, strong air circulation not only improves plant health, it also improves greenhouse cooling.
Conclusion
Misting fans provide cheaper greenhouse cooling and allow greenhouse owners to balance three essential growth factors: heat, humidity, and circulation. They lower temperature, increase humidity, and circulate the air. They're inexpensive, cheap to set up, and easy to maintain. They're a useful tool in both large and small greenhouses and the ideal cooling solution for serious growers.
