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To remove the moisture (water vapor) from the air the vapor must be condensed by passing the air across a cold surface that is cold enough to create water formation on the surface. Refrigeration evaporator coils achieve this by the refrigerant passing through tubes with fins that the air travels across. It must reduce the air temperature enough to reach 100% relative humidity(RH). Chillers pump chilled water/glycol through Heat exchangers of the same construction. The HEX must also reduce the temperature to reach 100% RH. This means the air can no longer hold the water vapor, the heat is released, this is latent heat. This is the heat energy that was used to turn the water into a vapor. The “Laws of Thermal Dynamics” state that it takes 1 BTU to change 1 pound of water 1F in 1 hour.
Refrigeration units and chilled water to air HEX units that are below dewpoint have an effect on latent heat and sensible heat. It varies based on time in contact with the passing air to release heat energy and how much the coil drops below dewpoint.
What can occur if not managed properly is that RH increases when the room or environment temperature is satisfied by being reduced too rapidly and not enough vapor has been removed. As an example, the environment dropped from 90F to 70F. The RH started at 80% but it is now 95% RH. The solution is to reheat or preheat the air passing through the air handling unit (AHU). Vapor is still removed and the environment temperature changes very little. With a properly designed AHU the greenhouse can be heated while being dehumidified.
Removing water from the air without a change in air temperature will reduce RH. Or you can raise the environment temperature without removing moisture and your RH is reduced. Plants transpiring will increase RH if the environment temperature remains the same.
It’s important to remember that relative humidity(RH) is a % of vapor in the air at a given temperature. If you reduce the temperature without reducing vapor the RH has increased possibly to dew point. Altitude is also a determining factor in the amount of moisture that air can hold.
By Pat King
Learn more about Evapotranspiration and The Water Cycle from the USGS by clicking here.
Dehumidifiers operate by absorbing heat from the air, in doing so they dehumidify as the air moves across the refrigerant chilled HEX evaporator. This cold air will be at the BTU rating of the unit. A 24,000 BTU unit will have 24,000 BTU of cold air discharged. When absorbing heat into the refrigerant it absorbs until the refrigerant evaporates inside the HEX and moves on. More refrigerant takes its place to absorb more heat.
The chilled evaporator HEX is at such a temperature it will collect moisture from the air moving across the evaporator. Although the refrigerant is evaporating the humidity is condensing to become water.
Now we have 24,000 BTU of heat in the refrigerant and it must be discharged. The refrigerant has moved into the condenser HEX while under pressure created by the compressor. The heat is removed is when the dry cold air moves across the condenser HEX. Remember that there is 24,000 BTU of cold air to remove 24,000 BTU of heat from the under pressure hot refrigerant. These would counter each other if perfectly equal.
There is a misconception that all of the heat from the compressor is absorbed into the refrigerant to help cool the compressor. Unfortunately it’s not. The electrical energy used to spin the compressor motor creates heat. The condenser fan motor creates heat also. There’s about 1,000 BTU of heat or more that doesn’t have a home so it migrates into the environment. If you insulate the compressor it will overheat and lock up.
The laws of thermal dynamics cannot be beaten but we can work around them.
DehuKing’s first solution is to use one remote dehumidifier with every 4 to 5 standard 2 tons 515 pint DehuKing Dehumidifier. This will counter all of the heat generated by the four or five dehumidifiers plus discharge some remaining cold air into the area. The beauty is that the remote dehumidifiers remove the same amount of moisture as the free hanging dehumidifier. It dehumidifies as it cools the environment (2 Ton = 515 pint). Please see the remote spec sheet on our website tech page.
The second DehuKing solution is to use the 4 ton 1,030 pints stand alone dehumidifier. This unit stands on its own four legs just on the other side of the greenhouse exterior wall. The dehumidifier has riser of 3’ that has a small head upon the top of the riser. This riser penetrates into the greenhouse and discharged 4 tons of dry chilled air into the environment. To compliment the machine hang up to 12 @ 2 ton 515 pint dehumidifiers in the environment or use more stand alone 4 ton units. Specs will soon be on the tech page of our Chillking website.
Contact Biotherm Solutions, DehuKing’s exclusive distributor, for additional information or to purchase.
Pathogenic fungi can be very destructive to an indoor garden or greenhouse. Much like pest insects, pathogenic fungi are capable, under the right circumstances, of quickly destroying an otherwise flourishing crop. To effectively defend a garden against such an attack, indoor horticulturists and greenhouse hobbyists should know how to prevent, positively identify, and treat the most common fungi pathogens. As with most garden disturbances, prevention is the most powerful defense. However, chances are good that even the most diligent growers will experience a hiccup or two when cultivating plants indoors or in a greenhouse. The two most common fungi pathogens to plague indoor horticulturists and/or greenhouse hobbyists are powdery mildew and botrytis (fruit or flower rot).
Powdery mildew is a fungal disease that can affect a wide variety of plants. Powdery mildew is a general term for the plant disease caused by multiple pathogenic fungi; all found in the order Erysiphales (a subcategory of the division Ascomycota).
Plants infected with powdery mildew look as if they have been sprinkled with white flour. Powdery mildew usually starts off as small, circular spots on the leaves, but can also be found on the stems or flowers. In some cases, powdery mildew can cause the leaves of a plant to twist, break, or become distorted. The white spots eventually spread and cover the majority of the leaf’s surface.
Although systemic fungicides are effective against powdery mildew, they should only be used on ornamental plants. For food crops or other consumables, the best treatment option for powdery mildew is some sort of organic-based fungicide. The most commonly used organic fungicides are sulfur-based fungicides, copper-based fungicides, neem-based fungicides, bicarbonate-based fungicides, botanical-based fungicides, and biological fungicides. Even when using an organic fungicide, it is of the utmost importance to follow the manufacturer’s application instructions for safety.
A key to preventing powdery mildew is to make sure the spores never enter a garden in the first place. Perhaps the most common way pathogenic fungi spores enter a garden is through the fresh air intake. By using an intake air filter, a grower can remove many of the spores and pest insects that could otherwise end up in the grow room. A HEPA filter on the ventilation’s intake can be a valuable tool to lessen the ability of powdery mildew spores to enter the garden. Fungi spores are microscopic and, even with intake filters, are almost impossible to stop from entering the grow space.
With this in mind, a grower should focus his or her attention on humidity control as another preventative measure. Maintaining proper atmospheric conditions will help prevent the humidity levels conducive for unwanted visitors. In layman’s terms, humidify levels are affected by the moisture content and the temperature in the garden area. This is why the temperature variance from the lights on cycle to the lights off cycle is an important factor to consider. Keeping the temperature variance between 10-15 degrees F from the lights on period to the lights off period will reduce the likelihood of condensation and unwanted humidity spikes. By controlling temperature variances, a grower automatically has more control over humidity and, therefore, can more effectively prevent pathogens. A general rule of thumb is to maintain a humidity level of 55% or under in an indoor garden or greenhouse.
BOTRYTIS (FRUIT OR FLOWER ROT)
Botrytis is a necrotrophic fungus that can affect many different plant species. In horticulture, it is commonly referred to as bud rot, fruit rot, flower rot or gray mold.
Botrytis mainly affects tender tissues, such as flowers, fruits, and seedlings, but can enter the plant’s tissue through pruning scars or other distressed or wounded tissue. Lower, shaded sections of a plant are usually the first to show signs of a botrytis infection. The first sign shown by a plant with a botrytis infection is a water-soaked, browned area. The distinctive browning is universal, regardless of the type of plant affected. After the initial browning, a silvery-gray fuzzy mat develops on or around the browned tissue. In extreme cases, or in cases where high humidity is prevalent, a brown, slimy substance can appear; this is actually the decimated plant tissue.
Botrytis-infected sections of a plant should be removed immediately in order to prevent it from spreading to other areas of the garden. If possible, bag the affected section of plant before cutting it. This should be done to limit the spreading of spores as the infected area is disturbed. After the infected sections of plant tissue have been removed, the rest of the garden should be treated with a biological fungicide. To prevent future outbreaks, it is a good idea for indoor and greenhouse growers to disassemble the grow room after the garden cycle and disinfect everything with a 5-10% bleach solution of a food-grade hydrogen peroxide solution. This will kill any remaining viable spores and reduce the chance of a future outbreak.
Keeping a clean grow room and removing any dying or dead plant material are good first steps for any indoor or greenhouse grower. In a sense, botrytis is an environmental disease. This means it can only develop when the environmental conditions are conducive to its growth. The prevention of botrytis is somewhat easier for indoor horticulturists because they have more control over the environmental conditions. Humidity is the biggest trigger for botrytis in an indoor garden. As long as the humidity is kept below 55%, botrytis is unlikely to develop. The other contributing environmental factor is temperature. Botrytis can only germinate on damp of wet plant tissue in temperatures between 50-70 degrees F. However, once the fungus has developed, it can withstand a wider range of temperature and humidity. Botrytis grows most rapidly in lower temperatures paired with high humidity. The humidity levels in close proximity to the plants are generally much higher due to the plant’s transpiration processes. This is why air movement within the grow space is so important for maintaining proper humidity levels. To create good airflow, oscillating fans should be used to mix the humid air that is close to the plants, with the air in the rest of the room; this will help keep the room’s humidity uniform.
OPTIMAL HUMIDITY RANGE FOR INDOOR GARDENS AND GREENHOUSES
As previously mentioned, maintaining proper humidity levels in an indoor garden or greenhouse is very important when trying to prevent pathogenic fungi. Put another way, if humidity levels are kept in check, the pathogenic fungi’s ability to establish is hampered. The optimal humidity range for indoor gardens and hobby greenhouses is 50-60%. Even when an indoor garden is climate controlled by a mini-split air conditioner, a dehumidifier may have to be used to maintain the optimal humidity level. Again, it is important to remember how the garden’s temperature also affects the relative humidity levels. Controlling temperature variances will reduce spikes in humidity. A grower who invests in an atmospheric controller, which can be used to automate fans, air conditioning equipment, and dehumidifiers, will have a much easier time maintaining the optimal temperature and humidity. The controlled, consistent temperature and humidity levels are a strong defense against pathogens.
AIR PURIFICATION DEVICES
In addition to atmospheric control devices, which help automate the temperature and humidity in the garden, growers who wish to take pathogen prevention one step further can implement a standalone air purification device. When combined with an air intake filter and an atmospheric control system, a stand-alone air purification device can give even more protection against pathogenic fungi to an indoor garden or greenhouse crop. Essentially, these devices have an internal fan that circulates the air within the grow space; purifying the air in the process. The technology used in these devices can differ, but, most commonly, they either generate negative ions or utilize some sort of UV lighting. Some of the UV lighting systems will actually produce ozone in the purification process. Devices that produce a detectable amount of ozone can cause the ozone levels to build up in the grow space. This can damage essential oil production or, in extreme cases, become harmful to the gardener. Both the size of the grow rom and the amount of detectable ozone should be carefully considered to ensure the air purification unit will be safe for the particular garden application.
Perhaps the biggest draw to indoor and greenhouse gardening is the heightened level of control over the environment. That being said, a grower who fails to control his or her garden’s climate properly will likely have a continuous battle with pest insects and/or fungi pathogens. Ideally, a garden’s temperature (and temperature variances) would be controlled by an atmospheric controller. When the temperature of an indoor garden or greenhouse is automated, it makes it that much easier to control the relative humidity. However, it must be remembered that, plants are made mostly of water and go through a natural transpiration process as they grow. In other words, the plants themselves naturally increase the humidity level in an enclosed area as they grow. Without proper air movement in the grow space, the humidity levels close to the plants will be much higher than the ambient air. For atmospheric equipment to operate efficiently and effectively, the humidity of the room must be uniform. This is why an ordinary oscillating fan is such a crucial piece of equipment. If the ventilation system or air conditioning unit cannot, on its own, handle the increased humidity produced by the plants, a dehumidifier should be implemented to keep the humidity levels uniform. When humidity levels are kept in check, pathogenic fungi cannot establish. This is why the ultimate prevention and protection against these pathogens is humidity control. Horticulturists who prioritize uniform humidity levels and automatic control over the garden’s temperature and humidity will be better equipped to prevent pathogenic fungi such as powdery mildew and botrytis.
Eric Hopper resides in Michigan’s beautiful Upper Peninsula where he enjoys gardening and pursuing sustainability. He is a Garden & Greenhouse senior editor and can be contacted at [email protected]
Source: Eric Hopper; Garden & Greenhouse, July 2019
Source: HPAC Engineering
Self-contained, free-standing dehumidification units
DehuKing came to be because of demand. Our founding company has been building dehumidification for twenty years but as a part of their chiller operations. In recent years there is demand for independent freestanding dehumidification machines. DehuKing is introducing a full line of dehumidifiers made of stainless steel and upgraded heat exchangers. Even the footprint is smaller than competing machines.
DehuKing coils are inside the cabinet, this protects the coils from damage. DehuKing coils are angled in order to get more coverage as the air is drawn across the coil. The cooled dry air is drawn across the condenser and discharged at close to the environment temperature. Condensed water is collected in a stainless steel pan and directed to remote tanks or plants.
CopelandTM compressors* are used in DehuKing dehumidifiers, we use parts that are readily available locally. We use U.S. made parts when possible in our DehuKing dehumidifiers. GE motors, CopelandTM compressors, Emerson parts, A.O. Smith, Johnson controls, and many other fine American brands. DehuKing only buys an imported part when a U.S. built part is not available. Even then we make every effort to buy from an American company.
*At times it’s not possible to purchase a CopelandTM compressor, if so another brand of comparable value and performance will be substituted.
DehuKing builds dehumidifiers from 272 pints per day to 864 gallons per day. It is important to you that DehuKing does this as economically as possible. Power to condensation is listed on the spec’s page, watts used to a gallon condensed. You will find that we are very competitive in power used. Our parent company CHILLKING has manufactured chillers that use less power for twenty years. DehuKing dehumidifiers are engineered to save energy, outperform the competition, and be superior in construction and quality. Click for more information on operating costs compared to desiccant dehumidifiers and comparison to competitor’s refrigerant dehumidifiers.
In addition to these powerful dehumidifiers DehuKing manufactures chillers. When using a DehuKing Chiller, an air handler that is set up for dehumidification is used. It has a chilled water coil and a hot water coil. These can have a very small footprint based on the type fan used. The DehuKing dehumidifying air handler is installed inside and the DehuKing Chiller is installed outside to make a very solid DehuKing dehumidifier. These perform at the same rate as our DehuKing package units.
Every DehuKing has filtration. In addition DehuKing offers ionizers for the machines, ionized air increases plant growth and makes for stronger crops. Each machine can be ordered with charcoal filtration as well. It is important to us that your DehuKing machine does extras besides dehumidification. We at DehuKing want to increase air quality.
Some have used our machines to collect bathing water and even drinking water. TO BE USED AS DRINKING WATER REQUIRES NUTRIENTS ADDED. Disaster areas without power and working wells have ordered the DehuKing chiller dehumidifier combination and produced water. This is enough water for 86 people if they use 10 gallons per day each, very conservative use would allow for 160 people.
*Based on maximum relative humidity.
Source: The Center for Agriculture, Food and the Environment/UMass Amherst
Click here to learn more about reducing humidity in greenhouses from The Center for Agriculture, Food and the Environment/UMass Amherst.