Contractors Weigh In On New Liquid Desiccant System
But there’s a new liquid desiccant technology available, and it’s being marketed for commercial applications. The manufacturer says it can work just about anywhere, from fast-food restaurants to commercial office buildings. The company also states that the technology increases cooling capacity, reduces energy costs, and eliminates the need for an external heat source through a heat transfer process that provides all the energy needed for the collection and regeneration processes.
Contractors are excited about the technology, saying it’s cost effective, and even more importantly, that it works well to keep occupants comfortable.
Manufacturer Touts Dry ConditioningThe manufacturer introducing this new liquid desiccant system is DryKor, which hails from Israel and whose U.S. offices are based out of Fayetteville, GA. The company says that its system, which uses a liquid lithium chloride solution, provides dehumidification and cooling — or dry conditioning.
When used in conjunction with rooftop packaged conventional air conditioners or in stand-alone units, DryKor says its dry conditioning technology reduces both temperature and humidity. Therefore, it can be used as a substitute for air conditioning either in warm or cool, humid climates, where air conditioning is applied for dehumidification purposes only. Further, the company asserts, this technology increases cooling capacity, which allows for the downsizing of traditional hvac equipment to save on first costs.
Mike Ireland, owner and president of Efficient Systems, Beaumont, TX, is a definite supporter of the technology. He started installing the equipment at fast-food restaurants in January 2000 and was so pleased with the results, he stopped using active solid desiccant systems altogether.
“The liquid desiccant machine costs less, and it takes care of the process side and the regeneration side all within itself. It does not have to have another source of heat, which can be expensive. It does not have to have wasted heat given off. In a restaurant, you can’t use an enthalpy wheel, because there is no conditioned air by which to regenerate the wheel; it’s all being exhausted out the exhaust hoods,” says Ireland.
He also notes that with active wheels, all the Btu of latent heat that they absorb are given off as sensible heat. “If you have plenty of capacity to handle that extra heat on a really hot drybulb day, then you’re OK using the desiccant wheel. But then what happens on a dewpoint-condition day — 84Â° or 85Â°F and 150 grains of moisture? Your air conditioning equipment is so oversized, there’s no way you can pull the humidity out of the air because you don’t have enough run time, and at those conditions, your latent load tends to be just as much as your sensible load.”
With the liquid desiccant technology, the air is run through the process side of the lithium chloride, which is chilled as it absorbs moisture. The heat of vaporization gives off heat, and the chilled lithium chloride absorbs that heat. Therefore, what comes out of the unit and goes into the occupied space is not only drier air, it’s cooler air. The amount of cooling depends on how much moisture is coming into the system.
System Adjusts ItselfIreland says the equipment really shines on a typical Dallas drybulb day, which is about 100Â° and 90 grains of moisture. “In these conditions, you only have to remove about 25 grains of moisture, which, on this liquid desiccant unit, is very easy.
“But since there’s not a whole lot of moisture to remove, the chilled lithium does not have as much heat to pick up, so it ends up chilling the air even more. So on a really hot drybulb day, the unit actually becomes more of a sensible unit than it even does a latent unit. In other words, that’s what you need at that time.”
But say that all of a sudden a rainstorm blows in, and the temperature lowers to 84Â° and the grains of moisture now are at 150. Then the desiccant unit turns into a high-efficiency latent machine and doesn’t cool as much. “That’s one of the nicest things about this equipment,” says Ireland. “It can adjust its sensible to total ratio to anywhere from 0.15, which is as low as I’ve seen it on a muggy day, to 0.5 on a hot, drier day. The lithium chloride adjusts itself based on the moisture loads.”
Jim Spears, owner of Peninsular Mechanical Contractors, Clear-water, FL, is another contractor who likes what he sees in the liquid desiccant system. He notes that there is a critical problem with humidity in buildings in the geographical area that extends from the North Carolina coast southward and all the way over to Brownsville, TX.
In buildings that have high outside air requirements, such as restaurants, all the outside air is brought in through the air conditioner, dumped into the space, and ultimately ends up being exhausted through the kitchen hood.
“That’s great at noon or 1 p.m., when the internal load is quite high and the air conditioner runs,” says Spears. “But the problem we’ve found in this geographical area is during low-load periods of time, like at 8 or 9 a.m. when the temperature is 75Â° to 80Â° with 100% relative humidity.
“If you take that air and dump it into the space, you create a tremendous internal moisture load that the air conditioners are incapable of dealing with until later in the day when the compressors are running continuously.”
Spears likes that the DryKor technology allows the outside air to be treated during those “off” times of the day to dry the air out before it gets into the building. In addition, the equipment also provides cooling during those times of day so that the rooftop air conditioners will only need to run as the internal loads build up during the day.
Both Spears and Ireland say the equipment would work in a variety of commercial applications. “I would consider it for any application that has outside air requirements that occur during off-peak cooling hours,” says Spears. “Another advantage is that these devices are totally electric, so no new energy source is required.”
Ireland notes that installation and maintenance are a breeze as well. “I’m sorry to be so rosy about these systems,” he says. “But these systems have basically eliminated all the problems I had with active solid desiccant systems. Those problems being not having enough sensible capacity on a really hot day and then having to have another source of heat to regenerate the wheel. I just can’t think of any disadvantages.”
Sidebar: How It All WorksThere are three parts to the DryKor liquid desiccant system. First, there is the collection operation. Here, a cool, concentrated salt (lithium chloride) solution is continually added to the top of the media (a honeycomb cellulose material), which forms a liquid film that flows down (or floods) the surface of the media.
As the stream of air flowing in from the outside, called process air, comes in contact with the cool concentrated solution, the air’s water molecules react with the lithium chloride solution and the air is cooled. The salt solution absorbs or collects the humidity and generates heat.
As a result, the air flowing out is drier and cooler than the air flowing in. This dry, cool air is then pumped into the air conditioning system for further cooling, if needed, before being delivered into the indoor space. The lithium chloride solution, as a result of the process, becomes warm and diluted.
Second, there is the heat exchange operation. Here, a portion of the solution is pumped through a filter and a heat exchanger. By using a heat pump, the heat created during the collection operation is transferred to the regeneration operation. The heat is necessary for the regeneration of the lithium chloride solution.
The third and final operation concerns regeneration. The regeneration operation is similar to the collection operation, except that the lithium chloride solution is now heated to remove the moisture previously collected. The heated diluted solution is continually added to the top of the media. As in the collection operation, the solution forms a liquid film that flows down or floods the surface of the media.
As a stream of air, called the scavenger airstream, passes through the media, the moisture and heat in the solution is released into the airstream and carried outside. As a result of the regeneration operation, the lithium chloride solution is restored to its original strength. It is then pumped back to the collection side and added to the top of the media. During the regeneration process, the solution passes through a washable filter, which removes the particles from the solution. Results of a study done by an independent industrial testing laboratory in Israel show that this technology removes 77% of airborne particles larger than 5 microns. An added benefit of this air-washing process is that the air supplied into the indoor environment has a natural, fresh quality free of smoke and odors.
Publication date: 04/16/2001