Bry-Air delivers dessicant dehumidifier solutions for clients around the world, including in crucial applications for hospitals and water- and waste water treatment facilities.
Desiccant Dehumidification in Hospitals
In many health care facilities, there is a necessity to assure good indoor air quality, thus large quantities of outside air must be brought into the building through the ventilation system. This outside air can account for over 90% of the moisture load typically seen in many health care buildings. It is important to remember that bacteria travels on water vapor in the air so in order to avoid microbial growth and surgeon/patient discomfort, this moisture must be removed before the fresh air enters the building. This is particularly true in warm, humid climates.
Conventional air conditioning systems can create high humidity conditions. Cooling coils dehumidify by cooling air which is blown or drawn across the coil surface. The moisture condenses on the coil and drips down into the drain pan. However, the air leaving this coil is essentially saturated and can be as high as 95% relative humidity. In normal air conditioning applications with room temperatures of 72 to 75 °F, there is no particular difficulty associated with this cooling-based dehumidification system. However, when room temperatures must be held at 65°F and lower, conventional cooling systems cannot comply with humidity specifications of building codes without very low temperature, inefficient chilled water systems. In many critical care facilities, humidity can cause problems and expose the institution to unnecessary risk.
Surgical Staff Discomfort
The threat of HIV has led surgical staffs to heavy gowning that was not common in the past. Thick layers of protective garments have forced surgeons and their staffs to demand room temperatures as low as 61 to 65°F, which is turn makes humidity control difficult to achieve with conventional air conditioning systems. When the air is cooled, the humidity can rise to over 75% RH. These cool, damp conditions can cause the surgical staff to perspire and become very uncomfortable.
Hazardous Microbiological Growth
Many bacteria flourish in humid air. For instance, the bacteria responsible for Legionnaire’s (Legionella Pneumophila) survive best at relative humidity levels of 65%. But at relative humidity levels of 35% and lower the bacterium dies very quickly. Many viruses also thrive in high humidity conditions. For example, the Polio virus not only survives, but can actually multiply when the relative humidity is above 80%. Fungi and dust mites can also thrive in humid building materials, which can lead musty odors and respiratory problems associated with sick building syndrome. The high humidity levels found in ductwork downstream of cooling coils is an ideal environment for these types of organisms.
Desiccant dehumidifiers offer a proven alternative for humidity control at low temperatures. Unlike conventional cooling- based equipment, the moisture removal capacity of desiccant systems actually improves at lower air temperatures. Through the use of a Bry-Air desiccant dehumidifier, humid outside air is passed through a desiccant bed, which removes moisture by attracting the water molecules in a vapor state. The dry fresh air is then cooled by the existing HVAC system. Since this make- up air is dry, no moisture condenses to allow contamination to grow in drain pans. And. with low relative humidity downstream of the coil, moisture is not absorbed into duct linings and building materials where it could support microbial growth. Best of all, the air can be supplied to the room at 45% RH no matter how cool the room must be kept.
Benefits of Desiccant Dehumidification
- Most local codes require stringent humidity control in operating rooms a very difficult problem at room temperatures of 61-68°F. Bry-Air dehumidifiers allow you to meet all regulatory criteria for operating room humidity without disturbing the HVAC system in the balance of the building. In addition, because Bry-Air dehumidifiers eliminate high RH in the duct work, the HVAC system will comply with guidelines in ASHRAE Standard 62, which calls for keeping humidity in ductwork below 70%RH in order to avoid the risk of microbial contamination.
- When operating room humidity is controlled by a Bry-Air desiccant dehumidifier, there is no need to run the main chillers at a low chilled water temperature. With a higher temperature, your central system chillers run more efficiently, thus providing additional sensible cooling.
- With a Bry-Air dehumidifier, the surgeon can personally set the temperature and humidity that is most appropriate for each procedure. Those conditions will be maintained regardless of the time of year or capacity of the existing mechanical system in the rest of the building. The relative humidity can be easily controlled to 45% or lower, even at temperatures below 64°F.
Finally, there is some concern as to whether a liquid desiccant, such as Lithium Chloride, or a solid granular system, such as Silica Gel, is the better system to use. According to the ASHRAE Handbook on Equipment 1972 and 1988:
“Tests sponsored by ASHRAE at the University of Toledo on liquid sorption systems and at Pennsylvania State University on solid desiccants indicate that both types of systems have a bacteria removal effect of the same magnitude on air passing through the system. This significant lowering of bacteria levels combined with simultaneous dehumidification can be of paramount importance when air conditioning systems are utilized in hospitals, laboratories, food and pharmaceutical manufacturing environments.”
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Dehumidification in Water & Waste Water Facilities
When moisture in the air condenses onto cold pipes, valves, and pumps, a number of destructive effects can occur. High humidity resulting from a damp environment can cause corrosion of metal, deterioration of paint, and failure of electrical components. Sanitation also becomes a concern when a moist location acts as a breeding ground for the development of bacteria, fungus, and molds.
Typically water and waste water treatment facilities are designed to avoid contamination and corrosion in the pipes. Any contamination of water which could be consumed by humans or animals is carefully avoided. However, the condition of the outside of the pipes may be very different. Condensation will occur any time the pipe or valve surface temperature is below the dewpoint of the surrounding air. This condensation and subsequent corrosion problem generally takes place during the spring, summer, and fall months. In more humid climates the problem may be year-round.
In the past, one solution to this problem was to use a refrigeration type dehumidiﬁer to remove moisture from the air. This method, at ﬁrst, appears to be attractive because of the low cost and easy availability of residential and commercial grade refrigeration systems. In the summer months, this type of system is somewhat effective because the air temperature and dewpoint are high.
However, as these units operate by cooling the air to condense its moisture, their drying capacity is limited when the air is already cool. Many residential and commercial refrigeration units cannot adjust their cooling capacity. Thus, they over-cool the air, eventually freezing the moisture that condenses on the cooling coils. Once this occurs, all beneﬁcial dehumidiﬁcation stops and the coils must be defrosted.
This is the reason that refrigeration units are effective in the hot summer months but not in the cooler fall and spring months.
A Bry-Air desiccant dehumidiﬁer can provide year-round consistent humidity levels regardless of the season. There are no coils to freeze up and a humidistat guarantees warm dry air, on demand, regardless of ambient conditions.
Sizing the dehumidiﬁer
As a general rule, the CFM of dehumidiﬁed air required can be estimated by using the following formula:
CUBIC FEET OF CONDITIONED AREA DIVIDED BY 25 = DEHUMIDIFIED CFM REQUIRED
For example: Pipe tunnel – total volume is 100,000 cubic feet, including pipes, etc. – then 100,000 cubic feet divided by 25 equals 4,000 CFM of dehumidiﬁed air required.
Additional expenses for painting, curtailing rust and other problems brought on by high humidity can cost a typical water treatment facility from $10,000 to $50,000 per year.
Problems such as; sweating pipes, rotting of insulation or pipe coverings, pitting of electrical controls, added electrical motor maintenance, drips and puddles are but a few that can occur. In most cases, the cost of a Bry-Air dehumidiﬁer installation will pay for itself in two years or less by reducing these problems and the associated maintenance that goes along with them. As an added savings, gas can be used for reactivation and a heat recovery coil can also be included. A heat recovery coil can reclaim up to 60% of the reactivation exhaust heat.
Some sewage plants have gas available as a by-product.
A Bry-Air dehumidiﬁer, located in the pipe gallery or other area of high humidity, can maintain a range of 20% – 45% RH year round which completely eliminates condensation and sweating. This is accomplished through re-circulation and there is no need for make-up air. In addition the use of an after-cooling coil can be omitted in most installations since the warm, dry air from the dehumidiﬁer helps to heat the tunnels and pumping areas in the winter. Warm dry air is usually not objectionable in summer, since few people work in these areas regularly. This source of heat is an added advantage of the Bry-Air desiccant dehumidiﬁer, because the relative humidity is lowered and the capability of the air to carry away moisture is increased.
In the past 40 years Bry-Air has sold many desiccant dehumidiﬁers to water and waste water treatment facilities all over the world and in every state of the U.S. Engineers frequently, look to Bry-Air to provide them with years of trouble free, efﬁcient performance.
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