The role dehumidifiers play in business and industry today is changing. Once limited to specialized applications where process requirements dictate removal of moisture from ambient air, dehumidifiers are finding their way into a wide range of commercial and institutional HVAC applications. In addition to the historically identified benefits of reducing corrosion of equipment and materials, preventing condensation on cold surfaces, and controlling the growth of microscopic organisms, construction engineers, architects, and maintenance managers are finding that systems are right for their needs. use in a wide range of applications. .

dehumidification applications

One of the most common commercial and institutional applications for dehumidifiers is in computer rooms and areas with high-tech electronic equipment, which are sensitive to atmospheric humidity. In the heavily air-conditioned atmosphere where much of the equipment operates, relative humidity readings frequently exceed 75 percent. At these levels, atmospheric moisture promotes corrosion of metal contacts and components within the equipment, causing deterioration of system performance.

High speed paper feed printers absorb moisture, which causes frequent paper jams. Dehumidifying systems help provide precise humidity control, keeping the moisture content of the air low enough to avoid these problems, but high enough that static electricity does not become a problem.

Another institutional application where dehumidifiers have been used extensively is in health care facilities, particularly those with operating rooms and intensive care units. They have strict requirements governing the quality of the applied air. The supplied air is normally 100 percent outside air and must be controlled within a fairly narrow temperature and humidity band. In many cases, dehumidification systems are necessary to meet those requirements.

Another commercial application that has made extensive use of dehumidification systems is the grocery market industry. Grocery stores present unique humidity control problems to the HVAC systems engineer. High humidity levels cause frost to form on the cooling coils of frozen food cases, as well as on products on display. Frost on cooling coils increases cooling energy requirements. Frost on product decreases customer satisfaction and increases labor requirements. Dehumidification systems, by reducing relative humidity from the 60 percent to 65 percent range to the 50 percent range or less, greatly reduce the rate at which frost forms.

However, the use of dehumidification systems in commercial and institutional facilities is not limited to these specialized applications. The relative humidity of the air supplied to an area is an important component of the overall indoor air quality of the space. Building managers are finding that dehumidification systems can help many other facilities improve indoor air quality while reducing energy requirements.

System Advances

There are two main ways to remove moisture from a building’s air supply: cool the air below its dew point to condense water vapor, or pass the air over a material that readily absorbs water.

Systems that cool air below its dew point use mechanical refrigeration. Air passes over a cooling coil, causing some of the moisture in the air to condense on the surface of the coils and fall out of the airflow.

The relative humidity of the air leaving the coil is nearly 100 percent, so before it can be drawn into the conditioned space, it must be mixed with warmer air or reheated. Varying the temperature of the cooling coils controls the amount of moisture left in the supply air and the resulting humidity.

Although mechanical refrigeration dehumidification systems were popular in the past, their high energy costs forced building operators to look for other options. The option that has been most widely accepted for use in commercial, institutional and industrial installations is the desiccant system.

Desiccant dehumidification systems consist of a slowly rotating disk, drum, or wheel that is covered or filled with an absorbent. Air entering the facility passes through a portion of the wheel, where the desiccant absorbs moisture from the air.
As the desiccant frame slowly rotates, it passes through a second stream of hot air. The moist air is then exhausted from the facility. By continuously rotating, the desiccant wheel always has a newly regenerated area available for dehumidification.
The first generation systems used lithium chloride gas as a desiccant. A problem with these systems was when the reactivation heater was not working properly or the wheel was not turning. The lithium chloride continued to absorb water from the air stream, but without reactivation, the wheel became saturated with moisture. Once saturated, the lithium chloride separated from the wheel and was carried away by the airflow.

Costing several thousand dollars to replace the lithium chloride, maintenance managers soon modified the systems to include automatic alarms in the event the reactivation cycle was interrupted. New generation systems mainly use silica gel as desiccant. Silica gel does not lose its adherence to the spinning wheel when saturated.

By following a scheduled and preventative maintenance program that includes inspection of key system components, building maintenance managers can help ensure they get the most benefit from dehumidification system operation.

Desiccant System Maintenance

The most important maintenance activity for desiccant dehumidification systems is periodic inspection. Unfortunately for many system operators, the first indication of a system problem is rising humidity levels in the occupied space. This is particularly important for lithium chloride based systems as the cost to replace the desiccant material can be as high as $9,000-11,000. Consider these maintenance points:

• Air filters. To protect the desiccant from dirt build-up from the airflow through the wheel, air filters are installed on the intake side. To avoid reduced airflow due to clogged filters, inspect filters periodically. Inspection frequency depends on the level of materials present in the air.
• Transmission belts. Due to the low rotational speed of desiccant wheels, one or more drive belts transfer power from the motor to the wheel. Loose, damaged, or misaligned belts can slow or stop the wheel operation, reducing the effectiveness of the dehumidification system. In the case of lithium chloride desiccant, improperly rotating wheels can cause loss of desiccant. Inspect the entire drive system weekly, checking belts for signs of misalignment, wear, and slippage.
• Regenerator. It is one of the most critical components in the operation of a desiccant-based dehumidification system. Without the regenerator, there would be no way to remove moisture from the desiccant and the system would no longer be able to remove moisture from the building. Inspect regenerator operation weekly. Security controls and system malfunction alarms should be manually tested at least once a month.
• Seals. The absorption and regeneration parts of the wheel are separated by a system of partitions and seals. Over time, the seals can wear out, allowing air to flow between the two sections of the wheel. This mixing of airflows reduces the overall efficiency of the wheel. Under normal operating conditions, the seals can be expected to last approximately five years. However, they should be thoroughly inspected at least once a month for wear or damage.
• Contamination due to dirt in the drum. The effectiveness of the desiccant is highly dependent on the amount of surface area that comes into contact with the air stream. Accumulated dirt in the desiccant can reduce the effective surface area available for moisture absorption, reducing the overall effectiveness of the dehumidification system.
• Although the air filter system is designed to remove debris from the airflow, it is not 100 percent effective. Also, the process of water absorption and desorption by regeneration deposits a significant amount of dirt on the surface of the desiccant. The surface of the desiccant should be closely inspected at least once a month for dirt buildup. If a significant amount of dirt is found, the surface should be cleaned in accordance with the manufacturer’s recommendations.
• Desiccant. Although loss of desiccant is a bigger problem in lithium chloride based systems than those using silica gel, the desiccant can be damaged. Inspect the desiccant at least once a month for signs of loss or damage. If the system is shut down for maintenance, inspect the desiccant before turning it back on.
• Alarm and control system. Most desiccant systems are equipped with alarms that monitor the operation of key elements of the system, such as wheel rotation and regenerator. If the system uses a lithium chloride-based desiccant, those controls and alarms should be tested at least once a month. Systems using a silica gel desiccant do not require testing as frequently as the desiccant is not easily damaged by moisture saturations. However, the controls and alarms of these systems should also be tested periodically.