User Guide for Desiccant Dehumidification Technology

Executive Summary

Manufacturing industries have used desiccants in various applications for over 50 years, but have only recently begun to apply desiccant dehumidification systems (DDSs) to Heating, Ventilation, and Air-Conditioning (HVAC) applications. Depending on climate and facility loading, a high percentage of a building’s cooling load can be latent (moisture) load. Conventional cooling equipment operates at low temperatures to cool the air to its dew point temperature, where dehumidification via condensation on the coils begins.

It may then be necessary to reheat the air to a comfortable temperature before it enters the occupied space. DDSs, by contrast, remove water from the air by using a desiccant, or chemical drying agent. DDSs offer several benefits when used in conjunction with air-conditioning systems.

Removing moisture from the air by desiccation decreases the amount of vaporcompression energy needed to dehumidify the air being supplied to the user, and increases the comfort level in the conditioned space. Desiccant systems also decrease moisture accumulation in ducts and around coils, inhibiting the growth of mold and mildew.

While research in desiccant dehumidification technology development has been conducted for several years, commercial applications of desiccant dehumidification technology have been limited in the past by material and manufacturing considerations. Current desiccant dehumidification systems range in capacity to 30,000 cubic feet per minute (cfm) and are near the commercialization stage. Since these systems are heat driven (not electrically driven), conversion to a desiccant system can reduce
site peak electrical demand and levelize utility loads, allowing for more efficient power plant operation. Energy cost savings result from reduced chiller loads, reduced electricity peak demand, and elimination of air reheating requirements.

Desiccant dehumidification systems can also reduce or eliminate the use of harmful CFCs in the HVAC system by using natural gas or liquid propane gas (LPG) as the primary fuel for dehumidification.

“Conventional’’ Air-Conditioning/Ventilation Process

Conventional air-conditioning systems are typically controlled by a thermostat (or similar type receiver/controller combination). They operate in a manner that keeps the space dry bulb temperature from exceeding the thermostat setpoint.

To maintain that setpoint, conditioned air is typically introduced into the space approximately 20 °F* lower than the setpoint, so that the conditioned air can absorb the so-called “sensible” heat entering the space. Having absorbed this heat, air from the space is drawn back to the air-handling unit, where its temperature is again decreased before being returned to the space.