RP-1339 -- Selection Of Desiccant Equipment At Altitude

ASHRAE Standard 139 provides parameters which are used in the desiccant industry to calculate the performance of a desiccant dehumidifier. These parameters are the moisture removal capacity (MRC), regeneration specific heat input (RSHI), process outlet temperature, and pressure drop through the wheel. These performance parameters can be obtained from any manufacturer by means of performance curves or selection software. However, they are generally rated at sea level conditions.

Although some manufacturers provide a means for estimating the performance at altitude, there is no set methodology that is accepted by all. Therefore, the scope of this project involved examining how the performance parameters are affected by altitude and develop a general methodology that can be applied to any desiccant wheel to estimate performance at altitude. The research involved taking performance data at Mississippi State University (MSU) and the National Renewable Energy Laboratory (NREL) from a test cassette containing a 300 mm diameter and 100 mm depth solid desiccant wheel made of silica gel set for a geometric configuration of 50/50 split and rotation at 14 rph using set design inlet conditions.

Based on the analysis of result tests, it was found that by keeping the mass flow rate, inlet temperature, and inlet humidity ratio constant between sea level and altitude, the performance of a solid desiccant dehumidifier at altitudes up to 5000 ft (24.9 Hg or 12.2 psi atmospheric pressure) can be approximated to the sea level performance. However, the pressure drop through the wheel, which was the parameter most affected by altitude, varied proportional to the ratio of the atmospheric pressures between sea level and altitude. The results were adapted into a proposed methodology that can be used in industry practices to estimate desiccant dehumidifier performance at altitude using manufacturers performance data at sea level.



Product Code(s): D-RP-1339