4210 — Thermodynamic Assessment of Desiccant Systems with Targeted and Relaxed Humidity Control Schemes

The performance of desiccant systems for applications requiring stringent control of humidity under varying load conditions is evaluated in this paper. Feasibility of different alternatives is discussed, and the performance is examined from both first- and second-law perspectives. The analyses are performed using a program for a commercially available gas-fired desiccant system. The program predicts the properties of the supply air once the operating conditions are specified. Use of a single system with a proposed modification vs. dual-unit arrangement is the basis for categorization of the alternatives considered in this study.

Two scenarios are addressed with respect to the flexibility in humidity control. The first, labeled “targeted” control, pertains to maintaining the humidity level of supply air at a set point within a reasonable control band. The second approach is more flexible in that the controlled variable can assume any value below the set point; therefore, this approach is referred to as a “relaxed” scheme. It is also demonstrated that opportunity exists for downsizing the post cooling unit (designated for sensible load) by incorporating an evaporative cooling process.