Thermodyanamic behavior with cost predictions of residential desiccant cooling systems

Abstract

A computer model is developed to simulate the thermodynamic behavior of residential, desiccant space conditioning systems. Finite difference methods are used to model a rotating desiccant wheel and the results used to compile functional relations describing the desiccant-air-moisture behavior. Computer programs are written to simulate cooling cycles and combined with the desiccant wheel functional relations to determine an effective, practical cycle to be used in a cooling season simulation for a 1500 ft^2 house in Houston, Texas. The chosen cycle uses an indirect evaporative cooler, a direct evaporative cooler and one heat exchanger. A code is also developed to simulate flat plate solar collectors and thermal rockbed behavior for regeneration of the desiccant wheel. An hour by hour, five month cooling season simulation is performed using the National Climatic Center weather and solar data tapes for Houston. The simulation results in a cooling season, thermal coefficient of performance (COP) of 1.73. Comparing this system to a low efficiency conventional vapor-compression system, a cost analysis shows that such a system would have a payback of about nine years if used without the solar circuit. If used with a solar circuit that provided significant energy savings, it would probably never pay for itself at current energy costs. The predicted COP at ARI standard conditions is 1.66 for realistic component assumptions. Recommendations are made for improving the COP and further development of desiccant cooling cycles.