CH-24-C128 - Desiccant Enhanced Indirect Evaporative Cooling: Laboratory Testing

Indirect evaporative coolers have been shown to provide energy efficient cooling while maintaining a comfortable level of humidity. However, high capacity and high efficiency of indirect evaporative coolers has been limited to hot and dry climates. A new cooling technology has been invented called Desiccant-Enhanced Evaporative Cooling to provide efficient cooling in all climate zones. This technology uses liquid desiccant tanks that store energy to enable load shifting. The Western Cooling Efficiency Center HVAC lab at UC Davis tested a prototype in environmental chambers. The chambers were operated to mimic four weather types: hot and humid, hot and dry, mild and humid, and very hot and dry. The prototype was operated under a range of ventilation settings with outdoor air fractions of 35%, 42%, and 100%. The prototype Desiccant-Enhanced Evaporative Cooling system efficiency was limited by desiccant regeneration using electric resistance heating, as well as oversized fan and pump components. To better characterize the expected performance of the full-size system, the measured efficiency was adjusted to account for use of heat pump desiccant regeneration and appropriate fan and pump sizing. This technology has the potential for high efficiency operation with good cooling capacity even in hot and humid conditions where existing indirect evaporative cooling systems do not work well. When regenerating desiccant at the same time as cooling for steady state operation, the COP ranged from 3.2 in mild-humid conditions, to 4.8 in hot and humid conditions, to 23.4 in very hot and dry conditions. When load shifting by using desiccant from the tank, the adjusted COP ranged from 9.0 in mild-humid conditions, to 23.5 in hot and humid conditions, to 23.4 in very hot and dry conditions. In load shifting operation, using desiccant from the storage tank, the technology is expected to achieve very large efficiency gains compared to even the best vapor compression equipment. For Dedicated Outdoor Air System (DOAS) operation the design shows great promise for very high efficiency and good cooling capacity in a wide range of climates. The independent control of sensible cooling and latent cooling has the potential to eliminate overcooling for dehumidification and the associated reheat energy consumption with the vapor compression DOAS systems.