Advancing evaporative rooftop packaged air conditioning: A new design and performance model development

This paper presents a technological advancement in evaporative cooling rooftop air conditioning comprising a uniquely designed evaporative water cooler that includes a multi-stage hydronic unit and high thermal performance. In the new design, the water cooler is a counterflow air-to-air heat exchanger in which ambient air is pre-cooled in a dry path on one side of a heat transfer surface by water flowing on the other side of the surface. The water is then cooled by evaporation in a wet path by a secondary air stream flowing through the heat exchanger on the same side as the water but in the opposite direction. Outside air is cooled in the dry passages and then enters the wet passages at a lower wet bulb temperature than that of the outdoor air, potentially producing a lower sump water temperature compared to those produced by traditional evaporative condensers. We also developed a computer model to simulate the performance of the rooftop packaged unit. The model is based upon the Simulation Problem Analysis and Research Kernel (SPARK) simulation program and can be used to optimize component sizes and to perform an economic analysis. In addition, the model can be used for fault detection and diagnosis during operation. The simulation model was calibrated with experimental data obtained from the study and was then used for optimal sizing and performance tracking.

► Designed a hydronic rooftop packaged unit with significant efficiency improvement.
► The key advancement of the rooftop unit is the CEWC unit.
► The new rooftop unit can achieve a 25% reduction in overall annual energy use.
► The unit can achieve a 60% reduction in annual cooling energy use in dry climates.
► The simulation model could reasonably simulate the CEWC and the entire rooftop unit.