C009 -- System-Level Performance Modeling of a Sub-Wet Bulb Evaporative Chiller Coupled to a Microchannel Polymer Heat Exchanger for Residential Cooling Applications

Evaporative cooling technologies have the potential to dramatically reduce electrical energy consumption in hot and dry climates. A Sub-Wet bulb Evaporative Chiller (SWEC) can chill water to temperatures lower than wet bulb of outdoor air, making it desirable for cooling applications, similar to M-cycle indirect evaporative air coolers. However, the exiting water temperature from the SWEC is still significantly higher than that produced by a vapor compression unit. Hence, in order to effectively utilize this technology, it needs to be coupled with a high-effectiveness water-to-air heat exchanger. In this paper, a validated model of a SWEC, developed in prior work, is coupled with that of a counter-flow Microchannel Polymer Heat eXchanger (MPHX), currently being developed by the group. The SWEC is able to achieve sub-wet bulb temperatures via the configuration of four evaporative media sections sandwiched between four cross-flow air-to-air heat exchangers. An effectiveness-Number of Transfer Units (NTU) approach is used to model the SWEC. A sectional model for the MPHX, which includes potential for condensation in the air stream along the heat exchanger length as it is cooled by the chilled water, is developed. The two component-level models are coupled together to determine the system-level performance. The tradeoff between cooling capacity, system COP, and MPHX exit air temperature is discussed for a typical outdoor summer condition in California climate zone 12.