Paper Session 3: Presentation 3: System-Level Performance Modeling of a Sub-Wet Bulb Evaporative Chiller Coupled to a Microchannel Polymer Heat Exchanger for Residential Cooling Applications (AT-23-C009)
System-Level Performance Modeling of a Sub-Wet Bulb Evaporative Chiller Coupled to a Microchannel Polymer Heat Exchanger for Residential Cooling Applications (AT-23-C009)
Presenting Author: Emily Fricke, UC Davis, Davis, CA, USA
Author: Vinod Narayanan, Ph.D., UC Davis WCEC, Davis, CA, USA
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 when compared to indirect evaporative coolers. Furthermore, the chilled water can be used as thermal storage for potential peak load reduction. 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 [1], is coupled with that of a counter-flow Microchannel Polymer Heat eXchanger (MPHX), currently being developed by the group [2]. The SWEC is able to achieve sub-wet bulb temperatures via the configuration of four evaporative media sections sandwiched in between four cross-flow air-to-air heat exchangers. Outdoor air enters each cross-flow heat exchanger and is sensibly pre-cooled by outgoing cooler, higher-humidity air flow from the adjacent evaporative medium before passing through evaporative media. An effectiveness- Number of Transfer Units 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 in a typical residential building located in different climate zones in California. Cooling loads for a two-story 2,400 square foot home were simulated using EnergyPlus to consider a scenario where the system was appropriately sized for the cooling loads. The performance of this system is compared against a baseline SEER 14 vapor compression unit with a finned tube evaporator coil in terms of unmet load and hours, electrical energy usage, and COP.
[1] Yang, Y., V. Narayanan, T. Pistochini, and T. Ross. 2021. An Experimentally-Validated Model of a Cross-Flow Sub-Wet Bulb Evaporative Chiller. ASME Journal of Thermal Science and Engineering Applications, 13(2):021006 (12 pages).
[2] Rasouli, E., E. Fricke, and V. Narayanan. 2022. High efficiency 3-D printed microchannel polymer heat exchangers for air conditioning applications. Science and Technology for the Built Environment, 28(3):289-306.
Learning Objectives:
• Describe the advantages and limitations of the sub-wet bulb evaporative water chiller and polymer heat exchanger.
• Explain the system-level impacts of varying flow parameters on the combined performance of the chiller and heat exchanger.