Alternative refrigerants, room air conditioners, modeling, senior design
This paper presents the results of a senior design project that challenged a team of undergraduate students to reduce the environmental impact of a room air conditioner (RAC) by reducing its energy consumption and/or use of high-GWP refrigerants. Over the course of an academic year, the team was able to investigate, design, model, evaluate, and build a prototype improved RAC. The team began by reviewing literature on approaches that have been proposed to meet or exceed existing energy efficiency and refrigerant selection regulations. Based on these findings and the specified needs of the project sponsor, the team evaluated the appropriateness of different concepts for improving the existing R-410A RAC design and decided to pursue modifications to adapt the unit for R-1234yf. The first step in the redesign process was to develop a thermodynamic model of the existing system. Because very little information was known about the performance of the individual components in the existing RAC, some rough performance estimates were obtained through measurements. The model of the existing system was then modified to provide the same cooling capacity as the original unit but using R-1234yf, and a replacement compressor was selected based on the model results. After the replacement compressor and resized capillary tubes were installed in the RAC, the team was asked to test the prototype unit using R-1234ze instead of R-1234yf. Therefore, the model was modified to predict the cooling capacity of the unit using R-1234ze as the working fluid. The unit was tested using an environmental chamber to simulate the outdoor air conditions and a large room as the indoor environment. Although this setup could not ensure steady-state operation, air temperature measurements indicated that the room temperature did not vary more than 1.5°F over 12 minutes of RAC operation. The cooling capacity calculated based on experimental measurements agreed within 3% of the model predictions. While the team was able to modify the RAC to operate with R-1234ze and was able to predict the unit’s performance with reasonable accuracy, the modifications required a significantly larger compressor and capillary tubes. Therefore, the project clearly illustrated that fitting within the space and weight constraints of window units presents a significant challenge to implementing R-1234ze in RACs.