Tuesday, January 31, 2017: 11:15 AM-12:45 PM
Fundamentals and Applications
Chair:
J. Steven Brown, Ph.D., P.E., The Catholic University of America
Technical Committee: 1.1 Thermodynamics and Psychrometrics
Sponsor: Journal Policy Committee with Co-sponsors TC 1.3, TC 3.1, and TC 8.4
The seminar addresses low-GWP alternative refrigerants and their applications. As regulations and legislation become increasingly more widespread and restrictive, the HVAC&R industry will need to identify viable alternatives for existing refrigerant solutions. This environmentally-driven change is different than past ones since additional constraints are being placed on refrigerants in essence reducing the number of viable single-component solutions. The seminar highlights five papers appearing in ASHRAE’s Science and Technology for the Built Environment November 2016 edition (one dedicated specifically to low-GWP refrigerants.) The presentations focus on low-GWP halocarbon refrigerants containing unsaturated carbon bonds during boiling heat transfer and in system applications.
1 Insights into the Next Generation HVAC&R Refrigerant Future
Because of the relatively high GWPs of HFCs, policy and regulatory actions to reduce, restrict, and eliminate their use are increasing in number. These regulatory actions are leading to the development of unsaturated chlorinated and fluorinated hydrocarbons with lower GWPs. Tradeoffs between GWP, flammability, and specific capacity will need to be made possibly resulting in the need for changes to equipment designs. Some lower GWP refrigerants are already being introduced in many market segments. This presentation provides an overview of these refrigerants and presents the state of understanding and development of these alternatives by their environmental, safety, and design tradeoffs.
2 Model Validations for Low-GWP Refrigerants in Mini-Split Air-Conditioning Units
To identify low GWP refrigerants to replace R-22 and R-410A, extensive experimental evaluations were conducted for multiple candidates at standard test conditions and at high-ambient conditions. R-22 was compared to R-290, DR-3, ARM-20B, N-20B and R-444B in a mini-split air conditioning unit originally designed for R-22; R-410A was compared to R-32, DR-55, ARM-71A, and R-447A in a mini-split unit designed for R-410A. In addition, the experimental data was used to calibrate a physics-based equipment model, i.e. ORNL Heat Pump Design Model (HPDM).
3 Experimental Evaluation and Field Trial of Low GWP R404A Replacements for Commercial Refrigeration
Presented are two R404A replacements: R448A (non-flammable; GWP = 1273) and R455A (mildly flammable; GWP = 146). A commercially available R404A self-contained freezer showed that the compressor run-times of R448A and R455A are similar to R404A due to similar capacity. The 24 hour energy consumption is 9% lower for R448A and 6% lower for R455A compared to R404A. Results for R448A in a commercially available walk-in freezer/cooler matched the capacity of R404A with 4% to 8% higher efficiency. Finally, results of an actual supermarket refrigeration system conversion from R404A to R448A showed energy savings from about 9% to 20%.
4 Horizontal Convective Boiling of R448A, R449A and R452B within a Micro-Fin Tube
This paper presents local convective boiling measurements in a micro-fin tube for R448A, R449A, and R452B . An existing correlation was modified to predict multi-component mixtures, which predicted 98 % of the measurements to within ± 20 %. The results showed that refrigerant R452B exhibited the highest heat transfer among the three. For an example case, the heat transfer coefficients for R448A and R449A were roughly between 26% and 48% less than that of R404A; whereas, the R452B heat transfer coefficient was approximately 13% larger than that of R404A.