Long Beach Meeting, January 2017
Seminar 50: High Efficiency Commercial Refrigeration Systems with Natural Refrigerants
Chair: Georgi Kazachki, Ph.D., Fellow ASHRAE, Dayton Phoenix Group, Inc., Dayton, OH
Commercial refrigeration systems have been some of the largest contributors to refrigerant leaks, second to automotive air-conditioning. For this reason, they became the most intensely studied application for natural refrigerants, such as ammonia and carbon dioxide. These systems went through a substantial evolution in the last 10-15 years to accommodate ammonia and CO2 specific properties (safety class B2 for ammonia and low critical temperature and high pressures in certain conditions for CO2) and, at the same time, to be cost and efficiency competitive with the HFC systems. The seminar demonstrates the outcome of this evolution through the featured presentations.
1. Doing It All Efficiently with CO2 Refrigeration Anywhere in the World
Klaas Visser, P.E., Affiliate, KAV Consultants Pty Ltd, Kangaroo Flat, Australia
This presentation examines the benefits of Evaporative Condensers/Gas Coolers (EC/GCs) where the cooling medium temperature is the Ambient Wet Bulb Temperature (AWBT) and not the ambient dry bulb temperature as is the case with air cooled gas coolers. A 1% incidence AWBT of 28°C is not exceeded in 98% of the world’s climates. At a AWBT of 28°C it is relatively easy to achieve a gas cooler CO2 exit temperature 31°C and even 30°C at part load. This means that efficient CO2 refrigeration may be operated all over the world with the use of EC/GCs.
2. Design and Performance Validation of Ultralow Charge Ammonia Cascade System for Retail Food Environment
Masood Ali, Kysor/Warren, Columbus, GA
Natural refrigeration technology in supermarkets is driven by growing global concerns around energy and environment. Energy efficiency, safety and reliability are key characteristics of supermarket system design. A field test is carried out on a Supermarket with ammonia system as top cycle catering to MT and LT refrigeration loads. The entire system is designed with state-of-the-art energy efficient features and ultra-low ammonia charge @ 0.75 Lbs / TR. A brief overview of design considerations and test results are presented. Superior efficiency of ammonia is demonstrated in a side by side energy study with HFC that is validated by third party.
3. Opportunities for Utilizing Two-Phase Ejectors to Increase Efficiency of Commercial Refrigeration Systems Using Natural Refrigerants
Stefan Elbel, Ph.D., Member, Creative Thermal Solutions and University of Illinois at Urbana-Champaign, Urbana, IL
The low GWP of natural refrigerants makes them great candidates for commercial refrigeration. An important characteristic of transcritical CO2 cycles are the substantial throttling losses that negatively impact energy efficiency at high ambient temperatures. This presentation introduces numerous ways of improving COP at demanding outdoor conditions, and the emphasis will be on utilizing two-phase ejectors. A variety of cycle options exist that allow integration of ejectors, including utilization of the recovered energy to unload the compressor, to provide cooling at different temperature levels and to improve efficiency by using the ejector to drive refrigerant overfeed in liquid recirculation cycles.
4. Packaged Ammonia/CO2 Systems for Refrigeration
Scott Mitchell, Associate Member, Southern California Edison, Irwindale, CA
This presentation provides the final results from field testing of a packaged ammonia/carbon dioxide system installed in Irvine, CA. The unit was one of the first of its kind installed in North America and provides a glimpse at how natural refrigerants can be applied to systems where they previously were not used. The project was featured in a Feb 2016 ASHRAE Journal article.
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