Ejector Refrigeration Cycles: Classification of Thermodynamic Cycles with Ejectors

Introduction

It is estimated by US Department of Energy that 40% of all electricity usage in commercial buildings is related to HVAC systems. This 40% provides an attractive target for reducing future energy needs. Improved methods of heating, refrigeration, and air-conditioning that can be implemented cost effectively could provide a significant breakthrough in green energy efficiency. This describes the investigations conducted by the author during last 10 years to improve the efficiency of HVAC systems by use of one and two-phase ejectors.

There is an extensive body of previous knowledge and a large literature base regarding ejector applications in refrigeration dating back to the year of 1900 (Bergander, 2012). In spite of this, the ejector use in refrigeration systems was always considered as controversial at best, mainly because a lot of research has been conducted for many years with only theoretical results and without visible, commercial products. However, just recently (Sept 2009) it was disclosed by Denso Corp. of Japan that they developed an ejector-based, air conditioning (A/C) system to be installed in all Toyota cars and trucks starting with 2010 models outside of the US (Takeuchi, 2009). Further, this author's investigations demonstrated another example of effective use of ejectors in A/C systems: we were able to demonstrate the ejector-based air conditioning system for residential dwellings, which was able to considerably lower the ambient temperature, while using low-grade heat (solar, waste, etc.) as a main source of energy and further, to completely eliminate the compressor from the cycle (Butrymowicz & Bergander, 2010) . It is extremely encouraging that two very different approaches using different working fluids and heat sources have demonstrated the practical use of ejectors to provide economical cooling.

The research on the ejector application is consistent with present directions in the HVAC industry, which are: 1) improving the efficiency, 2) reducing the refrigerant charge and 3) reducing the footprint (size) of the refrigeration units. We believe that the ejector, when considered as a “technology platform” is capable to significantly contribute to all three above goals and therefore, it will attract more attention and research funding in the future. World demand for HVAC equipment is projected to increase over 5% per year according to the Fredonia Group’s new World HVAC Equipment study. Demand in the U.S. for HVAC equipment is forecasted to increase 3.2 percent per year to $15 billion annually in 2011. Sales will be driven by a projected recovery in residential construction along with ongoing strength in residential remodeling. Because of the large amount of HVAC equipment in place, the demand attributable to replacements and improvements makes up about 70% of total demand. The increasing interest in energy-efficient building systems and energy conservation will continue to drive growth in the replacement sector. This is well aligned with our value proposition.

While numerous publications describe the ejectors and their use, none of them to our best knowledge had attempted to classify various types of thermodynamic cycles where those ejectors can be applied. Consequently, the author proposes such classification, and he recognizes three distinctive “categories” of cycles with ejectors. This chapter discussed these categories in more details. The Category 1 (ejector installed on compressor suction), receives somewhat less attention because it has been well known and the intellectual property belongs to others. Most detailed discussion and research results are presented for the case where the ejector is installed on compressor discharge (Category 2), as this is the main area of the author’s expertise and involvement. As a result of his research in this field, he possesses the intellectual property in form of mentioned above US Patent that controls this specific area of application.