Next-generation equipment and services require next-generation research. The HVAC&R Research for the Twenty-First Century (21-CR) program, conducted by the Air-Conditioning and Refrigeration Technology Institute (ARTI), is a private-public sector collaboration designed to identify, prioritize, and undertake precompetitive research in several important focus areas.

One of those areas is high-efficiency equipment.

Two of these projects have recently been completed, others are under way, and new projects are being explored. The following is a discussion of research being pursued to date.


According to P. Elizabeth Jones, 21-CR project manager, the first energy efficiency project was in support of American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) research project 1121-TRP, “Evaluating the Ability of Unitary Equipment to Maintain Adequate Space Humidity Levels.”

The Phase 1 work has been completed. It comprised development of a plan to guide the evaluation of humidity control by unitary hvac equipment. Phase 2 will focus on analysis using computer simulations based on the evaluation plan, Jones said.

“The plan is based on separate evaluations of humidity control options and load requirements of commercial buildings,” she noted. “The analysis of control options describes the range of unitary options to address humidity control.”

The evaluation plan depicts five commercial buildings, including their physical and thermal building characteristics and schedules for loads and operations. Eight locations have been selected to represent a range of climate conditions and markets where dehumidification is important. The cooling and dehumidification requirements for each building, in each location, are to be evaluated with each of 17 equipment options. The complete evaluation set involves 1,360 annual simulations.

Results of the simulations will identify the performance of the various humidity control options in different types of installations and provide application guidance. Phase 2 has not been awarded as yet.

The next project is “An Assessment of the State-of-the-Art and Potential Design Improvements for Flat-Tube Heat Exchangers in Air Conditioning and Refrigeration Applications — Phase 1,” which has also been completed. This study is designed to evaluate air-side heat transfer. Another project will report on the refrigerant side, said Jones.

The study was conducted to evaluate air-side heat transfer and pressure drop performance of flat-tube heat exchangers in comparison with conventional round tube designs. It covers heat exchanger geometry and parametric effects. “These tubes are used commonly in radiators in automobiles,” Jones said. “This project has the goal of applying these tubes in air conditioners.”

Phase 2 is now under way. Testing is being performed on different types of fins. It will be completed in two years, Jones said. The study on the refrigerant side of flat tubes is scheduled for completion in April 2003.


Other projects currently in process include “Potential Benefits of Smart Refrigerant Distrib-utors.” The objective of this study is to determine potential cost benefits of developing a “smart” refrigerant flow distribution system for air-source evaporators.

The project will provide an experimentally verified computer simulation to predict the effect of various refrigerant and airflow distributions on air-source evaporator performance. This is expected to lead to general-purpose tools to help design smaller and more efficient evaporators. It is scheduled for completion in April 2002.

Another project is “High Condensing Temperature Heat Transfer Performance of Low Critical Temperature Refrigerants,” which examines the performance of two blends — R-404A and

-410A. The project will provide heat transfer data for the design of systems operating under high condensing temperature, near the critical point.

These data are expected to allow manufacturers to produce energy-efficient equipment that performs well at higher condensing temperatures. Testing has begun, Jones said, and is scheduled for completion in June 2003.

One more project is “Variable Primary-Flow Chilled-Water Systems: Potential Benefits and Application Issues.” The study will provide a comparison of constant- and variable-flow performance for various chiller types, plant configurations, load profiles, and energy rate structures.

The results are expected to lead to changes in building and chiller control systems to reduce pumping energy. The project is to be completed in May 2002.


A brand-new project, just recently announced, will study “Refrigerant/Oil Mixture Heat Transfer Data.”

Jones stated, “The objective of this study is a critical review on the heat transfer and pressure drop characteristics of refrigerant and oil mixtures.”

It will identify critical lubricant parameters, properties, and their influence on two-phase heat transfer, and will make suggestions for standardized data records for future research.

With this systematic research, the body of knowledge in the hvacr field will be expanded, providing building blocks for further improvements.

Publication date: 01/21/2002