1/10 TRANSCRITICAL CO 2 MOBILE HEAT PUMP AND A/C SYSTEM EXPERIMENTAL AND MODEL RESULTS C.W. Bullard, J.M. Yin, P.S. Hrnjak * Air Conditioning and Refrigeration Center (ACRC) University of Illinois, 1206 W. Green St. Urbana, IL 61801, USA ABSTRACT This article presents the results of the experimental runs of a prototype of R744 (CO 2 ) refrigeration system operating in a both air conditioning and heat pump mode when heat rejection is done in supercritical region. The prototype system is sized for a compact car. Data presented are in the limited range of operation. Further optimization and extension of operating range is underway. Test facilities for such experiments and systems are described. The prospect of extending the ability of a mobile a/c system to a mobile heat pump operation is very promising. INTRODUCTION Transcritical CO 2 systems are attracting significant attention in last several years not only due their environmental impact, but also due to unexpectedly good performance. The performance of some such systems were presented by Pettersen et al. (1993, 1994, 1997a and b), University of Maryland CEEE, several companies as well as by our group in Yin et al. (1998), Boewe et al. (1999a,b), Beaver et al. (1999a, b), etc… In few earlier articles we have analyzed and compared performance of a prototype of a transcritical CO 2 system with the same volume and air-side pressure drop of heat exchangers as in a typical, of-the-shelf R134a mobile system. Results showed slightly worse performance of CO 2 system at very high ambient temperatures (above 45 o C) close between 35 and 45 o C and better performance at lower ambient temperatures. We continue to working in the same area. There are four such systems that we are exploring at this moment. These systems are indicative of air conditioning systems used in typical compact cars and sport utility/military vehicles in the USA. Heat exchangers used in the baseline systems are typical for the respective vehicle size. The R744 systems are designed to have similar or smaller heat exchanger core volumes, face areas, and air side pressure drops. In this article we will focus to and present results for heat pump operation of the system first designed R744 system (MAC1) as shown in Table 1 and in the Figure 3. One of the reasons to be focused to heat pump application are our modeling analysis that indicated great potential of transcritical CO 2 system operation in the heat pump mode. Favorable heat pump operation could append additional reason for considering transcritical CO 2 systems as a viable alternative to existing R134a systems. * Author to whom correspondence should be addressed, pega@uiuc.edu