Predrag “Pega” Hrnjak RIP

USA: The University of Illinois Urbana Champaign has announced the death of Predrag “Pega” Hrnjak, the internationally renowned air conditioning and refrigeration research professor. He was 70.

Born in Yugoslavia (now Serbia), Hrnjak earned his DSc from the University of Belgrade, where he achieved the rank of associate professor. He joined the University of Illinois at Urbana-Champaign Department of Mechanical Engineering and Science in 1993, where he became Stoecker Faculty Fellow and Distinguished Research Professor, serving as the director of the Air Conditioning and Refrigeration Center (ACRC), an Industry/University Cooperative Research Center founded by the US National Science Foundation.

During his career, he mentored nearly 120 students to graduate degrees and welcomed close to 100 visiting scholars to his research team. His students have gone on to leadership positions in industry, national labs and public service, and to careers in academia—all around the world.

In the early days of the ACRC, while building his own research programme, Hrnjak assumed lead responsibility for design and construction of state-of-the-art laboratory facilities. His academic research ranged from fundamentals of refrigerant-lubricant mixtures and the dynamics of developing two-phase flow, to optimising the design of components and systems around the properties of various refrigerants and their compatible lubricants. 

During the CFC phaseout, Hrnjak was asked by an international consortium of automakers to lead the first carefully controlled side-by-side comparisons of several new generations of AC systems using HFC, HFO, hydrocarbon and carbon dioxide refrigerants.  Based on the results of his multi-year project, automakers were able to double the efficiency of their R134a systems by adopting many of the component technologies, such as internal heat exchangers and ejectors, developed for the competing systems.

In 2003, he founded Creative Thermal Solutions, an HVACR research and testing facility. What began as a “garage business” grew under Hrnjak’s leadership to the state-of-the-art, 930m² research facility it is today. 

His efforts at ACRC and CTS incubated a critical mass of enthusiastic researchers, engineers, and support staff of nearly 100 people working simultaneously on sustainable HVAC&R technologies. 

At CTS and Illinois, he was engaged in research on a wide range of “natural” refrigerant projects, from low-charge ammonia to ejectors for transcritical CO2 to some of the early CO2 mobile air conditioning systems.

Hrnjak’s global accolades include being made a Fellow of the American Society of Mechanical Engineers, a Fellow of the American Society of Air Conditioning and Refrigeration Engineers, Fellow of the Society of Automotive Engineers, the 2008 IEA Ritter von Rittinger Award, the 2011 IIR Gustav Lorentzen Medal, the 2012 Institute of Refrigeration J&E Hall Medal, and the 2019 ASHRAE Louise and Bill Holladay Distinguished Fellow Award. In 2012, he was named Academician of the Academy of Engineering Sciences of Serbia.