Experimental validation of a hybrid electric organic Rankine vapor compression cooling system

Abstract

Thermally activated chillers, such as absorption chillers and Organic Rankine Vapor Compression (ORVC) systems, offer promising solutions for improving efficiency and reducing emissions in heating, ventilation, and air conditioning (HVAC) applications. However, their adoption in the U.S. has been limited due to performance challenges with variable heat input. Integrating electric input into ORVC systems has been proposed as a solution to variable heat input performance degradation, but the concept has not experimentally validated. This study presents results from a 263 kW_th hybrid ORVC test facility operating in electric, thermal, and hybrid cooling modes under HVAC-relevant conditions. In hybrid cooling mode, compression in the vapor compression cycle was provided by an electric compressor and a thermally driven compressor. Three configurations were evaluated: parallel compressors, series compressors with the thermally driven compressor first, and series compressors with the electric compressor first. The optimal configuration (thermally driven compressor first in series) was tested with heat inputs ranging from fully thermal to fully electric operation. Testing was conducted with cooling duty at 175 kW, heat input at 91 °C, heat rejection at 30 °C, and cooling delivered at 9 °C. At low heat input (113 kW), the system achieved high thermal COP (1.02) and low electric COP (3.80), while at high heat input, the thermal COP was 0.54 and the electric COP was 8.76 at 331 kW. Performance surpassed purely thermal (COP_th = 0.42) and purely electric (COPe = 4.55) modes with heat input above 180 kW. Turbomachinery analysis identified compressor limitations, suggesting optimized selection could further enhance efficiency. This study establishes hybrid ORVC performance for HVAC applications.