Interaction effects and load-oriented scheduling of multiple actuators in a gas engine-driven VRF system under heating condition

Abstract

This study investigates the interactions among the liquid injection cooling expansion valve (LICV), hot gas bypass expansion valve (HGBV), and engine speed in a gas-engine-driven variable refrigerant flow system, with the aim of improving heating performance and primary energy efficiency. Under low-load conditions in practical heating applications, inadequate coordination among the three actuators tends to cause a marked reduction in system efficiency. A Box-Behnken response surface methodology was adopted to establish a model with LICV opening, HGBV opening, and engine speed as the independent variables, and indoor-unit heating capacity ( Q total ) and primary energy ratio (PER) as the response variables. The results reveal that the HGBV opening has the most significant effect on Q total and PER, followed by the LICV opening, while engine speed has the smallest effect. Incremental increases in any of the three variables degrade PER; however, higher engine speeds can mitigate the efficiency losses associated with bypass operations. The concurrent modulation of the LICV and HGBV induces a synergistic degradation of PER. A load-oriented steady-state actuator-scheduling method was developed using the fitted response surfaces. Within the tested heating condition and actuator range, the method reproduced the target indoor-unit heating capacity with relative errors below 5% in five validation cases. It should be noted that the current experimental validation was conducted only under specific conditions. Further validation under a wider range of operating conditions is still required before general application can be realized.