Energy efficiency and economic analysis of variable frequency drive and variable pitch system: A case study of axial fan in hospital

Abstract

Most hospitals use variable air volume systems to reduce their energy consumption while effectively responding to the frequently varying demands of cooling and heating. In this study, we applied the variable frequency drive (VFD) and variable pitch (VP) fan control methods to air handling units with axial fans in a tertiary hospital in Seoul, South Korea, and compared their power consumption and operating efficiencies according to the annual outdoor air intake rate schedule. The results of the comparison indicated that the VFD in the low-fan-output section and the VP method in the high-fan-output section consumed relatively less power. Concerning the economic feasibility analysis, we compared the annual operation and maintenance costs of the VFD and VP systems applied to the Air Handling Units (AHUs) in the hospital. In all cases, the annual energy consumption was lower in the VP than in the VFD; however, the VP was relatively high in maintenance and overhaul. It was shown that the VP is a more efficient control method due to the high-output operation of the AHUs for patient rooms. For other AHUs, the payback period was between 9 and 16 years when changing from VP to VFD. • Variable pitch control was energy conservative for the air handler operating at the high flow rate. • Variable frequency drive was energy efficient for the air handler at the low flow rate. • Operating cost of the variable pitch control was lower than that of the variable-frequency drive. • Maintenance cost of the variable pitch control was higher than that of the variable-frequency drive.