Automatic operation method using wireless sensor networks for variable refrigerant flow system: Switchless control variable refrigerant flow system

Variable refrigerant flow (VRF) systems autonomously operate using built-in sensors regulated by remote settings and indoor unit intake temperatures. However, in larger spaces with multiple indoor and outdoor units, autonomous VRF systems lack the benefits of an integrated system, such as balanced load distribution, coordinated operation, and efficient ventilation. To overcome these challenges, the authors developed a "switchless VRF system" designed for small to medium-sized buildings. This system improves comfort and energy efficiency by eliminating extensive control mechanisms and switches, ensuring uniform performance and greater energy saving. We performed detailed demonstration experiments to evaluate the system's effectiveness across four key functions (pre-cooling and pre-heating, human sensing HVAC control, outdoor unit rotation control, and indoor unit fan power reduction functions). In the first control, the VRF system demonstrated significant energy efficiency, achieving 18 % energy saving in summer pre-cooling. In the second, the human-detection ventilation control effectively modulated the ventilation volume by real-time monitoring of the number of occupants, resulting in approximately 35 % energy saving. In the third, the rotational control strategy enhanced the average COP of the outdoor units by 17.7 %. In the fourth, a reduction in indoor-unit fan power led to an overall power consumption decrease of 8.6 % by ceasing fan operation when the thermostat was deactivated. This innovation addresses the modern needs of building management and energy conservation, making it a viable option for enhancing HVAC operations.