Control scheme for automatic fan mode for use with variable refrigerant flow systems

A heating, ventilation, and air conditioning (HVAC) system comprising:

• an outdoor heat exchanger;
• a compressor fluidly coupled to the outdoor heat exchanger;
• a plurality of indoor heat exchangers corresponding to a plurality of enclosed spaces, the plurality of indoor heat exchangers coupled in parallel to the compressor;
• a plurality of variable-speed circulation fans, a first variable-speed circulation fan of the plurality of variable-speed circulation fans disposed with a first indoor heat exchanger of the plurality of indoor heat exchangers and configured to circulate air around the first indoor heat exchanger;
• a user interface configured to receive a setpoint temperature of a first zone corresponding to a first enclosed space;
• and
• a plurality of zone controllers electrically coupled to each variable-speed circulation fan of the plurality of variable-speed circulation fans, wherein each zone controller of the plurality of zone controllers is configured to:
• measure a temperature of a first enclosed space of the plurality of enclosed spaces, the first enclosed space containing the first indoor heat exchanger and the first variable-speed circulation fan;
• determine whether a difference exists between the measured temperature of the first enclosed space and the setpoint temperature of the first enclosed space;
• and
• responsive to a determination that a difference exists between the measured temperature of the first enclosed space and the setpoint temperature of the first enclosed space, adjust a speed of the first variable-speed circulation fan from a current speed to a new speed for a minimum time period before the new speed is subsequently changed using a timer unit.

A method of fan speed control for an HVAC system, the method comprising:

• measuring, with a temperature sensor, a temperature of a zone of a plurality of zones;
• communicating the measured temperature to a zone controller disposed within with the zone;
• receiving, by a user interface, a setpoint temperature of the zone;
• determining, by the zone controller, whether a difference exists between the measured temperature of the zone and the setpoint temperature of the zone;
• and
• responsive to a determination that a difference exists between the measured temperature and the setpoint temperature of the zone, adjusting a speed of a variable-speed circulation fan disposed within the zone from a current speed to a new speed for a minimum time period before the new speed is subsequently changed using a timer unit.