BACKGROUND OF THE INVENTION

The present invention relates to Heating, Ventilating, and Air Conditioning (HVAC) systems, and a fan controller controlled by a user, an HVAC system control board, a thermostat, or an energy management system.

Known smart thermostats may provide a fan control option to operate the fan for a fraction of an hour which may be set by a user to repeat every hour. For example, a non-patent publication by Ecobee Inc. describes an intermittent fan-on minimum setting operating on an hourly basis. “If the Fan Min On Time is set for 15 minutes or lower, the fan will operate in two separate segments across the hour; if the Fan Min On Time is set for 20 minutes or higher, the fan will run in four equal segments (of 5 minutes or more each) across the hour. If a heating or cooling cycle operates within any given hour, the length of either cycle will be deducted from the Fan Min On Time. For example, if your cooling runs for 5 minutes and your Fan Min On Time is set to 20 minutes, 5 minutes will be deducted from the Fan Min On Time.” See non-patent publication by Ecobee Inc., “How to control your HVAC system's fan with your ecobee thermostat” Date: Jan. 13, 2020, Page 7, Published by Ecobee Inc., 25 Dockside Dr., Suite 700, Toronto, ON M5A OB5, Canada

https://support.ecobee.com/hc/en-us/articles/360004798951-How-to-control-your-HVAC -system-s-fan-with-your-ecobee-thermostat. Also see non-patent publication by Google Inc. “How to Control Your Fan with a Nest Thermostat,” Date: Dec. 30, 2019, Pages 1, Published by Google, Inc., 1600 Amphitheatre Parkway, Mountain View, Calif. 94043 USA. https://support.google.com/googlenest/answer/9296419?hl=en.

Known fan controllers provide fan-off delays at the end of a fan G signal energized by itself without an AC Y signal or without a heat W signal and operate the fan longer than a user selected hourly or intermittent fan-on duration which increases fan energy use by 20 to 50%. Known fan controllers do not provide a solution to resolve the unresolved problem of increasing fan energy use during hourly or intermittent fan-on operation that wastes HVAC energy specifically when a building is unoccupied.

BRIEF SUMMARY OF THE INVENTION

Smart thermostats provide many methods for users to select an hourly fan-on duration control or an intermittent fan-on duration control for a fraction of an hour to operate a system fan/blower of a Heating, Ventilating, Air Conditioning (HVAC) system for a fraction of each hour. Known fan controllers that provide a fan-off delay using the fan G signal as a proxy for an Air Conditioning (AC) compressor Y signal (or “AC Y signal” or “compressor Y signal”) will provide a fan-off delay at the end of every fan G signal from the thermostat which will operate the fan longer than the user selected hourly or intermittent fan-on duration. The present invention smart thermostat fan controller monitors and detects when the fan G signal is energized without a thermostat call for cooling or without a thermostat call for heating, and does not provide a fan-off delay after the fan G signal from the thermostat is de-energized (without a thermostat call for cooling or heating) to avoid wasting fan energy.

Known fan controllers can inadvertently provide significantly more fan energy (e.g., 800 to 2400 kWh/yr) depending on the fan motor power (kilowatts or kW), hours of intermittent fan-on operation per year, and the fan-off delays provided by known fan controllers. The extra fan energy provided by known fan controllers that provide a fan-off delay after every fan-on period can be greater than the expected energy savings provided by smart thermostats. For example, if only 6 to 10 percent of smart thermostat users select a 30-minute intermittent fan-on duration per hour and also have a known fan controller that provides a fan-off delay after each intermittent fan-on duration, then the extra fan energy used by only the 6 to 10 percent of users with the known fan controller may increase energy use enough to offset or eliminate energy savings for the remaining 90 to 94% of users who do not select a 30-minute intermittent fan-on duration.

The smart thermostat fan controller resolves this problem and avoids wasting fan energy by monitoring the fan G signal input, the AC Y signal input, and the heat W signal input from the thermostat and not providing a fan signal output from a switching device and not energizing a fan relay and operating a system fan/blower of a HVAC system for a fan-off delay at the end of the fan G signal duration when the fan G signal input was previously energized and the AC signal input was not previously energized or when the fan signal input was previously energized and the heat W signal input was not previously energized. When only the fan G signal from the thermostat is energized without the AC Y signal or the heat W signal being energized, the smart thermostat fan controller provides the fan G signal output from the switching device to energize a fan relay and operate the system fan/blower.

The smart thermostat fan controller also energizes the at least one switching device and the fan signal output to energize a fan relay and operate the system fan/blower for a variable fan-off delay after the AC Y signal input (or heat W signal) input is de-energized. The variable fan-off delay occurs simultaneously with a thermostat fan-off delay or the thermostat fan-off delay is subtracted from the variable fan-off delay or the thermostat fan-off delay is zero. The smart thermostat fan controller may also detect and report a fan-on alarm message for a user to override a fan-on duration control to save energy and improve occupant comfort.

