# US 10,119,718 B2 · Methods and systems for monitoring an air filter of an HVAC system > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 10,119,718 B2 - Document ID: US10119718B2 - Status: Granted - Kind: B2 - Application number: 13/164,543 - Filed: 2011-06-20 - Published: 2012-12-20 - Granted: 2018-11-06 - Earliest claimed: 2011-06-20 - Assignees: Honeywell International Inc. - Applicants: Steven Hoglund; Reed Bisson - Inventors: Steven Hoglund; Reed Bisson - Web page: https://patentgrep.com/patent/US10119718B2 ## CPC - F24F 11/39: Monitoring filter performance - F24F 11/30: for purposes related to the operation of the system, e.g. for safety or monitoring - F24F 11/52: Indication arrangements, e.g. displays - B01D 46/0086: {Filter condition indicators} - F24F: AIR-CONDITIONING; AIR-HUMIDIFICATION; VENTILATION; USE OF AIR CURRENTS FOR SCREENING (removing dirt or fumes from areas where they are produced B08B15/00; vertical ducts for carrying away waste gases from buildings E04F17/02; tops for chimneys or ventilating shafts, terminals for flues F23L17/02) - B01D: SEPARATION (separating solids from solids by wet methods B03B, B03D; by pneumatic jigs or tables B03B; by other dry methods B07; magnetic or electrostatic separation of solid materials from solid materials or fluids, separation by high-voltage electric fields B03C; centrifuges, vortex apparatus B04; presses per se for squeezing-out liquid from liquid-containing material B30B9/02; treatment of water C02F, e.g. softening by ion-exchange C02F1/42; {arrangements of air intake cleaners in gas turbine plants F02C7/05} ; arrangements or mounting of filters in air-conditioning, air-humidification or ventilation F24F13/28) ## Abstract Methods and systems for monitoring an air filter installed in an HVAC system may include operating the HVAC system in an air filter monitoring mode such as, for example, a fan only mode, and measuring, for example, a differential pressure across the air filter when the HVAC system is operating in the air filter monitoring mode. The method may include evaluating a status of the air filter using, for example, the measured differential pressure value, and in some cases, display the status on a display of an HVAC controller. ## Claims ### Claim 1 A method of monitoring a status of an air filter of an HVAC system, wherein the HVAC system has a number of controllable HVAC components, the method comprising: placing the controllable HVAC components into a predetermined filter check state; while the controllable HVAC components are in the predetermined filter check state: measuring a first differential pressure value across the air filter at a first time; determining a status of the air filter based at least in part on the measured first differential pressure value; placing at least one of the controllable HVAC components into a different state other than the predetermined filter check state including activating one or more HVAC components that were not previously activated in the predetermined filter check state, and operating the HVAC system while the at least one of the controllable HVAC components is in the different state; after the HVAC system is operated with the at least one of the controllable HVAC components in the different state, placing each of the controllable HVAC components back into the predetermined filter check state; and while the controllable HVAC components are in their predetermined filter check state: measuring a second differential pressure value across the air filter at a second time; and determining the status of the air filter based at least in part on the measured second differential pressure value. ### Claim 2 (depends on 1) The method of claim 1, wherein the number of controllable HVAC components includes a fan and a heating element, and wherein the predetermined filter check state of the fan is “on” and the predetermined filter check state of the heating element is “off”. ### Claim 3 (depends on 2) The method of claim 2, wherein placing at least one of the controllable HVAC components into a different state other than the predetermined filter check state includes turning the heating element “on” or changing a speed setting of the fan. ### Claim 4 (depends on 1) The method of claim 1, wherein the number of controllable HVAC components includes a fan and a cooling element, and wherein the predetermined filter check state of the fan is “on” and the predetermined filter check state of the cooling element is “off”. ### Claim 5 (depends on 4) The method of claim 4, wherein placing at least one of the controllable HVAC components into a different state other than the predetermined filter check state includes turning the cooling element “on” or changing a speed setting of the fan. ### Claim 6 (depends on 1) The method of claim 1, wherein the number of controllable HVAC components includes a fan with a first non-zero fan speed and a second non-zero fan speed, and wherein the predetermined filter check state of the fan is at the first non-zero fan speed. ### Claim 7 (depends on 6) The method of claim 6, wherein placing at least one of the controllable HVAC components into a different state other than the predetermined filter check state includes changing the fan to the second non-zero fan speed. ### Claim 8 (depends on 1) The method of claim 1, wherein the number of controllable HVAC components includes a number of zone control dampers, and wherein the predetermined filter check state of the number of zone control dampers is “open”. ### Claim 9 (depends on 8) The method of claim 8, wherein placing at least one of the controllable HVAC components into a different state other than the predetermined filter check state includes closing at least one of the number of zone control dampers. ### Claim 10 (depends on 1) The method of claim 1, wherein the status of the air filter is determined by comparing the measured differential pressure values against a threshold differential pressure value. ### Claim 11 (depends on 10) The method of claim 10, wherein the threshold differential pressure value is determined by: while the controllable HVAC components are in the predetermined filter check state: measuring a calibration differential pressure across a clean air filter; determining the threshold differential pressure value based at least in part on the calibration differential pressure value. ### Claim 12 (depends on 10) The method of claim 10, wherein the threshold differential pressure value is determined by: while the controllable HVAC components are in the predetermined filter check state: measuring a calibration differential pressure across an air filter that is at least partially blocked; determining the threshold differential pressure value based at least in part on the calibration differential pressure value. ### Claim 13 (depends on 1) The method of claim 1, further comprising displaying the status of the air filter on a display of an HVAC controller. ### Claim 14 An HVAC controller for controlling an HVAC system having a number of controllable HVAC components and an air filter, the HVAC controller comprising: a controller; a memory coupled to the controller; a display coupled to the controller; wherein the controller is configured to place each of the controllable HVAC components into a predetermined filter check state at a first time, and while the controllable HVAC components are in the predetermined filter check state, receive a measure related to an amount of flow restriction presented by the air filter of the HVAC system, and then determine a status of the air filter based at least in part on the received measure related to an amount of flow restriction presented by the air filter, and then placing at least one of the controllable HVAC components into a different state other than the predetermined filter check state, wherein one or more components of the HVAC system are activated that were not previously activated while in the predetermined filter check state, and operating the HVAC system while the at least one of the controllable HVAC components is in the different state, the controller further configured to return the HVAC components to the predetermined filter check state at a second time; and the controller configured to display the status of the air filter on the display. ### Claim 15 (depends on 14) The HVAC controller of claim 14, wherein the measure related to an amount of flow restriction presented by the air filter of the HVAC system is a differential pressure across the air filter. ### Claim 16 (depends on 14) The HVAC controller of claim 14, wherein the measure related to an amount of flow restriction presented by the air filter of the HVAC system is an air flow through the filter. ### Claim 17 (depends on 14) The HVAC controller of claim 14, wherein the predetermined filter check state corresponds to a fan only mode. ### Claim 18 (depends on 17) The HVAC controller of claim 17, wherein the number of controllable HVAC components includes a number of zone control dampers, and wherein the predetermined filter check state of the number of zone control dampers is “open”. ### Claim 19 (depends on 14) The HVAC controller of claim 14, wherein the controller is configured to repeatedly place each of the controllable HVAC components into the predetermined filter check state, and while the controllable HVAC components are in the predetermined filter check state, receive a measure related to an amount of flow restriction presented by the air filter of the HVAC system, and then determine a status of the air filter based at least in part on the received measure related to an amount of flow restriction presented by the air filter. ### Claim 20 A method of monitoring a status of an air filter of an HVAC system of a building, wherein the HVAC system includes a number of controllable HVAC components, the method comprising: operating the HVAC system in a normal operating mode to control a temperature in the building; occasionally entering an air filter monitoring mode, wherein the air filter monitoring mode corresponds to a fan only mode of the HVAC system; while in the air filter monitoring mode, receiving a measure related to an amount of flow restriction presented by the air filter, and determining a status of the air filter based at least in part on the received measure related to the amount of flow restriction presented by the air filter; and displaying the status of the air filter on a display.