Economizer cooling delay correction

Abstract

A Fault Detection Diagnostic (FDD) correction method for increasing the cooling capacity delivered by an Air-Conditioning (AC) system with an economizer comprising: correcting/superseding at least one cooling fault/delay, the correcting/superseding selected from the group consisting of: correcting/superseding a High-limit-Shut-off-Temperature (HST) fault/delay based on detecting an Outdoor Air Temperature (OAT) is less than or equal to a High-limit-Control Temperature (HCT) during a thermostat call for cooling to enable economizer cooling otherwise delayed by the at least one HST fault/delay, superseding a thermostat second-stage time/temperature-deadband delay based on detecting an OAT is greater than or equal to an AC Control Temperature (ACT) during a call for cooling and energizing an AC compressor otherwise delayed by a thermostat second-stage time/temperature-deadband delay, superseding at least one economizer second-stage time/temperature delay based on detecting a thermostat second-stage cooling signal and energizing an AC compressor otherwise delayed by the at least one economizer second-stage time/temperature delay.

Claims

1. A cooling delay correction method for an Air Conditioning (AC) system comprising a fan, at least one AC compressor, an economizer and a thermostat, the method comprising: comparing an Outdoor Air-drybulb Temperature (OAT) to a High-limit Control Temperature (HCT) wherein the HCT is greater than or equal to a High-limit Shut-off Temperature (HST); comparing the OAT to an Air-conditioning Control Temperature (ACT) wherein the ACT is less than the HCT; increasing the amount of cooling capacity delivered to the conditioned space by the AC system based on detecting the OAT is less than or equal to the HCT at the beginning of a thermostat call for cooling or during the thermostat call for cooling; and energizing an economizer actuator to move an economizer damper to a fully open damper position for the fan to provide an outdoor airflow to enable an economizer cooling otherwise precluded or delayed by a HST deadband delay.

2. The method of claim 1, wherein the ACT is a default ACT or a user-selected ACT.

3. The method of claim 1, wherein the ACT varies from 60 degrees Fahrenheit (F) to the HCT and the HCT varies from 69 F to 80 F.

4. The method of claim 1, wherein the ACT is a Variable Economizer-drybulb Setpoint Temperature (VEST) and the VEST is adjusted based on a building occupancy, a geofencing signal, an occupancy schedule, or a conditioned space temperature.

5. The method of claim 1, further including detecting a thermostat second-stage cooling signal is energized and energizing the at least one AC compressor to provide mechanical cooling otherwise precluded or delayed by an economizer second-stage time delay.

6. The method of claim 1, wherein the increasing the amount of cooling capacity delivered to the conditioned space by the AC system further includes: enabling the economizer cooling otherwise precluded or delayed by a HST temperature delay.

7. The method of claim 1, wherein the increasing the amount of cooling capacity delivered to the conditioned space by the AC system further includes: enabling the economizer cooling otherwise precluded or delayed by a default HST or a user-selected HST which is less than the HCT.

8. The method of claim 1, wherein the increasing the amount of cooling capacity delivered to the conditioned space by the AC system further includes: detecting the OAT is greater than the ACT and the OAT is less than or equal to the HCT at the beginning of the thermostat call for cooling or during the thermostat call for cooling; and energizing an economizer actuator to move a damper to a fully open damper position for the fan to provide an outdoor airflow to enable an economizer cooling and energizing the at least one AC compressor without a thermostat second-stage cooling signal.

9. The method of claim 1, wherein the increasing the amount of cooling capacity delivered to the conditioned space by the AC system further includes: detecting the OAT is greater than the ACT and the OAT is less than or equal to the HCT at the beginning of the thermostat call for cooling or during the thermostat call for cooling; and energizing an economizer actuator to move a damper to a fully open damper position for the fan to provide an outdoor airflow to enable an economizer cooling and energizing the at least one AC compressor without a thermostat second-stage time or temperature delay.

10. The method of claim 1, wherein the increasing the amount of cooling capacity delivered to the conditioned space by the AC system further includes: detecting the OAT is greater than the ACT and the OAT is less than or equal to the HCT at the beginning of the thermostat call for cooling or during the thermostat call for cooling; and energizing an economizer actuator to move a damper to a fully open damper position for the fan to provide an outdoor airflow to enable an economizer cooling and energizing the at least one AC compressor without a thermostat second-stage time delay.

11. The method of claim 1, wherein the increasing the amount of cooling capacity delivered to the conditioned space by the AC system further includes: detecting a thermostat second-stage cooling signal; and energizing the at least one AC compressor without an economizer second-stage temperature delay.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

(1) The above and other aspects, features and advantages of the present invention will be more apparent from the following more particular description thereof, presented in conjunction with the following drawings wherein:

(2) FIG. 1 shows a flow chart according to the present invention of: 1) FDD cooling delay correction (CDC) method; 2) conventional economizer cooling; 3) DX AC cooling; and 4) a variable fan-off delay based on HVAC parameters. The method includes a permanent-magnet and magnetometer or other MEMS device to measure the physical position of the dampers and air temperature, RH, and CO2 sensors to control the economizer, AC compressor(s), and measure the Outdoor Airflow Fraction (OAF).

(3) FIG. 2 shows a flow chart according to the present invention of a FDD method during a thermostat call for heating. The method includes a magnetometer or other MEMS device to measure the physical position of the economizer dampers and air temperature, RH, and CO2 sensors to control the economizer and measure the OAF.

(4) FIG. 3 shows an OAF economizer calibration method for an HVAC system while the HVAC system is operating, according to the present invention.

(5) FIG. 4 shows a method for an HVAC Fault Detection Diagnostic (FDD) method while the HVAC system is operating, according to the present invention.

(6) FIG. 5 provides a chart showing the OAF versus the economizer control voltage on an HVAC system according to the present invention.

(7) FIG. 6 shows a table of damper position data, and equations 7, 9, 11, and 19, according to the present invention.

(8) FIG. 7 provides calculations of the FDD CDC savings from correcting the default 62 F HST and superseding the HST deadband delay fault.

(9) FIG. 8 provides calculations of the FDD Cooling Delay Correction (CDC) savings when the building is occupied.

(10) FIG. 9 provides calculations of the FDD CDC savings when the building is unoccupied.

(11) FIG. 10 provides measurements representing the FDD CDC cooling savings versus the temperature difference between the Conditioned Space Temperature (CST) and the OAT for an occupied and unoccupied building.

(12) FIG. 11 shows five tests of the known economizer cooling control and five tests of the present invention FDD cooling delay correction method.

(13) FIG. 12 provides a table of laboratory measurements of the total power (Watts), sensible cooling capacity (Btu per hour, Btuh), sensible Energy Efficiency Ratio (EER) (EER*s equal to Btuh divided by Watts), and energy savings for a packaged HVAC system with two compressors, a first-stage and a second-stage, and an economizer.

(14) FIG. 13 provides cooling savings versus OAT for the packaged HVAC system for OAT ranging from 55 to 100 F.

(15) FIG. 14 provides measurements representing the cooling energy savings (%) versus the cooling Part Load Ratio (PLR) for the present invention FDD variable fan-off delay method compared to known fixed fan-off delays of 45, 60, and 90-seconds, where the PLR is defined as the sensible cooling capacity for operating for less than 60 minutes divided by the total sensible cooling capacity for 60 minutes operation.

(16) FIG. 15 provides measurements representing the heating energy savings (%) versus the heating system PLR for the present invention FDD variable fan-off delay method compared to known fixed fan-off delays of 45, 60, and 90-seconds, where the PLR is defined as the heating capacity for a heating system operating for less than 60 minutes divided by the total capacity for the heating system operating for 60 minutes.

(17) FIG. 16 provides measurements representing the total HVAC system power (kW) versus time of operation for a known control and the present invention Fault Detection Diagnostics (FDD) fan-on method which overrides a continuous fan-on fault.

(18) FIG. 17 shows the economizer 783 installed into an HVAC system cabinet 780 showing an economizer perimeter gap 785 of an economizer frame where it connects to the HVAC system cabinet and the economizer hood 787 temporarily removed to allow the economizer perimeter gap 785 to be sealed.

(19) FIG. 18 shows measurements of OAF versus economizer actuator voltage measurements for economizer #1.

(20) FIG. 19 shows measurements of OAF versus economizer actuator voltage measurements for economizer #5.

(21) FIG. 20 shows a magnetometer co-planar with a magnet according to the present invention.

(22) FIG. 21 shows the magnet according to the present invention rotated 90 degrees.

(23) Corresponding reference element numbers indicate corresponding components throughout several views of the drawings.

DETAILED DESCRIPTION OF THE INVENTION

(24) The following description is of the best mode presently contemplated for carrying out the invention. This description is not to be taken in a limiting sense, but is made merely for the purpose of describing one or more preferred embodiments of the invention. The scope of the invention should be determined based on the claims.

(25) Where the terms “about” or “generally” are associated with an element of the invention, it is intended to describe a feature's appearance to the human eye or human perception, and not a precise measurement, or within 10 percent of a stated value. Drybulb temperature measurements at indicated without asterisks and corresponding wetbulb temperatures are indicated by the addition of an asterisk. As noted previously, temperatures in degrees Fahrenheit are indicated by an “F” directly following a number.

(26) FIG. 1 provides a flow chart for the present invention FDD CDC method to improve energy efficiency for a Heating, Ventilating, Air Conditioning (HVAC) system with an economizer and a thermostat by fully opening an economizer damper and simultaneously energizing a DX AC system (including the first-stage DX AC compressor and HVAC fan) based on receiving a first-stage cooling signal from a thermostat when the OAT is greater than the ACT and the OAT is less than or equal to the HCT. The FDD method may also comprise calibrating the economizer by sealing an economizer perimeter gap to reduce uncontrolled outdoor airflow, and determining a functional relationship between the economizer actuator voltage and a corresponding damper position OAF using a line-fit equation or least squares matrix regression equation (discussed in FIG. 5 and FIG. 6). The FDD method detects, reports, corrects, and supersedes economizer and HVAC faults including: an economizer deadband delay, a thermostat second-stage time or temperature deadband delay, an economizer second-stage mechanical cooling time delay or temperature delay, a cooling or heating short-cycle fault, fan-on setting fault, a sensor/damper/actuator fault, and an insufficient or excess outdoor air fault.

(27) The FDD method includes operating an HVAC fan for a variable fan-off delay after a thermostat call for cooling or heating based on a difference between a MAT and a SAT, where the MAT is based on an economizer damper position and an HVAC fan operating and providing a mixture of an outdoor airflow at an OAT and a return airflow at a RAT. The FDD method for overriding an economizer actuator control signal may be based on a geofencing/occupancy signal, and closing the economizer damper when the OAT conditions are above/below an OAT threshold temperature.

(28) The method uses a magnetometer, MEMS sensor, or other suitable sensor to measure the physical damper position and determine whether or not there is a fault with the economizer damper position actuator mechanism. The method determines a computed OAF with respect to a damper position command or the economizer actuator voltage command (i.e., closed, intermediate, or fully open position) where the computed OAF is based on the ratio of the difference between the RAT minus the MAT divided by the difference between the RAT minus the OAT. The computed OAF may also be based on humidity or CO2 measurements.

(29) FIG. 1 step 700 is the start of the FDD Cooling Delay Correction (CDC) method which detects, supersedes, and corrects: 1) an HST deadband delay, 2) a thermostat second-stage time delay or a thermostat second-stage deadband temperature delay; and 3) an economizer second-stage cooling signal time delay. In step 701, the method checks if the fan-on setting is enabled. If step 701 is Yes (Y), then the method proceeds to step 753 to Go to FIG. 2 FDD HVAC Methods. If step 701 is No (N), then the method proceeds to step 702 to check if there is a thermostat a call for cooling. In step 702, the method monitors signals from the thermostat to determine if there is a thermostat call for cooling. If the thermostat call for cooling has ended at step 702, then the method proceeds to step 752, and at end of thermostat call for cooling provides a variable fan-off delay based on at least one HVAC parameter selected from the group consisting of: a thermostat call for cooling, a cooling cycle duration P4, a thermostat call for heating, a heating cycle duration P3, and an air temperature difference between the MAT and the SAT where the MAT is based on a mixture of outdoor air and return air. If step 702 call for cooling is Yes (Y), then the method proceeds to step 703.

(30) At step 703 of FIG. 1, the FDD method determines if the air temperature, RH, CO2 sensors, and the magnetometer MEMS device are within expected tolerances. If step 703 is No (N), one or more sensors are an open circuit or a short circuit, then the method proceeds to step 716 to flag this fault and provide a FDD alarm “Fault: air temperature, RH, or CO2 sensor failure/fault” for sensors not working. If the OAT and RAT sensors are okay and step 703 is Yes (Y), then the method proceeds to 704. Otherwise, if the OAT and RAT sensors are faulted and the economizer controller cannot function, then the method continues to step 716 and on to step 708 (see below).

(31) At step 704 the method continuously monitors sensors to measure the OAT, RAT, and MAT and compute the OAF (described above). After step 704, the method proceeds to step 705. At step 705 the method checks if the OAT is less than the AC Control Temperature (ACT) or Variable Economizer-drybulb Setpoint Temperature (VEST). The ACT (or VEST) is based on at least one occupancy indicator selected from the group consisting of: an occupancy sensor signal, a geofencing signal, or an occupancy schedule (see previous description). The VEST may be adjusted up or down to allow conventional economizer cooling with the HVAC fan operating and fully open damper position to satisfy the call for cooling. During unoccupied periods with fewer people in the building and less of lights/equipment turned on, the VEST can be adjusted up to allow more economizer cooling to satisfy the call for cooling without AC compressor operation (i.e., preferrably OAT<66 to 69 F).

(32) If step 705 is Yes (Y), and the OAT is less than or equal to the ACT which may be the VEST, then the method proceeds to step 758. At step 758, the FDD CDC method corrects a default High-limit Shut-off Temperature (HST) and/or supersedes the HST deadband temperature (1 F or 2 F deadband or default 62 F HST) to fully open the damper. After step 758, the method proceeds to step 706. At step 706, the method provides economizer cooling with the damper fully open (or modulated during cold weather) using the HVAC fan without the first-stage DX AC compressor. If the thermostat call for cooling is not satisfied within a 2 to 60 minutes AND the CST increases by 3 F above the setpoint (or 2 F deadband above upper differential), then the thermostat second-stage cooling signal (Y2-I) is energized and the known prior art economizer controller will energize the first-stage signal (Y1) to energize the first-stage DX AC compressor. Energizing the first-stage signal (Y1) to operate the DX AC system (including the first-stage DX AC compressor and HVAC fan) will only happen if the economizer receives the thermostat second-stage cooling signal (Y2) signal.

(33) If step 705 is No (N), OAT is not less than or equal to the AC control temperature, then the method proceeds to step 707. At step 707, the FDD CDC method detects whether or not the OAT is greater than the ACT and the OAT is less than or equal to the HCT at the beginning of or during a call for cooling. Alternatively, at step 707, the FDD CDC method detects whether or not the OAT is less than or equal to the HST at the beginning of or during a thermostat call for cooling, and if Yes (Y).

(34) If step 707 is Yes (Y), then the FDD CDC method proceeds to step 755 and determines whether or not the thermostat second-stage cooling signal is energized. If step 755 is No (N), the thermostat second-stage cooling signal is not energized, then the FDD CDC method proceeds to 761 and corrects the HST fault (default or user-selected HST setting below the HST or the HCT) and/or supersedes the HST deadband delay and fully opens the damper to enable the economizer cooling otherwise precluded or delayed by the HST fault or the HST delay. After step 761, the FDD CDC method proceeds to step 718. If step 755 is Yes (Y), the method proceeds to step 757.

(35) At step 757, the FDD CDC method supersedes an economizer-second-stage time delay and proceeds to step 761. At step 761 the FDD CDC method corrects the default HST and/or supersedes the HST deadband (1 or 2 F HST deadband or default 62 F HST) which prevent the damper from fully opening. After step 761, the method proceeds to step 718.

(36) At step 718, the FDD CDC method corrects the at least one fault or supersedes the at least one delay selected from the group consisting of: an HST fault, an HST deadband delay, a thermostat second-stage time delay, a thermostat second-stage temperature deadband delay, an economizer second-stage time delay, and an economizer second-stage time temperature delay, wherein the at least one fault or at least one delay is used to determine when to energize the economizer cooling or at least one AC compressor (i.e., first-stage or second-stage). The correcting or superseding comprises: energizing an economizer actuator to move a damper to a fully open damper position for an HVAC fan to provide the economizer cooling and energizing at least one AC compressor selected from the group consisting of: a first-stage AC compressor (Y1), and a second-stage AC compressor (Y2) otherwise precluded or delayed by the at least one fault or the at least one delay.

(37) If step 707 is No (N), where the OAT is greater than the HCT, then the method proceeds to Step 708. At step 708, the FDD CDC method energizes the first-stage AC compressor and sets the damper to a minimum position to provide a minimum outdoor airflow to the conditioned space to satisfy the ASHRAE 62.1 minimum Indoor Air Quality (IAQ) requirements. Optionally, the FDD method may command the economizer actuator to modulate the damper position from a closed to fully open damper position based on a Demand Control Ventilation (DCV) control comparing a CO2 concentration measurement to an indoor air CO2 control threshold. The CO2 control threshold is typically 1200 ppm (per ASHRAE 62-2019, page 38 “maintaining a steady-state CO2 concentration in a space no greater than about 700 ppm above outdoor air levels will indicate that a substantial majority of visitors entering a space will be satisfied with respect to human bioeffluents (body odor). CO2 concentrations in acceptable outdoor air typically range from 300 to 500 ppm.” 1200 ppm CO2 threshold equals 700 ppm above the 500 ppm outdoor CO2 concentration). After step 708, the FDD CDC method proceeds to step 709.

(38) At step 709, the FDD CDC method determines whether or not the thermostat second-stage cooling signal is energized. If step 709 is No (N), the thermostat second-stage cooling signal is not energized, then the FDD CDC method proceeds to step 710 to check whether or not the damper position sensor indicates the dam per position is OK and at the correct position or stuck in a different position (see below). If step 709 is Yes (Y), the thermostat second-stage cooling signal is energized, then the FDD CDC method proceeds to step 759 and supersedes the economizer-second-stage time delay and for an HVAC system with two (or more) AC compressors (first-stage, second-stage, etc.). At step 759, for an HVAC system with two (or more) AC compressors (first-stage, second-stage, etc.), the FDD CDC method supersedes the economizer second-stage cooling signal time delay which prevents the thermostat second-stage cooling signal from energizing the 2nd-stage AC compressor (or higher stages). At step 759, the FDD CDC method may comprise superseding the second-stage cooling signal time delay by reducing the economizer second-stage cooling signal time delay, and in some instances, setting the economizer second-stage cooling signal time delay to zero.

(39) At step 710, the FDD CDC method checks if the damper position is okay and within +/−5% of the commanded position as determined by a magnetometer MEMS sensor checking if the dampers are in the correct position (within +/−5%)? If step 710 is Yes (Y), and the dampers are at the minimum position, the method proceeds to step 712 and continues to energize the AC compressor. If step 710 is No (N), where the magnetometer MEMS device indicates an incorrect damper position, then the method proceeds to step 728. If step 728 is Yes (Y), the dampers are in the closed position, then the method proceeds to step 734 to provide a FDD alarm “Fault: dampers not modulating.” From step 734, the method loops back to step 712 to continue economizer cooling. If step 728 is No (N), the magnetometer MEMS device indicates the dampers are not in a closed position, then the method proceeds to step 730.

(40) If step 730 is Yes (Y), the magnetometer MEMS device indicates the dampers are 100% open, then the method proceeds to step 732 and provides a FDD alarm “Fault: economizing when should not (see FIG. 3)” for maintenance, and proceeds to step 712 during the call for cooling. The FDD alarm in step 732 is discussed in FIG. 3. If step 730 is No (N), the dampers are not 100% open the method proceeds to step 736. If step 736 is No (N), the dampers did not move, then the method proceeds to step 734 and provides a FDD alarm “Fault: dampers not modulating (see FIG. 3)” and proceeds to step 712 during a call for cooling. The FDD alarm in step 734 is discussed in FIG. 3. If step 736 is Yes (Y), the method proceeds to step 740.

(41) If step 740 is No (N), the damper position is not at the minimum OAF position, then method proceeds to step 742. If step 742 is Yes (Y), the damper position is greater then the minimum position, then the method proceeds to step 744 and provides a FDD alarm “Fault: excessive outdoor air” entering the conditioned space for maintenance, and proceeds to step 750 to the OAF economizer calibration method FIG. 3 to correct this fault in the future when the thermostat is not calling for cooling. During a current thermostat call for cooling, the FDD method proceeds from step 744 to step 712 to continue the cooling process. If step 740 is Yes (Y), the method proceeds to step 748 “Go to HVAC FDD method” (FIG. 4) and loops back to step 702 to continue “thermostat call for cooling.” With the AC compressor(s) on and damper in minimum position, the dam. If step 742 is No (N), the damper position not greater than the minimum OAF damper position, then the method proceeds to step 746 to provide a FDD alarm “Fault: inadequate outdoor air” for maintenance, proceeds to step 750 to the OAF economizer calibration method FIG. 3 to correct this fault and proceeds to step 702 to continue “thermostat call for cooling.” During a current call for cooling, the FDD method may also proceed from step 746 to step 712 (skips previous FDD steps already performed) to continue energizing the first-stage cooling signal Y1 to energize the AC system (including the first-stage DX AC compressor and HVAC fan). If the thermostat second-stage cooling signal (Y2) is active, then the method energizes the second-stage cooling signal Y2 (to energize the second-stage AC compressor and second-stage cooling fan-motor speed, if applicable) and the method proceeds to step 714.

(42) If step 714 is No (N), where OAT and OA RH are not too high (i.e., OAT greater than 105 to 115 F or OA RH greater than 80 to 90%), then the method loops back to 702 to continue cooling until the thermostat call for cooling is satisfied. If step 714 is Yes (Y), then the method goes to step 711 and provides a: “FDD alarm or warning message OAT, outdoor air relative humidity, or outdoor air enthalpy greater than the outdoor air high-limit threshold” and the method proceeds to 713. At step 713, the method closes the dampers by overriding the economizer actuator voltage control signal based on a geofencing or an occupancy sensor signal (OCC). Closing the economizer dampers during hot weather improves comfort, reduces energy use, and meets the 10% minimum outdoor airflow requirements specified for most building occupancies in the ASHRAE 61.1-2019 Standard Ventilation for Acceptable Indoor Air Quality (discussed above). After step 713, the method proceeds to step 715. The method for method for sealing the economizer perimeter gap is shown in FIG. 17.

(43) At step 715, the FDD method checks if the SAT is too warm (i.e., above 65 F) based on monitoring the SAT using the temperature sensor 32 shown in FIG. 1 and FIG. 2. If step 715 is No (N) the SAT is not too warm indicating the DX AC compressor is able to meet the SAT temperature requirement, then the method loops back to 701 to continue cooling until the thermostat call for cooling is satisfied. If step 715 is Yes (Y), then the method proceeds to step 748 to go to the FDD Evaluation Method FIG. 4 to determine if another cooling fault is causing the SAT to be too warm. The FDD Evaluation Method is performed in real-time and will provide maintenance personnel with FDD alarms if the sensors are okay in step 716.

(44) After step 718 (FDD CDC fully opens economizer with HVAC fan and AC compressor(s)) or after step 706 (economizer cooling with the HVAC fan), the method continues to step 720. At step 720, the magnetometer MEMS sensor checks if the economizer damper is fully open or modulating? If step 720 is No (N), then the FDD CDC method proceeds to step 724 and provides a FDD alarm “Fault: not FDD CDC or economizing when should.” The method then loops back to step 722 to continue the economizer or FDD CDC method with whatever damper position is provided.

(45) If step 720 is Yes (Y), the magnetometer MEMS sensor shows dampers are fully open or modulating properly, then the FDD CDC method proceeds to step 722.

(46) If step 722 is Yes (Y), the OAT is less than the RAT or the HCT and the OAT is greater than the LEST or VEST and the thermostat first-stage cooling signal (Y1) is active with no thermostat second-stage cooling signal (Y2), then the FDD CDC method loops back to step 701 and continues to provide FDD CDC until the thermostat call for cooling is satisfied (i.e., no thermostat Y1 or Y2 signals).

(47) If step 722 is No (N), the OAT is greater than RAT or the economizer controller receives a thermostat second-stage cooling signal (Y2) where the CST is 2 F (default) above the first-stage thermostat differential (3 F above the setpoint) AND the timer from 2 to 60 minutes has been reached, then the method proceeds to step 712 to energize or continue to energize the first-stage (or second-stage) AC compressor cooling and the FDD cooling delay correction method proceeds to step 714.

(48) In some embodiments, the method includes providing FDD alarms regarding faults. In some embodiments the method communicates FDD alarms using wired or wireless communication to display fault codes or alarms on the present invention apparatus through a built-in display or external display through wired or wireless communication signals to a building energy management system, standard thermostat, WIFI-enabled thermostat, internet-connected computer, internet telephony system, or smart phone indicating maintenance requirements to check and correct damper position, evaporator airflow and/or refrigerant charge of the air conditioning system.

(49) FIG. 2 shows the heating economizer damper position FDD method using a magnetometer or other MEMS device to measure the physical position of the dampers and determine if there is a fault with the economizer damper positioning mechanism. The FDD process involves positioning the dampers to a fully closed position, intermediate position, and fully open damper position and the MEMS device is sampled to measure and store these positions. As the dampers modulate between the fully closed and fully open positions, the MEMS device provides an angular value and the physical position of the dampers can be calculated.

(50) Step 600 is the start of the heating economizer damper position FDD method. In step 601, the method checks if the fan-on setting is enabled. If step 601 is Yes (Y), then the method proceeds to step 653 to Go to FIG. 4 FDD HVAC Methods. If step 601 is No (N), then the method proceeds to step 602 to check if there is a thermostat a call for cooling. If step 602 is No (N), the thermostat call for heating has ended, then the method proceeds to step 652 and after a thermostat call for heating, the method provides a variable fan-off delay based on HVAC parameters where at least one HVAC parameter includes operating the fan for a variable fan-off delay after a heating cycle based on the absolute value of the air temperature difference between the SAT and the MAT wherein the MAT is based on a mixture of outdoor air and return air. At step 602, if Yes (Y), there is a thermostat call for heating, then the method proceeds to step 603.

(51) Step 603 determines if the air temperature, RH, CO2 sensors, and the magnetometer MEMS device within expected tolerances or failed/faulted. Step 603 continuously monitors the OAT, MAT, RAT, RH, and CO2, and computes the OAF based on air temperature, RH, or CO2 measurements.

(52) If step 603 is No (N), then the method proceeds to step 616 to flag this fault and provide a FDD alarm “Fault: air temperature, RH, or CO2 sensor failure/fault” for sensors not working. If the OAT and RAT sensors are okay, then the FDD method proceeds to step 604. Otherwise, if the OAT and RAT sensors are faulted and the economizer controller cannot work properly, then the FDD method continues to step 606 to energize the heating system.

(53) If step 603 is Yes (Y), then the method proceeds to continuously monitor the OAT, MAT, and RAT air temperature, RH, and CO2 sensors, and compute the OAF based on sensor measurements of air temperature, RH, and CO2 concentration.

(54) In step 606, the method energizes the heating system and the method proceeds to step 608. In step 608, the economizer positions the dampers to the minimum position to provide a minimum amount of outdoor air to the conditioned space to satisfy the ASHRAE 62.1 minimum IAQ requirements or Demand Control Ventilation (DCV) based on carbon dioxide thresholds (typically ˜1000 ppm per ASHRAE 62.1-2019). The method then proceeds to step 610.

(55) Step 610 uses the magnetometer MEMS device to determine if the actuator responded by positioning the damper to the correct minimum position. This will be indicated by the MEMS device providing an angular reading that the dampers have been positioned to the minimum position. If the dampers are at the minimum position, the method proceeds to step 612 and heating continues to be enabled. If the MEMS device indicates an incorrect damper position, then the method proceeds to step 628.

(56) If step 628 is (Y) the dampers are in the closed position, the method proceeds to step 634 and the economizer provides a FDD alarm “Fault: dampers not modulating.” If step 628 is No (N), the dampers are not in a closed position, then the method proceeds to step 630. If step 630 is Yes (Y), the dampers are 100% open, the method proceeds to step 632 and provides a FDD alarm “Fault: economizing when should not.”

(57) If step 630 is No (N), the dampers are not 100% open, then the method proceeds to step 636. If step 636 is No (N), the dampers did not move, then the method proceeds to step 634 and the economizer provides a FDD alarm “Fault: dampers not modulating.” If step 636 is Yes (Y), the dampers move, then the method proceeds to step 640. If step 640 is Yes (Y), the dampers are the minimum position, then the method proceeds to step 648 to go to the FDD evaluation method FIG. 4.

(58) If step 640 is No (N), the dampers are not at the minimum position, then method proceeds to step 642. If step 642 is Yes (Y), the damper position is greater then the minimum position, then the method proceeds to step 644 and provides a FDD alarm “Fault: excessive outdoor air” entering the conditioned space and proceeds to step 650 to go to the OAF economizer calibration method FIG. 3 to correct this fault. If step 642 is No (N), the dampers are less than the minimum position, then the method proceeds to step 646 and provides a FDD alarm “Fault: inadequate outdoor air” and proceeds to step 650 and to FIG. 3 of the OAF economizer calibration method to correct this fault.

(59) After step 610 the method proceeds to step 612 to enable or continue enabling the heating element and proceeds to step 614. If step 614 is Yes (Y) the economizer low limit setpoint OAT is too low during heating (OAT less than −20 F to 32 F), then the method goes to step 611 and provides a: “FDD alarm or warning: OAT less than the outdoor air low-limit threshold” and the method proceeds to 613 to close the dampers by overriding the actuator voltage control signal based on a geofencing or occupancy sensor signal (OCC). If step 614 is No (N), the method returns to step 602.

(60) At step 613, the microprocessor overrides the economizer actuator voltage control signal based on a geofencing or occupancy sensor signal (OCC) and closes the dampers. The method closes the economizer dampers to reduce excess outdoor airflow from entering the mixed air chamber to satisfy the thermostat call for heating and save energy. After step 613, the method proceeds to step 615.

(61) If step 615 is Yes (Y), the SAT is too cool (i.e., below 105 F or Temperature Rise [TR] less than 30 F), then the method proceeds to step 648 to go to the FDD Evaluation Method FIG. 4 to determine if another heating fault is present. If step 615 is No (N), the SAT is above hot (i.e., above 105 F or TR greater than 30 F) and the heating system is able to meet the SAT minimum requirement, then the method loops back to 602 to continue heating until the thermostat call for heating is satisfied.

(62) FIG. 3 shows an OAF economizer controller calibration method for an HVAC system with the HVAC fan-on during occupied or unoccupied periods according to the present invention. The OAF economizer calibration method starts at step 100. At step 101, the method comprises sealing the economizer perimeter gap 785 (see FIG. 17), if necessary. Known prior art economizer calibration methods do not seal the economizer perimeter gap 785 which allows unintended, uncontrolled, and unconditioned outdoor airflow to enter the economizer, HVAC system, and conditioned space whether or not the ventilation fan is operating. FIG. 17 shows the economizer hood 787 must be removed in order to properly seal the economizer perimeter gap 785. Sealing around the perimeter gap of the economizer frame where it connects to the HVAC system cabinet is performed with at least one sealant selected from the group consisting of: adhesive tape sealant, adhesive sealant, mastic sealant, or weatherstripping to reduce untended outdoor air leakage through the economizer perimeter frame to prevent unintended outdoor airflow during the off cycle or during the cooling or heating cycle. Sealing the economizer perimeter gap 785 includes sealing the metal surfaces between the economizer frame and the HVAC system cabinet 780 to reduce unintended outdoor airflow and increase cooling and heating efficiency by about 5 to 10% during severe hot or cold weather when the economizer dampers are closed or at minimum position during operation of the DX AC compressor(s). After the economizer perimeter gap is sealed, the OAF economizer calibration method proceeds to step 102 to calibrate the economizer damper position as a function of actuator voltage.

(63) At step 102 of FIG. 3 with the fan-on, the OAF calibration method monitors and stores the economizer actuator voltage “x.sub.i”, and the OAT (or t.sub.o), the Return Air Temperature (RAT) (or t.sub.r), the MAT (or t.sub.m), and compute the initial OAF (y) at step 102 using the following general OAF equation.

(64) $\begin{matrix} OAF = \frac{t_{r} - t_{m}}{t_{r} - t_{o}} & Eq . 1 \end{matrix}$

(65) Where, OAF=outdoor airflow fraction (dimensionless), and

(66) t.sub.m=mixed-air drybulb temperature or MAT (F).

(67) At step 102, if the economizer actuator voltage (x) is at the fully open, closed, or intermediate damper position or the method is looping back to step 102 from a previous OAF calibration, then one (or more) measurement steps may be skipped (i.e., from the previous OAF calibration).

(68) At step 103, the method checks if the absolute value of the OAT minus RAT |ΔT| is greater than a minimum temperature difference, preferably 10 F, and increasing to allow time to complete the calibration method, according to the following equation.
|ΔT|=|t.sub.o−t.sub.r|≥t.sub.min Eq. 3
Where, |ΔT|=absolute value of the OAT minus RAT (F),

(69) t.sub.o=outdoor-air drybulb temperature or OAT (F),

(70) t.sub.r=return-air drybulb temperature or RAT (F), and

(71) T.sub.min=the minimum temperature (preferrably 10 F) to obtain an accurate measurement of the OAF within a tolerance of +/−5% of the desired OAF.

(72) If the absolute value of |ΔT| is not greater than T.sub.min, then the method loops back to step 102. The OAF calibration steps for the fully open, closed, or intermediate damper positions shown in FIG. 3 may be performed in a different order. For example, the intermediate OAF.sub.i may be measured during a call for cooling or heating when the damper is in the minimum position and |ΔT|≥T.sub.min. After the call for cooling or heating, the closed OAF.sub.closed may be measured, and later during an unoccupied period the fully open OAF.sub.max may be measured.

(73) At step 103, if the |ΔT|≥T.sub.min, then the method proceeds to step 105 and energizes the actuator to the maximum actuator voltage, x.sub.max (typically 10V), to fully open the damper. The method proceeds to step 106 and waits for a minimum wait time (t.sub.min) for sensors to reach equilibrium. The minimum wait time (t.sub.min) may comprise waiting preferrably 5 to 10 minutes depending on sensor measurement stability. The method then proceeds to step 107 to check if the |ΔT| is greater than or equal to a minimum temperature difference |ΔT|≥T.sub.min? The minimum temperature difference is preferrably 10 F. If step 107 is No (N), then the method loops back to step 102, and returns to step 105 to finish calibration when |ΔT|≥10 F. If step 107 is Yes (Y), then the method proceeds to step 108 to measure and store the maximum actuator voltage, x.sub.max, and calculate the OAF.sub.max (y.sub.max) based on OAT (t.sub.o), RAT (t.sub.r), and MAT (t.sub.m) using the general OAF equation.

(74) The method then proceeds to step 110 to energize the economizer actuator to the closed damper position, x.sub.closed (2V). The method proceeds to step 111 and waits for a minimum wait time (t.sub.min) for sensors to reach equilibrium (to measure the OAT, RAT, and MAT), and proceeds to step 112 to check if the |ΔT| is greater than or equal to the minimum temperature difference (|ΔT|≥T.sub.min)? If step 112 is No (N), then the method loops back to step 102, and skips to step 110 to finish calibration. If step 112 is Yes (Y), then the method proceeds to step 113 to measure and store the closed actuator voltage, x.sub.max, and calculate the OAF.sub.closed (y.sub.closed) based on OAT (t.sub.o), RAT (t.sub.r), and MAT (t.sub.m).

(75) The method proceeds to step 115 to energize the economizer actuator to the intermediate damper position, x.sub.min (typically 2.8V or 2V plus 10% of the 2 to 10V range). The method proceeds to step 116 and waits for a minimum wait time (t.sub.min) for sensors to reach equilibrium (to measure the OAT, RAT, and MAT), and proceeds to step 117 to check if the |ΔT|≥T.sub.min? If step 117 is No (N), then the method loops back to step 102, and returns to step 115 to finish calibration. If step 117 is Yes (Y), then the method proceeds to step 118 to measure and store the intermediate actuator voltage, x.sub.i, and calculate the OAF.sub.i(y.sub.i) based on OAT (t.sub.o), RAT (t.sub.r), and MAT (t.sub.m).

(76) The method proceeds from step 118 to step 120 to check if the intermediate damper position OAF.sub.i is within the tolerance (typically +/−5%). If No (N), the method proceeds to step 122 to adjust the intermediate damper position (x.sub.i) with respect to the required OAF.sub.i and returns to step 115. If step 120 is Yes (Y), then the method proceeds to step 123 to calibrate the functional relationship between economizer control voltage, x.sub.i, and the corresponding damper position OAF.sub.i (y.sub.i), and precedes to step 124 (described below) and to step 126. At step 126, the method checks HVAC FDD? If step 126 is Yes (Y), the method proceeds to step 129 and goes to FIG. 4 “HVAC FDD methods” or goes to FIG. 1 to perform the FDD Cooling Delay Correction (CDC) method or goes to FIG. 2 to enable the heating economizer damper position FDD method. If step 126 is No (N), OAF calibration method ends.

(77) At step 123, the method determines a functional relationship between the economizer control voltage “x.sub.i” and corresponding damper position OAF.sub.i “y.sub.i” using a least squares regression equation method involving partial derivatives to minimize residuals for each ordered pair of the set of “y-versus-x” data using the following equations (also shown in FIG. 6).
y.sub.i=ax.sub.i.sup.2+bx.sub.i+c Eq. 7
Where, y.sub.i=OAF.sub.i based on the corresponding damper position (dimensionless),

(78) x.sub.i=the economizer actuator voltage from 2V closed to 10V fully open,

(79) a=regression coefficient,

(80) b=regression coefficient, and

(81) c=regression coefficient.

(82) The regression equation coefficients are calculated using the following matrix equations and measurements of the economizer actuator voltage “x” and the corresponding damper position OAF “y” for at least two damper positions, and preferably for at least three damper positions selected from the group consisting of: a closed damper position, at least one intermediate damper position, and a fully open damper position.

(83) $\begin{matrix} \underset{X}{\underset{︸}{[\begin{matrix} Σ x_{i}^{4} & Σ x_{i}^{3} & Σ x_{i}^{2} \\ Σ x_{i}^{3} & Σ x_{i}^{2} & Σ x_{i}^{} \\ Σ x_{i}^{2} & Σ x_{i}^{} & n \end{matrix}]}} \underset{\underset{C}{︸}}{[\begin{matrix} a \\ b \\ c \end{matrix}]} = \underset{\underset{Y}{︸}}{[\begin{matrix} Σ x_{i}^{2} y_{i} \\ Σ x_{i}^{} y_{i} \\ Σ y_{i}^{} \end{matrix}]} & Eq . 9 \end{matrix}$
Where, matrix X=the economizer actuator voltages in a 3×3 matrix X containing exactly one “n” element (x33), n−1 summations of x-values (x23 and x32), n summations of x-values to the power n−1 (x13, x22, x31), n−1 summations of x-values to the power n (x12, x21), and exactly one summation of x-values to the power n+1 (x11),

(84) matrix C=the coefficients of a quadratic regression equation in a 1×3 coefficient-matrix C containing coefficients “a” (c11), “b” (c12), and “c” (c13), and

(85) matrix Y=the corresponding damper position OAF measurements in a 3×1 matrix Y containing one summation of y-values (y31), one summation of x-values times y-values (y21), and one summation of x-values to the power n−1 times y-values (y11).

(86) The method includes solving the above equation by multiplying the 3×3 inverse-matrix X times the 3×1 matrix Y and obtaining the 3×1 regression equation coefficient-matrix C using the following equation.
C=X.sup.−1Y Eq. 11
Where, X.sup.−1=3×3 inverse-matrix X of the 3×3 matrix X calculated according to the following equation,

(87) C=3×1 (3 rows and 1 column) coefficient-matrix C containing coefficients, “a” (c11), “b” (c12), and “c” (c13) of the quadratic regression equation, and

(88) Y=3×1 matrix Y noted in the above equation.

(89) The method includes solving the inverse of the 3×3 matrix X using the following equations.

(90) $\begin{matrix} X = [\begin{matrix} h & k & n \\ i & l & o \\ j & m & o \end{matrix}] X^{- 1} = \frac{1}{\det X} [\begin{matrix} lb - om & nm - kp & ko - nl \\ oj - ip & hp - ni & ni - ho \\ im - lj & kj - hm & hi - ki \end{matrix}] & Eg . 13 \\ X^{- 1} = \frac{1}{\det X} [\begin{matrix} lb - om & nm - kp & ko - nl \\ oj - ip & hp - ni & ni - ho \\ im - lj & kj - hm & hl - ki \end{matrix}] & Eq . 15 \\ \frac{1}{\det X} = \frac{1}{hlp - imn + jko - hmo - jln - ikp} & Eq . 17 \end{matrix}$
Where, detX=determinant of matrix X which cannot equal zero.
After calculating the 3×1 coefficient-matrix C coefficients “a” (c11), “b” (c12), and “c” (c13), using the above equations, the method includes calculating the required intermediate economizer actuator voltage, “x.sub.r”, equal to a first quantity (minus “b”) plus a second quantity (square root of a third quantity (“b” squared) minus a fourth quantity (4 times “a”) times a fifth quantity (“c” minus the required intermediate damper position “OAF.sub.r”)) where the first quantity is divided by a sixth quantity (2 times “a”) according to the following equation. In Eq. 19, the variables “OAF.sub.r” (or “y.sub.r”) may be substituted with the variables “OAF” (or “y”) using any numerical value from 0 to 1.0 providing functional values of “x” that can range from the minimum to the maximum economizer control voltage “x.”

(91) $\begin{matrix} X_{r} = \frac{- b + \sqrt{b^{2} - 4 a (c - {OAF}_{r})}}{2 a} & Eq . 19 \end{matrix}$
Where, x.sub.r=the required intermediate economizer actuator voltage x.sub.r corresponding to the required intermediate damper position OAF.sub.r, and

(92) OAF.sub.r=the required intermediate damper position OAF.sub.r for the building occupancy.

(93) At step 124 of FIG. 3, the method stores the coefficients “a” (c11), “b” (c12), and “c” (c13) used to calibrate the economizer controller and obtain the functional relationship between the economizer actuator voltage, “x.sub.i”, and the corresponding damper position OAF “y.sub.i”. At step 124, the method may also store the economizer actuator voltage, “x.sub.i”, corresponding damper position “OAF.sub.i”, the required damper position “OAF.sub.r”, the fully open maximum OAF.sub.max, and the closed OAF.sub.closed, OAT (t.sub.o), RAT (t.sub.r), and MAT (t.sub.m). The method may also use outdoor, return, and mixed-air, wetbulb, relative humidity, or CO2 measurements. The method can also loop back to step 100 and measure OAT (t.sub.o), RAT, (t.sub.r), and MAT (t.sub.m), and compute a final intermediate damper position “OAF.sub.i” in step 120, and check whether or not the “OAF.sub.i” is within an acceptable tolerance of preferably +/−5% of OAF.sub.r in step 120.

(94) The OAF calibration method shown in FIG. 3 may be implemented manually or automatically on units with an analog economizer controller with temperature sensors and economizer actuator voltage output signals. The method may also be implemented on units with a digital economizer controller with FDD capabilities, temperature sensors, and economizer actuator voltage output signals. The method comprises: calibrating the economizer controller for the HVAC system by determining a functional relationship between an economizer actuator voltage “x” and a corresponding damper position Outdoor Airflow Fraction (OAF) “y” comprising: measuring the economizer actuator voltage “x” and the corresponding damper position OAF “y” to obtain a set of “y-versus-x” data for at least two damper positions, and preferably for at least three damper positions selected from the group consisting of: a closed damper position, at least one intermediate damper position, and a fully open damper position; and calculating coefficients of the functional relationship between the economizer actuator voltage “x” and the corresponding damper position OAF using the set of “y-versus-x” data; and calculating an intermediate economizer actuator voltage, “x.sub.i”, based on the corresponding intermediate damper position OAF “y.sub.i” (also referred to as“OAF.sub.i”).

(95) The method for calculating coefficients of the functional relationship may also comprise calculating coefficients of the functional relationship between the economizer actuator voltage “x” and the corresponding damper position OAF “y” by fitting an Nth order function to N+1 points, for example, using at least a first order line fit to a set of two “y-versus-x” data points, but preferably using at least a second-order line fit to a set of three “y-versus-x” data points to calculate the economizer actuator voltage, “x”, based on the second-order line fit and the corresponding damper position OAF “y.”

(96) The FDD method may comprise calculating coefficients of the functional relationship between the economizer actuator voltage “x” and the corresponding damper position OAF “y”, by fitting an Nth order function to N+1 or more points, using a least squares regression equation method. The least squares regression equation method uses partial derivatives to minimize residuals for each ordered pair of the set of “y-versus-x” data by expressing the least squares regression equation method in matrix form, comprising: forming a 3×3 matrix X containing exactly one “n” element (x33), n−1 summations of x-values (x23 and x32), n summations of x-values to a power n−1 (x13, x22, x31), n−1 summations of x-values to a power n (x12, x21), and exactly one summation of x-values to a power n+1 (x11); inverting the 3×3 matrix X to obtain a 3×3 inverse-matrix X; forming a 3×1 matrix Y containing one summation of y-values (y31), one summation of x-values times y-values (y21), and one summation of x-values to the power n−1 times y-values (y11); multiplying the 3×3 inverse-matrix X times the 3×1 matrix Y and obtaining a 3×1 regression equation coefficient-matrix C containing coefficients “a” (c11), “b” (c12), and “c” (c13); calculating the intermediate economizer actuator voltage, “x.sub.i”, based on a quadratic formula using coefficients “a” (c11), “b” (c12), and “c” (c13) and the intermediate damper position OAF “y.sub.i” (or “OAF.sub.i”) is subtracted from the coefficient “c” (c13).

(97) The economizer calibration method also comprises: measuring the economizer actuator voltage “x” and the corresponding damper position OAF “y” when an absolute value of a difference between the OAT and RAT is at least 10 F, where the damper position OAF is defined as a ratio of an outdoor air volumetric flow rate divided by a total HVAC system volumetric flow rate.

(98) The measurement of the intermediate damper position OAF “y.sub.i” is preferably made with the economizer actuator voltage “x” close to the middle of the economizer actuator voltage range.

(99) The economizer calibration method also comprises: measuring the set of “y-versus-x” data for the at least three damper positions and at least one fan-motor speed used by the HVAC system selected from the group consisting of: at least one fan-motor speed for the HVAC fan operating without heating or cooling, a first-stage cooling fan-motor speed, a second-stage cooling fan-motor speed, a first-stage heating fan-motor speed, a second-stage heating fan-motor speed, and a representative set of fan-motor speeds for a variable-speed fan-motor.

(100) The method may optionally comprise calculating the relative humidity (RH) or Carbon Dioxide (CO2) concentration (ppm) in the return air, mixed air, and outdoor air. The method may also comprise calculating humidity ratios (lbm/lbm) of return-air W.sub.r, outdoor-air, W.sub.o and mixed-air W.sub.m using the Hyland Wexler formulas from the 2013 ASHRAE Handbook. The method may also comprise calculating the saturation humidity ratio (W*.sub.m) from the saturation pressure (p.sub.ws).

(101) FIG. 4 shows a method for performing a FDD evaluation on an HVAC system while the HVAC system is operating. The method starts at step 130 and proceeds to step 131. If Step 131 is Yes (Y), a fan-on setting is operating, then the method proceeds to step 132 to check if the conditioned space is occupied based on a geofencing signal or an occupancy sensor signal. If step 132 is Yes (Y), then the method proceeds to step 136 to check the thermostat call for cooling. If step 132 is No (N), conditioned space is not occupied, then the method proceeds to step 133 to provide a “FDD alarm fan-on continuously fault or fan-on intermittently fault.” After step 133, the method proceeds to step 134 to determine whether or not to “override” the fan-on setting? If step 134 is No (N), the method loops back to step 136 to check the thermostat call for cooling. If step 134 is Yes (Y), override the fan-on setting, then the method proceeds to step 135 and overrides the fan-on setting. After step 134, the FDD method proceeds to step 185 to Go to FIG. 1 step 700 to continue the thermostat call for cooling for the FDD CDC method (including known economizer or DX AC cooling).

(102) If step 131 is No (N), the fan-on setting is not operating, then the method proceeds to Step 136 and checks whether or not the HVAC system is in cooling or heating mode. If in cooling mode, the method includes detecting and diagnosing low airflow and low cooling capacity faults in steps 138 through 185. In some embodiments in cooling mode, the method includes performing FDD of refrigerant superheat based on t*.sub.m and t.sub.o in steps 138 through 185. If in heating mode, the method includes FDD for low heating capacity and fan-on faults in steps 154 through 182.

(103) At step 138 of FIG. 4, the FDD method checks if the cooling system has operated for a minimum operating time (at least 5 minutes). If step 138 is Yes (Y), the cooling system is on for 5 minutes, then the method proceeds to step 144 (skip to next paragraph). If step 138 is No (N), then the method continues to step 139 to check for if the number of thermostat short-cycle cooling events is greater than N1 where N1 is based on at least one number of cooling short-cycles selected from the group consisting of: user-selected number of cooling short-cycles from 2 to 10, a number of cooling short-cycles based on the OAT, a number of cooling short-cycles based on a cooling capacity of the AC compressor, a number based on the cooling cycle duration.

(104) If step 139 of FIG. 4 is Yes (Y), the number of thermostat short-cycle cooling events is greater than N1, then the method proceeds to step 142 to provide an FDD alarm cooling short cycle fault, and proceeds to step 185 to Go to FIG. 1 step 700 to continue the thermostat call for cooling for the FDD CDC method. If step 139 is No (N), the number of thermostat short-cycle cooling events is not greater than N1, then the method proceeds to step 185 to Go to FIG. 1 for the FDD CDC method.

(105) At step 144 of FIG. 4, the method includes calculating the actual Temperature Split (TS) difference (dT.sub.a) based on the mixed-air drybulb temperature (t.sub.m) minus the supply-air temperature (t.sub.s) according to the following equation.
δT.sub.a=t.sub.m−t.sub.s Eq. 21

(106) At step 144, the method comprises calculating the target TS difference (dT.sub.t) across the cooling system evaporator and the delta TS difference (TS) defined as the actual TS minus the target TS. The method comprises calculating the target TS difference (dT.sub.t) using a target TS lookup table, where the independent variables are the evaporator entering mixed-air drybulb temperature, t.sub.m, and evaporator entering mixed-air wetbulb temperature, t*.sub.m. The method also comprises calculating the target TS difference (dT.sub.t) using the following equation.
dT.sub.t=C.sub.7+C.sub.8t.sub.m+C.sub.9t.sub.m.sup.2+C.sub.10t*.sub.m+C.sub.11t*.sub.m.sup.2+C.sub.12(t.sub.m×t*.sub.m) Eq. 23
Where, dT.sub.t=target temperature difference between mixed-air and supply-air in cooling mode (F),

(107) t.sub.m=measured mixed-air drybulb temperature (F),

(108) t*.sub.m=mixed-air wetbulb temperature (F),

(109) C.sub.7=−6.509848526 (F),

(110) C.sub.8=−0.942072257 (F.sup.−1),

(111) C.sub.9=0.009925115 (F.sup.−2),

(112) C.sub.10=1.944471104 (F.sup.−1),

(113) C.sub.11=−0.0208034037991888 (F.sup.−2)

(114) C.sub.12=−0.000114841 (F.sup.−2)

(115) At step 144, the method also includes calculating the delta TS difference (TS) based on the actual TS difference (dT.sub.a) minus the target TS difference (dT.sub.t) using the following equation.
DTS=dT.sub.a−dT.sub.t Eq. 25
Where, DTS=delta TS difference between actual TS and target TS (F).

(116) At step 146 the method checks whether or not the delta TS difference is within plus or minus of the delta TS threshold, preferably ±3 F (or a user input value). If the delta TS difference is within plus or minus of the delta TS threshold (or the user input value), then the cooling system is within tolerances, no FDD alarm signals are generated, and the method proceeds to step 148 to check if the delta TS difference is less than −3 F.

(117) If step 148 is No (N), then the method determines the TS>3 F indicating low airflow, then the method continues to step 150 and reports an FDD alarm fault: “low airflow” which can cause ice to form on the air filter and evaporator and block airflow and severely reduce cooling capacity and efficiency. The method then proceeds to step 185, Go to FIG. 1 step 700 and continue the call for cooling for the FDD CDC method.

(118) If step 148 is Yes (Y), the delta TS difference (TS) is less than a negative minimum delta TS difference threshold (preferably less than −3 F or a user input value), then the method proceeds to step 152 and provides a FDD alarm fault: “low cooling capacity” which can be caused by many faults including excess outdoor airflow, dirty or blocked air filters, blocked evaporator caused by dirt or ice buildup, blocked condenser coils caused by dirt or debris buildup, low refrigerant charge, high refrigerant charge, refrigerant restrictions, or non-condensable air or water vapor in the refrigerant system.

(119) After step 152, the method proceeds to step 185, Go to FIG. 1 step 700 and continue the thermostat call for cooling for the FDD CDC method.

(120) If step 146 is no, then the method proceeds to step 140 to check if the AC compressor is turning off before satisfying the thermostat call for cooling. If step 140 is Yes (Y), then the method proceeds to step 141 to override the thermostat call for cooling and turn off the cooling system by de-energizing the cooling signal to the AC compressor. Step 140 can be determined based on the Temperature Split (TS) between the MAT and RAT. If the TS is decreasing during the call for cooling, then the method will detect the AC compressor is turning off before satisfying the thermostat. The FDD method can also use a wired or wireless signal to detect the AC compressor contactor signal being de-energized by the control board during the call for cooling indicating a short-cycle fault. After step 141, the FDD method proceeds to step 142 and generates a FDD alarm reporting a “cooling short-cycle” fault via display, text, email, or other message. If step 140 is No (N), then the method loops back to step 138.

(121) The FDD method for heating starts when step 136 is No (N), the thermostat is not calling for cooling, and then the method proceeds to step 137 to check if the thermostat is calling for heating. If step 137 is No (N), then the method loops back to step 132 to check the fan-on setting? If step 137 is Yes (Y), the thermostat is calling for heating, then the method proceeds to step 154.

(122) At step 154 of FIG. 4, the FDD method checks if the heating system has operated for a minimum heating operating time (at least 5 minutes). If step 154 is No (N), then the method continues to step 155 to check for if the number of thermostat short-cycle heating events is greater than N1 where N1 is based on at least one number of heating short-cycles selected from the group consisting of: user-selected number from 2 to 10, a number based on the OAT, a number based on a heating capacity, a number based on the heating cycle duration. If step 155 is Yes (Y), the number of thermostat short-cycle cooling events is greater than N1, then the method proceeds to step 158 to provide an FDD alarm heating short cycle fault. If step 155 is No (N), the number of thermostat short-cycle heating events is not greater than N1, then the method loops back to step 183 to Go to FIG. 2 step 600 to continue the thermostat call for heating.

(123) Step 156 and checks for a heating short-cycle (i.e., successive short-cycle heating operation) or detecting heating system turning off before satisfying the thermostat call for heating. Step 156 can be determined based on the Temperature Rise (TR) between the SAT and the MAT. If the TR is decreasing during the thermostat call for heating, then the FDD method will detect the heating system is turning off before satisfying the thermostat. The FDD method can also use a wired or wireless electrical signal to detect the burner signal for a gas furnace or heat pump compressor signal being de-energized by the control board during the call for heating indicating a short-cycle fault. If step 156 is Yes (Y), then the method proceeds to step 157 to override the call for heating and turn off the heating system by de-energizing the signal to the heat source. After step 157, the FDD method proceeds to step 158 and generates a FDD alarm reporting a heating short cycle fault via display, text, email, or other message. If step 156 is No (N), then the method loops back to 154 and checks if the heating system has been operating for greater then a minimum run time, preferably ten minutes.

(124) After at least the minimum heater run time of the heating system operation at Step 160, the method includes calculating the actual temperature rise (dTR.sub.a) for heating based on the supply-air temperature minus the mixed-air temperature according to the following equation.
δTR.sub.B=t.sub.s−t.sub.m Eq. 27

(125) At step 162, the method includes checking whether or not the heating system is a gas furnace, and if the method determines the heating system is a gas furnace, then the method proceeds to step 164.

(126) At step 164, the method includes calculating the minimum acceptable target supply-air temperature rise for a gas furnace which is preferably a function of airflow and heating capacity based on furnace manufacturer temperature rise data, and is preferably 30 F as shown in the following equation.
δTR.sub.t.sub.furnace=30 Eq. 31

(127) Where, δTR.sub.t.sub.furnace=minimum acceptable furnace temperature rise.

(128) The minimum acceptable furnace temperature rise may vary from 30 to 100 F or more depending on make and model, furnace heating capacity, airflow, and return temperature.

(129) At step 164, the method also includes calculating the delta temperature rise for the gas furnace heating system, DTR.sub.furnace, according to the following equation.
ΔTR.sub.furnace=δT.sub.a−δTR.sub.t.sub.furnace Eq. 33

(130) At step 170 the method includes calculating whether or not the delta temperature rise for the furnace is greater than or equal to 0 F according to the following equation.
ΔTR.sub.furnace=δT.sub.a=δTR.sub.t.sub.furnace≥0 Eq. 35

(131) At step 170, if the method determines the delta temperature rise for the furnace is greater than or equal to 0 F, then the gas furnace heating system is considered to be within tolerances, no FDD alarm signals are generated, and the method includes a loop to continue checking the temperature rise while the furnace heating system is operational using steps 160 through 170.

(132) At step 170, if the method determines the delta temperature rise for the furnace is less than 0 F, then proceeds to step 172.

(133) At step 172, for a gas furnace heating system, the method comprises preferably providing at least one FDD alarm signal reporting a low heating capacity fault which can be caused by excess outdoor airflow, improper damper position, improper economizer operation, dirty or blocked air filters, low blower speed, blocked heat exchanger caused by dirt buildup, loose wire connections, improper gas pressure or valve setting, sticking gas valve, bad switch or flame sensor, ignition failure, misaligned spark electrodes, open rollout, open limit switch, limit switch cycling burners, false flame sensor, cracked heat exchanger, combustion vent restriction, improper orifice or burner alignment, or non-functional furnace. After step 172, the method loops back to step 183 to Go to FIG. 2 step 600 to continue the call for heating.

(134) At step 162 of FIG. 4, the method includes checking whether or not the heating system is a gas furnace, and if the method determines the heating system is not a gas furnace, then the method proceeds to step 170.

(135) At step 174, the method includes checking whether or not the heating system is a heat pump, and if the method determines the heating system is a heat pump, then the method proceeds to step 176.

(136) At step 176, the method includes measuring the target temperature rise for heat pump heating based on the minimum acceptable target temperature rise which is preferably a function of OAT as shown in the following equation based on heat pump manufacturer minimum acceptable temperature rise data.
δTR.sub.t.sub.heat pump=[C.sub.21t.sub.o.sup.2+C.sub.22t.sub.0+C.sub.23] Eq. 37

(137) Where, δTR.sub.t.sub.heat pump=minimum acceptable heat pump temperature rise,

(138) C.sub.21=0.0021 (F.sup.−1),

(139) C.sub.22=1.845 (dimensionless), and

(140) C.sub.23=8.0 (F).

(141) Temperature rise coefficients may vary depending on user input, heat pump model, heating capacity, airflow, OAT, and return temperature. Minimum temperature rise coefficients for a heat pump are based on an OAT ranging from −10 F to 65 Fahrenheit, airflow from 300 to 400 cfm/ton, and return temperatures from 60 to 80 F.

(142) At step 176, the method also includes calculating the delta temperature rise for the heat pump heating system according to the following equation.
ΔTR.sub.heat pump=δT.sub.a−δTR.sub.t.sub.heat pump Eq. 38

(143) At step 178, the method includes calculating whether or not the delta temperature rise for the heat pump heating system is greater than or equal to 0 F according to the following equation.
ΔTR.sub.heat pump=δT.sub.a−δTR.sub.t.sub.heat pump≥0 Eq. 39

(144) At step 178, if the method determines the delta temperature rise for the heat pump is greater than or equal to 0 F, then the heat pump heating system is considered to be within tolerances, no FDD alarm signals are generated, and the method includes a loop to continue checking the temperature rise while the heat pump heating system is operational using steps 160 through 178.

(145) At step 178 of FIG. 4, if the method determines the delta temperature rise for the heat pump is less than 0 F, then the method proceeds to step 172.

(146) At step 172 of FIG. 4, for a heat pump heating system, the method includes preferably providing at least one FDD alarm signal reporting a low heating capacity fault to check the system for low heating capacity. After step 172, the method loops back to step 183 to Go to FIG. 2 step 600 to continue the call for heating.

(147) At step 174, if the method determines the heating system is not a heat pump, then the method proceeds to step 180.

(148) At step 180, the method measures the target temperature rise for the hydronic heating system based on the minimum acceptable target supply-air temperature rise according to the following equation which is preferably a function of hot water supply temperature and may vary from 18 to 73 F depending on airflow, coil heating capacity, and hot water supply temperature, t.sub.hw.
δTR.sub.t.sub.hydronic=[C.sub.25t.sub.hw+C.sub.26] Eq. 41

(149) Where, δTR.sub.t.sub.hydronic=minimum acceptable hydronic temperature rise,

(150) C.sub.25=0.35 (F.sup.−1), and

(151) C.sub.26=−24 (F).

(152) The method also includes the following simplified equation to measure the target temperature rise for the hydronic heating system for all systems regardless of hot water supply temperature.
δTR.sub.t.sub.hydronic=C.sub.27 Eq. 42

(153) Where, δTR.sub.t.sub.hydronic=minimum acceptable hydronic temperature rise,

(154) C.sub.27=19 F.

(155) At step 180, the method also includes calculating the delta temperature rise for the hydronic heating system according to the following equation.
ΔTR.sub.hydronic=δT.sub.a−δTR.sub.t.sub.hydronic Eq. 43

(156) At step 182, the method includes calculating whether or not the delta temperature rise for the hydronic heating systems greater than or equal to 0 F according to the following equation.
ΔTR.sub.t.sub.hydronic=δT.sub.a−δTR.sub.t.sub.hydronic≥0 Eq. 45

(157) At step 182 of FIG. 4, if the method determines the delta temperature rise for the hydronic heating system is greater than or equal to 0 F, then the hydronic heating system is considered to be within tolerances, no FDD alarm signals are generated, and the method includes a loop to continue checking the temperature rise while the hydronic heating system is operational using steps 160 through 182.

(158) At step 182 of FIG. 4, if the method determines the delta temperature rise for the hydronic heating system is less than 0 F, then the method proceeds to step 172.

(159) At step 172 of FIG. 4, for a hydronic heating system, the method includes preferably providing at least one FDD alarm signal reporting a low heating capacity fault to check the system for low heating capacity. After step 172, the method loops back to step 183 and Go to FIG. 2 step 600 call for heating.

(160) FIG. 5 provides a graph showing the Outdoor Airflow Fraction (OAF) versus economizer damper actuator control voltage (x) for an HVAC system according to a known control 5 and the present invention 7. The known control 5 assumes OAF is proportional to economizer actuator voltage (0% OAF at 2V and 100% OAF at 10V). The present invention economizer calibration method 7 determines a functional relationship between the economizer actuator voltage “x” and the corresponding damper position OAF “y” based on a set of “y-versus-x” data for at least two or more damper positions selected from the group consisting of: a closed damper position, at least one intermediate damper position, and a fully open damper position. FIG. 5 shows the economizer calibration method 7 measuring the following “y-versus-x” data: 1) a closed damper position x.sub.3=2V and OAF.sub.3closed=15% at 3, 2) at least one intermediate damper position x.sub.7a=6.8V and OAF.sub.7a=41% at 7a, and 3) a fully open damper position x.sub.13=10V and OAF.sub.13 max=74% at 13. These “y-versus-x” data are used to calculate the coefficients of a first-order (or greater) line fit regression equation, or a least-squares matrix-regression equation.

(161) FIG. 6 shows the method based on the set of “y-versus-x” data, a second-order polynomial quadratic regression equation 7, the least-squares matrix-regression equations 9 and 11, and a quadratic formula equation 19 with coefficients a, b, and c that provides the solution to the quadratic regression equation 7. Equation 19 provides the following economizer actuator voltage “x.sub.i” of 3.46V based on a damper position OAF “y.sub.i” of 0.20 (20%) at 7b (see FIG. 5). The known control 5 at 6.8V assumes an OAF of 60% at 5a which is 19% greater than the measured OAF of 41% at 7a. The known control was originally set to 6.8V at 5a by a technician who used two fingers placed between the damper blades to set the actuator voltage. The known control 5 provides user inputs to set the minimum position (MIN POS) based on voltage. The known control 5 can be set to 3.6V (based on 0.2 times 8V range equals 1.6V plus 2V offset) shown in FIG. 5 at 5b. The actuator control voltage of 3.6V provides a measured OAF of 21% which is only 1% greater than the required OAF of 20% at 7b. For the economizer tested, the actuator control voltage was set to 6.8V providing a measured OAF of 41% which is 21% more outdoor air than the required 20% OAF at 3.46V at 7b. FIG. 5 shows for the economizer tested, the known control 5 is only accurate for the economizer actuator voltages of 3.6V+/−0.1V. Otherwise the known control 5 significantly overestimates the OAF from 3.7V to 10V and significantly underestimates the OAF from 2V to 3.5V.

(162) FIG. 6 illustrates how a set of “y-versus-x” data are used in a least squares matrix regression equation method to determine coefficients of the Eq. 7 least-squares matrix-regression equation. The Eq. 19 quadratic formula provides the method for calculating the economizer actuator voltage, “x”, based on the corresponding damper position OAF “y”. FIG. 6 provides a table of the set of “y-versus-x” data based on measurements of the economizer actuator voltage “x.sub.i” and corresponding measurements of the damper position OAF.sub.i “y.sub.i” data. FIG. 6 shows the measurement data entered into matrix X and matrix Y in Eq. 9. FIG. 6 shows the inverse-matrix X is multiplied by matrix Y to calculate the coefficient-matrix C quadratic regression coefficients in Eq. 11. FIG. 6 shows how the Eq. 19 quadratic formula is used with the required intermediate damper position “OAF.sub.r” (y.sub.i=OAF.sub.r=0.2) to calculate the required intermediate economizer actuator voltage “x.sub.r” (x.sub.i=x.sub.r) from “y-versus-x” measurements per step 100 through step 124 of FIG. 3 to verify that the “OAF.sub.i” is preferably within an acceptable tolerance of the required intermediate damper position. Preferably, the economizer calibration method is performed with the economizer perimeter gap sealed to reduce unintended and uncontrolled outdoor airflow and when the difference between OAT and RAT is at least 10 F and preferably greater than 20 F. Preferably the economizer calibration method is performed to obtain a set of “y-versus-x” data for at least three damper positions selected from the group consisting of: a closed damper position, at least one intermediate damper position, and a fully open damper position. Preferably, the at least one intermediate damper position measurement is close to the middle of the economizer actuator voltage range (i.e., 6 V if the offset is 2V and closed position is 2V and the fully open position is 10V) to provide an upward-opening regression curve with a positive “a” coefficient. Measuring multiple intermediate damper positions will provide a more accurate calibration curve. For HVAC systems with multiple-speed or variable-speed fan motors, the “y-versus-x” measurements should be made at each of the fan-motor speeds to provide a complete economizer calibration database of the set of “y-versus-x” data.

(163) FIG. 7 provides calculations of the FDD CDC savings from correcting the known prior art default 62 F High-limit Shut-off Temperature (HST) (63 F minus 1 F deadband), and superseding the known prior art −1 F and −2 F HST deadband delays. The present invention FDD CDC moves the damper to the fully open position when OAT is less than or equal to ≤HST and closes the damper when OAT increases to greater than or equal ≥(HST plus 2 F). The FDD CDC method moves the damper to the fully open position and energizes at least one AC compressor when OAT is greater than the ACT and OAT is less then or equal to the HCT. Savings are based on comparing the same building with the present invention FDD CDC HST of 71 F for CZ06 and HST of 75 F for CZ13 and CZ15. The FDD CDC HST values are referenced to the ASHRAE 90.1 and CEC Building Energy Efficiency Standards. The calculations are based on hourly simulations of the annual energy use for a commercial retail building prototype using the DOE-2.2 building energy analysis program (LBNL 2014). Known economizer controllers use a 2 F deadband to reduce or eliminate “hunting” where the economizer opens and closes dampers multiple times during a call for cooling when the OAT is vacillating above or below the HST. The FDD CDC method prevents economizer “hunting,” and also prevents overshooting the HCT when the damper is in the fully open position, by superseding at least one thermostat second-stage time/temperature delay and energizing an AC compressor otherwise delayed by the at least one thermostat second-stage time/temperature delay. By energizing the AC compressor when the damper is in the fully open position, the FDD CDC method is able to quickly satisfy the call for cooling and prevent hunting and overshooting. FIG. 7 shows the FDD CDC method provides average savings of 1.3 to 12.5%. The average savings assume 50% weighting for correcting the known prior art default 62 F HST, 45% weighting for correcting the −1 F HST deadband, and 5% for correcting the −2 F HST deadband. The savings for correcting the default 62 F HST are 2.8 to 23.8% savings, savings for correcting the −1 F HST deadband are −0.1% to 1%, and savings for correcting the −2 F HST deadband are −0.1 to 2.3%. In the hotter climate zones (CZ13 and CZ15), the 75 F HST recommended by the ASHRAE 90.1 and the CEC Building Energy Efficiency Standards requires 0.1% more cooling energy compared to 74 F or 73 F HST (i.e., −1 F or −2 F deadband delays). The known prior art −1 F to −2 F deadband delays cannot be changed by user inputs. The known prior art reduces cooling capacity, efficiency, and occupant comfort. The FDD CDC method provides a solution to resolve these problems.

(164) FIG. 8 provides calculations of the FDD CDC method savings for an HVAC system with an economizer based on hourly building energy simulations of a commercial retail building when the building is occupied. The building energy simulations are based on the US Department Of Energy (DOE) DOE-2.2 building energy analysis program (LBNL 2014). The DOE-2 building energy analysis program is used to predict the energy use and cost for residential and commercial buildings based on a description of the building layout, constructions, usage, lighting, equipment, and HVAC systems. The FDD CDC savings are calculated using the following heat balance equations to determine how much extra DX AC compressor energy is required to remove heat from the room air due to the thermostat second-stage time delay (t.sub.d) or thermostat second-stage dead band (T.sub.d). The time delay can vary by 2 to 60 minutes and the deadband delay can vary from 2 to 10 F depending on default settings or user-selected thermostat settings. The net sensible heat removal rate Q.sub.net (column g) is calculated as follows.
Q.sub.net=Q.sub.sc+Q.sub.e+Q.sub.i Eq. 46
Where, Qnet=net DX AC sensible heat removal rate (Btu) (column g), Q.sub.sc=average DOE-2 hourly DX coil sensible cooling (Btu) (column e), Q.sub.e=average DOE-2 hourly economizer heat removal (Btu) (column b), Q.sub.i=average DOE-2 hourly sensible heat load (Btu) added to the room air volume from the building shell, infiltration, and solar radiation as well as internal sensible heat loads generated by occupants, lights, and equipment (column c). The peak internal loads are 250 Btu/hour-person from occupants, 5.1 Btu/ft.sup.2 (1.5 Watts/ft.sup.2) from lighting, and 3.1 Btu/ft.sup.2 (1 W/ft.sup.2) from equipment. The magnitude of the sensible heat load varies based on the building type and schedules (hour, day, week and month). The retail building is modeled with peak occupancy of 45 people, 6400 ft.sup.2 of conditioned sales floor area, 1600 ft.sup.2 of conditioned non-sales floor area, 80000 ft.sup.3 of total interior volume, 0.25 window-to-wall ratio in sales area (no windows in non-sales area), 25 tons of mechanical AC compressor cooling (300,000 Btu/hr), 9400 cfm airflow (376 cfm/ton), 0.14 OAF when the economizer is closed (2V), 0.3 OAF when the economizer is at the minimum position, and 0.663 OAF when the economizer is fully open (10V).

(165) FIG. 8 shows the economizer average heat removal varies from −4876 at 75 F OAT to 63302 at 63 F OAT (column b), and the sensible cooling load varies from −54363 to −61636 Btu per hour (column c). The following heat balance equation is used to determine the corrected DOE-2 DX AC power input for each hour.
e.sub.c=e.sub.ac(1−Q.sub.v/Q.sub.ac) Eq. 47
Where, e.sub.c=corrected DOE-2 AC power (kWh) (column i), e.sub.ac=average DOE-2 hourly DX AC plus fan power (kWh) (column h), Q.sub.v=−2285 Btu or quantity of heat in the room air volume which caused the Conditioned Space Temperature (CST) to increase by the 2 F thermostat deadband (Btu) (column d) calculated as room volume times the air specific heat (0.244 Btu/F-lbm) times the average air density (0.073 lbm/ft.sup.3) times 2 F.
Δe.sub.ft=1−e.sub.ac/e.sub.c Eq. 48
Where, Δe.sub.ft=FDD CDC savings occupied FIG. 8 or unoccupied FIG. 9 (column j). FIG. 8 indicates that the known prior art economizer controller cannot satisfy the thermostat call for cooling and exceeds the thermostat second-stage time delay and the thermostat second-stage temperature deadband (“Yes” in column f) when the building is occupied and the OAT ranges from 63 F to 75 F. This unresolved issue is caused by the thermostat second-stage time delay and thermostat second-stage temperature deadband delay preventing the thermostat from energizing the second-stage cooling signal for the economizer to energize the first-stage AC compressor to cool the conditioned space and prevent the CST from increasing by 2 F to 4 F. The FDD CDC method supersedes the thermostat second-stage time delay/temperature-deadband delay and energizes the AC compressor with the fully open damper position to allow the HVAC fan to provide a maximum amount of outdoor airflow for cooling when the OAT is greater than the ACT and the OAT less than or equal to least one HCT at the beginning of a thermostat call for cooling. The FDD CDC methods saves 14 to 29% compared to the known prior art control when the building is occupied (column j). Annual savings are 7.2+/−2.9% depending on the commercial building type, HVAC system, occupancy schedule, thermostat, economizer controller, and climate zone.

(166) FIG. 9 provides calculations of the FDD cooling delay correction savings when the building is unoccupied using the same equations discussed above. FIG. 9 shows the sensible cooling load from people, lights, and equipment ranges from −21925 to −23686 Btu per hour (column c), and the economizer heat removal ranges from −4876 at 75 F OAT to 29213 at 69 F OAT. The unoccupied cooling load from people, lights, and equipment is 61% less than the occupied cooling load shown in FIG. 8 (column c). FIG. 9 indicates that the known prior art economizer controller cannot satisfy the thermostat call for cooling and exceeds the thermostat second-stage time delay and the thermostat second-stage temperature deadband (“Yes” in column f) when the building is unoccupied and the OAT ranges from 69 F to 75 F. The FDD CDC method supersedes the thermostat second-stage time delay and the thermostat second-stage deadband delay and energizes the AC compressor and fully opens the damper to provide the maximum amount of outdoor airflow for cooling when the OAT is greater than at least one low-limit control temperature and the OAT less than or equal to least one high-limit control temperature at the beginning of a thermostat call for cooling. The FDD CDC methods saves 12.4 to 16% compared to the known prior art control when the building is unoccupied (column j).

(167) FIG. 10 shows a curve 809 representing the FDD cooling delay correction savings versus CST minus OAT temperature difference for an occupied building. FIG. 10 also shows a curve 810 representing the FDD cooling delay correction cooling savings for an unoccupied building. The savings range from 12 to 29% for a CST-OAT temperature difference from 0 F to 12 F. FIG. 10 shows how the FDD cooling delay correction ACT varies depending on the building occupancy. When the building is occupied economizer cooling is able to meet the load up to 63 F or CST-OAT difference of 12 F due to the sensible cooling load from people, lights, and equipment. When the building is unoccupied economizer cooling is able to meet the load up to 69 F or CST-OAT difference of 6 F due to less cooling loads from people, lights, and equipment. Known prior art economizer controllers allow economizer cooling to attempt to satisfy the thermostat call for cooling with a thermostat first-stage time delay of 2 to 60 minutes and temperature deadband of 2 to 4 F. The known prior art control causes CST to increase by 2 to 4 F above the setpoint which increases AC compressor operation and energy use and decreases thermal comfort. The present invention FDD CDC method provides the VEST to automatically determine when to increase the cooling capacity delivered to the conditioned space by the AC system depending on the OAT and the building occupancy to maximize cooling efficiency and thermal comfort.

(168) FIG. 10 provides two trendline regression equations.
y=0.126646e.sup.−0.07046 x Eq. 49
Where, y=occupied FDD CDC plus fan savings based on Δe.sub.ft in FIG. 8, and x=CST minus OAT with low-limit 63 F OAT and high-limit OAT of 69 to 80 F depending on climate zone. The low-limit OAT is the temperature below which the economizer can fully meet the sensible load and not the economizer-lock-out temperature.
y=0.12191e.sup.−0.046637 x Eq. 50
Where, y=unoccupied FDD CDC plus fan savings based on Δe.sub.ft in FIG. 9, and x=unoccupied CST minus OAT with low-limit OAT of 69 F and high-limit OAT of 69 F to 80 F depending on climate zone. Eq. 49 and Eq. 50 can be used to calculate savings for the FDD CDC method superseding the thermostat second-stage time delay and the thermostat second-stage deadband delay. The regression equations can be used with the equation provided in FIG. 13 to calculate cooling savings for the FDD CDC method superseding the thermostat delays and the economizer time delay (see below).

(169) FIG. 11 shows five tests of the known economizer cooling control 666 with average application cooling sensible Energy Efficiency Ratio* (EER*) of 8.6 where EER* is the ratio of sensible cooling energy output in British thermal units (Btu) divided by the total energy input in kilo Watt hours (kWh). The known economizer control positions the dampers at the minimum OAF damper position actuator voltage command of 2.8 Volts with the DX AC compressor energized and a fixed fan-off delay operating for 80 seconds after the end of the DX AC cooling cycle.

(170) FIG. 11 also shows five tests of the present invention FDD cooling delay correction control 777 with average application cooling sensible Energy Efficiency Ratio* (EER*) of 13.1 with average EER* improvement of 51.5% and average savings of 32.9%. The FDD cooling delay correction control positions the dampers at the fully open OAF damper position actuator voltage command of 10 Volts with the AC compressor energized and a variable fan-off delay after a cooling cycle based on the air drybulb temperature difference between the MAT and the SAT wherein the MAT is based on a mixture of outdoor air and return air and the fan-off delay operates until the MAT minus SAT drybulb temperature difference is less than 6 F.

(171) FIG. 12 provides a table of laboratory test measurements of the OAT [column a], total power (Watts) [column b], sensible cooling capacity (Btuh) [column c], sensible Energy Efficiency Ratio (EER*s) [column d=c/b], economizer only cooling savings for a packaged HVAC system with an economizer, fully open damper, and HVAC fan [column e], and the present invention FDD Cooling Delay Correction (CDC) savings for a packaged HVAC system with an economizer, fully open damper, and HVAC fan plus a first-stage and a second-stage AC compressor [column f]. The laboratory maintains 75 F drybulb and 62 F wetbulb indoor conditions to emulate an occupied commercial building during the testing period. FIG. 12 shows the economizer only cooling savings [column e] are negative (−25.3%) at 65 F OAT compared to the FDD CDC method which is more efficient at 65 F OAT. The economizer is 11.5% more efficient at 60 F OAT, and 27.3% more efficient at 55 F compared to the FDD CDC method. The FDD CDC cooling method provides cooling savings when the building is occupied during economizer operation from about 63 F to 75 F. The FDD CDC method also provides cooling savings when the building is occupied during mechanical cooling with the economizer damper in the minimum position when the OAT is greater than 75 F OAT.

(172) FIG. 13 shows the economizer cooling savings 819 going from 27.3% at 55 F OAT, crossing 0% at about 61.9 F OAT, and going down to −30% at 65.49 F OAT based on data provided in FIG. 12. FIG. 13 also shows the FDD CDC cooling savings 821 going from −1.9% at 55 F OAT to 47.2% at 100 F OAT. The economizer cooling savings 819 with fully open damper and the FDD CDC cooling savings 821 with fully open damper plus first- and second-stage AC compressor intersect at 61.054 F with the same savings of 5.45%. The FDD CDC method provides annual savings of approximately 4.9+/−1.1% depending on the commercial building type, HVAC system, economizer and thermostat settings, occupancy schedule, and climate zone. The known prior art economizer energizes the second-stage AC compressor after a default 4 to 120 minute time delay which increases energy use and reduces thermal comfort. The following trendline regression equation can be used to calculate FDD CDC cooling savings for superseding the economizer second-stage time delay.
y=0.844407 Ln(x)−3.417134 Eq. 51
Where, y=the FDD CDC savings for superseding the economizer second-stage time delay, and x=OAT from 55 to 120 F. Eq. 51 can be used to calculate FDD CDC savings during periods of time when a known prior art economizer controller provides a second-stage time-delay during economizer cooling or AC compressor mechanical cooling. Eq. 51 can also be used with Eq. 49 and Eq. 50 from FIG. 10 to calculate FDD CDC savings from superseding the economizer second-stage time delay and the thermostat second-stage time delay/temperature-deadband delay.

(173) FIG. 13 shows negative economizer-only savings 819 for OAT greater than 62.5 F when a building is occupied, are not obvious to persons having ordinary skill in the art who assume economizers provide enough cooling to meet commercial building cooling loads when the OAT is between 69 F and 75 F. The California Energy Commission 2019 Building Energy Efficiency Standards require a high-limit economizer drybulb setpoint temperature of 69 F to 75 F based on climate zone.

(174) FIG. 14 provides curve 829 representing a power-function regression curve of the cooling energy savings (%) versus cooling system Part Load Ratio (PLR) for the present invention FDD variable fan-off delay method compared to a known cooling control with a fixed fan-off delay of 45, 60, and 90-seconds. The cooling PLR is defined as the sensible cooling capacity provided by a cooling system operating for less than 60 minutes divided by the total sensible cooling capacity for the cooling system operating for 60 minutes. The FDD variable fan-off delay method energizes an HVAC fan control (G) signal to operate an HVAC fan for a variable fan-off delay after a thermostat call for heating wherein the variable fan-off delay is based on an air temperature difference between a Mixed Air Temperature (MAT) and a Supply Air Temperature (SAT) wherein the MAT is based on a mixture of air at the OAT and the RAT, and the MAT varies based on a position of the economizer damper and the OAT and the RAT. Known prior art economizers do not have an HVAC fan (G) output to energize the HVAC fan. Known fixed fan-off delays are provided by the on-board HVAC system controls or a thermostat, and not the economizer controller. Known fixed fan-off delays are generally less than 90 seconds leaving considerable energy in the HVAC system that is wasted. The method energizes the HVAC fan control signal and operates the HVAC fan for the variable fan-off delay until an absolute value of the air temperature difference between the MAT and the SAT is 4 to 8 F.

(175) FIG. 15 provides curve 839 representing a power-function regression curve representing the total heating system energy savings (%) versus heating system PLR for the present invention FDD variable fan-off delay method compared to known fixed fan-off delays of 45, 60, and 90-seconds. The heating PLR is defined as the heating capacity for a heating system operating for less than 60 minutes divided by the total heating capacity for the heating system operating for 60 minutes. The FDD variable fan-off delay is based on an air temperature difference between a MAT and a SAT wherein the MAT is based on a mixture of air at the OAT and the RAT and the MAT varies based on the economizer damper position and the OAT and the RAT. The method energizes the HVAC fan and operates the HVAC fan for the variable fan-off delay until an absolute value of the MAT and SAT difference is between 4 and 8 F.

(176) FIG. 16 shows a curve 811 representing the total HVAC system power (kW) versus time of operation for a known thermostat 815 fan-on setting causing constant fan power, short cycling, and increased HVAC power and energy consumption. FIG. 16 also shows a curve 813 representing an embodiment of the present invention Fault Detection Diagnostics (FDD) method 817 detecting, reporting, and overriding a fan-on setting and turning off an HVAC fan when the building is unoccupied or the fan-on time (F6) is greater than a Threshold Fan-on Time (TFT).

(177) FIG. 17 shows the economizer 783 installed into the HVAC system cabinet 780 and the economizer perimeter gap 785 of the economizer frame where it connects to the HVAC system cabinet. The economizer perimeter gap 785 allows unintended, uncontrolled, and unconditioned outdoor airflow to enter the economizer, HVAC system, and conditioned space whether or not the ventilation fan is operating. The economizer 783 is designed to be considerably smaller than the opening in the HVAC system cabinet in order to allow easy installation and removal. The economizer hood 787 must be removed in order to properly seal the economizer perimeter gap 785.

(178) Virtually all economizers installed on packaged HVAC systems have an economizer perimeter gap 785 between the economizer frame and an opening in the HVAC system cabinet where the economizer is inserted and installed into the HVAC system cabinet 780. The economizer perimeter gap 785 allows unintended, uncontrolled, and unconditioned outdoor airflow to enter the economizer, HVAC system, and conditioned space whether or not the ventilation fan is operating. The economizer hood 787 must be removed in order to properly seal the economizer perimeter gap. Sealing around the perimeter gap of the economizer frame where it connects to the HVAC system cabinet is performed with at least one sealant selected from the group consisting of: adhesive tape sealant, adhesive sealant, mastic sealant, or weatherstripping to reduce untended outdoor air leakage through the economizer perimeter frame to prevent unintended outdoor airflow during the off cycle or during the cooling or heating cycle. Sealing the economizer perimeter gap 785 includes sealing the metal surfaces between the economizer frame and the HVAC system cabinet 780 to reduce unintended outdoor airflow and increase cooling and heating efficiency. Sealing the economizer perimeter gap should be performed during installation and setup of an economizer to calibrate the economizer controller actuator voltage and ensure the corresponding damper position OAF requirements are achieved.

(179) FIG. 18 shows measurements of OAF versus economizer actuator voltage measurements for economizer #1. The known control 801 assumed OAF is proportional to the economizer actuator voltage. The known control 801 assumes zero (0%) OAF at the 2V closed damper position, and 1.0 (100%) OAF at the 10V maximum or fully open position. FIG. 18 shows the measured OAF with unsealed economizer perimeter gap for the FDD calibration method 802, and the second-order line fit regression equation: y=0.0076 x.sup.2−0.0107x+0.1024. FIG. 18 also shows the measured OAF with sealed economizer perimeter gap 785 for the FDD calibration method 803, and the second-order line fit regression equation: y=0.0079 x.sup.2−0.0131x+0.0673. Sealing the perimeter gap 785 reduces the OAF from 0.123 to 0.082 (4.1%) at the 2V closed damper position, but only reduces the OAF from 0.75 to 0.73 (2%) at the 10V maximum or fully open damper position.

(180) FIG. 19 shows measurements of OAF versus economizer actuator voltage measurements for economizer #5. The known control 805 assumed OAF is proportional to the economizer actuator voltage with zero (0%) OAF at the 2V closed position and 1.0 (100%) OAF at the 10V maximum or fully open position. FIG. 19 shows the measured OAF with unsealed economizer perimeter gap for the FDD calibration method 807 and the first-order line fit regression equation y=0.0563 x−0.0923. FIG. 19 also shows the measured OAF with sealed economizer perimeter gap 785 for the FDD calibration method 809 and the first-order line fit regression equation y=0.06805 x−0.02433. Sealing the perimeter gap 785 reduces the OAF from 0.235 to 0.14 (9.5%) at the 2V closed damper position, but only reduces the OAF from 0.663 to 0.658 (0.05%) at the 10V maximum or fully open damper position.

(181) FIG. 20 shows a magnetometer 450 co-planar with a magnet 454. The magnetic field generated by the permanent magnet is in the Z plane of the 3-dimensional Micro-Electro-Mechanical Systems (MEMS) magnetometer 450.

(182) FIG. 21 shows the magnet 456 rotated 90 degrees from the position shown in FIG. 20. The magnetic field is in the Y plane of the 3-dimensional MEMS magnetometer 460. The magnetometer 460 is mounted to a stationary frame of an economizer to allow at least one wire to carry the magnetometer 460 measurement signal to an electronic device or economizer controller embodying the present invention to determine the position of the damper in a 3-dimensional coordinate system.

(183) While the invention herein disclosed has been described by means of specific embodiments and applications thereof, numerous modifications and variations could be made thereto by those skilled in the art without departing from the scope of the invention set forth in the claims.

Economizer cooling delay correction

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F24F2110/10

MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING

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F24F2110/22

MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING

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G05B23/0218

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F24F11/38

MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING

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G05B15/02

PHYSICS

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Y02B30/70

GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS

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F24F11/63

MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING

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F24F2140/40

MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING

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F24F2120/10

MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING

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G05B2219/2614

PHYSICS

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F24F11/49

MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING

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F24F2110/70

MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING

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F24F2110/12

MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING

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G05B19/042

PHYSICS

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F24F11/74

MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING

International classification

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F24F11/49

MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING

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F24F11/38

MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING

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F24F11/63

MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING

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F24F11/74

MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING

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G05B23/02

PHYSICS

Classification Explorer

G05B19/042

PHYSICS

Abstract

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Description