Economizer controller calibration
An economizer controller calibration method, comprising: sealing an economizer perimeter gap between the economizer frame and a Heating, Ventilating Air Conditioning (HVAC) system cabinet to reduce an uncontrolled outdoor airflow; determining a functional relationship between an economizer actuator voltage (x) and a damper position Outdoor Airflow Fraction (OAF) (y); monitoring the economizer actuator voltage (x) and measuring at least one airflow characteristic to calculate the damper position OAF (y) and obtain a set of x-versus-y data for at least two damper positions: closed, intermediate, and fully-open; calculating at least two coefficients of the functional relationship using the x-versus-y data; calculating a target economizer actuator voltage (x t ) as a function of a required OAF r (y r ) using the functional relationship; and positioning the damper using the target economizer actuator voltage (x t ) to provide the target damper position OAF r (y r ) within a tolerance of the required OAF r (y r ).
1. An economizer controller calibration method, the method comprising:
monitoring or measuring an economizer actuator voltage (x) and measuring at least one airflow characteristic and calculating a corresponding damper position Outdoor Air Fraction (OAF) (y) of an economizer controller of an economizer of a Heating, Ventilating, Air Conditioning (HVAC) system;
obtaining a set of x-versus-y data for at least two damper positions selected from the group consisting of: a closed damper position, at least one intermediate damper position, and a fully open damper position;
determining a functional relationship between the economizer actuator voltage (x) and the corresponding damper position OAF (y) by calculating at least two coefficients of the functional relationship using the set of x-versus-y data;
calculating a target economizer actuator voltage (x t ) as a function of a required OAF r (y r ) using the functional relationship; and
positioning the damper using the target economizer actuator voltage (x t ).
2. The method of claim 1 , further including sealing an economizer perimeter gap between an economizer frame and a HVAC system cabinet to reduce an uncontrolled excess outdoor airflow through the economizer perimeter gap between the economizer frame and the HVAC system cabinet, the sealing comprising: applying a sealing material over or into the economizer perimeter gap between the economizer frame and the HVAC system cabinet.
3. The method of claim 1 , wherein the OAF is calculated based on a ratio of a numerator comprising: a Return Air Temperature (RAT) minus a Supply Air Temperature (SAT) plus a fan heat temperature increase, divided by a denominator comprising: the RAT minus an Outdoor Air Temperature (OAT), wherein the SAT, the RAT, and the OAT are measured with the closed damper position and a HVAC fan operating and a cooling system or a heating system not operating.
4. The method of claim 3 , wherein the fan heat temperature increase is a 0.5 to 2 F temperature increase depending on fan power.
5. The method of claim 1 , wherein the method of determining the functional relationship between the economizer actuator voltage (x) and the corresponding damper position OAF (y) comprises fitting an Nth order function to N+1 measurements of the economizer actuator voltage (x) and the corresponding damper position OAF (y).
6. The method of claim 1 , wherein the at least two damper positions comprises at least three damper positions, and the at least one intermediate damper position comprises at least one intermediate damper position OAF (y i ) with the economizer actuator voltage (x) close to a middle of a voltage range.
7. The method of claim 1 , wherein calculating the coefficients of the functional relationship between the economizer actuator voltage (x) and the corresponding damper position OAF (y) comprises using a least squares regression equation method for n ordered pairs of the set of x-versus-y data by expressing the least squares regression equation method in matrix form, the least squares regression equation method 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 the x-values to a power n−1 (x13, x22, x31), n−1 summations of the x-values to a power n (x12, x21), and exactly one summation of the 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 the y-values (y21), and one summation of the x-values to the power n−1 times the 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 a first coefficient a (c11), a second coefficient b (c21), and a third coefficient c (c31) of the functional relationship; and
calculating the target actuator voltage (x t ) based on a quadratic formula using the first coefficient a (c11), the second coefficient b (c12), and the third coefficient c (c13) and the target damper position OAF (y t ) is subtracted from the third coefficient c (c13).
8. The method of claim 7 , wherein calculating the target actuator voltage (x t ) based on a quadratic formula further comprises calculating a numerator comprising the sum of a negative number one times the second coefficient b (c21) plus a square root of a first difference between the second coefficient b (c21) squared minus four times a first coefficient a (c11) times a second difference between the third coefficient c (c31) minus the required OAF r (y r ) wherein the numerator is divided by a denominator comprising a number two times the first coefficient a (c11).
9. The method of claim 1 , wherein determining the functional relationship comprises monitoring or measuring the set of x-versus-y data for the at least two damper positions and at least one fan-motor speed for a HVAC fan operating by itself.
10. The method of claim 5 , wherein fitting an Nth order function to N+1 measurements of the economizer actuator voltage (x) and the corresponding damper position OAF (y), comprises calculating three coefficients of a second order functional relationship between the economizer actuator voltage (x) and the corresponding damper position OAF (y) by fitting a second order function to three measurements of the economizer actuator voltage (x) and the corresponding damper position OAF (y).
11. The method of claim 5 , wherein fitting an Nth order function to N+1 measurements of the economizer actuator voltage (x) and the corresponding damper position OAF (y), comprises calculating the coefficients of the second order functional relationship between the economizer actuator voltage (x) and the corresponding damper position OAF (y) by solving three equations in three unknowns using the set of x-versus-y data.
12. The method of claim 1 , further including comparing a target damper position OAFt (yt) to the required OAFr (yr) and adjusting the target economizer actuator voltage (xt) to reduce a difference between the target damper position OAFt (yt) and the required OAFr (yr) based on the target economizer actuator voltage (xt) minus a ratio of a numerator comprising the target damper position OAFt (yt) minus the required OAFr (yr) divided by a derivative of the functional relationship with respect to the target economizer actuator voltage (xt).
13. The method of claim 3 , wherein the fan heat temperature increase is based on a temperature increase between the SAT and the RAT with the damper closed.
14. The method of claim 3 , wherein the fan heat temperature increase is based on a temperature increase between the SAT and the RAT with a damper assembly sealed with an impermeable membrane to reduce or eliminate an outdoor airflow from mixing with a return airflow.
15. The method of claim 3 , wherein the fan heat temperature increase is based on a temperature increase between the SAT and the RAT when the OAT is within +/−0.5 F of the RAT.
16. The method of claim 1 , wherein determining the functional relationship comprises monitoring or measuring the set of x-versus-y data for the at least two damper positions and at least one fan-motor speed including a first-stage cooling fan-motor speed.
17. The method of claim 1 , wherein determining the functional relationship comprises monitoring or measuring the set of x-versus-y data for the at least two damper positions and at least one fan-motor speed including a second-stage cooling fan-motor speed.
18. The method of claim 1 , wherein determining the functional relationship comprises monitoring or measuring the set of x-versus-y data for the at least two damper positions and at least one fan-motor speed including a first-stage heating fan-motor speed.
19. The method of claim 1 , wherein determining the functional relationship comprises monitoring or measuring the set of x-versus-y data for the at least two damper positions and at least one fan-motor speed including a second-stage heating fan-motor speed.
20. The method of claim 1 , wherein determining the functional relationship comprises monitoring or measuring the set of x-versus-y data for the at least two damper positions and at least one fan-motor speed including a representative set of fan-motor speeds for a variable-speed fan-motor.