Linearization of airflow through zone dampers of an HVAC system
A control system can provide a linear behavior of airflow as a function of damper position of each zone damper in an HVAC system. The control system incrementally closes each zone damper from a fully open position to a fully closed position, and records static pressure measurements with each change in damper position. Then, using a mathematical model that is derived from the second fan law, a correction is calculated for each damper position of each zone damper based on the recorded static pressure measurements to provide corrected damper positions at which the airflow through the zone damper exhibits a linear behavior. The corrected damper positions are stored and used during an operational cycle of the HVAC system to obtain a precise airflow through the zone dampers.
1. A heating, ventilating, and air-conditioning (HVAC) system comprising:
a fan configured to provide an airflow through the HVAC system;
a damper configured to adjust the airflow through the HVAC system by transitioning between multiple different damper positions; and
a controller configured to:
output instructions for the fan to provide a fixed rate of the airflow through the HVAC system;
record a respective static pressure across the HVAC system for each of the multiple different damper positions while the fan is providing the fixed rate of the airflow through the HVAC system;
determine a corrected intermediate position based at least in part on the respective static pressures corresponding to each of the multiple different damper positions; and
store the corrected intermediate position in a memory associated with the controller, the controller being configured to adjust a position of the damper during an operational mode of the HVAC system based at least in part on the corrected intermediate position.
2. The HVAC system of claim 1 , wherein the different damper positions comprise an open position, a closed position, and at least one intermediate position between the open position and the closed position.
3. The HVAC system of claim 2 , wherein recording the respective static pressure across the HVAC system for each of the multiple different damper positions comprises:
recording a first static pressure when the damper is in the open position,
recording a second static pressure when the damper is in the at least one intermediate position, and
recording a third static pressure when the damper is in the closed position.
4. The HVAC system of claim 3 , wherein determining the corrected intermediate position comprises:
calculating a first system constant associated with the at least one intermediate position based at least in part on the first static pressure, the second static pressure, and the third static pressure; and
calculating a system constant correction associated with the at least one intermediate position, the system constant correction based at least in part on:
a second system constant associated with the at least one intermediate position in a linear system, and
the first system constant.
5. The HVAC system of claim 4 , wherein the controller is configured to calculate the corrected intermediate position of the damper based at least in part on the system constant correction associated with the at least one intermediate position.
6. The HVAC system of claim 4 , wherein calculating the first system constant comprises calculation of a mathematical model that is derived from a second fan law.
7. The HVAC system of claim 6 , wherein the mathematical model comprises:
K
n
=
(
1
-
SP
position
(
n
)
SP
closed
)
(
1
-
SP
open
SP
closed
)
wherein K n is the first system constant, SP position(n) is the second static pressure, SP closed is the third static pressure, and SP open is the first static pressure.
8. The HVAC system of claim 4 , wherein generating the system constant correction associated with the at least one intermediate position comprises:
Correction
Percentage
n
=
(
K
n
_
ideal
+
K
n
+
1
)
(
K
n
+
K
n
+
1
)
wherein K n_ideal is the second system constant, K n is the first system constant, and K n+1 is a third system constant associated with a damper position of the damper that is adjacent to the at least one intermediate position.
9. The HVAC system of claim 8 , wherein the controller is configured to calculate
K
n_ideal
=
Damper
Position
n
Total
Number
of
Damper
Positions
wherein Damper Position n is a damper position of the damper that is adjacent to the at least one intermediate position.
10. The HVAC system of claim 9 , wherein calculating the corrected intermediate position of the damper comprises:
Corrected Damper Position n =Damper Position n −(1−Correction Percentage n )×(Damper Position n −Damper Position n+1 )
wherein Damper Position n corresponds to the at least one intermediate position of the damper and Damper Position +1 is a damper position of the damper that is adjacent to the at least one intermediate position.
11. The HVAC system of claim 1 , wherein the damper is configured to control the airflow through the HVAC system to a particular zone of the HVAC system.
12. The HVAC system of claim 11 further comprising a zone panel configured to adjust the damper positions of the zone damper based on instructions from the controller.
13. A controller comprising:
one or more processors; and
a memory having instructions stored thereon that, when executed by the one or more processors, cause the controller to:
output instructions for a fan to provide a fixed rate of airflow through an HVAC system;
output instructions for a damper of the HVAC system to transition between different damper positions;
record a respective static pressure across the HVAC system for each of the different damper positions while the fan is providing the fixed rate of the airflow through the HVAC system;
determine a corrected intermediate position based at least in part on the respective static pressures corresponding to each of the different damper positions; and
store the corrected intermediate position in a memory associated with the controller such that the controller can adjust a position of the damper during an operational mode of the HVAC system based at least in part on the corrected intermediate position.
14. The controller of claim 13 , wherein the different damper positions comprise an open position, a closed position, and at least one intermediate position between the open position and the closed position.
15. The controller of claim 14 , wherein recording the respective static pressure across the HVAC system for each of the different damper positions comprises:
recording a first static pressure when the damper is in the open position,
recording a second static pressure when the damper is in the at least one intermediate position, and
recording a third static pressure when the damper is in the closed position.
16. The controller of claim 15 , wherein determining the corrected intermediate position comprises:
calculating a first system constant associated with the at least one intermediate position based at least in part on the first static pressure, the second static pressure, and the third static pressure; and
calculating a system constant correction associated with the at least one intermediate position, the system constant correction based at least in part on:
a second system constant associated with the at least one intermediate position in a linear system, and
the first system constant.
17. The controller of claim 16 , wherein the instructions, when executed by the one or more processors, further cause the controller to:
calculate the corrected intermediate position of the damper based at least in part on the system constant correction associated with the at least one intermediate position.
18. The controller of claim 16 , wherein calculating the first system constant comprises calculation of a mathematical model that is derived from a second fan law.