Pressure dependent variable air volume control strategy

• US 5,769,315 A
• Filed: 07/08/1997
• Issued: 06/23/1998
• Est. Priority Date: 07/08/1997
• Status: Expired due to Fees

• Current Assignee: Johnson Controls Technology Company (Johnson Controls International plc)
• Original Assignee: Johnson Service Company
• Inventors: Drees, Kirk H.
• Primary Examiner(s): Wayner, William E.
• Application Number:
  US08/889,201
• Time in Patent Office: 350 Days
• Field of Search: 236/49.3, 236/78, 165/217, 165/216, 454/255
• US Class Current: 236/49.3
• CPC Class Codes: F24F 11/30 for purposes related to the operation of the system, e.g. for safety or monitoring
• CPC Class Codes: F24F 11/62 characterised by the type of control or by internal processing, e.g. using fuzzy logic, adaptive control or estimation of values
• CPC Class Codes: F24F 11/76 by means responsive to temperature, e.g. bimetal springs
• CPC Class Codes: F24F 13/14 built up of tilting members, e.g. louvre
• CPC Class Codes: G05D 23/192 using a modification of the thermal impedance between a source and the load

Abstract

A control strategy for rejecting supply air temperature disturbances in variable air volume air conditioning units using staged DX cooling. The strategy, and corresponding system, minimizes supply air temperature disturbances by controlling zone air dampers through a mapping of zone heat transfer requirements and damper positions. The mapping maintains a zone temperature setpoint, even with relatively large temperature swings caused by system-supplied conditioned air. The primary parameter that is controlled by the strategy of the present invention is a heat transfer rate associated with a temperature-controlled zone. The control strategy of the present invention estimates the zone heat transfer rate at a particular sampling instant and controls the damper position in response thereto.

Claims

1. A method of minimizing air flow disturbances in a multi-zone air conditioning system, comprising the steps of:

setting an air flow rate for conditioned air supplied to a climate controlled zone to maintain a zone temperature at a zone setpoint;

measuring deviation from the zone setpoint at first and second sampling instants within a sampling period;

estimating a zone heat transfer rate at the second sampling instant based on the setpoint deviation; and

adjusting the air flow rate in response to the step of estimating a zone heat transfer rate to minimize zone air flow disturbances.

2. The method of claim 1, wherein the step of adjusting the zone air flow rate comprises adjusting a zone damper through control of a zone variable to affect the flow rate of the conditioned air into the zone.

3. The method of claim 2, wherein the step of adjusting the zone damper is controlled through the step of calculating a zone damper function by mapping the air flow rate to a zone damper position.

4. The method of claim 3, wherein the step of mapping the air flow rate is controlled through the step of controlling supply air pressure.

5. The method of claim 3, further comprising the step of minimizing system instability due to process interactions by the steps of:

1) selectively controlling the zone damper function in each of a predetermined number of zones;

2) filtering an output of a zone damper control function;

3) filtering a supply air temperature measurement; and

4) rejecting supply air temperature disturbances due to changes in operating system cooling stages.

6. The method of claim 2, wherein a variable used in the step of adjusting the zone damper is selected from the group consisting essentially of:

zone heat transfer rate, static zone pressure, supply air temperature, zone setpoint temperature, air velocity, and controller gain.

7. The method of claim 1, wherein the step of measuring deviation from the zone setpoint comprises measuring a difference between the zone temperature setpoint and a measured zone temperature.

8. The method of claim 1, wherein the step of estimating a zone heat transfer rate at the second sampling instant based on the setpoint deviation is dependent on the sampling period and controller integral time.

9. An air conditioning unit, comprising:

an air conditioner;

a regulator coupled to the air conditioner that regulates the amount of conditioned air introduced into a zone;

a controller operatively connected to both the air conditioner and the regulator that is programmed to control operation of the air conditioner and the regulator; and

a sensor operatively connected to the regulator and the controller via a closed feedback loop that senses the zone temperature and transmits a sensed zone temperature signal to the controller;

the controller calculating an estimate of a zone heat transfer rate based on the sensed temperature and the zone temperature setpoint, and controlling operation of the regulator based on the estimated zone heat transfer rate to minimize supply air disturbances.

10. The apparatus of claim 9, wherein the regulator comprises a supply air duct that channels air flow from the air conditioner to the zone via a duct outlet;

and

an adjustable air damper connected to the duct outlet in proximity to the regulated zone that controls the flow of conditioned air into the zone in response to air damper control commands from the controller.

11. The apparatus of claim 10, wherein the controller comprises a feed-forward controller that maps a relationship between the estimated zone heat transfer rate and a position of the adjustable air damper.

12. The apparatus of claim 11, wherein the feed-forward controller lumps a steady state energy balance with a damper map for damper control purposes.

13. The apparatus of claim 12, wherein the damper map relates a damper conditioned air flow rate to damper position.

14. The apparatus of claim 9, wherein the estimated zone heat transfer rate is also a function of proportional controller gain and a previously estimated zone heat transfer rate.

15. The apparatus of claim 14, wherein the estimated zone heat transfer rate is calculated from the following equation:

##EQU8## where Q_zn,n is an estimate of the heat advected into the zone at the n^th sampling instant, Q_zn,n-1 is an estimate of the heat advected into the zone for the n-1 sampling instant, K_c is the proportional controller gain, t_I is the controller integral time, D_a is the sampling period, e_nis the error at the n^th sampling instant, and e_n-1 is the error at the (n-1)^th sampling instant.