AIRFLOW MANAGEMENT SYSTEMS AND METHODS FOR FILTERED AIR SYSTEMS

Abstract

Systems and methods for controlling operation of one or more fans of an air handling system having one or more filters or filter banks. A current air volume at an inlet side of the fan(s) is determined. In some embodiments, the inlet side air volume is determined via sensed pressure at the inlet side (e.g., pressure transducer open to a flow station at the inlet side). A controller operates to control or regulate a speed of the fan in a manner that maintains a constant air volume through the air handling system, for example based upon a comparison of the current air volume at the fan with a target air volume.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This U.S. patent application claims the benefit of the filing date of U.S. Provisional Patent Application Ser. No. 63/396,325, filed Aug. 9, 2022, the entire teachings of which are incorporated herein by reference.

BACKGROUND

The present disclosure relates to systems and methods for controlling airflow in an air handling duct system. More particularly, it relates to systems and methods for maintaining consistent air volume in a filtered air system, for example over a full range of static pressure over the life of an air filter.

Conventional HVAC systems are well-suited for providing temperature-controlled airflow to multiple rooms or areas of a facility. Some environments, however, require highly specialized air handling or ventilation systems. Operating rooms, surgical suites, and clean rooms are a few examples of critical environments in which the provision of highly filtered air flow and multiple air volume changes are necessary. Accurate volumetric control of airflow can be highly important for these critical environment airflow and supply air applications.

In general terms, critical environment airflow systems typically have one or more fans (or blowers) forcing air though ductwork to/from one or more filter banks, and oftentimes utilize air from the facility's standard HVAC system. Over time, as particulates accumulate, the filter bank(s) restrict airflow, resulting in a reduction in airflow velocity through the ducting. To overcome the reduced airflow, the fan(s) are caused to operate at a higher power level. Traditional volume control systems utilize an automatic damper or venturi valve to regulate the system static pressure, thereby changing the air volume. While increasing or reducing the static pressure of the system is an effective way to control air volume, it fails to capitalize on energy savings opportunities. Alternate methods use the controller in an electrically commutated motor (ECM) fan to internally manage fan speed based on torque, but torque is not directly related to volume so this is not as accurate of a control method.

SUMMARY

The inventor of the present disclosure recognized that a need exists for improved air volume stability in highly filtered airflow systems.

Some aspects of the present disclosure are directed toward systems and methods for controlling operation of one or more fans of an air handling system having one or more filters or filter banks. A current air volume at an inlet side of the fan(s) is determined. In some embodiments, the inlet side air volume is determined via sensed pressure at the inlet side (e.g., pressure transducer open to a flow station at the inlet side); this active pressure method for determining or measuring volume at the fan inlet can eliminate the need for a straight duct prior to a velocity pressure reading. A controller operates to control or regulate a speed of the fan in a manner that maintains a constant air volume through the air handling system, for example based upon a comparison of current air volume at the fan with a target air volume.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of portions of an air handling system and with which the control systems and methods of the present disclosure can be used;

FIG. 2 is a schematic illustration of portions of another air handling system and with which the control systems and methods of the present disclosure can be used; and

FIG. 3 is an example of a possible system and fan static pressure curves for a filtered airflow system.

DETAILED DESCRIPTION

Aspects of the present disclosure relate to filtered air handling systems, air handling system volume controllers, and methods for operating a filtered air handling system to provide constant air volume over time. With this in mind, FIG. 1 schematically illustrates portions of one example of an air handling system 20 (referenced generally) with which the controllers and methods of the present disclosure are useful. In general terms, the air handling system 20 includes a fan (or blower unit) 30, a first filter or filter bank 32 and a second filter or filter bank 34. Duct 36 fluidly connects the first filter bank 32 with an inlet side 38 of the fan 30, whereas duct 40 fluidly connects an outlet side 42 of the fan 30 with the second filter bank 34. An inflow duct 44 connects an upstream side of the first filter bank 32 to a supply of entering air (labeled generally at 46). An outflow duct 48 extends from a downstream side of the second filter bank 34, to direct delivered air (labeled generally at 50) to a process or space of interest (e.g., a critical environment).

In many respects, the air handling system 20 is of a conventional configuration and thus can have one or more additional components and/or flow paths as known in the art. With the general arrangement of FIG. 1, the fan 30 operates to draw the entering air 46 through the first filter bank 32 and into the fan inlet side 38; air is discharged from the fan outlet side 42 through the second filter bank 34 and delivered to the process or space of interest via the outflow duct 48. The fan 30 can be of a conventional, variable speed design, and may or may not be provided as part of an air handler unit. In more general terms, the fan 30 incorporates features that facilitate control over an operational speed, such as an electronically commutated motor (ECM) driving an impeller, or compatibility with a variable frequency drive (VFD).

With the above in mind, some control systems and methods of the present disclosure include controlling a speed of the fan 30 as a function of or based upon measured or sensed air volume at the inlet side 38 of the fan 30. In some embodiments, an active pressure airflow reading or measurement is obtained via a flow station 60 provided with or assembled to the inlet side 38 of the fan 30. The flow station 60 can be of a type known in the art, and generally configured to measure air volume in a duct system. As understood by one of ordinary skill, flow stations can utilize or incorporate various techniques for measuring air volume. With some known constructions, the flow station 60 is configured to measure total pressure and static pressure at a point in the ductwork. Total pressure is the sum of static pressure and velocity pressure. Thus, velocity pressure can be determined/calculated from sensed or measured total pressure and static pressure. Velocity pressure is directly related to the velocity of air in the duct. As such, where the cross-section area of the duct is known, air volume can be determined/calculated from the cross-sectional area and the determined velocity pressure. As a point of reference, with this technique (i.e., determining air volume from sensed total pressure and static pressure), a minimum length of straight duct equal to 7.5 times the duct diameter is recommended. Another technique for determining air volume is referred to as the “active pressure” methods, and is specific to fan designs. In general terms, a static pressure port is installed in the inlet ring of the fan at the point of greatest constriction. A differential pressure is measured between this point in the inlet ring and the static pressure in the duct just prior to the inlet of the fan. The energy conservation principle is then used to calculate an air volume. Notably, the active pressure method does not require a 7.5 times the diameter straight duct prior to the measurement point.

With the above in mind, and with the non-limiting example of FIG. 1, an active pressure technique is utilized to determine air volume at the fan 30. The flow station 60 provides a sample of airflow at the inlet side 38. A pressure transducer 62 or similar-type sensor is connected to the flow station 60, for example via pneumatic tubing 64, and provides a measurement of a differential pressure at the inlet side 38, serving as an active pressure airflow reading. Information or data from the pressure transducer 62 is signaled (via wired or wireless connection) to a controller 66 (e.g., programmable logic controller or PLC) that is otherwise operable to control or dictate a speed of the fan 30. The controller 66 is programmed to covert the pressure reading (e.g., provided as an analog signal) to an air volume value. Further, the controller 66 is programmed to, or operates protocols (e.g., an algorithm) formatted to, determine a target fan speed corresponding with a preset air volume target. Where the determined air volume value differs from the air volume target, the controller 66 operates to continuously adjust the speed of the fan 30 to achieve the preset air volume target. For example, a protocol performed by the controller 66 can include or be based upon a difference between the target air volume and the measured or estimated current air volume. In some embodiments, the controller 66 can be programmed to determine an error rate (e.g., percentage) as a function of the difference between the target and current air volumes at the fan 30 (e.g., (target air volume—current air volume)/target air volume×100). The controller 66 can further be programmed with various fan speed adjustment parameters that each correspond with various determined differences (or range of differences) between target and current air volumes (including adjustment parameters that increase fan speed where the current air volume is less than the target air volume, and that decrease fan speed where the current air volume greater than the target air volume). The fan speed adjustment parameters and corresponding error values or ranges can be stored in a look-up table or the like that is accessible by the controller 66. In some non-limiting examples, the fan speed adjustment parameters stored by the controller 66 can be in terms of percent change in fan speed (e.g., where the current air volume is found to be 20% above the target air volume, the corresponding fan speed adjustment parameter can implicate a 10% decrease in fan speed). Other techniques, protocols or algorithms appropriate for determining a fan speed adjustment parameter based upon current air volume at the fan 30 are also acceptable. In some examples, the fan speed adjustment parameters are selected or formulated to effect relatively minor or subtle changes or adjustments in fan speed, intending to reduce the “error” between current and target air volume by relatively small amount (e.g., 5-8%). With these and related techniques, as the differential pressure across the filter banks 32, 34 increases with filter loading, the system static pressure will increase resulting in a reduction of air volume from the fan 30. From the flow station measurement, the controller 66 recognizes the change in air volume and operates to increase the speed of the fan 30 to compensate.

In some non-limiting examples, the controller 66 can be programmed to determine or estimate a current air volume at the fan 30 and effect adjustments to the speed of the fan 30 based on the current air volume as described above on a regular basis or cycles (e.g., every two minutes, every one minute, every thirty seconds, etc.). In some embodiments, the controller 66 is programmed to obtain two or more current air volume measurements (or measurements of the parameter from which air volume at the fan 30 can be determined as described above) for each adjustment cycle, and applies an average of the measurements (or some other statistically meaningful value based upon the two or more measurements) for purposes of determining an error and/or fan speed adjustment parameter (e.g., where fan speed consideration/adjustment is performed every minute, air volume at the fan can be determined or sampled over 30 seconds, and an average of the samples applied as the current air volume). Other techniques for designating or determining a current air volume at the fan 30 for purposes of fan speed adjustment are also acceptable.

In some examples, programming to effect the control processes of the present disclosure is provided as programming software to a PLC-type or similar controller. In other embodiments, the controller 66 can have access to, or includes, a processor and associated memory; the processor accesses instructions and/or information stored in the memory to effect the control processes of the present disclosure (e.g., the processor executes machine readable instructions contained in the memory or includes circuitry to perform computations). With these and related embodiments, the machine readable instructions may be loaded in a random access memory (RAM) for execution by the processor from their stored location in a read only memory (ROM), a mass storage device, or some other persistent storage (e.g., non-transitory tangible medium or non-volatile tangible medium).

As explained above, the systems and methods of the present disclosure are useful with a number of differently-configured air handling systems. For example, another air handling system 100 is shown in FIG. 2. The air handling system 100 is configured to provide clean, filtered air to a critical environment 102. The air handling system 100 includes first and second fans 110a, 110b, first and second return air filters (or filter banks) 112a, 112b, and first and second supply air filters (or filter banks) 114a, 114b. The filters 112a, 112b, 114a, 114b can assume various forms, and in some embodiments are HEPA filters. Ductwork 116 fluidly connects the various air handling system components relative to the critical environment 102, with the fans 110a, 110b operating to establish an airflow path identified by the arrows P through the ductwork 116. The unique airflow path P established by so-installed air handling system 100 will result in a unique system pressure condition. A controller 120 (e.g., PLC) controls operation (e.g., speed) of the fans 110a, 110b. While a single controller 120 is shown as prompting/controlling operation of both fans 110a, 110b, in other embodiments, two (or more) controllers can be provided, each dedicated to a respective one of the fans 110a, 110b. A flow station or measurement station 130a, 130b is provided at the inlet side of each of the fans 110a, 110b. The flow stations 130a, 130b can each have the construction as described above (e.g., a pressure transducer or similar-type sensor connected to the corresponding flow station 130a, 130b, for example via pneumatic tubing, that provides a measurement of a differential pressure at the inlet side of the corresponding fan 110a, 110b) or any other construction from appropriate for obtaining measurements from which air volume at the corresponding fan 110a, 110b can be determined.

The controller(s) 120 is programmed to, or operates one or more protocols or algorithms formatted to, determine or measure air volume at the inlet side of each of the fans 110a, 110b (e.g., via the corresponding active pressure measurement), select an adjustment parameter for the corresponding fan 110a, 110b to provide the desired air volume based upon the determined inlet side air volume (e.g., the process as described above), and provide control signal(s) to the fans 110a, 110b that effect the selected speed as described above. Notably, the fan control methods of the present disclosure can be performed independent of, or without determining, a system pressure of the airflow path P. In some embodiments, each fan 110a, 110b is controlled by its own, dedicated algorithm, but all of the fans 110a, 110b are controlled to the same target air volume. With these and related techniques, the systems and methods of the present disclosure can control a plurality of fans in series to automatically balance air volumes and maintain uniformity across all fans.

As the filters 112a, 112b, 114a, 114b load with dust and debris, the filter static pressure increases, thus changing the system pressure of the air handling system 100. The controller 120 effectively recognizes this system pressure change at the inlet side of the fans 110a, 110b via sensed fan air volume parameters at the flow stations 130a, 130b and operates to continuously adjust the speed of the fans 110a, 110b to maintain the desired air volume over the life of the filters 112a, 112b, 114a, 114b.

In some embodiments, the controller 120 is electronically connected to a display (not shown), either directly or indirectly (e.g., the controller 120 can be provided as part of a computer-like device that further includes a display screen; can be electronically connected (wired or wirelessly) to a separate computing device such as a HVAC system controller or building management system controller; etc.). With these and related embodiments, the controller 120 can be programmed to prompt the display to provide a user with various information and/or notifications. For example, with some systems and methods of the present disclosure, a user can be notified, at the display, when filter static pressures exceed the static pressure capacity of the corresponding fan 110a, 110b.

As a point of reference, FIG. 3 provides an example of air handling system dynamics over the life of an air filter. First, second, and third system curves 210, 212, and 214 each represent a unique system pressure condition based on the air handling system's ductwork configuration (e.g., bends and other restrictions in ducting) and the loading or static pressure condition of the system's air filter. Each system curve 210-214 can be generated by calculating the resistance of each element of the air handling system at a designated duty point or air volume, and the sum of these resistances at the duty point and a number of other volumes. Plotting these points on the volume/pressure graph results in the system curve, and reflects the resistance created at a set number of air volumes. Over time, the ductwork configuration does not change, but the static pressure condition of the filter does (as the filter becomes loaded with particles). Thus, the first system curve 210 represents a clean filter condition; the second system curve 212 represents a moderately loaded filter condition; the third system curve 214 represents a dirty filter condition. An essentially infinite number of additional system curves can be derived for and/or applied to the control process, each indicative of a different filter static pressure condition.

First, second, and third fan curves 220, 222, 224 each represent air volume performance or rating of the fan of the air handling system at a specific fan speed. Each fan speed change creates a new fan curve (i.e., the fan speed giving rise to the first fan curve 220 differs from that of the second and third fan curves 222, 224). Because most variable speed fans can be controlled to incrementally operate at a plethora of speeds up to a maximum rate, a virtually infinite number of other fan curves can be derived.

At any point in time, the operating point of the fan at a particular fan speed is determined by the intersection point of the corresponding fan curve with the currently-applicable system curve and represents the airflow and pressure achieved in the system. For example, where the fan is operating at the fan speed giving rise to the second fan curve 222 and the filter is in a moderately loaded condition, the operating point is the intersection between the second fan curve 222 and the second system curve 212.

The graph of FIG. 3 further includes or designates a desired constant volume line 230 that represents the desired air volume of the air handling system. The desired air volume can be selected or established by a user or system installer based on various factors. Rather than controlling the fan based on the virtually infinite number of possible system curves and fan curves, the systems and methods of the present disclosure are premised upon measured actual air volume at the fan and the set air volume target 230 as described above.

With the systems and methods of the present disclosure, the fan(s) are constantly or consistently adjusted to operate the fan at a speed that results in the air handling system generating a constant, or nearly constant, air volume. As the filter(s) of the air handling system continue to load with dirt and debris, the systems and methods of the present disclosure continue to adjust the fan speed to maintain an intersection point along the desired constant volume line 230. When the filter(s) are later changed out with a new, clean filter, the fan speed is reduced to maintain the desired constant air volume. Because beneficial fan control is provided independent of an actual system curve, the systems and methods of the present disclosure facilitate complete installation configuration flexibility, and is self-balancing. Controlling air volume by varying fan speed is more energy efficient than varying system static pressure.

Although the present disclosure has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes can be made in form and detail without departing from the spirit and scope of the present disclosure.

Claims

1. A method of operating an air handling system including a fan directing airflow through a filter, the method comprising:

obtaining a current air volume at the fan;

comparing the current air volume with a target air volume; and

adjusting a speed of the fan based upon the comparison.

2. The method of claim 1, wherein the step of comparing includes determining a difference between the current air volume and the target air volume.

3. The method of claim 1, wherein the step of comparing includes determining an error rate as a percent difference between the current air volume and the target air volume.

4. The method of claim 1, wherein the step of adjusting includes selecting a fan speed adjustment value from a plurality of adjustment values based upon a determined difference between the current air volume and the target air volume.

5. The method of claim 1, further comprising:

repeating the steps of obtaining, comparing and adjusting on a regular basis.

6. The method of claim 5, wherein the regular basis is at least once every two minutes.

7. The method of claim 1, wherein the step of obtaining includes determining an average air volume from a plurality of air volume measurement at the fan.

8. The method of claim 1, wherein the step of obtaining includes measuring a differential pressure at the fan.

9. The method of claim 1, wherein the step of obtaining includes interfacing with a flow station provided at the inlet side of the fan.

10. The method of claim 9, wherein the step of obtaining further includes sensing a pressure at the flow station.

11. The method of claim 10, wherein the step of obtaining further includes providing a pressure sensor open to the flow station.

12. The method of claim 1, wherein the fan is one of a plurality of fans provided with air handling system, the method further comprising:

obtaining a current air volume at each of the plurality of fans;

comparing the current air volume at each of the plurality of fans with a target air volume; and

adjusting a speed of the each of the plurality of fans based upon the corresponding comparison.

13. The method of claim 12, wherein the same target air volume is utilized with each of the plurality of fans.

14. The method of claim 1, further comprising:

notifying a user when filter static pressure exceeds a static pressure capacity of the fan.