Air flow control damper with linear performance characteristics comprising an air foil control blade and inner annular orifice

Abstract

An air flow control damper consisting of either a tubular or rectangular casing, an internal annular orifice and within the orifice a rotatable circular or rectangular blade with an air foil profile. The blade may be either single or multi-part. The air flow control blade is designed to rotate on a shaft from an open position to a closed position modulating the air flowing through the casing. This damper exhibits a very low pressure drop—important for energy conservation—and a linear hystersis free performance curve—important when maintaining pressures in critical spaces.

Description

FIELD OF INVENTION

This invention relates to an air flow control damper which is capable of stable performance curve as well as linear and hystersis free control of the air flowing to or from a space. A very low pressure drop is desirable where compliance with current energy codes is desired. Minimal noise and suitability for DDC control are other attributes.

BACKGROUND OF THE INVENTION

Critical spaces need very close pressure and volume control to maintain the design environmental conditions. These spaces require special pressures—positive or negative to the surrounding spaces. Examples are Research Laboratories which are normally negative to the surrounding spaces to contain odors and fumes. Or, as an alternative, clean spaces may require a positive pressure which prevents contaminated air from entering the clean space. Additionally some spaces are designed for varying flow rates between maximum and minimum low flow rates (VAV) and must maintain the same space pressures during all conditions. This ability to maintain constant pressure differences is often a design challenge in research laboratories where both space occupancy and hood usage change dramatically during a 24 hr period. A desirable air flow control damper design would be capable of maintaining a constant pressure in spaces with these varying flow rates.

There are three currently popular air flow damper designs; one is with a flat damper blade with a low pressure drop but its performance is not linear, an airfoil damper with a series of inflatable airfoil blades but operable only by compressed air and a venturi damper but with very high pressure drop.

Linear performance is normally described as a constantly rising pressure volume curve from wide open to a closed tight condition and duplicating this curve when returning from close off to a wide open position. When there is no difference between the rising curve and the returning curve the resultant curve is often called hysterisis free performance and is desirable because the space pressures under changing flow rates can be easily predicted. Hystersis free performance is desirable in larger spaces which are served by a group of dampers in parallel and each of the dampers must contribute a constant pressure in spite of the varying flows through various damper sizes.

A low pressure drop through the damper is desirable when designing for equalized pressures throughout complex duct systems and is often mandated by current codes to minimize energy consumption.

Instrument air has been a dependable method of damper actuation for years but has been replaced by electronic Direct Digital Control where special software control is required.

Often air flow control dampers are required to accurately and repetitively control very low flow rates. The damper position for this requirement is normally very close to closed. To accurately control this very small amount of air at this blade position the valve must exhibit a linear characteristic curve without hystersis.

The flow rate entering a damper is modulated by the rotation of the damper blade from wide open through a 90 deg angle to a fully closed position. A tubular damper without an inner annular ring is very popular because of its low cost and low pressure drop. But in a tubular damper without an internal annular orifice the velocity discharges from the modulating air flow control blade directly against the inner surface of the tubular casing restricting the air flowing through the damper. This restriction often called an impact loss which causes a much lower flow than is actually possible if the air did not impact the casing as well as causing an unstable (non constantly rising) pressure volume curve. An internal annular orifice in cooperation with an air flow control blade permits the air flow to be discharged from the blade into the space behind the internal orifice without significant impact or loss of pressure against the inner surface of the casing. The unimpeded discharge of the air behind the annular orifice re-establishes a stable performance curve. The use of an internal annular orifice is shown in Jacobs (U.S. Pat. No. 5,518,446) but only as a stop to assist closure—he does not teach the use of an internal annular ring as a means to reduce the impact loss and to achieve hystersis free performance. Additionally Knecht (U.S. Pat. No. 3,070,345) also shows an internal annular ring but also only to assist final closure of the damper.

The radial width of the annular orifice is important because the slope of the characteristic curve is determined by the ratio of the gross area of the casing to the net area within the annular ring. An example—the smaller the net free area within the annular orifice compared the gross area of the casing the less throughput of air flow there will be as well as a steeper performance curve. A good ratio will result in a low wide open pressure drop to meet current codes and a constantly rising slope of the air flow curve to repetitively modulate the airflow as the space loads change.

If the blade surface is flat the air discharging from the blade and impacting the inner surface of the casing will collapse behind the blades into the area of negative pressure behind the blade contributing to the unstable performance characteristics. By adding an an airfoil profile to the upper blade surface the air flow discharges from the leaving edge of the blade in a non-turbulent manner minimizing the negative pressure back of the blade and there by permitting a much larger percentage of flow to continue through the damper. This stable characteristic curve from a wide open blade position to very close to close-off position permits a wide turn-down with a single blade and shaft.

George (U.S. Pat. No. 6,991,177) teaches an extended turndown by means of separate blades in separate parallel channels with a resulting more complex construction. George does not teach the need for linear performance characteristics required for maintaining constant offsets and space pressures in critical spaces when using a VAV system design. McCabe et al (2002/0175307) and Moore et al (U.S. Pat. No. 6,557,826) also disclose multi blade dampers but do not teach the use of an inner orifice or the need for linear performance without hystersis. Day (U.S. Pat. No. 3,011,518) clearly teaches the importance of non turbulent flow contributing to a stable performance curve but did not anticipate a single or multi rotatable blade design suitable for electronic (DDC) control.

A tubular design is popular since it connects efficiently to commonly used tubular ductwork. But square or rectangular shapes are also important since these shapes meet special space requirements in buildings. These square and rectangular shapes are equally adaptable to an internal equivalent of the annular ring. In this case the equivalent to the annular ring can be descried as an internal flange fixed to the inner surface of the square or rectangular shape. The square or rectangular blade cooperates with the internal square orifice in the same manner as the circular blade cooperates with the internal annular orifice the tubular damper. This cooperation minimizes the impact of the air flow (and the resultant energy loss) against the inner surfaces of the damper and results in a lower pressure drop and linear performing damper.

The airfoil shape also permits the air to be discharged with a minimum of turbulence. This minimum turbulence as well as minimizing the negative area back of the blade substantially reduces the acoustical spikes at certain frequencies. This contributes to a lower over all noise spectrum

The single blade is the least expensive shape to manufacture but does not equally modulate the upper half of the airstream as well as the lower half. In the single blade design during modulation a large percentage of the air flows through the upper half of the inner annular ring. An alternate design splits the single blade design into two equal segments. In this embodiment, each segment is mounted on a common shaft or alternatively on its own shaft and each interacting with 180 deg circumference of the inner annular ring. The shafts are mounted very close to each other and are connected by a linkage on the exterior of the casing. An air flow control blade split in the manner described with both halves opening equally will equally modulate the upper half of the airstream as well as the lower half of the air stream. This form of split blade design is also suitable for a square or rectangular shape.

A valve with two blades of unequal area will provide a much larger turndown ratio (the ratio of the maximum to the minimum flow) than a valve with one blade or a valve with two half blades of equal area. This is very useful when the loads in a space vary widely and the air flow has to meet these loads exactly. For example a valve with two half-blades of equal area can be shown to process say a maximum of 2000 cfm and a minimum of 250 cfm or a turn down ratio of 8/1. In contrast a valve with one partial blade with an area of 75% of the orifice and the smaller partial blade 25% of the orifice can be shown to process a maximum of 2000 cfm and a minimum of 62.5 cfm or a turndown ratio of 35/1

Another form of flow control blade may include a series of radially mounted “pie” shaped blades actuated by a centrally mounted gear. This profile form collaborates with the inner annular ring after about a 45 deg rotation.

Some applications require a virtually noisefree damper design. While the vorticies shed by the blade may be reduced by careful design of the internal surfaces of the damper additional attenuation may be required. By designing the exterior casing with a series of perforated holes and enclosing a fiberglass insulation around this casing with a second solid outer casing a large reduction of radiated noise may be achieved. This method of treating radiated noise reduction within tubular casings was taught by Coward (U.S. Pat. No. 3,540,547) and is applicable to the instant invention. This form of noise attenuation is also suitable for a square or rectangular shape. This design is useful for broadcast studios music hall and the like.

Additionally mounting of an air flow control blade on a shaft permits the use of an electronically driven actuator suitable for DDC control. The blade position through the actuator is controlled by the software managing the space environment. This software may be located in adjacent computers and communicates with the actuators by means of analog (varying) electronic signals. An alternate means of actuation is a pneumatic (instrument air) signal from air compressors. While both electronic and pneumatic actuation are used the electronic method is more popular because more software programs can be developed and the accuracy and repetition of the programs is better than pneumatic systems.

A common method of measuring the flow of fluids is to measure the pressure drop across an orifice. In the instant invention the inner annular ring acts as an accurate measuring orifice to indicate the flow of the air through the valve. By properly locating two pressure taps on either side of the orifice and 90 degrees to the direction of the flow through the orifice an accurate pressure reading proportional to flow can be recorded. An added advantage is that the annular ring (measuring orifice) is within the length of the valve not requiring any additional space or accessories. This form of flow measurement is also suitable for a square or rectangular shape.

OBJECTIVES OF THIS INVENTION

Therefore the instant invention exhibits the following attributes; a linear characteristic with no hystersis, a choice of air control blade designs, a low pressure drop which complies with current Codes, a quiet valve with no predominate acoustical frequencies, suitable for electronic actuation and a choice of dampers shapes.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 shows a side view of an ordinary control damper composed of an outer casing (1) with a flat air control blade (2) and without a internal orifice. Also shown is the flat blade a primarily open position. Again the airflow patterns (3) are shown deflected by the blade most of which pass through the damper parallel to the axis of the damper and the remainder will impact the inner surface of the outer casing shown. In this instance there is a minimal amount of the air flow impacting the inner surface of the outer casing (1).

FIG. 2 shows that same ordinary control damper with an outer casing (1) with the flat control blade (2) at a mid point position approximately 45 deg to the axis of the casing. Also shown are air flow patterns (3) deflected by the blade (2) most of which pass through the damper at about a 45 deg angle to the axis of the damper and the remainder will impact the inner surface of the outer casing (1) with some force and loss of energy prior to passing through the damper.

FIG. 3 shows the same ordinary control damper with an outer casing (1) and with the flat air control blade (2) in a very close (75 deg) to a closed position. Also shown are air flow patterns (3) deflected by the blade (2) some of which pass through the damper at about a 75 deg angle to the axis of the damper and the remainder will impact the inner surfaces of the outer casing (1) with greater force and loss of energy prior to passing through the damper.

FIG. 3b shows a theoretical performance curve of an ordinary control damper (5) without any impact loss with a flat air control blade with impact loss.

FIG. 4 shows the instant invention as a control damper with an outer casing (1), an inner annular orifice (6) and a cooperating flat air control blade (2) in a primarily open position. Also shown are air flow patterns (3) deflected by the blade (2) most of which pass through the damper parallel to the axis of the casing and the remainder will flow into the space behind the inner annular orifice prior to passing through the damper.

FIG. 5 shows the instant invention as a control damper with an inner annular orifice (6) and a flat air control blade (2) in a mid point position prox 45 deg to the axis of the outer casing. Also shown are air flow patterns (3) deflected by the blade (2) some of which pass through the damper at about 45 deg to the axis of damper and the remainder flow into the space behind the inner annular ring with minimal turbulence and loss of energy prior to passing through the damper.

FIG. 6 shows the instant invention with an inner annular orifice (6) and with the flat control blade (2) in a very close to closed position (75 Deg). Also shown are air flow patterns (3) some of which pass through the damper at about a 75 deg angle to the axis of the damper. The remainder will flow into the space behind the inner annular orifice with minimal turbulence and loss of energy prior to passing through the damper.

FIG. 6b shows a comparison of a theoretical performance curve (5) with the actual performance curve (7) of the instant invention with an inner annular ring.

FIG. 7 shows the instant invention as a control damper with an outer casing (1), with an inner annular orifice (6) and the air flow control blade (2) modified with an air foil shape (8) fixed to a shaft (14). The blade is fixed in a mid point position approximately 45 degrees to the axis of the outer casing. The control blade (2) is modified to include an airfoil profile (8) reducing the turbulence of the air flow patterns discharging from the blade. Also shown are air flow patterns (3) deflected by the airfoil blade most of which pass through the damper at about a 45 deg angle to the axis of the damper. The the remainder will flow into the space behind the inner annular orifice with minimal turbulence and loss of energy prior to passing through the damper.

FIG. 8 shows the instant invention with an outer casing (1), an inner annular orifice (6) and the modified air flow control blade (2) in a close to closed position (75 deg). The control blade (2) is modified to exhibit an airfoil profile (8) reducing the turbulence of the air flow (3) patters discharging from the blade. Also shown are air flow patterns (3) deflected by air foil profile blade (8) some of which pass through the damper at about a 75 deg angle to the axis of the damper and the remainder will flow into the space behind the inner annular orifice with minimal turbulence and minimal loss of energy prior to passing through the damper.

FIG. 9a shows the instant invention with an outer casing (1) an inner annular orifice (6), a multi-part air flow control blade with each part blade having an equal area (9) with the modified air foil profile (8) in a very close to a mid point position (45 deg). Also shown are air flow patterns (3) deflected by each equal part of the air flow control blade. Each half of the airstream (3) will pass through one of two blades of the damper at about a 45 deg angle to the axis of the damper casing and the remainder of each of the air steam will flow into the space behind each half portion of the inner annular orifice with minimal turbulence and loss of energy prior to passing through the damper.

FIG. 9b shows the instant invention with an outer casing (1) an inner annular orifice (6), a multi-part air flow control blade but with each part blade having an area unequal to the other (9) and with both control blades (8) in a very close to a mid point position (45 deg). Also shown are air flow patterns (3) deflected by each un-equal part of the air flow control blade. Each portion of the airstream (3) will pass through one of two blades of the damper at about a 45 deg angle to the axis of the damper casing and the remainder of each of the air steam will flow into the space behind each half portion of the inner annular orifice with minimal turbulence and loss of energy prior to passing through the damper.

FIG. 10 shows a cross sectional view of the instant invention with an internal perforated casing (10), a second solid exterior casing (11) and a sound attenuating material (12) within the void between the two casings.

FIG. 11 shows a cross sectional view of the instant invention with two pressure sensing taps located close to the inner annular orifice but on opposite sides of the orifice.

FIG. 12 Shows various damper shapes which may be required when the installation will not accept the preferred round shape. In addition to the preferred round shape oval, square and rectangular shapes are shown.

Claims

1. In an air flow control valve comprising outer casing, an inner annular orifice and a cooperating flat air control blade fixed to a rotating shaft. The annular ring provides sufficient space that the air passing through the casing will minimally impact the inner surface of the casing.

2. the instant invention as described in claim 1 combined with a perforated inner casing and an additional exterior solid exterior casing and with a sound attenuating material enclosed within the void between the inner and exterior casings.

3. the instant invention as described in claim 1 manufactured in various shapes to efficiently fit the installation including round, oval, square and rectangular.

4. in the instant invention as described in claim 1 the installation of two static pressure taps on either side and in close proximity to the orifice. The two pressure taps will measure the pressure drop across the office which is proportional to the flow through the damper.

5. In an air flow control valve comprising an outer casing, an inner annular orifice and a cooperating air foil shaped air control blade fixed to a rotating shaft. The annular orifice provides sufficient space that the air passing through the casing the air will minimally impact the inner surfaces of the casing.

6. The instant invention as described in claim 5 combined with a perforated inner casing and an additional exterior solid exterior casing and with a sound attenuating material enclosed within the void between the inner and outer casings.

7. the instant invention as described in claim 5 manufactured in various shapes to efficiently fit an installation including round, oval square and rectangular

8. in the instant invention as described in claim 5 the installation of two static pressure taps on either side and in close proximity to the orifice which will measure the pressure drop across the office which is proportional to the flow through the damper.

9. In an air flow control valve comprising an outer casing, an inner annular orifice and a cooperating multi part air foil shaped air control blade. Each part of the multi part blade may have equal or unequal areas and are fixed to one or more rotating shafts. The inner annular orifice provides sufficient space that the air passing through the casing the air will not impact the surfaces of the casing.

10. the instant invention as described in claim 9 combined with a perforated inner casing and an additional exterior solid exterior casing and with a sound attenuating material enclosed within the void between the two casings

11. in the instant invention as described in claim 9 the installation of two static pressure taps on either side and in close proximity to the orifice which will measure the pressure drop across the orifice which is proportional to the flow through the damper.

12. the instant invention as described in claim 9 manufactured is various shapes to efficiently fit the installation including round, oval square and rectangular