US20110039491A1

US20110039491A1 - Low Mixing Ventilation Jet

Info

Publication number: US20110039491A1
Application number: US12/542,045
Authority: US
Inventors: H. Ezzat Khalifa; Mark Glauser
Original assignee: Syracuse University
Current assignee: Syracuse University
Priority date: 2009-08-17
Filing date: 2009-08-17
Publication date: 2011-02-17

Abstract

A ventilation system with hardware to direct two independent airflows, wherein an outer airflow (at least partially) surrounds the an inner airflow. Preferably the inner and outer airflows come from different sources such that the air of the inner airflow has higher associated costs than the air of the outer airflow. For example, the inner airflow may be more cleaned and/or more thermally conditioned than the outer airflow. The inner airflow may have a different velocity than the outer airflow. Preferably, the ventilation system is a PVD, but other applications are also contemplated, such as: (i) spot-cooling; (ii) air curtains (for example for a refrigerated food section or case in a market); (iii) medical devices (for example, oxygen supply devices, “blankets” of thermally conditioned and/or cleaned air for infants, patients in surgery or burn victims, shields of cleaned air for protection against microbes for patients with compromised immune systems); (iv) personal humidifiers; (v) personal dehumidifiers; (vi) thermal and/or humidity control for plant or animal enclosures; and/or (vii) any other ventilation system for controlling at least one type of air characteristic (see Definitions section).

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to ventilation systems and more particularly to ventilation systems for providing cleaned air (see Definitions section), thermally conditioned air (see Definitions section) and/or humidity-controlled air to a particular zone.
2. Description of the Related Art
It is often desirable to provide cleaned, thermally conditioned and/or humidity controlled air to a particular zone. As one example of this, research indicates that providing building occupants with devices to control the flow of air in their immediate environments to their personal preferences can enhance their satisfaction and work performance. A couple examples of such research are set forth in: (i) Arens, E., T. Xu, K. Miura, Z. Hui, M. Fountain, and F. Bauman (1998), “A study of occupant cooling by personally controlled air movement”, Energy and Buildings, vol. 27, pp. 45-49 (1998); (ii) Melikov, A. K., R. Cermak and M. Majer, “Personalized Ventilation: Evaluation Of Different Air Terminal Devices”, Energy And Buildings, 34, 829-836 (2002) (Melikov 1”; (iv) Melikov, A. K., “Personalized Ventilation”, Indoor Air, Vol. 14, Suppl. 7, 157-167 (2004) (“Melikov 2”); and (v) Melikov, et al., “Performance Of Personalized Ventilation In Conjunction With Mixing And Displacement Ventilation”, HVAC&R Research, Vol. 12, No. 2:295-311 (“Melikov 3”). This personalized control of air flow can be achieved by delivering conditioned air to each individual through an individually controlled personal ventilation device (PVD) (see Definitions section), placed within the individual's workstation.
Depending on their associated air supply, PVD may deliver an air flow that has been cleaned, thermally conditioned and/or humidity-controlled. PVDs that deliver a cleaned airflow with a relatively low concentration, rather than a just thermally conditioned recirculated airflow, generally provide considerable improvement in the air quality in the breathing zone for the individual user.
Although several PVDs have been developed, and tested, the extent of the market for PVDs is limited by cost of the PVD itself and also by concern that allowing each individual to control his or her personal air flow will lead to increased energy consumption and associated energy cost. These cost concerns are especially important for buildings with a large number of workstations where PVDs might be installed. With current PVDs, the individualized local control of an individual's workstation environment may indeed lead to increased energy consumption, when compared with other conventional building ventilation systems that are more centrally controlled. For example, the systems tested in Melikov 3 supplied as much as 15 liters per second (˜30 cubic feet per minute) of fresh air through the PVD nozzle to achieve high air quality in the breathing zone. This is considerably higher than the total amount of fresh air (˜7-10 liters per second) indicated by ASHRAE, Ventilation for Acceptable IAQ, Standard 62 (2004) for a typical room occupied by a single person.
Various investigators have studied the effect of PVDs on air quality in a person's breathing zone (BZ), notably at UC Berkeley/Lawrence Berkeley National Laboratory (LBNL) and at the Danish Technical University. In these studies a variety of PVD configurations comprising simple round or rectangular nozzles placed at different locations on or in the vicinity of the desktop have been investigated. For example: (i) FIG. 1 shows prior art PVD 100; (ii) FIG. 1 shows prior art PVD 200; and (iii) FIG. 3 shows prior art PVD 300. As shown in FIG. 1, there are many alternative locations that a PVD nozzle can be placed within an individual's workstation. Some of these alternative locations are further from the BZ than others, but, regardless of location and distance, the nozzle is oriented to directed a jet of air to the vicinity of the BZ. A study by Fanger et al. (“Fanger”) showed that improvement in air quality beyond minimally acceptable levels can have a substantial beneficial affect on satisfaction and productivity. In Fanger, a relatively large rate volumetric flow of air was used to improve the air quality beyond minimally acceptable levels.
Prior art PVDs are generally subject to a large degree of ventilation jet mixing, and this has an adverse affect on the air quality of the air that reaches the individual user of the PVD. In PVDs 100, 200, 300, simple jets of conditioned air issue from rectangular or round nozzles aimed at the person's body or head. FIG. 4 shows a typical air mixing pattern 500 produced by prior art PVDs 100, 200, 300, the pattern including: clean air 502; nozzle 504; potential core 506; mixing region boundary 508; user 510; emerging jet 512; and entrainment arrows E. In pattern 500, jet 512 of clean air 502 is propelled by the PVD to emerge from nozzle 504. As the clean air moves away from the nozzle in the direction of user 510, its central portion forms the shape of potential core 506, which remains substantially clean over length L. Surrounding the potential core is a mixing region, which is located between mixing region boundary 508 and the potential core. In the mixing region, ambient air travels in the direction of entrainment arrows E according to a phenomenon known as entrainment. Because of the mixing, the air in the mixing region is a mix of clean air and polluted, ambient air.
More specifically, clean air flow originating at the emerging jet entrains surrounding polluted air through turbulent mixing in the shear layer between the airflow and its surrounding essentially still air. The clean, conditioned core 506 of the airflow (or jet) is narrowed over length L by this turbulent mixing. By the time the jet arrives at the breathing zone of user 510, the potential core has been narrowed down to nothing, so that, as shown in FIG. 4, the potential core terminates at point 514, short of the BZ of user 510. This means that the air that reaches the BZ has been considerably contaminated by the polluted ambient air, which reduces or even eliminates the usefulness of the PVD. One potential solution is to locate the nozzle outlet closer to the BZ, but this solution has the following potential drawbacks: (i) additional nozzle hardware required; (ii) nozzle can interfere with user's movements; (iii) nozzle can interfere with users lines of vision; and/or (iv) nozzle becomes distracting due to proximity to the user's face.
It has been determined that the length L—that is, the length over which the potential core of a clean air jet completely disappears—is approximately equal to 4-6 times the nozzle width or diameter. For example, the core of a neutrally buoyant turbulent jet issuing from a 4-inch nozzle will completely erode in as little as 1.5 feet, regardless of the velocity at which it leaves the nozzle. This imposes limitations on how far from the person's face the nozzle is to be placed. The person's face must be well within the jet's potential core to minimize exposure to the surrounding pollutants.
Some prior art research of turbulent jets will now be discussed. The length L of the potential core of an air jet can be significantly increased if the primary core jet is shrouded by a secondary co-flowing air jet. The effect of the ratio of the speed of the secondary jet to the primary jet, called m, on the length of the potential core, L, is shown in the graph 520 of FIG. 5, which is from a book entitled Theory of Turbulent Jets by G. N. Abramovich (“Abramovich”). As shown in FIG. 5 at reference numeral 522, at a co-flowing secondary jet velocity ˜40% of the primary jet's (that is, m=0.4), the length of the primary jet's potential core of a free jet will be doubled in comparison with a similar primary jet in a still medium. However, Abramovich does not disclose any useful or commercial applications of this scientific research relating to co-flowing air jets.
U.S. Pat. No. 5,056,718 (“Wakefield”) discloses a jetting nozzle for producing a high velocity fluid. The nozzle produces a high velocity, fluid jet (called the inner jet), and a second, lower velocity fluid jet (called the outer jet). The outer jet is directed by the Wakefield nozzle geometry to surround the inner jet. Wakefield discloses fourteen potential applications for the Wakefield nozzle. In many of these applications, the inner and/or outer jets are specified to be liquid jets. In several other applications, there is an outer jet of air, but no inner jet. For example, the fourteenth application disclosed in Wakefield is “cooling and air conditioning,” and Wakefield specifies that only its outer jet should be used in the cooling and air conditioning applications of the Wakefield nozzle. One of the applications disclosed in Wakefield that does potentially utilize both the inner jet and the outer jet is described as follows: “12. Mixing. (Outer and inner jets of the same or different fluids.) Owing to the high turbulence in the mixing zone, the device may be used as a two- or three-component mixer. The three components would be inner jet, outer jet and ambient fluid. Two components would be outer jet and ambient fluid.”
U.S. Pat. No. 6,883,721 (“Marin”) discloses a system for lancing gas including an inner conduit and an outer conduit that is concentric with the inner conduit and surrounds it. Gas is expelled from the concentric conduits toward the vicinity of a primary flame or fuel stream to aid combustion or fuel ignition. The gas in the inner conduit may be oxygen-enriched air, while the gas in the second conduit may be oxygen-enriched air, nitrogen or argon. Marin states that the use of concentric conduits increases oxygen concentration at greater penetration distances. Marin does not disclose any non-combustion related applications for its concentric gas nozzles.
Description of the Related Art Section Disclaimer: To the extent that specific publications are discussed above in this Description of the Related Art Section, these discussions should not be taken as an admission that the discussed publications (for example, published patents) are prior art for patent law purposes. For example, some or all of the discussed publications may not be sufficiently early in time, may not reflect subject matter developed early enough in time and/or may not be sufficiently enabling so as to amount to prior art for patent law purposes. To the extent that specific publications are discussed above in this is a is Description of the Related Art Section, they are all hereby incorporated by reference into this document in their respective entirety(ies).

BRIEF SUMMARY OF THE INVENTION

The present invention relates to ventilation (see Definitions section) nozzles and new applications for ventilation nozzles. The ventilation nozzles of the present invention provide (at least) two airflows wherein on outer airflow (at least partially) surrounds an inner airflow. Preferably, the outer airflow has different temperature, humidity and/or cleaned air (see Definitions section) than the inner airflow, and is therefore less expensive to produce than the inner airflow. The outer airflow decreases the degree of jet mixing and entrainment of the inner airflow.
Through the use of present invention, higher BZ air quality and enhanced satisfaction can be achieved at no penalty in net energy consumption, or possibly even at a lower energy consumption for cleaning and/or thermal conditioning. This may be possible because the 15-20 cfm of clean air per person indicated in ASHRAE Standard 62 for acceptable indoor air quality (IAQ) is based on conventional mixing ventilation systems, which use the clean (fresh) air to dilute the concentration of indoor pollutants in the occupied spaces, thus producing acceptable air quality. As mentioned above in the discussion of Fanger, improvement in air quality beyond the acceptable level: (i) has a substantial positive affect on satisfaction and productivity, but (ii) requires a relatively large volumetric flow of clean air when prior art ventilation systems are used. This large volumetric flow has commensurately large energy costs associated with: (i) thermal conditioning; (ii) filtering/cleaning and/or (iii) moving the air. On the other hand, the present invention can provide similar levels of clean air to a user's BZ using a smaller volumetric flow having commensurately lower energy costs.
On the other hand, with the present invention, the PVD delivers the clean air of the inner airflow directly to the breathing zone with the help of the less-cleaned and/or thermally-conditioned outer airflow. An effective delivery system for the inner airflow requires only supply a fraction of the ASHRAE Standard amount of clean air required by whole room mixing ventilation systems. PVDs of the present invention can result in net energy savings and reduced inhalation exposure to indoor pollutants by reducing the entrainment of surrounding indoor pollutants in the PVD clean, inner airflow. Because the clean and/or thermally-conditioned inner airflow is relatively volumetrically small and delivered efficiently through space to the individual's breathing zone, the present invention may lead to net energy savings compared to both conventional centralized ventilation systems and conventional PVDs.
In ventilation systems according to the present invention, the outer airflow may, or may not, have a different velocity at the point of departure from the nozzle than the inner airflow. The inner and outer airflows are directed by the nozzle in at least substantially the same direction (that is, the airflow direction), but the inner and outer airflows may or may not leave the nozzle at the same location as measured along the airflow direction. Preferably the use of the outer airflow extends the length of the potential core of the inner airflow. Preferably, the use of the outer airflow will cause air to have characteristics (for example, temperature, humidity and/or cleaned air characteristics) more similar to that of the inner airflow at a greater distance from the nozzle.
Preferably, the use of the outer airflow will save on air treatment costs needed to achieve a given quality of air at a given distance from the nozzle. This cost savings may arise, in whole or in part, from the fact that less air treatment is needed due to the reduced mixing and entrainment as explained above. For example, assume a first ventilation system according to the present invention where only the inner airflow is cooled X degrees relative to ambient air temperature (that is, A-X degrees) at the point at which the air leaves the inner nozzle, and the outer airflow is not cooled (that is at A degrees). Assume, a second ventilation system having only a single airflow that is cooled to A-Y degrees where the air leaves the nozzle. In order to get the same degree of cooling at a given distance from the nozzle, generally speaking: (i) X<Y; and/or (ii) the volumetric rate of the inner airflow of the first ventilation system will be less than the volumetric rate of the second ventilation system. This means that the first ventilation system according to the present invention will generally be less expensive to operate than the second ventilation system according to the prior art.
The Definitions section defines the terms “air characteristic” and “air characteristic type.” In some embodiments of the present invention, the respective air supplies of the inner airflow and outer airflow may be controlled to make a smoother gradient, with respect to some air characteristic, across the combined cross section of the inner and outer airflows. For example, assume a first ventilation system according to the present invention where the inner airflow is cooled to ambient temperature minus X degrees (that is, A-X degrees), and the outer airflow is cooled to A-Y degrees. Further assume a second ventilation system according to the present invention that achieves identical cooling at the same distance from the nozzle, but where the outer airflow is not cooled at all (that is, outer airflow at temperature of A), and the inner airflow temperature is cooled to A-Z degrees, where X<Z and Y<Z. In some air cooling applications, it may be cheaper to use the first ventilation system where both the inner and outer airflows are somewhat cooled, in favor of the second ventilation system where only the inner airflow is cooled, albeit cooled to a greater degree. The first ventilation system, with its smoother temperature gradients across the airflow cross section may also be more comfortable for users.
In some ventilation systems according to the present invention, a first type of air characteristic may be adjusted (relative to ambient air conditions) in the inner airflow, while a second type of air characteristic may be adjusted (relative to ambient air conditions in the second airflow. For example, the inner airflow may have a controlled relative humidity while the outer airflow may have a controlled absolute temperature. As a further example, the inner airflow may be controlled in both its temperature and chemical composition, while the outer airflow may be controlled in its chemical composition only (that is, provided at ambient temperature).
According to a first aspect of the present invention, a ventilation system for providing air to a ventilated space with ambient air includes a primary air supply, a secondary air supply, a secondary air supply and a secondary nozzle. The primary air supply includes primary air having at least one air characteristic (see definitions section) different than the corresponding air characteristic of the ambient air. The primary nozzle is adapted and located to direct an inner airflow of primary air from the primary air supply into the ventilated space. The secondary air supply includes secondary air. The secondary nozzle is adapted and located to direct an outer airflow of secondary air from the secondary air supply into the ventilated space. The primary nozzle and the secondary nozzle are located relative to each other such that the outer airflow from the secondary nozzle at least partially surrounds the inner airflow from the primary nozzle.
According to another aspect of the present invention, a ventilation system for providing air to a ventilated space with ambient air includes a primary air supply, a secondary air supply, a secondary air supply and a secondary nozzle. The primary air supply includes primary air having an air characteristic at a primary air characteristic level which is different than the corresponding level of the air characteristic of the ambient air. The primary nozzle is adapted and located to direct an inner airflow of primary air from the primary air supply into the ventilated space. The secondary air supply includes secondary air having the air characteristic at a secondary air characteristic level which is different than the corresponding level of the air characteristic of the ambient air. The secondary nozzle is adapted and located to direct an outer airflow of secondary air from the secondary air supply into the ventilated space. The primary nozzle and the secondary nozzle are located relative to each other such that the outer airflow from the secondary nozzle at least partially surrounds the inner airflow from the primary nozzle. The secondary air characteristic level is closer than the primary air characteristic level to the corresponding level of the air characteristic of the ambient air.
According to another aspect of the present invention, a ventilation system for providing air to a ventilated space with ambient air includes a primary air supply, a secondary air supply, a secondary air supply and a secondary nozzle. The primary air supply includes primary air having a first air characteristic at a first characteristic level for the primary air supply which is different than the corresponding level of the first air characteristic of the ambient air. The primary nozzle is adapted and located to direct an inner airflow of primary air from the primary air supply into the ventilated space. The secondary air supply includes secondary air having a second air characteristic at a second air characteristic level for the secondary air supply which is different than the corresponding level of the second air characteristic of the ambient air. The secondary nozzle is adapted and located to direct an outer airflow of secondary air from the secondary air supply into the ventilated space. The primary nozzle and said secondary nozzle are located relative to each other such that the outer airflow from the secondary nozzle at least partially surrounds the inner airflow from the primary nozzle. The first air characteristic has a different air characteristic type than the second air characteristic.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a first embodiment of a prior art PVD;

FIG. 2 is a second embodiment of a prior art PVD;

FIG. 3 is a third embodiment of a prior art PVD;

FIG. 4 is a schematic of an air flow pattern typical of prior art ventilation systems;

FIG. 5 is a graph showing a relationship between co-flowing airflow velocities and potential core length;

FIG. 6 a schematic of an air flow pattern produced by ventilation systems according to the present invention;

FIG. 7 is a top view of a first embodiment of a ventilation system according to the present invention;

FIG. 8 is a front view of the first embodiment ventilation system;

FIG. 9 is a front view of a portion of a ventilation system according to the present invention;

FIG. 10 is a front view of a portion of a ventilation system according to the present invention;

FIG. 11 is a front view of a portion of a ventilation system according to the present invention;

FIG. 12 is a front view of a portion of a ventilation system according to the present invention;

FIG. 13 is a side view of an air curtain device according to the present invention;

FIG. 14 is a front view of a portion of a ventilation system according to the present invention;

FIG. 15 is a front view of a portion of a ventilation system according to the present invention;

FIG. 16 is a front view of a portion of a ventilation system according to the present invention;

FIG. 17 is a front view of a portion of a ventilation system according to the present invention;

FIG. 18 is a front view of a portion of a ventilation system according to the present invention;

FIG. 19 is a perspective view of a nozzle assembly according to the present invention;

FIG. 20 is a graph comparing nozzle assembly performance; and

FIGS. 21A, B and C are schematic views of airflow patterns.

DETAILED DESCRIPTION OF THE INVENTION

Before discussing specific embodiments, the theoretical basis of the present invention will first be discussed. An air jet issuing from a nozzle into still or co-flowing air at a different velocity experiences shear at its boundary. For sufficiently high jet Reynolds number, turbulence is produced in the shear layer between the jet and its surrounding medium, and the resulting turbulent eddies greatly enhance the transport of momentum, energy and species in this shear layer. As a result, the potential core of the jet gradually erodes due to the entrainment of low momentum fluid from the surrounding medium into the jet. This turbulent transport also enhances the entrainment of species from the surrounding medium into the jet's mixing zone. It has been recognized that the turbulent momentum diffusivity in such free shear layers is proportional to the width of the shear layer and the difference between the jet centerline velocity and the velocity of the surrounding medium (zero for still air).
For gases, the turbulent diffusivity for species transport is proportional to the momentum diffusivity, since the transport mechanism for both momentum and species is the same turbulent eddies. This means that the turbulent diffusivities for momentum and species (or energy) could be reduced if the surrounding medium co-flows parallel to the primary jet at a velocity that is close to the jet's. Research has shown that the length, L, as discussed above in connection with FIG. 5. The disclosed invention takes advantage of this effect.
The embodiments that follow emphasize personal ventilation systems, but some embodiments of the present invention may be directed to other applications, such as: (i) spot-cooling; (ii) air curtains (for example for a refrigerated food section or case in a market); (iii) medical devices (for example, oxygen supply devices, “blankets” of thermally conditioned and/or cleaned air for infants, patients in surgery or burn victims, shields of cleaned air for protection against microbes for patients with compromised immune systems); (iv) personal humidifiers; (v) personal dehumidifiers; (vi) thermal and/or humidity control for plant or animal enclosures; and/or (vii) any other ventilation system for controlling at least one type of air characteristic (see definitions section).
FIG. 6 shows airflow pattern 600, which is an exemplary embodiment of the type of airflow patterns produced by PVDs, and other ventilation systems, (for example, directed ventilation systems) according to the present invention. Pattern 600 includes: cleaned air 602; primary nozzle 604; potential core 606; mixing region boundary 608; potential core termination region 614; secondary nozzle 630; secondary airflow 632; ambient air 634; and entrainment lines E. The primary nozzle 604 of a suitable cross section, round, oval, rectangular or any other suitable shape, is aimed at the space or target to be ventilated. The primary nozzle issues a primary airflow from a primary air supply (not shown), where the primary air supply has been: (i) cleaned; (ii) thermally conditioned; and/or (iii) humidity-controlled. The primary airflow exits the primary nozzle at a primary velocity and a primary volumetric flow rate.
The primary nozzle is surrounded by secondary nozzle 630. The outlet of the secondary nozzle has a larger outer perimeter than that of the primary nozzle and completely surrounds the outer perimeter of the outlet of the primary nozzle in this preferred embodiment. The secondary nozzle issues a secondary airflow from a secondary air supply (not shown). In this example, the secondary air supply is recirculated room air. Alternatively, the air of the secondary air supply may also be: (i) cleaned; (ii) thermally conditioned; and/or (iii) humidity-controlled. The secondary airflow co-flows with the primary airflow and moves in the same direction as the primary jet, as shown in FIG. 6. The secondary airflow exits the secondary nozzle at a secondary velocity and a secondary volumetric flow rate. The secondary velocity is preferably: (i) less than the primary velocity; but (ii) close to the primary velocity for optimal performance. Preferably, the secondary velocity can be adjusted independently of the primary velocity.
The primary and secondary nozzles need not be concentric; for example, it may be desirable to offset the secondary nozzle downward to cover more of the person's torso to achieve a higher level of thermal comfort. The secondary, co-flowing airflow isolates the primary airflow from the surrounding “polluted” ambient air 634 and reduces the shear stress at the edge of the primary airflow's potential core 606, thus reducing turbulent mixing and entrainment of the primary airflow. In this manner, the length L of the potential core, taken from the outlet of the primary nozzle to the potential core termination region 614, is significantly extended. This extension of the potential core can lead to many benefits in various applications of ventilation systems according to the present invention, such as: (i) in PVD applications, clean fresh air is delivered over a larger region in the user's BZ; (ii) in PVD applications, the primary volumetric flow rate may be reduced without reduction in user satisfaction and comfort; (iii) in spot-cooling (or spot-heating) applications, more effective cooling or heating at a given distance from the primary nozzle outlet and at a given primary volumetric flow rate; (iv) in air curtain applications, more effective curtain type functionality; (v) in medical devices applications, improved physiological effectiveness; (vi) in personal humidifier and/or dehumidifier applications, improved user comfort at a given distance from the outlet of the primary nozzle; and (vii) in plant or animal enclosures, enhanced health and/or comfort for the enclosed plants or animals.
In PVD applications, the nozzle assembly of the ventilation system may be mounted in a desk, a piece of office furniture or in a the wall or partition, and is preferably fed by a conventional personal environmental control system (PECS), as is known in the art. The PECS contains fans, valves, controls, and filters, and may also be equipped to perform thermal conditioning of either the primary or both the primary and secondary airflows and/or to clean recirculated air to be fed through the nozzle assembly. The nozzle assembly is adjustable either manually via louvers (or other known flow directors) or automatically via electronic controls to allow it to be accurately aimed at the person's BZ or body. The flows through both nozzles are adjustable by means of suitable fans or valves inside the PECS. The secondary airflow velocity preferably can be increased or decreased to adjust the length of the primary airflow's clean air core 606.
In pattern 600, the following qualities and quantities may be static during ventilation system operation, or may change dynamically over time as the ventilation system operates: (i) primary airflow cleaned air characteristics; (ii) degree of primary airflow thermal conditioning; (iii) degree of primary airflow humidity control; (iv) secondary airflow cleaned air characteristics; (v) degree of secondary airflow thermal conditioning; (vi) degree of secondary airflow humidity control; (vii) primary velocity; (viii) primary volumetric flow rate; (ix) secondary velocity; and/or (x) secondary volumetric flow rate.
FIGS. 7 and 8 show ventilation system 700 according to the present invention including: primary nozzle 704; primary airflow 712; secondary nozzle 730; secondary airflow 732; support member 736; primary nozzle conduit 738; primary propulsion device 740; primary supply conduit 742; primary air supply 744; secondary nozzle conduit 746; secondary propulsion device 748; secondary supply conduit 750; secondary air supply 752; and support spokes 754. Primary propulsion device 740 moves the primary air from air supply 744 through primary supply conduit 742, primary nozzle conduit 738, primary nozzle 704 and out of the primary nozzle outlet as primary airflow 712. Secondary propulsion device 748 moves the secondary air from air supply 752 through secondary supply conduit 750, secondary nozzle conduit 746, secondary nozzle 730 and out of the secondary nozzle outlet as secondary airflow 712. The airflow pattern of primary airflow 712 and secondary airflow 732 into ambient air 734 is similar to pattern 600 discussed above.
Support spokes 554 support and center the outlet of primary nozzle within the interior space of the outlet of the secondary nozzle. Preferably these spokes should block as little of the secondary airflow as possible and be as aerodynamically slippery as possible so as not to impede the secondary airflow and/or increase the amount of energy necessary to drive the secondary airflow at a given secondary volumetric flow rate. Also, the space between the outer edge of the primary airflow and the inner edge of the secondary airflow should be made as small as possible to minimize turbulent flow in between the primary airflow and the secondary airflow. For this reason, the primary nozzle should not be made thicker than needed to withstand operational stresses and strains without failure. As shown in FIG. 7, the primary nozzle protrudes somewhat beyond the secondary nozzle in the direction of airflow AF. Alternatively, the primary and secondary nozzles could extend to the same point in the AF direction, or the secondary nozzle could extend further than the primary nozzle in the AF direction.
As mentioned above in connection with pattern 600, the use of the secondary airflow reduces turbulent mixing and entrainment and thereby lengthens the potential core of the primary airflow, with advantageous results. Preferably, the primary air is has better cleaned air characteristic(s) (for example, has a lower concentration of particulate pollutants) than the secondary air, and/or is thermally conditioned to a greater degree than the secondary air. For this reason, an arrangement like that embodied in the present invention would achieve equal or better air quality at a reduced primary volumetric flow rate, which means less energy consumption in both producing primary air for the primary air supply and in propelling the primary airflow. This decreased energy consumption reduces cost.
FIG. 9 shows the primary nozzle outlet 904 and the secondary nozzle outlet 930 for an embodiment of a ventilation system 900 according to the present invention. It is noted that the center of primary outlet 904 is considerably offset from the center of secondary outlet 930.
FIG. 10 shows the primary nozzle outlet 1004 and the secondary nozzle outlet 1030 for an embodiment of a ventilation system 1000 according to the present invention. It is noted that secondary nozzle outlet 1030 does not completely surround primary nozzle outlet 1004. Although this arrangement is non-preferred because there will be turbulent mixing between the primary airflow and the ambient air in the portion of the perimeter of the primary airflow that is not surrounded by the secondary airflow, there may be good reasons to use such an arrangement. For example, if the primary airflow were being used to cool a surface that ran parallel to the primary airflow, then system 1000 would allow the primary airflow to be located in greater proximity to the parallel surface.
FIG. 11 shows the primary nozzle outlet 1104 and the secondary nozzle outlet 1130 for an embodiment of a ventilation system 1100 according to the present invention. It is noted that: (i) the outlet of neither the secondary or primary nozzles are circular; and (ii) the outlets of the primary and secondary nozzles are not the same shape as each other. the shape of the primary and secondary nozzles is preferably determined by the pattern of air characteristic(s) that are desired in the space to be ventilated, and also on any physical constraints within this space.
FIG. 12 shows the primary nozzle outlet 1204 and the secondary nozzle outlets 1230 for an embodiment of a ventilation system 1200 according to the present invention. It is noted that the secondary nozzle is made up of a plurality of small openings. As used herein, a “nozzle” may include more than one opening so long as the openings get their air from the same air supply.
FIG. 13 shows an air curtain device 1300 embodiment of the present invention including: primary nozzle outlet 1304; the secondary nozzle outlet 1330; chilled interior space 1370 and insulated chamber wall 1372. It is noted that secondary nozzle outlet 1330 does not completely surround primary nozzle outlet 1304. Device 1300 gives an idea of some of the novel applications that the airflow patterns of the present invention may make possible and/or feasible. Specifically, device 1300 is a chilled display case for beverages with an air curtain formed across its front opening. Because or the use of the secondary airflow through outlet 1330, the primary airflow through outlet 1304 may have sufficient integrity such that a front door can be omitted from the air curtain device, in order to allow users freer physical and visual access to the contents of the chilled interior space 1370.
FIG. 14 shows the primary nozzle outlet 1404 and the secondary nozzle outlet 1430 for an embodiment of a ventilation system 1400 according to the present invention. Secondary outlet 1430 surrounds primary outlet 1404 for only a length of X, where X happens to be equal to 0.1*pi*D, or one tenth of the perimeter of the primary airflow. For purposes of this document, and to ensure clarity in the interpretation of this document, one airflow is considered to partially surround another only if it surrounds at least 10% of the perimeter, as it does in system 1400. This 10% need not be continuous.
FIG. 15 shows the primary nozzle outlet 1504 and the secondary nozzle outlet 1530 for an embodiment of a ventilation system 1500 according to the present invention. Secondary outlet 1530 surrounds primary outlet 1504 for a length of Y, where Y happens to be equal to 0.5*pi*D, or one half of the perimeter of the primary airflow. For purposes of this document, and to ensure clarity in the interpretation of this document, one airflow is considered to substantially surround another only if it surrounds at least 50% of the perimeter, as it does in system 1500. This 50% need not be continuous.
FIG. 16 shows the primary nozzle outlet 1604 and the secondary nozzle outlet 1630 for an embodiment of a ventilation system 1600 according to the present invention. In order to determine what proportion of the perimeter of primary outlet 1604 is surrounded by secondary outlet 1630, the arc lengths Z would be measured and summed, and then this quantity would be divided by the primary perimeter. Although it is preferable for the primary perimeter to be completely surrounded by the secondary outlet, as shown above in FIG. 7, there may be embodiments where merely partially surrounding, or merely substantially surrounding, is the optimal design solution of all factors (for example, geometry of the nozzle supply conduits).
FIG. 17 shows ventilation system 1700 according to the present invention including: primary nozzle outlet 1704; secondary nozzle outlet 1730; tertiary nozzle outlet 1780; and quaternary nozzle outlet 1782. In this embodiment there are more than two layers of nested airflows. This embodiment may be preferred for applications where a smooth gradient is desired to be set up across the cross section of the combined airflow. For example, assume that the primary velocity is controlled to be greater than the secondary velocity, and the secondary velocity is controlled to be greater than the tertiary velocity and the tertiary velocity is controlled to be greater than the quaternary velocity. In the case of this kind of velocity control, there will be a smoother gradient of velocity taken in the airflow direction, across the cross sectional profile of the combined airflow. This smooth gradient may further reduce entrainment and turbulent mixing even relative to the embodiments of the present invention discussed above.
Furthermore, velocity is not the only gradient which may be smoothed across the cross sectional profile of the combined airflow. Other parameters that can be controlled to form a smooth gradient include: (i) temperature; (ii) humidity; (iii) cleaned air characteristic. For example, the air supplies may be controlled so that the primary airflow has a lower concentration of particulate pollution than the secondary airflow and the secondary airflow is controlled to have a lower concentration of particulate pollution than the tertiary airflow and the tertiary airflow is controlled to have a lower concentration of particulate pollution than the quaternary airflow (which may be, for example recirculated air with the same concentration of particulate pollution as the ambient air). For a given degree of cleanness of the primary airflow, this arrangement would provide a smoother gradient of degree of cleanness across the cross-sectional profile of the combined airflow. Usually, the cost of the primary air to supply the primary airflow will be the largest per unit volume, regardless of whether the air characteristic(s) being controlled are cleaned air characteristic(s), temperature and/or humidity.
By controlling the air characteristic(s) to form a smooth gradient, not only may the turbulent mixing be reduced, as discussed above, but the diffusion may be reduced as well to thereby get a desired quality of air, at some given distance from the nozzles at the lowest possible cost. Also, user comfort and satisfaction over time may be enhanced. For example, in a PVD application, the users BZ may move over time as the user shifts back and forth. By using a smooth gradient of cleanness, the user will still be breathing somewhat cleaned air as her BZ shifts out of alignment with the potential core of the primary airflow. By using a smoother gradient of temperature, the user is less likely to experience extremes of hot and cold as she moves in and out of perfect alignment with the central axis of the primary airflow. This may be especially important in medical applications so that important physiological parameters like temperature, (low) microbe concentration or oxygen richness do not get out of control too quickly as the patient makes small motions relative to the primary airflow cross section. Although this concept of controlled gradients of air characteristic(s) has been explained in connection with the four airflow embodiment of system 1700, it should be understood that the same logic and advantages may apply for embodiments of the present invention with fewer airflows.
FIG. 18 shows the primary nozzle outlets 1804 and the secondary nozzle outlet 1830 for an embodiment of a ventilation system 1800 according to the present invention. It is noted that the primary nozzle is made up of a plurality of small openings. This is not generally preferred because the multiple primary outlets will tend to introduce turbulent flow at their perimeters. Nevertheless, there may be some applications where this type of multiple opening primary outlet is preferable.
In some embodiments of the present invention, it may be preferable to control a different air characteristic in the primary airflow than in the secondary airflow. As one example, assume that it is cheaper to heat recirculated air than it is to heat oxygen enriched air. However, it is desired to make a device that supplies both heat and oxygen enriched air to a user. Using the present invention, the primary airflow may be oxygen enriched while the secondary airflow may be heated. By controlling a different air characteristic in the primary airflow than the secondary airflow, the aggregate air costs may be minimized relative to what they would be if a single airflow were controlled to have both desired air characteristics.
Now, some design considerations for PVD applications of the present invention will be identified. The design of a PVD preferably provides several important objectives, some of which may appear to be contradictory: (i) PVD airflow should provide high-quality (fresh) air to the BZ; (ii) potential core of the jet should extend as close to the BZ as practically possible; (iii) airflow velocity near the face should be high enough to penetrate the human thermal plume (U_f=≧0.3 m/s); (iv) maximize energy-efficiency; (v) minimize volumetric flow rate of cleaned air; (vi) aesthetically considerations; (vii) ergonomic considerations; (viii) PVD hardware integrates unobtrusively in the room and its furnishings; (ix) PVD hardware and airflow does not adversely affect comfort; (x) PVD nozzle placed ≧0.4 m from face; and (xi) air velocity at face ≦1.0 m/s.
With respect to objective (v), preferably the PVD will require no greater fresh air supply rate than would be needed to ASHRAE Standard 62-2004 using a conventional whole room ventilation system. Also with respect to objective (v), the volumetric rate sum of PVD cleaned air and general ventilation (GV) cleaned air should not exceed the ASHRAE-62 value of ˜7 l/s. Preferably, the PVD cleaned air would have a volumetric flow rate of less than ˜3 l/s. It is noted that the use of a secondary airflow to extend the potential core of the primary airflow, according to the present invention, can help facilitate a more optimal balance of fulfillment of some, or all, of these objectives (i) through (xi).
The size (diameter) of the secondary nozzle should preferably be such that the target is about 4-6 diameters away from the nozzle. To ensure that the secondary flow has low turbulence, the nozzle contours should be designed to minimize boundary layer build-up and separation, and an appropriate number of screens should be placed at the exit to break-up the eddies (reduce the turbulence length scale). FIG. 19 shows a nozzle 1900 that has been tested with very good results. Graph 2000 of FIG. 20 compares the results for this prototype nozzle with and without the co-flow. In graph 2000, the light dots represent a single nozzle with x/D=7.8031, and the darker dots represent a co-flow nozzle with x/D of 7.8031. As shown by graph 2000, the disclosed invention can result in a near doubling of the air quality in the BZ (from 0.4 for the single nozzle to close to 0.8 for the co-flow nozzle with nearly matched primary and the secondary velocities and a nozzle exit turbulent intensity of ˜2% for both).
As noted above, the nozzle assembly may be mounted in the desk, a piece of office furniture or in a wall or partition. A particularly suitable arrangement is a corner placement in an office or a cubicle where the ducting and the supply box feeding the PV nozzle are placed in the usually unutilized dead corner. The flow could be split between two or more nozzles to allow for more ergonomic integration in the office environment. In such a case, the co-flow nozzles would deliver high BZ air quality even with the reduced flow through each nozzle. At such low flows per nozzle, improvement in BZ air quality will be very difficult, if at all possible to achieve with a conventional small nozzle.
As mentioned above, preferably the primary and secondary airflows are as close to each other as possible. However, some embodiments of the present invention may include primary and secondary airflows that are somewhat spaced apart. This affect of this spacing will now be discussed. In turbulent jets of practical interest, turbulence is generated as a result of the fluid shear stresses at the interface between two fluids at different speed, e.g., a jet in a motionless medium of approximately the same density. Although turbulence (turbulent eddies) is generated by velocity gradients, once generated, turbulent eddies also contribute to the vigorous lateral transport (mixing) of species and thermal energy.
This generation of turbulence and associated vigorous mixing of momentum, species and energy can be reduced if the velocity gradients (shear) can be reduced or eliminated. This is the purpose of this invention: to use the momentum of a co-flowing stream of ambient air to reduce shear and turbulence production at the boundary of a stream of a different chemical composition (e.g., higher degree of cleanliness) or temperature (higher or lower than ambient). Specifically this invention is intended to protect a clean and thermally conditioned stream of air (primary stream) from being degraded by uncontrolled turbulent mixing with contaminated and less thermally conditioned surrounding medium.
As shown in FIGS. 21A, B and C, two jets 2112, 2132 issue from nozzles or slots 2104, 2130 at approximately the same speed in the same direction, from left to right, albeit with different concentrations or temperatures. In FIG. 21A, the two nozzles are separated by a distance larger than the width of either one. The jets behave as if they are independent of each other and there is no interaction of the shear layers of the two jets. Each of the two jets forms its own mixing layers with the surrounding essentially motionless medium, within which vigorous mixing is induced by the shear-generated turbulence at the boundary between the jet core and the surrounding motionless medium. The result of this turbulent mixing is rapid erosion of the jets' potential cores (the wedge or cone shaped regions).
In FIG. 21B, the two jets are closer together, but still separated by a significant gap. The mixing layers of the jets 2112, 2132 begin to interact and coalesce. The shear at the lower boundary of jet 2112 and the upper boundary of jet 2132 is lowered and the erosion of the jet cores is somewhat reduced, causing the potential cores to extend farther than in Case A (and pull closer together farther away from the nozzles.
In FIG. 21C, the two nozzles are placed immediately next to one another, separated only by a thin wall. The shear layers between the two jets practically disappear and the two jets merge as one larger jet a very short distance away from the nozzles. The composite core erodes at a much lower rate and extends much farther to the right. This is the preferred arrangement for reducing mixing and extending the jet much farther toward the target.
The present invention would work best when the primary and secondary nozzles are close to one another as shown in FIG. 21C. The benefits decrease as the gap (G) between the two nozzles increases. In the preferred embodiments, this gap must be kept smaller than the width of the smaller of the two nozzles.

DEFINITIONS

The following definitions are provided to facilitate claim interpretation and claim construction:
Present invention: means at least some embodiments of the present invention; references to various feature(s) of the “present invention” throughout this document do not mean that all claimed embodiments or methods include the referenced feature(s).
First, second, third, etc. (“ordinals”): Unless otherwise noted, ordinals only serve to distinguish or identify (e.g., various members of a group); the mere use of ordinals implies neither a consecutive numerical limit nor a serial limitation.
Ventilation system: any system to move air (that is, any gas) within a space that is or may be occupied by living things; ventilation systems are not limited to systems that move air directly into or out of a person's lungs and also not limited to systems that move air directly into or out of a person's BZ; ventilation systems do not include: (i) systems that move liquid(s); and/or (ii) systems that supply gas to combustions or combustion fuel streams.
Personal ventilation device (PVD): any device (including personal environmental modules (PEMs)) for directing air flow(s) into the ambient atmosphere towards the vicinity of an individual user; a PVD includes at least the hardware necessary to direct air flow(s) to the vicinity of an individual, and may or may not include the hardware necessary to supply the air or to propel the air out of the body of the PVD and into the atmosphere.
Air: any substance in a gaseous phase.
Cleaned air: air that has a different composition than ambient air; for example, air with a low concentration and/or size of particulate pollutants relative to ambient air would be cleaned air, but this definition also extends to, for example, oxygen rich air that has a higher concentration of oxygen than the ambient environment.
Thermally conditioned air: air that is controlled to be warmer or cooler and/or more temperature stable than ambient air.
Air characteristic, type of air characteristic: Refers to any air characteristic of interest including the following types of air characteristics: (i) absolute temperature, (ii) relative temperature, (iii) absolute humidity, (iv) relative humidity; (v) composition at the molecular level (for example, proportion of oxygen); (vi) composition at the particulate level (for example, concentration of a particulate pollutant or set of pollutants); or (vii) composition at the atomic level (for example, relative isotope concentrations).
To the extent that the definitions provided above are consistent with ordinary, plain, and accustomed meanings (as generally shown by documents such as dictionaries and/or technical lexicons), the above definitions shall be considered controlling and supplemental in nature. To the extent that the definitions provided above are inconsistent with ordinary, plain, and accustomed meanings (as generally shown by documents such as dictionaries and/or technical lexicons), the above definitions shall control. If the definitions provided above are broader than the ordinary, plain, and accustomed meanings in some aspect, then the above definitions shall be considered to broaden the claim accordingly.
To the extent that a patentee may act as its own lexicographer under applicable law, it is hereby further directed that all words appearing in the claims section, except for the above-defined words, shall take on their ordinary, plain, and accustomed meanings (as generally shown by documents such as dictionaries and/or technical lexicons), and shall not be considered to be specially defined in this specification. Notwithstanding this limitation on the inference of “special definitions,” the specification may be used to evidence the appropriate ordinary, plain and accustomed meanings (as generally shown by dictionaries and/or technical lexicons), in the situation where a word or term used in the claims has more than one alternative ordinary, plain and accustomed meaning and the specification is actually helpful in choosing between the alternatives.
Unless otherwise explicitly provided in the claim language, steps in method steps or process claims need only be performed in the same time order as the order the steps are recited in the claim only to the extent that impossibility or extreme feasibility problems dictate that the recited step order (or portion of the recited step order) be used. This broad interpretation with respect to step order is to be used regardless of whether the alternative time ordering(s) of the claimed steps is particularly mentioned or discussed in this document.

Claims

1. A ventilation system for providing air to a ventilated space with ambient air, the system comprising:

a primary air supply comprising primary air having at least one air characteristic different than the corresponding air characteristic of the ambient air; a primary nozzle adapted and located to direct an inner airflow of primary air from said primary air supply into the ventilated space;

a secondary air supply comprising secondary air; and

a secondary nozzle adapted and located to direct an outer airflow of secondary air from said secondary air supply into the ventilated space, wherein said primary nozzle and said secondary nozzle are located relative to each other such that the outer airflow from said secondary nozzle at least partially surrounds the inner airflow from said primary nozzle.

2. The system of claim 1 wherein said primary nozzle and said secondary nozzle are located relative to each other such that the outer airflow substantially surrounds the inner airflow.

3. The system of claim 2 wherein:

said profile nozzle is shaped so that the inner airflow has a substantially circular profile;

said secondary nozzle is shaped so that the outer airflow has a substantially circular profile; and

the inner airflow and the outer airflow are at least substantially concentric.

4. The system of claim 1 further comprising:

primary propulsion hardware adapted and located to propel primary air from said primary air supply to and through said primary nozzle at a first velocity; and

second propulsion hardware adapted and located to propel secondary air from said secondary air supply to and through said secondary nozzle at a second velocity.

5. The system of claim 4 wherein:

said primary nozzle defines a primary nozzle width; and

said primary and secondary air propulsion hardware and said primary and secondary nozzles are adapted and located so that a potential core of the inner airflow is greater than 6 times the primary nozzle width.

6. The system of claim 4 wherein:

said primary nozzle defines a primary nozzle width; and

said primary and secondary air propulsion hardware and said primary and secondary nozzles are adapted and located so that a potential core of the inner airflow is greater than 10 times the primary nozzle width.

7. The system of claim 4 wherein said primary air supply, said primary propulsion hardware, said primary nozzle, said secondary air supply, said secondary propulsion hardware and said secondary nozzle are adapted to be used as a PVD.

8. The system of claim 4 wherein said primary air supply, said primary propulsion hardware, said primary nozzle, said secondary air supply, said secondary propulsion hardware and said secondary nozzle are adapted to be used as a spot-cooling device.

9. The system of claim 4 wherein said primary air supply, said primary propulsion hardware, said primary nozzle, said secondary air supply, said secondary propulsion hardware and said secondary nozzle are adapted to be used as an air curtains.

10. The system of claim 4 wherein said primary air supply, said primary propulsion hardware, said primary nozzle, said secondary air supply, said secondary propulsion hardware and said secondary nozzle are adapted to be used as medical device.

11. The system of claim 4 wherein said primary air supply, said primary propulsion hardware, said primary nozzle, said secondary air supply, said secondary propulsion hardware and said secondary nozzle are adapted to be used as a personal humidifiers and/or dehumidifiers.

12. The system of claim 4 wherein said primary air supply, said primary propulsion hardware, said primary nozzle, said secondary air supply, said secondary propulsion hardware and said secondary nozzle are adapted to be used as a device for thermal and/or humidity control for plant or animal enclosures.

13. The system of claim 1 wherein:

the primary air in said primary air supply is thermally conditioned to be at a different temperature than the temperature of the ambient air; and

the secondary air in said secondary air is thermally conditioned to be at a different temperature than the temperature of the ambient air.

14. The system of claim 1 wherein the primary air in said primary air supply is humidity controlled to be at a different humidity than the humidity of the ambient air.

15. The system of claim 1 wherein the primary air in said primary air supply is cleaned air.

16. The system of claim 15 wherein the primary air in said primary air supply has a lower concentration and/or size of particulate pollutants than the ambient air.

17. The system of claim 15 wherein the primary air in said primary air supply has a different chemical composition than the ambient air.

18. The system of claim 15 wherein the primary air in said primary air supply is thermally conditioned to be at a different temperature than the temperature of the ambient air.

19. A ventilation system for providing air to a ventilated space with ambient air, the system comprising:

a primary air supply comprising primary air having an air characteristic at a primary air characteristic level which is different than the corresponding level of the air characteristic of the ambient air;

a primary nozzle adapted and located to direct an inner airflow of primary air from said primary air supply into the ventilated space;

a secondary air supply comprising secondary air having the air characteristic at a secondary air characteristic level which is different than the corresponding level of the air characteristic of the ambient air; and

a secondary nozzle adapted and located to direct an outer airflow of secondary air from said secondary air supply into the ventilated space, wherein said primary nozzle and said secondary nozzle are located relative to each other such that the outer airflow from said secondary nozzle at least partially surrounds the inner airflow from said primary nozzle;

wherein the secondary air characteristic level is closer than the primary air characteristic level to the corresponding level of the air characteristic of the ambient air.

20. A ventilation system for providing air to a ventilated space with ambient air, the system comprising:

a primary air supply comprising primary air having a first air characteristic at a first characteristic level for the primary air supply which is different than the corresponding level of the first air characteristic of the ambient air;

a secondary air supply comprising secondary air having a second air characteristic at a second air characteristic level for the secondary air supply which is different than the corresponding level of the second air characteristic of the ambient air; and

wherein the first air characteristic has a different air characteristic type than the second air characteristic.