Abstrict An air curtain providing an air stream across a doorway between
areas of relatively cool and warm air masses and continuously monitoring
the condition, e.g., temperature, pressure and flow rate, of one
or both air masses and the air stream. The air curtain has a control
system including an electronic controller operating a heater and
fan and receiving air characteristic inputs from temperature, pressure
and flow rate sensors. The controller monitors these inputs continuously
and processes them to operate the heater and fan according to algorithms
designed to minimize air cross-filtration and energy consumption
while maintaining the temperature and humidity of the air stream
at a point substantially along a line representing the mixing of
anteroom air and the air stream that is substantially tangent to
the psychrometric saturation curve. A method of maintaining a non-saturated
air stream across a freezer doorway, so as to prevent condensation
and reduce the formation of fog and frost at the doorway, is also
disclosed.
Claims Accordingly, to apprise the public of the full scope of the invention,
the following claims are made:
1. An apparatus for forming an air stream across a doorway between
areas of relatively cool and warm air masses including a supply
air plenum with an outlet aperture at a first side of the doorway,
a return air duct with an inlet aperture at a second side of the
doorway and an intermediate air duct extending between the supply
plenum and return air duct, the apparatus comprising: an air mover
for moving an air stream across the doorway into the inlet aperture
to the return air duct through the intermediate air duct to the
supply air plenum and out of the outlet aperture; a heater in thermal
communication with the air stream for warming the air stream; an
electronic control unit controlling the operation of the heater;
a first air sensor located in one of the relatively cool and warm
air areas providing an air characteristic input to the control unit;
and a second air sensor located in contact with the air stream providing
an air stream characteristic input to the control unit; wherein
the control unit continuously monitors the air characteristic input
and the air stream characteristic input and operates the heater
to maintain the temperature of the air stream at a point substantially
along a line representing the mixing of the air stream with one
or both of the air masses that is tangent to the psychrometric saturation
curve.
2. The apparatus of claim 1, wherein the first air sensor is located
in the relatively warm air area.
3. The apparatus of claim 2, wherein the first air sensor includes
a first temperature sensor and a first humidity sensor and the second
air sensor includes a second temperature sensor and a second humidity
sensor, wherein the first and second temperature sensors provide
respective first and second temperature signals to the control unit
and the first and second humidity signals provide respective first
and second humidity signals to the control unit.
4. The apparatus of claim 3, wherein the second air sensor is located
downstream from the air mover.
5. The apparatus of claim 4, wherein the second air sensor is located
in the supply air plenum.
6. The apparatus of claim 5, wherein the heater is located in the
intermediate air duct.
7. The apparatus of claim 6, wherein the control unit is programmed
with a parabolic approximation of the saturation curve.
8. The apparatus of claim 7, wherein the parabolic approximation
is generated by the equation y=0.139x.sup.2 +0.2803x+4.1766, wherein
y is in units of grains of water per pound of dry air and x is in
units of temperature in degrees Fahrenheit.
9. The apparatus of claim 8, wherein the mixing line is defined
by the equation y=[(H.sub.as -H.sub.a)/(T.sub.as -T.sub.a)]x+H.sub.as
wherein H.sub.as and H.sub.a are the humidity of the air stream
and anteroom air from the relatively warm air area, respectively,
in grains of water per pound of dry air and T.sub.as and T.sub.a
are the temperatures of the air stream and the anteroom air, respectively,
in Fahrenheit.
10. The apparatus of claim 1, further including: a first pressure
sensor located in the relatively cool air area providing a cool
air pressure input to the control unit; and a second pressure sensor
located in the relatively warm air area providing a warm air pressure
input to the control unit; wherein the control unit continuously
monitors the pressure input signals and operates the air mover to
minimize cross-filtration through the doorway.
11. The apparatus of claim 1, further including an air speed sensor
detecting air velocity through the doorway and providing a cross-filtration
air speed input to the control unit, wherein the control unit continuously
monitors the air speed input to minimize cross-filtration through
the doorway.
12. The apparatus of claim 1, wherein the air stream includes dehumidified
air flow drawn into the air stream.
13. The apparatus of claim 1, further including a filtration system
removing contaminants in the air stream.
14. A method of maintaining a non-saturated air stream across a
doorway between areas of relatively cool and warm air masses so
as to prevent condensation and the formation fog or frost at the
doorway, wherein the air stream is generated by an air curtain including
a supply air plenum with an outlet aperture at a first side of the
doorway through which an air stream is forced across the doorway
to an inlet aperture of a return air duct at a second side of the
doorway, the method comprising: monitoring continuously the condition
of the air stream and the condition of at least one of the relatively
cool and warm ambient air areas; and conditioning the air stream
to maintain the temperature and humidity of the air stream at a
point substantially along a line representing the mixing of the
air stream with one or both of the air masses that is tangent to
the psychrometric saturation curve.
15. The method of claim 14, wherein the air curtain includes a
heater, an electronic control unit and temperature and humidity
sensors, wherein the control unit controls operation of the heater
according to temperature and humidity input received from the temperature
and humidity sensors.
16. The method of claim 15, further comprising: monitoring the
pressure of the relatively cool air and the relatively warm air;
and adjusting the air stream flow rate so to minimize cross-filtration
through the door way.
17. The method of claim 16, wherein the air curtain further includes
an air mover generating the air stream and wherein the control system
further includes pressure sensors, wherein the control unit operates
the air mover according to input from the pressure sensors.
18. The method of claim 14, further comprising: monitoring the
flow rate of air flowing away from the air stream; and adjusting
the air stream flow rate so to minimize cross-filtration through
the door way.
19. The method of claim 14, further comprising mixing air from
the cool air area into the air stream.
20. The method of claim 14, further comprising mixing de-humidified
air into the air stream.
21. The method of claim 14, further comprising filtering the air
stream to remove contaminants therein. Description CROSS-REFERENCE TO RELATED APPLICATIONS
Not Applicable
STATEMENT OF FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an apparatus for preventing cross-filtration
of relatively cool and warm air masses at the opening of a refrigerated
space, and particularly, for an air curtain that continuously monitors
and optimizes the condition of the circulating air stream to eliminate
the formation of fog and frost at the opening.
2. Background and Description of the Prior Art
Refrigerated warehouses typically have one or more cold storage
rooms adjacent to rooms at more moderate temperatures. At open doorways
between these rooms some of the lighter, warm air will flow into
the cool area primarily through the top of the doorway (warm air
infiltration) in exchange for heavier, cool air at the bottom of
the doorway (cold air exfiltration). Depending upon the conditions
of the two air masses, this cold air exfiltration and warm air infiltration
can cause numerous problems. Infiltrating warm air can carry more
moisture than cool air and tends to become supersaturated within
the cold room or at the door opening, which leads to precipitation
or airborne ice crystals at the doorway. The humid warm air also
leads to ice build-up within the cold room, especially on the floor,
doors, walls, evaporator coils, and/or products adjacent to the
doorway and inflates energy costs for refrigerating the cold rooms.
The exfiltrating cool air tends to mix with the humid warm air to
cause fog at the warmer side of the doorway. The fog reduces visibility
and can lead to wet slippery floors at the doorway.
There have been many attempts in the prior art to minimize the
adverse effects of the colliding air masses at the doorways of cold
storage rooms. Commonly, a physical barrier of some type is utilized
at the doorway. Such barriers include sliding doors having overlapping
edges or sweeps that reduce the air flow through the gaps around
the door panels. Sliding doors hamper passage through the doorway
and allow heavy infiltration during high door operation periods.
These high door operation periods can cause ice build-up and mass
air infiltration and exfiltration. Another type of physical barrier
is a strip door with transparent plastic or vinyl strips hanging
from the doorway header. Strip doors are typically low-cost but
they impede passage through the doorway, and the strips can separate
with use allowing cross-filtration of the air. Once this begins
to occur, the strips can become coated with ice so as to reduce
visibility through the doorway and allow for greater air infiltration.
Rather than a physical barrier, the doorways of cold storage rooms
can be "closed" by an active air barrier, commonly referred
to as an "air curtain", allowing unobstructed passage
through the doorway. An air curtain is formed by a fan or air mover
producing a relatively high velocity air stream across the doorway,
either from side to side or top to bottom, to counteract the forces
of the cross-filtrating air masses. A heater may be used to condition
the air stream so as to maintain the temperature of the air sufficient
to prevent saturation (and thus condensation) of the air at the
doorway.
One known air curtain apparatus is disclosed in U.S. Pat. No. 4,516,482.
This patent discloses an air curtain vestibule mounted at a freezer
door having duct-work containing an air mover and a heater. The
apparatus is designed to heat the air curtain to a temperature sufficient
to avoid super-saturation of air infiltrating the freezer and saturation
of exfiltration air entering the outside of the freezer (the warmer
side). This is accomplished by heating the recirculating air to
a temperature that brings the mixed air to a point along a line
tangent to the saturation curve (100% humidity line) on the psychrometric
chart. This allows for air infiltration and exfiltration without
condensation. The recirculating air temperature is determined based
on normal operating conditions of the freezer and the anteroom (outside
the freezer) and the heater is set to maintain this temperature.
U.S. Pat. No. 6,106,387 discloses a similar air curtain, however,
using an electronic controller and a plurality of temperature and
humidity sensors. Like the '482 patent, the heater is operated to
maintain a pre-selected temperature that results in a relative humidity
along a line tangent to the saturation curve on the psychrometric
chart.
Since these systems maintain a pre-selected temperature, they do
not adjust operating parameters in response to transient or changed
conditions of the air masses, for example, due to significant changes
in weather or anteroom conditions. As such, the system can operate
improperly (causing fog or frost) and in an energy inefficient manner
until the condition returns to normal or until the improper condition
is detected and the system is manually reconfigured to adjust operating
parameters, which may require one or more time consuming and costly
service calls.
SUMMARY OF THE INVENTION
The present invention improves upon prior art air curtains by continuously
monitoring the state, for example the temperature and humidity,
of one or both ambient air masses and the curtain air stream. The
air stream is then conditioned in a way that minimizes air cross-filtration
and energy consumption while maintaining the temperature and humidity
of the air stream at a point substantially along or slightly below
a line representing the mixing of the air masses and the air stream
that is tangent to the psychrometric saturation curve.
In particular, the present invention is an apparatus for forming
an air stream across a doorway between relatively cool and warm
air areas. The apparatus includes an air mover for moving an air
stream across the doorway and a heater in thermal communication
with the air stream for warming the air stream. The apparatus also
includes an electronic control unit controlling the operation of
the heater as well as at least one air sensor located in at least
one of the air areas providing an air input to the control unit
and a second air sensor located in communication with the air stream
providing an air stream input to the control unit. The control unit
continuously monitors the air and air stream inputs and operates
the heater to maintain the temperature of the air stream at a point
substantially along a line representing the mixing of air from one
or both of the relatively warm and cool air areas and the air stream
that is tangent to the psychrometric saturation curve.
The invention also provides a method of maintaining a non-saturated
air curtain across a doorway between relatively cool and warm air
areas so as to prevent condensation and the formation fog and frost
at the doorway. The method includes monitoring continuously the
condition of the relatively warm and/or cool ambient air areas and
the condition of the air stream and conditioning the air stream
to maintain its temperature and humidity at a point substantially
along or slightly below a line that is tangent to the psychrometric
saturation curve representing the mixing of the air and the air
stream.
By continuously monitoring the state of the air stream and at least
one of the air masses, the apparatus of the present invention can
efficiently prevent the air stream from becoming saturated and forming
condensation at the doorway. The heater is operated by the controller
in real-time to maintain the temperature and relative humidity of
the air stream just below saturation. The controller approximates
the psychrometric curve using a unique quadratic equation and computes
the necessary air stream temperature by evaluating the mixing line
equation with the values input by the temperature and humidity sensors.
This temperature also corresponds to the lowest approximate air
stream temperature maintaining non-saturation, thereby minimizing
heat input (and associated costs) and improving energy efficiency
of the system.
In a preferred form, the apparatus is an air curtain having a supply
air plenum with an outlet aperture at a first side of the doorway,
a return air plenum with an inlet aperture at a second side of the
doorway and an intermediate air plenum extending between the supply
and return air plenums. The air curtain includes pairs of temperature
and humidity sensors, one pair preferably located in the relatively
warm air area and the other pair located in the air stream. The
temperature and humidity sensors provide signals to the control
unit indicating the temperature and humidity at the warm area and
the air stream, which are processed by the control unit for operation
of the heater.
In other preferred forms, the air curtain further includes pressure
sensors located in the relatively cool and warm air areas providing
respective cool and warm air pressure input signals to the control
unit. The control unit continuously monitors the pressure input
and operates the air mover at a threshold pressure differential
to minimize cross-filtration through the doorway. The air curtain
can also include an air speed sensor detecting air velocity through
the doorway and providing an air cross-filtration speed input to
the control unit. The control unit continuously monitors the air
cross-filtration speed input signal and operates the air mover to
minimize cross-filtration through the doorway. Still further, the
air curtain can be designed to mix dehumidified air flow with the
air stream, for example, air from the cool air area.
The air curtain thus substantially reduces cross-filtration, and
the related adverse effects, of two or more adjacent air masses
at the opening of a cooled space. In particular, the air curtain
substantially reduces warm air infiltration and cold air exfiltration.
By continuously monitoring pressure sensors located in the relatively
cool and warm air areas and/or the velocity of air passing through
the doorway, the air mover can be operated in real-time to adjust
the air curtain speed as needed due to random or other changes in
the state of the air masses. The air curtain of the present invention
also reduces or eliminates air stream saturation and condensation
by mixing dehumidified or low moisture air with the air stream.
The foregoing and other objects and advantages of the invention
will appear from the following description. In this description
reference is made to the accompanying drawings which form a part
hereof and in which there is shown by way of illustration a preferred
embodiment of the invention. Such embodiment does not necessarily
represent the full scope of the invention, however, and reference
must be made therefore to the claims for interpreting the scope
of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a front view of an air curtain vestibule of the present
invention;
FIG. 2 is a schematic view showing the air curtain vestibule with
a control system;
FIG. 3 shows a simplified psychrometric curve with data points
for cool room conditions of 0.degree. F., 60% relative humidity,
point A, and warm room conditions of 35.degree. F., 85% relative
humidity, point B, and showing a mixing line (dashed) of the air
masses without conditioning the air curtain and a mixing line tangent
to the saturation curve after the air curtain is heated and its
relative humidity has been lowered; and
FIG. 4 is a plot of a parabolic approximation of the psychrometric
curve.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to FIGS. 1 and 2, an air curtain 10 for forming an air
stream across a doorway 12 between relatively cool and warm air
areas, such as at a cold storage room or freezer, has a supply air
plenum 14, a return air duct 16 and an intermediate air duct 18.
The air curtain 10 is placed on the floor around the doorway 12
and secured to a jamb structure, preferably at the cool side, such
that the supply air plenum 14 is along one side of the doorway 12
and the air return duct 16 is along the other side. Placing the
air curtain on the cool side of the wall provides for direct introduction
of low moisture cool room air into the air stream. The intermediate
air duct 18 extends along the top of the doorway 12 and joins the
supply plenum 14 and return 16 air duct. The supply plenum 14 and
return 16 air duct have open top ends that mate with openings at
the ends of the intermediate air duct 18 so that air can pass through
the intermediate air duct 18 from the return air duct 16 to the
supply air plenum 14. Air from the intermediate air duct 18 is redirected
by diverter assemblies 24 and exits the supply air plenum 14 through
an outlet aperture 20 at its inner face that extends longitudinally
substantially the height of the doorway 12. Air from the supply
air plenum 14 is received by the return air duct 16 through an air
inlet aperture 22 at its inner face that extends substantially the
height of the doorway 12. The inlet aperture 22 opening size decreases
from bottom to top to equalize the amount of air taken in along
its length. The air curtain 10 thus provides an air pathway through
the ductwork and across the doorway 12.
Preferably, a nozzle assembly 26 is mounted along the outlet aperture
20 to direct the air in a desired pathway across the doorway 12.
The nozzle assembly 26 preferably is horizontally adjustable and
sized to reduce turbulence. Within the intermediate air duct 18,
the recirculating air stream, cold air mass, and warm air mass will
mix so as to reduce the overall moisture content of the air. The
moisture content can be further reduced by introducing additional
cool air through an additional opening in the intermediate air duct
18.
The intermediate air duct 18 houses an air mover 28, such as a
squirrel cage type centrifugal fan capable of operating at 5,000
CFM, to generate and circulate the air stream. The air mover 28
draws air into the inlet aperture 22 of the return air duct 16,
through the intermediate air duct 18 and expels it into the supply
air plenum 14 to exit the outlet aperture 20 and form a high-speed
substantially laminar (non-turbulent) curtain of air across substantially
the entire doorway 12, as indicated by the arrows in FIG. 1. The
air stream can have a uniform velocity along the entire length of
the outlet aperture 20 or the velocity of the air steam can be varied
at different heights, for example, so that higher velocity air flows
at the top or bottom. In any event, air flow is directed across
the bottom half at a sufficient volume and rate to reduce significant
cold air exfiltration into the warm air side and across the top
half to prevent warm air infiltration into the cool air side. The
air stream takes a curvilinear path away from the door opening to
the inside face of the return air duct 16 due to the cold air pressure.
Referring to FIG. 2, the air curtain 10 includes a condition control
system including a heater 30, an electronic control unit (ECU) 32
and a plurality of air sensors. The heater 30 may be of any suitable
type, such as a passive resistance heater mounted within the intermediate
air duct 18 or a forced air heat exchanger mounted outside the ductwork.
The ECU 32 preferably includes a programmable logic controller (PLC),
a user interface display, an input module and an output module interconnected
by a standard bus. The output module of the ECU 32 is electrically
coupled to the air mover 28 and the heater 30. The input module
of the ECU 32 is electrically coupled to the sensors. Preferably,
the air sensors include two sets of temperature and humidity sensors.
One set of temperature and humidity sensors 34 is located in the
path of the air stream, preferably in the supply air plenum 14 near
the outlet aperture. This set of sensors is used to provide feedback
to the ECU 32 as to the conditions of the air curtain. The other
set of sensors 36 is located in the relatively warm side, preferably
mounted six inches off the wall and three feet from one side of
the doorway. This set of sensors is used by the ECU 32 to provide
data points corresponding to warm side air conditions that are used
to adjust the temperature and humidity of the air stream.
A preferred ECU 32 is commercially available from Siemens AG of
Munich, Germany. Specifically, the PLC is sold as the Simatic S7-200
(model No. 214-1BD21-0XB0) the display is a text display sold as
the Simatic TD 200 (model No. 272-0AA20-0YA0); the input module
is a 12-bit analog input module with four input points sold as EM231
(model No. 231-0HC21-0XA0); and the output module is a 12-bit analog
out module with two output points sold as EM232 (model No. 232-0HB21-0XA0).
The PLC can be programmed on an IBM compatible microprocessor based
computer using the ladder logic program available from Siemens.
The sets of humidity and temperature sensors are preferably combination
sensors commercially available as ACI/TT100/RH3-D-4X from Automation
Components, Inc. of Middleton, Wis. The sensors have an operating
range of -30.degree. F. to 130.degree. F. and 0% to 100% relative
humidity. It should be noted, however, that other control units
and sensors could be used to practice the invention.
The control system continuously monitors the condition of the air
in the air stream as well as the condition of the warm side air.
It should be noted that the cool side air could be monitored instead
of or in addition to the warm side air, however, this is unnecessary
in many applications because the cool side air is often in a freezer
or other cold storage room in which the air condition is maintained
at a nearly constant temperature and relative humidity. The ECU
32 processes the inputs received from the sensors 34 and 36 according
to an algorithm designed to maintain the air curtain at temperature
and relative humidity just below the saturation line so as to prevent
condensation and minimize the energy required to heat the air.
The logic controller of the ECU 32 is programmed to include a parabolic
approximation of the saturation (or 100% relative humidity) curve
of the psychrometric chart. A simplified version of the psychrometric
chart is shown in FIG. 3. The saturation curve is approximated to
simplify computation and avoid mathematical complications in the
control circuit. The saturation curve is approximated by the following
quadratic equation:
in which y is in units of grains of water per pound of dry air
and x is in units of temperature in degrees Fahrenheit. The approximation
curve is plotted as a solid line in the graph of FIG. 4.
To avoid condensation at the air curtain, the mixed air must be
conditioned to prevent it from becoming saturated. The temperature
and moisture in the mixed air falls along a diagonal process or
mixing line plotted on the psychrometric chart (see lines AC and
CB of FIG. 3). Condensation is avoided as long as the mixing line
is below the saturation curve. A mixing line that intersects a point
on the psychrometric chart corresponding to the condition of one
of the air masses and that is tangent to the saturation curve represents
the minimum temperature and maximum moisture content the air curtain
can sustain without becoming saturated. Thus, the amount of heat
or cooling (and thus energy) to be added to the air curtain is minimized
at this point.
The process or mixing line of the air masses that is tangent to
the approximation curve is computed by the equation:
y=[(H.sub.as -H.sub.a)/(T.sub.as -T.sub.a)]x+H.sub.as
in which H.sub.as and H.sub.a are the humidity of the air stream
and the anteroom warm side air, respectively, in grains of water
per pound of dry air and T.sub.as and T.sub.a are the temperatures
of the air stream and the anteroom warm air, respectively, in .degree.
F. T.sub.a and H.sub.a are data points collected by the anteroom
warm air sensors 36 and T.sub.as and H.sub.as are data points collected
by the air stream sensors 34 at the outlet aperture 20 of the supply
air plenum 14. The relative humidity measurements of the sensors
can be converted to grains using the equation:
Generally, the warm air temperature and relative humidity values
are variable in that they are subject to the weather conditions
and anteroom conditions. The ECU 32 processes the data collected
from the sensors using these equations to arrive at the desired
temperature of the air stream given the conditions of the warm side
air and falling along a tangent mixing line. If the condition of
the warm side air changes, the ECU 32 will process the data and
control the heater 30 as needed to raise or lower the air stream
temperature. Note that while not shown in the drawings, a cooling
coil could be mounted in the ductwork to more rapidly cool the air
stream in response to changing air conditions, however, this is
largely unnecessary in the described embodiment because the air
curtain is mounted at the cool side.
By way of example, FIG. 3 shows an application in which the sensors
36 detect that the warm side air is at 35.degree. F. and 85% relative
humidity (point B) and the cool side air is at 0.degree. F. and
60% relative humidity (point A). Ordinarily, the air between the
cool and warm air masses would mix along dashed line BA. Mixing
line BA intersects the saturation curve at points D and E and is
almost entirely in the supersaturated region above the saturation
curve. Air mixed along this line will result in condensation at
the doorway, thus leading to the formation of frost and fog. However,
by heating the air stream and controlling the air mixture percentages
of warm side air, cold side air and air stream air, the slope of
the mixing line can be changed. Using the above equations, the ECU
32 can calculate a point C corresponding to the air stream temperature
and relative humidity that lies along a mixing line extending from
point B and tangent to the saturation curve, shown as line CB .
As can be seen, the cool side air to nozzle air mixing ling AC and
the warm side air to nozzle air mixing line CD are both below the
saturation curve so condensation will not occur.
Changes in the warm side air condition are detected by the sensors
36 which causes the ECU 32 to calculate a new temperature and relative
humidity point for the air stream that falls along a new mixing
line tangent to the saturation curve and intersecting the new warm
side air condition. The ECU 32 continuously monitors the sensors
and performs these calculations to set the air curtain temperature
(and thus relative humidity) as needed to bring the mixing line
tangent to the saturation curve (or slightly therebelow).
By continuously monitoring the state of the air stream and at least
one of the air masses, the apparatus of the present invention can
prevent the air stream from becoming saturated and forming condensation
at the doorway. The heater is operated by the controller in real-time
to maintain the temperature and relative humidity of the air stream
(and thus any cross-filtrating air) just below saturation. This
temperature also corresponds to the lowest approximate temperature
maintaining non-saturation, thereby minimizing heating costs and
improving energy efficiency of the system.
Referring again to FIG. 2, the vestibule could also include a set
of pressure or air flow sensors 40, one on each side of the doorway,
to detect the actual or expected cross-filtration of the air masses.
In other words, the sensors could detect the pressure differential
between the relatively warm and cool sides and/or the velocity of
air flowing off of the air curtain (generally transverse to the
doorway) to determine the amount of air from either side passing
through the doorway. The values input from the sensors 40 could
then be processed by the ECU 32 to control the operation of the
air mover 28. That is, the velocity of the air curtain could be
increased as needed to reduce bulk air movement through the doorway.
Additionally, while not shown, the nozzle assembly could be powered
and electrically coupled to the ECU 32 to change the direction of
the air stream. For example, the nozzle assembly could be moved
to point the air stream more directly at the higher pressure side.
Still further, the nozzle assembly could have upper, middle and
lower blade sections that could be independently operated by the
ECU 32 to direct portions of the air curtain in different directions
and at different velocities. For example, the upper portion of the
air curtain could be directed toward the warm side to combat warm
air infiltration and the lower portion of the air curtain could
be directed toward the cool side to prevent cool air exfiltration.
The air curtain thus substantially reduces cross-filtration, and
the related adverse effects, of two or more adjacent air masses
at the opening of a cooled space. In particular, the air curtain
substantially reduces warm air infiltration and cold air exfiltration
out of the cooled space. By continuously monitoring pressure sensors
located in the relatively cool and warm air areas and/or the velocity
of air passing through the door way, the air mover can be operated
in real-time to adjust the air curtain speed as needed due to random
or other changes in the state of the air masses.
The air curtain could also be made to introduce low moisture air
into the air curtain. For example, component 50 could be mounted
over an opening in the intermediate air duct 18 upstream from the
heater 30. This component could be simply a gate operated by the
ECU 32 to let in air from the cool side, which typically has a low
moisture content due to its low temperature. The component 50 could
also be a dehumidifier or a part of a larger dehumidification system
that supplies reduced moisture content air to the air curtain. Such
a dehumidifier/dehumidification system would preferably carry in
external air or air from the warm side that has a relatively high
temperature, thus further lowering the energy needed to heat the
air curtain. The dehumidification system and the opening to the
ductwork could also be controlled by the ECU 32. Further, the air
curtain could also include an air filtration system such as unit
60 mounted over an opening in the return air plenum 16 and using
conventional filters and techniques for removing small particles
and contaminants from the air curtain. A desiccant, such as silica
gel, for example, could be used to dry the air.
Illustrative embodiments of the invention have been described in
detail for the purpose of disclosing a practical, operative structure
whereby the invention may be practiced advantageously. However,
the apparatus described is intended to be illustrative only, and
the novel characteristics of the invention may be incorporated in
other structural forms without departing from the scope of the invention.
For example, although described herein as mounted in the cool side,
the air curtain could be mounted within the doorway or at the warm
side. Moreover, the air curtain could be used in conjunction with
any suitable conventional panel or strip doors providing a physical
barrier covering the doorway. In that case, however, the doors preferably
would be suitable for operation by the ECU and the air curtain would
include sensors for detecting traffic through the doorway so that
the doors could be opened automatically per use or be held open
continuously during high traffic times of the day. |