Title: Method and apparatus for delivering conditioned air using pulse modulation
Abstract: A method and apparatus for delivering conditioned air using short duty cycles during which a damper is fully open for a time and fully closed for the remaining time. Conditioned air is continuously supplied to a plenum at low pressure and is applied to the space when the damper is open and blocked when the damper is closed. The proportion of on to off time during each duty cycle is adjusted to meet the load. When several supply terminals serve a space, their duty cycles are staggered to avoid fan instability. A special motor is coupled directly to the damper shaft for fast opening and closing of the damper. A magnetic latch holds the damper open or closed until the motor moves it again.
Patent Number: 6,945,866 Issued on 09/20/2005 to Demster
| Inventors:
|
Demster; Stanley J. (Lenexa, KS)
|
| Assignee:
|
AirFixture L.L.C. (Kansas City, MO)
|
| Appl. No.:
|
150266 |
| Filed:
|
May 17, 2002 |
| Current U.S. Class: |
454/248; 454/292; 454/354 |
| Intern'l Class: |
F24F 007/08 |
| Field of Search: |
454/237,245,246,247,248,292,354
|
References Cited [Referenced By]
U.S. Patent Documents
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| 5911747 | Jun., 1999 | Gauthier.
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| 6185943 | Feb., 2001 | Kopko.
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| 6260375 | Jul., 2001 | Kuo.
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| 6267666 | Jul., 2001 | Wilhelmi.
| |
| 6405543 | Jun., 2002 | Kopko.
| |
Primary Examiner: Tapolcai; William E.
Attorney, Agent or Firm: Shook, Hardy & Bacon L.L.P.
Claims
1. A method for delivering conditioned air to a room having a first ceiling overlying
the room, an upper ceiling located above the first ceiling and an interstitial
space above the room at least partially defined by the upper ceiling and the first
ceiling, said method comprising:
separating said space into a supply plenum and a return plenum via a second ceiling
positioned intermediate the first and upper ceilings, said supply and return plenums
together occupying a substantial portion of the volume of said interstitial space
and being located generally one above the other;
delivering conditioned air to said supply plenum;
discharging the conditioned air from said supply plenum into the room;
directing return air from the room into said return plenum; and
discharging the return air from said return plenum.
2. A method as set forth in claim 1, wherein said step of delivering conditioned
air to said supply plenum comprises delivering conditioned air to said supply plenum
at a pressure of less than about 0.10 inch wg.
3. A method as set forth in claim 2, wherein said step of delivering conditioned
air to said supply plenum comprises delivering conditioned air to said supply plenum
at a pressure of approximately 0.05 inch wg.
4. The method of claim 3, wherein the step of directing return air from the room
into said return plenum comprises maintaining said return plenum at a lower pressure
than said supply plenum.
5. A method for delivering conditioned air to a room having an overlying ceiling
and a substantially open space above the ceiling, said method comprising:
seperating said space into a supply plenum immediately overlying said ceiling
and adjacent thereto and a return plenum immediately overlying said supply plenum;
applying conditioned air to said supply plenum to maintain said supply plenum
at a low positive pressure;
selectively discharging conditioned air through said ceiling into the room;
maintining said return plenum at a lower pressure than said supply plenum; and
providing a return air path from the room through said ceiling and supply plenum
to said return plenum to accommodate flow of return air from the room to said return
plenum.
6. Apparatus for delivering conditioned air to a room having a first ceiling
and a space above the first ceiling, said apparatus comprising:
an upper ceiling positioned above the first ceiling, said space above the first
ceiling being at least partially defined by the upper ceiling and the first ceiling;
a supply plenum in said space;
a return plenum in said space, said supply plenum and said return plenum together
occupying substantially the entirety of said space;
a source of conditioned air connected with said supply plenum to deliver conditioned
air thereto;
an air register in the ceiling arranged to direct conditioned air into the room
from said supply plenum; and
a return air path extending from the room to said return plenum to direct return
air to said return plenum.
7. Apparatus as set forth in claim 6, wherein:
said supply plenum immediately overlies said ceiling; and
said return plenum immediately overlies said supply plenum and is separated therefrom.
8. The method of claim 1, wherein the supply plenum immediately overlies the
first ceiling and is at least partially defined by the first ceiling and the second
ceiling and wherein the return plenum immediately overlies the second ceiling and
is at least partially defined by the second ceiling and the upper ceiling.
9. The method of claim 8, wherein the return air that is directed from the room
into the return plenum passes through a passage between the room and return plenum
and wherein the passage passes through the supply plenum.
10. The method of claim 1, wherein the first ceiling is a suspended ceiling.
11. The method of claim 5, wherein the conditioned air applied to the supply
plenum is applied at a pressure of less than about 0.10 inch wg.
12. The method of claim 5, wherein the room further includes an upper ceiling
positioned above the overlying ceiling and wherein the substantially open space
is at least partially defined by the upper ceiling and the overlying ceiling.
13. The method of claim 12, wherein the substantially open space is separated
into the supply and return plenums via an intermediate ceiling, wherein the intermediate
ceiling is positioned between the upper and overlying ceilings.
14. The method of claim 6, wherein the source of conditioned air connected with
the supply plenum has a pressure of less than about 0.10 inch wg.
15. The method of claim 7, wherein the room further includes a second ceiling
positioned above the first ceiling, wherein the supply plenum is at least partially
defined by the first ceiling and the second ceiling, and wherein the return plenum
is at least partially defined by the second ceiling and the upper ceiling.
16. Apparatus for delivering conditioned air to a room having a ceiling and a
space above the ceiling, said apparatus comprising:
a supply plenum in said space;
a return plenum in said space, said supply plenum and said return plenum together
occupying substantially the entirety of said space and bordering a majority of
the ceiling surface;
a source of conditioned air connected with said supply plenum to deliver conditioned
air thereto;
an air register in the ceiling arranged to direct conditioned air into the room
from said supply plenum; and
a return air path extending from the room to said return plenum to direct air
to said return plenum.
17. A method for delivering conditioned air to a room having a first ceiling
overlying the room, an upper ceiling located above the first ceiling and an interstitial
space above the room at least partially defined by the upper ceiling and the first
ceiling, said method comprising:
separating said space into a supply plenum and a return plenum said supply and
return plenums together occupying a substantial portion of the volume of said interstitial
space and wherein a portion of at least one of said plenums is partially bound
by said first ceiling, and wherein at least some of the conditioned air in the
supply plenum abuts the first ceiling;
delivering conditioned air to said supply plenum;
discharging the conditioned air from said supply plenum into the room;
directing return air from the room into said return plenum; and
discharging the return air from said return plenum.
18. The method of claim 17, wherein a portion of at least one of said plenums
is partially bound by said upper ceiling.
19. The method of claim 18, wherein a portion of the supply plenum is below a
portion of the return plenum, wherein the supply plenum is partially bound by said
first ceiling, and wherein return plenum is partially bound by the upper ceiling.
20. A method for delivering conditioned air to a room having a first ceiling
overlying the room, an upper ceiling located above the first ceiling and an interstitial
space above the room at least partially defined by the upper ceiling and the first
ceiling, said method comprising:
separating said space into a supply plenum and a return plenum, said supply and
return plenums together occupying a substantial portion of the volume of said interstitial
space and wherein a portion of at least one of said plunums is partially bound
by said first ceiling, and wherein at least some of the conditioned air in the
return plenum abuts the upper ceiling;
delivering conditioned air to said supply plenum;
discharging the conditioned air from said supply plenum into the room;
directing return air from the room into said return plenum; and
discharging the return air from said return plenum.
21. The method of claim 20, wherein at least some of the conditioned air in the
supply plenum abuts the first ceiling.
22. A method for delivering conditioned air to a room having a first ceiling
overlying the room, an upper ceiling located above the first ceiling and an interstitial
space above the room at least partially defined by the upper ceiling and the first
ceiling, said method comprising:
separating said space into a supply plenum and a return plenum,said supply and
return plenums together occupying a substantial portion of the volume of said interstitial
space and wherein a portion of at least one of said plenums is partially bound
by first ceiling, and wherein the space is separated into the supply and return
plenums via a second ceiling positioned intermediate the first and upper ceilings;
delivering conditioned air to said supply plenum;
discharging the conditioned air from said supply plenum into the room;
directing return air from the room into said return plenum; and
discharging the return air from said return plenum.
23. The method of claim 22, wherein a portion of the supply plenum is below a
portion of the return plenum, wherein the supply plenum is partially bound by said
first and second ceilings, and wherein return plenum is partially bound by said
second and upper ceilings.
Description
FIELD OF THE INVENTION
This invention relates generally to the delivery of conditioned air for heating,
cooling, ventilating and/or otherwise treating the air in buildings and other spaces.
More particularly, the invention is directed to a method and apparatus that makes
use of pulse modulation techniques for the delivery of air.
BACKGROUND OF THE INVENTION
Conventional systems for delivering air for the heating and cooling
of buildings use one of three different techniques. A constant volume system continuously
supplies a constant volume of air and varies the temperature of the air that is
being supplied in order to achieve a temperature change in the space. Variable
volume systems operate under simple on/off control or use analog throttling damper
or fan modulation to vary the flow rate.
All of these conventional systems have serious shortcomings. A typical constant
volume system uses a thermostat in the space that senses the ambient temperature
and sends a feedback signal. If the air temperature is above the set point temperature,
the air supply temperature is reduced. Conversely, the air supply temperature is
increased if the sensed temperature is below the set point. Although constant volume
systems are relatively simple and provide good ventilation, they have suffered
a decline in popularity due primarily to their energy inefficiency. The problem
is that when the load is low, a constant volume system delivers more air than is
necessary to maintain the set point temperature. This results in a waste of fan
energy which takes on increasingly adverse significance as energy costs increase.
Variable volume on/off systems are widely used because they are simple,
economical to install and relatively inexpensive to operate. However, there are
important disadvantages in that there is no ventilation during off cycles, the
temperature in the space is non-uniform, there is considerable noise variation
between on and off cycles, there is by necessity a significant dead band in the
thermostat control, and they are not practical for use other than in single zone systems.
Variable volume systems that vary the flow using variable dampers or variable
fans are advantageous in that they are able to closely track the load in the space
and are efficient in fan energy use. However, they are also characterized by relatively
high costs and complexity, noise variation caused by flow modulation, ineffective
ventilation, and inadequate mixing at low air volumes and load.
Analog modulation techniques for varying the airflow are particularly disadvantageous
when the air quantity is reduced under conditions of low loading. When the flow
if reduced, there is also a reduction in the air momentum, velocity, air throw,
air mixing and air induction. This results in poor comfort to the occupants of
the space and a compromise in the thermal efficiencies of the system. These problems
have been addressed by using air terminals in which the discharge area is restricted
to maintain a relatively constant velocity as the flow rate is reduced. However,
there is still a reduction of mass in the discharge air and associated limitations
in the kinetic energy, momentum, mixing, induction and air throw. At low supply
pressure, these problems are especially pronounced. For all of these reasons, the
so-called constant velocity, variable area devices are deficient as to the range
of loading conditions they can successfully handle.
Response rates have been another problem associated with variable damper
mechanisms. Standard practice is to provide a slow opening and closing time for
the damper in order to better match the dynamic response of the space to the response
of the controls, the sensing elements and the damper mechanism. If the response
is too rapid, unstable control of the damper can result and cause a "hunting" condition
in which the damper is repeatedly repositioned without producing the correct air
quantity. Conversely, if the damper opens and closes too slowly, the control of
the temperature in the space suffers. This condition is referred to as "drift"
and often results from efforts at avoiding the hunting effect at the expense of
transient response. Reaching a compromise where the system is well tuned is always
challenging and often labor intensive even if successful.
A further problem with prior art dampers is that they are subject to noise that
results mainly when the air velocity changes. Air flowing through small areas at
low flow rates can cause vibration of the hardware components and can also result
in objectionable noise from the air itself. The result is that noise at objectionable
levels can be produced, with varying noise at different flow rates making the situation
even less acceptable.
Treating air in other ways such as for high or low humidity, oxygen depletion,
or excessive carbon dioxide is subject to the same problems.
BRIEF SUMMARY OF THE INVENTION
The present invention is directed to an improved method and apparatus for delivering
conditioned air that makes use of pulse modulation to overcome or at least significantly
reduce the problems that have plagued air delivery systems in the past.
It is an important object of the invention to provide a method and apparatus
for
delivering air in a manner to achieve full mass, full kinetic energy, full momentum,
full induction, and maximum flow and velocity for complete mixing of the supply
air with the air in the space regardless of the load conditions.
Another important object of the invention is to provide a method and apparatus
of the character described that makes use of a low supply pressure (preferably
less than 0.25 inch w.g.).
A further object of the invention is to provide a method and apparatus of the
character
described that generates only minimal noise (preferably noise that is inaudible
to humans in a typical environment).
A still further object of the invention is to provide a method and apparatus
of
the character described in which there is no "hunting" or "drifting" of a damper
or other flow control device.
Yet another object of the invention is to provide a method and apparatus of the
character described that is economical to install and efficient in operation.
Still another object of the invention is to provide a method and apparatus
of the character described in which the set point temperature can be closely maintained
to maximize comfort in the area to which conditioned air is being supplied.
Another object of the invention is to provide an improved air terminal and
damper construction that exhibits improved performance in the delivery of conditioned
air to buildings and other spaces, particularly in the areas of effective mixing,
more uniform temperatures, less fan energy use, effective ventilation, and in other
performance characteristics.
A still further object of the invention is to provide, in a method and apparatus
of the character described, a terminal unit that does not require balancing.
Yet another object of the invention is to provide a method and apparatus of the
character described in which variable air volume and constant air volume devices
can be used in the same system. In this regard, the air terminal unit has a maximum
air flow volume that depends on the discharge area of the outlet rather than on
a damper. Consequently, some of the terminals can be equipped with dampers to achieve
variable air volume operation (by means of pulse modulation), and other terminals
can lack a damper to operate in a constant volume mode.
A further object of the invention is to provide a method and apparatus of the
character
described in which the terminals are pressure dependent. Because the terminal air
volume is controlled by the pressure and the duration of the damper open condition
during each duty cycle, the pressure can be varied to achieve different throw characteristics
of the terminal. At the same time, the damper provides the desired volume rate
of flow independently of the pressure.
These and other objects are achieved by providing a uniquely arranged air delivery
system that uses pulse modulation to control the delivery of conditioned air. In
accordance with a preferred embodiment of the invention, conditioned air is supplied
at a low pressure to one or more terminal units that apply the air. Each terminal
unit is equipped with one or more specially constructed dampers that are cycled
between fully open and fully closed positions to either supply air at full velocity
and throw or cut off the air almost completely.
The dampers are uniquely constructed to maintain the space at the set point temperature
by opening during part of each relatively short duty cycle and closing during the
remainder of the cycle. The ratio of time open to time closed during each cycle
determines the time-averaged quantity of conditioned air that is delivered to the
space and is dependent upon the load which is sensed by a thermostat or other control.
The duty cycles occur intentionally faster than any temperature changes that the
thermal sensor can detect. However, the average rate of flow resulting from the
on/off cycles is controlled in a manner to keep the dampers open sufficiently that
the average flow rate satisfies the set point temperature.
A "pulse" of air in the system of the present invention results from air delivered
at full pressure and volume to the terminal unit for a period of time adequate
to establish the full throw of the terminal. The duration of the damper opening
is sufficient to allow the jet or plume of air to fully develop.
Among the advantages of this pulse modulation technique is that each damper
is either fully open or fully closed and does not float at partially open positions.
This binary type operation allows a low supply pressure to be used because whenever
the damper is opened, it is fully open and delivers the air at full velocity, full
mass and full throw so that thorough mixing is achieved with the same momentum
and the same kinetic energy each time the damper opens. Consequently, low pressure
flow can be taken advantage of without encountering significant difficulties, and
the air distribution problems that are prevalent with variable volume prior art
systems are avoided. Also, there are no noise problems or damper "drift" or "hunting" problems.
The present invention is characterized by a control system in which different
dampers can be opened and closed at different times while maintaining the same
duty cycle for each damper. Preferably, the terminals are controlled in a daisy
chain fashion where an "open" pulse applied to the first terminal is delayed by
a preselected time delay to the second terminal and by another time delay if a
third terminal is present, and so on. The result is that each terminal has the
same on/off cycle duration, but the cycles are staggered in time to stabilize the
air delivery and fan operation. If all dampers opened at the same time and closed
at the same time, the flow would go from zero to maximum all at once, and there
would be unstable flow patterns and unstable fan conditions that could potentially
cause problems.
The present invention further contemplates a terminal and damper drive construction
that exhibits improved performance making them particularly well suited for use
in a pulse modulated system, as well as in other types of systems that can take
advantage of their performance characteristics. In this respect, the damper is
controlled by a special motor that rapidly opens and closes the damper without
objectionable noise and with only minimal wear over a large number of cycles. Further,
the outlet size of the terminal unit can be made adjustable in order to provide
a number of performance advantages.
Other and further objects of the invention, together with the features of novelty
appurtenant thereto, will appear in the course of the following description.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
In the accompanying drawings which form a part of the specification and are to
be read in conjunction therewith and in which like reference numerals are used
to indicate like parts in the various views:
FIG. 1 is a diagrammatic view of a conventional air delivery system of the type
commonly found in the prior art;
FIG. 2 is a diagrammatic elevational view of an air delivery system constructed
according to a preferred embodiment of the present invention;
FIG. 3 is a fragmentary elevational view on an enlarged scale of the detail
identified by numeral 3 in FIG. 2, with portions broken away for purposes
of illustration;
FIG. 4 is a top perspective view of an air terminal unit that may be incorporated
in the present invention;
FIG. 5 is a sectional view taken generally along line 5—5
of FIG. 3 in the direction of the arrows, with a portion broken away for purposes
of illustration;
FIG. 6 is a sectional view taken generally along line 6—6
of FIG. 5 in the direction of the arrows, with the broken lines indicating the
dampers in their closed positions;
FIG. 7 is a fragmentary sectional view on an enlarged scale taken generally
along line 7—7 of FIG. 5 in the direction of the arrows;
FIG. 8 is a schematic diagram of a control system that may be used with an air
delivery system in accordance with the present invention;
FIG. 9 is a fragmentary diagrammatic view of an alternative terminal unit having
an adjustable baffle plate;
FIG. 10 is a flow diagram of a control system that may be used with an air delivery
system in accordance with the present invention;
FIG. 11 is a flow diagram of an increase open time routine used in the system
of FIG. 10;
FIG. 12 is a flow diagram of a decrease open time routine used in the system
of FIG. 10;
FIG. 13 is a flow diagram of an open pulse output routine used in the system
of FIG. 10; and
FIG. 14 is a flow diagram of a close pulse output routine used in the system
of FIG. 10.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to the drawings in more detail, FIG. 1 diagrammatically illustrates
a typical prior art air delivery system of the type used to deliver conditioned
air to a room
10 formed within a building
12 having walls
14
and a roof
16. A false ceiling
18 for the room
10 is spaced
below the roof
16 in order to provide an open interstitial space
20
above the ceiling. A fan or other source of heated or cooled air (not shown) supplies
conditioned air to a supply duct
22 which extends in the space
20.
The duct
22 in turn supplies one or more smaller ducts
24 that lead
to ceiling mounted terminals
26. The terminals
26 diffuse the condition
air into the room
10. One or more return grills
28 which may be in
the ceiling allow the return air to exhaust from the room
10. The fan (not
shown) which supplies duct
22 and the heating or cooling unit which heats
or cools the air are controlled in a conventional manner by a thermostat or other
temperature sensor (also not shown) located within the room
10.
In order to provide sufficient space for installation of the ductwork and other
equipment, it is typical for the space
20 to have a height of 36 inches
or more between the ceiling
18 and the roof
16.
Referring now to FIG. 2 in particular, the present invention is directed
to an air delivery system that is improved in a number of respects from the conventional
system shown in FIG.
1 and other types of known systems. A building
30
includes a floor
32 and walls or partitions
34 which divide the space
within the building into a number of different rooms
36. The building
18
has a roof
38, below which a false or dropped ceiling
40 is provided
to overlie the rooms
36. An interstitial space
42 is provided between
the ceiling
40 and the roof
38 but can be only approximately 18-24
inches high in contrast to the typical 36 inch height required of the space
20
in a conventional system such as that of FIG.
1.
The system of the present invention may be equipped with a roof top unit
44
that includes a fan
46 and suitable equipment (not shown) for heating and
cooling air, as well as filters and other conventional devices. One or more supply
plenums
48 are formed in the space
42 within enclosures
50
which may locate the plenum or plenums
48 immediately above the dropped
ceiling
40. Preferably, there is only a single plenum
48 occupying
a large portion of the interstitial space
42, although a number of plenums
48 all connected and receiving air at the same pressure can be used. The
discharge side of the fan
46 connects with a duct
52 that leads to
the plenums
48 in order to supply conditioned air to the plenums. Each supplied
plenum
48 is provided with one or more terminal units
54 which may
be mounted on the ceiling
40 and supply the conditioned air from the plenums
48 into the underlying rooms
36. Although for simplicity each plenum
48 is illustrated as having a single terminal unit
54, it is contemplated
that each plenum
48 will be equipped with a relatively large number of the
terminal units, as will be explained more fully.
FIGS. 3 and 4 best illustrate the construction of each of the terminal units
54. Each of the terminal units
54 may be mounted adjacent to an opening
56 which is formed in the ceiling
14. Each terminal unit includes
a hood
58 having bottom edges
60 that may rest on top of the ceiling
14 adjacent to the opening
56. An upturned cylindrical collar
62
is formed on the top portion of the hood
58 and presents within it a circular
passage
64 through which the conditioned air flows downwardly into the interior
of the hood.
The hood
58 includes an annular shoulder
66 which is horizontal
and is located immediately outwardly of the collar
64. A horizontal baffle
plate
68 is suspended from the shoulder
66 by a plurality of hanger
brackets
70. The baffle
68 is located at approximately the same level
as the ceiling
14 but is smaller than the opening
56 in order to
provide an outlet
72 through which the air within hood
58 discharges
into the underlying room, as indicated by the directional arrow
74 in FIG.
3.
A horizontal mounting plate
76 is secured on top of the collar
64
and supports a damper housing which is generally identified by numeral
78.
The damper housing
78 may be rectangular and may be equipped with one or
more dampers
80. As shown in the drawings, two dampers
80 may be
provided, although a different number of dampers may be used in each terminal unit.
The damper housing
78 has an open top that opens into the plenum
48
in order to receive the conditioned air that is supplied to the plenum. The flow
of air downwardly through the damper housing
78 into the hood
58
is controlled by the dampers
80. As best shown in FIG. 6, each damper
80
may take the form of a flat damper blade mounted on a horizontal shaft
82.
As the shafts
82 are turned, the dampers
80 rotate between the fully
open position shown in solid lines in FIG.
6 and the fully closed position
shown in broken lines in FIG.
6. In the fully open position, each damper
80 has a vertical orientation so that maximum flow through the damper housing
78 is provided. In the closed position, each damper
80 extends horizontally,
and the two dampers occupy substantially the entirety of the inside of the damper
housing
78 in order to substantially block the flow of conditioned air from
the plenum
48 into the hood
58. The dampers
80 do not provide
a perfect seal within the damper housing so that some air passes through the damper
housing even when the dampers are closed. Thus, the construction provides controlled
leakage when the dampers are closed. Each damper
80 rotates through an arc
of 90° between the open and closed positions of the damper.
Each of the dampers
80 is equipped with an actuator which may take the
form of a special electric motor
84 for rotating the damper between its
open and closed positions. As best shown in FIGS. 4 and 5, the motors
84
are mounted within a motor housing
86 secured to one end of the damper housing
78. The shafts
82 extend through the damper housing
78 and
are supported for rotation on the damper housing. Each shaft
82 extends
into the motor housing
86 and connects with a rotor
88 which forms
part of the motor.
Referring to FIG. 7 in particular, each rotor
88 is cylindrical
and is located outside of a stator
90 mounted to the housing
86.
The stator
90 has one pair of opposed windings
92 which are maintained
at the same polarity and another pair of opposed windings
94 that are maintained
at the same polarity as one another but a different polarity than the windings
92. The rotor
88 is ferromagnetic and has a pair of opposite poles
96 that are of the same polarity as each other. Another pair of opposed
poles
98 on the rotor
88 have the same polarity as each other but
opposite to the poles
96. The current flow in the windings
92 and
94 may be reversed in order to actuate the motor and rotate the damper
80
through a 90° arc from the open position to the closed position or from the
closed position to the open position.
The motor
84 is provided with a magnetic latching arrangement that includes
a permanent magnet
100 mounted on the outside of the rotor
88 adjacent
to one of the poles
96. Four metal studs
102 are secured to the housing
86 and are spaced 90° part at locations where the magnet
100
aligns with one of the posts
102 whenever the windings
92 and
94
are aligned with the magnetic poles
96 and
98. Alignment of the magnet
100 adjacent to one of the posts
102 acts to releaseably latch the
rotor
88 in place to latch the damper
80 in its open and closed positions
without the need for mechanical stops.
The stator
90 is preferably secured to a printed circuit board
104
(FIG. 3) that is secured to housing
86 and contains circuitry providing
an interface between the motor and a control circuit that controls the open and
closed position of the damper in a manner that will be explained more fully. Each
damper shaft
82 is directly connected with the rotor
88 so that the
damper can be quickly rotated between its open and closed positions. The energizing
current to the windings
92 and
94 is preferably momentary current
that is applied only for sufficient time to place the rotor into rotation. When
the rotor has turned through an arc of 90°, it is latched in place by the
magnetic attraction between the magnet
100 and the metal stud
102
that is then in alignment with the magnet. Consequently, the dampers
80
are quickly rotated between the open and closed positions and are latched in whichever
position they are rotated to by the magnetic latching arrangement. This is all
accomplished without the need for mechanical stops or seals on the motor or damper.
While the dampers
80 are preferably butterfly type dampers of the type
shown, other types of dampers can be used, including shutter type dampers, slide
valves or other suitable types of damper mechanisms having a suitable actuator.
The damper mechanism of the present invention is characterized by the ability
to replace other dampers to improve system performance. By way of example, a damper
mechanism of the type shown in U.S. Pat. No. 6,019,677 can be replaced by the damper
of the present invention.
With reference to FIG. 2, each of the rooms
36 may be equipped with a
thermostat
106 or other sensor. The thermostat
106 may be set at
a selected temperature set point and may be provided with a sensing element for
sensing the ambient air temperature in the room
36. Signals from each thermostat
106 or other sensor are provided to the control circuitry for the dampers
along suitable wiring
108.
With continued reference to FIG. 2 in particular, the ceiling
40 above
each room
36 is provided with one or more return registers
110 located
between the supply plenums
48. A return plenum
112 is provided in
the space
42 and occupies the part of the space that is not occupied by
the supply plenums
48. The return plenum
112 receives air through
the return grills
110 and connects through a return duct
114 with
the suction side of the fan
46.
The control system for the dampers is an important aspect of the invention and
is illustrated schematically in FIG. 8. A control circuit
116 receives input
signals from the thermostats
106 or other sensors in the different rooms
36. Based on the signals received from the thermostats
106 or other
sensors (which may sense various conditions such as air temperature, humidity,
mean radiant space temperature, oxygen depletion, carbon dioxide excess or other
conditions requiring conditioned air), the control circuit
116 provides
control signals to the motors
84 which operate the dampers for the different
rooms
36. The control circuit
116 may provide an "open" signal to
motor
84 on line
118 and a "close" signal to motor
84 on line
120. When an open signal is applied on line
118, the motor
84
is activated to rotate the corresponding damper
80 to the open position,
and the damper remains latched in that position until a close signal is provided
on line
120. Then, the motor rotates the damper to the closed position.
The control of the dampers is a unique aspect of the present invention and involves
assigning to each of the dampers a duty cycle having a fairly short duration, normally
under two minutes and often amounting only to seconds. During each duty cycle,
the damper
80 is maintained open (or "on") for a time period that is dependent
upon the set point temperature and the actual temperature in the space. During
the remainder of each duty cycle, the damper is maintained closed (or "off"). The
duration of each "open" or "on" time period is adjusted in order to maintain the
set point temperature. By way of example, if the maximum air flow volume for one
of the rooms
36 is 100 cfm, the damper can be maintained open during the
entirety of each duty cycle in order to provide 100 cfm to the room. If the duty
cycle is 60 seconds long, the damper can be maintained open for 48 seconds of each
duty cycle and closed for 12 seconds in order to deliver 80 cfm to the space. To
provide 40 cfm, the damper can be maintained open for 24 seconds and closed for
36 seconds.
Other duty cycles can be used. For example, the duty cycle can be only 10 seconds
or less long, and the damper will then normally open and close relatively often.
Conversely, if the duty cycle is two minutes long, then the damper will open and
close relatively infrequently. The length of the duty cycle can be selected to
meet whatever conditions are expected, depending upon the many variables that are
involved. Normally, the duty cycle will have a duration shorter than temperature
changes that the thermostat or other sensor can sense. It is contemplated that
in most applications, the duty cycle will be 12-60 seconds.
As a typical operational example, there may be a duty cycle of 12 seconds in a
system having a maximum airflow capacity of 100 cfm. When the load is 50%, the
damper would be open for six seconds of each duty cycle and closed for the remaining
six seconds of each duty cycle in order to provide an average airflow of 50 cfm.
During the "on" part of the duty cycle, 100 cfm flows into the room. During the
"off" cycle, there is almost no air delivered to the room, although a small amount
of leakage is intentionally allowed as being beneficial for maintaining a steady
state in the plenum.
Contrasting this with a conventional modulated damper system, the damper
would be modulated to a half open position until 50 cfm was delivered continuously
to the space. With a conventional "on/off" system, the air supply would be on for
five minutes or so and then off for five minutes or so to provide an average operational
time of 50%. In this type of system, the "on" cycle is typically five minutes,
as compared to a six second "on" cycle with the system of the present invention.
The present invention contemplates that the fan
46 will operate continuously
and will maintain the plenums
48 at a constant and relatively low pressure.
By way of example, the typical plenum pressure is less than 0.10 inch wg and more
preferably approximately 0.05 inch wg, with an internal loss of 0.01 inch wg or
even less in most cases. Thus, there is a low pressure drop through the terminal
units
54 in order to maintain the passage of air at a level below the human
hearing range.
Also, whenever the damper
80 is open for the terminal unit
54,
the air velocity and throw is constant in order to achieve thorough mixing and
efficient distribution of the heated or cooled air throughout the room
36.
It is contemplated that each space that is being supplied with conditioned air
will be equipped with a relatively large number of terminal units
54. Ten
or more terminal units per space is not unusual, although more or less can be used.
In order to maintain stable fan static pressure and airflow stability, the terminal
units
54 for a particular space are synchronized such that their duty cycles
are initiated at different times. For example, the terminal units
54 which
supply one of the rooms
36 can be connected in a daisy chain fashion so
that the second terminal begins its duty cycle at a time delayed relative to the
start of the duty cycle for the first terminal. Similarly, the third terminal is
delayed in the initiation of its duty cycle and so on. This staggered arrangement
of the duty cycles avoids a condition where the fan senses the airflow going from
full value to zero and vice versa almost instantaneously which would happen if
all of the terminals were open and closed at the same time. By virtue of this staggering
of the duty cycles for the terminals, the fan stability and airflow stability are
enhanced considerably.
In operation of the air delivery system, each of the terminals
84 is "on"
during part of its duty cycle and "off" during the remainder of its duty cycle.
During the "on" part of each duty cycle, the damper
80 is fully open to
provide maximum air into the room in order to supply conditioned air (heated, cooled
or otherwise treated) for satisfying the load conditions. During the "off" portion
of the duty cycle, the damper
80 is fully closed to block the flow of conditioned
air into the room. The thermostat
106 continuously senses the conditions
in the room
36 and signals the control circuit
116 to provide a comparison
with the set point temperature. For example, if the duty cycle is set at 12 seconds
with 6 seconds on and 6 seconds off during each duty cycle in a heating mode, and
the temperature in the room
36 is lower than the set point temperature,
the control circuit
116 takes corrective action by increasing the "on" part
of the duty cycle and decreasing the "off" part of the duty cycle. The "on" part
of the duty cycle may be increased to 7 seconds and the "off" time reduced to 5
seconds. If the set point temperature is then satisfied, this condition is maintained.
If the set point temperature is exceeded in the heating mode, the "on" portion
of each duty cycle is decreased and the "off" portion is increased as necessary
to maintain the set point temperature. A similar process takes place during the
operation of the system in the cooling mode.
It is noteworthy that the duty cycles are set at a relatively short duration
that
is not long enough for the thermostat
106 to sense temperature changes during
any given duty cycle. The control circuit
116 does not react to any conditions
during any individual duty cycle but rather is responsive to the average conditions
that result from a relatively large number of duty cycles. The average rate of
flow that is effected over time by the on/off operation of the dampers is controlled
by the control system. The flow that is provided in the system is an average based
on a large number of on/off cycles that are not individually detected by the thermostat
or by the occupants of the space.
A number of advantages are obtained by this technique. Because the damper is
either
fully open or fully closed, the discharge is always at the same air velocity, the
same mass, the same mixing, the same kinetic energy, the same momentum, the same
induction and the same throw. The acoustical problems and lack of thorough mixing
that result from prior systems are overcome by the "binary" nature of the system
of the present invention which essentially provides a number of "pulses" of conditioned
air at much faster intervals than occur with conventional "on/off" systems. Also,
a low pressure supply can be used to advantage.
While the terminal unit shown is advantageous in many respects, other types
of air diffusers can be used. Outlet configurations such as a linear slot configuration
and various other configurations can be employed.
It is contemplated that the duty cycle for each terminal
54 will be the
same as for other terminals that serve the same space. However, this is not necessary
in all cases. It is also contemplated that the duty cycle can be constant over
time and that only the portion of each duty cycle that is "on" will change in order
to meet the load conditions, or the duty cycle can be lengthened or shortened if
necessary or desirable to meet the load and maintain effective operation of the system.
It is contemplated that the terminal units
54 which serve a given room
36 will be spaced apart uniformly in a grid pattern to provide the air at
equally spaced locations throughout the room. While ceiling mounted terminals
54
can be used, it is also possible to provide floor mounted registers or wall mounted
registers. Further, although the invention lends itself well to the plenum type
system shown in FIG. 2, it can also be used with a system having separate duct
work such as shown in FIG.
1. The plenum system is desirable because the
height of the space
42 can be reduced substantially compared to the height
required in the space
20 of a system that requires extensive duct work.
The system of the present invention entails an air supply device supplying air
at a substantially constant pressure, an air distribution means which may be a
plenum or duct and is preferably a plenum, an air terminal for discharging the
air, and a device such as a thermostat for sensing a condition in the space to
which the air is to be supplied. It is a particular feature of the invention that
a system of this type allows the use of a terminal device that does not need balancing.
Also, variable air volume devices and constant air volume devices can easily be
mixed in a single system. In this respect, some or all of the terminal units can
be equipped with dampers to provide variable air volume capability, while other
of the terminal units can lack a damper so that they always operate under constant
air volume conditions. It is important in connection with the air terminal that
its air flow volume has a fixed maximum volume that is not a function of the damper
but instead depends upon the discharge area of the outlet from the terminal.
In regard to the terminals, it is important that they are pressure dependent
devices.
Because the terminal air volume is controlled by the pressure and the duration
of the damper open condition during each duty cycle, the use of pressure dependent
terminals allows the pressure to be varied in order to achieve varying throw characteristics
of the terminal, while the damper provides the correct volume independently of
the pressure. As a result, one terminal size can be provided and will cover a wide
range of applications. Additionally, noise and turn down problems that are characteristic
of conventional air terminals are avoided due to the volume control methodology
employed in the present invention.
As previously indicated, the system of the present invention lends itself well
to a system that uses plenums such as the plenums
48 and the return plenum
112 rather than conventional ductwork. One advantage of such a plenum system
is that there is considerable space available above the ceiling
40 that
is not occupied by ductwork so that other devices can be wired, plumbed or otherwise
equipped in the space above the ceiling. For example, an integral ceiling unit
can be provided that incorporates a terminal unit, a return register, and one or
more other devices, including fire sprinklers, lights, smoke detectors and other
devices. The fixtures, pipes, conduits, electrical wiring and other components
required in systems of this type can make use of the space that is available due
to the absence of ductwork. By eliminating duct work and locating the return and
supply plenums in close proximity, it is possible to construct a multi-function
device with integration of fixtures heretofore impractical. For example, prior
attempts to integrate a light fixture with a supply duct/
