U.S. patent number 3,674,203 [Application Number 05/058,314] was granted by the patent office on 1972-07-04 for air conditioning system.
This patent grant is currently assigned to Carrier Corporation. Invention is credited to William L. McGrath.
United States Patent |
3,674,203 |
McGrath |
July 4, 1972 |
AIR CONDITIONING SYSTEM
Abstract
A system for supplying treated air to an enclosure, including a
heat exchanger through which a heat exchange medium flows and a fan
arranged to route air to be treated over the heat exchanger in heat
transfer relation with the medium. A control operates to vary the
speed of the fan in response to changes in room temperature. One or
more damper assemblies operate to maintain the discharge of treated
air from the system at a substantially constant velocity,
irrespective of the speed of the fan.
Inventors: |
McGrath; William L. (Syracuse,
NY) |
Assignee: |
Carrier Corporation (Syracuse,
NY)
|
Family
ID: |
22016049 |
Appl.
No.: |
05/058,314 |
Filed: |
July 27, 1970 |
Current U.S.
Class: |
236/38; 236/78R;
236/78D |
Current CPC
Class: |
F24F
11/76 (20180101); G05D 23/1906 (20130101); F24F
5/0003 (20130101); G05D 23/24 (20130101) |
Current International
Class: |
F24F
5/00 (20060101); F24F 11/053 (20060101); F24F
11/04 (20060101); G05D 23/24 (20060101); G05D
23/20 (20060101); F24f 011/04 () |
Field of
Search: |
;236/38,49 ;98/40 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Michael; Edward J.
Claims
I claim:
1. An air conditioning system for supplying treated air to an
enclosure, comprising:
A. a heat exchanger;
B. means to supply heat exchange medium to said exchanger;
C. a fan arranged to pass air to be treated over said heat
exchanger in heat transfer relation with said heat exchange
medium;
D. a motor arranged to drive said fan, said motor being adapted to
be connected to a source of energy;
E. means responsive to temperature in the treated enclosure to vary
the speed of said fan motor to regulate the quantity of air being
delivered by said fan;
F. means to supply the treated air in a single stream from the heat
exchanger through an outlet to the enclosure, the pressure in said
air supply means being a function of the quantity of the air
supplied thereto;
G. means operable to regulate the supply of treated air discharged
in a single stream through the outlet into the enclosure from said
supply means, said heat exchanger being disposed in said air supply
means between said fan and said regulating means, said regulating
means being responsive to the pressure in said supply means, said
regulating means being operable to maintain the discharge of the
single stream of treated air at a pre-determined velocity
irrespective of variations of pressure in said supply means, said
regulating means comprising a single damper blade mounted adjacent
the outlet responsive to the pressure of the treated air in said
air supply means to discharge the single stream of treated air into
the treated enclosure; and
H. biasing means connected to said damper blade to move said damper
blade in a direction opposite to the direction said damper blade is
moved by the force created by said pressure in said supply means.
Description
BACKGROUND OF THE INVENTION
This invention relates to an air conditioning system and, more
particularly, to an arrangement for controlling the discharge of
treated air from said system.
Air conditioning apparatus of the type employing a heat exchange
coil to circulate a heat exchange medium therethrough, for example,
chilled or warmed water, and having a fan for bringing air to be
conditioned into heat exchange relation with the medium flowing
through the coil are well known and widely employed by those
skilled in the air conditioning art. Such apparatus are generally
referred to as fan coil units.
Fan coil units are employed with central station cooling and
heating machinery for conditioning multi-room buildings, such as
motels, hotels, and apartments. Such apparatus afford a relatively
effective means for simultaneously conditioning a plurality of
areas in a common enclosure, while providing individual control by
the occupants of each area. In addition, fan coil units are
relatively simple to install and to maintain in operating condition
and are relatively inexpensive, making such units particularly
suitable for low-cost multiple dwelling housing. However, some
problems have been encountered which reduce the overall efficiency
and effectiveness of their operation.
For example, the on-off cycling of the typical fan coil unit
creates annoying sound variances. In addition, an on-off type of
control does not provide uniform air distribution. Particularly,
temperature variations of a considerable magnitude above and below
the room setpoint may be produced in portions of the room, the
variations being caused by stratification of the air during the off
cycle.
To overcome these problems, a variable speed control for the fan
motor, to modulate the discharge of conditioned air from the
apparatus, has been considered. A typical fan motor control is the
subject of co-pending application, Ser. No. 58,315, filed July 27,
1970, Ronald L. Roof, inventor. The variable fan speed control
obviates the noise problem by continuously operating the fan at the
lowest speed consistent with the cooling or heating load thereon.
However, at low fan speeds, problems have resulted due to the low
velocity of the conditioned air being discharged into the
conditioned space, particularly when the air is at a relatively
cold temperature. Such low velocity causes the air stream to lose
momentum, resulting in the relatively cold air spilling into the
room, rather than following a trajectory above the occupied space
until mixing is complete, thus causing discomfort to the occupants
by producing wide variations in temperature across the room and
from floor to head level.
It has been proposed prior to this invention, for example see U.S.
Pat. No. 2,112,955, to employ a plurality of counterweighted blades
in the discharge outlet to regulate the flow of treated air. The
movement of the blades varied in response to changes of static
pressure in the supply duct in communication therewith. The object
of the prior art was to maintain the velocity of the discharged air
substantially constant, irrespective of the magnitude of static
pressure. However, such multi-bladed outlets did not function as
desired, particularly at low static pressure. At such low
pressures, the discharged air streams would be relatively small in
height due to the movement of the blades, acting to reduce the area
of the discharge outlet. The thin air streams presented an
increased surface area for the induced room air to be mixed
therewith. By thus increasing the rate at which the treated air and
room air mixed, the dissipation of the energy of the discharged
treated air also increased, resulting in a loss of velocity. Thus,
the prior art discharge outlets did not prove satisfactory.
The object of this invention is an improved air conditioning system
employing novel conditioned air discharge devices operable to
maintain the velocity of the air discharged into the conditioned
space at a substantially constant magnitude, irrespective of
variations in the static pressure resulting from changing the speed
of the fan employed in such system.
SUMMARY OF THE INVENTION
This invention relates to an air conditioning system and, more
particularly, to an improved air discharge device for regulating
the flow of treated air from such system.
The system includes an air conditioning apparatus employing a heat
exchanger adapted to receive a heat exchange medium such as chilled
or warmed water which may be treated in a central station or other
remote location. A fan is operable to route air to be treated over
said heat exchange coil in heat exchange relationship with the
medium flowing therethrough. A temperature sensing element is
installed in the area being conditioned, and is operable to
generate a signal, the magnitude thereof being related to the
sensed temperature in the conditioned area. The signal is supplied
to the fan motor and is operable to vary the speed thereof in
proportion to the temperature of the room to vary the static
pressure produced by the treated air.
The treated air from the heat exchange medium is passed to one or
more outlets of the system. At each outlet, a damper assembly
operates in response to the static pressure of the treated air
supplied thereto, to vary the discharge area of the outlet, to
maintain the discharge of air at substantially constant velocity,
irrespective of the static pressure of the treated air. It should
be understood that although the term "substantially constant
velocity" is employed hereinafter, the term as used includes
maintaining the discharge velocity at a predetermined minimum at
minimum load, and increasing the velocity as the load increases
.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a somewhat schematic cross-sectional view of an air
conditioning system and apparatus embodying my invention, and
includes a schematic wiring diagram of the control employed in the
apparatus;
FIG. 2 is a somewhat schematic cross-sectional plan view,
illustrating the invention being employed to simultaneously
discharge treated air into a plurality of areas; and
FIG. 3 is a perspective view of the embodiment of the invention
shown in FIG. 2.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to the drawings, there is shown a preferred embodiment of
an air conditioning system including the invention disclosed
herein.
Referring in particular to FIG. 1, reference numeral 10 indicates
an area in an enclosure which is to be treated by having air at a
predetermined temperature discharged therein. Although it is within
the scope of the invention to have only one such area or room being
conditioned, it should be understood that several rooms, each
employing a separate discharge air control device, may be
conditioned simultaneously, as is illustrated by FIGS. 2 and 3.
Area 10 includes ceiling 11.
The embodiment illustrated by FIG. 1 includes an air conditioning
system employing air conditioning apparatus 12. Apparatus 12
includes a heat exchange coil 13 to which a heat exchange medium,
such as cold or warm water, is supplied via conduit 14. The heat
exchange medium is supplied at a predetermined temperature which is
regulated by central station refrigeration machinery (not shown).
The heat exchange medium is returned to the central station
machinery via conduit 15. Fan 16, operatively connected to motor
17, routes ambient air over the heat exchange coil in heat transfer
relation therewith. The ambient air is treated by passing in heat
transfer relation with the heat exchange medium flowing through the
coil.
A discharge air control device 18, to be more fully explained
hereinafter, is operable to regulate the discharge of treated air
from apparatus 12 into area 10. The air conditioning apparatus 12
is disposed in housing 20 which includes upper wall 22 and lower
wall 23, said walls defining a plenum 20'. Upper wall 22 is
connected to the lower surface of the ceiling 11 by suitable means
(not shown).
Communicating with plenum 20' is discharge air control device 18.
The opening may include a discharge grille 25, attached to walls 51
and 53, to define the exit from the apparatus.
Control device 18 disposed in housing 20 includes blade 19
connected to bottom wall 53 by means such as bearing member 54,
which functions as a pivot or fulcrum. Frame member 28', connected
to blade 19 to pivot therewith, has rod 28 extending therethrough.
Counterweight 27 is suitably connected to one end of rod 28, and
the opposed end has a portion 29 for receiving a tool such as a
screwdriver which may be employed to vary the distance between
counterweight 27 and pivot 54. Stop member 60 limits the movement
of device 18 to provide a maximum discharge opening which may be
varied by repositioning the member. As shall become more apparent
hereinafter, control device 18 operates to regulate the discharge
of treated air from apparatus 12 to the area being treated 10.
In accordance with this invention, it is desirable to operate fan
motor 17 at a variable speed. Preferably, fan motor 17 is an
alternating current motor which is connected to a source of
alternating current, such as power line terminals L.sub.1 and
L.sub.2. Switch 30 operates to connect the motor 17 to the source
of electrical current. Switch 30 is preferably a bi-directional
gated solid state switch of a type sold under the trademark
"Triac." Switch 30 is provided with a gate 31 in series with a
secondary winding 32 of a pulse transformer by which the switch is
triggered to a conducting state by either a positive or negative
pulse being applied to gate 31. Switch 30 should be sufficiently
fast in operating so that it may be switched on during any desired
portion of each half cycle of alternating current supplied to motor
17 to arrive at a desired average power, so that the motor speed
and consequent fan speed is varied in accordance with the capacity
demand of the room served by the system.
A control circuit is provided to control the operation of switch 30
in accordance with the desired speed of the motor 17. As shown in
the drawing, a full wave diode rectifier circuit 34 is connected in
series with a dropping resistor 35 to provide a source of D.C.
voltage across a series connected resistor 36 and Zener diode 37.
It will be appreciated that Zener diode 37 has a very low
resistance characteristic such that it provides a constant voltage
drop across its terminals. A series circuit comprising unijunction
transistor 39 having one base 40 connected in series with resistor
38 and another base 41 connected in series with the primary winding
33 of the pulse transformer is connected across Zener diode 37 to
provide a constant voltage to the series circuit.
Thermostat elements 44 and 45 are connected in series with the
constant voltage provided by Zener diode 37. Element 44 is
preferably a variable resistance element, such as a potentiometer,
that may be selectively regulated by the occupant to obtain a
desired temperature in the enclosure. Element 45 is preferably a
NTC thermistor, positioned to sense the temperature of the air in
the enclosure as shall be explained hereinafter. Elements 44 and 45
operate in combination to provide a voltage signal, the magnitude
thereof being related to the temperature of the air sensed and to
the mode of operation of the apparatus. Switch 47 is of the type
known as a double-pole, double throw switch. Switch 47 selectively
connects the terminals of elements 44 and 45 in the circuit
depending upon whether heating or cooling is desired. The operation
of switch 47 is controlled by bimetal 46 which is mounted about
conduit 14, in heat transfer relation therewith, to sense the
temperature of the medium flowing therethrough.
Emitter 42 of unijunction transistor 39 is connected through a
diode 48, which prevents leakage current from charging capacitor
43. Additionally, the circuit includes diode 55 which prevents
current flow in an undesirable direction. Connected in series with
capacitor 43 is resistor 56. Capacitor 43 and resistor 56 combine
to provide a "fixed ramp" voltage signal to transistor 39 as is
obvious to those skilled in the art. It may be desirable in
practice to add various additional circuits to prevent spurious
gating of switch 30.
It will be appreciated that the circuit shown is illustrative
generally of a phase control type of motor speed control. The
circuit shown is merely illustrative of one type of motor speed
control system, and other types of motor speed control can be
adapted to this invention.
In operation, switch 30 is in a nonconducting state, and motor 17
is deenergized until a pulse is applied to gate 31. A charge builds
up on charging capacitor 43 at a rate which is determined by the
resistance of resistor 56. Since resistor 56 is fixed, the charging
rate of capacitor 43 is fixed. When the charge on capacitor 43
reaches a predetermined value, a predetermined voltage signal is
supplied to transistor 39. This signal is referred to as the "ramp"
voltage. The magnitude thereof is insufficient to place transistor
39 in its conductive state. To the ramp is added a second voltage
signal, which is known as the "pedestal." The magnitude of the
"pedestal" voltage is variable and is dependent upon the
temperature of the air in the enclosure and upon the mode of
operation. When the combined ramp and pedestal signal reaches a
predetermined value, transistor 39 becomes conductive, discharging
a pulse through primary winding 33 of the pulse transformer. A
pulse is thereby induced in secondary winding 32 of the pulse
transformer which is applied to gate 31 of switch 30, causing the
switch to conduct.
Switch 30 is preferably a solid state device having the
characteristic that once it is turned on by a pulse being applied
to gate 31, it remains in the conducting state until the current
through the device becomes zero. Consequently, switch 30 remains
conducting after a pulse is applied to gate 31 until the end of the
half cycle of the alternating current during which it begins
conducting. The value of the electrical components are chosen so
that switch 30 is turned on for a time during each half cycle by
the control circuit such that the power supplied to motor 17 is
just sufficient to rotate fan 16 at a speed which provides the
desired air flow over heat exchange coil 13. The manner in which
elements 44 and 45 operate to regulate the speed of motor 17 shall
be explained more fully hereinafter.
As noted hereinbefore, it is desirable to operate the fan motor and
thus the fan at the lowest speed consistent with the cooling or
heating load on the air conditioning apparatus, to obviate the
difficulties presented by the on-off cycling of a typical fan coil
unit. However, as also noted hereinbefore, by producing a
concurrent decrease in the velocity of the air being discharged
when the fan speed is decreased, poor air distribution has resulted
due to air spilling into the room, particularly when the air is at
a relatively cold temperature.
The present invention relates to an air discharge control which
tends to maintain the velocity of the air being discharged from the
apparatus at a constant magnitude, irrespective of the speed of the
fan.
In particular, as the speed of the fan 16 decreases, the quantity
of air being routed over heat exchange coil 13 is reduced. The
reduction in air flow produces a reduction in pressure in plenum
20' of housing 20. Counterweight 27, due to the reduction in force
acting on blade 19, moves in a counterclockwise direction, pivoting
control device 18 upwardly to partially close the discharge
opening, for example to the dotted line position shown in FIG. 1.
The reduction in the discharge opening, caused by the rotation of
blade 19 to the dotted line position, compensates for the reduction
in static pressure to thus maintain the velocity of the air
discharged from the apparatus substantially constant.
Counterweight 27 functions to rotate the blade to a position
related to the speed of fan 16. Thus, as the fan speed increases,
the force acting on blade 19 is increased, thereby causing the
blade to move in a clockwise direction to thereby increase the
discharge opening from the apparatus. The increased size of the
discharge opening compensates for the increase of static pressure.
It is thus readily observable that the size of the opening is a
function of the static pressure produced by the air routed over
heat exchange coil 13. Since the static pressure is a function of
fan speed, the position of the blade is modulated in response to
the speed of the fan to maintain the desired substantially constant
velocity of the air being discharged.
Element 45 is positioned to sense the temperature of the air in the
enclosure. Preferably, the thermistor will sense the temperature of
the air being returned to the apparatus prior to its being treated,
particularly when the apparatus is being employed to simultaneously
treat the air in a plurality of areas, as shown in FIGS. 2 and 3.
When a relatively cold heat exchange medium is flowing in conduit
14, bimetal 46 positions switch 47 to connect thermistor 45 and
variable resistor 44 in the control circuit as shown in the solid
line position of FIG. 1. Conversely, when a relatively warm heat
exchange medium is flowing through conduit 14, the bimetal
positions switch 47 so variable resistor 44 and thermistor 45 are
connected in the circuit as shown in the dotted line position.
Assume a relatively cold medium is flowing through the conduit and
thus elements 44 and 45 are connected in their solid line position.
Since thermistor 45 is of the NTC type, its resistance goes down as
room temperature increases. Thus, when the room temperature is
above a preselected point, as determined by the setting of element
44, the resistance of thermistor 45 is of a relatively small
magnitude. The pedestal voltage is therefore relatively large in
magnitude, and transistor 39 is placed in its conducting state at a
relatively rapid pace, thereby increasing the current flow through
fan motor 17 to increase the speed thereof.
As the speed of fan 16 increases, the air flow is concurrently
increased, thus increasing the static pressure in plenum 20'. The
increased force acting on blade 19 pivots the blade about bearing
54 in a clockwise direction, thus increasing the discharge opening.
As noted before, the increased discharge opening offsets the
increase of static pressure in the plenum which would otherwise
increase the velocity of the air being discharged. The proportional
increase in the size of the opening maintains the velocity of the
air being discharged at a substantially constant magnitude. If the
velocity were to increase beyond a predesigned point, annoying and
undesirable drafts of relatively cold air would be present in the
room being treated. Conversely, if the velocity were to be reduced
below the predetermined point, the air would spill into the room;
and portions of the room remote from the discharge opening would
not receive any treated air.
As the temperature of the air in the room decreases, the resistance
of the NTC thermistor 44 increases, thereby reducing the rate at
which transistor 39 is placed in its conducting state. This
decrease delays the triggering of switch 30, thereby decreasing the
current flow to fan motor 17 to thereby decrease the speed
thereof.
The reduced static pressure in plenum 20', caused by the reduction
in the speed of fan 16, causes the blade to be positioned to
decrease the size of the discharge opening from apparatus 12 as
hereinbefore described.
Assume now that a relatively warm heat exchange medium is flowing
through conduit 14. Bimetal 46 positions switch 47 to connect
elements 44 and 45 in the circuit as shown in the dotted line
position of FIG. 1. As the temperature of the room is below the
selected point, the resistance of the NTC thermistor is of a
relatively large magnitude. Thus, the pedestal voltage supplied to
transistor 39 is of a relatively large magnitude and the transistor
is placed in its conducting state at a relatively rapid pace.
Switch 30 is thence triggered relatively early in the alternating
current cycle to increase the current flow to fan motor 17 to
increase the speed of fan 16. Concurrently, the pressure in plenum
20' is increased, and control device 18 is positioned to increase
the size of the discharge opening as heretofore explained.
As the temperature in the room increases, the resistance of
thermistor 45 concurrently decreases, thereby decreasing the
current flow to the fan motor to decrease the speed thereof.
The reduction in speed of fan 16 operatively connected to fan motor
17 decreases the pressure in plenum 20', thereby decreasing the
size of the discharge opening from apparatus 12 as heretofore
explained. Thus, the size of the discharge opening is modulated in
response to the speed of the fan to maintain the velocity of the
air being discharged at a substantially constant value.
Referring now to FIGS. 2 and 3, there is illustrated an embodiment
indicating the manner in which the invention may be employed to
simultaneously treat the air in a plurality of areas or rooms in a
common enclosure, such as the several rooms in a house or an
apartment in an apartment building.
Thermal elements 144 and 145 are similar to elements 44 and 45 of
FIG. 1. Element 145 is positioned to sense the temperature of the
air returning to apparatus 112, prior to its being routed over heat
exchange coil 113 by fan 116.
The treated air having passed in heat transfer relation with the
heat exchange medium flowing in coil 113 and supplied thereto via
conduit 114 passes through duct 120. Duct 120 has a plurality of
outlets therefrom, as defined by discharge housings 121 and 121',
the housings delivering treated air into rooms 110 and 110'
respectively. The rooms are separated by common wall 100 through
which duct 120 passes. Damper blades 119 and 119', regulated in the
same manner as blade 19 previously described, control the discharge
of treated air from the respective openings to maintain the
velocity thereof substantially constant.
If the occupant of room 110 desired a different air temperature in
his room than that called for by the thermostat setting, the
occupant may vary the outlet opening from housing 121 by varying
the position of the maximum opening stop 160. Thus, for a given
flow of air as provided by fan 116, a different discharge velocity
may be obtained by each of the occupants of a plurality of rooms
served by the common apparatus 112.
The present invention produces a relatively constant velocity air
stream irrespective of changes in the speed of a fan employed in
the air conditioning system. The system is relatively inexpensive
and easy to regulate and is thus particularly adaptable for
treating air in multi-room housing projects.
Additionally, it should be understood that although the system is
shown installed so that the treated air discharged therefrom is
substantially adjacent the ceiling of the room being treated, it is
within the scope of this invention for the discharge therefrom to
be positioned in any other convenient manner. For example, the unit
may be installed substantially adjacent to the floor, with the
discharge therefrom being located so the treated air is discharged
in a vertical direction. Furthermore, although the invention has
been embodied in a system including a fan coil unit, it should be
understood that the invention may be employed in a similar manner
with other types of air conditioning equipment employing a fan.
In addition to the advantages previously discussed which are
obtained by operating the fan continuously, it has been determined
that a more efficient control of the humidity level, when the
apparatus is operating on cooling mode, may be obtained by
continuously operating the fan, rather than employing an on-off
cycle, or modulating the cold water flow to the heat exchange
coil.
While I have described and illustrated a preferred embodiment of my
invention, it should be understood that my invention is not limited
thereto, since it may be otherwise embodied within the scope of the
following claims.
* * * * *