US3653590A

US3653590A - Air conditioning apparatus

Info

Publication number: US3653590A
Application number: US58313A
Authority: US
Inventors: Ralph Elsea
Original assignee: Carrier Corp
Current assignee: Carrier Corp
Priority date: 1970-07-27
Filing date: 1970-07-27
Publication date: 1972-04-04
Anticipated expiration: 1989-04-04

Abstract

Apparatus 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 supply duct, including one or more damper assemblies provided to regulate the discharge of treated air from the system, delivers the treated air to the enclosure. The position of the damper assemblies is modulated in response to the temperature of the air in the enclosure. A pressure responsive element operates to sense the variations in pressure in the supply duct produced by the modulation of the damper assemblies and creates a control signal which operates to vary the speed of the fan in response to the changes in pressure to maintain the pressure in the duct substantially constant.

Description

O United States Patent 1151 3,653,590 Elsea 1 Apr. 4, 1972 [54] AIR CONDITIONING APPARATUS Primary Examiner-Edward J. Michael [72] Inventor Rflph Elsa, Syracuse, NY Attorney-Harry 6. Martin, Jr. and 1. Raymond Curtin [73] Assignee: Carrier Corporation, Syracuse, NY. ABSTRACT 22] Fil d; J l 27, 1970 Apparatus for supplying treated air to an enclosure including a heat exchanger through which a heat exchange medium flows [2H APPI- NW 58,313 and a fan arranged to route air to be treated over the heat exchanger in heat transfer relation with the medium. A supply [52] "an/4933mm duct, including one or more damper assemblies provided to [51] In CL I um 7/00 regulate the discharge of treated air from the system, delivers 58 Field of Search ..236/l B 1 1 as treated The damp" I semblies is modulated in response to the temperature of the [56] References Cited air in the enclosure. A pressure responsive element operates to sense the variations in pressure in the supply duct produced UMTED STATES N S by the modulation of the damper assemblies and creates a control signal which operates to vary the speed of the fan in 2,223,287 1 1/1940 Kmgsland ..236/l B response to the changes in pressure maintain the measure in 3,486,693 12/ 1969 Stang et al. ..236/ll X the duct substantially constant- 3,489,345 11/1970 'Moreland ..236/il X 1 Claim, 2 Drawing Figures Patented April 4, 1972 ON E T 8 8 ATTORNEY AIR CONDITIONING APPARATUS BACKGROUND OF THE INVENTION This invention relates to air conditioning apparatus and, more particularly, to an arrangement for controlling the discharge of treated air from said apparatus.

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 tin 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 offcycle.

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.

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 rooms, 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.

Furthermore, 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 of fan operation or modulating the cold water flow to the heat exchange coil.

The object of this invention is an improved air conditioning apparatus employing a novel arrangement for controlling the flow of treated air to the enclosure which is compatible with a variable speed control for the fan motor.

SUMMARY OF THE INVENTION This invention relates to air conditioning apparatus, and more particularly to an improved arrangement for controlling the flow of treated air from such apparatus.

The apparatus includes 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 transfer relation with the medium flowing therethrough. The treated air from the heat exchange medium is supplied through an air passage to one or more outlets.

A temperature sensing element is installed in the area being treated and is operable to generate a signal, the magnitude thereof being related to the sensed temperature in the treated area. The signal is supplied to means operable to vary the size of the discharge area of the outlet to provide a quantity of treated air in proportion to load requirements of the area.

By modulating the area of the discharge outlet, the pressure in the supply air passage is varied in proportion thereto. A pressure sensing element is disposed in the air passage to sense the variations of pressure therein. of pressure therein. The pressure responsive element generates a signal which is proportional to the sensed temperature and supplies said signal to the fan motor control circuit. The speed of the fan is thereby modulated to maintain a predetermined static pressure in the air passage regardless of the area of the discharge outlet. By maintaining the static pressure substantially constant, the discharge velocity will also be maintained substantially constant, thereby obviating the problems hereinbefore discussed.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic view of a fan coil unit of the type described equipped with a control circuit illustrating the invention; and

FIG. 2 is a schematic diagram illustrating the circuit used to convert conventional AC voltage to DC voltage to provide a source of power for the circuit illustrated in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawing, there is shown a preferred embodiment of air conditioning apparatus including the invention disclosed herein.

Reference numeral 10 indicates an area or 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 several rooms, each employing apparatus embodying the subject of this invention, may be conditioned simultaneously.

The illustrated embodiment includes 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 an electric motor 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.

The air conditioning apparatus 12 is mounted in a structure or casing 17 which defines an air passage through which the treated air is supplied to at least one outlet 18 for delivery to the room or enclosure being treated. Damper 19 regulates the passage of air to the enclosure from outlet 18. The manner in which damper 19 is controlled in accordance with the invention disclosed herein shall be more fully explained hereinafter.

As noted hereinbefore, it is desirable to regulate the quantity of treated air being supplied to the enclosure in accordance with the load requirements thereof. By regulating the position of damper 19 to vary the discharge area from outlet 18, it is possible to modulate the supply of treated air as is desired by varying the speed of fan 16, thereby eliminating the prior art difficulties noted hereinbefore.

The novel arrangement herein disclosed operates to maintain the velocity of the treated air discharged into the enclosure substantially constant regardless of the quantity of air being supplied. Any desirable velocity level, within the capability of the fan, may be selected, either by adjustment or design, to be compatible with the requirements of the space.

The control circuit provided for obtaining the desirable features hereinbefore described is merely illustrative, and other control schemes that might perform a similar function may be employed in lieu thereof.

The control circuit includes a voltage transformer operable to reduce the line voltage represented by lines L and L to a smaller voltage for control purposes. The voltage transformer includes a primary winding 20 and a secondary winding 21. Preferably, the current flowing through lines L and L is 60 cycle alternating current. Since the control circuit, to be more fully explained herein, utilizes solid state components operable on direct current, a full wave diode rectifier circuit 22 is provided as a source of DC voltage, the DC voltage source being represented by +E, abd E,.

Resistors

66 and 67 and

capacitors

68 and 69 are provided to filter the DC voltage signal.

Thermostat elements

23 and 24 are connected in series with the source of DC voltage. Element 24 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 23 is preferably a NTC thermistor positioned to sense the temperature of the air in the enclosure.

Elements

23 and 24 operate in combination to provide a variable voltage signal. When the temperature of the enclosure is above the setpoint established by thermal element 24, the voltage signal is of a relatively large magnitude and of a positive polarity, whereas when the temperature is below the setpoint, the voltage is of a relatively large magnitude and of a negative polarity.

The voltage signal from

elements

23 and 24 is supplied to a first input of operational amplifier 26 through resistor 25. The manner in which operational amplifier 26 functions shall be more fully explained hereinafter. Operational amplifier 26 also has supplied thereto a +E, voltage through line 70 and a -E, voltage through line 71.

Connected to the output of the operational amplifier is a first diode 27 and a second diode 28. Diode 28 permits only passage of a negative voltage signal, whereas diode 27 only permits passage of a positive voltage signal.

Connected in series with diode 27 is relay coil 32, the energization thereof operating to close normally open switch 33. Connected in series with diode 28 is relay coil 30, the energization thereof operating to close normally open switch 31.

Connected to the output from either switch 31 or switch 33 is double-pole, double throw switch 34. Switch 34 includes a first pole 39 which selectively connects either terminal 37 or terminal 38 in the circuit. Terminal 37 is connected into the circuit when the apparatus is providing relatively cold air, whereas terminal 38 is connected in the circuit when the apparatus is providing relatively warm air. Switch 34 also includes pole 40 which selectively places either terminal 35 or terminal 36 into the circuit. Terminal 35 is placed in the circuit when the apparatus is providing relatively cold air, and terminal 36 is placed in the circuit when the apparatus is providing relatively warm air.

Switch 34 may be controlled manually or may be operated automatically by means such as a bimetal switch which would be placed in heat transfer relation with the heat exchange medium flowing to heat exchange coil 13.

Connected in series with switch 34 are

windings

41 and 42 of reversible motor 43, having line voltage supplied thereto via lines L, and L The energization of winding 41, prior to the energization of winding 42, will actuate the motor so that the damper will rotate in a counterclockwise direction so that the discharge area of outlet 18 is increased.

Conversely, the energization of winding 42, prior to the energization of winding 41, will actuate motor 43 so that damper 19 will rotate in a clockwise direction to decrease the discharge area from outlet 18. Motor 43 is operatively connected to damper 19 via shaft 44. Capacitor 65 is included between

windings

41 and 42 to establish the necessary phase displacement therebetween.

Operatively connected to shaft 44 is shaft 47. Shaft 47 has movably connected thereto wiper 46 of potentiometer 45. The rotation of shaft 44 so as to decrease the area of discharge outlet 18 will rotate wiper 46 in a clockwise direction, whereas rotation of shaft 44 so as to increase the area of discharge outlet 18 will rotate wiper 46 in a counterclockwise direction.

Connected in series with potentiometer 45 is a second double-pole, double throw switch 50. Switch 50 includes arm 51 and arm 52. As shown by the solid line,

arms

51 and 52 are positioned for cooling mode operation. As shown by the dotted lines of the Figure, 51 and 52 are positioned for heating mode operation. The operation of switch 50 may be manually or automatically regulated.

Connected in series with switch 50 and potentiometer 45 are fixed

resistors

48 and 49.

Lines

76 and 77 are connected to the source of rectified DC voltage so as to bring the supply voltage to potentiometer 45.

Depending upon the mode of operation and the position of wiper 46 as determined by the position of damper 19, either a positive polarity or a negative polarity voltage signal will be supplied via line 72 and resistor 54 to a second input of operational amplifier 26, the signal being proportional to the position of the damper.

The operational amplifier compares the voltage signal regulated by potentiometer 45 to the voltage signal regulated by

thermal elements

23 and 24 to operate motor 43 so that the position of damper 19 is modulated in response to the temperature of the enclosure.

Positioned in the air passage defined by structure 17 is a pressure sensing device 63. As the position of damper 19 is varied, the static pressure in the air passage will be simultaneously varied. Device 63 is positioned so as to sense the variations in pressure caused by the movement of damper 19.

Device 63 includes arm 64 mounted to pivot about fulcrum 61. Connected to one end of arm 64 is wiper 62 of potentiometer 60. Wiper 62 is connected to arm 64 so that as the static pressure in the air passage increases, the wiper rotates so as to increase the resistance presented by potentiometer 60. Conversely, as the static pressure in the air passage decreases, wiper 62 will rotate about pivot 61 so as to decrease the resistance presented by potentiometer 60.

Connected in series with one terminal of the potentiometer 60 is trigger diode 55 sold under the trademark Diac." Connected to one side of the source of alternating current represented by line L is capacitor 57. The other side of capacitor 57 is connected to form a junction with one side of trigger diode 55. Connected to the second side of diode 55 is the gate 56' of a bi-directional gated solid state switch 56 of a type sold under the trademark Triac.

Switch 56 is triggered to a conducting state by either a positive or a negative pulse being applied to gate 56. Switch 56 should be sufficiently fast in operating so it may be switched on during any desired portion of each half-cycle of alternating current supplied to the motor driving fan 16 to arrive at a desired average power. The motor speed and the fan speed are thus varied in accordance with the capacity demand of the room served by the system.

To better understand the manner in which the control circuit operates in accordance with the invention, assume that cooling mode operation is desired and that the temperature of the enclosure is above the setpoint The magnitude of the variable voltage control signal controlled by

thermal elements

23 and 24 will be sufficient to cause operational amplifier 26 to pass a positive polarity voltage signal from line 70 to line 29.

The +E, voltage signal will pass through diode 27 and energize coil 32, thereby closing switch 33.

Upon closure of switch 33, line voltage represented by L and L will pass through arm 39 of double-pole, double-throw switch 34 which is in contact with terminal 37 to first energize coil 41 of motor 43. The motor will thus be actuated to turn shaft 44 in a counterclockwise direction to open damper 19.

As damper 19 moves in a counterclockwise direction wiper 46 of potentiometer 45 simultaneously moves in the same direction, the position thereof being related to the position of the damper. Double-pole, double-throw switch 50 is set for cooling mode operation. Therefore, arm 52 is in a position in which the +E, control signal will pass through resistor 49 and wiper 46 to line 72, the magnitude of the signal being proportional to the position of the damper. When the position of the damper has reached an equilibrium point in relation to the temperature of the enclosure, the magnitude of the control signal in line 72, as determined by the position of wiper 46, will be equal to the magnitude of the variable voltage control signal regulated by

thermal elements

23 and 24 and will thus place operational amplifier 26 in a nonconducting state, turning off motor 43.

As damper 19 moves in a counterclockwise direction, the static pressure in the air passage decreases. Wiper 62 will move in a direction so as to decrease the resistance presented by potentiometer 60, thereby increasing the rate at which capacitor 57 is charged. When the charge on capacitor 57 reaches a predetermined value, the trigger diode 55 will be placed in a conducting state, thereby passing a pulse to a gate 56 of switch 56. When switch 56 is placed in its conducting state, current will flow to the motor driving fan 16 at an increased rate to increase the speed thereof. Thus, it is apparent that as the position of the damper is moved in a counterclockwise direction to increase the area of the discharge opening, the static pressure in the air passage is decreased; and simultaneously therewith, the speed of the fan is increased, thereby increasing the flow of air through the air passage to increase the static pressure to its desired predetermined point. By thus maintaining the static pressure substantially constant, the velocity of the air being discharged will also remain substantially constant to obviate the problems hereinbefore discussed.

if the temperature of the enclosure has fallen below the setpoint during cooling mode operation, the magnitude of the variable voltage control signal supplied to operational amplifier 26 will be such that a negative polarity control signal will pass from line 71 to line 29. i

The E, control signal will pass through diode 28, thereby energizing relay coil 30, thus closing switch 31.

When switch 31 closes, line voltage will pass to terminal 35 of double-pole, double-throw switch 34 and will flow through arm 40 to coil 42, thus energizing motor 43 to cause shaft 44 to rotate in a clockwise direction.

Wiper 46 of potentiometer 45 will simultaneously move in a clockwise direction. Arm 51 of double-pole, double-throw switch 50 will provide a -E, voltage signal through line 76 and resistor 48 to the wiper. The magnitude of the voltage signal will be determined by the position of the wiper relative to the resistance elements of potentiometer 45. The variable voltage signal will then flow through line 72 to resistor 54 and operational amplifier 26. When the magnitude thereof is equal to the magnitude of the variable control signal regulated by

thermal elements

23 and 24, operational amplifier 26 will become nonconductive.

Simultaneously, as the damper is moved in a clockwise direction, wiper 62 of potentiometer 60 moves in a direction to increase the resistance thereof due to the reduction of the static pressure in the air passage.

As the resistance of the potentiometer is increased, the rate at which capacitor 57 is charged is decreased, thereby delaying the time during the half cycle in which trigger diode 55 is placed in a conducting state to supply a pulse to gate 56.

As the pulse to gate 56' is delayed, the placing of switch 56 into a conducting state is similarly delayed, thereby delaying the time during the half-cycle in which the current is passed to the motor driving fan 16, thereby reducing the speed thereof. Thus, the speed of the fan is reduced as the static pressure in the air passage is increased, thereby decreasing the flow of air through the air passage to decrease the static pressure therein to its predetermined level, thus tending to maintain the discharge velocity substantially constant.

Assume now that the enclosure requires heating. Doublepole, double throw switch 34 will be set so that arm 39 will be in contact with terminal 38, and arm 40 will be in contact with terminal 36. If the temperature of the enclosure is below the setpoint, the variable voltage control signal passing through resistor 25 to operational amplifier 26 will be of a magnitude to provide a negitive polarity control signal throu h line 71 to line 29. The voltage signal Wlii pass throug diode 28,

thereby energizing coil 30 and closing switch 31.

Line voltage will then pass through terminal 35. terminal 38, and arm 39, to first energize coil 41. thereby causing motor 43 to rotate in a counterclockwise direction to open damper 19 as is desired to obtain a greater quantity of treated air. Wiper 46 will simultaneously move in a counter clockwise direction. Double-pole, double-throw switch 50 is set for heating mode operation. The E, voltage signal will pass through line 76, arm 51 and resistor 49 to wiper 46. The variable voltage signal thus generated will then pass through line 72 to resistor 54, terminating at operational amplifier 26.

Similarly, as in the cooling mode of operation, when the damper 19 has moved in a counterclockwise direction, the wiper of potentiometer 60 has moved in a clockwise direction, thereby increasing the rate at which capacitor 57 is charged. As discussed before, when the charging rate of capacitor 57 is increased, the speed of the motor driving fan 16 is also increased as is desired when the damper is moved so as to increase the discharge area of outlet 18.

If, during heating mode operation, the temperature of the enclosure rises above the set point, the control circuit will operate to close the damper 19 to the proper position for the required quantity of treated warm air.

The invention disclosed herein will pennit operation of the fan at a variable speed to supply a variable quantity of treated air in proportion to the demands of the enclosure. By regulating the speed of the fan as the position of the damper is varied, the static pressure in the air passage will remain substantially constant, thereby maintaining the discharge velocity of the treated air substantially constant as is desired to obviate the problems hereinbefore discussed.

As is apparent to one skilled in the art, the control circuit may be suitably modified to permit simultaneous control of more than one damper being served by the same air conditioning apparatus.

While I have described and illustrated a preferred embodiment of my invention, it should be understood that the invention is not limited thereto but may be otherwise embodied within the scope of the following claims.

1. An air conditioning apparatus for regulating the temperature of air circulating within an enclosure comprising a structure forming an air passage having an outlet through which treated air is delivered to the enclosure; a heat exchanger in said passage adapted to be connected to a source of heat exchange medium for treating air flowing through said passage; a damper in said passage adjacent the outlet for modulating the area of said outlet; means including a thermistor for sensing the temperature of air in the enclosure and a variable resistance element selectively regulable to provide a desired temperature in the enclosure, said thermistor and said element cooperating to provide a variable voltage signal which is a function of the sensed temperature; means for receiving said signal including means for actuating said damper in response to said signal to modulate the area of said outlet; a fan in said air passage adapted to receive air from the enclosure and to circulate the air through said heat exchanger to the enclosure through said outlet; and electric motor for actuating said fan; means for sensing the change in pressure produced in said air passage by the modulation of said outlet area including means to generate a second control signal which is a function of the sensed pressure; means for energizing said motor; means for receiving said second control signal cooperating with said energizing means to vary the speed of the motor and thus the speed of the fan as a function of the magnitude of the signal thereby maintaining a predetermined pressure condition within the air passage to maintain the discharge of treated air into said enclosure at a substantially constant velocity irrespective of the area of said outlet.