US3388860A

US3388860A - Automatic temperature controls

Info

Publication number: US3388860A
Application number: US575626A
Authority: US
Inventors: Andrew P Kruper
Original assignee: Westinghouse Electric Corp
Current assignee: McQuay Perfex Inc
Priority date: 1966-08-29
Filing date: 1966-08-29
Publication date: 1968-06-18
Anticipated expiration: 1985-06-18
Also published as: JPS4513627B1

Description

June 18, 1968 A. P. KRUPER 3,388,860

AUTOMATIC TEMPERATURE CONTROLS Filed Aug. 29, 1966 FlG.l.

F COOLING CONTROL THERMISTORW l2 I6 HEATING CONTROL THERMISTOR .--I3A s v WATER ll TEMPERATURE RESPONSIVE THERMISTORS CENTRAL HOT AND 001.0 WATER souRcE F IG. 2. COOLING CONTROL WATER TEMPERATURE 24 THERMIISTORI I RESPQNSIIVE TH RM ToR WATE'R TEMPERATURE HEATTMG CONTROL MoToR RESPONSIVE THERMISTOR THERMISTOR 7 |NvENToR= ANDREW P. KRUPER,

saw/M m ATTORNEY United States Patent 3,388,860 AUTOMATIC TEMPERATURE CONTROLS Andrew P. Kruper, Pittsburgh, Pa, assignor to Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation 08 Pennsylvania Filed Aug. 29, 1966, Ser. No. 575,626 21 Claims. (Cl. 236-1) This invention relates to controls for the motors of blowers of, and for the valves of, air cooling and heating units, and has as an object to improve such controls.

The rooms of many modern motels, hotels, and other buildings are cooled in summer by circulating a chilled fluid from a central source through heat exchange coils within the rooms, and are heated in winter by circulating a heated fluid from the central source through the coils. Each coil in each room has a motor-driven blower for circulating the room air, and each room has a thermostat which opens a valve to turn on the cold fluid to its coil, and which closes the valve to turn oh the cold fluid to its coil, and starts and stops respectively, its blower motor during cooling operation, and which opens a valve to turn on the hot fluid to its coil, and which closes the valve to turn off the hot fluid to its coil, and starts and stops respectively, its blower motor during heating operation. The speeds of the blower motors can be adjusted by hand only to lo-med-hi speeds.

This invention automatically modulates the speed of such a blower motor, and the opening and closing of such a valve, in accordance with the difference between the temperature within a room, and the setting of the room temperature responsive means. During cooling operation, the blower speed and the valve opening increase with increasing room temperature, thereby providing more cooling, and decrease with decreasing room temperature, thereby providing less cooling. During heating operation, the blower speed and the valve opening decrease with increasing room temperature, thereby providing less heating, and increase with decreasing room temperature, thereby providing more heating.

This invention will now be described with reference to the annexed drawings, of which:

FIG. 1 is a diagrammatic view of an air conditioning system embodying this invention, and

FIG. 2 is a circuit schematic of the controls used for varying the speed of the blower motor, and the opening and closing of the valve, of FIG. 1.

Referring first to FIG. 1 of the drawings, a conventional, central source 10 of cold and hot water is connected by a main supply pipe 11, and a branch supply pipe 11A, to a heat exchanger 12 in a room of a multi-room building to be cooled or heated. The heat exchanger 12 is connected by a branch, water return pipe 13A, and a main, water return pipe 13, to the source 10. Other heat exchangers in other rooms would be connected by branch pipes to the pipes 11 and 13. The source 10 may be controlled by an operator to continuously supply cold water through the pipe 11 during summer operation, and to continuously supply hot water through the pipe 11 during winter operation. A blower F, driven by an electric motor M moves room air over the surface of the heat exchanger 12. A valve V of the modulating type may be connected in the pipe 11A, and may be variably Opened and closed by a conventional solenoid S.

Temperature responsive means such as

NTC thermistors

16 and 17 are supported within the room containing the heat exchanger 12. Temperature responsive means such as

NTC thermistors

18 and 19 are in heat exchange contact with the water supply pipe 11. NTC thermistors have negative temperature coefiicients of resistance.

Referring now to FIG. 2 of the drawings, the motor M and the solenoid S are connected in parallel, and to AC 3,388,860 Patented June 18, 1968 supply line L1, and are connected in series with diode 22, silicon controlled rectifier SCR, and diode 21 to AC supply line L2. A conventional rectifier bridge B includes the

diodes

21 and 22, and series-connected

diodes

20 and 23. The junction of the

diodes

20 and 22 is connected through a resistor 50 to positive DC bus 24. The junction of the

diodes

21 and 23 is connected to minus DC bus 25. A Zener diode 27 is connected to the

busses

24 and 25, and serves as a voltage regulator.

A fixed resistor 26 is connected to the bus 24, and in series with the thermistor 18 to the bus 25. The thermistor 16 is connected to the bus 24, and in series with variable resistor 28 to the bus 25. The junction of the resistor 26 and the thermistor 18 is connected through diode 29 to the junction of the thermistor 16 and the resistor 28. A. fixed resistor 30 is connected to the bus 24, and in series with capacitor 31 to the bus 25. The junction of the resistor 30 and the capacitor 31 is connected through diode 32 to the junction of the thermistor 16 and the resistor 28, and to emitter 33 of unijunction transistor 34. Base terminal 35 of the transistor 34 is connected through fixed resistor 36 to the bus 25, and to gate 46 of the silicon controlled rectifier SCR. Base terminal 37 of the transistor 34 is connected through fixed resistor 38 to the bus 24. The thermistor 17 is connected to the bus 25, and in series with variable resistor 39 to the bus 24. The junction of the thermistor 17 and the resistor 39 is connected through diode 40 to the junction of the resistor 30 and the capacitor 31. The thermistor 19 is connected to the bus 24, and in series with fixed resistor 41 to the bus 25. The junction of the thermistor 19 and the resistor 41 is connected through diode 42 to the junction of the thermistor 17 and the resistor 39. Slider 42 of the resistor 28 is electrically connected to the bus 25, and is mechanically connected by linkage 43 to slider 44 of the resistor 39. The slider 44 is electrically connected to the junction of the resistor 39 and the thermistor 17. The

sliders

42 and 44 can be adjusted by the linkage 43 to vary the operating points of the

thermistors

16 and 17 respectively.

The thermistor 16 is the room cooling control means. The thermistor 17 is the room heating control means. The resistances of the

thermistors

16 and 17 decrease with an increase in room temperature, and increase with a decrease in room temperature. The

thermistors

18 and 19 respond to the temperature of the water supplied through the pipe 11. Their resistances increase when cold water is supplied, and decrease when hot water is supplied. The thermistor 19 is used to prevent the heating control thermistor 17 from functioning during cooling operation, and the thermistor 18 is used to prevent the cooling control thermistor 16 from functioning during heating operation.

The resistor 30, the capacitor 31, the transistor 34, the silicon controlled rectifier SCR, the bridge B, and the motor M are connected in a conventional speed control circuit such as is disclosed in the GE SCR Manual, Third Edition, page 132.

Cooling operation The water in the supply pipe 11 is cold so that the resistances of the

thermistors

18 and 19 are high. The resistances of the cooling control thermistor 16 and the resistor 28 with which it is in series, are about equal at medium speed of the motor M, and medium opening of the valve V. The high resistance of the thermistor 18 causes its junction with the resistor 26 to be at a higher voltage than that at the junction of the cooling control thermistor 16 and the resistor 28 so that the diode 29 is .back biased so that there can be no flow through it resulting from changes in the resistance of the cooling control thermistor 16, and there can be flow resulting.

I a from such changes, through the diode 32, to charge the capacitor 31.

The resistances of the resistor 39 and the thermistor 17 are about equal at the medium speed of the motor M, and the medium opening of the valve V. Since the thermistor 19 is cold and has a high resistance, the voltage at the junction of the thermistor 19 and the resistor 41 is lower than that at the junction of the heating control thermistor forward biased and conducts, shunting current away from the heating control thermistor 17. The voltage at the junction of the resistor 39 and the thermistor 17 is lower than that at the junction of the resistor 28 and the cooling control thermistor 16 so that the diode 40 is back biased. The voltage at the junction of the resistor 30 and the capacitor 31 is higher than that at the junction of the thermistor 17 and the resistor 39. Thus, the heating control thermistor 17 is effectively disabled.

The voltage at the junction of the cooling control thermistor 16 and the resistor 28 is equal to the resistance .of the resistor 28 divided by the sum of the resistances of the thermistor 16 and the resistor 28, multiplied by the voltage between the

busses

24 and 25. An increase in room temperature causes the resistance of the thermistor 16 to decrease, increasing the voltage at the junction of the thermistor 16 and the resistor 28, charging through the diode 32, the capacitor 31 to a higher initial voltage which added to the voltage applied from the positive bus 24, through the resistor 30, to the capacitor 31 during each half-cycle, causes the transistor 34 to conduct earlier during each half-cycle. When the transistor 34 conducts, it discharges the capacitor 31 into the gate 46 of the silicon 17 and the resistor 39 so that the diode 42 is controlled rectifier SCR, causing the latter to conduct 7 and to supply current to the motor M to speed it up conformably with the increase in room temperature, and to supply current to the solenoid S to cause it to increase the opening of the valve V conformably with the increase in room temperature.

A decrease in room temperature causes the resistance of the cooling control thermistor 16 to increase, decreasing the voltage at the junction of the thermistor 16 and the resistor 28, decreasing the voltage at the junction of the resistor 30 and the capacitor 31, charging the latter to a lower initial value so that the transistor 34 is caused to conduct later during each half-cycle, causing the silicon controlled rectifier to conduct later during each half-cycle, decreasing the speed of the motor M, and decreasing the opening of the valve V conformably with the decrease in room temperature.

Heating operation The water in the supply pipe 11 is hot so that the resistances of the

thermistors

18 and 19 are low. The resistances of the heating control thermistor 17 and the resistor 39 are about equal at medium motor speed and medium valve opening. The decreased resistance of the thermistor 19 causes its junction with the resistor 41 to be at a higher voltage than that at the junction of the thermistor 17 and the resistor 39 so that the diode 42 is back biased so that there can be no current flow through it resulting from changes in the resistance of the heating control thermistor 17, and there can be current flow resulting from such changes, through the diode 40 to charge the capacitor 31.

The resistance of the resistor 28 and the thermistor 16 are about equal at medium motor speed and medium valve opening. Since the thermistor 18 is hot and has a low resistance, the voltage at its junction with the resistor 26 is lower than that at the junction of the cooling control thermistor 16- and the resistor 28, so that the diode 29 is forward biased and conducts, shunting current from the cooling control thermistor 16. The voltage at the junction of the resistor 28 and the thermistor 16 is lower than that at the junction of the heating control thermistor 17 and the resistor 39 so that the diode 32 is back biased. The voltage at the junction of the resistor 30 and the capacitor 31 is higher than that at the junction of the thermistor 16 and the resistor 28. Thus, the cooling control thermistor 16 is etfectively disabled.

The voltage at the junction of the heating control thermistor 17 and the resistor 39 is equal to the resistance of the thermistor 17 divided by the sum of the resistances of the thermistor 17 and the resistor 39, multiplied by the voltage between the

bosses

24 and 25. An increase in room temperature causes the resistance of the thermistor 17 to decrease, decreasing the voltage at the junction of the thermistor 17 and the resistor 39, resulting in the capacitor 31 being charged through the diode 40 to a lower 7 initial voltage which added to the voltage applied from the positive bus 24, through the resistor 30 during each half-cycle, causes the transistor 34 and the silicon controlled rectifier SCR to conduct later during each halfcycle, thereby reducing the speed of the motor M, and the opening of the valve V, conformably with the increase in room temperature.

A decrease in room temperature causes the resistance of the heating control thermistor 17 to increase, increasing the voltage at the junction of the thermistor 17 and the resistor 39, increasing the voltage at the junction of the resistor 30 and the capacitor 31, charging the capacitor 31 to a higher initial voltage so that the transistor 34 and the silicon controlled rectifier SCR are caused to conduct earlier during each half-cycle, and increasing the speed of the motor M, and the opening of the valve V, conformably with the decrease in room temperature.

Each room in a multi-room building served by a central source of hot and cold fluid, could have its temperature controlled as described in the foregoing in connection with a single room.

While NTC thermistors have been disclosed as temperature sensing and control means, PTC thermistors, and modulating thermostats of the bellows or diaphragm type which vary electrical resistances with changes in temperature as disclosed in Patent No. 3,264,839 of J. R. Harnish, could be used with appropriate changes in the circuit of FIG. 2. The water temperature responsive thermistors could be replaced with on-otf thermostats with appropriate changes in the circuit of FIG. 2.

While the valve V has been disclosed as a modulating .valve, it could be an on-ofi? valve, being opened at currents above a predetermined current through its solenoid S, and being closed at currents below the predetermined current.

What is claimed is:

1. An air temperature control system comprising a heat exchanger, supply means for selectively supplying said exchanger with a cooling fluid or a heating fluid, a blower for moving air over the. surface of said exchanger, an electric motor for driving said blower, electric supply connections, air temperature responsive means, and means including said responsive means connected to said motor and to said connections for increasing the speed of said motor on an increase in air temperature,

and decreasing the speed of said motor on a decrease in air temperature, 'when cooling fluid is supplied by said supply means to said exchanger, and for decreasing the speed of said motor on an increase in air' temperature, and increasing the speed of said motor on a decrease in air temperature, when heating fluid is supplied by said supply means to said exchanger.

2. A system as claimed in claim 1 in which said means connected to said motor and to said connections includes means responsive to the temperature of the fluid supplied by said supply means to said exchanger.

3. An air temperature control system comprising a heat exchanger, supply means for selectively supplying said exchanger with a cooling fluid or a heating fluid, a blower for moving air over the surface of said exchanger, an electric motor for driving said blower, electric supply connections, first air temperature responsive means, second air temperature responsive means, means for disabling said first responsive means when cooling fluid is supplied by said supply means to said exchanger and for disabling said second responsive means when heating fluid is supplied by said supply means to said exchanger, and means including said second responsive means connected to said motor and to said connections for increasing the speed of said motor on an increase in air temperature, and decreasing the speed of said motor on a decrease in air temperature, when cooling fluid is supplied by said supply means to said exchanger, and including said first responsive means connected to said motor and to said connections for decreasing the speed of said motor on an increase in air temperature, and increasing the speed of said motor on a decrease in air temperature, when heating fluid is supplied by said supply means to said exchanger.

4. A system as claimed in claim 3 in which said means for disabling said first and second responsive means comprises means responsive to the temperature of the fluid supplied by said supply means to said exchanger.

5. An air temperature control system comprising a heat exchanger, supply means for selectively supplying said exchanger with a cooling fluid or a heating fluid, a blower for moving air over the surface of said exchanger, an electric motor for driving said blower, AC supply connections, rectifier means, a solid-state switch connected in series with said rectifier means and said motor to said connections, said switch having a gate which causes said switch to conduct during a portion of each half-cycle when current is applied to said gate, air temperature responsive means, and means including said responsive means for causing current to be applied to said gate to cause conduction of said switch for longer periods of time during half-cycles on an increase in air temperature, and for causing current to be applied to said gate to cause conduction of said switch for shorter periods of time during half-cycles on a decrease in air temperature, when cooling fluid is supplied by said supply means to said exchanger, and for causing current to be applied to said gate to cause conduction of said switch for shorter periods of time during half-cycles on an increase in air temperature, and for causing current to be applied to said gate to cause conduction of said switch for longer periods of time during half-cycles on a decrease in air temperature, when heating fluid is supplied by said supply means to said exchanger.

6. A system as claimed in claim 5 in which said means including said responsive means includes means responsive to the temperature of the fluid supplied by said supply means to said exchanger.

7. A system as claimed in claim 5 in which said means for causing current to be applied to said gate includes a transistor which is arranged to supply current to said gate when said transistor conducts, and in which said means including said responsive means includes means for causing said transistor to conduct earlier during each half-cycle on an increase in air temperature, and to conduct later during each half-cycle on a decrease in air temperature, when cooling fluid is supplied by said supply means to said exchanger, and for causing said transistor to conduct later during each half-cycle on an increase in air temperature, and to conduct earlier during each half-cycle on a decrease in air temperature, when a heating fluid is supplied by said supply means to said exchanger.

8. A system as claimed in claim 5 in which said supply means includes a fluid supply pipe connected to said exchanger, in which a valve is connected in said pipe, in which electric means is provided for adjusting said valve towards open position on an increase in current through said electric means, and for adjusting said valve towards closed position on a decrease in current through said electric means, and in which said electric means is connected in series with said solid-state switch and said rectifier means.

9. A system as claimed in claim 8 in which said means including said responsive means includes means responsive to the temperature of the fluid flowing through said pipe.

10. A system as claimed in claim 7 in which said means including said responsive means includes means responsive to the temperature of the fluid supplied by said supply means to said exchanger.

11. An air temperature control system comprising a heat exchanger, supply means for selectively supplying a cooling fluid or a heating fluid to said exchanger, a blower for moving air over the surface of said exchanger, an electric motor for driving said blower, AC supply connections, rectifier means, a solid-state switch connected in series with said rectifier means and said motor to said connections, said switch having a gate which causes said switch to conduct during a portion of each half-cycle when current is applied to said gate, means including a transistor arranged to apply current to said gate when said transistor conducts, first and second air temperature responsive means, each comprising a resistor having a resistance which varies with temperature, means for disabling said first responsive means when a cooling fluid is supplied by said supply means to said exchanger, means for disabling said second responsive means when a heating fluid is supplied by said supply means to said exchanger, means including said second responsive means for causing said transistor to conduct earlier during each half-cycle on an increase in air temperature, and to conduct later during each half-cycle on a decrease in air temperature, when cooling fluid is supplied by said supply means to said exchanger, and means including said first responsive means for causing said transistor to conduct later during each half-cycle on an increase in air temperature, and to conduct earlier during each half-cycle on a decrease in air temperature, when a heating fluid is supplied by said supply means to said exchanger.

12. A system as claimed in claim 11 in which said supply means includes a fluid supply pipe connected to said exchanger, in which a valve is connected in said pipe, in which electric means is provided for adjusting said valve towards open position on an increase in current through said electric means, and for adjusting said valve towards closed position on a decrease in current through said electric means, and in which said electric means is connected in series with said solid-state switch and said rectifier means.

13. A system as claimed in claim 12 in which said disabling means includes means responsive to the temperature of the fluid supplied by said supply means through said pipe to said exchanger.

14. A system as claimed in claim 11 in which said disabling means includes means responsive to the temperature of the fluid supplied by said supply means to said exchanger.

15. A system as claimed in claim 14 in which said first and second responsive means are thermistors.

16. A system as claimed in claim 13 in which said first and second responsive means are thermistors.

17. A system as claimed in claim 11 in which said first and second responsive means are thermistors.

18. An air temperature control system comprising a heat exchanger, supply means for selectively supplying a cooling fluid or a heating fluid to said exchanger, a blower for moving air over the surface of said exchanger, an electric motor for driving said blower, AC supply connections, rectifier means, a solid-state switch connected in-series with said rectifier means and said motor to said connections, said switch having a gate which causes said switch to conduct during a portion of each half-cycle when current is applied to said gate, a capacitor, a transistor connected to said capacitor and said gate so as to discharge said capacitor into said gate when said transistor conducts, said transistor having a control electrode connected to said capacitor, means for supplying a DC Voltage during each half-cycle to said control elec trode, first and second air temperature responsive thermistors, means including said second thermistor for providing an initial voltage on said capacitor which increases sponsive to the temperature of the fluid supplied by said supply means to said exchanger, means including said third thermistor for disabling said first thermistor when cooling fluid is supplied by said supply means to said exchanger, and means including said fourth thermistor for disabling said second thermistor when heating fluid is supplied by said supply means to said exchanger.

19. A system as claimed in claim 18 in which said supply means includes a fluid supply pipe connected to said exchanger, in which a valve is connected in said pipe, in which electric means is provided for adjusting said valve towards open position on an increase in current through said electric means, and for adjusting said valve towards closed position on a decrease in current through said electric means, and in which said electric means is connected in series with said solid-state switch and said rectifier means.

23. An air temperature control system comprising a heat exchanger, supply means including a fluid supply pipe for selectively supplying a cooling fluid or a heating fluid to said exchanger, a valve in said pipe, electric means for adjusting said valve towards open position on an increase in current through said electric means and for adjusting said valve towards closed position on a decrease in current through said electric means, AC supply connections, rectifier means, a solid-state switch connected in series with said rectifier means and said electric means to said connections, said switch having a gate which causes said switch to conduct during a portion of each half-cycle when current is applied to said gate, means including a transistor arranged to apply current to said gate when said transistor conducts, first and second air temperature responsive means, each comprising a resistor having a resistance which varies with temperature, means for disabling said first responsive means when a cooling fluid is supplied by said supply means to said exchanger, means for disabling said second responsive means when a heating fluid is supplied by said supply means to said exchanger, means including said second responsive means for causing said transistor to conduct earlier during each half-cycle on an increase in air temperature, and to conduct later during each half-cycle on a decrease in air temperature, when cooling fluid is supplied by said supply means to said exchanger, and means including said first responsive means for causing said transistor to conduct later during each half-cycle on an increase in air temperature, and to conduct earlier during each half-cycle on a decrease in air temperature, when a heating fluid is supplied by said supply means to said exchanger.

21. A system as claimed in claim 20 in which said responsive means are thermistors, in which said means for disabling said second responsive means comprises a third thermistor responsive to the temperature of the fluid supplied by said supply means to said exchanger, and in which said means for disabling said first responsive means comprises a fourth thermistor responsive to the temperature of the fluid supplied by said supply means to said exchanger.

References Cited UNITED STATES PATENTS 3,196,629 7/1965 Wood 62183 3,211,214 10/1965 Chambers 236-78 X EDWARD J. MICHAEL, Primary Examiner.

Claims

1. AN AIR TEMPERATURE CONTROL SYSTEM COMPRISING A HEAT EXCHANGER, SUPPLY MEANS FOR SELECTIVELY SUPPLYING SAID EXCHANGER WITH A COOLING FLUID OR A HEATING FLUID, A BLOWER FOR MOVING AIR OVER THE SURFACE OF SAID EXCHANGER, AN ELECTRIC MOTOR FOR DRIVING SAID BLOWER, ELECTRIC SUPPLY CONNECTIONS, AIR TEMPERATURE RESPONSIVE MEANS, AND MEANS INCLUDING SAID RESPONSIVE MEANS CONNECTED TO SAID MOTOR AND TO SAID CONNECTIONS FOR INCREASING THE SPEED OF SAID MOTOR ON AN INCREASE IN AIR TEMPERATURE, AND DECREASING THE SPEED OF SAID MOTOR ON A DECREASE IN AIR TEMPERATURE, WHEN COOLING FLUID IS SUPPLIED BY SAID SUPPLY MEANS TO SAID EXCHANGER, AND FOR DECREASING THE SPEED OF SAID MOTOR ON AN INCREASE IN AIR TEMPERATURE, AND INCREASING THE SPEED OF SAID MOTOR ON A DECREASE IN AIR TEMPERATURE, WHEN HEATING FLUID IS SUPPLIED BY SAID SUPPLY MEANS TO SAID EXCHANGER.