US2349671A - Control of refrigeration - Google Patents

Description

May 23, 1944. A. a. NEWTON CONTROL OF REFRIGERATION Filed D90; 23, 1940 2 Sheets-Sheet 1 INVENTQR Alwim B. New-tom BY AngRNEv May 23,; 1944. NE N 2,349,671

CONTROL OF REFRIGERATION Filed Dec. 23, 1940 2 Sheets-Sheet 2 INVENTOR. Alwin. B. Nzwloru ATTORN EY Patented May 23, 1944 CONTROL OF REFRIGERATION Alwin B. Newton, Minneapolis, Minn, assignor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn, a corporation of Delaware Application December 23, 1940, Serial No. 371,352

17 Claims.

My invention relates to control of cooling syste s for refrigerated spaces or compartments wherein it is desirable that the temperature in the compartment be maintained at a desired value and also that the cooling unit be kept free from frost. My invention is particularly adaptable to systems employing brine as a cooling agent.

An object of my invention is to provide an improved control arrangement for cooling systems employin a cooling agent such as brine wherein circulation of the cooling agent is begun only when the cooling unit has defrosted and the temperature of the refrigerated space has risen to a predetermined value.

Another object of the invention is to provide an arrangement as set forth in the foregoing object wherein circulation of the cooling agent is prevented when its temperature is above a predetermined value.

Another object of my invention is to provide an improved control arrangement for refrigerated compartments wherein the flow of cooling agent is modulatingly controlled, but wherein cooling agent ma be supplied only after the cooling unit has defrosted and wherein the supply is terminated when the temperature of the unit has fallen to a predetermined relatively low value.

Another object is to provide a brine cooling system having a fan for blowing air over the cooling unit and controls for the fan whereby it is operated whenever there is a demand for refrigeration even though refrigeration is not begun until the unit has defrosted.

Other objects and advantages of m invention will become apparent from the following detailed description and annexed drawings wherein:

Figure 1 represents diagrammatically a brine cooling system embodying one form of my invention therein.

Figure 2 represents diagrammatically a brine cooling system embodying a second form of my invention.

In Figure l of the drawings I have represented a brine cooling system for a compartment H! to be refrigerated. Within the compartment it is a coil II for the cold brine. Numeral l2 desighates a drip pan underneath the coil for catching water which drips from the coil when it is defrosted. Numeral i 3 des gnates a fan for blowing air over the coil, the fan being driven by an electric motor is. A source of cold brine is provided, the brine being cooled within a tank 14. The brine is withdrawn from the tank H! by a centrifugal circulating pump l5 through a pipe l6 and discharged from the circulator I5 through a pipe I! to the coolin coil H. The brine is returned from the cooling coil H to the tank M through a pipe I8. The circulator I5 is driven by an electric motor 20 by means of a shaft 2|, and the manner of control of the electric motor 29 forms the principal feature of my invention.

Means are provided for cooling the brine in the tank 14 including a refrigeration system of the compression type, generally designated by the numeral 25. The refrigeration system 25 includes a compressor 26 driven by an electric motor 271 through a belt 28. The compressor discharges into a condenser 29 through a pipe 36, and the condenser 2i] is connected to an expansion valve 3| by a pipe 32. The outlet of the expansion valve 3| is connected to an evaporator 33 which is disposed in the brine in the tank It, and the outlet of the evaporator 33 is connected to the suction side of the compressor by a pipe 35. The expansion valve 3| is of a well-known type having a pressure chamber therein which is connected to a thermal bulb 35 b means of a capillary tube 35. The thermal bulb 35 contains a volatile liquid and is disposed adjacent the outlet of the evaporator 33, and may be clamped thereto as shown so as to be responsive to the temperature of the refrigerant in the outlet. Valve 3| is of a type which maintains a constant degree of superheat at the outlet of the evaporator.

The compressor motor 21 is controlled by a switch 39. The switch is automatically operated in response to a temperature bulb 40 which is disposed in the brine within tank M and which is connected to the switch mechanism by capillary tube ll. The switch 39 is of a known type which is closed whenever the temperature of the brine in tank l4 rises to a predetermined temperature at which a certain pressure is developed within the bulb 45. The switch 39 is opened in response to the bulb 4!] when the temperature of the brine in tank I4 falls to a predetermined low value. Whenever the switch 39 is closed, the compressor motor 27 is energized through the following circuit: From Wire 42 through switch 39, wire 43, the compressor motor 27 and back to wire 44, the wires 42 and 44 being connected to any suitable source of power not shown.

The motor 29 which drives the circulator i5 is controlled by a unitary control device 50. The unitary controller 56 comprises a casing within which is mounted an expansible and contractible bellows 5| and a second expansible and contractible bellows 52. The bellows 5| is connected to a thermal bulb 53 containing a volatile liquid disposed adjacent the outlet of the brine coil II, by means of a capillary tube 54. The pressure developed within the bellows 5| is therefore proportional to the temperature at the outlet of the brine coil II. The bellows 5| has an operating stem which bears against a pivoted lever 55 which lever is normally biased in a counter-clockwise direction by a coil spring 56 attached to a side wall of the casing of the controller 58. The lever 55 carries an insulating pad 51 and attached thereto is a contact bracket 58 carrying electrical contacts 59 and 60. The contact 59 cooperates with a contact 6| carried on a contact bracket 62. The contact 68 lies underneath or below bracket 62 out of its path of movement and cooperates with a contact 63 carried on a contact bracket 64 secured at 64A. The contact brackets 62 and 64 are flexible and bracket 62 bears against a cam 65 which acts as a stop, and the bracket 64 bears against a cam 66 which acts as a stop. The cams 65 and 66 are mounted on separate shafts which are adjustable from outside the casing of controller 58 and by adjusting these cams the brackets 62 and 64 are movable and consequently the position of contacts 6| and 63 is thereby adjustable. When the temperature at the outlet of the coil II rises, the pressure within the bulb 53 and bellows 5| increases causing the bellows 5| to expand moving the lever 55 to the right and moving contacts 59 and 68 towards their associated contacts 6| and 63. As the temperature at the outlet of the coil H rises, contacts 59 and 6| are first brought into engagement and contacts 68 and 63 are later brought into engagement at a predetermined higher temperature, and normally the bracket 64 is so adjusted that this temperature will be one above freezing such as 33 or 34 F., for example. As the temperature at the outlet of the coil |I falls, the pressure within bulb 53 and bellows 5| decreases causing the bellows to contract moving lever 55 to the left. This moves contacts 59 and 68 away from their associated contacts. Contacts 68 and 63 disengage first and contacts 59 and 6| disengage later at a lower temperature, and this temperature is determined by the adjustment of cam 65 and normally the adjustment of this cam is such that the temperature at which contacts 59 and 6| disengage is relatively low for example, this temperature may be 18 F.

The bellows 52 is connected to a thermal bulb 18 containing a volatile liquid, and disposed in 4 the brine in tank I4, by means of a capillary tube II. The bellows 52 therefore expands and contracts in accordance with the temperature afiecting bulb I8. The bellows 52 has an operating stem which normally bears against a pivoted lever 72 which i normally biased in a clockwise direction by a coil spring 13 which is attached to a side wall of the casing of the controller 58. At its lower end, lever 72 carries a horizontal pusher member 74 which cooperates with a contact bracket I5 and further having an offset extension 15A which cooperates with the lower end of contact bracket 64. The bracket I5 carries an electrical contact I6 which cooperates with a contact TI on a terminal 18. The lower end of bracket 64 carries a contact 79 which cooperates with a contact terminal 86. The contacts just described are normally closed and are only opened when the temperature of the brine in take l4 rises to a rela iv ly high value at which the brine would not produce proper refrigeration in the compartment I8. Thus the automatic switch 39 previously described which controls the compressor motor 21 may be set to maintain the brine in tank I4 at a temperature anywhere from 0 F. to 15 F., for example. Then the coil spring I3 may be adjusted so that the bellows 52 will open its associated contacts at a temperature somewhat above 15 F., that is, the bellows 52 may open its associated contacts when the brine temperature rises somewhat above the value at which it is normally maintained and which may occur under heavy load requirements. Thus as the temperature eifecting bulb I8 rises, the bellows 52 expands, moving lever I2 to the right. When this happens, the extension 14A of pusher I4 first engages the bracket 64 moving the said bracket to the right and. disengaging contacts I9 and 80. The parts-may be so adjusted and arranged that this occurs at a temperature of 25 F., for example. As the temperature effecting bulb I8 continues to rise, pusher 14 engages the lower end of bracket I5 moving contact I6 out oj-f-engagement with contact TI, and this m a .yi"|: ccur at a temperature of 30 F. of the bri ne, for example.

The controller 59 also includes a relay or starter designated by the numeral 83, the relay 83 including a winding 84 having an armature associated therewith which is arranged to actuate a pair of bridging members 85 and 86. The bridging member 85 carries contacts 81 and 88 which are moved into engagement with fixed contacts 89 and 98 respectively when the relay coil 84 is energized. Similarly, the bridging member 86 carries contacts 9| and 92 which are brought into engagement with fixed contacts 93 and 94 when the relay coil 84 is energized.

Numeral 96 designates an overload device including overload contacts 91 which are normally closed, but which are arranged to be opened in response to heat from a heating device 98 which is connected in the load circuit of motor 28 as will presently be described. The overload device 98 is of a known type and therefore need not be described in further detail.

Within the refrigerated compartment I0 is a thermostat I88, the thermostat I88 comprising an expansible and contractible bellows I8I containing a volatile liquid which expands and contracts in accordance with the temperature in the refrigerated compartment I8. The bellows I 8| has an operating stem which bears against a lever I82 which is pivoted as shown and which is normally biased in a clockwise direction by a coil spring I83. The lever I82 carries a mercury switch I84 which has a pair of electrodes at its left end as shown. Whenever the temperature within the compartment I8 is below a predetermined value, the thermostat I08 assumes a posithe switch 39 will cycle the compressor motor 21 on and off in response to the bulb 48 so as to maintain the brine within tank I4 at a predetermined temperature which may be 15 F., for Inasmuch as the brine is not being example.

circulated through the coil I I at this time, the temperature of coil II will rise, and as it rises the pressure developed within bulb 53 will increase as described above, causing the bellows 5| to expand. As the bellows 5| expands, the lever 55 will be moved to the right first bringing contacts 59 and BI into engagement as described above. Nothing will happen when contacts 59 and GI are brought into engagement. As the temperature at the outlet of coil II continues to increase causing bellows 5| to expand further, the contacts 60 and 63 will be brought into engagement. This will occur when the temperature at the outlet of coil II has increased to 33 or 34 F. for example, as described above. Inasmuch as this temperature is above freezing, it will not occur until the coil II has defrosted. After the contacts operated by bellows 5| have been closed as just described, if the switch I04 is closed or whenever thereafter that the switch I04 does become closed in a response to demand, for refrigeration in the compartment I0, a circuit for the relay or starter 83 will be completed as follows: From wire II to terminal I8, through contacts 11 and I6, bracket I5, wire I08, mercury switch I04, wire I23, wire I09, bracket 82, contacts BI and 59, bracket 58, contacts 60 and 63, bracket 64, contacts I9 and 80, wire IIO, contact 90, wire I I I, contacts 91 of the overload device, wire II2, relay winding 84, wire II3, through terminals H4 and H5 and back to wire H6. The wires I01 and H6 may be connected to any suitable source of power not shown. Completion of the circuit just described will energize the relay 83 causing the bridge members 85 and 86-to move their associated contacts into engagement with their respective fixed contacts. Engagement of contacts 81 and 89 and contacts 88 and 90 will complete a maintaining circuit for the winding 84 which is independent of contacts 80 and 83 operated by bellows 5| and contacts I9 and 80 operated by bellows 52. This circuit is as follows: From wire I0I to terminal I8, through contacts I1 and I6, bracket I5, wire I08, mercury switch I04, wire I23, wire I09, bracket 62. contacts 5! and 59, bracket 58, wire III, contacts 89 and 81. bridge member 85, contacts 88 and 98, wire III, contacts 91, wire I I2, winding 84, wire II3, terminals I I4 and I I5 back to wire I I6. Thus after completion of this maintaining circuit, it will be seen that the relay will remain energized even though the contacts 68 and 83 should become engaged or even if the contacts I9 and 80 should become disengaged.

Whenever thermostat I00 closes switch I04 in response to a demand for cooling, the fan motor I9 is energized through the following circuit: From wire I01 to terminal I8, through contacts I1 and I8, bracket I5, wire I08, switch I04, wire I23, wire I24, fan motor I9 and wire I back to wire H6. The fan will be operated Whenever there is a demand for refrigeration by thermostat I00 even though contacts 60 and 63 have not closed and this operation of the fan will hasten defrosting of unit II and closure of contacts 60 and 53.

When contacts 9| and 93 and contacts 92 and 94 are brought into engagement, a circuit for the circulator motor 20 is completed as follows: From wire IIJI to terminal I8 through wire I20, heating element 98 of the overload device, contacts 93 and 9|, bridge member 89, contacts 92 and 94, wire I2I, motor 20, wire I22 terminals I I4 and H5 back to wire I I6. Upon energization of motor 20, the circulator will be started in operation and brine will be circulated through the coil I I for producing refrigeration in the compartment I0 until the circulator is stopped. It is to be seen that the circulator is only started when the temperature of the coil II has risen to a value at which it has defrosted, and when the thermostat I00 indicates a need for refrigeration in the compartment III. The temperature of the brine in tank I4 must also be at a low enough value so that proper refrigeration can be produced in compartment III, that is, the contacts operated by bellows 52 must be closed.

The motor 20 will remain in operation for circulating brine until the thermostat I00 becomes satisfied so as to open the above described maintaining circuit or until the temperature at the outlet of coil I I falls to a predetermined low value which may be 18 F, for example, as pointed out above, at which the contacts 59 and SI are disengaged. The circulator motor 20 may also be stopped in the event that by reason of heavy load conditions, the temperature of the brine should rise to a high enough value to cause disengagement of contacts I6 and II which are in the above described maintaining circuit for relay 83.

In the event there is an overload in the circuit of the circulator motor 20, the heating element 93 will act to cause opening of the overload contacts 97 which will deenergize the relay 83 and interrupt the circuit of motor 20.

From the foregoing, it is to be understood that I have provided an arrangement for a brine cooling system wherein circulation of brine is begun only after the temperature of the cooling unit or coil has risen to a value at which the coil has defrosted, and when the thermostat in the refrigerated compartment indicates a need for refrigeration. The circulation of brine continues either until the temperature at the outlet of the cooling coil falls to a predetermined value or until the thermostat in the refrigerated compartment becomes satisfied. In order for the brine c rculator to be operated the temperature of the brine at the source, that is in the tank I4, must be at a low enough value such that proper refrigeration can be produced in the compartment I0. Those skilled in the art will appreciate that my arrangement provides for operating the brine circulator only when refrigeration s required, and only after the cooling unit has defrosted whereby needless accumulation of frost on the coil is eliminated and there is no necessary operation of the brine circulator.

Referring to the contacts operated by the bellows 52. it is to be understood that these contacts need not necessarily be within and a part of the controller 59. but if desired, these contacts may form part of a thermostat disposed in or adjacent the tank I 4.

Referring to Figure 2 of the drawings I have shown a modified form of my invention wherein the flow of brine to the cooling coil is modulatingly varied. In Figure 2, numeral 2) indicates a refrigerated compartment having a brine cooling coil 2II therein. Numeral 2I2 designates a pipe connected to a source of refrigerated brine which may have a temperature of 15 F. for example, and numeral 2I3 designates a pipe through which brine is returned to the source. The inlet of the coil 2II is connected to the pipe 2!?! the outlet of the coil 2II is connected to the pipe 2I3. Various other coils similar o the coil 2 ma l b connected to the pipes 2I2 and 2I3 in the same manner. The

supply of brine to the coil 2 is controlled by a modulating valve 2I4 which is of a known type. The valve 2l4 has an auxiliary switch 2I1 actuated by the operating mechanism of the valve which is normally closed but which is opened when the valve is in closed position. Power for operation of the valve 2| 4 is supplied by wires 2I5 and H6 which are connected to any suitable source of power not shown.

The controls for the valve 2|4 include a thermostat 220 within the refrigerated compartment 2H1. The thermostat 220 is of the proportioning type including a coiled bimetal element 22l arranged to operate a slider 222 which cooperates with an electrical resistance 223. The arrangement is such that the slider 222 slides over the resistance 223 so that the slider and resistance form a potentiometer, the slider moving to the right on a fall in temperature and to the left on a rise in temperature. Numeral 224 designates a second resistance over which the slider 222 sweeps. The purposes of the resistance 224 will presently be described. Numeral 226 designates a humidistat comprising a humidistatic element 221 of a well-known type and which may be of a type using hair as the moisture responsive means. The humidistatic element 221 is connected to a pivoted slider 228 which is normally biased in a clockwise direction by a coil spring 229 and which is adapted to slide over a resistance 236, the slider 228 and resistance 230 forming a second. potentiometer.

The controls for the valve 2|4 also include a relay 23l comprising a winding 232 having an armature associated therewith which is arranged to move a pair of switch blades 233 and 234 to the right into engagement with fixed electrical contacts 235 and 236 respectively when the relay is energized. When the relay is deenergized, the switch blades are in the position shown, and in this position the blade 234 engages a fixed contact 231. The relay 23l is controlled by a thermostatic device 246 and a second thermostatic device 24!. The thermostatic device 240 comprises an expansible and contractible bellows 242 connected to a thermal bulb 243 by capillary tube 244. The bulb 243 contains a volatile liquid and is disposed adjacent the inlet of the coil 2 so as to be responsive to the temperature thereof, so as to cause the bellows 242 to expand and contract in accordance with the temperature at the inlet end of coil 2H. The bellows 242 has an operating stem which normally bears against a pivoted lever 245 which is normally biased in a clockwise direction by a coil spring 246. The lever 245 carries a mercury switch 241 having a pair of electrodes at its left end as shown. When the temperature at the inlet of coil 2 is below a predetermined value the bellows 242 is in a contracted position and has the mercury switch 241 pen as shown. Whenever the temperature at the inlet of coil 2 rises to a predetermined value a pressure is developed within the bulb 243 and bellows 242 which causes the bellows to expand sufficiently to move lever 245 in a counterclockwise direction causing the mercury switch 241 to close.

The thermostatic device 24l is very similar to the device 242, the device 24! comprising an expansible and contractible bellows 250 connected to a bulb 25| by a capillary tube 252. The bulb 25| contains a volatile liquid and is disposed adjacent the outlet of the coil 2 so as to be responsive to the temperature thereof and to thereby cause the bellows 250 to expand and contract in accordance with the temperature at the outlet of the coil. The bellows 250 has an operating' system which normally bears against a pivoted lever 253 which is normally biased in a clockwise direction by a coil spring 254. The lever 253 carries a mercury switch 255 which is adapted to be closed when the temperature effecting bulb 25l is above a predetermined value. Whenever the temperature affecting bulb 251 falls below this predetermined value, the bellows 250 contracts moving lever 253 in a clockwise direction so as to cause mercury switch 255 to open.

The thermostatic device 240 is normally set so that mercury switch 241 is not closed until the temperature affecting bulb 243 has risen to a value of 33 or 34 F. for example, that is, at a temperature high enough to insure that the coil 2| I has defrosted. The thermostatic device 2 is set so that the mercury switch 255 is normally closed except when the .temperature affecting bulb 25l falls to a predetermined relatively low value which may be 18 F. for example. This temperature of 18 F. is very little above the temperature of the brine being admitted to coil 2| I, the temperature of which may be 15 F. as mentioned above, and indicates that coil 2 II has accumulated a substantial amount of frost and is doing very little cooling. Switch 255 acts as a defrosting switch as will presently be described.

The left end of resistance 223 is connected to the valve operating mechanism of valve 2I4 by wires 260 and 26l as shown. The right end of resistance 223 is connected to the operating mechanism of valve 2 l4 by wires 262 and 263 as shown. The midpoint of resistance 224 is connected to the fixed contact 236 by wires 264 and 265. The switch blade 234 of relay 23l is connected to the operating mechanism of valve 2| 4 by a wire 266 as shown. The lower end of resistance 230 is connected to wire 26l by a wire 216 and the upper end of resistance 230 is connected to wire 263 by wires 212 and 213. Slider 228 is connected to the juncture of wires 264 and 265 by a wire 215. The contact 231 with which blade 234 of relay 23| is in engagement when the relay is deenergized is connected to the juncture of wires 212 and 213 by wire 214 as shown. From the foregoing, it is obvious that the potentiometers formed by the temperature responsive controller and the humidity responsive controller are connected in parallel. The temperature responsive controller 220 forms the primary control for the valve 214 and the humidity controller acts as a compensator. The control arrangement as described for the valve 2 l 4 is substantially the same as that disclosed in detail in the patent of John E. Haines No. 2,173,331 and reference may be had to this patent for a detailed disclosure of the structure and operation of ystems of this type.

The operating mechanism of the valve 2l4 is such that when the voltage drop between wires 26! and 266 i reduced relative to the voltage drop between wires 263 and 266 the valve is moved in opening direction and when the voltage drop between wires 263 and 266 is reduced relative to the voltage drop between wires 26] and 266, the valve is moved in closing direction. The potentiometers formed by controllers 220 and 226 control the relative amounts of the voltage drops just referred to and thereby the position of valve 2i 4 is controlled in the same manner as in the Haines patent referred to above. When relay 23l is deenergized as shown in Figure 2, the sliders 222 and 228 are disconnected from the operating mechanism of the valve 2l4 inasmuch as blade 234 is out of engagement with contact 236 and, as

a result, the controllers 226 and 226 are ineffective to exert any control over the valve 214. With the relay deenergized as shown, blade 234 is in engagement with contact 231, and under these circumstances wires 263 and 266 are directly connected so that there is no voltage drop between them and, as a result, the valve 214 i operated to fully closed position. This circuit for causing complete closure of the valve is as follows: From valve 2H5 through wire 266 to switch blade 23 5, contact 231, wire 214 and wire 213 back to wire 263 which is connected to valve 2 I l.

The controller 228 may have a total differential of 5 for example. That is, the slider 222 may be at the left end of resistance 223 when the temperature in the refrigerated space is 35 F. and the slider may be at the right end of resistance 223 when the temperature in the refrigerated space 2E8 is 30. When the temperature in the refrigerated space 2l8 is at the desired value, however, the slider 222 assumes a position substantially at the midpoint of resistance 223 and under these circumstances the temperature is 33 F. The operating differential of the controller 228 is relatively narrow however, and movement of the slider 222 over the resistance 223 an amount corresponding to a temperature change of only one or two degrees in the refrigerated compartment is sufficient to cause the valve 2M to operate entirely between its fully opened and closed positions. As in the Haines patent, the controller 226 which acts as a compensator has less effect on the operating mechanism of the valve 214 than does the controller 22!]. The function of the controller 226 is to move the control point of the controller 226 from one position to another along the resistance 223. The manner of operation of the valve 2M in response to the controllers 22:") and 226 will be explained more in detail presently.

With the parts in the position shown, the valve 2M is closed, and with no brine flowing through the coil 2 its temperature rises and when its temperature has risen to a value of 33 or 34 F. at which the coil has defrosted, the bulb 223 will cause the bellows 242 to expand sufliciently to close mercury switch 261. When mercury switch 241 closes a circuit is completed for the winding 232 of relay 23l as follows: From a wire 28!] through winding 232, wire 28f, mercury switch 241, wire 262 to wire 283, the wires 286 and 283 being connected to any suitable source of power not shown. At the time relay 23l is energized, the mercury switch 255 will be closed because, as pointed out above, this switch is normally closed unless the temperature at the outlet of coil 2 falls to a predetermined low value of 18 F. for example. When relay 23! is energized, blades 233 and 234 are moved to the right into engagement with their associated contacts 235 and 236, blade 234 moving out of engagement with contact 231 and interrupting the above described closing circuit for valve 2 l 4. Engagement of blade 234 with contact 236 completes the cir-- cuit connection from the slider 222 of thermostatic controller 220 through resistance 224 to wire 266, that is, to the intermediate wire connected to the operating mechanism of valve 2H1. Engagement of blade 234 with contact 236 also connects slider 228 with the intermediate wire 266 of valve 2M inasmuch as slider 228 is connected to wire 265 by wire 215. Completion of these connections places the thermostatic controller 220 in operative control of the valve 2M with the humidity responsive controller 226 now efiective to act as a compensator.

At the time the relay 23I is energized, the controller 220 will usually have slider 222 at the left end of resistance 223, it being understood of course that at this time the temperature in the refrigerated compartment will be relatively high inasmuch as the temperature at the outlet of coil 2 has risen to 33 or 34 F. for causing closure of mercury switch 241. When the controllers 228 and 226 are in operative control of the valve 2M, they control the relative voltage drops between wires 26! and 266 and between wires 263 and 266. Thus at the time that relay 231 is energized with the slider 222 of controller 220 at the left end of resistance 223, the voltage drop between wires 26l and 266 will be at a minimum relative to the voltage drop between wires 263 and 266. Under these circumstances the valve 214 will be operated to wide open position to admit a maximum flow of brine to the coil 2! I.

When valve 2M is moved out of closed position, auxiliary switch 2 l 1 is closed completing a maintaining circuit for relay 23I as follows: From wire 238 through winding 232, wire 284, auxiliary switch 2H, wire 2B1, contact 235, blade 233, wire 285, mercury switch 255, wire 286 to wire 263. This circuit is independent of switch 241.

As the temperature in the refrigerated compartment falls due to the flow of brine through the coil 2| l, element 22! will cause slider 222 to move to the right along resistant'e 223. As slider 222 approaches the midpoint of resistance 223 the controller 220 will begin to effectively control the valve 2 l 4 and will move it towards closed position, the valve assuming a position of course depending upon the position of the slider 222 with respect to the resistance 223. Whenever the slider 222 is moved out of its midposition with respect to resistance 223, the valve 2I4 will be moved correspondingly to adjust the flow of brine so as to maintain the desired temperature in the refrigerated compartment 2H! which, for example, may be 33 F. as described above. Thus if the temperature rises above the desired value of 33, the slider 222 will be moved to the left along resistance 223 which will reduce the Voltage drop between wires 268 and 264 relative to the voltage drop between wires 262 and 264. Inasmuch as wires 260 and 262 are connected to wires 26l and 263 respectively and as wire 264 is connected to wire 266 through the switch blade 234, the variations in the voltage drops will be impressed on the operating mechanism of valve 2M and it will be moved in opening direction an amount sulficient to cause the temperature to return to the desired value of 33 F. causing the slider 222 to be moved back to the midpoint of resistance 223. In the event the temperature in the refrigerated compartment falls below the desired value of 33 F., the slider 222 will be moved to the right along resistance 223 and the voltage drops will be varied relatively in the opposite direction, and valve 2! will correspondingly be moved an amount in closing direction proportional to the amount that the temperature deviates from the desired value of 33 F. This movement of the valve in closing direction will cause the temperature to return towards normal and the slider 222 will be returned to its position at the midpoint of resistance 223.

As pointed out above, the controller 226 is a compensating controller and it has a smaller effect upon the operating mechanism of the valve 2|4 than the controller 226. The efiect of the compensating controller 226 is to move the con trol point of controller 220 from one position to another along resistance 223. Thus upon an increase in humidity in the refrigerated compartment indicating a need for more dehumidification, the humidity responsive element 221 will expand causing the slider 228 to move downwardly along resistance 230. Inasmuch as the controllers 226 and 226 are connected in parallel, this action of controller 226 has the same effect as movement of slider 222 to the left along resistance 223. In other words, the voltage drop between wires 26| and 266 will now be reduced relatively to the voltage drops between wires 263 and 266, and the valve will tend to move in opening direction an amount proportional to the variation in humidity. As a result of this movement of the valve 2|4 in opening direction, the controller 226 will now have to respond to a lower temperature in the refrigerated compartment 2 0, that is, it will have to move to the right along resistance 223 in order to assume a position wherein it may now again effectively assume control of the valve 2 l4. In other words, movement of the valve 2 l4 in response to the controller 226 causes the controller 220 to assume a new control point at which it controls the valve 2|4. Upon a decrease in humidity in the refrigerated compartment slider 228 is moved upwardly along resistance 230 and the voltage drops between wires 26| and 266 and between wires 263 and 266 are varied relatively in the opposite manner. As a result, the valve 2 I4 is moved in a closing direction and the control point of controller 226 is moved to the left proportionately a corresponding amount.

Thus as described above, the controllers 220 and 226 jointly control the admission of refrigerant, that is, brine to the cooling coil 2|| so as to maintain both the temperature and humidity at the proper values. The controllers 220 and 226 may be so correlated as to maintain a desired effective temperature in the compartment 2| 0.

Resistance 224 is known as a corrector resistance, the purpose of which will now be explained. When the slider .222 of controller 220 moves in one direction or the other along resistance 223, the relative voltage drops between wires 26| and 266 and between wires 263 and 266 is varied, as pointed out above. However, as the slider 222 approaches one end or the other of the resistance 223 the rate of variation in these relative values of voltage drops changes, that is, it is not uniform, and to compensate for this lack of uniformity in the rate of change of the voltage drops, the resistance 224 is employed. As the slider 222 moves to the right or left, more or less of resistance 224 is placed in circuit with wires 264 and 265, that is the intermediate wire leading to the operating mechanism of valve 2 I4. This ad. ditional resistance placed in circuit with the intermediate wire of the operating mechanism of the valve compensates for the lack of uniformity in the rate of variation in the voltage drops. This is explained more particularly in the patent to Haines referred to above.

As the flow of brine through the cooling coil 2H progresses, the cooling load in the refrigerated compartment will be reduced and correspondingly a reduced flow .of brine will be required to maintain the desired temperature of 33 F. Normally there will be a rise in temperature of the brine as it passes through the coil 2| For instance, if it is admitted at a temperature of 15 F., normally the temperature at the outlet of the coil will be in the vicinity of 25 F. As the flow of brine through the coil is reduced in volume, normally the temperature at the outlet of the coil will tend to rise somewhat due to the reduced flow so that mercury switch 255 will remain closed. However, if frost accumulates on the coil 2| to such an extent as to materially impair its refrigerative eiiiciency, the brine passing therethrough will not absorb very much heat and consequently the temperature of the brine at the outlet will fall to a lower value and may fall to a temperature below 18 F., causing the pressure within bulb 25| and bellows 250 to {diminish contracting bellows 250 and opening switch 255. Opening of this switch interrupts the maintaining circuit of relay 23|, deenergizing the relay causing the switch blades 233 and 234 to assume the positions shown in Figure 2. This disconnects the controllers 220 and 226 from the valve 2|4 and again completes the circuit above described for causing complete closure of valve 2|4. Switch 241 will of course be open at the time switch 255 is opened because switch 241 is closed only when the temperature at the inlet of coil 2 has risen to 33 F. or 34 F. and this switch has a relatively narrow differential. That is, the temperature at the inlet of the coil would not be as high as 33 F. or 34 F. when it is 18 F. at the outlet. When the relay is deenergized in response to opening of switch 255, it will not be reenergized for causing the valve 2|4 to reopen until coil 2 has defrosted so as to close switch The cooling requirementsin compartment 2|6 may become substantially fully met without the coil 2|| having become frosted. The controller 226 may operate the valve 2|4 to fully closed position or to substantially fully closed position without the coil 2| I having become frosted, that is, the cooling requirements in the compartment 2|0 may become substantially fully met so that little or no flow of brine is required to maintain the temperature at the desired value of 33 F. If the valve 2|4 is closed in this manner the auxiliary switch 2|'| will be opened, interrupting the maintaining circuit of relay 23| and deenergizing the relay. If the relay is thus deenergized, the controllers 226 and 226 will be disconnected from the valve 2|4 and the relay 23| will not be again energized until switch 241 has closed.

Fromthe foregoing it will be apparent to those skilled in the art that in the present embodiment of my invention I have provided a very desirable arrangement wherein refrigeration is initiated only after the cooling unit or coil has defrosted,

and during the progress of refrigeration the flow of cooling agent is varied in a manner to maintain a desired temperature value at all times in the refrigeration compartment. When the temperature of the brine at the outlet of the coil falls to a relatively low value indicating that there is a substantial accumulation of frost on the coil, the flow of brine is discontinued until defrosting of the coil takes place. Also, when the cooling requirements in the refrigerated compartment are substantially or fully met the supply of brine or other cooling agent is terminated and it is not reinitiated until the temperature of the unit has risen to a predetermined value.

The embodiments of my invention which I have disclosed are representative of its preferred forms and are illustrative of various modifications and changes which may be made in it. There are forms and variations of the invention which will occur to those skilled in the art which have not been disclosed herein. My disclosure is therefore to be interpreted as illustrative rather than in a limiting sense and the invention is to be limited only as determined by the claims appended hereto.

I claim as my invention:

I. In apparatus of the character described, in combination, means forming a compartment to be refrigerated, a cooling unit in said compartment, means forming a source of cold brine, means for controlling the circulation of brine through said unit, control apparatus associated with the controlling means comprising means responsive to the temperature of the unit and means responsive to a condition of the air in the compartment for initiating circulation of brine When the temperature of the unit reaches a value high enough to have defrosted the unit and said condition has attained a predetermined value, and means responsive to the temperature of the brine for preventing circulation of brine when the temperature of the brine is above a predetermined value.

2. In apparatus of the character described, in combination, means forming a compartment to be refrigerated, a cooling unit in said compartment, means forming a source of cold brine, means for controlling the circulation of brine through said unit, control apparatus associated with the controlling means comprising means responsive to the temperature of the unit and means responsive to a condition of the air in the compartment for initiating circulation of brine when the temperature of the unit reaches a value high enough to hav e geggs teitlg e unit and said condition has attained a predetermined value, means for cooling said brine, means re sponsive to the temperatureof the brine controlling the cooling means, and means responsive to the temperature of the brine for preventing circulation of brine when the temperature of the brine is above a predetermined value.

3., ,In apparatus of the character described, in combination, means forming a compartment to be refrigerated, a cooling unit in said compartment, means whereby cooled brine may be circulated through the unit, control apparatus for controlling the flow of brine through the unit comprising means responsive to a psychrometric condition of the air in the compartment and means responsive to the temperature of the unit, the control apparatus being arrafi'gd tdinitiate circulation of brine only when the unit has reached a temperature at which it has defrosted, and means influenced by the temperature of the brine to terminate circulation thereof through the unit when it is below a predetermined value, said means responsive to a psychrometric condition of the air in the compartment being of a ype arranged to modulatingly Vary the flow of brine after flow has been initiated.

4. In apparatus of the character described, in combination, means forming a compartment to be refrigerated, a cooling unit in said compartment, means whereby cooled brine may be circulated through the unit, control apparatus for controlling the flow of brine through the unit comprising means responsive to a psychrometric condition of the air in the compartment and means responsive to the temperature of the unit, the control apparatus being arranged to initiate circulation of brine only when the unit has reached a temperature at which it has defrosted, and means influenced by the temperature of the brine to terminate circulation thereof through the unit when it is below a predetermined value, said control apparatus comprising a valve controlling the brine flow, and means comprising a relay controlling the valve, said means responsive to the temperature of the unit controlling an energizing circuit for the relay and said means influenced by the temperature of the brine controlling a maintaining circuit for the relay.

5. In apparatus of the character described, in combination, means forming a compartment to be refrigerated, a cooling unit in said compartment, means whereby cooled brine may be circulated through the unit, control apparatus for controlling the flow of brine through the unit comprising means responsive to a psychrometric condition of the air in the compartment and means responsive to the temperature of the unit, the control apparatus being arranged to initiate circulation of brine only when the unit has reached a temperature at which it has defrosted, and means influenced by the temperature of the brine to terminate circulation thereof through the unit when it is below a predetermined value, said means responsive to a psychrometric condition of the air in the compartment including a valve, and being of a type arranged to modulatingly vary the flow of brine after flow has been initiated.

6. In apparatus of the character described, in combination, means forming a compartment to be refrigerated, a cooling unit in said compartment, means whereby cooled brine may be circulated through the unit, control apparatus for controlling the flow of brine through the unit comprising means responsive to a psychrometric condition of the air in the compartment and means responsive to the temperature of the unit, the control apparatus being arranged to initiate circulation of brine only when th unit has reached a temperature at which it has defrosted, means influenced by the temperature of the brine to terminate circulation thereof through the unit when it is below a predetermined value, said means responsive to a psychrometric condition of the air in the compartment including a valve,

and being of atype arranged to modulatingly I vary the flow of brine after flow has been initiated, means comprisin a relay cooperating with said valve means and arranged to cause said valve to be controlled by said means responsive to a psychrometric condition so as to close said valve, circuit means for energizing said relay controlled by said means responsive to the temperature of the unit, and means forming a maintaining circuit for the relay controlled by said means influenced by the temperature of the brine.

7. In apparatus of the character described, in combination, means forming a compartment to be refrigerated, a cooling unit in said compartment, means whereby a cooling agent may be circulated through said unit, valv means controlling the fiow of cooling agent through said unit, means including a relay controlling the valve means, means responsive to a condition of the unit controlling an energizing circuit for the relay, said relay being arranged to normally cause opening of the valve means upon energization thereof, means responsive to a condition of the unit controlling a maintaining circuit for the relay, the relay being arranged to cause closure of the valve means upon deenergization of the relay, and means responsive to a psychrometric condition of the air in the compartment arranged to modulatingly vary the position of the valve means after the valve means has been opened in response to energization of the relay.

8. In apparatus of the character described, in combination, means forming a compartment to be refrigerated, a cooling unit in said compartment, means whereby cooled brine may be circulated through the unit, control apparatus for controlling the flow of brine through the unit comprising means responsive to a psychrometric condition of the air in th compartment and means responsive to the temperature of the unit, the control apparatus being arranged to initiate circulation of brine only when the unit has reached a temperature at which it has defrosted, said means responsive to a psychrometric condition of the air in the compartment being of a type arranged to modulatingly vary the flow of brine after flow has been initiated.

9. In apparatus of the character described, in combination, means forming a compartment to be refrigerated, a cooling unit in said compartment, means whereby a cooling agent may be circulated through the unit, control apparatus for controlling the flow of cooling agent through the unit comprising means responsive to a psychrometric condition of the air in the compartment and means responsive to the temperature of the unit, the control apparatus being arranged to initiate circulation of cooling agent only when the unit has reached a temperature at which it has defrosted, said means responsive to a psychrometric condition of the air in the compartment being of a type arranged to modulatingly vary the flow of cooling agent in accordance with flow requirements necessary to maintain said condition at a predetermined value, and means associated with said last means for discontinuing the flow of cooling agent entirel when flow requirements have been reduced to a minimum until the unit again reaches said aforementioned temperature.

10. In apparatus of the character described, in

' combination, means forming a compartment to be refrigerateda cooling unit in said compartment, means forming a source of coolin agent, means for controlling a circulation of cooling agent through said unit, control apparatus associated with the controlling means comprising means responsive to the temperature of the unit,

means responsive to a condition of the air in the compartment for initiating circulation of cooling agent when the temperature of the un t means comprising a relay controlling the valve, said means responsive to the temperature of the unit controlling an energizing circuit for the relay and means associated with the valve controlling a maintaining circuit for the relay, said last means being arranged to interrupt the maintaining circuit when the valve is in a minimum flow position.

12. In apparatus of the character described, in combination, means forming a compartment to be refrigerated, a cooling unit in said compartment, means whereby cooling agent may be circulated through the unit, control apparatus for controlling the flow of cooling agent through the unit comprising means responsive to a psychrometric condition of the air in the compartment, means responsive to the temperature of the unit,

the control apparatus being arranged to initiate circulation of COOIillg agent only when the unit has reached a temperature at which it has defrosted, means influenced by the temperature of the cooling agent to terminate circulation thereof through the unit when it is below a predetermined value, said means responsive to a psychrometric condition of the air in the compartment including a valve, and being of a type arranged to modulatingly var the flow of coolin agent after flow has been initiated, means comprising a relay cooperating with said valve means and arranged to cause said valve to open or close, circuit means for energizing said relay controlled by said means responsive to the temperature of the unit, means forming a, maintaining circuit means associated with said valve means for inreaches a value high enough to have defrosted the unit and said condition has attained a predetermined value, and means for circulating airover said unit whenever said means responsive to a condition of the air in the compartment demands circulation of cooling agent even though the temperature of the unit has not risen high enough to defrost it.

11. In apparatus of the character described, in combination, means forming a compartment to be refrigerated, a cooling unit in said compartment, means whereby cooling agent may be circulated through the unit, control apparatus for controlling the flow of cooling agent through the unit comprising means responsive to a psychrometric condition of the air in the compartment and means responsive to the temperature of the unit, the control apparatus being arranged to initiate circulation of cooling agent only when the unit has reached a temperature at which it had defrosted, said control apparatus comprising a valve controlling the flow of cooling agent,

terrupting said maintainin circuit when the valve is in a minimum flow position.

13. In apparatus of the character described, in combination, means forming a compartment to be refrigerated, a cooling unit in said compartment, means whereby a cooling agent may be circulated through the unit, said agent being of a type which does not change its physical state at normal operating temperatures of said unit, means responsive to the temperature of the unit for initiating flow of cooling agent after the unituntil the unit has defrosted.

14. In apparatus" of the character described, means forming a compartment to be refrigerated, a cooling unit in said compartment, means comprising a source of cold brine, means for controlling a circulation of brine through said unit,

; control apparatus associated with the controlling means comprising means responsive to the temperature of the unit, means responsive to a condition of the air in the compartment for initiating circulation of brine when the temperature of the unit reaches a value high enough to have defrosted the unit and said condition has attained a predetermined value, and means for circulating air over said unit whenever said means responsive to a condition of the air in the compartment demands circulation of brine even though the temperature of the unit has not risen high enough to defrost it.

15. A system of the character described comprising in combination, a space to be cooled, a

cooling coil for cooling said space, means conducting cooling fluid to said coil for circulation therethrough, said fluid being of a type which does not change its physical state under normal operating temperatures of said coil, and means for defrosting said coil, said defrosting means including means for stopping circulation of fluid through said coil when the temperature of the fluid leaving said coil is so low as to indicate a frosted condition of the coil and preventing such circulation until the temperature of the fluid has risen to a value indicating that the coil has been defrosted.

16. A system of the character described comprising in combination, a space to be cooled, a

cooling coil for cooling said space, means conducting cooling fluid to said coil for circulation therethrough, said fluid being of a type which does not change its physical state under normal operating temperatures of said coil, and means for defrosting said coil, said means including means for stopping circulation of fluid through said coil when the temperatureof the fluid leaving said coil is so low as to indicate a frosted condition of the coil and preventing such circulation until the temperature of the fluid has risen to a value indicating that the coil has been defrosted, and means responsive to a psychrometric condition of the air in said space preventing circulation of fluid through said coil upon a decrease in the value of said condition.

17. A system of the character described comprising in combination, a space to be cooled, a cooling coil for cooling said space, means conductin coolin fluid to said coil for circulation therethrough, said fluid being of a type which does not change its physical state under normal operating temperatures of said coil, and means for defrosting said coil, said means including means for stopping circulation of fluid through said coil when the temperature of the fluid leaving said coil is so low as to indicate a frosted condition of the coil and preventing such circulation until the temperature of the fluid has risen to a value indicating that the coil has been defrosted, and means responsive to a psychrometric condition of the air in said space preventing circulation of fluid through said coil upon a decrease in the value of said condition, said defrosting means acting, each time the circulation of fluid is stopped, to prevent further circulation until the temperature of the fluid is such as to indicate that the coil has been defrosted.

ALWIN B. NEWTON.

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