US3479836A

US3479836A - Defrost control system using a fluid amplifier

Info

Publication number: US3479836A
Application number: US685593A
Authority: US
Inventors: William L Mchale
Original assignee: Robertshaw Controls Co
Current assignee: Robertshaw Controls Co
Priority date: 1967-11-24
Filing date: 1967-11-24
Publication date: 1969-11-25
Anticipated expiration: 1986-11-25
Also published as: FR1592834A; GB1229003A

Description

Nov. 25, 1969 w. L. MQHALE 3,

DBFROST CONTROL .SYSTEM USING A FLUID AMPLIFIER Filed Nov. 24, 1967 a a2 52% g es 50 7e ,62 as 70 76 0 58 INVENTOR W! LLJAM L. [We HALE ATTORNEYS United States Patent "ice U.S. Cl. 62-140 6 Claims ABSTRACT OF THE DISCLOSURE A defrost control system having a pressure operated device controlling the operation of a compressor and a circulation fan in a cooling system and wherein the defrost control system includes a fluid amplifier for amplifying pressure sensed at an evaporator and communicating the amplified pressure to the pressure operated device.

BACKGROUND OF THE INVENTION The present invention pertains to defrost control systems and more particularly, to pressure operated defrost control systems.

Conventional cooling systems for refrigeration systems, air conditioning systems and the like utilize a compressor for supplying a refrigerant through a condenser to an evaporator where the refrigerant absorbs heat and is then returned to the compressor to complete the cycle. A fan is conventionally employed to force air past the evaporator to cool it and then circulate the cooled air to the area to be cooled. During operation of such cooling systems, ice and frost accumulate on the evaporator due to condensation of moisture in the air being cooled, and this accumulation of ice and frost reduces the area of the evaporator available for heat exchange, thereby decreasing the efliciency of the system. The accumulation of ice and frost also reduces the passage of air over the evaporator which further decreases the efficiency of the system and increases the pressure differential across the evaporator by increasing the pressure upstream of the evaporator and decreasing the pressure downstream of the evaporator.

The pressure differential across the evaporator has been utilized in the past to control the defrosting of the evaporator. That is, the pressure at the evaporator is monitored, and when it obtains a predetermined value, the defrosting cycle commences. These pressure operated defrost control systems have not provided maximum efficiency, as yet, due to their insensitivity to small changes in pressure.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to construct a pressure operated defrost control system using a fluid amplifier to increase sensitivity.

Another object of the present invention is to use a pressure operated device in combination with a fluid amplifier in a defrost control system.

A further object of the present invention is to employ a fluid amplifier to communicate an amplified pressure at an evaporator to a pressure operated device in a defrost control system.

The present invention is advantageous over prior pressure operated defrost control systems due to its increased sensitivity to pressure changes which permits more accurate commencing of the defrost cycle to increase efficiency of the associated cooling system.

The present invention is generally characterized in that defrosting means for an evaporator in a cooling system is controlled by a pressure operated device which is con- 3,479,836 Patented Nov. 25, 1969 trolled by the pressure at the evaporator as amplified by a fluid amplifier.

Other objects and advantages of the present invention will become apparent from the following description of the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of a defrost control system according to the present invention; and

FIG. 2 is a side elevation with parts broken away and with parts in section of a detail of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 illustrates an embodiment of a defrost control system according to the present invention as used with a conventional cooling system having a compressor 10, a condenser 12, an evaporator 14 and a fan 16. Evaporator 14 is disposed within duct work 18, and a conduit carries a refrigerant from compressor 10 to evaporator 14 through condenser 12, and a conduit 22 returns the refrigerant to compressor 10. A pressure sensor 24 is disposed upstream of evaporator 14 and communicates through a conduit 26 with a fluid amplifier 28 at a control nozzle 30. As shown, fluid amplifier 28 includes control nozzles 30 and 32, a power nozzle 34 and

outlet passages

36 and 38. A relatively high pressure air pump 40 communicates with power nozzle 34 through a conduit 42. Control nozzle 32 is unconnected in the embodiment of FIG. 1 and is plugged; however, if differential action is desired, control nozzle 32 may communicate with a pressure sensor located downstream of evaporator 14. Control nozzle 32 may also be the sole control for fluid amplifier 28 by allowing it to communicate with a pressure sensor located downstream of evaporator 14 and plugging control nozzle 30. Outlet passage 36 is used as a dump for mainstream flow through fluid amplifier 28, and the pressure at outlet passage 36 is the complement of the pressure at outlet passage 38 thereby providing a differential output. If desired, outlet passage 36 may communicate with a pressure sensitive switch to provide an indication when the system is in its defrost condition. Outlet passage 38 communicates with a pressure operated device 44 at a pressure sensing port 46. The internal structure of the fluid amplifier used in the present invention is not critical, and any conventional fluid amplifier may be used provided its outlet passage pressure is proportional to the pressure at its control nozzle.

Any conventional pressure operated device may be used in the system of FIG. 1, and one such pressure operated device is shown in FIG. 2, generally indicated at 44. Pressure operated device 44 includes a pressure sensing port 46 which communicates with outlet passage 38 of fluid amplifier 28, a pressure sensing port 48 which is exposed to the atmosphere and

terminals

50 and 52. Port 46 is located in a lower casing 54, and port 48 and

terrninals

50 and 52 are located in an upper casing 56. Lower casing 54 and upper casing 56 are attached to gether at their peripheral flanges, and a flexible diaphragm 58 is secured at its periphery between the peripheral flanges of

casings

54 and 56. A diaphragm pan 60 is aflixed to diaphragm 58 and a cylindrical member 62 has a lower portion attached to pan 60. A spring 64 is mounted in compression between an upper portion of member 62 and upper casing 56. The upper portion of member 62 is attached to a blade 66 and is supported by legs which extend from the lower portion of member 62 and are spaced to provide ample area for passage of a blade 66 which is supported by a mounting wall 68 along with a rigid support member 70. Terminal 50 extends through wall 68 and connects with blade 66. Member 70 extends in spaced parallel relation with blade 66 from wall 68 and has a shoulder portion that engages one end of a U-shaped roll spring 72 which is disposed in an opening in blade 66 to form a conventional snap acting switching mechanism. Terminal 52 extends through a mounting wall 74 and connects with a contact 76 which is secured to wall 74 and located so as to make contact with a contact 78 that is attached to the free end of blade 66. Blade 66 is also attached to a rod 80 which extends from a housing 82, and when pressure operated device 44 is in its second state the upward movement of blade 66 will cause rod 80 to extend above housing 82 to permit manual resetting of the device by pushing down on rod 80. Port 46 communicates with a chamber 84 defined by lower casing 54 and diaphragm 58, and port 48 communicates with a chamber 86 defined by upper casing 56 and diaphragm 58.

The electrical circuitry and the operation of the system of FIG. 1 are described using the pressure operated device shown in FIG. 2; however, it is noted that the pressure operated device is shown in FIG. 2 as a basic design in order to more clearly describe the present invention and many complex mechanisms may be included therein to provide complete automatic operation.

The electrical circuitry of FIG. 1 includes power leads L and L which are adapted to be connected to a suitable source of electricity. L is connected through a control switch 88, fan 16 and compressor to terminal 52 of pressure operated device 44 and through control switch 84 and air pump to L which is also connected to terminal of pressure operated device 44.

In operation, the cooling system of FIG. 1 is controlled by switch 88. When cooling is desired, switch 88 is closed which energizes air pump 40, fan 16 and compressor 10 to place the system in its normal cooling condition since pressure operated device 44 is in its first state in which contacts 76 and 78 are closed, as shown in FIG. 2. Compressor 10 forces the refrigerant through condenser 12 and evaporator 14 to cool the air forced past the evaporator by fan 16, and the pressure sensed by pressure sensor 24 is communicated to control nozzle 30 of fluid amplifier 28 by conduit 26. A relatively high pressure mainstream of air is forced through power nozzle 34 and

outlet passages

36 and 38 by air pump 40, and the flow of air in

outlet passages

36 and 38 is controlled by control nozzle 30 which deflects the mainstream in accordance with the pressure communicated to it. Initially, the mainstream flows predominantly through outlet passage 36; however, as the pressure upstream of evaporator 14 increases, control nozzle 30 increases deflection of the mainstream to outlet passage 38 which in- 0 creases the pressure therein in proportion to the increase of pressure upstream of evaporator 14. Consequently, increased pressure upstream of evaporator 14 due to accumulation of ice and frost thereon, causes increased pressure at outlet passage 38.

The pressure in chamber 84 of pressure sensitive device 44 is directly responsive to the pressure at outlet passage 38, and chamber 86 is at atmospheric pressure. Thus, the force above diaphragm 58 is provided by atmospheric pressure and the force from spring 64 and the force below diaphragm 58 is provided by the pressure at outlet passage 38. As the pressure in chamber 84 increases, diaphragm 58 begins to deflect upward which causes an upward movement of blade 66, and when blade 66 moves past the center of roll spring 72, the free end of blade 66 moves with snap action to abut the top of wall 74. Thus, contacts 76 and 78 open after the pressure upstream of evaporator 14, as amplified by fluid amplifier 28, reaches a predetermined value.

The opening of contacts 76 and 78 starts the defrost cycle since compressor 10 and fan 16 are deenergized. The ambient temperature of evaporator 14 causes the ice and frost accumulated thereon to melt, and when this process is completed the system is ready to return to its normal cooling condition. In order to return the system to its normal cooling condition, pressure operated device 44 must be returned to its initial state wherein contacts 76 and 78 are closed to allow energization of compressor 10 and fan 16, and this may be accomplished either manually by pushing rod 80 or by including a mechanism within the pressure operated device responsive to the temperature of evaporator 14 as shown by US. Patent No. 3,299,237 assigned to Robertshaw Controls Company.

When the need for cooling has been satisfied, switch 88 is opened which deenergizes compressor 10, fan 16 and air pump 40. While the system is off, any ice and frost that has accumulated on evaporator 14 melts, and the system will be prepared to enter its normal cooling condition whenever switch 88 is closed again.

Faster defrosting of evaporator 14 may be accomplished by locating a heating element near evaporator 14, placing a third contact on the top of wall 74 in pressure operated device 44 and connecting one terminal of the heating element to the third contact and the other terminal of the heating element to L through switch 88. Thus. when pressure operated device 44 is in its second state with contacts 76 and 78 open, the third contact and contact 78 are closed which completes a circuit from L through the third contact, contact 78, the heating element and switch 88 to L to heat evaporator 14 and accelerate its defrosting.

The sensitivity of conventional defrost control systems using a pressure operated switch directly sensing the pressure at the evaporator can be increased four to five times by utilizing a fluid amplifier in accordance with the present invention.

Inasmuch as the present invention is subject to many modifications, variations and changes in details, it is intended that all matter contained in the specification or shown in the drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. In a defrost control system, the combination comprising cooling means including an evaporator,

means for defrosting said evaporator,

pressure sensing means located near said evaporator,

pressure operated means for controlling said defrosting means, and

fluid amplifying means including an air pump providing a source of air pressure, said fluid amplifying means being connected with said pressure sensing means and said pressure operated means whereby air pressure applied to said pressure operated means is an amplification of pressure sensed near said evaporator.

2. The combination as recited in claim 1 wherein said pressure operated means has a first state and a second state and includes a pair of electrical contacts which are closed when said pressure operated means is in its first state and open when said pressure operated means is in its second state.

3. The combination as recited in claim 2 wherein said cooling means includes a compressor for supplying a refrigerant to said evaporator and a fan for forcing air past said evaporator to cool it and circulating the cooled air and said defrosting means includes means connecting said compressor and said fan in series with said pair of contacts whereby said compressor and said fan are deenergized to permit said evaporator to defrost when said pressure operated means is in its second state.

4. The combination as recited in claim 1 wherein said cooling means includes a fan for forcing air past said evaporator to cool it and circulating the cooled air and said pressure sensing means is located between said fan and said evaporator whereby accumulation of frost and ice on said evaporator causes an increase in pressure sensed by said pressure sensing means.

5. The combination as recited in claim 1 wherein said fluid amplifying means includes a proportional fluid amplifier having a control nozzle communicating with 3,479, 836 5 6 said pressure sensing means and an outlet passage com- References Cited municating with said pressure operated means. UNITED STATES PATENTS 6. The combination as recited in claim 5 wherein said pressure operated means is responsive to the pressure at g i said outlet passage of said proportional fluid amplifier to be in a first state when the outlet passage pressure is MEYER PERLIN Primary Examiner below a predetermined value and a second state to permit defrosting of said evaporator when the outlet passage pres- US. Cl. X.R. sure exceeds the predetermined value. 62-151, 276