DE-AC05-960R22464 awarded by the U. S. Department of Energy to Lockheed Martin Energy Research Corporation, and the U. S. Government has certain rights in this invention.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention generally relates to refrigeration systems. More particularly, the present invention relates to apparatuses and methods for the control of the defrosting of an evaporator coil of an evaporator in a refrigeration system.

2. Description of the Related Art Refrigeration systems are well known in the art and generally include a compressor, a condenser and condenser fan, capillary tubes between the components which contain a refrigerant, an evaporator that has an evaporator coil formed of the capillary tubes therein and an evaporator fan, and a thermostatic relay coupled to a power supply to engage the refrigeration system. Three components of the typical refrigeration system that utilize electric power to operate are the compressor, the condenser fan, and the evaporator fan.

In operation, the compressor cycles on and off to compress the refrigerant which then passes to the condenser which cools and liquefies the refrigerant and discharges the excess heat to the environment. The liquid refrigerant then passes to the evaporator where the refrigerant absorbs the ambient heat and is vaporized such that cooling is produced by the evaporator coil and ambient air is passed thereover by the evaporator fan and cooled. The cooling of the ambient air passing around the evaporator coil causes condensate, and subsequently, frost to build up on the evaporator coil as the

system operates. Such frost must be removed in order for the evaporator to function properly and have convection from the evaporator coil adequately cool the air during the refrigeration cycle.

There are other apparatuses and methods known in the art to defrost the evaporator coil in addition to the activation of the evaporator fan while the refrigeration system otherwise cycles off. Hot gas can be gathered from the discharge of the compressor and passed in proximity to the evaporator coil through the use of an additional hot gas line with associated valves and controls. Electrical heating elements can also be provided in proximity to the evaporator coil, or in conjunction with an evaporator fan to provide radiant heat to the evaporator coil sufficient for defrosting.

Another method of defrosting is simply to cycle the compressor off for a sufficient duration to allow the evaporator coil to warm and the condensate thereupon to drain, but such method is slow and unpractical for very cold refrigerant temperatures, i. e. far below 32°F. Accordingly, the off-cycle activation of the evaporator fan is the simplest and therefore most common device utilized to defrost in the evaporator coil in typical refrigeration systems.

In a setting where a significant amount of refrigeration is needed to maintain a refrigerated environment, such as in a retail setting or with a refrigerated vending machine, the typical refrigeration system engages the evaporator fan continuously to fan the external (ambient) air over the evaporator coil to effectively defrost the evaporator coil. Consequently, even when the compressor is inactive in the typical retail refrigeration system, the evaporator fan is active and consumes power. The continuously operating evaporator fan motor also creates heat that is transferred to the refrigeration system and refrigerant, thus increasing the thermal load to the system.

Accordingly, a system that is capable of activating the evaporator fan or other evaporator coil defrosting device for a sufficient duration to defrost the evaporator coil, and then deactivating the evaporator fan or other evaporator coil defrosting device until again needed, would represent a significant improvement over the prior art refrigeration systems.

SUMMARY OF THE INVENTION The present invention is an apparatus and method for controlled defrosting of an evaporator coil used in refrigeration systems having an evaporator including an evaporator coil. The preferred device for evaporator coil defrosting is an evaporator fan that is connected to an evaporator coil defrosting device control, such as a relay switch, and the evaporator fan relay switch is also connected to a power source, whereby the evaporator fan relay switch selectively activates and deactivates the evaporator fan to prevent and/or melt frost on the evaporator coil. In one embodiment, the evaporator fan relay switch includes a timer such that the evaporator fan is activated for a predetermined duration sufficient to defrost the evaporator coil under ambient conditions. In another embodiment, the evaporator coil defrosting device control includes a sensor that senses one or more parameters, such as frost build-up, on the evaporator coil and activates the evaporator fan in response the detection of a change in a sensed parameter of the evaporator coil, such as frost build-up, thus providing feedback control of the evaporator coil defrosting device.

A present inventive refrigeration system is therefore provided that includes the common components of a refrigeration system, namely a compressor, a condenser including a condenser fan, an evaporator including an evaporator coil and an evaporator coil defrosting device, such as an evaporator fan, and at least one tube in fluid communication with the compressor, condenser, and evaporator coil. The tube contains a refrigerant that is passed through the evaporator coil and vaporizes thereby absorbing ambient heat and accordingly cooling the evaporator coil. The inventive refrigeration system further contains the novel element of an evaporator coil defrosting device control, such as an evaporator fan relay switch, connected to and selectively activating the evaporator coil defrosting device, such as an evaporator fan. The refrigeration system further includes a thermostatic relay switch connected to a power source, and also connected to the compressor, the condenser fan, and the evaporator coil defrosting device control, as opposed to the evaporator coil defrosting device itself. The thermostatic relay switch selectively activates and deactivates the refrigeration system when refrigeration is needed.

The inventive evaporator coil defrosting device control therefore provides an inventive method of defrosting an evaporator coil in a refrigeration system having an evaporator including an evaporator coil and an evaporator defrosting device, where the evaporator coil defrosting device control is connected the evaporator coil defrosting device and a power source. The inventive method preferably includes the steps of : operating the refrigeration system such the frost builds upon the evaporator coil; activating the evaporator coil defrosting device with the evaporator coil defrosting device control to defrost the evaporator coil; and deactivating the evaporator coil defrosting device upon the evaporator coil being substantially defrosted. If the evaporator coil defrosting device includes a timer, then the step of activating the evaporator coil defrosting device is activating the evaporator coil defrosting device for a predetermined duration. And if the evaporator coil defrosting device control includes a sensor for sensing frost or other parameters of the evaporator coil, then the step of activating the evaporator coil defrosting device is activating the evaporator coil defrosting device upon the sensor sensing frost or a predetermined change in a sensed parameter of the evaporator coil.

Accordingly, it is the primary object of the present invention to provide an evaporator coil defroster that adequately defrosts an evaporator coil without continuous operation of an evaporator fan or other evaporator coil defrosting device. Thus, the present invention provides a refrigeration system that has commercial advantage as it provides economical refrigeration without the expense of the continuous operation of an evaporator fan or other evaporator coil defrosting device. The present invention also reduces the thermal load from an otherwise continuously operating evaporator fan motor, and consequently reduces wear on the components of the refrigeration system as the cycling of compressor is reduced in both duration and frequency. Furthermore, the present invention has industrial applicability as it can be installed in both existing and new refrigeration systems to improve efficiency.

Other objects, advantages, and features of the present invention will become apparent after review of the hereinafter set forth Brief Description of the Drawings, Detailed Description of the Invention, and Claims.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a representative diagram of a refrigeration system embodied with an evaporator fan relay switch having a timer to control the duration of activation of the evaporator fan.

Fig. 2 is a representative diagram of a refrigeration system embodied with an feedback-controlled evaporator fan relay switch including a sensor on the evaporator coil.

DETAILED DESCRIPTION OF THE INVENTION Referring now to the drawings in which like numerals represent like components throughout the several views, Fig. 1 illustrates the presently inventive refrigeration system 10 comprised of a compressor 12, a condenser 14 which includes a condenser fan 16, an evaporator 18 including an evaporator coil 20 and an evaporator fan 22. Other evaporator coil defrosting devices as know in the art can be substituted for or used in conjunction with the evaporator fan 22. There is at least one capillary tube 24 in fluid communication with said compressor, said condenser, and said evaporator coil. The capillary tube (s) 24 is filled with a refrigerant, such as freon or another volatile agent.

The present inventive refrigeration system 10 further includes an evaporator coil defrosting device control, shown as evaporator fan relay switch 26, for selectively activating and deactivating evaporator fan 22 to defrost evaporator coil 20 after the compressor cycles off. The evaporator fan relay switch 26 is also connected to a power source 27 to thus selectively provide electricity to the evaporator fan 22 for defrosting.

This is in contrast to the prior art refrigeration systems, typically in high demand systems, that have the evaporator fan operate continuously and cycling off solely when the entire system is shut off at the master control for the refrigeration system.

The refrigeration system 10 further preferably includes a thermostatic relay switch 30, as is known in the art, that is connected to a power source 27, and also connected to compressor 12 (at connection 34), the condenser fan 16 (at connection 32), and can be alternately connected to the evaporator fan relay switch 26 instead of

the direct power supply as shown. The thermostatic relay switch 30 preferably includes sensing bulb 36, or a like sensor, which monitors the environment the that the unit refrigerates, and upon a specific activation temperature being reached, selectively activates at least the compressor 12 of the refrigeration system 10 to refrigerate the temperature-controlled environment.

Evaporator fan relay switch 26 is embodied with a timer such that the activation of evaporator fan 22 will be only for a predetermined duration that is sufficient to defrost the evaporator coil 20. For example, in a typical commercial vending machine application, a sufficient duration of activation of the evaporator fan 22 under ambient conditions is 3 minutes after the compressor 12 has cycled off. Longer durations of evaporator fan activation are alternately used if the refrigeration system operates in significant humidity or temperature.

The main components of the refrigeration system, such as the compressor 12, condenser 14 and evaporator 18, are well known in the art, and one of skill in the art can determine the optimal configuration and arrangement of them for a particular refrigeration application. Furthermore, while the present inventive refrigeration system can be used in virtually any refrigeration system, the present invention is particularly useful for high demand refrigeration systems such as those used in retail settings and in commercial vending machines.

The evaporator coil defrosting device control, such as evaporator fan relay switch 26 as embodied herein can be installed in an existing refrigeration system having the components as set forth above to create the present inventive refrigeration system with an evaporator coil defrosting device control. In a typical refrigeration system, the evaporator fan relay switch 26 is installed between an existing power source 27 and the existing evaporator fan 22 and the timer is set for an optimum duration for defrosting the evaporator fan for the specific refrigeration system.

With reference to Fig. 2, another embodiment of the present invention is illustrated in refrigeration system 38 which includes a feedback-controlled evaporator coil defrosting device control, shown as evaporator fan relay switch 40 which includes a sensor 44 for sensing frost on the evaporator coil 18 whereby the evaporator fan 22 is activated upon the detection of frost on the evaporator coil 20, and deactivated upon

frost being no longer detected. The sensor 44 is shown as being a thermocouple detecting the temperature of the evaporator coil 18 that deactivates the evaporator fan 22 upon the evaporator coil 18 reaching a predetermined temperature above freezing (32°F). Both the feedback-signals for operation of the feedback-controlled evaporator relay switch 40 and the specific parameter detected on the evaporator coil 18 (such as moisture, temperature, and/or conductivity) can be changed to suit a particular application. Any parameter can be alternately sensed on the evaporator coil 18, although it is preferable that the sensed parameter be indicative of frost forming on the evaporator coil 18. Additionally, one or more sensors are alternately used, and each can sense the same or alternate parameters of the evaporator coil 18 and the evaporator coil defrosting device control, such as feedback-controlled evaporator fan relay switch 40, can activate the evaporator coil defrosting device, such as the evaporator fan 22, upon the occurrence of one or more changes in the sensed parameters of the evaporator coil 20.

The sensor 44 is preferably connected to feedback-controlled evaporator fan relay switch 40 through a communication line 46, although other forms of wireless communication between the sensor 44 and the feedback-controlled evaporation fan relay switch 40 are alternately used to transmit the frost-sensing, or other parameter sensing signals. Through the use of the sensor 44, the feedback-controlled evaporator fan relay switch 40 can activate the evaporator fan 22 for the precise duration for evaporator coil 18 defrost, and is thus more economical in operation than evaporator fan relay switch 26 of Fig. 1, which includes a simple timer. However, the timer control of evaporator fan relay switch 26 is simpler and more economical to manufacture and a feedback-controlled evaporator coil defrosting device control.

Additionally, the evaporator coil defrosting device controls as disclosed herein, such as the evaporator fan relay switch 26 and the feedback-controlled evaporator fan relay switch 40, are alternately used with other defrosting devices as are known in the art, such as hot gas discharge and electrical elements in proximity to the evaporator coil. If the evaporator coil defrosting device control includes a timer, then the requisite duration of activation of the evaporator coil defrosting device will vary in accord with the efficiency of the defrosting device. The feedback-controlled evaporator coil

defrosting device control, however, is simple to use with defrosting devices other than the evaporator fan because of the precise activation of the defrosting device preferably only when frost is present on the evaporator coil.

The present inventive refrigeration system accordingly provides an inventive method for defrosting an evaporator coil in a refrigeration system, as shown in Figs. 1 and 2. The inventive method includes the steps of : (1) operating the refrigeration system 10,38 such that the frost builds upon the evaporator coil 18; (2) activating the evaporator fan 22 with the evaporator fan relay switch 26,40 to defrost the evaporator coil 18; and (3) deactivating the evaporator fan 22 upon the evaporator coil 18 being substantially defrosted. If the evaporator fan relay switch 26 (Fig. 1) includes a timer, then the step of activating the evaporator fan 22 with the evaporator fan relay switch 26 to defrost the evaporator coil 18 is activating the evaporator fan 22 for a predetermined duration. If the evaporator fan relay switch 40 is feedback-controlled (Fig. 2) and includes a sensor 44 for sensing frost, or monitoring other parameters of the evaporator coil 18, then the step of activating the evaporator fan 22 is activating the evaporator fan upon the sensor sensing frost or a predetermined change in another sensed parameter of the evaporator coil.

While there has been shown the preferred and alternate embodiments of the present invention, it is to be understood that certain changes can be made in the forms and the arrangement of the components and in the steps of the inventive method without departing from the spirit and scope of the invention as set forth in the Claims appended herewith. In addition, all elements recited in means-plus-function language are intended to include any structure, material, or act for performing the recited function in combination with the other claimed elements as would be known to one of skill in the art.