Apparatus and method for evaporator defrosting

Refrigeration – Automatic control – Preventing – removing or handling atmospheric condensate

Reexamination Certificate

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Details

C062S156000, C062S197000, C062S277000, C062S512000, C062SDIG002

Reexamination Certificate

active

06250090

ABSTRACT:

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 defrosting of an evaporator, and especially the evaporator coil, in a refrigeration system.
2. Description of the Related Art
Refrigeration systems are well known in the art and a closed-flow refrigeration system generally includes a compressor, a condenser and condenser fan, a refrigerant tube between the components, an expansion device such as a capillary tube, an evaporator that has an evaporator coil and an evaporator fan, and a thermostatic relay coupled to a power supply to engage the refrigeration system. 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 excess heat from the refrigerant environment. The liquid refrigerant then passes to the evaporator and is expanded or vaporized in the evaporator and the expanding refrigerant absorbs the ambient heat of the evaporator such that the evaporator produces cooling, and ambient air is passed thereover by the evaporator fan and a stream of cool air is thus generated.
The cooling of the ambient air passing through the evaporator and around the evaporator coil causes condensate, and subsequently, frost to build up on the evaporator as the refrigeration system operates. Such frost must be removed in order for the evaporator to function properly and have convection with the evaporator adequately cool the ambient air during the refrigeration cycle. In order to minimize frost in the evaporator, most refrigeration systems therefore maintain activation of the evaporator fan to defrost the evaporator and evaporator coil when the refrigeration cycle is not active, i.e. the compressor and condenser are not running and compressed cooled refrigerant is not flowing.
There are other apparatuses and methods known in the art to defrost the evaporator coil in addition to the method of activating the evaporator fan while the refrigeration system otherwise cycles off. A hot gas defrosting system gathers hot gas from the discharge of the compressor and passes it through the evaporator in proximity to the evaporator coil through the use of an additional hot gas line with associated valves and controls. Furthermore, the use of hot gas for defrosting provides a thermal shock to the components of the evaporator that increases wear and necessity of repair of such components.
Electrical heating elements are sometimes provided in, or in proximity to, the evaporator and evaporator coil, or in conjunction with an evaporator fan to provide heat to the evaporator and evaporator coil sufficient for defrosting. The electrical elements, however, are quite inefficient and consume significant power in producing energy. Moreover, the use of electrical elements can also create a thermal shock to the evaporator components and cause deleterious effects similar to the use of a heat gas line.
Another known method of defrosting the evaporator is simply to cycle the compressor off for a sufficient duration to allow the evaporator to warm and the condensate thereupon to drain. However, such method is slow and unpractical for very cold refrigerant temperatures, i.e. far below 32° F., and is impractical for refrigeration systems that must provide a significant amount of refrigeration.
Accordingly, an apparatus and method of defrosting the evaporator and evaporator coil of a refrigeration system that is efficient, simple, and which does not cause a significant thermal shock to the evaporator components during defrosting would represent an improvement over the prior art evaporator defrosting devices and methods.
SUMMARY OF THE INVENTION
The present invention is an apparatus and method for defrosting an evaporator of a refrigeration system. A refrigeration system includes at least one compressor, at least one condenser, at least one evaporator, with a refrigerant tube in fluid communication with each compressor, condenser, and evaporator, with a refrigerant flowing through said refrigerant tube. The present refrigeration system also includes the inventive element of at least one first refrigerant expansion device in fluid communication with the refrigerant tube such that the refrigerant flows therethrough, and each first refrigerant expansion device is located in the refrigerant tube between each condenser and evaporator. The first refrigerant expansion device selectively expands or vaporizes the refrigerant passing therethrough prior to the refrigerant passing through the evaporator whereby the refrigerant absorbs ambient heat as it passes through the evaporator.
The present inventive refrigeration system, further, includes the inventive element of at least one second refrigerant expansion device in fluid communication with the refrigerant tube such that refrigerant flows therethrough, and the second refrigerant expansion device is located in the refrigerant tube between each evaporator and each compressor. The second refrigerant expansion device selectively expands refrigerant passing therethrough after the refrigerant has passed through the evaporator and before passing through a compressor. Thus, the second refrigerant expansion device allows the refrigerant to pass through the evaporator in liquid form with expansion of the refrigerant, and thus the cooling effect, occurring after. This capability allows the warmer liquid refrigerant to pass through the evaporator and evaporator coil thereby defrosting the evaporator, and then expands the refrigerant so that the refrigerant can be again compressed in the compressor and transported through the refrigerant tube.
Because the inventive refrigeration system controls when the refrigerant is expanded, the present inventive refrigeration system includes a defrosting control connected to each first refrigerant expansion device and each second refrigerant expansion device. The defrosting control therefore selectively defrosts an evaporator by deactivating the first refrigerant expansion device and activating the second refrigerant expansion device to allow the warm liquid refrigerant to pass through and defrost the evaporator. And once the refrigeration cycle has resumed, the first refrigerant expansion device is activated and the second refrigerant expansion device is deactivated to cause cooling expansion of the refrigerant to occur in the evaporator.
The defrosting control preferably includes a timer to have the defrosting cycle run for a predetermined duration. The defrosting control alternately includes one or more sensors to sense one or more parameters of the evaporation and the defrost control defrosts the evaporator upon a predetermined charge in the sensed parameter. One preferred sensor is a frost sensor on the evaporator coil which effects the defrosting of the evaporator while frost is detected.
In another embodiment, the inventive refrigeration system includes at least one first refrigerant bypass located in the refrigerant tube and the first refrigerant bypass selectively directs the refrigerant to bypass each first refrigerant expansion device. The first refrigerant bypass allows the use of a static refrigerant expansion device, such as a capillary tube, for the first refrigerant expansion device, and the defrosting control then activates or deactivates the refrigerant bypass instead of activating the first refrigerant expansion device directly. Accordingly, the inventive refrigeration system can alternately include at least one second refrigerant bypass located in the refrigerant tube and the second refrigerant bypass selectively directs the refrigerant to bypass each second refrigerant expansion device. When the refrigeration system includes a second refrigerant bypass, the defrosting control likewise is connected to each second refrigerant bypass and activates or deactivates the second refrigerant bypass directly in conjunction with the first refrigerant expansion device or first refrigerant bypass t

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