1. Field of the Invention
This invention relates to a movable member configured to partially or fully isolate a heat exchanger from an environment. In one example, the movable member is disposed within a cooling system such as a freezer, and isolates one or more heat exchangers within the freezer from an interior of the freezer during a defrost operation.
2. Description of the Related Art
In cooling systems such as freezers and refrigerators, moisture from the air entering the cooling system through open doors, small passages in the walls or floors, and from the product stored within the cooling system frequently collects on heat exchanger coils and heat exchanger fins in the form of ice. During long operation, ice can accumulate on the coils and fins creating a blockage that impedes the airflow over the heat exchanger and creates a loss in efficiency in operation of the cooling system.
Typical heat exchangers increase or decrease temperature by running fluid through manifolds that feed loops of tubes. The tubes frequently have fins attached to them. The purpose of the fins is to increase the effective surface area of the tubes in order to increase the rate of heat exchange. Air flow is typically provided by fans which blow or draw air across the finned tubes. A heat exchanger rating, typically listed in British Thermal Units “BTU,” depends on the number of air cycles which go through the finned tubes per minute. In a freezing application, constriction of the fins or tubes due to ice build up reduces the number of air changes that are allowed to occur. This in turn reduces the heat exchanger's capacity. Accordingly, many heat exchangers in cooling systems must be regularly defrosted in order to maintain sufficient cooling capacity. In order to provide efficient defrosting of individual heat exchangers without requiring defrosting an entire freezer, sequential defrost units have been developed.
One objective of a sequential defrost unit is to maintain temperature and freezing/cooling of stored or processed product while providing defrost in one or more heat exchangers at a time. One issue in providing sequential defrost is a difficulty in effectively isolating the one or more heat exchangers in the defrost stage while running other heat exchangers in the cooling system.
Some conventional sequential cooling systems are designed with sufficient capacity to allow for at least one heat exchanger to be defrosted while the remaining heat exchangers can accommodate the refrigeration load in the application. In other words, if the required cooling capacity is ninety tons of refrigeration, one would provide a one-hundred-and-twenty ton capacity in four heat exchangers, i.e., thirty tons in each heat exchanger. With the above-noted arrangement, when one heat exchanger is in defrost, the remaining three heat exchangers provide the required ninety ton refrigeration capacity. Conventional sequential cooling systems often attempt to isolate the heat exchanger undergoing defrost with mechanical louvers or shutters. However, the louvers or shutters themselves can become coated or clogged with ice and cease to adequately isolate the heat exchanger during its defrost stage. In some cases, the shutters freeze in the open or closed position. When this clogging occurs, air flow around the heat exchanger undergoing defrost can be disrupted, which can result in an increased amount of time required to defrost the heat exchanger. Furthermore, warm air from the heat exchanger undergoing defrost can leak into the cooling system at large, resulting in an increased heat load on the heat exchangers that are not being defrosted.