Methods and systems for defogging transparent doors in display cases

A system for defogging doors to a display case is described and includes an electric motor and an air moving device. The air moving device is operatively coupled to the electric motor and positioned to provide an output proximate to at least one door of the display case. The motor is configured to operate at a first speed under standard closed door conditions, at a second speed when the door of the display case is open, and at a third speed for a predetermined length of time after the door is moved from an open position to a closed position.

BACKGROUND OF THE INVENTION

The field of the invention relates generally to display cases, and more specifically, to methods and systems for defogging transparent doors in display cases.

In a transparent door display case, especially a display case that is refrigerated, energy efficiency and consumer product visibility are key. In order to persuade consumers to buy products, the vendors try to make the product visible to the consumer. Fog or condensation accumulated on a transparent door, for example, a door that is at least partially made of glass, may hide the product from the consumer. Hindering the consumer's view of the product may negatively affect the likelihood the consumer will buy the product.

When a transparent door display case has an open door, the evaporator fan tends to blow cold air to the outside of the case and allow warm air into the case. At least one result is that the refrigeration system must work harder to remove this heat and return the inside of the display case to the desired internal temperature. Additionally, if the air transitioned into the display case is of relatively high moisture content, faster icing of the evaporator coils is one possible result. As such, the refrigeration system must incorporate additional defrosting cycles. Defrosting cycles not only use energy, but they also add heat to the system that must be removed by refrigeration cycles.

One current technology for dealing with air exchange between the inside of a display case and the outside environment when a door is opened is an air curtain. One down side of an air curtain, however, is that complicated ductwork is required to generate a proper air curtain, reducing the amount of merchandise space. Providing an air curtain also increases the static loading on the evaporator fan. As such, a higher output motor that consumes more energy is required.

One alternative considered to prevent air exchange is to shut off the evaporator fan motor when the display case door is open. This solution results in additional wear on the motor and related electrical systems due to the constant cycling of motor contactors and motors repeatedly pulling inrush currents in response to the repeated opening and closing of the display case doors. Constantly turning on and off the evaporator fan motors can also create an audible annoyance to the consumer in terms of widely varying air noise.

Most existing technologies for removing fog/condensate from glass require applying heat in some form. Any heat added to the display case system requires the refrigeration system to work that much harder. The refrigeration compressor is the single largest consumer of energy in the display case system. Anti-fog glass can be effective in a wide range of operating conditions, but not all operating conditions. Adding extra airflow across the glass for a short period of time will help the anti-fog glass be more effective in a wider range of conditions. In some display case applications, blowing extra air may be just as effective with regular, lower cost glass as it is with the more expensive anti-fog glass.

BRIEF DESCRIPTION OF THE INVENTION

In one aspect, a system for defogging doors to a display case is provided. The system includes an electric motor and an air moving device operatively coupled to the electric motor. The air moving device is positioned to provide an output proximate to at least one door of the display case. The motor is configured to operate at a first speed under standard closed door conditions, at a second speed when the door of the display case is open, and at a third speed for a predetermined length of time after the door is moved from an open position to a closed position.

In another aspect, a method for controlling an operating speed of a motor configured to drive an air moving device is provided where the air moving device is configured to direct air along a planar surface of a door of a display case. The method includes operating the motor at a nominal operational speed under standard closed door conditions, operating the motor at an operational speed that is lower than the nominal operational speed when a sensor coupled to the motor indicates the door has been opened, and operating the motor at an operational speed that is higher than the nominal operational speed, for a predetermined period of time, when the sensor indicates the door has been closed.

In still another aspect a display case is provided. The display case includes a transparent door configured to provide access to an interior of the display case, an electric motor, an air moving device configured to be driven by the motor, and a sensor. The air moving device is configured to provide an airstream along a length of an interior of the transparent door. The sensor is operatively coupled to the motor. The sensor in a first state is indicative of the door being closed and configured to cause the motor to run at a nominal speed. The sensor in a second state is indicative of the door being open and configured to cause the motor to run at a speed lower than the nominal speed. The motor, upon sensing that the door has been closed, is configured to run at a speed higher than the nominal speed, for a predetermined length of time, after which the motor runs at the nominal speed.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1is a block diagram of a display case door defogging system10that includes a motor12and an air moving device14. In the exemplary embodiment, air moving device14is a fan and will be referred to herein as fan14. However, air moving device14may include a fan, a blower, or any other device that allows defogging system10to function as described herein. Fan14is operatively connected to motor12, and positioned to provide an output proximate to a glass door20of a display case22. Although described herein as glass door20, door20may include any transparent material that allows display case22to function as described herein. For example, door20may include a transparent section made from glass, plastic, acrylic glass, or any other substantially transparent material.

In the exemplary embodiment, defogging system10is configured such that motor12causes fan14to operate at a nominal operational speed under standard closed door conditions, to operate at a low operational speed when the door20of the display case22is open to minimize heat transference, and to operate at a higher than nominal speed for a predetermined length of time, shortly after the door20is closed, in order to timely remove accumulated fog and/or condensation from the door. In one embodiment, the length of time the motor12operates at the higher than nominal speed may be adjusted by the end user. In an exemplary embodiment, a door switch30or other door activated sensor is incorporated into system10to sense door position, and hence indirectly controls the operating speed of motor12, and subsequently an amount of air output by fan14. Switch30can operate a single motor or effect more than one motor in a display case22. In an alternative embodiment, motor12may sense door open events automatically by, for example, drastic, substantially instantaneous changes in load.

In one embodiment, motor12is a multispeed induction motor operatively connected to switch30and further connected to an external timer32. In another embodiment, motor12is a multispeed brushless DC (direct current) motor, also referred to herein as a multispeed ECM (electronically commutated motor), operatively connected to switch30and timer32. In one embodiment, the timer32is built into the ECM, for example, within the electronics/software associated with the ECM. In at least one embodiment, the timer32is operable to control an amount of time the motor12operates at higher than nominal speed. In another embodiment, motor12is a multispeed ECM having a controller therein which includes electronics and any software that is necessary for load sensing and/or timing to minimize heat transference for maximum system efficiency and to clear fog on the door more quickly for improved product visibility.

The system10provides a method for using multiple motor operating points to improve application (e.g., display case) system efficiency and minimize fogging of the glass door so that product being displayed for sale remains visible to the consumer. Multiple operating points can be achieved in a variety of ways. For an induction motor, multiple operating points can be accomplished through multiple windings, winding taps, or using an electronics circuit operable to apply power to motor12and controlled through switch30. Examples of such electronic circuits include a voltage chopper circuit and a variable frequency drive circuit.

For an ECM, multiple operating points may be achieved using electronics hardware and/or software inside the controller. As described above, there are three basic operating conditions: normal operation, low airflow, and high airflow. Normal operation is the standard operating mode for the application. In examples described herein, the standard operating mode for display case22includes motor12operating at a nominal speed. Low airflow operation is used when the door to the case is opened to minimize how much cold air from inside the case is exchanged with the warm air outside the case, thereby minimizing the work the refrigeration system has to do to maintain a desired temperature within the display case. High airflow operation is used when it is sensed that a door has recently been closed. The high airflow operation supplies an extra amount of air across the inside of the door to more quickly clear any fog or condensation that formed on the inside of the door when it was opened and exposed to warm, moist air that may be present in the ambient environment. The relatively quick defogging time associated with the high airflow operation is utilized to increase an amount of time the product inside the case is visible to a consumer through a clear display case door.

Objectives associated with the above described embodiments include providing a simple, low cost method to improve system efficiency while also maximizing merchandise visibility. As described, this can be done with different motor technologies and accessories. Embodiments that utilize an ECM are further described in the following paragraphs as they generally are equipped with the electronics needed to implement the described embodiments.

The electronics provided with an ECM motor system may be configured for multiple motor operating speeds by configuring those electronics to provide built in delays and/or timer transitions between operating points. In one embodiment, a simple door activated switch can be used to evoke different operating conditions, for example, different operating speeds. For more sophisticated models with known nominal parameters, the ECM is operable to automatically switch between operating speeds based on the load that is sensed, thereby eliminating the need for a door activated switch.

More specifically and in regard to the above mentioned ECM implementation, an ECM motor has three leads: Line (L)40, Neutral (N)42, and Speed2(S2)44. When a line voltage is applied between L40and N42, motor12runs at the nominal operating point. An operating point is defined as an operating speed and direction of rotation. With line voltage applied between L40and N42, if S244is then shorted to N42, the low airflow operating point is enacted. With line voltage applied between L40and N42and S244shorted to N42, if S244is then removed from connection with N42, motor12will run at the high airflow operating point for a predetermined length of time (T). In an exemplary embodiment, T is configured in the electronics/software associated with the ECM. Once T elapses, without any other changes, motor12will return to the nominal operating point. If at any point line voltage is removed, the motor will cease to operate. When power is reapplied between L40and N42, the nominal operating point will resume unless S244is shorted to N42, in which case the low airflow operating point will be enacted.

In the display case application, these modes of operation are typically controlled with door-activated switch30(shown inFIG. 1). The switch30would be a normally closed switch and would connect between N42and S244, meaning that when the door20is closed, an actuator on switch30is depressed and the connection between N42and S244is open. The motor12would be running at either the nominal operating point or the high airflow operating point depending on the previous operating state. When the door20is opened, the switch30resumes the normally closed state and shorts S244to N42. The low airflow operating point is then enacted.

In at least one embodiment, timer32is also operable to control a length of time motor12operates at the low airflow operating point. Timer32may be configured to monitor a length of time beginning when S244is shorted to N42and motor12is operated at the low airflow operating point. If motor12is operating at the low airflow operating point for longer than a predetermined time (T2), motor12is directed to return to the nominal operating point, regardless of whether S244remains shorted to N42. Monitoring the time motor12operates at the low airflow operating point facilitates maintaining the temperature inside display case22and protecting products stored in display case22in the event door20is left in an open position for an extended period of time. In some embodiments, display case door defogging system10also includes an alarm system46that produces a signal when T2is exceeded. In the exemplary embodiment, alarm system46activates an alarm to provide a notification to, for example, a store employee, that door20has been open for a period of time longer than T2. In an exemplary embodiment, door defogging system10, and more specifically, timer32, resumes normal operation once switch30is toggled.

FIG. 2is a flowchart50illustrating a method for efficiently maintaining the clarity of a door for a display case. The method includes operating52the motor12(shown inFIG. 1) and thus the fan14(shown inFIG. 1) at a nominal operational speed under standard closed door conditions, that is, during periods when the door20to the display case22is closed. When the door20to the display case22is opened, the motor12and thus the fan14, are configured to operate54at an operational speed that is lower than the nominal operational speed in order to minimize heat transference. When it is sensed that the door20to the display case22has been closed, the motor12and thus the fan14are configured to operate56at a speed higher than the nominal speed for a predetermined amount of time, shortly after the door20is closed, in order to timely remove fog and condensation from the door.

As described herein, using a high fan speed for a short period of time helps to clear fog more quickly, which maintains product visibility. Smaller transitions in motor speed are likely to be less noticeable by a consumer viewing and selecting items in a refrigerated display case.