Patent Application
20240003615
The present disclosure relates generally to a method for control of vapor pressure deficit for food preservation in a refrigerator.
Typically, refrigeration is used to maintain a food storage compartment at a desired temperature to reduce food decay and increase the useful life of stored food products. However, temperature is not the only variable affecting food preservation. Humidity is also critical to effective food preservation and storage. For example, fresh fruits and vegetables are living tissues. Although they are no longer attached to a plant, they breathe, and their composition and physiology continue to change after harvest. The cellular breakdown and death of fresh fruits and vegetables are inevitable but can be slowed with optimal storage conditions. Water loss results in weight loss, wilting, and shriveling, while free water or condensation facilitates pathogen growth.
In a refrigerator, it is common to control the temperature of a compartment within a tight band. However, controlling humidity is much more difficult because a refrigerator is not equipped with an active humidifier. Accordingly, strict temperature control in a refrigerator can lead to an unfavorable vapor pressure deficit condition within the food storage compartment that leads to accelerated spoilage of the stored food products.
The present subject matter provides a method for control of vapor pressure deficit for food preservation in a refrigerator. The method includes measuring the temperature and humidity of the food storage compartment, determining the vapor pressure deficit in the food storage compartment, and adjusting the temperature in the food storage compartment to maintain the vapor pressure deficit within the desired range. Aspects and advantages of the invention will be set forth in part in the following description, may be apparent from the description, or may be learned through practice of the invention.
In one example aspect, a method for preserving food inside a refrigerator is provided. The refrigerator including a compartment for storing food. The method includes measuring the humidity in the compartment and measuring the temperature in the compartment. The vapor pressure deficit in the compartment is determined. The temperature in the compartment is adjusted to maintain the vapor pressure deficit in the compartment within a desired range.
In another example aspect, a method of preserving food inside a refrigerator is provided. The refrigerator includes a plurality of compartments for storing food. The method includes measuring the humidity in each of the plurality of compartments and measuring the temperature in each of the plurality of compartments. The vapor pressure deficit is determined in each of the plurality of compartments. Vapor pressure deficit control is selected for at least one of the plurality of compartments. For each of the plurality of compartments for which vapor pressure deficit control is selected, the temperature is individually adjusted in each of the selected compartments to maintain the individual vapor pressure deficit in each of the selected compartments within an individually desired range. For each of the plurality of compartments for which vapor pressure deficit control not selected, the temperature is individually adjusted in each of the unselected compartments within an individually desired range without regard to the vapor pressure deficit in any of the unselected compartments.
In another example aspect, a refrigerator for storing food is provided. The refrigerator includes at least one food storage compartment; at least one thermometer; at least one hygrometer; a sealed system configured for cooling air in the at least one food storage compartment; and a controller. The controller is configured to: 1) receive a measured temperature from the thermometer and a measured humidity from the hygrometer and to calculate a vapor pressure deficit based on the measured temperature and measured humidity and 2) activate or deactivate the sealed system. When the vapor pressure deficit is within a desired range, the controller deactivates the sealed system. When the vapor pressure deficit is outside of the desired range, the controller activates the sealed system. The controller may be configured to repeat the determination of the vapor pressure deficit and activate or deactivate the sealed system periodically to maintain the vapor pressure deficit within the desired range, as long as the temperature is within the limits for safe food storage.
These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.
A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures.
Reference now will be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents.
As used herein, the terms “includes” and “including” are intended to be inclusive in a manner similar to the term “comprising.” Similarly, the term “or” is generally intended to be inclusive (i.e., “A or B” is intended to mean “A or B or both”). Approximating language, as used herein throughout the specification and claims, is applied to modify any quantitative representation that could permissibly vary without resulting in a change in the basic function to which it is related. Accordingly, a value modified by a term or terms, such as “about,” “approximately,” and “substantially,” are not to be limited to the precise value specified. In at least some instances, the approximating language may correspond to the precision of an instrument for measuring the value. For example, the approximating language may refer to being within a ten percent (10%) margin.
Refrigerator doors 30 are rotatably hinged to an edge of housing 10 for selectively accessing fresh food chamber 20. In addition, a freezer door 132 is arranged below refrigerator doors 130 for selectively accessing freezer chamber 22. Freezer door 32 is coupled to a freezer drawer (not shown) slidably mounted within freezer chamber 22. Refrigerator doors 30 and freezer door 32 are shown in a closed configuration in
Refrigerator appliance 100 also includes a dispensing assembly 40 for dispensing liquid water and/or ice. Dispensing assembly 40 includes a dispenser 42 positioned on or mounted to an exterior portion of refrigerator appliance 100, e.g., on one of doors 30. Dispenser 42 includes a discharging outlet 44 for accessing ice and liquid water. An actuating mechanism 46, shown as a paddle, is mounted below discharging outlet 44 for operating dispenser 42. In alternative exemplary embodiments, any suitable actuating mechanism may be used to operate dispenser 42. For example, dispenser 42 can include a sensor (such as an ultrasonic sensor) or a button rather than the paddle. A user interface panel 48 is provided for controlling the mode of operation. For example, user interface panel 48 includes a plurality of user inputs (not labeled). Discharging outlet 44 and actuating mechanism 46 are an external part of dispenser 42 and are mounted in a dispenser recess 50.
The refrigerator 100 may also include data storage device (not shown) and a food detection device (not shown) in signal and/or operative communication with the controller. In embodiments, the food detection device is any sensor capable of identifying the food(s) contained in the food storage compartment without the active input of the user. Examples of food detection devices include cameras, RFID readers, bar code scanners, and the like.
The controller 200 may be adapted to allow different modes of operation for the refrigerator 100. In an exemplary embodiment, the refrigerator 100 may be operated in one of four (4) modes—standard mode, manual VPD control mode, semiautomatic VPD control mode, and automatic VPD control mode. As used herein, “standard mode” may correspond to a mode wherein the refrigerator operates to tightly control temperature without regard to the VPD, e.g., as is typical in known refrigerators. As used herein, “manual mode” may correspond to a mode wherein the refrigerator operates to control VPD, in the manner described herein, and the desired VPD and desired temperature range for the compartment are selected by the user. As used herein, “semiautomatic mode” may correspond to a mode wherein the refrigerator operates to control VPD, as described herein, and the user selects a food or food type and the VPD and temperature range for the compartment are selected by the controlled based on data stored in the controller (or a data storage device). As used herein, “automatic mode” may correspond to a mode wherein the refrigerator operates to control VPD, as described herein, and refrigerator identifies the food(s) stored in the compartment with a food detection device and the VPD and temperature range for the compartment are selected by the controller based on the identified food(s) and data on the appropriate VPD for various food(s) stored in the controller (or the data storage device) without active input by the user.
In example embodiments, the user may select the desired mode of operation the refrigerator by any convenient mechanism. For example, the refrigerator may include local controls (e.g., buttons or a control pad) to select the desired mode and other required inputs (e.g., desired VPD and/or temperature range or food type). Alternatively, the refrigerator may be connected to a smart device, such as a smart phone, tablet, computer, e.g., via Wi-Fi or Bluetooth, and the mode of operation of the refrigerator and other inputs may be selected by the user using the smart device.
When required for any of the VPD control modes, the controller 200 determines the vapor pressure deficit (VPD) as discussed in greater detail below. The controller 200 compares the VPD to a desired VPD chosen by the user using an input 220 or determined by the controller 200 (as discussed below). The controller 200 then determines the temperature required to achieve and maintain the VPD in the desired VPD range. The controller 200 then engages or activates evaporator 120, evaporator fan 130, compressor 140, condenser 150, and condenser fan 160 to cool the food storage compartment 110 or disengages or deactivates the evaporator 120, evaporator fan 130, compressor 140, condenser 150, and condenser fan 160 to allow the temperature in the food storage compartment 110 to rise, as appropriate to achieve and maintain the VPD in the desired VPD range. In this example embodiment, the above steps are repeated periodically to maintain close VPD control.
In an example embodiment of the present subject matter, the controller 200 determines the VPD using the Tetens equation to calculate the saturation vapor pressure (Ps). (Teten, O., Uber einige meteorologische, Begriffe Z. Geophys, 6: 297-309 (1930), which is incorporated by reference in its entirety). This equation states:
P
s(T)=0.61078 exp(17.269 T/(T+273.3))
where:
Using the calculated saturation vapor pressure (Ps) at the known temperature (T), the actual vapor pressure (PVAP) may be calculated:
P
VAP
=P
s(T)*H/100
where:
Finally, the VPD can be determined by subtracting the actual vapor pressure from the saturation vapor pressure
VPD=P
s(T)−PVAP
where:
The loss of water from a food product and/or presence of free water condensation is related to the VPD, i.e., the difference between the actual humidity of the surrounding air and the maximum amount of water that the air can hold. While the above definition for VPD is commonly used, the primary driving force for moisture loss from food is the water vapor pressure difference that exists between the food surface and its surroundings. Thus, the most relevant vapor pressure difference at the food surface is:
VPD
surf
=P
s(Tsurf)−Ps(T)*H/100
In most scenarios, a reasonable approximation can be made that the surface of the stored food item (Tsurf) is at the same temperature as the storage compartment as reported by the thermometer (i.e. Tsurf=T). In such situations, VPDsurf equals VPD.
However, if this is not true, an offset value may be added to the thermometer measurement based on the type of food stored to determine the approximate surface temperature of the food such that Tsurf=T+Offset. As noted above, fresh fruits and vegetables are living tissues. And, although the fruits and vegetables are no longer attached to a plant, the fruits and vegetables breathe, and their composition and physiology continue to change after harvest. The cellular breakdown and death of fresh fruits and vegetables are inevitable but may be slowed with optimal storage conditions. Water loss may result in weight loss, wilting, and shriveling. The loss of water is driven by the VPD at the surface of the food. The greater the VPD at the surface of the food, the greater and more rapid the loss of water from the food product. This loss of moisture can lead to the decay of the stored food product. As discussed above, in most circumstances the VPD at the surface of the food is closely associated with the VPD as calculated form the surrounding air and the two may be used interchangeably.
On the other hand, if the VPD is low and the temperature decreased, the amount of water in the air can exceed the saturation vapor pressure. When this occurs, the water will condense out of the air and coalesce on the surfaces of the refrigerator and the food products stored therein. This free, liquid water on the fresh fruits and vegetables can also lead to decay of the stored food product due to pathogen growth.
Another important consideration in refrigerated food storage is temperature control. Freezing fresh fruits and vegetables can lead to damage due to ice crystal formation and the resultant damage to the cellular structure of the fruits and vegetables. Conversely, elevated storage temperatures can allow for accelerated growth of pathogens, which leads to decay. Accordingly, in an example embodiment of the present subject matter, in addition to the tight control of the VPD, control of the temperature of the food storage compartment within a range safe for food storage is required. In an example embodiment, the temperature range that is safe for food storage is from 32° F. to 45° F., from 33° F. to 42° F., or from 34° F. to 37° F.
As can be appreciated from the equations above, VPD is dependent on temperature and humidity. As previously noted, in a refrigerator, it is common to have direct control the temperature of a compartment. Thus, as represented in
Schematically, if the determined VPD is higher than the desired range, then the temperature is lowered (by engaging the cooling cycle) to lower the saturation vapor pressure. Theoretically, if the absolute humidity inside a compartment is kept constant, in other words, if there is no moisture generation or loss inside the compartment, the VPD decreases if the temperature is allowed to decrease. This is because the saturation pressure of water vapor decreases rapidly with temperature whereas the actual vapor pressure of water inside the compartment decreases so slightly that it can be essentially considered a constant. Conversely, if the determined VPD is lower than the desired range, then the temperature is allowed to increase (by disengaging the cooling cycle) to increase the saturation vapor pressure. Again, theoretically, the vapor pressure is essentially constant and the increase in the saturation vapor pressure would increase in VPD.
However, under real world conditions, the operation of the sealed system to regulate temperature involves the operation of an evaporator. Accordingly, during cooling, humidity is initially removed to cool the air in the compartment. Thus, depending on humidity, fan speeds, and starting temperature, the operation of the sealed system can lower temperature while actually increasing VPD due the removal of moisture by evaporation. This can be mitigated in various ways. For example, the fans can be operated at higher speeds or a fan defrost of the evaporator can be carried out to re-introduce the moisture into the compartment. In sum, the initial operation of the sealed system may increase VPD, but once the compartment allowed to equilibrate, the VPD will decrease as desired.
In an example embodiment of the present subject matter, the refrigerator may include a mechanism for heating the food storage compartment. Examples mechanisms for such heating include a defrost heater, a meat pan heater and the like. In an example embodiment, the heater may be used in conjunction with the sealed system to provide control over the temperature in the food storage compartment, and as discussed above, provide tight VPD control.
In an example embodiment of the present subject matter, the desired VPD range is a VPD range that produces relatively small loss of water from the stored food product, while also avoiding condensation in the food storage compartment. Generally, the desired VPD range will be dependent on the type of food being stored and will avoid approaching a VPD of 0 to prevent or reduce condensation. In an example embodiment of the present subject matter, the desired VPD range is between about 0.05 and about 0.85, between about 0.05 and about 0.50, between about 0.07 and about 0.15, between about 0.15 kPa and about 0.22 kPa, between about 0.22 kPa and about 0.30 kPa, between about 0.30 kPa and about 0.37 kPa, or between about 0.30 kPa and about 0.45 kPa.
In an example embodiment of the present subject matter, the desired range for the VPD may be set using any convenient mechanism. The mechanism for setting the desired range for VPD may be entry of the desired range into the controller during manufacture, i.e., a default setting. The mechanism for setting the desired range for VPD may be the input 220 incorporated into the refrigerator 100 or connected remotely to the controller allowing the user to select the desired range. In an example embodiment, the input 220 may be a touch pad, a button or plurality of buttons, a dial, or any other user interface, adapted to allow the user to manually input the desired range for VPD. In another example embodiment, the input 220 allows the user to input a numeric range for the VPD. In yet another example embodiment, the input 220 allows the user to select a food to be stored and the controller selects an appropriate desired range for VPD based on the food selected.
In example embodiments of the present subject matter, the refrigerator 100 may include a plurality of food storage compartments 110 and may include VPD control in any one or more of the plurality of food storage compartments. In such an example embodiment, each food storage compartment may include a separate thermometer and hygrometer. Moreover, each food storage compartment may individually cooled or not, as appropriate by the controller and sealed system. In an example embodiment, one or more of the food storage compartments may kept under tight VPD control and one or more other food storage compartments may be kept under conventional tight temperature control, as desired by the user.
This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.
