US20180187968A1

US20180187968A1 - Refrigeration unit with air humidity monitoring

Info

Publication number: US20180187968A1
Application number: US15/739,235
Authority: US
Inventors: Niels Liengaard; Hanna Koezle; Antje Engstler
Original assignee: BSH Hausgeraete GmbH
Current assignee: BSH Hausgeraete GmbH
Priority date: 2015-06-26
Filing date: 2016-06-02
Publication date: 2018-07-05
Also published as: CN107810375A; WO2016206938A1; CN107810375B; EP3314181A1; DE102015211960A1

Abstract

A refrigeration appliance includes a storage chamber, an evaporator that cools the storage chamber, and a processing unit configured to assign values for the air humidity in the storage chamber and an evaporation temperature of the evaporator to one another, at a given temperature of the storage chamber, under the assumption that the absolute water vapor content of the air of the storage chamber is the same as that of water-vapor-saturated air at the evaporation temperature. This assignment makes it possible on one hand to estimate the relative air humidity in the storage chamber on the basis of the temperatures, and on the other hand to control the air output temperature, at constant temperature in the storage chamber, in order to influence the air humidity therein.

Description

The present invention relates to a refrigeration appliance, in particular a household refrigeration appliance.
The relative air humidity present in a storage chamber of a refrigeration appliance is of major significance for the shelf life of food therein. A high level of air humidity is desirable in particular for storing fresh vegetables. In refrigeration appliances in which air is circulated between the storage chamber and a heat exchanger, typically in what are referred to as no-frost refrigeration appliances, such a high level of air humidity is difficult to maintain, as when the air is cooled to below its dew point on a surface of the heat exchanger, it loses moisture there, said moisture having to be discharged from the refrigeration appliance and eliminated. This water loss causes the vegetables to wilt rapidly.
In order to be able to store vegetables for longer, vegetable compartments have been developed, which comprise a container that can be closed with a lid. When the container is sealed, the moisture given off by vegetables contained therein cannot escape and at the same time the container can be cooled by cold air circulating over its outer surfaces. A limited exchange of air can be permitted between the container interior and its surroundings through an adjustable opening in the container, so that different air humidity values can be set in the container based on the size of the opening. It is difficult to measure this air humidity and display it on the outside of the refrigeration appliance so that it is visible to a user, as the air humidity sensor would have to be positioned in the container and its output signal would have to be transmitted from the container, which can be moved about in the refrigeration appliance, to a display instrument of the refrigeration appliance, without restricting the freedom of movement of the container.
Air humidity is therefore generally not measured and the user generally does not know the actual level of air humidity in the container. Said user can therefore essentially only use his/her own observations to determine the degree of opening of the container that is appropriate for specific chilled goods. Such observations are however complicated by the fact that the air humidity in the interior of the container is not only a function of the size of the opening but is also influenced, indirectly, by ambient conditions by way of the operating time of the evaporator. This makes it difficult for the user to identify a relationship between the degree of opening of the container and the shelf life of the chilled goods.
It is the object of the invention to create a refrigeration appliance and an operating method for a refrigeration appliance, which allow the user to monitor the air humidity in the refrigeration appliance more effectively.
The object is achieved on the one hand by a refrigeration appliance with a storage chamber and an evaporator that cools the storage chamber, wherein a processing unit is designed to assign values for air humidity in the storage chamber and an evaporation temperature of the evaporator to one another at a defined temperature of the storage chamber, under the assumption that the absolute water vapor content of the air in the storage chamber is the same as that of water vapor-saturated air, i.e. air with 100% relative humidity, at the evaporation temperature.
The assignment can be made in different directions and serve different purposes. In a first embodiment sensors are provided to measure the temperature of the storage chamber and the evaporation temperature and the processing unit is designed to adopt a value of the evaporation temperature as defined on assignment, to estimate the corresponding air humidity at the temperature of the storage chamber for said value and to display the air humidity thus estimated on a display instrument. This allows a user to reach a quantitative conclusion about the air humidity in the storage chamber without an air humidity sensor having to be provided directly therein, which is problematic in particular when the storage chamber is configured as a pull-out box as is usually the case for vegetable compartments.
Even more important than knowledge of the air humidity in the storage chamber is the ability of a user to set the air humidity in the storage chamber specifically. Therefore in a second embodiment the assignment is made in the reverse direction. To this end an operating element is provided to set the air humidity in the storage chamber as a set point variable and the processing unit is connected to the operating element and designed to estimate a target value of the evaporation temperature for a defined set point value of the air humidity as set at the operating element on assignment and to align the real evaporation temperature of the evaporator with the target value. When the air in the storage chamber in contact with the evaporator is cooled down to the evaporation temperature, only the amount of water vapor that corresponds to 100% relative air humidity at the evaporation temperature can be retained therein. By selecting an appropriate evaporation temperature it is possible to set a desired relative air humidity for the same air after heating to the temperature of the storage chamber.
In order to allow control of the evaporation temperature, the evaporator can be part of a refrigerant circuit, in which the throughput of a compressor can be controlled in order to vary the pressure in the evaporator.
Alternatively or additionally the evaporation temperature can also be influenced by controlling the opening cross section of at least one throttle valve connected in series upstream or downstream of the evaporator.
When the temperature of the storage chamber is constant, if a high level of air humidity is to be maintained in the storage chamber, the evaporation temperature must be set higher than for a low air humidity value.
In particular but not only in the case of a no-frost model refrigeration appliance, with an evaporator chamber separated from the storage chamber, a fan with controllable throughput can be provided to circulate air between the evaporator and the storage chamber.
The faster the fan operates, the smaller the temperature difference between upstream and downstream sides of the evaporator. When it operates slowly, the heat input at the downstream end of the evaporator is small and a low evaporation temperature can be established there, which removes a large amount of moisture from the air flowing through; when the fan operates quickly, a lot of heat reaches the downstream region of the evaporator so a higher evaporation temperature results with a constant refrigerant throughput. Therefore the control circuit can predefine a higher fan speed to maintain a high level of relative air humidity in the storage chamber at the defined temperature than when a low level of air humidity is set.
The object of the invention is also a method for estimating the relative air humidity in a refrigeration appliance, in particular a refrigeration appliance as described above, with the steps

- a) measuring the temperature of the storage chamber,
- b) measuring an evaporation temperature of the evaporator,
- c) calculating the relative humidity of air at the temperature of the storage chamber, the absolute moisture content of which is the same as that of water vapor-saturated air at the evaporation temperature.

The relative humidity thus calculated can be displayed on a display instrument of the refrigeration appliance as an estimated value for the relative air humidity in the storage chamber of the refrigeration appliance.
A further object of the invention is a method for operating a refrigeration appliance, in particular a refrigeration appliance as described above, with the steps

a′) determining a set point temperature of a storage chamber,
b′) determining a set point air humidity of the storage chamber,
c′) setting an evaporation temperature of the evaporator such that the absolute moisture content of water vapor-saturated air at the evaporation temperature is the same as that of air with the set point air humidity at the set point temperature.

Further features and advantages of the invention will emerge from the description of exemplary embodiments which follows with reference to the accompanying figures, in which:

FIG. 1 shows a block diagram of an inventive refrigeration appliance;

FIG. 2 shows a schematic cross section through a part of the housing of the refrigeration appliance; and

FIG. 3 shows a diagram of the relationship between evaporation temperature and relative air humidity in the vegetable compartment of the refrigeration appliance

FIG. 1 shows a block diagram of a household refrigeration appliance with a number of storage chambers 1, 2, 3, each cooled by an evaporator 4, 5 or 6. The evaporators 4, 5, 6 are connected to one another in series in a refrigerant circuit. FIG. 1 shows three storage chambers and evaporators but the principle of the invention set out in the following can also be applied to refrigeration appliances with any number of storage chambers, including just one.
A speed-regulated compressor 7 is connected to a suction connection of the last, 6, of the evaporators connected in series. A control circuit 8 controls the speed of the compressor 7 based on temperatures measured in the storage chambers 1, 2, 3 by means of temperature sensors 9 to 11 to a value, at which the output of the compressor 7 suffices to meet the cooling requirements of the storage chambers 1 to 3. In the simplest instance such regulation can be based on incrementing the compressor speed when the temperature in one of the storage chambers 1, 2, 3 moves out of a set point interval in an upward direction and decrementing said speed when it moves out of the interval in a downward direction.
The refrigerant, which has been compressed in the compressor 7 and adiabatically heated in the process, outputs its heat to the surroundings by way of a condenser 12, passing back from there to the evaporators 4, 5, 6.
Connected in series upstream of each evaporator is a throttle valve 13, 14 or 15, which can be controlled by the control circuit 8. The throttle valves 13, 14, 15, which are connected one after the other, form a flow resistance, which determines the mass throughput of the refrigerant circuit. The way in which the flow resistance is distributed to the individual throttle valves 13, 14, 15 is variable, in other words when one of the throttle valves is narrowed, another can be widened, so that the mass throughput remains the same. It is thus possible for example to raise the pressure and therefore the evaporation temperature in the evaporator 4 by reducing the flow resistance of the throttle valve 13 and at the same time increasing the flow resistance of the throttle valve 14, without this affecting pressure and temperature in the downstream evaporators 5, 6.
According to one embodiment of the invention the relationship between opening cross sections to be set at the valves 13, 14 in order to vary the pressure in the evaporator 4 and at the same time keep the pressures in the evaporators 5, 6 constant, is preprogrammed in the control circuit 8. In a second embodiment after the throttle valve 13 has been adjusted, the throttle valve 14 is set in such a manner that an operating point of the compressor 7 characterized by speed and electric power consumption is restored, thereby ensuring that the mass throughput of the refrigerant circuit is kept constant.
FIG. 2 shows a schematic cross section through a part of the housing of the refrigeration appliance with the storage chamber 1. The storage chamber 1 is shown here as the lowest storage chamber of the housing but it can also be in other positions. The position of the storage chamber 1 in the lower region of the housing close to a base allows a pull-out box 16 to facilitate access to the chilled goods stored therein. In contrast to conventional refrigeration appliances the pull-out box 16 is not closed and does not need to be, in order to protect its contents against drying out. In order to protect the chilled goods from contact with pooled water, a grid or mesh can advantageously be the substrate for the chilled goods instead of the pull-out box 16.
The evaporator 4 is a no-frost evaporator accommodated in an evaporator chamber 18 separated from the remainder of the storage chamber 1 by a wall 17. It also comprises a fan 19, which can be operated at variable speed by the control circuit 8 in order to suck air through the evaporator 4 and guide the air thus cooled back into the storage chamber 1 and around the pull-out box 16 by way of a rear wall channel 20.
The temperature sensor 9 is positioned at a point of the storage chamber 1 where it is protected from a direct flow of air exiting from the rear wall channel 20, in this instance for example in a side wall of the refrigeration appliance housing, opposite a side of the pull-out box 16.
A further temperature sensor 21 is provided in the evaporator chamber 18 and can be positioned directly in the evaporator 4 itself; FIG. 2 shows it downstream of the evaporator 4 at a point where it is directly exposed to the flow of air cooled to the evaporation temperature in the evaporator 4.
In normal operating conditions the evaporator is always several ° C. colder than the air in the storage chamber 1. When this air cools to below its dew point as it passes through the evaporator 4, some of the moisture carried with it condenses on the evaporator 4 and the air exiting from the evaporator 4 has a relative humidity of 100%. When this air passes back into the storage chamber 1 and heats up to the temperature prevailing there, its relative humidity drops accordingly, according to the formula
$\begin{matrix} r = 100 \cdot 10 \frac{a TD}{b + TD} - \frac{a T}{b + T}, & (1) \end{matrix}$
where T is the air temperature in the storage chamber 1 measured by the air sensor 9 and TD is the evaporation temperature measured by the temperature sensor 21 and the constants a, b can have different values depending on the type of phase transition taking place at the evaporator 4. At an evaporation temperature over 0° C., for a phase transition from vapor to water, a=7.5, b=237.3, at an evaporation temperature below 0° C. and for a phase transition from vapor to ice the values are a=9.5 and b=265.5. An evaporation temperature >0° C. is sufficient for the storage chamber 1 to be used as a vegetable compartment.
A display instrument 22, on which the control circuit 8 outputs the estimated value for air humidity in the storage chamber 1 as calculated according to the above formula (1), can be arranged, as shown in the figure, on the outside of the housing of the appliance or it can be mounted inside adjacent to the storage chamber 1 at a point where it is only visible when the door 23 opens.
Clearly the above formula is not simply suitable for estimating the air humidity in the storage chamber 1 with knowledge of the values measured by the temperature sensors 9, 21; conversely for a defined set point temperature of the storage chamber 1 and a set point air humidity of the storage chamber 1 set at an operating element 24 by a user a temperature can be determined, which, if measured by the sensor 21, would give the desired air humidity in the storage chamber 1. FIG. 3 shows a schematic diagram of the relationship between evaporation temperature TD, storage chamber temperature T and relative humidity r. If the evaporation temperature TD were equal to the compartment temperature T, there would be no condensation at the evaporator 4, no moisture would therefore be extracted from the storage chamber 1 and the air humidity r could reach a value of 100%. As the evaporator 4 has to be colder than the chamber 1 in order to cool it, in practice TD is smaller than T and an air humidity r of below 100% is reached. In practice the evaporation temperature TD is always a few ° C. below the compartment temperature T, for example at a set point temperature of the storage chamber of +3° C., the evaporator 4 can be regulated to a temperature TD of +1° C., meaning that the extraction of moisture from the air at the evaporator 4 is minimal and the relative air humidity r, which is established in the storage chamber 1, is just below 100%. With a lower evaporation temperature TD of for example −5° C. much more moisture is eliminated at the evaporator 4 so that a lower relative air humidity r is established in the storage chamber 1. The control circuit 8 is thus able, based on the values measured by the temperature sensors 9, 21, to establish a relative air humidity in the storage chamber 1 as predefined by the user at the operating element 24. No lid is therefore required on the pull-out box 16 to keep the air humidity in the interior of the pull-out box high. It is therefore possible with the inventive refrigeration appliance to keep chilled goods that are sensitive to evaporation fresh for a long time without a lid impeding access to the chilled goods.

REFERENCE CHARACTERS

1 Storage chamber
2 Storage chamber
3 Storage chamber
4 Evaporator
5 Evaporator
6 Evaporator
7 Compressor
8 Control circuit
9 Temperature sensor
10 Temperature sensor
11 Temperature sensor
12 Condenser
13 Throttle valve
14 Throttle valve
15 Throttle valve
16 Pull-out box
17 Wall
18 Evaporator chamber
19 Fan
20 Rear wall channel
21 Temperature sensor
22 Display instrument
23 Door
24 Operating element

Claims

1-10. (canceled)

11. A refrigeration appliance, comprising:

a storage chamber;

an evaporator for cooling said storage chamber; and

a processing unit configured to assign values for air humidity in said storage chamber and an evaporation temperature of said evaporator to one another at a defined temperature of said storage chamber, under an assumption that an absolute water vapor content of air in said storage chamber equals an absolute water vapor content of water vapor-saturated air at the evaporation temperature.

12. The refrigeration appliance according to claim 11, which further comprises:

sensors for measuring the temperature of said storage chamber and the evaporation temperature;

said processing unit being configured to estimate the air humidity by assignment to a defined value of the evaporation temperature; and

a display instrument connected to said processing unit for displaying an estimated air humidity.

13. The refrigeration appliance according to claim 11, which further comprises:

an operating element for setting the air humidity in said storage chamber as a set point variable;

said processing unit being connected to said operating element and being configured to estimate a target value of the evaporation temperature by assignment to a defined value of the air humidity and to align a real evaporation temperature of said evaporator with the target value.

14. The refrigeration appliance according to claim 13, which further comprises a compressor having a mass throughput being used by said processing unit to control the evaporation temperature of said evaporator.

15. The refrigeration appliance according to claim 13, which further comprises at least one throttle valve connected in series with said evaporator, said at least one throttle valve having an opening cross section being used by said processing unit to control the evaporation temperature of said evaporator.

16. The refrigeration appliance according to claim 11, wherein the evaporation temperature is higher for a high defined value than for a low defined value of the air humidity, at a defined temperature of said storage chamber.

17. The refrigeration appliance according to claim 11, which further comprises a fan with a controllable throughput for circulating air between said evaporator and said storage chamber.

18. The refrigeration appliance according to claim 17, wherein the refrigeration appliance is a no-frost appliance.

19. The refrigeration appliance according to claim 17, wherein said fan has a throughput being higher for a high defined value of air humidity than for a low defined value of air humidity, at a defined temperature of said storage chamber.

20. A method for estimating a relative air humidity in a refrigeration appliance or a household refrigerator having a storage chamber and an evaporator for cooling the storage chamber, the method comprising the following steps:

a) measuring a temperature of the storage chamber;

b) measuring an evaporation temperature of the evaporator; and

c) calculating a relative humidity of air at the temperature of the storage chamber, while an absolute moisture content of the air in the storage chamber is equal to an absolute moisture content of water vapor-saturated air at the evaporation temperature.

21. A method for operating a refrigeration appliance or a household refrigerator having a storage chamber and an evaporator for cooling the storage chamber, the method comprising the following steps:

a′) determining a set point temperature of the storage chamber;

b′) determining a set point air humidity of the storage chamber; and

c′) setting an evaporation temperature of the evaporator to cause an absolute moisture content of water vapor-saturated air at an evaporation temperature to be equal to an absolute moisture content of air having the set point air humidity at the set point temperature.