CH709751A2 - Cooling device with a work space with several temperature zones. - Google Patents

Abstract

In a refrigerator, the work space (1) is divided into two temperature zones (2, 3), wherein in the upper temperature zone (3) a higher temperature is to be maintained than in the lower one. Furthermore, air conveying means (10, 11, 12, 13) are provided for introducing air from a cooling module (8) from below into the work space (1) and removing it from above from the work space (1) and returning it to the cooling module (8). The controller (14) of the apparatus is arranged to maintain a first set temperature in the lower temperature zone and a second set temperature in the upper temperature zone by a) controlling the flow rate of the air conveyors (10, 11, 12, 13) Air and b) the temperature of the cooling module (8) depending on the desired temperatures in the temperature zones selects.

Description

Field of invention

The invention relates to a refrigerator, in particular a refrigerator or a freezer, according to the preamble of claim 1, and a method for operating such a refrigerator.

background

It is known to subdivide the usable space of a refrigerator, in particular a refrigerator, into several temperature zones, for example into a lower temperature zone and an upper temperature zone. Different target temperatures are specified for these temperature zones, e.g. 0–2 ° C for the lower temperature zone and 4–6 ° C for the upper temperature zone. In this way, articles can be stored in the lower temperature zone which should be kept relatively cool, e.g. Meat, while articles are stored in the upper temperature zone which should not be kept quite as cold, e.g. Cheese.

[0003] Devices are also known in which cooling air is circulated between a cooling module and usable space. If two temperature zones with different temperatures are to be implemented in devices of this type, separate air feeds into the individual zones or additional, individually controllable coolants are required.

Presentation of the invention

The object is to provide a device of the type mentioned, which is simple in terms of apparatus.

This object is achieved by the device according to claim 1. Accordingly, the device has the following components: A usable space with at least one lower and one upper temperature zone: The usable space is used to accommodate the goods to be cooled. - A cooling module for cooling air: This is e.g. around the evaporator of a heat pump or around the cold side of a Peltier element. - Air conveying means to introduce the air from the cooling module from below into the usable space and to divert it from above out of the usable space and return it to the cooling module: These air conveying means include, for example, a fan and suitable air ducts. - A controller: The controller is used to control the components of the device. It is designed to maintain a first target temperature in the lower temperature zone and a second target temperature in the upper temperature zone by controlling the following two variables depending on the (measured or estimated) current temperature in the first and second temperature zones: a ) the flow rate of the air conveyed by the air conveying means and also b) the temperature of the cooling module.

The invention is based on the knowledge that the temperatures in the two temperature zones can be set independently of one another within wide ranges by suitable choice of the two variables mentioned. This is described in more detail below.

The invention also relates to a method for operating such a cooling device, in which the current temperatures are measured in the lower and the upper temperature zone and the flow rate and the temperature of the cooling module are selected depending on the deviation of the current temperatures from setpoints.

Brief description of the drawings

[0008] Further refinements, advantages and applications of the invention emerge from the dependent claims and from the description that follows with reference to the figures. 1 shows a schematic section through a cooling device, FIG. 2 shows the temperature depending on the position in the usable space for various flow velocities v and initial temperatures T0, FIG. 3 shows the correction for too low a temperature at location x1 and FIG Correction for too low a temperature at location x2.

Ways of Carrying Out the Invention

The device according to FIG. 1 has a useful space 1, which is at least conceptually divided into a lower temperature zone 2 and an upper temperature zone 3, the lower temperature zone 2 being arranged lower than the upper temperature zone 3.

The utility space 1 is closed off by a door 4 on the user side.

The useful space 1 is advantageously air-permeable in the vertical direction, i.e. that cooling air can rise through the useful space 1 from the lower end of the useful space to the upper end of the useful space.

As shown, the two temperature zones 2 and 3 can be separated from one another by a partition plate 5 which has at least one air passage opening. Such a partition plate 5 reduces the temperature exchange between the two temperature zones caused by diffusion and radiation, but still allows the air to flow from the bottom to the top.

The device according to FIG. 1 also has a heat pump comprising a compressor 6, a condenser 7, an evaporator 8 and a throttle (not shown) between the condenser 7 and the evaporator 8. When the compressor 6 is in operation, the evaporator 8 becomes cooled and the condenser 7 heated.

In addition, air conveying means are provided which comprise an air outlet 10 at the upper end of the usable space 1, a connecting duct 11, a fan 12 and an air inlet 13 at the lower end of the usable space 1.

In the present embodiment, the air outlet 10 at the upper end of the usable space 1 consists of several openings on the ceiling of the usable space, which connect the usable space to the connecting duct 11. The air inlet 13 is formed in a similar manner by several openings on the floor of the utility space. The openings of the air outlet 13 and of the air inlet 10 can, however, also be arranged, for example, in the area of the edges of the ceiling or the floor of the usable space 1, possibly behind suitable screens.

The capacity of the fan 12, i.e. the flow velocity of the air in the usable space 1 is advantageously such that the usable space 1 has a laminar flow of air, i.e. there is no turbulence in the air when it flows through the useful space 1.

With the air conveying means, air can be sucked out of the usable space 1 above, whereupon this air is passed through the connecting channel 11 and fan 12 to the evaporator 8 and is cooled there. From the evaporator 8, the air returns to the useful space 1 via the air inlet 13.

The so acquired the system heat is removed via the condenser 7, which is cooled, for example, with ambient air (not shown).

A controller 14 is provided for controlling the components of the device. This has the necessary hardware and software components to control the system in the manner described below.

The controller 14 preferably has a memory in which setpoint temperatures for the upper and lower temperature zones 3 and 2 are stored. These target temperatures are advantageously between 0 and 10 ° C., the target temperature for the lower temperature zone being lower than for the upper temperature zone, in particular by at least 1 ° C.

The controller 14 can further have input means (not shown) which allow the user to specify one or both of these target temperatures, but in this case the controller 14 should ensure that the target temperature for the lower temperature zone is lower than for the upper temperature zone, again in particular by at least 1 ° C.

In addition, two temperature sensors 17 and 18 are shown in FIG. The first temperature sensor is located at a height x1 in the lower temperature zone 2 and the second temperature sensor 18 is located at a height x2 in the upper temperature zone 3.

When the air cooled by the evaporator 8 flows through the useful space 1 from bottom to top in direction x, it heats up. In the equilibrium state of the device, the heating is due to the fact that the air on the side walls of the usable space is heated, since the insulation of the usable space is not ideal.

It can be shown that the temperature T (x) as a function of the position x (ie the vertical position in the usable space 1) in the equilibrium state of the system, neglecting the heat exchange via diffusion and radiation, and assuming a constant density the air, can be estimated approximately by the following relationship:

T0 denotes the temperature at the lower end of the usable space, U the ambient temperature, k a constant proportional to the thermal conductivity of the side walls, and v the flow velocity of the air in useable space 1.

The temperature T0 is also referred to below as the initial temperature, and for the sake of simplicity it is equated with the temperature of the evaporator 8 or cooling module.

As can be seen from equation 1, the temperature of the air in usable space 1 rises from bottom to top. The speed of the increase is essentially given by the flow speed v of the air, while the initial temperature T0 essentially corresponds to the temperature of the evaporator 8. Both of these parameters can be varied by the controller 14: The (mean) flow velocity v can be varied by varying the speed of the fan 8 or by operating the fan in short intervals with a suitable on / off ratio. The (average) initial temperature T0 can be varied by varying the output of the heat pump or by operating the compressor in short intervals with a suitable on / off ratio.

Fig. 2 shows the course of the temperature T in the useful space 1 as a function of the height position x. The curve 20 shows the temperature profile for a given initial temperature T0 and a certain flow velocity v.

If the flow velocity v is now increased, but the initial temperature T0 is left constant, the curve is less steep (see curve 21).

If, on the other hand, the flow velocity V is reduced with the initial temperature T0 remaining the same, the curve is steeper (curve 22).

If, however, the flow velocity v is kept constant, but the initial temperature T0 is reduced, then the temperatures in the cooling chamber are generally lower (curve 23), whereas higher temperatures result (curve 24) at a higher initial temperature T0.

Fig. 2 illustrates that by suitable choice of the parameters T0 and v, the temperatures T1 and T2 in the lower temperature zone 2 and the upper temperature zone 3 at the locations x1 and x2 can be selected essentially independently of one another by the initial temperature T0 and the flow velocity v can be set appropriately. In other words, for given values T1 = T (x1) and T2 = T (x2), equation 1 can be solved according to parameters T0 and, provided that the conditions resulting from equation 1 and the physical laws, such as T1 < T2, T1 <U and T2 <U, are observed.

In this way, it is possible to achieve the two desired temperatures T1 and T2 in the lower and in the upper temperature zone 2 and 3 by the power of the fan 12 and thus the flow rate v and the power of the compressor 6 and thus the temperature of the evaporator 8 can be selected appropriately by the controller 14.

If, for example, as illustrated in Fig. 3, at the current flow rate and initial temperature T0 ', the temperature T2 in the upper temperature zone 3 is correct, but the temperature T1' in the lower temperature zone 2 is too low, the controller 14 increases the temperature of the evaporator 8 to a higher value T0> T0 ́, and it also increases the flow velocity to a slightly higher value v ́> v, whereby the temperature curve begins at a higher value T0 but increases less rapidly.

If, however, as illustrated in Fig. 4, at the current flow velocity v 'and initial temperature T0', the temperature T1 in the lower temperature zone 2 is correct, but the temperature T2 'in the upper temperature zone is too low, the control reduces 14 reduces the flow velocity to a value v <v ́ (which makes the curve steeper) and reduces the initial temperature slightly to a value T0 <T0 ́.

In this way, rules for changing the values of v and T0 for the different deviation scenarios can be found, and / or equation 1 allows the direct approximate calculation of the suitable values of the flow velocity v and initial temperature T0 for given values of the temperatures T1 and T2.

Equation 1 represents a very simple model which the controller 14 can use to calculate the temperature profile in the useful space 1 as a function of the flow velocity v and the initial temperature T0. The thermal conductivity k in equation 1 can e.g. be fixed by the manufacturer, while the second parameter, the ambient temperature U, can either be measured directly with a suitable temperature sensor or estimated based on the current temperatures T1 and T2 with a known flow velocity v and initial temperature T0.

The controller 14 can also use a more complex thermal model of the usable space, which, for example, also takes into account the thermal masses and current temperatures of the goods to be stored in the lower and upper temperature zones as model parameters, and / or which are related to the temperature changing density of air. In particular, the thermal masses and current temperatures are included in the model as parameters that are unknown a priori. However, they can be estimated by the controller 14 during operation by means of a compensation calculation (ie "curve fitting") by measuring the temperatures at the locations x1 and x2 as a function of time, the flow velocity v and the initial temperature T0, and then used for improved control of the device will.

In other words, the controller 14 can thus be configured to use a mathematical model, described by parameters, of the thermal properties of the usable space 1 to select the flow velocity v and the initial temperature T0. The parameters of the model can e.g. the above-mentioned values of k and / or U and / or the thermal mass and / or instantaneous temperature of the loads and / or the air in the temperature zones. In addition, the controller 14 is designed to measure at least one, preferably several, temperatures in the usable space as a function of time, the flow velocity v and the initial temperature T0 and thereby determine the parameters of the model.

In this way, the controller can estimate what influence changes in the flow velocity v and the initial temperature T have on the temperature distribution in the useful space 1, which allows it to regulate the temperatures in the two temperature zones more precisely.

While preferred embodiments of the invention are described in the present application, it should be clearly pointed out that the invention is not limited to these and can also be carried out in other ways within the scope of the following claims.

Claims (9)

1. A refrigerator, especially a refrigerator or freezer, with a usable space (1) with at least one lower and one upper temperature zone (2, 3), a cooling module (8) for cooling air, Air conveying means (10, 11, 12, 13) to introduce the air from the cooling module (8) from below into the usable space (1) and from above out of the usable space (1) and to return it to the cooling module (8) and a controller (14), characterized in that the controller (14) is designed to maintain a first target temperature in the lower temperature zone (2) and a second target temperature in the upper temperature zone (3) by setting a flow rate (v) of the air conveying means (10, 11, 12, 13) conveyed air and a temperature (T0) of the cooling module (8) depending on an instantaneous temperature in the lower and upper temperature zones (2, 3). 2. Cooling device according to claim 1, wherein in the lower temperature zone (2) a first temperature sensor (17) is arranged and the controller (14) is designed to measure the temperature at the first temperature sensor (17) by controlling the flow rate (v) and the To regulate the temperature (T0) of the cooling module (8). 3. Cooling device according to one of the preceding claims, wherein a second temperature sensor (18) is arranged in the upper temperature zone (3) and the controller (14) is designed to measure the temperature at the second temperature sensor (18) by controlling the flow rate (v) as well as the temperature (T0) of the cooling module (8). 4. Cooling device according to one of the preceding claims, wherein the air conveying means (10, 11, 12, 13) have an air inlet (13) at a lower end of the useful space (1) and an air outlet (10) at an upper end of the useful space (1) exhibit. 5. Cooling device according to claim 4, wherein the conveying means are designed for laminar flow through the usable space (1) with air. 6. Cooling device according to one of the preceding claims, wherein the temperature zones (2, 3) are separated from one another by a partition plate (5), the partition plate (5) having at least one air passage opening. 7. Cooling device according to one of the preceding claims, characterized in that the controller (14) is designed to use a mathematical model, described by parameters, of thermal properties of the usable space (1) to select the flow rate (v) and the initial temperature (T0) , and wherein the control (14) is further designed to measure at least one, preferably several temperatures in the useful space (1) as a function of time, the flow rate (v) and the initial temperature (T0) and thereby determine the parameters of the model . 8. Cooling device according to one of the preceding claims, wherein the first target temperature is lower than the second target temperature, and in particular wherein the first target temperature is at least 1 ° C lower than the second target temperature. 9. The method for operating the cooling device according to one of the preceding claims, characterized in that the current temperatures are measured in the lower and the upper temperature zone and, depending on a deviation of the current temperatures from setpoints, the flow rate (v) and also the temperature (T0 ) of the cooling module (8) can be selected.