Patent Application
20050028541
The present invention relates to a refrigeration device with two temperature zones cooled by condensers arranged in a common coolant circuit and a method for operating such a refrigeration device.
In refrigeration devices moisture enters the interior of the refrigeration device by way of air exchange via door openings. This moisture condenses on surfaces, on which the dew point falls below. In higher-quality equipped refrigeration devices glass plates are being used increasingly as aprons, on which condensing moisture becomes particularly visible. Likewise, moisture condenses also on cold wares, which can be damaged directly thereby, e.g. when wrapped in paper. These problems appear especially in regions or in meteorological conditions at high humidity in moderate temperatures, as well as in high ambient temperatures, thus generally in subtropical/Mediterranean to tropical climes.
To prevent or restrict this type of condensation ventilators are being incorporated into cool rooms of refrigeration devices more and more. The rapid airflows generated by the latter reduce condensation.
The reinforced airflows generated by such a ventilator also result in an increased heat transmission rate on surfaces. In this way heat and moisture are exchanged more quickly inside the coolroom, resulting in a more even distribution of temperature and humidity in the coolroom.
The increased airflow speed also strengthens the heat exchange between the coolroom and the condenser provided to cool it. This means that the evaporation temperature of the coolant circulating in the condenser rises, and the refrigerating capacity of the condenser is greater than in a refrigeration device without ventilator with unchanged condenser geometry.
This leads to problems whenever a ventilator is supposed to be used to prevent condensation in a refrigeration device with two temperature zones, in which the two temperature zone are cooled by a condenser arranged in a common coolant circuit. Since the same coolant stream flows through both condensers in succession, they can both, depending on whether the coolant circuit is operational or not, in each case cool or not cool at the same time. Only a thermostat in one of the zones in general regulates refrigeration devices with a coolant circuit and two different temperature zones. This is usually in the zone with the higher temperature. The temperature in the second, colder zone then depends on the thermostat setting or the operating time of the coolant circuit, required to maintain the desired temperature in the first zone. With appropriate dimensioning of the heat exchanger the temperature in the second zone can be “set” within certain bounds, but depends in each case on the operating time of the coolant circuit, required to maintain the set temperature in the first temperature zone. This means that the temperature in the second zone is influenced by the same values as those in the first zone and is dependent on the selected thermostat setting. The ambient temperature is one of the influential factors, apart from frequency of operation and loading. At low ambient temperatures the operating time of the coolant circuit is no longer adequate to supply the deeper tempered zone with cold.
With a ventilator now provided in the zone with the higher temperature, consideration can be given to sizing of the condenser, in which the dimensions of the condenser of the warmer zone are reduced according to the improvement in heat exchange efficiency through airflow. It does not yet, however, provide a solution to the abovementioned problem. Rather, excessive reduction of the condenser leads to the additional problem, where cool goods, blocking the flow path of air without ventilator and condenser, can impair the effective refrigeration capacity. When this occurs the operating times of the condenser are extended, required for maintaining the set temperature in the warmer zone, the cooler zone is sub-cooled, and energy consumption rises.
To maintain the temperatures in both temperature zones in each case in a set range at lower ambient temperatures, a solution is disclosed in EP-0-959 311 for providing a heating element in the higher temperate zone, which in the event that a temperature detected in the deeper temperature zone exceeds a preset limit value, to artificially cause additional heat input in the higher temperature zone, which then results in the coolant circuit being set in motion, in order to cool both zones together in a desired temperature range. This method is however not completely satisfactory, as it leads to an increased power consumption of the refrigeration device.
The object of the present invention is to provide an operating method for a refrigeration device and a refrigeration device, which enable operation of a ventilator in a temperature zone of the refrigeration device, without the dimensions of the condenser in this zone having to be excessively reduced. This task is solved by a method comprising the features of Claim 1 or a refrigeration device having the features of Claim 8. Through intermittent operation of the fan, whereby non-operational phases of the fan coincide at least partly with operational phases of the coolant circuit, at least during such coincidence the efficiency of heat exchange is the same on the condenser as in a refrigeration device without a fan, though in the remaining period, which will in general make up the predominant proportion of the operating time of the refrigeration device, the fan is effective enough to prevent condensation.
According to a particularly simple configuration of the invention the fan runs only in non-operational phases of the coolant circuit. Compared to a conventional thermostat-controlled refrigeration device with two temperature zones cooled by a coolant circuit this solution requires practically no additional control expenditure.
As a consequence of a further developed configuration there is also the possibility that fan and coolant circuit run at the same time, though the portion of operating time of the refrigeration device, in which this is the case, is fixed depending on the ambient temperature of the refrigeration device. This portion is preferably the greater, the higher the ambient temperature. In this way to a certain extent the temperatures in both temperature zones are neutralised; in the event of high ambient temperatures, where the heat input from outside is high in both temperature zones and the operating times of the coolant circuit required for maintaining a set temperature in the warmer temperature zone are so long that the danger of sub-cooling the colder zone occurs, the efficiency of the condenser is improved through simultaneous operating of coolant circuit and fan, such that the required operating times of the coolant circuit are shorter than without the fan operating. At low ambient temperatures by contrast the coolant circuit and the fan run with little or no intersecting, resulting in lengthy operating times of the coolant circuit, which also suffice for adequate cooling of the lower temperature zone.
Another, alternative or complementary option is to detect the temperatures in both temperature zones of the refrigeration device, whereby one of the thus detected temperatures is employed to fix the operational phases of the coolant circuit and the other temperature is employed to fix the portion of the operating time of the refrigeration device, in which the fan and coolant circuit run at the same time.
Further features and advantages of the invention will emerge from the following description of embodiments with reference to the attached figures, in which:
In the configuration of an inventive refrigeration device illustrated in
Reference is first made to the variant containing the freezer section temperature sensor 7 and the external temperature sensor 12.
In the case of a low external temperature Ta the heat input from the outside to the cooler and freezer section is minimal, and the intervals without successive operational phases of the condenser 3 are relatively large. To guarantee adequate cooling of the freezer section in this situation, the required condenser operational time is not to be further curtailed by running the fan 9. Fan and condenser therefore run in precise push-pull mode.
In the case of a higher external temperature Tb the interval between successive operational phases of the condenser shortens, and the portion of the condenser operational phases on the overall operating time of the refrigeration device increases. However, the cooling requirement of the freezer section 2 does not increase to the same extent as that of the freezer section, so that in the case of excessive operating time of the condenser there is the danger of sub-cooling of the freezer section 2. This danger is not avoided by the fan being switched on and off with a pulse-width repetition rate d during the operational phase of the condenser 3, whereby the exact numerical value of the pulse-width repetition rate d depends on the value of the measured external temperature. Due to the two-part fan operation in the operational phases of the condenser 3 the latter are shortened, such that the cold input to the freezer section 2 takes on a suitable value.
In the event of a higher external temperature Tc this pulse-width repetition rate d can finally reach the value 1, i.e. the fan 9 runs continuously, independently of whether the condenser 3 runs or not.
Suitable values for d as a function of the external temperature can be determined experimentally and can be stored e.g. in the form of a table in the control unit 10.
An alternative operating method, which can be carried out in a refrigeration device with freezer section temperature sensor 13, is described with reference to the flow diagram of
This value can be selected randomly, since it converges towards a favourable value during operation of the refrigeration device.
When inspection S2 of the freezer section temperature T1, indicates that the former exceeds an upper edge T1+ of a permissible temperature range, the control unit 10 switches on the coolant circuit (S3); at the same time the fan 9 is actuated with the fixed pulse-width repetition rate d (S4). This is continued to the point where inspection S5 indicates that the temperature T1, has reached or fallen below the lower limit T1− of the permissible temperature range of the freezer section 1.
Next, a test is done to determine whether the temperature T2 of the freezer section 2 is also within the permissible range. If its upper limit T2+ is exceeded (S6), then this shows that the freezer section 2 is not sufficiently supplied with cold, and that accordingly longer operating times of the coolant circuit would be desirable. As a consequence in step S7 the pulse-width repetition rate d is decremented, to accomplish just this. If the result in step S8 vice versa is that the temperature T2 falls below the lower limit T2− of the permissible range, then in step S9 the pulse-width repetition rate d is incremented. When the temperature T2 is within the range [T2−, T2+], the pulse-width repetition rate d is correct and remains unchanged.
Then the control returns to step S2. In this way, during several operational phases of the coolant circuit the pulse-width repetition rate d converts towards a value, which ensures measured cooling of the freezer section, and if the ambient temperature of the cooling requirement of the freezer section changes e.g. as a consequence of a change, then the pulse-width repetition rate d is automatically compared to this changed requisite.
The pitch of incrementing or decrementing in step S9 or S7 can be made proportional to the difference between T2 and a temperature in the range [T2−, T2+], e.g. (T2−+T2+)/2, in order to reach rapid convergence of d with strong standard deviations and fine regulating, which does lead to oscillations of d, with small standard deviations.
Of course it is also possible to fit out the refrigeration device both with the external temperature sensor 12 and also with the freezer section sensor 13. This allows in each case the pulse-width repetition rate d adapted to the method shown in
| Number | Date | Country | Kind |
|---|---|---|---|
| 10139834.4 | Aug 2001 | DE | national |
| PCT/EP02/08958 | Aug 2002 | WO | international |
