In cooling devices, humid air in the surroundings causes frost formation on evaporator since it has the coldest surface in the compartment. The accumulated frost on the evaporator surface should be removed by a defrost procedure applied at specific time intervals. The period of the defrost procedure is either determined by defrost control algorithms constructed with respect to certain parameters such as the amount of the frost accumulated on the evaporator, the frequency of the opening of the refrigerator door or the energy consumption, or defrost procedure is applied at predetermined intervals for a fixed amount of time. Although with defrost procedure the efficiency of refrigeration is increased by preventing the accumulation of frost, the result is an increase in the cost of energy consumption because the procedure requires large amount of energy thereby affecting the consumer negatively. Electric distribution companies charge different tariffs for energy consumed at different periods of time in a day, so that, the applications that require large amount of energy are done at light load hours when the general energy consumption is relatively low. In cooling devices the time of the preset defrost periods may coincide with any electric consumption rate segment of the day, may it be a cheap discount rate segment, or an expensive high consumption rate segment, which, in turn, projects onto the consumer as high electric consumption expense.

In the United States Patent Document US5515692, by continuously measuring energy consumption level of a cooling system, the amount and the period of consumption are monitored, wherein defrost procedure is applied when energy consumption level is at a minimum.

In the European Patent Application EP0285035, a description is given of an arrangement to operate an electrical home device when the preselected tariff or a cheaper tariff is in force, if at least two electric consumption tariffs are in application.

The aim of the present invention is the realization of a cooling device and a control method thereof, wherein defrost cycles are adjusted according to the electric tariff such that energy consumption expenditures are minimized.

The cooling device and its control method designed to fulfill the objectives of the present invention are illustrated on the attached figures where: Fig. l-is a perspective view of a cooling device.

Fig. 2-is a schematic representation of a control card, a defrost unit, a compressor and a control panel.

Fig. 3-is a flowchart of a control method for a cooling device.

Elements shown on figures are numbered as follows: 1. Cooling device 2. Compressor 3. Evaporator 4. Defrost unit f 5. Control card 6. Control panel 7. Clock circuit The cooling device (1) preferably a no-frost refrigerator comprises a compressor (2) providing the realization of refrigeration cycle; an evaporator (3) wherein cooling of the internal volume of the cooling device (1) is achieved; a defrost unit (4) providing the removal of the frost accumulated on the evaporator; a control card (5) containing fixed or flexible defrost algorithms which determine the work schedule of defrost unit

(4), and start and finish hours of the cheap electric consumption tariff determined by electric distribution companies, wherein the periods of defrost procedure, where large amounts of energy are consumed and which are determined by algorithms, are altered with respect to the start and finish hours of the cheap electric consumption tariff in order to reduce electric consumption expenditures; a control panel (6) wherein the start and finish hours of the cheap electric consumption tariff application are entered; and a clock circuit (7) providing the perception of the information concerning the time entered to control panel (6).

The control card (5) can delay or precede the predetermined work time of defrost unit (4) with respect to the recorded start and finish hours of cheap electric consumption tariff. If there is an oncoming defrost procedure according to the predetermined algorithm at the times close to the start of cheap electric consumption tariff and within the expensive tariff period, the control card (5) delays this defrost procedure to be applied later within the cheap tariff period, and records the new defrost time delayed to the cheap tariff period. If there is an oncoming defrost procedure according to the predetermined algorithm at the times a little after the finish of cheap electric consumption tariff and within the expensive tariff period, the control card (5) precedes this defrost procedure to be applied within the cheap tariff period, and records the new defrost time preceded as to be within the cheap tariff period.

If there is a change at the start and finish hours of cheap electric consumption tariff, new tariff information can be recorded and the defrost unit (4) can be operated accordingly.

In order to explain the control method of the cooling device according to the present invention, the following symbols are utilized: Tstart: is the start hour of the cheap electric consumption tariff determined by electric distribution company.

Tfinish: is the finish hour of the cheap electric consumption tariff determined by electric distribution company.

Td : is the starting times of the periodic defrost procedures.

Tl : is the time interval preceding the cheap electric consumption tariff period determined by the manufacturer in order to delay the periodic defrost procedures which take place in the expensive tariff slot preceding the start of the cheap electric consumption tariff. For example, if the length of Tl is specified as 4 hours, the defrost procedure that should start 4 hours (or less) before the start of the cheap tariff, is delayed as to be performed within the cheap tariff period.

T2: is the time interval following the cheap electric consumption tariff period determined by the manufacturer in order to move the periodic defrost procedures which have remained within the expensive tariff period and after the finish of cheap electric consumption tariff period to an earlier time slot. For example, if the length of T2 is specified as 2 hours, the defrost procedure that should start within 2 hours after the finish of the cheap tariff is moved to an earlier time slot as to be performed in the cheap tariff period.

Tdn: is the new defrost periods altered and reset with respect to the cheap electric tariff.

The defrost procedure of the cooling device (1) is controlled as follows : - Run the cooling device (1) (100), - Record the start hour of cheap electric consumption tariff (Tstart) and the finish hour of cheap electric consumption tariff (Tfinish) (101), - Determine the next periodic defrost time (Td) (102), - Check whether the defrost time (Td) is within the time interval between the start and finish hours of the cheap electric consumption tariff (Tstart Td Tfinish) (103),

- If Tstart 0 Td D Tfinish then initiate defrost procedure at the periodic defrost time (Td) by checking with the clock circuit (7) (104), - Go to step (102) where the next periodic defrost time (Td) is determined, - If the defrost time (Td) is not within the time interval between the start and finish hours of the cheap electric consumption tariff, then check whether the defrost time (Td) is within the before-cheap-tariff time interval (T1) (105), - If the defrost time (Td) is within the before-cheap-tariff time interval (T1), then delay the periodic defrost procedure (Td) as to be performed between the starting time (Tstart) and the finishing time (Tfinish) of the cheap tariff period (106), Initialize the defrost procedure at the new periodic defrost time (Tdn) by checking with the clock circuit (7) (107) - Go to step (102) where the next periodic defrost time (Td) is determined, - If the defrost time (Td) is not within the before-cheap-tariff time interval (Tl), then check whether it is within the after-cheap-tariff time interval (T2) (108), - If the defrost time (Td) is within the after-cheap-tariff time interval (T2), then precede the periodic defrost procedure (Td) as to be performed between the starting time (Tstart) and the finishing time (Tfinish) of the cheap tariff period (109), Initialize the defrost procedure at the new periodic defrost time (Tdn) by checking with the clock circuit (7) (107), - Go to step (102) where the next periodic defrost time (Td) is determined, - If the defrost time (Td) is not within the after-cheap-tariff time interval (T2), then initialize the defrost procedure at the periodic defrost time (Td) by checking with the clock circuit (7) (104), - Go to step (102) where the next periodic defrost time (Td) is determined.

In order to decrease the electric consumption cost, together with the method which is the subject of the present invention, an electric consumption meter adjusted to both cheap and expensive electric tariff should be used. The defrost periods set in the

cooling device (1) by the manufacturer will be reset for a later or earlier time so that more predefined defrost procedures are completed within the cheap electric tariff determined by the electric distribution company and less predefined defrost procedures are completed within the expensive electric tariff, thereby decreasing the electric consumption expense of the consumer.