A New Control System of a Household Refrigerator-Freezer

This paper will present the structure of the new system, the control scheme and its performance test results. In this new system, the damper in the conventional refrigerator is replaced by an additional cooling fan Thus, it uses two cooling fans: one (F-fan) is to provide cooled air for freezing compartment (F-compartment) and the other (R-fan) is for refrigerating compartment (R-compartment), respectively. The F-fan and the R-fan are controlled independently by thermo-sensors installed in the F and R-compartments. Experimental results show improved performance of the new refrigerator over the conventional refrigerator. Among them is the lower fluctuation of the R-compartment temperature, which has a significant effect in lowering the refrigerating temperature and storing foods fresh longer. It can quickly response to the load change in the R-compartment The air-defrosting by the use of the R-fan was proved to be an efficient method in saving the energy consumption during the defrosting cycle. INTRODUCTION Household refrigerator-freezer systems can be classified as direct and indirect cooling systems. The direct cooling system utilizes natural convection to cool food storage volume. It has inherent advantages of high energy efficiency and simple structure. This cooling type is used in small size refrigerator and still widely used in European market for bigger size. As the refrigerator becomes bigger, the direct cooling system encounters with a problem in controlling temperatures in the F and R-compartments as mentioned by Onishi. By that reason, large size refrigerators over 200 liters usually adopt the indirect cooling system The indirect cooling system has a cooling fan to circulate cold air through an evaporator and refrigerator-freezer compartments. In this cooling system, the cooling fan and the compressor are typically controlled by a temperature controller installed in the Fcompartment A damper controls R-compartment temperature by regulating cold air flow rate. A limitation in this type refrigerator comes from the fact that the temperature of the R-compartment depends entirely on the F-compartment temperature. If the R-compartment is excessively loaded, the temperature in the Rcompartment rises too hlgh while the temperature in the F-compartment is still below its preset temperature. However, the compressor would not restart because the control operation is based on the F-compartment temperature. As a result, the Rcompartment often fails to maintain its temperature range. Hence, the F-compartment based control has to sacrifice the refrigerating performance to some extent, while it gives good performance in frozen food storage. Some refrigerators are designed to be controlled by the R-compartment temperature in order to improve refrigerating performance, but at the sacrifice of the freezing performance. The new control system development was intended to achleve more improved refrigerating performance without any degradation of the freezing performance. This purpose was obtained by the use of two independently operating cooling fans. DESIGN OF NEW REFRIGERATOR WITH TWO COOLING FANS The conventional indirection cooling system refrigerator has a cooling fan that blows cold air into food storing compartments; usually F and R-compartments. The fan is always running during the compressor is active. As shown in Fig. 1, the cold air is distributed into F and R-compartments. The system control is based on the F-compartment