The Development Of High Efficiency Air Conditioner With Two Compressors Of Different Capacities

An air-conditioner driven by two compressors with different capacity was developed to improve energy efficiency by use high efficiency components and load matching. An algorithm for driving the two-compressor system was devised for optimum capacity modulation, and seasonal energy efficiency increased by 22%, when compared with that of a conventional air-conditioner of the same rated cooling capacity. If this achievement converted to electric power consumption, we confirmed that the monthly electric power consumption decreases 35% with the new system. INTRODUCTION The energy efficiency regulation of air-conditioner becomes tightened every year, because of the worldwide environmental protection movement. However, it became more difficult than ever, to reduce energy consumption without retail price increase. It is known that a variable speed compressor system shows higher efficiency, but the higher cost has not attracted consumers as many as the manufacturers expected. Therefore a new method was developed to improve the efficiency without adopting the expensive variable speed compressor. There are two ways in indicating the energy efficiency, COP (Coefficient of Performance) and SEER (Seasonal Energy Efficiency Ratio). So far, the investigation for high efficiency was focused on the first method, but, in the view of saving the running cost during the cooling season, the second method which is represented by SEER can be more useful. The reason why the capacity modulation method is powerful to increase the energy efficiency of air-conditioning system is as follows. When measuring COP, the test unit operates at one rated test condition, but SEER considered entire cooling load conditions include the rated and minimum condition. In COP measuring system, there is an underlying assumption that the system with higher efficiency at one test condition would show higher efficiency at other operating conditions. But, this measurement omits the fact that the frequent cyclic start-and-stop operation of a compressor could lead to a sharp decrease in energy efficiency, which occurs at a minimum or low cooling loads. When the compressor stops, the high pressure refrigerant migrates into the low pressure side to level out the pressure difference. When the compressor starts, it takes time to recover the high pressure, and it is one of the main reason for the energy loss in the constant capacity air-conditioner. When the cooling load is low, the variable capacity system slows down, and reduces the number of cyclic start and stop operation of the compressor, which saves lots of energy consumption. Figure 1 lists several ways of capacity modulation. In this study, two-compressor system was selected based of a previous research results in Kim et al . A capacity modulation system driven by two compressors was studied and its operating characteristics and energy saving effects were discussed. EFFICIENCY IMPROVING TECHNIQUE Synopsis To increase the efficiency of air-conditioning system, it is necessary to improve the performance of compressor itself and design the heat exchanger efficiently to reduce the pressure gap between the condenser and evaporator. And another important thing is to develop the high efficiency components of system for reducing the power consumption. For example, we need to use high efficient circuit parts, which operate the compressor and the fan, and the chassis with less resistance and the fan with large air-flow. Also it is necessary to change the operation mode to minimum for preventing waste of electricity in case of light cooling load. Actually it means that, in the minimum operation mode, each components of the system also become high efficiency as they were at the rated operation mode. In this study, we tried to increase the efficiency by means of decreasing the power consumption. Using this concept, we can make the high-efficiency system not only in the minimum load but also in the rated load. With this system we saved a lot of electric power in summer season. The representative application technique is as follows; new cycle technique using a common accumulator, low vibration and resonance prevention design of pipe system, the optimum design of evaporator and condenser, the high efficiency motor (SRM: Synchronize Reluctance Motor) for indoor unit fan, a newly-developed outdoor axial fan, the optimized algorithm to control the degree of superheat and the room temperature, the minimization of a waiting electric power with SMPS (Switching Modulation Power Supply). With these techniques, we can save the power consumption by 35% compared with the existing model,. The typical specification and results are shown in Table 1. New Cycle With A Common Accumulator The schematic of system with a common accumulator and check valves is shown in Figure 2. Normally, in two compressors system, it is easy to occur the mal-distribution of the oil, and the reason is as follows. When the evaporated refrigerant flows into two compressors, the flow type of refrigerant is the annular flow. At this time, the vapor refrigerant and some oil which flow through the center of pipe can be distributed according to the capacity of compressors, but some of oil which flows on the wall of pipe is different in distribution effected by the shape and the mounted angle of the distributor and operation condition of compressor, so there will be the mal-distribution of oil in two compressor system. To overcome this effect, the common accumulator is newly developed as shown in Figure 3. Figure 1: Classification of capacity modulation. Capacity Modulation Control of RPM Variable Speed Constant Displacement Control of Stroke Distance Constant Speed Variable Displacement Inverter