تجزیه و تحلیل عملکرد ارائه شده در تهویه مطبوع معکوس کننده چندنوعی

An analysis was conducted for a multi-type inverter air conditioner with a linear electronic valve as the expansion device and a variable speed compressor. The system performance was analyzed with variations of operating frequency of the compressor, cooling load imposed on the system and cooling load fraction (i.e. load ratio) between rooms in which is installed an evaporator. The optimum opening of the electric expansion valve (EEV) was calculated when the compressor operating frequency was specified at a given cooling load. As compressor operating frequency increased with cooling load increment, the EEV should have adjusted to get wide openings to get an optimum COP of the system. While total cooling load of the system was constant, the cooling load fraction changed due to the cooling load differences between each room in the multi-type air conditioning system with a number of evaporators and EEVs. The operating frequency of the compressor was increased with increment of the load ratio, and consequently, the power consumption of the compressor increased. The increment of the load ratio, which means increasing the load difference between each room, causes a reduction of the system performance (COP), although the total cooling capacity was constant.

Air conditioners are the necessities of life at home and in public areas due to the large demand for comfort in the thermal environment of living space in modern society. The conception of air conditioning has now developed from one air conditioner for one house to independent air conditioning for separate rooms. A multi-type air conditioner is the system that could distribute cooling capacity to different spaces. The system consists of a number of indoor units and only one outdoor unit. The electric expansion valves (EEVs) control the capacity of the system with varying refrigerant mass flow rates passing through the evaporators according to the cooling loads of each evaporator. Fig. 1shows a schematic diagram of the multi-type air conditioner with two evaporators. Full-size image (17 K) Fig. 1. Multi-type inverter air conditioner with two evaporators and EEVs. Figure options The load of the system is widely changed due to the system having a number of evaporator with only one outdoor unit. The performances of the compressor and the expansion device are affected by those load variations. A variable speed compressor was used in order to cover the load variation. The system with the variable speed compressor can control the cooling capacity by changing its operating frequency. However, there should be limits of control when the system uses constant area expansion devices, such as a capillary tube or a short tube orifice. Variable area expansion devices (like an EEV) are needed in multi-type inverter air conditioners to control the mass flow rate of the refrigerant concerning the variable speed compressor. The research trend of the multi-type air conditioner may be divided as follows: a control logic of the variable speed compressor; an optimum distribution of the refrigerant to the evaporator with cooling loads; a method of seasonal energy efficiency ratio calculation; a control method of the EEV etc. As one of the researches on the multi-type inverter air conditioner, Fujita et al. [1] studied the capacity and refrigerant flow rate control in the multi-type air conditioner with EEV. He improved the comfort, reliability and working efficiency of the system by use of control technology with the EEV and a twin rotary compressor. Okuzawa [2] optimized the superheat temperature in a multi-type system by use of PI control logic and improved the response to a variation of load. He used a horizontally installed twin rotary compressor and four to six evaporators. For a study on the refrigerant flow rate control, Krakow et al. [3] calculated the effect of refrigerant flow rate and capacity control method on the performance of a heat pump and shows 5% energy saving with those methods. He changed the opening of an orifice tube and the refrigerant charge as a flow rate control method and used a variable speed compressor as a capacity control method. A simulation model for a single unit air conditioning system with a variable speed compressor and an EEV was developed in this study. Performance analyses were conducted with variation of operating frequency of the compressor and openings of the EEV. In addition, analysis on the multi-type system that has a number of evaporators and EEVs was performed to determine the optimum operating frequency of the compressor and openings of the EEV. The object of this study is to study system performance variations with cooling load in an inverter air conditioner with EEV and with the load ratio of each evaporator of the multi-type inverter air conditioning system.

A system simulation program has been developed to analyze the performance of the multi-type air conditioner with two evaporators and EEVs. A parametric study was conducted with variation of the compressor operating frequency, the loads of the conditioned rooms, the opening area of the EEV etc. In an inverter air conditioner with EEV, there are limitations of the operating frequency of the variable speed compressor to cover the given cooling load. The operating frequency selection in the inverter air conditioner should be the lowest frequency to get the highest COP within the variable range of the compressor operating frequency when the system capacity matches the imposed cooling load on the system. When the cooling load of the system changes, the COP variation at constant operating frequency is of parabolic shape with cooling load by changing the EEV openings. If the cooling load increases, the system has to increase the operating frequency because of the limitation of the cooling capacity of the system at a fixed operating frequency. Consequently, the maximum COP at an operating frequency decreases with cooling load like as shown in Fig. 8 even after adjusting the EEV opening. For the multi-type air conditioner with two evaporators and EEVs, the COP of the system decreases with an increase of the load ratio due to increasing the compressor operating frequency as the load difference between the evaporators increases. The multi-type air conditioner mainly controls the total capacity by compressor operating frequency. Although, if the cooling loads are different from room to room, the major control parameter of the system is the EEV opening for changing the refrigerant mass flow rate through the evaporators.