图5（b）显示与三个电压时的湿度（相对湿度）。
阀的电压为0 V时的湿度增加和饱和率。
在其他两种情况下，湿度的降低，然后增加和饱和曲线图所示。
5（B）。
虽然也有一些分歧的情况下，相对湿度增加，在一般情况下，由于温度降低。
为了降低湿度，潮湿的空气干燥加热器芯，或在传统的系统从发动机的热空气混合。
加热和风扇转速的组合控制也使用，但它是很难控制系统中的温度和湿度的同时。
在本文章中，有一个精确的控制，压缩机，电磁阀控制温度，除湿转子控制湿度。
（5）加热器的核心有传统系统的特点，也与热水器的核心能力为1200 W的使用。
它被放置在空调出点打击，并用于通断控制。
热水器在目前的制度，当然不需要。
3.目前系统的温度和湿度控制4.目前系统和传统系统的能量之间的比较.由于压缩机的能源消耗是亲部分的扭矩，扭矩测量。
B曲线图。
12描述了PD 控制下的传统系统，曲线图A扭矩响应时间。
12（二）目前的控制下，我们的除湿系统的响应。
在控制后的初始地区，本系统和传统系统之间的扭矩的差异很小，原文：High energy efficiency desiccant assisted automobile air-conditioner and its temperature andhumidity control systemK. Nagaya*, T. Senbongi, Y. Li, J. Zheng, I. MurakamiDepartment of Mechanical Engineering, Gunma University Kiryu, Gunma 376-8515, JapanReceived 9 November 2004; accepted 6 December 2005Available online 19 January 2006Abstract: The energy efficiency is of importance in air conditioning systems for automobiles. The present article provides a new type air con-ditioning system for automobiles in which energy loss is small in comparison with the previous system. In the system, a desiccant is installed in the air conditioning system for controlling both temperature and humidity. The control is performed by an electromagnetic control valve, which controls an inclination of the rotating plate of a compressor. It is difficult to control both temperature and humidity precisely, because there are some delays in the control due to the time of heat exchange and that of coolant flow from the actuator (elec-tromagnetic valve) to the evaporator. In order to have precise control, this article also presents a method of control with consideration of control delays. The energy of our system is compared with that in the previous conventional system in the same condition. It is shown that our controlled results and energy efficiency are better than those in the previous system.Keywords: Automobile; Car; Air conditioner; Desiccant; Temperature control; Humidity control; Low energy; Energy loss1. IntroductionRecently, air conditioners with small energy loss and low environmental hazard are required, and a number of interesting studies have been reported for building air con-ditioners and automobile air conditioners [1–12] . In the studies, various methods were discussed for decreasing energies and environmental hazard based on thermo-dynamics and fluid dynamics, and optimal conditions were found experimentally [1–8]. Recently, theoretical and numerical approaches were also given [9–12] . In the sys-tems presented in the above papers, the cooling systems were discussed mainly. In air conditioners, both the tem-perature and humidity should be controlled simulta-neously. However, the studies on the humidity decreasing system have not been investigated thoroughly. Inconven-tional air conditioners, in general, the humidity is con-trolled by a heater, and so the system has a small energy efficiency for controlling humidity. The energy loss due to the humidity control is also important factor in the air con-ditioning system. From the situation, Subramanyam et al.presented the system of a desiccant assisted air-conditioner [13,14] , in which the reheat system was not required. The system can be used in usual building air conditioners, but it has not been applied to automobile air conditioners.For an automobile, a small energy loss air conditioner isstrongly required, because the compressor is driven by the engine. Since the air was cooled at lower temperature, then reheated to have dry air in the system, the energy efficiency decreases, and it is difficult to control humidity exactly.When the humidity is large, one feels uncomfortable, even if the temperature is in the comfortable range. There is the relation between the temperature and humidity in which one feels comfortable. Hence, both the temperature andhumidity have to be in the appropriate range. not controlled exactly, although the humidity is decreased by the reheat system.The object of this paper is to present an air conditioner for automobiles from a stand point of engineering applica-tions, which can control both temperature and humidity, and whose energy efficiency is large in comparison with previous automobile air conditioners. In order to have such a system, the desiccant [13,14] is utilized for the automobile air conditioner. The air conditioning system of the automo-bile is somewhat different from building air conditioners, and so the control system and the control algorithm are important. In this article, an air conditioning system using the desiccant is presented, in which the compressor is con-trolled by an electromagnetic valve. Since there is a time delay in the system due to coolant fluid flow and heat exchange, a control method is also presented with consid-eration of the time delay. The torque of the system is com-pared with the conventional system for the same temperature and humidity.2. Development of an automobile air conditioner using desiccants2.1. Geometry of the systemAlthough there are a few changes, the cooling system used in this experiment is the same as the usual automobile air conditioner in which R134A is used as the working fluid.Fig. 1 shows the geometry of the automobile air-con-ditioner system presented in this article.In order to drive the compressor, an induction motor instead of an engine Is used, in which motor 1 drives pulley 3 and 4, and its tor-que is transmitted to compressor 5. When clutch 6 of com-pressor 5 works, the rotary motion of the motor is transformed to the reciprocating motion.It compresses the coolant in the compressor whose pressure is controlled by an electromagnetic valve 7. Condenser 9 cools the cool-ant, and liquid tank 10 separates the liquid from the vapor and so only the liquid coolant is supplied to evaporator 11. Evaporator 11 gets the heat, and the coolant fluid becomes gas due to the evaporation. This cycle is repeated, and the air temperature decreases around the evaporator. In the system, although the temperature decreases, the humidity increases. Both temperature and humidity are of impor-tance for making comfortable atmosphere, and so the cooled air is heated in the usual air conditioner to have low humidity air. In the system, although the humidity decreases, its control is not perfect, because it is difficult to control the humidity in the system. In addition, since the cooled air is heated, the temperature of air should be cooled under the required temperature. This means that the energy loss will be large.A desiccant is appropriate for having dry air, becausethe desiccant rotor works under low temperature, and so the present article uses desiccant rotor 14 as shown in Fig. 1 . To have the same humidity in the experiment,humidifier 15 supplies humid air to the experiment. It is not required in the real air conditioner of course.2.2. Elements used in the systemIn the above-mentioned system, temperature–humidity sensor 13 detects the temperature and the humidity at the blow out point of the air conditioner, torque meter 2 detects the torque of the compressor shaft, and signals of those are input to Digital signal processor 19 (DSP19). Using these signals, DSP 19 calculates the appropriate con-trolvoltage of the electromagnetic valve in the compressor as mentioned below. The elements used in this system are.as follows:(1) Electromagnetic clutch 6.Clutch 6 allows on–off control of the transmission con-nection between the driving shaft of the motor and the compressor shaft. This is also used as a safety device, cut-ting the transmission when condenser 9 freezes. When the temperature increases, it makes a connection of the trans-mission again.(2) Evaporator fan 12.Evaporator fan 12 cools the evaporator, and so the evaporation increases when the fan speeds increases. To compare the present system and a conventional system, the experimental conditions should be the same, and so the experiment is made in the constant fan speed.(3) Desiccant 14.Since, the low constant speed is desirable for the desic-cant rotor for having enough efficiency as mentioned in Refs.[13,14] , on–off control is utilized for the desiccantrotor. Fig. 2 shows the comparison of a conventional sys-tem (Fig. 2(a)) and the present system ( Fig. 2(b)).In the conventional system, since the suction air is cooled by the evaporator, and reheated by a heater core, cooled and low humidity air flows in the car room. In this case, the temperature of cooled air has to be significantly smaller than the desired temperature because of reheating. This means that the strong over cooling is required in thecon-ventional system. While, in our system, dry air from the desiccant is mixed to the suction air, and so cooled and low humidity air is created. Although the temperature of dry air from the desiccant is slightly larger than the desired temperature, the temperature of cooled air is close to the desired temperature. This enables the energy loss due to over cooling small in our system. Fig. 3 shows the geometry of the desiccant rotor in which the silica gel is installed. Moistures of suction air are absorbed in silica gel when the air passes through the desiccate area, and dry air flows out. Wet air flows out when the rotor rotates at the repro-duction area, where the heated air flows in the wet silica gel, because the moisture in the gel flows out under heated air created by a heater. Air cools the gel when the heated region is rotated into the recovery region. Repeating this cycle, dry air can be obtained from the rotor. The desiccant used in this experiment is as follows: flow rate = 100 m 3/h,and moisture absorbing capacity = 350 g/h. Fig. 4 depicts he relation between the absolute humidity after procession and suction absolute humidity for this desiccant.The effects of the desiccant and the humidifier on the tem-perature and humidity are first investigated. When only thedesiccant works, the temperature converges to about 31℃, and when only the humidifier works, the temper also con-verges about 31℃. When both the desiccant and humidifier work, the temperature converges about 34℃. As for the humidity, the desiccant is capable to decrease the humidityuntil 5%. The humidity of the humidifier is controlled, and it creates humidity until 60%. The settling time for both the temperature and the humidity were about 180 s.In order to dry the silica gel in the desiccant rotor, this system uses an electric heater. Recently, a method of using engine heat is discussed for having dry air instead of using the heater. In the present system, although a tube supply-ing the heat from a radiator to the silica gel rotor is required, the method is also applicable, so the energy due to the heater is not required in such system.(4) Electromagnetic valve 7 in compressor 5.Since a real time control of the temperature is required in this system, the compressor with an electromagnetic valve is appropriate. The electromagnetic valve controls an inclination of the plate with pistons for a plate–piston type compressor, in which piston the electromagnetic valve controls strokes. The compressor used in this experiment is MLA6167A made by Calsonic Co. Ltd, which is used in a usual automobile air conditioner.The performance test was carried out for this compres-sor under non-control. Fig. 5(a) shows the temperature ver-sus time for three cases of electromagnetic valve voltages (0, 6 and 12 V). The test was made continuously, and so the value at 600 s is the same as the initial value of the next case. When there is no input voltage to the valve, the temperature decreases with time. This means that the com-pressor works without valve control. The temperature decreases when the valve voltage increases as shown in curves for 6 V and 12 V. The result of 12 V is shown as the special case, because the temperature under the freezing point is not used in the air conditioner. From the figure, the capacity of the compressor is enoughFig. 5(b) shows the humidity (relative humidity) versus time in three voltages. The humidity increases and satu- rates in case of 0 V valve voltage. In the other two cases, the humidity decreases, then increases and saturates as shown in the curves in Fig. 5 (b). Although there are a few differences in the cases, the relative humidity increases, in general, because of decreasing temperature. In order to decrease the humidity, wet air is dried by the heater core or by mixing heated air from the engine in conventional systems. The combination controls of heating and fan speed are also used, but it is difficult to control both tem- perature and humidity in the system simultaneously. In the present article, to have a precise control, the electro- magnetic valve in the compressor controls temperature, and the desiccant rotor controls humidity.(5) Heater core.To have the characteristic of the conventional system, a heater- core with capacity of 1200 W was also used. It was laid at the blow out point of the air conditioner, and on–off control is used. In the present system, the heater is not required of course.3. Temperature and humidity control for the present system4. Comparison between energies for the present system and the conventional systemSince, the conventional system reheats the air for obtaining low humidity air, a large over cooling is required. The over cooling consumes the energy in the compressor. In the present system, using the desiccant, the over cooling is significantly small in comparison with the conventional system. To clarify it, the energies consumed in the compres- sors are investigated for both our system and the conven- tional system. The experiments are performed in the sameconditions in both cases.Since the consumed energy in the compressor is in pro- portion to the torque, the torque is measured. Curve B in Fig. 12 depicts the time response of the torque for the con- ventional system under the PD control, and curve A in Fig. 12(b) the response for our desiccant system under the present control. At the initial region after the control, the difference of the torques between the present system and conventional system is small, but after 40 s, repetitions of large torques are observed in the conventional system, while in our system, small torques with small oscillations are observed. It is clear that the total torque of the present system is smaller than that of the conventional system. The mean values of the torques are shown inTables 3–5 for three shaft rotation speeds. Since, the region from 0 to 100 s is unsteady under the control, the mean values are obtained in two cases of the time from 0 to 100 s (0℃ in the tables) and the time after 100 s (100℃in the tables). The tables imply that the torque is depending on the speed, and the energy loss can be decreased about 27% for 900 rpm, 18% for 1800 rpm, and 17% for 2400 rpm by using the present system. Although a maintenance work in the silica gel will be required, this is the advantage of our system.5. ConclusionA desiccant assisted automobile air conditioner control system has been presented, in which both temperatureand humidity are controlled precisely. In order to control the system, an adaptive control combining the PD control was presented. Experimental test have been carried out for a prototype system made in this experiment. It is ascertained that, it is difficult to control the humidity at the blow-out point of the air-conditioner in the conventional system, while our system can control both the temperature and the humidity. In addition, energy consumption of our system is smaller than that of the conventional system.。