Yolcu taşıtlarının iklimlendirilmesi
Air conditioning of passenger vehicles
- Tez No: 75597
- Danışmanlar: DOÇ. DR. FERİDUN ÖZGÜÇ
- Tez Türü: Yüksek Lisans
- Konular: Makine Mühendisliği, Mechanical Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1998
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Makine Ana Bilim Dalı
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 52
Özet
ÖZET Taşıtlarda yolcu konforu ve yakıt tüketimi birbirine bağlı iki önemli özelliktir. İklimlendirme sisteminin güç tüketimi azaltılarak yakıt ekonomisinin geliştirilmesi, bu sistemin her bir elemanının veriminin yükseltilmesi, optimum çalışma kontrolünün sağlanması ve soğutma yüklerinin azaltılması ile mümkündür. İklimlendirme sistemi, taşıtlarda orjinal donanım olarak bulunmakta veya sonradan ilave edilmektedir. Optimum şartlar, genel taşıt dizaynına uygun iklimlendirme sistemi ve elemanları ile sağlanabilir. Bu çalışmada, genel olarak iklimlendirme sisteminin teorisinden bahsedilmiş, otomobil ve otobüs iklimlendirme sistemlerinin genel dizaynı içinde taşıt soğutma yükleri ve bunlara tesir eden faktörler incelenmiş, donanımların taşıta yerleştirilmesi, soğutma kompresörünün tahriki, kapasitesi ve hava dağıtım sistemleri üzerinde durulmuştur. Taşıt iklimlendirme sisteminin nasıl test edilmesi gerektiği ve değerlendirmelerin hangi kriterlere göre yapılacağı, Fransız araç üreticisi Renault S. A firmasında uygulanan prosedür esas alınarak açıklanmıştır. viii
Özet (Çeviri)
SUMMARY AIR CONDITIONING OF PASSENGER VEHICLES The heater unit alone is not capable of providing a comfortable environment at all times. When the outside temperature climbs beyond 20 °C, the air must be cooled to achieve the required interior temperatures. Here, compressor driven refrigeration units with R 12 (to be phased out in favor of the more environmentally compatible R 134a by 1995 ) refrigerant are used. An engine driven pump compresses the vaporous refrigerant, generating heat in the process. The refrigerant is the pumped to the condenser, where it cools and returns to a liquid state here, the refrigarent releases the energy which it receives in the compressor and the heat absorbed in the evaporator into the enviroment. An expansion valve sprays the cooled liquid into the evaporator, where the evaporation process serves to extract heat from the incoming stream of fresh air, thereby cooling it. Moisture is extracted from the refrigerated air as condensation, reducing the air's humidity to the desired level. Evaporators and condensers are generally designed as tube and fin heat exchangers. The evaporator is located before the heater core in the fresh air stream. Because precise regulation of the cooling process cannot be achieved by simply activating and deactivating the refrigeration circuit, the evaporator must permanently furnish undercooled air, which the heater core then warms to the desired temperature. The vehicle's climate control system provides for the following: a) A comfortable climate for all passengers, b) An environment calculated to minimize driver stress and fatigue, c) More recent units use filters to remove particulate matter (pollen, dust ) and even odors from air, d) Good visibility through all windows, and windshield. An air-conditioner is operated to make a hot and humid passenger compartment a more comfortable environment. Recently, however, with the improvement in vehicle fuel economy, the allowable power consumption for the air-conditioner has been decreasing, in relation width the overall power consumption of the vehicle. It is thus becoming important to trade off the comfort in the passenger compartment and the vehicle fuel economy when a new vehicle is developed. Methods of reducing the power consumption of air-conditioners are, improvement of efficiency of each equipment comprising the air-conditioner system, optimum control of air-conditioner to maintain moderate temperature for IXpassengers, and reduction of heat loads into the passenger compartment directly affecting the power consumption of the air-conditioner. As a motor car has an extremely large ratio of window area to its interior volume compared to a building, the handling of heat loads from solar radiation is important. When a heat balance model of the passenger compartment is formed, assuming that heat transmission of body conforms to one- dimensional heat conduction, heat load absorbed by each part on the passenger compartment acts only to increase the temperature distribution. Air-conditioning of vehicles poses specific problems not seen in air-conditioning of buildings. For instance, a vehicle has an extremely large window area compared with the volume of the passenger compartment, and it is separated from the high temperature engine compartment by an insufficiently heat- insulated wall. These characteristics make the heat balance of a vehicle different from that of a building. The heat quantity of solar radiation to roof and doors is reflected or absorbed by the surfaces and a part of the absorbed heat acts to increase the air temperature in the compartment through the body. Moreover, heat quantity of solar radiation to each window glass is reflected absorbed or transmitted and a part of the absorbed heat penetrates into the passenger compartment. Some of the heat passing through the window glass is absorbed into the interior parts. The rest is reflected on the surfaces of the interior parts and goes out again through the window glass. Heat load penetrating from the engine compartment into the passenger compartment is assumed to be proportional to the difference of the air temperatures of each compartment A blower motor is mounted in the passenger compartment, such as under the instrument panel. Thus, the power consumption of the motor is one of the air-conditioning heat loads. A driver's work load is light, sitting on his seat, 200 kcal/h, while other passengers sitting on their seat, without moving produce 100 kcal/h. Heat load into the passenger compartment by ventilation is assumed to be proportional to the difference of the enthalpies of atmospheric air in the passenger compartment respectively. The heat load of solar radiation penetrating through roof and doors is assumed to be largely affected by the paint colour. In order to ascertain its influence quantitatively, it is necessary to determine the solar radiation absorptivityof the painted body. A black coloured body absorbs double the heat quantity of solar radiation that a white coloured body does. Characteristic values of glass such as reflection, absorption and transmission for solar radiation are different according to the material, thickness and incidence angle. Heat capacity of parts is obtained as a product of specific heat and weight of materials comprising the main parts of the instrument panel, seat and console box arranged in various positions in the passenger compartment. Solar radiation is absorbed and scattered in the atmosphere on its way to the earth's surface. Of the solar radiation, the radiation acting as thermal energy on objects on the earth's surface such as a vehicle is divided into direct solar radiation reaching the earth's surface directly through the atmosphere and sky solar radiation reaching the earth's surface as scattered light in the atmosphere. The respective amounts of direct and sky solar radiation are obtained. It is found that the transmissivity of the atmosphere on solar radiation is slightly changed in measurement according to the influence of cloud cover as 0.58 to 0.70 but nearly corresponds with 0.64 in the statistics. Calculating the heat load penetrating into the passenger compartment from the roof in the stable situation by means of the absorptivity of paint plate on solar radiation obtained, the difference between black and white is 5 to 8 % for the entire air-conditioning heat load, differing according to the running conditions. This means a difference ofabout2.5°Cintermsof air temperature in the passenger compartment when parked under the blazing sun for along period. Regarding ordinary and infrared absorption glass commonly used as vehicle window glass and special infrared reflection glass. If infrared reflection glass is applied to all windows, a reduction of air- conditioning heat load from solar radiation in order of about 700 watt/m2 is possible comparing to ordinary glass. This value corresponds to a reduction of air temperature in the passenger compartment of about 7°C when parked under the blazing sun for a long period in midsummer. Assessing the influence of heat capacity of the interior parts of air temperature in the passenger compartment while running at a fixed speed and operating the air-conditioner after long parking in the blazing sun, there is a reduction of 2 to 3°C 10 minutes after starting if the heat capacity of the interior parts is reduced by 20 to 40 % from the present situation. The heat load by ventilation accounts for about 50% of the entire load. In the fresh air mode commonly used in ordinary driving, the XIexamination of the proper relation between the reduction of the heat load and the securing of the ventilation performance is expected to be a future problem. For vehicle window glass, high transmissicity of visible rays required in order to secure safe visibility, and shielding characteristic against infrared rays is desirable in view of the need for reduction of air-conditioning heat load. The types in the lower right area are considered suitable for vehicle window glass. The types included in the area are infrared absorption and infrared reflection glass. The difference of characteristics of both types is how they absorb or reflect the energy of the infrared region. The infrared absorption glass has a higher heat load compared with that of the infrared reflection glass, as a part of absorbed energy enters the passenger compartment by convection. The reduction of the heat load of about 600 to 700 watts is possible by employing infrared reflection glass transmissicity windows compared to values obtained with ordinary glass. If infrared reflection glass is used for all windows, the air temperature in the passenger compartment is decreased by about 10°C at the start of running compared to ordinary glass and about 8° C ten minutes after starting. The reduction on the heat load by infrared reflection glass or the decrease of the air temperature in the passenger compartment affects the power consumption of the air-conditioning of a small-sized passenger vehicle, it is found that a reduction of 10 to 20% of compressor capacity,and about 740 watts of power consumption of the compressor is possible if the effect air-conditioning for ordinary glass can be maintained. In addition, the reduction of load on solar radiation from window glass exerts a favourable influence on the thermal sensation of the passengers. Thus it is expected to bring about a more comfortable passenger compartment. The heat quantity of solar radiation to roof and doors is reflected or absorbed by the surfaces and a part of the absorbed heat acts to increase the air temperature in the compartment through the body. Moreover, heat quantity of solar radiation to each window glass is reflected absorbed or transmitted and a part of the absorbed heat penetrates into the passenger compartment. Some of the heat passing through the window glass is absorbed into the interior parts. The rest is reflected on the surfaces of the interior parts and goes out again through the window glass. We see that comfort cooling and fuel consumption in vehicles are important features which affect other. Improvement in fuel economy in vehicles by reducing power consumption of air-conditioning system, is obtained by improving the of each element,maintaining optimum control xiiof the system and reducing cooling loads of vehicles. The air-conditioners are available as factory installed or can be added to the vehicles in the field by automible dealers or various air-conditioning dealers. In each case, the optimum conditions can only be obtained by using the air conditioners convenient for the general vehicle design.
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