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Air-conditioning system of an intelligent vehicle-cabin
APPLIED ENERGY
Applied Energy 83 (2006) 545–557
www.elsevier.com/locate/apenergy
Air-conditioning system of an intelligent vehicle-cabin K. David Huang a, Sheng-Chung Tzeng b,*, Tzer-Ming Jeng c, Wing-Ding Chiang a b c
a Graduate School of the Vehicular Engineering, Dayeh University, Changhua, Taiwan 500, ROC Department of Mechanical Engineering, Chienkuo Technology University, Changhua, Taiwan 500, ROC Department of Mechanical Engineering, Air Force Institute of Technology, GangShan 820, Taiwan, ROC
Accepted 16 May 2005 Available online 13 February 2006
Abstract If vehicles can be more comfortable, safe, energy efficient and humanized, it will be very beneficial. This study introduces an ‘‘Airflow Management’’ technique to control the airflow in the vehicle cabin for the purpose of achieving a regional steady-state temperature. With this new concept, each passenger in a different area of the compartment can be satisfied with respect to his/her unique temperature demands. The airflow is controlled by air inlets and outlets, with fans for the modulation of airflow directions and rates. The temperature in each zone can be controlled by the modulation of the airflow. The concepts in this study are relevant to all kinds of regional air-conditioning in any enclosed space. Ó 2005 Elsevier Ltd. All rights reserved. Keywords: Airflow management; Regional air conditioning; Intelligent vehicle-cabin
*
Corresponding author. Tel.: +886 4 7111111x3132; fax: +886 4 7357193. E-mail addresses: [email protected], [email protected] (S.-C. Tzeng).
0306-2619/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.apenergy.2005.05.006
546
K.D. Huang et al. / Applied Energy 83 (2006) 545–557
1. Introduction In a developed industrial-civilization, vehicles are the people’s main means of transportation. Whether the air-conditioning system in the vehicle cabin is good or not decides the degree of comfort, traffic safety as well as health. Take Asia as an example. Vehicles equipped with an air-conditioning system accounted for around 10% in early 1970, and grew up to about 98% [1] in 2004, so that an air-conditioning system is already regarded as essential for vehicles. However, the design of the air-conditioning system for the vehicles is still not intelligent, that is, it needs to be regulated to the stable temperature in a certain zone to meet individual demands. In 2000, Ono et al. [2] applied numerical simulation and flow field visualization technology to improve the air-conditioning design technology. The outtake wind-speed of the air conditioning was set to be 5 m/s and the outtake temperature to be 15 °C to compare different flow-field structures and temperature distributions under different amounts of heat radiation. The study helped improve air-conditioning technology. In 2002, Huang and Han [3] conducted an analog analysis on the regional air-conditioning in their research, in which the air-conditioning system in the cabin of a small car (equipped with two extra air-outtakes) was separated into the front and rear sections by a flow field with a temperature difference of around 6.5 °C, so that the front and rear cabins are at different temperatures. The air-conditioning system of the vehicle – when being driven, will be subject to the influence of a changing environment. In 2001, Fujita [4] adopted a CFD simulation and experimental measurements to compare the different effects on a thermal manikin under different environments. The experiment adopted large radiative bulbs as the analog of sunshine from outside the car and put a driver and a passenger into the cabin (regardless of the manikins’ own physiological and breathing rates with 20 thermal sensors on each body). The paper proposed that the influence on the compartment varies with heat load, air conditioning and environment, which shows that the air-conditioning system is subject to the influence of the environmental temperature. Martinho et al. in 2002 [5] studied the influence on the flow-field structure and temperature distribution in the vehicle cabin provided with manikins (regardless of the manikins’ own physiological and breathing rates), as shown in Fig. 1. Eight wind-speed sensors were placed in the compartment, and tests were undertaken on the manikins equipped with 16 thermal sensors in terms of the influence on the temperature, velocity field and the manikins in the cabin with, or, without other manikins present under different air-outtake temperatures and wind speeds. The engine load and fuel rate will be increased when the air-conditioning system is turned on in the car. In 1998, Barbusse et al. [6] pointed out in their research that, under the environmental temperature of 30 °C, the demand is for 3.1 litres of fuel for each 100 km journey, and 3.8 litres in case of 40 °C. The fuel rate is reduced by a maximum of 20% in a car driven without air conditioning. Global petroleum energy is estimated to be used up in about 40 years. If the car’s air-conditioning is reduced to only that which is necessary, the fuel rate will be decreased, so contributing to energy thrift.
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Fig. 1. Experimental regional air-conditioning system (see Table 1 for the significance of numbers 1 to 9).
2. Experimental infrastructure The research refits a group of air outtakes/intakes, so dividing the cabin of the vehicle (a Ford Liata) into four airflow cells. The air outtake/intake design proposed in the research is not exclusive. The target of regional air-conditioning can be achieved by locating the appropriate air outtakes and intakes in the flow cells, plus proper control. In the present research, the airflow field structure is controlled within the closed vehicle cabin, only the initial design of air outtake/intake positions is changed, and the airflow is limited in the controlled area. The convection effect is much greater than the diffusion effect, while the air is flowing in the different regions. Each region is not divided by real objects, so that the required temperature is available in each region. All the regions are separate, i.e., without mutual interference, which enables intelligent regional air-conditioning to ensue. For example, when the intelligent air-conditioning is turned on only in the region of the assistant driver’s seat, the air uptake is used as an airflow barrier between the left and right passengers’ temperature-regions, so that the assistant driver’s seat can be divided into independent flow-field regions (by means of a vortex); the air outtake and intake on the right maintain a suitable temperature for the passengers in this region. Moreover, when a passenger goes into the cabin, he or she can set the suitable temperature to satisfy his or her desire. Fig. 1 shows the experimental rig. There is an air-temperature sensor under the headrest of each seat to scout the surrounding temperature as the main control parameter. Then the control setting and the surrounding temperature will be compared and sampled by means of the control module to control accurately the air speeds and pressures in the passengers outtake and intake, and control the region within the range of the temperature set by the controller. To sustain a suitable ‘‘sitting’’ environment, i.e., to enable the regulation of the
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intelligent regional air-conditioning, the environmental temperature (i.e., the regional constant temperature) in the cabin is monitored continuously.
3. Experimental method 3.1. The experimental rig This makes use of independent flow cells to achieve the target of regional air-conditioning. The settings of the temperature and pressure sensors used in the experiment are shown in Fig. 1 and Table 1. For the air conditioning associated with the driver’s seat, one can, respectively, open the right air-outtake and-intake and the uptake as shown in Fig. 2. A resistance temperature-detector transmits a signal to the computer through the sampling equipment, so that variations of temperature Table 1 Positions of installed temperature and pressure sensors No.
Position of temperature sensors (RTD)
No.
Position of pressure sensors
1 2 3 4 5 6 7 8 9
Center of right airflow-inlet Head position of right front-seat Bottom of right head-pillow Head position of right back-seat Center of top airflow-inlet Center of left airflow-inlet Head position of left front-seat Bottom of left head-pillow Head position of left back-seat
1 2
Center of right airflow outlet Center of left airflow outlet
Fig. 2. Outtake and intake positions.
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can be sampled continually to within an error of ±0.23 °C. The pressure sampling of the air intake measures the differential pressure, positive pressure and vacuum to within ±0.16 Pa (in case of 20 Pa). The air outtake employs a hot-wire anemometer to measure the air flow-rate. The wind speed sampling enables one to deduce the average speed by dividing the air outtakes in each experiment into six parts and thereby determine the speed of the middle point of each part of every air outtake to within ±0.4 m/s (in case of 7 m/s). 3.2. Control strategy The controller manages the maintenance of the temperature set by the user in each region. It converts the resistance temperature detector (RTD) signals between the headrest and chair back into temperatures to control the wind speed of the air outtake. The angle of the air jet and the air-intake pressure are shown in Fig. 3 with the following control strategy: Decide where in the vehicle cabin is the required control region, and transmit the signals from the headrest air-temperature sensor to the regional temperature controller. Compare the headrest air-temperature within the control region and the preset temperature to judge the fan’s rotational speed. Sample the signals of the headrest air-temperature sensor from the control region and the non-control region, and monitor whether the temperature in the non-control region is influenced, so as to limit the effective management of the independent flow-field structure in the control region without influencing the flow field in the non-control region. Judge whether the flow field in the control region has been established completely. When the flow field has been established, compare the signals of the headrest airtemperature sensor in the control region with the preset temperature, and then adopt different running modes of the fan to reach the temperature set by the users rapidly and steadily. When the temperature in the control region is higher than the preset temperature by over 2 °C (exclusive of 2 °C), the fan will be running at full speed, so that the control region will reach the preset temperature rapidly. When the temperature in the control region is lower than the set temperature by a maximum of 2 °C, ranging from high to low temperatures, the fan will run with a non-step variable speed to enable the temperature in the control region to reach the steady required temperature. The pressure in the air intake is controlled by the air-intake pressure controller after the temperature in the control region becomes steady, and the signals from the headrest air-temperature sensor in the control region are returned to the regional temperature controller to monitor the flow field in the cabin continuously. The air outtake angle and the air intake pressure are managed by their respective controllers to assure that the flow field in the control region does not influence that in the other control regions. The air outtake angle is adjusted by the air-outtake angle
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Fig. 3. Control strategy.
controller and fine-tuned by the stepping motor. The outtake angle can be adjusted from left-to-right and up-to-down. Then the temperatures between the control region and non-control region are again compared to judge whether the flow field in the control region has been established. The speed of rotation of the fan at the air intake is controlled by the air-intake pressure controller, so as to control the air intake pressure. The temperatures between the control region and non-control region are again compared after this adjustment to determine whether the flow field in the control region has been established.
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Table 2 Test conditions Test parameters
Case I
Case II
Case III
Set temperature for right front-seat (°C) Maximum controlled right-inlet airflow-speed (m/s) Right airflow inlet angle (upward from horizontal (°) Airflow inlet-speed at top (m/s) Outlet pressure at right front seat (Pag) Control of right-inlet airflow-speed Manikin Real man
22 5 35.5 4.3 5.5 Ú
18 and 22 3.2 33.5 3.7 5.5 Ú Ú
18 and 22 3.3 33.5 3.5 5.2 Ú Ú
3.3. Experimental setting The experimental measuring condition is that the insolation gain is nil. The car’s air-conditioning system generally takes 18 °C as the default temperature. According to overseas statistics, human beings will be most comfortable between 18 and 22°C [7]. Therefore, as per the setting in Table 2, the experiment proceeds for measurements under 18 and 22 °C, respectively, in the following three cases. 3.3.1. Case I – before putting in the manikin The environmental temperature is between 29.9 and 30.5 °C; the right passenger’s outtake angle is 35.5°, and the average air speed is between 3.1 and 3.2 m/s. The average air speed is worked out by dividing the right air outtakes in each experiment into six parts to measure the speed of the middle point of each part of every air outtake, respectively, and then the sum is divided by six. The uptake is straight down with an average air speed ranging from 3.1 to 3.3 m/s. The average air speed is worked out by dividing the air uptake in each experiment into three parts to measure the speed of the middle point of each part of every air uptake, respectively, and dividing the sum by three. The right passenger’s intake pressure is between 4.8 and 5.9 Pag, as shown in Fig. 1. 3.3.2. Case II – after putting in the manikin The environmental temperature is around 29.1 °C, the right passenger’s outtake angle is 35.5°, the uptake is straight down with an average air speed of around 4.3 m/s, and the right passenger’s intake pressure is around 5.5 Pag, as shown in Fig. 1. 3.3.3. Case III – after putting in physiological and breathing heat-gains (from a real person) The environmental temperature is around 24.1 °C, the right passenger’s outtake angle is 33.5°, the average air speed is around 3.3 m/s, the uptake is straight down with an average air speed of around 3.5 m/s, and the right passenger’s intake pressure is around 5.2 Pag, as shown in Table 1. Because human-breathing will influence the air-temperature sensor, which will further lead to an experimental error,
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it is necessary to move the temperature sensor upwards from the right front row to the position between the two eyes before the measurement. 3.4. Experimental procedure Firstly, verify that the experimental instruments and the measuring points are in the correct relative positions, and start up the engine and turn on the air conditioning. When the outtake and intake reach the required conditions, turn off the engine, open the car door to measure the current boundary-conditions, and then close the door to keep the cabin temperature even. When all this is completed, start up the engine, fix the revs to 1500 rpm, and turn on the air conditioning to set the temperature to enable the controller to control the cabin temperature within this temperature range. Then start the experimental measurements and keep a record of the experimental data. The experiment ends when the cabin temperature becomes steady; then record, the final boundary values, such as the air speed and temperature at the outtake and the pressure at the intake.
4. Results and discussions The intelligent regional air-conditioning system is designed to create an independent flow field structure based on the convection effect being much greater than the diffusion effect. The cabin is divided into four regions with separate temperature sections. The experimental result on the refit car shows that when a single cabin area’s outtake/intake is open, regions with clear-cut separate flow field structures can established. Fig. 2 indicates the independent flow-fields are generally established at the right outtake/intake, where the airflows from the high pressure area to the low pressure area, plus the uptake air that blows straight down, forming an air curtain separating the left and right flow fields. The right outtake and intake is mainly to control the right front row’s temperature-distribution. For example, when the passenger in the right front row prefers a lower temperature, he/she can turn up the air speed at the right outtake, so that the regional temperature can drop quickly to the user’s set-temperature to meet the comfort demand of the passenger. Yet its flow field will not influence any other area’s flow fields, which fulfils the purpose of regional airconditioning. 4.1. Case I – before putting in the manikin Judging from the temperature field experiment as shown in Fig. 4, when the right front-headrest temperature sensor senses that the surrounding temperature meet the controller’s preset temperature, the fan will cease to run to maintain the right front row at a temperature around 22 °C, the left front row around 28 °C, and the left and right rear rows around 29.5 °C. With the temperature difference between left and right up to 6 °C and that at the rear row up to 7.5 °C, the driver and passengers can feel different temperatures, which means that the cabin’s
K.D. Huang et al. / Applied Energy 83 (2006) 545–557
Temperature[˚C]
right back–seat left back–seat left front–seat left head–pillow
553
right front–seat right head–pillow right airflow–inlet top airflow–inlet
30 28 26 24 22 20 18 16 14 12 10 8 0
5
10
15
20
25 30 35 Time [min]
40
45
50
55
60
Fig. 4. The passenger front-seat is set to be 22 °C without the manikin.
temperature-distribution has met the demand of regional air-conditioning. Now it is time to establish independently a flow field to control the regional temperature. A further experimental measurement will proceed by putting in the manikin and physiologically-generated heat to observe the distribution of temperature and the change in the flow field. 4.2. Case II – after putting in the manikin Judging from the above experimental result, prior to putting in the manikin, a regional temperature section is already available. After the manikin is put in, the temperature distributions from the experimental results in Figs. 5 and 6, when the right row air-conditioning system is turned on and the controller is set to 18 °C, the right front-headrest temperature sensor will sense a temperature of around 18 °C, and the right front-row temperature sensor will sample a temperature of around 18 °C. When the controller presets the temperature to be 22 °C, the right front headrest temperature sensor will sense a temperature of around 22 °C, and the right front temperature sensor will sample a temperature of around 22.5 °C, which means that the flow-field structure is not yet influenced, so that the regional temperature can be controlled accurately within the range of the preset temperature. However, other regions are influenced by conduction and radiation, resulting in a drop of 2–4 °C to reach 25–26 °C, i.e., a minor influence. Compared with Case I, in this experiment, even if the air speed at the uptake is adjusted from 4.3 to 3.7 m/s, the temperature will still be controlled within the range of
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right back–seat left back–seat left front–seat left head–pillow
right front–seat right head–pillow right airflow–inlet top airflow–inlet
30
Temperature[˚C]
28 26 24 22 20 18 16 14 12 10 8 0
5
10
15
20
25 30 35 Time [min]
40
45
50
55
60
Fig. 5. The passenger front-seat is set to be 18 °C with the manikin.
Temperature[˚C]
right back–seat left back–seat left front–seat left head–pillow
right front–seat right head–pillow right airflow–inlet top airflow–inlet
30 28 26 24 22 20 18 16 14 12 10 8 0
5
10
15
20
25 30 35 Time [min]
40
45
50
55 60
Fig. 6. The passenger front-seat is set to be 22 °C with the manikin.
the preset temperature. Its purpose is to divide the flow field. An excessive air speed will strengthen the diffusion effect [8], which might influence other regional temperatures.
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Temperature[˚C]
right back–seat left back–seat left front–seat left head–pillow
555
right front–seat right head–pillow right airflow–inlet top airflow–inlet
26 25 24 23 22 21 20 19 18 17 16 15 14 13 0
5
10
15
20
25
30 35 40 Time [min]
45
50
55
60
Fig. 7. The passenger front-seat is set to be 18 °C with physiological and breathing heat-gains.
Temperature[˚C]
right back–seat left back–seat left front–seat left head–pillow
right front–seat right head–pillow right airflow–inlet top airflow–inlet
26 25 24 23 22 21 20 19 18 17 16 15 14 13 0
5
10
15
20
25 30 35 Time [min]
40
45
50
55
60
Fig. 8. The passenger front-seat is set to be 22 °C with physiological and breathing heat-gains.
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4.3. Case III – after putting in physiological and breathing heat gains (from a real person) The regional air-conditioning system enables one to control the right front passenger’s seat within the range of the preset temperature accurately. After a real person is put in, the influence of the human body (including the breathing heat and the physiological heat) on the regional temperature-distributions is shown in Figs. 7 and 8. When the temperature is preset to be 18 and 22 °C, the temperature of the right front row and right headrest will be between 18 and 22 °C when the cabin becomes steady, while that of the other positions will drop to 23.5–24 °C due to radiation and conduction. Therefore, the regional air-conditioning system still functions well with a real passenger present.
5. Conclusions The influences on the regional air-conditioning system as a result of introducing a manikin or a real person into the cabin are as follows: Before the manikin is put in, open the right front outtake to control the regional temperature, and let the uptake divide the flow field, so that the left and right flow fields will not influence each other. The experimental result for the temperature field clearly shows that there is a large gap between the temperatures of the left and right seats and that of the rear row. It is advisable to create an independent flow-field for the right front row to control the regional temperature, so as to fulfil the goal of the intelligent regional constant-temperature air-conditioning. Judging from the experimental measurements for the temperature field provided with the manikin present, under the outtake/intake control, the independent flow field is still available. Judging from Case I and Case II, the uptake is designed to divide the flow field, whose air speed will have much less influence on the whole temperature field than the airflow of the right outtake. After the real person is put in, both the physiological and breathing heats from the human body will influence the whole cabin’s temperature. Judging from the experimental results, the cabin temperature distribution can still be controlled accurately within the temperature range preset by the controller, which indicates that the physiological and breathing heats from the human body have little influence on the flow field structure, so the regional temperature can be maintained within the preset temperature range to enable the intelligent regional airconditioning. This research aims to limit energy consumption by means of the independent airflow cell, so as to divide the cabin into four regions with different temperatures to meet different personal demands. The intake and outtake designs in this experiment are simply an example. Judging from the experimental results, when the airflow cell is applied to a small car, regional air-conditioning is available even when only the right front air-conditioning system is turned on. This concept can be
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applied to a closed air-conditioning system, such as a bus, a train and a room. The regional air-conditioning is available when the air conditioning is turned on for a single region, which can help to diminish energy expenditures yet provide comfort.
References [1] Barbusse S, Gagnepain L. Automobile air-conditioning: its energy and environmental impact. ADEME Transport Technologies Department 2003. [2] Ono K, Matsumoto H, Himeno R. An application of volume rendering visualization technique to the HVAC design in a vehicle cabin. JSCFD 2000. [3] Huang L, Han T. Validation of 3-D passenger compartment hot soak and cool-down analysis for virtual thermal-comfort engineering. SAE Technical Papers SP-1679, 2002.. [4] Fujita A, Kanemaru J, Nakagawa H, Ozeki Y. Numerical simulation to predict the thermal environment inside a car cabin. JSAE 2002;3–4/140. [5] Martinho NAG, Ramos JAE, Silva MCG. Thermal environmet in the cabin of a multi-purpose vehicle. In: 8th International conference air-distribution in rooms. ROOMVENT; 2002.. [6] Barbusse S, Clodic D, Roume´goux JP. Automobile air-conditioning. Effect in terms of energy and the environment, vol. 60. Elsevier Science; 1998. p. 3–18. [7] What you need to know about temperature in places of work, the occupational safety and health service. Department of Labour, Wellington, New Zealand, 1997.. [8] Chung KC, Lee CY. Predicting air flow and thermal comfort in an indoor environment under different air-diffusion models. Build Environ 1996;31:21–6.
Applied Energy 83 (2006) 545–557
www.elsevier.com/locate/apenergy
Air-conditioning system of an intelligent vehicle-cabin K. David Huang a, Sheng-Chung Tzeng b,*, Tzer-Ming Jeng c, Wing-Ding Chiang a b c
a Graduate School of the Vehicular Engineering, Dayeh University, Changhua, Taiwan 500, ROC Department of Mechanical Engineering, Chienkuo Technology University, Changhua, Taiwan 500, ROC Department of Mechanical Engineering, Air Force Institute of Technology, GangShan 820, Taiwan, ROC
Accepted 16 May 2005 Available online 13 February 2006
Abstract If vehicles can be more comfortable, safe, energy efficient and humanized, it will be very beneficial. This study introduces an ‘‘Airflow Management’’ technique to control the airflow in the vehicle cabin for the purpose of achieving a regional steady-state temperature. With this new concept, each passenger in a different area of the compartment can be satisfied with respect to his/her unique temperature demands. The airflow is controlled by air inlets and outlets, with fans for the modulation of airflow directions and rates. The temperature in each zone can be controlled by the modulation of the airflow. The concepts in this study are relevant to all kinds of regional air-conditioning in any enclosed space. Ó 2005 Elsevier Ltd. All rights reserved. Keywords: Airflow management; Regional air conditioning; Intelligent vehicle-cabin
*
Corresponding author. Tel.: +886 4 7111111x3132; fax: +886 4 7357193. E-mail addresses: [email protected], [email protected] (S.-C. Tzeng).
0306-2619/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.apenergy.2005.05.006
546
K.D. Huang et al. / Applied Energy 83 (2006) 545–557
1. Introduction In a developed industrial-civilization, vehicles are the people’s main means of transportation. Whether the air-conditioning system in the vehicle cabin is good or not decides the degree of comfort, traffic safety as well as health. Take Asia as an example. Vehicles equipped with an air-conditioning system accounted for around 10% in early 1970, and grew up to about 98% [1] in 2004, so that an air-conditioning system is already regarded as essential for vehicles. However, the design of the air-conditioning system for the vehicles is still not intelligent, that is, it needs to be regulated to the stable temperature in a certain zone to meet individual demands. In 2000, Ono et al. [2] applied numerical simulation and flow field visualization technology to improve the air-conditioning design technology. The outtake wind-speed of the air conditioning was set to be 5 m/s and the outtake temperature to be 15 °C to compare different flow-field structures and temperature distributions under different amounts of heat radiation. The study helped improve air-conditioning technology. In 2002, Huang and Han [3] conducted an analog analysis on the regional air-conditioning in their research, in which the air-conditioning system in the cabin of a small car (equipped with two extra air-outtakes) was separated into the front and rear sections by a flow field with a temperature difference of around 6.5 °C, so that the front and rear cabins are at different temperatures. The air-conditioning system of the vehicle – when being driven, will be subject to the influence of a changing environment. In 2001, Fujita [4] adopted a CFD simulation and experimental measurements to compare the different effects on a thermal manikin under different environments. The experiment adopted large radiative bulbs as the analog of sunshine from outside the car and put a driver and a passenger into the cabin (regardless of the manikins’ own physiological and breathing rates with 20 thermal sensors on each body). The paper proposed that the influence on the compartment varies with heat load, air conditioning and environment, which shows that the air-conditioning system is subject to the influence of the environmental temperature. Martinho et al. in 2002 [5] studied the influence on the flow-field structure and temperature distribution in the vehicle cabin provided with manikins (regardless of the manikins’ own physiological and breathing rates), as shown in Fig. 1. Eight wind-speed sensors were placed in the compartment, and tests were undertaken on the manikins equipped with 16 thermal sensors in terms of the influence on the temperature, velocity field and the manikins in the cabin with, or, without other manikins present under different air-outtake temperatures and wind speeds. The engine load and fuel rate will be increased when the air-conditioning system is turned on in the car. In 1998, Barbusse et al. [6] pointed out in their research that, under the environmental temperature of 30 °C, the demand is for 3.1 litres of fuel for each 100 km journey, and 3.8 litres in case of 40 °C. The fuel rate is reduced by a maximum of 20% in a car driven without air conditioning. Global petroleum energy is estimated to be used up in about 40 years. If the car’s air-conditioning is reduced to only that which is necessary, the fuel rate will be decreased, so contributing to energy thrift.
K.D. Huang et al. / Applied Energy 83 (2006) 545–557
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Fig. 1. Experimental regional air-conditioning system (see Table 1 for the significance of numbers 1 to 9).
2. Experimental infrastructure The research refits a group of air outtakes/intakes, so dividing the cabin of the vehicle (a Ford Liata) into four airflow cells. The air outtake/intake design proposed in the research is not exclusive. The target of regional air-conditioning can be achieved by locating the appropriate air outtakes and intakes in the flow cells, plus proper control. In the present research, the airflow field structure is controlled within the closed vehicle cabin, only the initial design of air outtake/intake positions is changed, and the airflow is limited in the controlled area. The convection effect is much greater than the diffusion effect, while the air is flowing in the different regions. Each region is not divided by real objects, so that the required temperature is available in each region. All the regions are separate, i.e., without mutual interference, which enables intelligent regional air-conditioning to ensue. For example, when the intelligent air-conditioning is turned on only in the region of the assistant driver’s seat, the air uptake is used as an airflow barrier between the left and right passengers’ temperature-regions, so that the assistant driver’s seat can be divided into independent flow-field regions (by means of a vortex); the air outtake and intake on the right maintain a suitable temperature for the passengers in this region. Moreover, when a passenger goes into the cabin, he or she can set the suitable temperature to satisfy his or her desire. Fig. 1 shows the experimental rig. There is an air-temperature sensor under the headrest of each seat to scout the surrounding temperature as the main control parameter. Then the control setting and the surrounding temperature will be compared and sampled by means of the control module to control accurately the air speeds and pressures in the passengers outtake and intake, and control the region within the range of the temperature set by the controller. To sustain a suitable ‘‘sitting’’ environment, i.e., to enable the regulation of the
548
K.D. Huang et al. / Applied Energy 83 (2006) 545–557
intelligent regional air-conditioning, the environmental temperature (i.e., the regional constant temperature) in the cabin is monitored continuously.
3. Experimental method 3.1. The experimental rig This makes use of independent flow cells to achieve the target of regional air-conditioning. The settings of the temperature and pressure sensors used in the experiment are shown in Fig. 1 and Table 1. For the air conditioning associated with the driver’s seat, one can, respectively, open the right air-outtake and-intake and the uptake as shown in Fig. 2. A resistance temperature-detector transmits a signal to the computer through the sampling equipment, so that variations of temperature Table 1 Positions of installed temperature and pressure sensors No.
Position of temperature sensors (RTD)
No.
Position of pressure sensors
1 2 3 4 5 6 7 8 9
Center of right airflow-inlet Head position of right front-seat Bottom of right head-pillow Head position of right back-seat Center of top airflow-inlet Center of left airflow-inlet Head position of left front-seat Bottom of left head-pillow Head position of left back-seat
1 2
Center of right airflow outlet Center of left airflow outlet
Fig. 2. Outtake and intake positions.
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can be sampled continually to within an error of ±0.23 °C. The pressure sampling of the air intake measures the differential pressure, positive pressure and vacuum to within ±0.16 Pa (in case of 20 Pa). The air outtake employs a hot-wire anemometer to measure the air flow-rate. The wind speed sampling enables one to deduce the average speed by dividing the air outtakes in each experiment into six parts and thereby determine the speed of the middle point of each part of every air outtake to within ±0.4 m/s (in case of 7 m/s). 3.2. Control strategy The controller manages the maintenance of the temperature set by the user in each region. It converts the resistance temperature detector (RTD) signals between the headrest and chair back into temperatures to control the wind speed of the air outtake. The angle of the air jet and the air-intake pressure are shown in Fig. 3 with the following control strategy: Decide where in the vehicle cabin is the required control region, and transmit the signals from the headrest air-temperature sensor to the regional temperature controller. Compare the headrest air-temperature within the control region and the preset temperature to judge the fan’s rotational speed. Sample the signals of the headrest air-temperature sensor from the control region and the non-control region, and monitor whether the temperature in the non-control region is influenced, so as to limit the effective management of the independent flow-field structure in the control region without influencing the flow field in the non-control region. Judge whether the flow field in the control region has been established completely. When the flow field has been established, compare the signals of the headrest airtemperature sensor in the control region with the preset temperature, and then adopt different running modes of the fan to reach the temperature set by the users rapidly and steadily. When the temperature in the control region is higher than the preset temperature by over 2 °C (exclusive of 2 °C), the fan will be running at full speed, so that the control region will reach the preset temperature rapidly. When the temperature in the control region is lower than the set temperature by a maximum of 2 °C, ranging from high to low temperatures, the fan will run with a non-step variable speed to enable the temperature in the control region to reach the steady required temperature. The pressure in the air intake is controlled by the air-intake pressure controller after the temperature in the control region becomes steady, and the signals from the headrest air-temperature sensor in the control region are returned to the regional temperature controller to monitor the flow field in the cabin continuously. The air outtake angle and the air intake pressure are managed by their respective controllers to assure that the flow field in the control region does not influence that in the other control regions. The air outtake angle is adjusted by the air-outtake angle
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Fig. 3. Control strategy.
controller and fine-tuned by the stepping motor. The outtake angle can be adjusted from left-to-right and up-to-down. Then the temperatures between the control region and non-control region are again compared to judge whether the flow field in the control region has been established. The speed of rotation of the fan at the air intake is controlled by the air-intake pressure controller, so as to control the air intake pressure. The temperatures between the control region and non-control region are again compared after this adjustment to determine whether the flow field in the control region has been established.
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Table 2 Test conditions Test parameters
Case I
Case II
Case III
Set temperature for right front-seat (°C) Maximum controlled right-inlet airflow-speed (m/s) Right airflow inlet angle (upward from horizontal (°) Airflow inlet-speed at top (m/s) Outlet pressure at right front seat (Pag) Control of right-inlet airflow-speed Manikin Real man
22 5 35.5 4.3 5.5 Ú
18 and 22 3.2 33.5 3.7 5.5 Ú Ú
18 and 22 3.3 33.5 3.5 5.2 Ú Ú
3.3. Experimental setting The experimental measuring condition is that the insolation gain is nil. The car’s air-conditioning system generally takes 18 °C as the default temperature. According to overseas statistics, human beings will be most comfortable between 18 and 22°C [7]. Therefore, as per the setting in Table 2, the experiment proceeds for measurements under 18 and 22 °C, respectively, in the following three cases. 3.3.1. Case I – before putting in the manikin The environmental temperature is between 29.9 and 30.5 °C; the right passenger’s outtake angle is 35.5°, and the average air speed is between 3.1 and 3.2 m/s. The average air speed is worked out by dividing the right air outtakes in each experiment into six parts to measure the speed of the middle point of each part of every air outtake, respectively, and then the sum is divided by six. The uptake is straight down with an average air speed ranging from 3.1 to 3.3 m/s. The average air speed is worked out by dividing the air uptake in each experiment into three parts to measure the speed of the middle point of each part of every air uptake, respectively, and dividing the sum by three. The right passenger’s intake pressure is between 4.8 and 5.9 Pag, as shown in Fig. 1. 3.3.2. Case II – after putting in the manikin The environmental temperature is around 29.1 °C, the right passenger’s outtake angle is 35.5°, the uptake is straight down with an average air speed of around 4.3 m/s, and the right passenger’s intake pressure is around 5.5 Pag, as shown in Fig. 1. 3.3.3. Case III – after putting in physiological and breathing heat-gains (from a real person) The environmental temperature is around 24.1 °C, the right passenger’s outtake angle is 33.5°, the average air speed is around 3.3 m/s, the uptake is straight down with an average air speed of around 3.5 m/s, and the right passenger’s intake pressure is around 5.2 Pag, as shown in Table 1. Because human-breathing will influence the air-temperature sensor, which will further lead to an experimental error,
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it is necessary to move the temperature sensor upwards from the right front row to the position between the two eyes before the measurement. 3.4. Experimental procedure Firstly, verify that the experimental instruments and the measuring points are in the correct relative positions, and start up the engine and turn on the air conditioning. When the outtake and intake reach the required conditions, turn off the engine, open the car door to measure the current boundary-conditions, and then close the door to keep the cabin temperature even. When all this is completed, start up the engine, fix the revs to 1500 rpm, and turn on the air conditioning to set the temperature to enable the controller to control the cabin temperature within this temperature range. Then start the experimental measurements and keep a record of the experimental data. The experiment ends when the cabin temperature becomes steady; then record, the final boundary values, such as the air speed and temperature at the outtake and the pressure at the intake.
4. Results and discussions The intelligent regional air-conditioning system is designed to create an independent flow field structure based on the convection effect being much greater than the diffusion effect. The cabin is divided into four regions with separate temperature sections. The experimental result on the refit car shows that when a single cabin area’s outtake/intake is open, regions with clear-cut separate flow field structures can established. Fig. 2 indicates the independent flow-fields are generally established at the right outtake/intake, where the airflows from the high pressure area to the low pressure area, plus the uptake air that blows straight down, forming an air curtain separating the left and right flow fields. The right outtake and intake is mainly to control the right front row’s temperature-distribution. For example, when the passenger in the right front row prefers a lower temperature, he/she can turn up the air speed at the right outtake, so that the regional temperature can drop quickly to the user’s set-temperature to meet the comfort demand of the passenger. Yet its flow field will not influence any other area’s flow fields, which fulfils the purpose of regional airconditioning. 4.1. Case I – before putting in the manikin Judging from the temperature field experiment as shown in Fig. 4, when the right front-headrest temperature sensor senses that the surrounding temperature meet the controller’s preset temperature, the fan will cease to run to maintain the right front row at a temperature around 22 °C, the left front row around 28 °C, and the left and right rear rows around 29.5 °C. With the temperature difference between left and right up to 6 °C and that at the rear row up to 7.5 °C, the driver and passengers can feel different temperatures, which means that the cabin’s
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Temperature[˚C]
right back–seat left back–seat left front–seat left head–pillow
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right front–seat right head–pillow right airflow–inlet top airflow–inlet
30 28 26 24 22 20 18 16 14 12 10 8 0
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40
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60
Fig. 4. The passenger front-seat is set to be 22 °C without the manikin.
temperature-distribution has met the demand of regional air-conditioning. Now it is time to establish independently a flow field to control the regional temperature. A further experimental measurement will proceed by putting in the manikin and physiologically-generated heat to observe the distribution of temperature and the change in the flow field. 4.2. Case II – after putting in the manikin Judging from the above experimental result, prior to putting in the manikin, a regional temperature section is already available. After the manikin is put in, the temperature distributions from the experimental results in Figs. 5 and 6, when the right row air-conditioning system is turned on and the controller is set to 18 °C, the right front-headrest temperature sensor will sense a temperature of around 18 °C, and the right front-row temperature sensor will sample a temperature of around 18 °C. When the controller presets the temperature to be 22 °C, the right front headrest temperature sensor will sense a temperature of around 22 °C, and the right front temperature sensor will sample a temperature of around 22.5 °C, which means that the flow-field structure is not yet influenced, so that the regional temperature can be controlled accurately within the range of the preset temperature. However, other regions are influenced by conduction and radiation, resulting in a drop of 2–4 °C to reach 25–26 °C, i.e., a minor influence. Compared with Case I, in this experiment, even if the air speed at the uptake is adjusted from 4.3 to 3.7 m/s, the temperature will still be controlled within the range of
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right back–seat left back–seat left front–seat left head–pillow
right front–seat right head–pillow right airflow–inlet top airflow–inlet
30
Temperature[˚C]
28 26 24 22 20 18 16 14 12 10 8 0
5
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25 30 35 Time [min]
40
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Fig. 5. The passenger front-seat is set to be 18 °C with the manikin.
Temperature[˚C]
right back–seat left back–seat left front–seat left head–pillow
right front–seat right head–pillow right airflow–inlet top airflow–inlet
30 28 26 24 22 20 18 16 14 12 10 8 0
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25 30 35 Time [min]
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55 60
Fig. 6. The passenger front-seat is set to be 22 °C with the manikin.
the preset temperature. Its purpose is to divide the flow field. An excessive air speed will strengthen the diffusion effect [8], which might influence other regional temperatures.
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Temperature[˚C]
right back–seat left back–seat left front–seat left head–pillow
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right front–seat right head–pillow right airflow–inlet top airflow–inlet
26 25 24 23 22 21 20 19 18 17 16 15 14 13 0
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30 35 40 Time [min]
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Fig. 7. The passenger front-seat is set to be 18 °C with physiological and breathing heat-gains.
Temperature[˚C]
right back–seat left back–seat left front–seat left head–pillow
right front–seat right head–pillow right airflow–inlet top airflow–inlet
26 25 24 23 22 21 20 19 18 17 16 15 14 13 0
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Fig. 8. The passenger front-seat is set to be 22 °C with physiological and breathing heat-gains.
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4.3. Case III – after putting in physiological and breathing heat gains (from a real person) The regional air-conditioning system enables one to control the right front passenger’s seat within the range of the preset temperature accurately. After a real person is put in, the influence of the human body (including the breathing heat and the physiological heat) on the regional temperature-distributions is shown in Figs. 7 and 8. When the temperature is preset to be 18 and 22 °C, the temperature of the right front row and right headrest will be between 18 and 22 °C when the cabin becomes steady, while that of the other positions will drop to 23.5–24 °C due to radiation and conduction. Therefore, the regional air-conditioning system still functions well with a real passenger present.
5. Conclusions The influences on the regional air-conditioning system as a result of introducing a manikin or a real person into the cabin are as follows: Before the manikin is put in, open the right front outtake to control the regional temperature, and let the uptake divide the flow field, so that the left and right flow fields will not influence each other. The experimental result for the temperature field clearly shows that there is a large gap between the temperatures of the left and right seats and that of the rear row. It is advisable to create an independent flow-field for the right front row to control the regional temperature, so as to fulfil the goal of the intelligent regional constant-temperature air-conditioning. Judging from the experimental measurements for the temperature field provided with the manikin present, under the outtake/intake control, the independent flow field is still available. Judging from Case I and Case II, the uptake is designed to divide the flow field, whose air speed will have much less influence on the whole temperature field than the airflow of the right outtake. After the real person is put in, both the physiological and breathing heats from the human body will influence the whole cabin’s temperature. Judging from the experimental results, the cabin temperature distribution can still be controlled accurately within the temperature range preset by the controller, which indicates that the physiological and breathing heats from the human body have little influence on the flow field structure, so the regional temperature can be maintained within the preset temperature range to enable the intelligent regional airconditioning. This research aims to limit energy consumption by means of the independent airflow cell, so as to divide the cabin into four regions with different temperatures to meet different personal demands. The intake and outtake designs in this experiment are simply an example. Judging from the experimental results, when the airflow cell is applied to a small car, regional air-conditioning is available even when only the right front air-conditioning system is turned on. This concept can be
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applied to a closed air-conditioning system, such as a bus, a train and a room. The regional air-conditioning is available when the air conditioning is turned on for a single region, which can help to diminish energy expenditures yet provide comfort.
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