intelligent solar powered automobile ventilation system

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Intelligent solar-poweredautomobile-ventilation system

K. David Huang a, Sheng-Chung Tzeng b,*, Wei-Ping Ma c,

Ming-Fung Wu a

a Graduate School of the Vehicular Engineering, Dayeh University, Changhua 500, Taiwan, ROCb Department of Mechanical Engineering, Chien Kuo Institude of Technology, Changhua 500, Taiwan, ROC

c Department of Information Management, Lan Yang Institute of Technology, Ilan 261, Taiwan, ROC

Accepted 19 March 2004

Available online 1 June 2004

Abstract

This study adopts airflow management technology to improve the local temperature dis-

tributions in an automobile to counteract the greenhouse effect. The automobiles temperature

can be reduced to almost the outside temperature before the driver or passenger gets into the

vehicle. When the engine is idling, the greenhouse-control system can be activated to remove

the hot air from the car. An appropriate negative pressure is maintained to prevent stuffiness

and save energy. The greenhouse-control system requires electrical power when the engine is

idle, and a battery cannot supply sufficient power. An auxiliary solar-power supply can save

energy and reduce the greenhouse effect of sunlight, while creating a comfortable traveling

environment. It ensures that the engine is not overburdened and increases its service life,

conserving energy, protecting the environment and improving comfort.

2004 Elsevier Ltd. All rights reserved.

Keywords: Air flow management; The greenhouse effect; Auxiliary solar-power supply

1. Introduction

The average temperature during the summer typically exceeds 300 K in

subtropical or tropical regions. Furthermore, the greenhouse effect causes the

* Corresponding author. Tel.: +886-4-711-1111x3132; fax: +886-4-735-7193.

E-mail address: [email protected](S.-C. Tzeng).

0306-2619/$ - see front matter 2004 Elsevier Ltd. All rights reserved.

doi:10.1016/j.apenergy.2004.03.010

www.elsevier.com/locate/apenergy

Applied Energy 80 (2005) 141154

APPLIED

ENERGY
http://mail%20to:%[email protected]/http://mail%20to:%[email protected]/


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temperature in automobiles to reach 333 ! 343 K [13] in open parking lots; peoplecannot usually endure such temperatures comfortably. Moreover, the instrumenta-

tion panel, leather seats and plastic accessories, among other items, age rapidly if

exposed to these temperatures for a long period. When the air conditioner is turned

on and the engine has not reached its working temperature, additional loading will

occur, increasing the waste of fuel and the abrasion of the engine. An air conditioner

cannot effectively adjust the temperature within a short period, so developing the

automobiles greenhouse ventilation system is essential.

Removing hot air from within an automobile requires opening a door, activatingthe engine and turning the A/C to its peak power. However, reducing the temper-

ature markedly takes some time. If the engine has not reached a proper working

Nomenclature

CP specific heat (J kg1

K1

)E gross energy (J kg1)

g gravitational acceleration (m s2)

k thermal conductivity (W m1 K1)

p pressure (N m2)

Pr Prandtl number

q heat flux (W m2)

T temperature (K)

u; v;w velocity components (m s1)x;y;z rectangular coordinates

Greek symbols

b coefficient of thermal expansion,b 1=qoq=oTP

dij Kronecker delta,dij 0 for i6j;

1 for i j

j turbulent kinetic-energy (m2 s2)

l dynamic viscosity (kg s1 m1)

s tensor stress (N m2)

Superscripts time-averaged quantity0 fluctuation quantity

Subscripts

eff effective

i;j; l coordinate components laminart turbulent

1 free stream

142 K.D. Huang et al. / Applied Energy 80 (2005) 141154


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temperature, then the heavy-duty operation will lead to speedy abrasion of me-

chanical components and an increase the fuel consumption. Sheathing paper,

weather windows and shading curtains can be used to control an automobiles

temperature, but they are not very effective. Heat accumulated in an automobilecannot be easily removed and the temperature cannot be reduced to close to that of

the outdoor environment if the temperature distribution in the vehicle is not effec-

tively controlled.

An energy-efficient greenhouse for heating, cooling and dehumidification appli-

cations was described by Chou et al. [4]. Airflow arose from the interactions and

energy exchanges between components within the greenhouse and the external en-

vironment via infiltration and the ventilation process. Their study found that the

conditions of the greenhouse air were greatly influenced by the conditions of the

outdoor air. In the present study, the greenhouse ventilation system runs normally

when the engine is idle, but it cannot be powered by a battery. An auxiliary powersupply system, that automatically powers the greenhouse ventilation system using

solar energy and without increasing the loading of the battery, must be designed to

prevent shortages or deep discharging of the battery power, and the consequent

reduction in the service life of the battery due to the long-time operation. Currently

available alternative sources are solar energy, wind power, geothermal power and

tidal power, among others. However, the latter three are geographically restricted,

and their stability is a difficulty. The solar-energy module can be applied to absorb

solar power and turn it into electric power during driving or parking. Then, a

voltage-stabilizing circuit can output a stable voltage and supply the power con-

sumed by both the safety control system and the greenhouse ventilation system.

Surplus power generated by the solar energy module can be used to charge the

battery in order to ensure that the power supplied to the automobiles electric system

suffices in the absence of solar energy [5,6]. Thus, the solar module can serve as an

auxiliary power-supply, and contribute to reducing the greenhouse effect caused by

sunlight.

2. Methodology

Based upon integrated CAD (Computer Aided Design) and CAE (Computer

Aided Engineering) software, this study establishes a realistic numerical model of the

automobile, and designs a control system that occupies very limited space to try to

achieve optimum performance.

2.1. Design ideology and infrastructure

When an automobile parks in the open air, its temperature rises rapidly as fervent

sunlight enters. Hence, a solar-energy module, which is covered with a transparent

colloid protective layer, should be placed in the hardboard on the top support. It canthen prevent the heat radiation from being transmitted into the automobile via

mechanical components, while absorbing and storing solar energy as an auxiliary

K.D. Huang et al. / Applied Energy 80 (2005) 141154 143


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power-supply. Additionally, the module can power the ventilating fan to exhaust the

hot air and suppress the greenhouse effect.

The greenhouse monitoring system becomes operational when the engine is

idle. It therefore enables the status of the engine to be judged with the help of thegreenhouse controller. When the engine is in its operating mode, the greenhouse

controller continuously monitors its status while the control system is idle. When the

engine is idle, the greenhouse controller determines whether the temperature exceeds

the preset value using an air-temperature detector. If the temperature is below the

preset value, then the greenhouse controller monitors the temperature through the

air-temperature detector whenever the control system is idle. When the internal

temperature exceeds the specified threshold, the greenhouse controller compares the

temperature inside with that outside the car. When the internal temperature exceeds

the external temperature, the ventilating fan will continue to exhaust the hot air and

open the inlet valve to absorb the outdoor air. Otherwise, it will close the inlet valve,inactivate the ventilating fan and monitor the difference between the temperatures

inside and outside the car. Fig. 1 presents the infrastructure of the system.

Fig. 1. Greenhouse ventilation system.



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The automobiles auxiliary solar-power supply continuously powers the safety

control system and the air quality and greenhouse ventilation system. Fig. 2 shows

the architecture of this system. The electrical capacity of the solar-energy module is

directly proportional to its collector area, and also varies with the intensity of illu-mination. Therefore, a group of voltage-stabilizing circuits is required to maintain

the charge at 12 V for the monitoring and driving systems. If the power supplied by

the solar-energy module is excessive or insufficient, the batteries store or supply

power, respectively: the switchover of the loop of the electric system is controlled by

a control circuit. If the solar electric-power is adequate, then the ventilating fan (air

inflow) will be activated as the electric power is transmitted to the forced-ventilation

system and detector: the battery stores any surplus power. In the case of insufficient

solar electric-power, the battery will power the ventilating fan and the detector in

order to achieve the optimal performance.

2.2. Numerical model

2.2.1. Physical and mathematical model

A solid model was built using Pro-E software to measure the physical dimensions

of the automobile. Then, Gambit software was applied to trim the solid model and

generate the grid of the flow field. Fig. 3 shows the computational domain of

physical model.

The following assumptions are made with respect to the simulation of streamlines,

saving computing time and maintaining the physical properties of the system:(1) Newtonian fluid,

(2) steady state,

(3) effects of gravity and buoyancy are considered,

(4) uniform air velocity at the outlet,

(5) k e turbulence model.

Fig. 2. Circuit diagram of auxiliary power-supply.



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The following are the governing equations:

Continuity equation:

ou

ox

ov

oy

ow

oz

0: 1

Momentum equation:

q o

oxjuiuj

1

q

op

oxi

o

oxjleff

oui

oxj

ouj

oxi

2

3

oul

oxldij

o

oxj

qu0iu

0j

gibT T1: 2

Energy equation:

o

oxi

uiqE p o

oxj

j CPlt

Prt

oT

oxj

uisijeff; 3where E is the gross energy, keffis the effective thermal-conductivity, and the tensor

force of the effective the shear stress sijeffis given by the formula

Fig. 3. Computational domain of physical model (unit: cm).



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sijeffleffoui

oxj

ouj

oxi

2

3leff

oul

oxldij: 4

The turbulence equation, which was proposed by Spalart and Allmaras in 1992 tomodel the turbulent kinematic viscosity, is primarily related to the eddy viscosity [7].

2.2.2. Simulation conditions

2.2.2.1. Identification of collected sunshine. This experiment endeavors to measure the

changes in the intensity of sunlight using a sunlight recorder. When the sunlight

enters the glass of the vehicle window, the practical effect of the residual sunlight can

be obtained by subtracting the effect of the reflected sunlight. The data measured at

the four corners and the center of the window, and the average values, are calculated.

The formula for converting sunshine illuminance (lx) to heat flux (q) isq lx/107.5.

2.2.2.2. Heat flux. The heat sources of the automobiles are internal heat and heat

absorbed by the glass window. Heat radiation enters the automobile through three

areas the front and rear windshields (which directly absorb light) and a general

absorption area. The gross energy of the light directly absorbed is the product of the

practical residual energy (that enters through the windshield) and the absorptivity of

the materials. The gross energy reflected from the areas that directly absorb light

equals the practical residual energy (which enters through the windshield) minus the

gross energy absorbed by the front and rear areas that absorb light directly. The

gross energy over the absorption area is equal to the practical residual energy (which

enters through the vehicles windows on both sides) plus the gross energy reflectedfrom the front and rear areas that directly absorb light.

RHG (relative heat gain) in W/m2 is determined using the following formula,

provided by the ASHRAE (American Society of Heating, Refrigerating and Air

Conditioning Engineers, Inc.) [8] to identify the edge conditions of the window glass

RHG 630 C 8 ksum 5

of which the right-hand first item is represented by the heat radiation that enters

through the windows andCis the sheltering coefficient; the right-hand second item is

represented by the thermal conduction due to the difference between the tempera-

tures of the windows on both sides, andksumpresents the thermal conductivity during

Table 1

Set simulated air outlet and inlet in greenhouse ventilation system

Position of air inlet Outlet pressure (Pa) Inlet pressure (Pa)

Case I Rear shelf board (near front of rear

windshield)

0 )6

Case II Placed vertically at top support 0 )6

Case III Placed laterally at top support 0 )10

Case IV Placed laterally at front of topsupport (near to front of front

windshield)

0 )

10



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daytime in the summer. The heat flux through the glass is 23.2 W/m2, when only

thermal conduction is considered.

2.2.2.3. Pressures at air outlet and inlet. The pressure at the air outlet of the green-house ventilation system is set to zero, and that at the air inlet is set to )6 and

)10 Pa, as listed in Table 1.

2.3. Numerical method and grid system

This study seeks to determine the numerical simulation solutions using the finite-

volume method and the segregated solution method as in FLUENT software. The

SIMPLE method [9] is applied to correlate the pressure and velocity solutions during

the iteration process. The optimum grid is determined by the adaptive gradient

within the adaptation grid options. Where the gradient varies widely, the gridnumber is increased; in other places, the grid number is reduced. A comparison of

five discrete grid numbers, such as 1,274,571, 844,747, 770,000, 504,434 and 364,025,

and the proof test of the functions of the adaptive grid lead to setting the grid

number of the greenhouse ventilation system to 770,000. A staggered grid is applied

in the grid calculation, with proper relaxation factors, to obtain the correct and

stable values.

3. Results and discussion

3.1. Air inlet placed at rear shelf-board

The air inlet is placed at the rear shelf-board because flexible installation and

piping are required to avoid obstructing the firewall, the steering column and the

shockproof steel-skeleton. Its proximity to the front windshield places it in one of

the high-temperature zones of the automobile, yielding the simulation results

plotted in Fig. 4. The temperature rises primarily because the low-temperature air

is heated by the heat radiation that enters the automobile through the windows.

Then, hot air flows upwards, causing heat to accumulate. The air inlet in case I isclose to the rear windshield, which stands a little apart from the high-temperature

zone and the largest thermal source, which is the front instrument board and the

steering wheel; the air inlet absorbs only the hot air around the passenger seats

and the rear shelf board, so it cannot easily exhaust uniformly all of the hot air

in the vehicle. When the pressure at the air inlet is )6 Pa, the temperature near

the drivers seat is approximately 304 ! 310 K. Fig. 5 plots the temperaturedistribution.

Case I reveals that, rather than expelling the heat via a strong negative-pres-

sure zone, a smaller negative-pressure zone should be created within the high-

temperature or high-pressure zone, and the difference between pressures usedto exhaust the heat without any additional energy loss due to mechanical

components.



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3.2. Air inlet placed vertically at the center of the top support

When the air inlet is placed vertically at the center of the top support, according to

the simulation, the heat will continuously enter the automobile and open the ven-

tilation system. Fig. 6 shows the temperature distribution in the center section one

hour after the ventilation system has been turned on. The simulation demonstrates

that exhausting heat in case II is easier than doing so in case I, because the high-

temperature zones in case II are much smaller than those in case I. The temperature

around the drivers seat is 303fi 309 K.

The hot mechanical members at the front and rear ends of the car heat-up the

surrounding air (around the steering wheel, the front instrument board and the rearshelf board, for example). The hot air moves upward towards the center of the top

support through the front and rear windshields. However, the top support is at an

angle to the direction of flow of the hot air in case II, and the low-temperature air at

the air outlets over the seats flows towards the air inlet due to the inertia effect, which

acts in the same direction as the inertia of the low-temperature air. Fig. 7 shows the

temperature distribution; the air inlet exhausts only the hot air that flows across it,

especially in the front part of the vehicle.

3.3. Air inlet placed laterally at the top support

When the air inlet is placed laterally at the center of the top support, according to

the simulation, the heat continuously enters the automobile and the ventilation

Fig. 4. Temperature distribution of central section of automobile in case I.



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system is opened. Fig. 8 plots the temperature distribution one hour after the ven-

tilation system has been turned on. The simulation reveals that exhausting heat in

case III is easier than in the other cases, because the high-temperature zones in case

III are much smaller than those in the other cases. Hence, the air inlet pressure in

case III will rise to )10 Pa from )6 Pa, making the value of desirable temperature

easier to attain.

The air inlet in case III can exhaust the heat effectively, primarily because most ofthe heat radiation enters the automobile through the front and rear windshields.

However, heat is absorbed from the hot air by the steering wheel, front instrument

board, passenger seats and rear shelf-board surrounding the air. Influenced by the

inertial effect of the air outlet of the front and rear windshields, the flow of the hot air

towards the top support and air outlet accelerates along the direction of the cabin

outlines. The air inlet in case III is laterally placed at the center of the top support,

and so exhausts a substantial amount hot gas from the front and rear windshields

(which face the direction of flow of the hot air). However, the air inlet in case II is

vertically placed on the top support, and so can exhaust the hot air smoothly, only

changing the flow direction.The considered cases imply that the following principles must be observed when

placing an air inlet to exhaust effectively the heat of automobiles. Firstly, the air faces

Fig. 5. Air-flow paths from steering wheel and front instrument board to air inlet in case I.



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Fig. 6. Temperature distribution in the central section to the left of the steering wheel in case II.

Fig. 7. Air-flow paths near the front seat in case II.



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Fig. 8. Temperature distribution in the central section of the automobile in case III.

Fig. 9. Temperature distribution in the central section to the left of the steering wheel in case IV.



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the direction of flow of the hot air to optimize the exhaust; secondly, the air inlet is

arranged in or near the high-temperature/high-pressure zones, so the hot air is ex-

hausted according to the difference between pressures. In a simulation environment,

in which these principles are followed (i.e. given strong sunshine at the front of the

automobile), in case IV, the air inlet is moved to the back of the front windshield,

allowing hot air to be exhausted effectively, as shown in Fig. 9. The effectiveness

follows primarily from the proximity of the air inlet to the steering wheel and to its

orientation with respect to the direction of flow of hot air, which allows it to exhaust

the air rapidly. Fig. 10 indicates the temperature distribution.

4. Conclusions

This study demonstrates that an air inlet should be placed in high-temperature or

high-pressure zones, to enable the hot air to be exhausted rapidly, according to the

difference of local pressures. Some innovative improvements were made to the dis-

tribution of temperature, and the piping design within a limited space, so optimizing

the design of the greenhouse ventilation system.

In case I, the air inlet is placed at the rear shelf-board, and the air exhaust per-

forms poorly, primarily because the air inlet in case I is near to the rear wind-shield, which stands a little apart from the high-temperature zone and the

largest thermal source, which is the front instrument panel and the steering wheel.

Fig. 10. Path in central section to left of steering wheel in case IV.



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Hence, the air inlet absorbs only the high-temperature air around the passenger

seats and the rear shelf-board, making it difficult to achieve uniform exhausting

of all the hot air in the vehicle.

In case II, the air inlet is placed vertically at the center of the top support. Theresults concerning air exhaust are somewhat better than those in case I, primarily

because the hot mechanical members in the front and rear ends heat the surround-

ing air. Hot air moves towards the center of the top support passing the front and

rear windshields. The air inlet in case II is placed at the top support, so facilitating

the exhausting of the hot air in the automobile. However, in case II, the top sup-

port is at an angle to the direction of the flow of the hot air, and the low-temper-

ature air at the air outlets over the seats flows towards the air inlet by inertia, so

the air inlet can exhaust only the hot air that flows across it.

In case III, the air inlet is placed laterally at the center of the top support. The

results concerning the exhausting of air are significantly improved, mainly becausemost of the heat radiation enters the automobile through the front and rear wind-

shields. However, when the heat is absorbed by the steering wheel, front instru-

ment board, rear passenger seats and rear shelf board, the surrounding air is

heated. Influenced by the inertial effect of the air outlets at the front and rear

windshields, the flow of hot air accelerates towards the top support and air outlet,

along the direction of the cabin outlines. The air inlet in case III is placed laterally

at the center of the top support, and so exhausts hot gas from near the front and

rear windshields. However, the air inlet in case II was vertically placed on the top

support, and so could smoothly exhaust the hot air.

Case IV exhibits the best air-exhausting performance of all cases, primarily be-

cause the air inlet is near to the steering wheel and is orientated in relation to

the flow of the hot air; it can exhaust the hot air rapidly under the preset pressure

difference of)10 Pa at the air inlet.

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intelligent solar powered automobile ventilation system

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