An innovative solution to a passenger car cabin cooling – A concept study

AMITH VISHWANATH, AKSHAY V RAO, NAGARJUNA N, ANAND RAVI

7th SEM TCE, BNMIT, Bangalore

amithvishwanath007@gmail.com Phone +917795738488

Abstract- A passenger car cabin heats up when parked outside

in hot sun. It causes not only discomfort but also consumes

enough fuel to cool the cabin quickly with conventional car air

cooling system. A green energy solution with solid state

refrigeration to solve this problem has been discussed in this

paper.

Keywords—Thermo electric cooler, Peltier effect, thin film solar

cells, Heating Ventilation and Air Conditioning (HVAC), PV cells

I. INTRODUCTION

In Indian cities, parking space for passenger cars is a

premium. Specially, in crowded business areas, cars are to be

parked wherever space is available. When a car is parked in

open space on a sunny day, the cabin becomes hot due to

trapping of heat inside the cabin (fig -1). It can be avoided

only if the car is parked inside a building or under a covered

parking. When the car needs to be started, lot of discomfort is

felt and lot of fuel gets wasted to cool the cabin. Some of the

problems caused by these heating results in following issues:

Discomfort in handling hot car parts while handling

Vehicle battery begins to degrade

The inside of the vehicle will not be safe to sit in until it is

cooled down by outside air or air conditioning, which will

slowdown the vehicle

Car cabin electronics could be affected

Food or drink in the car loses its freshness

Plastic water bottles in the vehicle will be heated up and

release dangerous chemicals to the stored water

Figure -1 : Heat gets trapped inside a car by radiation

II. SOLUTION TO THE PROBLEM

A. Literature survey

Car cabin cooling system has been considered as an add-on

comfort or a luxury system in the Indian car market context.

As the economic status of the country has improved over past

two decades, several so called ‘luxury’ systems are being

treated as essential systems in the passenger car segment[1].

The economy segment of cars that have hit Indian roads have

smaller cabin space, and generally do not come with any air

cooling system. Generally, Indian summer duration is about

eight to nine months in a year. The day temperatures in the

vast plains of Indian subcontinent reach as high as 45oC.

When the car is left in open spaces, cabin gets heated up. Due

trapping of heat in a cabin, temperature tremendously

increases approaching almost 60 °C.[2]. This will make the

driver and passenger become uncomfortable while entering the

car. Generally car cooling system if found in a car is switched

on till heat inside reduces to comfortable levels. During this

mode of operation, car cooling system takes the hot air inside

the car and cools it. There would be considerable requirement

of fuel for this operation [2][3]. If the air outside the car is

drawn in to vent the hot air forcibly, car cabin cools to a

comfortable level. If the air outside is hot, this mode venting

hot air would not be a better solution.

B. Conventinal solutions

A hot body like the cabin of the car can be cooled by convection. If cooler air from the ambient can be forced into the cabin, hotter air can be vented out. Generally, a driver tends to open all windows of the car for some time after moving the car. During this movement, fresh air comes in to expel the hot trapped air (fig 2). However, it takes some more time before hot seats gets cooled to comfortable levels. This concept can be made into a simple mechanism by adding few vent fans which continue to be operational when the car is parked and all windows closed. The only issue is the power required to drive the fans. Running these fans with the car battery is a ready solution. We can modify the car cabin air cooling system to keep car fans running when the car is parked. This option might look simple, but drains off the car battery soon and might result in starting problem if battery drains too much. Still the venting of hot air will not fully stop the cabin from heating car seats, steering wheels, car doors and roof too. The only way of cooling it would be to keep the car refrigeration system operational. In few premium segment cars, there is a separate air conditioning system driven by a separate engine but that adds up to both the car cost as well as the fuel consumption and it is not a green economy solution. The function of the car air conditioning is shown in figure 3.

Figure 2- A car cooling by convection

III. CAR REFRIGERATION SYSTEM

A. A conventional car refrigeration

Heating Ventilation and Air Conditioning (HVAC) is the

technology for automotive ambient comfort. HVAC works

with power drawn from the car engine to maintain pleasant

climate inside the cabin by controlling cabin temperature.

Now a day’s HVAC is available in most of passenger cars.

The system comprises one or more blower, electronic control

elements, and refrigeration unit coupled with suitable ducts

through which air is transferred to the cabin.

The basic principle behind the operation of cabin temperature

control is the conduction and convection. Heat is transferred

from a low-temperature region to a high-temperature region in

the vehicle [4].

Figure -3 : A conventional refrigeration system

The cold liquid refrigerant, coming out of expansion value and

entering into the evaporator, is at lower temperature and lower

pressure. On passing through the evaporator coils refrigerant

absorbs the heat from the air that is blown through the coils

and gets converted to low temperature, low pressure vapor.

The air blown by the blower over the evaporator in turn gets

cooler and vented into the cabin. The compressor absorbs

vapor refrigerant from the suction line and compresses the

vapors to high superheat vapor, which is passed through the

evaporation valve to get cooled refrigerant. The surer heated

vapor flowing through the condenser pipes, which is hotter

than the ambient, transfers the heat to environment. (fig 30

Such a conventional refrigeration system requires prime

mover to run the compressor. Generally a part of the engine

power is used to drive it. In order to run this system, it is

essential to have engine switched on always. There are several

moving parts in the system. It has to handle high pressure

tubing, liquid refrigerant which have its own limitations

[4][6].

B. A thermo electriic refrigeration

Thermoelectric coolers (TECs), also known as Peltier coolers,

are solid-state heat pumps that utilize the Peltier effect to

move heat. Passing a current though a TEC transfers heat from

one side to the other, typically producing a heat differential of

around 40°C—or as much as 70°C in high-end devices—that

can be used to transfer heat from one place to another.

Figure 4: . Thermoelectric Cooler Peltier Module (two

modules connected in series)

when electric current passed across the junction of two

dissimilar conductors, depending on the direction of the

current, the overall effect could be either heating or cooling.

This effect can be harnessed to transfer heat, creating a heater

or a cooler. TECs are constructed using two dissimilar semi-

conductors, one n-type and the other p-type. The two

semiconductors are positioned thermally in parallel and joined

at one end by a conducting cooling plate (typically of copper

or aluminum). (fig 4)

A voltage is applied to the free ends of two different

conducting materials, resulting in a flow of electricity through

the two semiconductors in series. The flow of DC current

across the junction of the two semi-conductors creates a

temperature difference. As a result of the temperature

difference, Peltier cooling causes heat to be absorbed from the

vicinity of the cooling plate, and to move to the other end of

the device

Figure 5 - A peltier cooler concept

C. A thermoelectric refrigeration unit

The thermoelectric cooling system refrigerates without

refrigerant and without the use of mechanical devices (fig 5) .

The advantages are as follows:

No moving parts and hence little or no maintenance.

No refrigerants, such as potentially harmful CFCs.

Enables reduced low-noise operation of cooling fans,

while providing greater cooling power.

Suitable for manufacture in mass.

Lightweight.

Easy to control by voltage / current

Quick response.

D. A prtotype unit

Figure 6: A prototype cooler fan

A TEC device (TEC1-12706) needs to be sandwiched between

two heat sinks and two CPU fans are to be run to take the

heat away from the heat sink. When power is applied to the

TEC, it produces a differential heat across the device. It takes

away the heat from a hotter environment and transfers to the

hotter end. A fan needs to take the heat away and dissipate

into ambient. Figure 6 shows the scheme of construction of a

heat pump and installation in a car. Figure 7 shows the

typical CPU cooling heat sink and a fan assembly.

Figure -7 : Two CPU fans used as blowers

E. Implementataion scheme for a car

Figure 8- An implementataion scheme for a car cabin cooling

Installation of the car cabin cooling system is shown in figure 8. A micro controller based system needs to be built to set the temperature levels. Usage of the system does not require additional energy, since it works on solar energy harvesting. This system can also be used in addition to the existing car air conditioner during hot day driving

IV. GREEN ENERGY SOLUTION

A. Solar energy harvesting

The car cabin is getting heated due to the solar energy.

Usage of the solar energy itself to cool the cabin would be a

innovative solution. There are two possible ways of

implementing the same.

Usage of solar cells to obtain electrical energy. Use

this energy to run a air conditioning system.

Use solar energy to produce a cooling effect directly:

This requires extensive work in the field of micro

fluidics and these aspects are beyond the scope of this

concept study [7].

Photovoltaic (PV) energy harvesting is a green energy

solution. This being a virtually inexhaustible source of power

with little or no adverse environmental effects, is most suitable

solution. Outdoor PV harvesting solutions have today been

powered by specially tuned amorphous silicon (aSi)

technology. In recent years new PV technologies have come

to the forefront in Energy Harvesting such as Dye Sensitized

Solar Cells. The dyes absorb light much like chlorophyll does

in plants. Electrons released on impact, escape to the layer of

TiO2 and from there diffuse, through the electrolyte. The dye

can be tuned to the visible spectrum and much higher power

can be produced. Photovoltaic solar panels convert solar

radiation (termed “insolation”) into Direct Current (DC)

electricity. When referring to electrical generation, insolation

is described at watts per square meter. Photovoltaic solar

systems typically contain several panels wired together

(termed an array), electrical disconnects, over current

protection (circuit breakers or fuses), inverter, junction box,

and other specialized equipment depending on application.

Now a days low cost, thin film (fig 9) solar panels are

available and these can be pasted on the body of the car. These

films produce enough power to run a air condition system.

Figure 9 : Thin film solar cells for car top

V. CONCLUSION

A concept has been discussed in this paper. A proof of concept

study has been conducted with two CPU cooling fans and a

thermo electric cooler device (TEC1-12706 Thermoelectric

Cooler Peltier Module 12V 92W). The prototype unit was

able to provide sufficiently cool air to demonstrate the

concept. A complete implementation on a car cabin needs to

be taken up.

ACKNOWLEDGMENT

The authors would thank Sri Bhanu Prashanth, HOD, ECE, BNMIT, Bangalore for the support and guidance in carrying out this concept study. We would like to express our sincere thanks to Sri A N Viswanatha Rao, scientist, DRDO for motivating us to take up this interdisciplinary study.

REFERENCES

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