Analysis of the Thermal Comfort in Car
Various scientists and researchers are performing numerous researches on the thermal comfort in the vehicles, which lead to achieve many enhancements in the automotive domains. The thermal comfort is very essential in the vehicles without which may lead to cause several problems to the people using vehicles.
Introduction
Overview
Since the PMV values are not
suitable for describing the discomfort feeling, Predicted Percentage of
Dissatisfied was calculated for the PMV. The thermal indices used in the
assessment of the PMV index and PPD.
This thermal comfort
remains important for the health of the passengers and the vehicles. There were
several developments occur in the vehicles such as automotive glazing upon
thermal comfort, addition of ventilation and air conditioning systems, effects
of heating, and all other factors influencing vehicles. The more focus is
needed on the vehicles in the thermal environment as it had the reason for
improving human’s life. The passengers either driver or people using vehicles
are facing challenges to overcome the heat during the time of hot summer and
cold during the time of winter. They require few adjustments to the environment
inside the vehicles. For the children or kids and the elder people who suffer
from the heart problems are easily viable to the risks inside the vehicles when
the thermal comfort is not present and lack of the air conditioning system can
lead to serious problems (Croitoru C.,et.al, 2015).
Several accidents occurred based
on the environmental imbalance within the vehicles. The thermal environment
inside the vehicle requires appropriate designs and air conditioning systems. Even
in some countries, few regulations are developed for demanding conservation of
the energy and reduction of emissions in the vehicles. The research about the
thermal comfort leads not only for developing good thermal environment but also
enhances the control measures within the thermal environment such as use of air
conditioning systems and reduction in the fuel consumptions (Ružic D., Casnji
F. 2012).
The thermal comfort is defined as
the sensation about the thermal effects within the vehicles that expresses good
satisfaction levels in the environment. The thermal comfort in car is
considered the mandatory factor for designing the thermal environments. The
thermal comfort is a feeling of ease that leads to motivation and good focus in
the physical states with enhancement in the efficiency at work and quality of
life.
In vehicles, temperature and
fresh air always remain to be mandatory. For making the factors air and
temperature to remain in the vehicles, most of the vehicles use the HVAC
systems. Several researches are conducted to optimize the HVAC systems within
the firm. Most of the vehicles at present use basic heating, air conditioning
systems, and ventilation that support meeting the requirement for thermal
comfort of the most occupants. There are some problems hidden, which remain to
be present and need solutions for resolving those problems. It may include
local thermal discomfort, mold, bad air quality, and much more (Rugh, J. P.,
Bharathan, D., 2005).
Most of the drivers and
passengers are feeling discomfort with the thermal imbalance in the vehicles
while riding the vehicles. The thermal environment must be balanced with the
use of appropriate systems to maintain heating as low, ventilation as optimum,
and required air conditioning system to make temperature as low. Though the
vehicles have implemented various systems within the environment to balance the
thermal discomfort, probably certain factors affect the thermal comfort within
the vehicles (Haller G., 2006).
Aim
The key purpose of the study is
to research the basic thermal comfort concepts in car and their impacts over
the people in real time. Though the vehicles utilized various systems within
the environment for balancing the thermal discomfort, probably certain factors
affect the thermal comfort within the vehicles. The study intends to research
about those factors that really affects the thermal atmosphere.
In this study, the factors that influence
the thermal comfort are identified. The thermal comfort in different vehicles such
as car is assumed and how thermal comfort is influenced in the car. The study
covers about the research about the thermal comfort, thermal factors in cars,
thermal models, and the dissimilarities in the assumed vehicle. The study
finally concludes with the discussion and conclusion depicting future research.
Different measures and recommendations are proposed to enhance the thermal
comfort in car by considering the factors affecting the thermal comfort as
determined from predicted mean vote [PMV] with the thermal equation and ASHRAE
seven-point index. The measures to balance the thermal comfort within the cars
by using HVAC systems are described. Though the cars have implemented various
systems within the environment to balance the thermal discomfort, probably
certain factors affect the thermal comfort within the vehicles.
Research Methodology
This study involves the method of
analysis using literature review. By considering the topic about thermal
comfort within the vehicle and all other relevant concepts, the author develops
the paper. During the course of study, the author researches in depth about the
vehicles with relevant topics in internet, books, and articles. Various parameters
that affect the thermal comfort in vehicles are researched from the review of
the research articles and the recommendations to reduce the impacts of these
factors.
The research methodology includes
the following steps for the study:
·
Problem Statement
·
Identification of the parameters
·
Recommendations to improve the system
Problem Statement
For using vehicles for transport,
the environment within the vehicles must have suitable measures for occupants.
The environment inside the vehicles must be favoured to the occupants. If the
environment is not having that suitability for occupants, it will create
irritation and cause discomfort to the occupants. This remains the key problem.
In this case study, the considered vehicle is car, and the factors including
measurable factors and personal factors are identified and analyzed with
inclusion of Predicted Percentage of Dissatisfied [PPD] index and Predicted
Mean Vote [PMV] index.
Identification of the factors
The factors are identified and
categorized into two types as follows:
·
Measurable factors
·
Personal factors
The measurable factors consist of
the factors of air velocity, air temperature, relative humidity, and radiant
temperature. The personal factors consist of the clothing insulation, and the
activity level. These six factors are assumed primary for supporting criteria
to thermal comfort. Apart from this, the Fanger model based upon various heat
balance theories and thermoregulation supports predicting the thermal comfort.
However, PMV will be assumed only during the homogenous conditions and not
applicable for non-homogenous conditions, as they will not give any accurate
outcomes. The PMV values are not enough for discomfort as they lead to
determine the PPD values (Hott M. V. M., et.al, 2009).
Recommendations to improve the system
Recommendations to improve the system
Recommendations are proposed
after analysis about the factors affecting the thermal environment within the
car. These recommendations help to balance the thermal environment of the car
and the range of PMV is determined for the optimum thermal comfort as per
ASHRAE Standards.
Analysis and Results
The study covers the analysis of
the factors influencing the thermal comfort within the vehicles for the people
either driver or passenger travelling inside. Most of the passengers utilize
the car for transport motivation especially from a location to other
irrespective of the long or short drives (Chakroun C., Al-Fazed S, 1997).
However, people either riding or
sitting inside the car feel discomfort if they do not provide with the
appropriate environment. The temperature is one of the key variables that
contribute to thermal discomfort, as the people inside the car may feel hot or
cold that may cause them to irritable mood.
The thermal comfort is expressed
as state of mind for the people that enable the satisfied thermal environment.
In other words, the thermal comfort remains the reflection to the subjective
sensation of the human being toward the thermal surrounding.
The research is lead by
considering the different model and approaches for identifying factors affecting
thermal comfort in cars.
Thermal Factors – Air Temperature, Air Velocity,
human activity, Clothing insulation, Mean radiant temperature, and Relative
Humidity
Other Factors
Fanger’s thermal model
Various factors are identified in
the study, which have serious impacts over the occupants within the car for
thermal discomfort.
Thermal Factors
The thermal factors include the Air
Temperature, Air Velocity, human activity, Clothing insulation, Mean radiant
temperature, and Relative Humidity. These factors are widely affecting the
thermal comfort in the car (Guan Y., et.al, 2003).
Air temperature
The air temperature is one of the
key factors that are expressed as the average temperature of air, which wanders
over the body as per the time and place. The temperature within the vehicles
mostly relies on the season time and location of car. Mostly the air within the
car remains inhomogeneous if it possesses air conditioning system. In the
summer months, the interior air temperature needs to maintain at the range of
23 degree Celsius to 28 degree Celsius. The needs must be well defined for the
temperatures. For the occupants, who are standing and sitting have different
spatial average temperature in their head, ankle, and waist. The air temperature
is very high at the ankle level when compared to the temperature at head level
within the car. The variations in the location lead to cause thermal discomfort
that influences the driver. The air temperature relies on the location of the
cabin space for vehicles (Alahmer A., 2011).
Mean Radiant Temperature
The mean radiant temperature is
one of the key factors that influence the thermal comfort. This temperature
remains the constant temperature of the imaginary enclosure that leads to heat
loss by radiation with the person as in actual space (Shuster, A. A., 1998). The
performance of the radiation metrics and angular factors remains to be the apt
measurement method for the mean radiant temperature. For the surfaces known
with the temperature separating the area of the passenger, then the temperature
that splits the area of the passenger within the vehicle can be considered.
Air Velocity
The air velocity is one of the
key factors that influence the thermal comfort. This air velocity remains the
average velocity of the air that the occupant body exposed within car with
respect to the location and time. The performance of the radiation metrics and
angular factors remains to be the apt measurement method for the mean radiant
temperature (Madsen, T. L., 1986).
The airflow however causes
variations to the air velocity, climatic conditions, and variations in heat
loss. The air velocity relies on several factors in the environment inside the
vehicle such as the airflow, local air velocity, and temperature.
For the surfaces known with the
temperature separating the area of the passenger, then the temperature that
splits the area of the passenger within the vehicle can be considered.
Relative Humidity
The relative humidity is one of
the key factors that are expressed as the ratio of the quantity of water vapour
present in the air to the quantity of water vapour, which is available at a
particular pressure and temperature.
The following table gives the
values for air humidity values in association with that of the temperature of
the inside and the outside environments.
Season
|
Out
Temperature
|
In
Temperature
|
Minimum
humidity in %
|
Maximum
humidity in %
|
Winter
|
< + 20
|
22
|
35
|
70
|
Summer
|
+ 20
|
22
|
N/A
|
70
|
+ 25
|
23
|
N/A
|
65
|
|
+ 30
|
25
|
N/A
|
60
|
|
+ 32
|
26
|
N/A
|
55
|
The relative humidity remains to
be not influencing thermal comfort for the range from 30 % to 70 %. The
relative humidity for the cabin environment produces different effects by changing
the humidity within the environment at the cabin and occupants by distinct
analysis methods and simulation models.
Human Activity
Human Activity is one of the
personal factors that influence the thermal comfort in the car. The human
activity needs energy for doing any activities that in turn leads to create
heat for managing the internal temperature of the body about 36.5 degree
Celsius. When the activities are performed at higher levels, it will lead to
creation of more heat that leads to secrete over sweat thus causing discomfort
to the occupants. If there is no activity, only little heat is produced that
leads the temperature of the skin to fall down and person will feel cold and
uncomfortable too (Musat,R. and Helerea E, 2009).
The activity level has intense
effect upon thermal comfort, thermal sensation, and temperature preferences.
The metabolic rates are varied as per activity of the humans.
For instance, the basic activity
corresponds to the metabolic rates are given as follows:
Lying down: 0.8 met; Seated
Office: 1.2 met; Sitting: 1.0 met; Medium work: 2.0 met; Light work: 1.6 met;
Heavy work: 3.0 met.
Clothing Insulation
The clothing insulation is a key
variable that influences the thermal comfort. The clothing is required for
protecting the human body at different climatic conditions and supports thermal
regulation of the body to manage the temperature of the skin and the
environment. The clothing insulation is measured by the insulating properties
of the cloth and it is mentioned in clo.
For example, the winter outdoor
clothing consists of the thermal insulation range about 2 to 3 clo; normal
indoor clothing has about 1.2 to 1.5 clo; summer indoor clothing has about 0.8
to 1.2 clo; indoor, lightweight clothing has about 0.3 to 0.5 clo.
Other Factors
The other factors, which affect
the thermal comfort, are environmental factors, human organism, clothing, heat
balance, season, climate, age, health, and expectation. For human organism,
other factors influencing the thermal comfort are metabolic rates, activity
types, age, weight, and gender. The other factors of clothing include structure
of the materials, thermal resistance to wear, number of layers, and much more.
Apart from these factors, age, health, climate, season, and expectation remain
as the other factors, which affect the thermal balance and thermal comfort (ZhOU
Q., 2013).
Discussion
The use of the ASHRAE Standard 55
supports defining the thermal comfort and even helps to find the heat balance
equation as follows:
S = M + W + R + C + K
– E – RES [W/m2]
M – rate of metabolic heat
created; S – rate of heat stored; R – rate of heat exchange by radiation; W –
rate of mechanical task completed; K – rate of heat exchange by conduction; C –
rate of heat exchange by convection; RES – rate of heat exchange by respiration;
E – rate of heat exchange by evaporation
RES = Cres + Eres; where Cres –
0.0014 M (34 – ta) ; Eres – 0.0173 M (5.87 – Pa)
Eres – latent heat loss by
evaporation of heat and water vapour; Cres – sensible heat loss by convection
Pa – ambient water vapour pressure [kPa]
ta – ambient air temperature
Thus, from the equation, it is
evident that thermal comfort is affected by the factors as discussed prior.
As per Fanger’s thermal comfort
equation,
F (M, Icl, v, tmrt,
ta, Pa) = 0, where Icl is cloth index, M is the metabolic rate, v is air
velocity (m/s), tmrt is mean radiant temperature, ta is ambient air
temperature, and Pa is ambient water vapour pressure [kPa] (Fanger, P.O., 1970).
For relating all these factors,
Fanger proposed Predicted Mean Value [PMV] with the thermal comfort equation
and ASHRAE seven-point index.
PMV varies from +3 to -3 each
denoting distinct thermal sensation as hot, warm, slightly warm, neutral,
slightly cool, cool, and cold.
ASHRAE comfort
standard
ASHRAE developed the industry
standard for comfort requirements and it is known as the ASHRAE Standard 55
that insists the conditions of the thermal environment for human occupancy. The
main use of this standard is to denote about the distinct mixture of thermal
factors for environment within the space. Most of the comfort zone is
identified by the values of PMV from -0.5 to 0.5 with the metabolic rates from
1.0 met to 1.3 met and cloth insulation is between 0.5 clo and 1.0 clo (ASHRAE,
1992).
Conclusion
The problem in the vehicles exists
regarding the thermal comfort to the occupants. Most of the occupants are not
feeling comfort. It is clear that the thermal comfort of the car is influenced
by various factors. These factors are identified by in-depth research reviews
with the collection of the articles, and relevant journals associated to the
thermal comfort.
From this study, it is clear that
the thermal comfort relies on several factors and these factors really affect
the occupants inside. In order to achieve the thermal comfort within the cars,
the research about the factors and associated models on the thermal comfort is
essential. The study ensures about the research on several factors influencing that
of the thermal comfort and the other factors based on the consideration of the
Predicted Mean Vote.
It is concluded that the thermal
comfort relies on the relative humidity, mean radiant temperature, air
temperature, and air velocity. The other two factors, which possess tendency to
influence the thermal comfort in the car, are clothing insulation and human
activity level. Thus, these six factors are assumed as the important factors
for influencing the thermal comfort.
Apart from these factors, the
other factors may influence these factors irrespective of the time such as
health, gender, sex, age, and much more. Each factor relies on several factors
and these factors determine about the thermal comfort. During the time of design
and development of heating systems, air conditioning systems, and ventilation
systems. The factors affecting the thermal comfort along with the
specifications for each factor and their variations are included. The standard values
of ASHRAE help to develop suitable systems for the car as they result to the
fact about the range of PMV at which the thermal comfort lies. This is very
important metric in development of future measures to the car enhancing thermal
comfort.
Future Works
The future works for maintaining
the thermal comfort include the consideration of the determined factors while
developing the systems such as heating systems, air conditioning systems, and
ventilation systems. The heating system in the car must be implemented in such
a way it must balance the thermal imbalance and provide sufficient heat within
the environment for the occupants to operate. In the same way, the ventilation
systems must be provided with the sufficient airflow to balance the air
velocity and can even support managing the variations in the heat. Similarly,
the air conditioning systems can balance the thermal environment inside the car
by cooling the available occupants and lowers the temperature. However, these
systems create variations in the temperature at distinct levels ranging from
ankle to head levels. While designing and developing such ventilation systems, heating
systems, and air conditioning systems, the factors influencing the thermal
comfort must be considered along with the specifications for each factor and
their variations and the range of PMV and PPD further improves the systems.
Gantt Chart
Activity
|
Week1-Week2
|
Week2-Week3
|
Week3-Week4
|
Week4-Week5
|
Week5-Week6
|
Week6-Week7
|
Week7-Week8
|
Week8-Week9
|
Week9-Week10
|
Selection of Topic
|
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Introduction
|
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Setting the Aims
&
Objectives
|
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Literature Review
|
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Research Methodology
|
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Analysis & Results
|
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Discussion
|
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Conclusion
|
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Future Scope
|
References
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humidity and temperature control on in-cabin thermal comfort state, in, Clemson
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Environmental Conditions for Human Occupancy”, Atlanta, 1992.
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