Task 1: Identify the Decision Situation
1.1 Application Domain
The main objective of this project is to design a solar powered ventilation system for a parked vehicle.
1.2 Description of the System
One of the worst things about parking your vehicle outside on a hot day is coming back to a vehicle
whose internal temperature is upwards of 100 oF. This system would detect the internal temperature of
the vehicle, then it would convert the sun’s rays into electrical energy that would then power a
ventilation system to help flush out the hot air. All of this would be automatic and require no input from
the user. This independent nature of the system makes it an option as an aftermarket product for
existing vehicles. The system would consist of a solar panel, fans, temperature sensors, and a controller.
Figure 1 – Toyota Prius
1.3 Description of the Specific Design Decision
The design decision of the project is to choose the best combination of different components to provide
the most efficient cooling of the air inside of a vehicle, while still maintaining a low cost. We would like
to minimize the size of the exhaust fans and solar panel while maximizing the flow rate of air into and/or
out of the vehicle.
1.4 Authority of Decision Maker
Unfortunately, it is not possible to control all of the design parameters. We do have control on many
parameters like cost, solar panel size, flow rate, and fan size. The parameters that we do not have
control over are ambient temperature, initial temperature inside the vehicle, and heat flux from the sun.
Task 2: Determine an Objectives Hierarchy
For this project, we have chosen the fundamental objective to be to maximize customer satisfaction of
the system. From this starting point, we came up with our fundamental objectives hierarchy and its
supplemental means objectives network. We decided that the customer would be interested in the
aesthetics, cost, usability, and performance of the system. These objectives were then broken down
further. The aesthetics were broken down into visual and audible. We wish to minimize the size of the
system and the noise created by the system. The performance is also broken down into temperature
and time to cool. We wish to minimize the internal temperature of the vehicle and minimize the time
required to reach this temperature.
Maximize Customer
Satisfaction of System
Maximize Aesthetics
Minimize
Size
Solar Panel
Minimize
Noise
Minimize Cost
Minimize Difficulty of
Using System
Minimize
User Input
Fan
Figure 1. Fundamental Objectives Tree
Maximize
Performance
Temperature
Time to Cool
The means objectives are objectives that help achieve the fundamental objectives. They are good for
implementing the fundamental objectives and for identifying solution alternatives.
Maximize Vehicle Enjoyment
Maximize Aesthetics
of Vehicle
Minimize Size
of System
Minimize
Fan Size
Minimize
Noise
Generated
by System
Minimize Cost of
System
Minimize Difficulty of
Using System
Minimize
User Input
Maximize
Performance
Minimize Time
to Cycle Air
Minimize Internal
Vehicle Temperature
Maximize Flow Rate
of Exhaust Fan
Minimize
Solar Panel
Size
Maximize Fan Speed
Maximize Electrical
Power
Maximize Solar
Panel Size
Figure 2. Means Objectives Hierarchy
Maximize Fan Size
After creating and analyzing our objectives hierarchy, we determined that our most important
objectives are:
1) Minimize the size of the system
2) Maximize flow rate
3) Minimize user input
From the aesthetics we decided that the consumer of the system would typically be away from the
parked vehicle and therefore minimizing the size is more important than minimizing the noise as these
are contradictory objectives.
The attributes that we will be focusing on are fan size, solar panel size, flow rate of air, and isolating the
system from the rest of the vehicle. All of these parameters can be modeled with the exception of
isolating the system. We can, however, analyze our system after it is designed to confirm that it does
not depend upon user inputs.
Task 3: Identify the Design Alternatives
For our project, there are many design alternatives to take into consideration.
1) The first thing that we need to consider is the flow rate of the system. This decision will
involve many lower level decisions such as the size, speed, and number of fans as well as
whether there is only an exhaust or an intake and an exhaust.
2) We will need to decide on a temperature threshold. We could have a single temperature
threshold that turns the system on when the temperature is above the threshold and off
when it is below. To prevent the system from constantly switching on and off as the
threshold is crossed we could also have two different temperature thresholds, an on
threshold and an off threshold, that turn the system on and off, respectively. For example,
the system would turn on when the internal temperature of the car reaches 90 degrees
Farhenheit and remain on until the internal temperature reaches 70 degrees Fahrenheit. We
will also have to choose the actual value for the threshold(s). As a more complicated
alternative the desired temperature could be based on the ambient temperature and the
heat flux from the sun. We could then calculate what temperature is possible and attempt
to maintain that temperature.
3) We will also need to decide on the size of the solar panel. The entire size of the system is
dependent upon the size of the fans and the solar panel, but the size of the solar panel is a
critical decision. It is the largest factor in the cost of the system and determines the power
available for the fans.
Task 4: Identify the Structure of the Design Problem
The following table describes the remaining decision elements including chance events and calculated
outcomes.
Name
Heat Flux
Type
Chance Event
Electrical Power
Calculated Outcome
Number of Fans
Ambient Temperature
Decision based on Calculated
Outcome
Decision based on Calculated
Outcome
Decision based on Calculated
Outcome
Chance Event
Internal Temperature
Noise
Calculated Outcome
Calculated Outcome
Size of Fans
Speed of Fans
Description
The amount of heat flux that is received
by the solar panel
The amount of electrical power out of
the solar panel
The number of fans in the system used
to ventilate vehicle
The physical size of the fans, referring to
the diameter
The rotational speed of the fans
The ambient temperature of the air
surrounding the vehicle
The internal temperature of the vehicle
The level of sound generated by the fans
in dB
An influence diagram helps you decompose and organize decisions so that you can determine what
interactions there are in the decision making process. In our influence diagram the fundamental
decisions are size of the solar panel and flow rate of the system. The chance events are the heat flux and
the ambient temperature. Once the flow rate is determined the size, speed, and number of fans need to
be determined simultaneously. These three variables have a correlation that can be related to the flow
rate. Therefore, the three decisions considered as one is a calculated result of flow rate. Our utility in
our influence diagram is our fundamental objective, customer satisfaction.
Size of Solar Panel
Flow Rate
Heat Flux
Electrical Power
Fan Speed
# of Fans
Size of Fans
Ambient
Temperature
Size of System
Noise
Customer
Satisfaction
Figure 3. Influence Diagram
Internal
Temperature
Task 5: Identify the Simulation Scenario for an Energy-Based System Model
5.1 Design Objectives that Require an Energy-Based Model
In order to satisfy our fundamental objective, we will model the following systems:
1)
2)
3)
4)
Transfer of heat to electrical energy through the solar panel
Thermal energy transfer from the sun to the air inside the vehicle
Thermal energy transfer from the ambient air to the air inside the vehicle through the fans
The controller and temperature system that will determine when to turn the system on and
off
5.2 Energy Based Models for HW3
There are two main systems that we will model in Dymola for homework 3. The two systems are:
1) The energy transfer of heat to electrical power by the solar panel
2) The transfer of thermal energy between the sun, the air inside the vehicle, and the ambient
air outside the vehicle
5.3 Physical Phenomena and Energy Domains
1) Heat transfer (radiation, convection, conduction)
2) Electric phenomena (energy transfer)
5.4 Assumptions
Assumptions can be made to simplify our model and make it relative within the scope of this project.
The most significant assumptions are:
1) Constant heat flux applied to the solar panel
2) Uniform temperature distribution within the vehicle
3) Constant ambient temperature
Task 6: Assess the Plan
As the project stands, we currently have one uncertainty. None of the group members have any
experience with solar panels; therefore, we are unsure if we will be able to easily model the transfer of
sunlight to electrical energy. Our assumption of a constant heat flux from the sun should make the
model relatively simple, but if the system becomes too complex, we could substitute the solar panel
with a battery.
Task 7: Learning Objectives
Andrew Byrley
I am currently studying towards my Masters with a focus on automation and robotics. My career goal is
to design robots and machines for defense applications. I never received much experience in the design
process in my undergraduate career, so I am thankful for this class to help me get that exposure. Also, I
am very excited to learn a new programming language and computer program in Modelica and Dymola.
David Creasy
This semester I am finishing my Masters Degree with a focus on design. I enjoy the challenge of design
problems and the opportunity to creatively solve them. From this course I hope to improve my
understanding of modeling a system and add Dymola to the tools available to me. In the past I have
modeled systems in a much more rudimentary way and hope to be able to solve more complex
problems more efficiently.