Architecture 418
Designing with Natural Forces
Spring 2014
Peter Simmonds
Course Title:
Designing with Natural Forces 418
"Investigation of how natural forces affect Architecture and Natural Ventilation of spaces
to provide ventilation and occupant comfort."
Course:
When:
Where:
Instructor:
ARCH 418
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Peter Simmonds
Course Description:
The phenomenon of natural ventilation is quite often misunderstood. It is not simply a way of orientating
the building in the correct direction or having openings in the façade that will facilitate air movement
through a space. This course will examine the physical factors in design through a series of lectures and
design Charrettes. In this process the students will learn the various ecological factors that can impact the
environment such as:
 Topography and the site
 Sun exposure
 Wind dynamics
 Aero Physics
 Wind Driven Ventilation
 Buoyancy Driven Ventilation
 Stack Ventilation in High Rise Buildings
 Adaptive Comfort for Occupants

The course will be broken down into two sections, with the following subsections:
Part One- Natural ventilation
a. Introduction to terminologies and analytical tools through readings from reader
b. Introduction to available computer tools
c. Introduction to adaptive comfort for naturally ventilated spaces.
d. Analysis of wind driven ventilation
e. Analysis of buoyancy driven ventilation
f. Stack ventilation in High Rise Buildings
g. Discussions of practical applications
Part Two- Adaptive Comfort
a. Introduction to Adaptive Comfort
b. Analysis of comfort criteria
c. Mean Monthly and Running Mean Temperatures
d. Practical examples of adaptive comfort compliance
e. Midterm Exams (2x)
f. Homework
g. Final Exam
In its simplest form, natural ventilation is as simple as opening a window or door; it permits some form of
air exchange with the outdoors. At the other end of the spectrum, natural ventilation implies an engineered
balance of driving forces and pressure losses to move air through a building at predictable minimum flow
rates, to provide adequate ventilation for air quality, for thermal comfort and to manage heat loads.
Humans have a long history with natural ventilation. It has been used to ventilate all-types of buildings
from hospitals, schools and homes, to electrical sub-stations and industrial facilities.
Natural ventilation requires the management of the two principal driving forces: the buoyancy force
associated with a temperature difference and the kinetic force associated with wind movement. In each
case, pressure differences are set up between the indoor and outdoor environment, which drives the airflow.
The restraint on natural ventilation is associated with pressure losses as air moves through openings
(expansion and contraction of flow area), turns corners and passes through screens or filters.
Some buildings are difficult to ventilate naturally in a “managed” way. Very tall buildings can be difficult
to ventilate naturally because the combination of wind and stack effect pressures can lead to adverse flow
directions — people in one location receiving the stale air from those in another. Wind pressures can also
Course Syllabus
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Architecture 418
Designing with Natural Forces
Spring 2014
Peter Simmonds
lead to uncomfortable conditions. It is possible to naturally ventilate super-tall buildings but this feature
must be designed-in from the beginning. Some jurisdictions (e.g. Chicago) require that all residences have
operable windows, even though in some cases, these windows are not useful to the occupant.
In general, natural ventilation works best when the outside air temperatures are just below what would
generally be considered comfortable indoor conditions. However, the outdoor temperature that will lead to
acceptable indoor temperatures depends greatly on the internal heat loads (from human occupants,
equipment, lights, solar gain, etc.) and the flow rate that can be achieved.
The American Society of Heating, Ventilating and Air Conditioning Engineers (ASHRAE) Standard 55
(2010) has a discussion on thermal comfort that includes a chart highlighting the acceptable indoor
temperatures in naturally ventilated buildings. The key is that occupants must be given some measure of
control over their environment.
Design of natural ventilation in a complex building, or where natural ventilation is the only form of
ventilation, can involve intuitive experience as well as hard science. In each case, the form of the building
will be important and various features of the building’s architecture can enhance natural ventilation or work
against it.
Designing natural ventilation is the art of balancing driving forces and pressure losses to achieve a desired
minimum air flow rate. The required minimum flow rate need not be constant. In general there are three
different criteria for identifying the minimum flow rate:
a. The human biological requirement established in codes and by organizations (e.g.
ASHRAE, NBCC, CIBSE) and sometimes simply referred to as 20 cfm/person
(10L/s/person);
b. The flow required to maintain human or equipment temperature limits. ASHRAE 55
suggests that acceptable temperatures range from 17º to 31º C depending on the outdoor
temperature;
c. The flow to maintain contaminants (e.g. carbon dioxide concentrations) at a maximum
allowable limit.
Various tools are available to assess natural ventilation and the use of one tool over another depends on the
driving forces and critical nature of the flow.
Stack effect
Stack effect is a phenomenon present in all vertical shafts that are at different temperatures from outdoors.
This includes chimneys and buildings. A building’s shafts include the vertical HVAC risers, elevator and
stairwell shafts. The temperature difference sets up a scenario where there is a density difference indoors to
out.
This pressure difference provides a driving force for air movement. If there are openings in the building
façade (even if they are very small cracks) then there will be air flow in at the bottom and out at the top for
a heating-climate scenario.
Stack effect flows in shorter buildings and chimneys (e.g. 5 story’s) are a few Pascal’s (PSI), compared to
wind pressures which can be measured in 10s of Pascal’s (PSI). Hence it is possible for a slight wind to
overwhelm the natural stack effect. A robust design of natural ventilation in a building that uses stack effect
as a driving force will be configured so that at worst the wind effects will be benign and if possible they
will assist. It is important that all wind conditions and directions be considered because the “prevailing”
wind is not always one that exists more than 50% of the time.
This course will cover both residential and commercial buildings and will also discuss the application of
natural ventilation and occupant comfort for different climates, such as hot and humid climate for example.
Vasari will also be used to evaluate ambient conditions on the buildings.
You will be graded on attendance and participation in the following three areas:
Classroom Discussion /Team presentation
10%
Assignments
20%
Midterm Papers (2x)
40%
Final exam & Quizzes
30%
Total
100%
Course Syllabus
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Architecture 418
Designing with Natural Forces
Spring 2014
Peter Simmonds
Assignments
There will be two assignments to evaluate the potential of natural ventilation and ad. these will be returned
and discussed in class with solutions.
A final grade shall be awarded using the following guidelines:
1. General rule:
A. Excellent ~ weighted average ≥ 90%
B. Superior ~ weighted average ≥ 80% but less than 90%
C. Medium ~ weighted average ≥ 70% but less than 80%
D. Inferior ~ weighted average ≥ 60% but less than 70%
F. Failure ~ weighted average less than 60% (Note: This is a firm cut-off average, not subject to the
exception identified hereafter!)
2. Exception: The instructor reserves the right to adjust the low end weighted average cut-off score based
upon the statistical distribution of the semester averages for A, B, or C final grades. For instance, if there is
a large gap in the weighted averages at 88%, then the instructor may decide to award an A grade to all
students above that value. This is done at the instructor’s discretion and in no way should be constructed to
mean that it will be done each and every semester. If a student wishes to earn a particular final grade then
the student should on earning the minimum weighted averages described in the general rule.
EXTRA-CREDITS: There will be extra credit problems, assignments or participations. These extra
problems or assignment to help those students who feel that there is a need to improve their grade by
performing some extra work.
QUALITY: All deliverables shall be graded for quality and content, 60% and 40% respectively. See the
instructor’s memorandum: Quality Standards for Deliverables. Sloppy, illegible, disorganized deliverables
are not acceptable for engineer work and shall negatively impact your course grade.
STATEMENT FOR STUDENTS WITH DISABILITIES
Any student requesting academic accommodations based on a disability is required to register with
Disability Services and Programs (DSP) each semester. A letter of verification for approved
accommodations can be obtained from DSP. Please be sure the letter is delivered to me (or to TA) as early
in the semester as possible. DSP is located in STU 301 and is open 8:30 a.m.–5:00 p.m., Monday\ through
Friday. The phone number for DSP is (213) 740-0776.
STATEMENT ON ACADEMIC INTEGRITY
USC seeks to maintain an optimal learning environment. General principles of academic honesty include
the concept of respect for the intellectual property of others, the expectation that individual work will be
submitted unless otherwise allowed by an instructor, and the obligations both to protect one’s own
academic work from misuse by others as well as to avoid using another’s work as one’s own. All students
are expected to understand and abide by these principles. Scampus, the Student Guidebook, contains the
Student Conduct Code in Section 11.00, while the recommended sanctions are located in Appendix A:
http://www.usc.edu/dept/publications/SCAMPUS/gov/. Students will be referred to the Office of Student
Judicial Affairs and Community Standards for further review, should there be any suspicion of academic
dishonesty. The Review process can be found at: http://www.usc.edu/student-affairs/SJACS/.
Required reading:
USC Natural Ventilation Guidelines (produced from 418 in 2012)
Mechanical and Electrical Systems, by Grondzik, Kwok, Stein and Reynolds,
CIBSE, Natural Ventilation Design Guide.
AIVC Design Guide
ASHRAE Standard 55, 2013
Course Syllabus
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Architecture 418
Designing with Natural Forces
Spring 2014
Peter Simmonds
Proposed schedule of classes
Week 1
Introduction
Week 2
Discussion on AIVC and CIBSE Methods
Week 3
Student Self-study- Comparison of different methods
Week 4
Buoyancy Driven Ventilation
Week 5
introduction to COMFEN
Week 6
Analysis using COMFEN
Week 7
Wind Driven Ventilation study with Vasari
Week 8
Wind Driven Ventilation study using COMFEN
Week 9
Neutral plane
Week 10
spring Break
Week 11
Introduction to Adaptive Comfort
Week 12
Practical Examples 1
Week 13
Practical Examples 2
Week 14
Stack Ventilation in High Rise Buildings
Week 15
design guide revue
Week 16
final review of design guide
References:
[1] J.W. Axley, S.J. Emmerich, A method to assess the suitability of a climate for natural ventilation of
commercial buildings, in: Proceedings of the Indoor Air, 2002.
[2] J.W. Axley, Application of Natural Ventilation for U.S. Commercial Buildings – Climate Suitability,
Design Strategies & Methods, and Modeling Studies. GCR- 01-820, National Institute of Standards and
Technology, 2001.
[3] S.J. Emmerich, W.S. Dols, J.W. Axley, Natural Ventilation Review and Plan for Design and Analysis
Tools. NISTIR 6781, National Institute of Standards and Technology, 2001.
[4] ASHRAE Standard 55-2004, Thermal Environmental Conditions for Human Occupancy, Am. Soc. of
Heating Refrigerating and Air-conditioning Engineers, 2004.
[5] ASHRAE, ASHRAE Handbook – Fundamentals, ASHRAE, 2009.
[6] R.J. de Dear, G.S. Brager, Developing an adaptive model of thermal comfort and preference, ASHRAE
Transactions 104 (Part 1A) (1998).
[7] G.J. Levermore, A.M. Jones, A.J. Wright, Simulation of a naturally ventilated building at different
locations, ASHRAE Transactions 106 (Part 2) (2000).
[8] ASHRAE, Standard 62.1-2010, Ventilation for Acceptable Indoor Air Quality, ASHRAE, 2010.
[9] ASHRAE, Indoor Air Quality Guide – Best Practices for Design, Construction, and Commissioning,
ASHRAE, 2009.
[10] J. Axley, S.J. Emmerich, G. Walton, W.S. Dols, An Approach to the Design of Natural and Hybrid
Ventilation Systems for Cooling Buildings (2002) Indoor Air Proceedings, in: 9th International Conference
on Indoor Air Quality and Climate, 2002.
[11] G.S. Brager, R.J. de Dear, Thermal adaptation in the built environment: a literature review, Energy and
Buildings 27 (1) (1998) 83–96.
[12] J.F. Nicol, M.A. Humphreys, Adaptive thermal comfort and sustainable thermal standards for
buildings, Energy and Buildings 34 (6) (2002) 563–572.
[13] J.F. Nicol, M.A. Humphreys, Derivation of the adaptive equations for thermal comfort in free-running
buildings in European Standard EN15251, Energy and Buildings 45 (1) (2010) 11–17.
Course Syllabus
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