Autodesk Sustainable Design Curriculum
Lesson Four: Modeling Human Comfort
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Thermal Comfort and Thermal Discomfort
Modeling Thermal Comfort with Psychrometric Charts
Visual Comfort
Acoustic Comfort for Sustainable Design
© 2009 Autodesk
Human Comfort
Once the placement, layout, and massing for the project have been studied, the next step in
sustainable design is to analyze human comfort needs, and how this can be optimized through
natural daylighting, heating, cooling, and ventilation strategies.
Designing buildings with careful attention to human comfort parameters can contribute
significantly to a carbon-neutral solution.
This lesson provides a transition from the analysis of generalized siting, orientation, massing,
and layout concerns, to a study of the shell components of a building, its exterior walls,
fenestration, and roof.
Just as general conceptual design decisions are made with respect to the local climate, each of
the specific shell elements contributes to the interior climate of the building.
As you choose between individual windows or a type of curtain wall, your decisions directly
affect human comfort levels within the building.
Once the basic concepts and measures of human comfort (thermal, visual, and acoustic) are
understood, designing for these factors can be addressed.
© 2009 Autodesk
Human Comfort and the Physical Properties of Building Materials
BIM and its three-dimensional modeling capabilities also enable modeling of the physical
properties of the materials used to construct frames, surfaces, enclosures, and envelopes.
By knowing the surface areas, volumes, densities, and masses of the walls, floors, and ceilings
that define the building’s interior spaces and exterior envelopes, designers can perform a
variety of very powerful analyses that can help them achieve the goals of sustainable design.
These analyses rely on the application of scientific models of the behavior of construction
materials, enclosed air spaces, HVAC systems, and mechanical, electrical, and plumbing (MEP)
systems.
Designers and engineers create mathematical models, computer simulations, and practical rules
of thumb by measuring the thermal behavior of building materials in laboratory settings and by
taking measurements in existing buildings.
Properties such as thermal mass, conductivity, and specific heat capacity of the building
envelope all have an impact on how much and how fast heat is transferred into and out of a
building.
© 2009 Autodesk
Modeling Human Comfort
BIM tools and methodologies enable designers to accurately integrate the many different ways
of modeling building spaces, materials, and systems with a variety of models.
These models come from the fields of human physiology, psychology, health, and well-being and
are used to describe the human experience of indoor environmental quality. Central to this level
of analysis is the notion of human comfort.
Understanding human comfort in the built environment begins with an understanding of
clothing. Clothing protects the body from exposure to sun, wind, precipitation, and extremes in
temperature. The phenomenon of biological homeostasis demands that clothing be adjustable
depending on changes in physical metabolism and external climate.
Architecture extends the range of situations where people do not need to rely on significant
changes to their clothing or metabolic activity in order to remain comfortable.
© 2009 Autodesk
Modeling Human Comfort
Human physical comfort is contextual.
It depends on what you are doing; for example, whether you are exercising or sitting and reading.
This context of activity is temporal. How long will you be sitting and reading before you decide to
get up and walk around?
Designing for comfort takes into account the transitions that people experience in their minds and
bodies as they move from one state to another and from one place to another.
Humans are both conscious and unconscious of their physiological responses to the environment,
and scientists continue to attempt to model these responses in terms of comfort, discomfort,
acclimatization, and adaptation of the various senses: somatic (including temperature and
pressure), vision, hearing, smell, and taste.
Key components of human physiological responses to the environment include:
• Thermoregulation
• Water balance and excretion
• Locomotion
• Changes in nutrition
• Energy metabolic rates, body weight regulation, and gas exchange
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Thermal Comfort
Because of the wide range of physiological and psychological responses people have to their
environment, there is no one definition of thermal comfort that fits everyone.
However, organizations such as ASHRAE (American Society of Heating, Refrigerating, and Air
Conditioning) have collected extensive data on comfort. This data has been used to develop
statistical definitions of the indoor conditions that will be comfortable by a specified percentage
of occupants of the space.
The purpose of ASHRAE Standard 55, Thermal Environmental Conditions for Human Occupancy,
is “to specify the combinations of indoor space environment and personal factors that will
produce thermal environmental conditions acceptable to 80% or more of the occupants within a
space” (ASHRAE 1992). According to ASHRAE Standard 55, there are six primary factors that
affect thermal comfort. Two of these factors are personal:
• Metabolic rate
• Clothing insulation
And the remaining four factors are environmental:
• Air temperature
• Radiant temperature
• Air speed
• Humidity
© 2009 Autodesk
Thermal Discomfort
People employ adaptive strategies to cope with their thermal environment; for example, adding
or removing clothing, unconsciously changing posture, choosing heating, moving to cooler
locations away from heat sources, and so on.
Problems arise when this choice to remove a jacket, or move away from heat source, is not
available and people can no longer adapt.
Local thermal discomfort can be caused by:
• Draft, for example, air speed > 0.15m/s (0.492 ft/s at an air temperature of 20°C/68°F, or
>0.1m/s (0.328 ft/s) if on the back of the neck).
• Asymmetrical thermal radiation (front to back or head to foot).
• Vertical air temperature differences.
Because thermal comfort is psychological, it may affect a person’s overall morale. Low levels of
thermal comfort can lead to increases in employee complaints, falling levels of productivity, and, in
some cases, refusal to work in a particular environment.
Some aspects of the thermal environment, such as air temperature, radiant heat, humidity, and air
movement, may also contribute to the symptoms of Sick Building Syndrome.
© 2009 Autodesk
Thermal Comfort
Thermal comfort is contextual. It depends on what you are doing, for example, whether you are
exercising or sitting and reading. This context of activity is temporal. How long will you be
sitting and reading before you decide to get up and walk around?
Designing for human comfort takes into account the transitions that people experience in their
minds and bodies as they move from one state to another and from one place to another.
Humans are both conscious and unconscious of their physiological responses to the
environment, and scientists continue to attempt to model these responses in terms of comfort,
discomfort, acclimatization, and adaptation of the various senses: somatic (including
temperature and pressure), vision, hearing, smell, and taste.
Because human comfort is subjective, it can be difficult to define scientifically. This challenge has
prompted researchers to explore the full range of human discomfort.
Key components of human physiological responses to the environment include:
• Thermoregulation
• Water balance and excretion
• Locomotion
• Changes in nutrition
• Energy metabolic rates, body weight regulation, and gas exchange
© 2009 Autodesk
Thermal Comfort
Metabolism and Energy Production in the Human Body
Energy production in the human body takes place continuously through the metabolic processes
that oxidize food into energy. This energy is partly converted into external mechanical work,
while the rest is released as internal body heat.
According to the ASHRAE Fundamentals Handbook, the typical heat output of a human male
body ranges from 70 watts of heat output during the sleeping state to 115 watts in a seated and
awake state, to 440 watts during heavy work, up to approximately 585 watts when engaged in
athletics.
The heat generated is transported from the warm body core to the body surface partly by
conduction through the tissues and partly by blood flow to the skin.
For a seated person at 20°C/68°F, most heat is emitted as sensible heat (approximately 78%)
and 22% as latent heat. For heavy work, a smaller ratio of sensible heat is emitted
(approximately 40%), and a greater portion is latent heat (approximately 60%).
© 2009 Autodesk
Thermal Comfort
Clothing
The surface temperature of the body is affected by the amount of heat transferred from the
body core, the heat losses from the body, and also by the insulation value of the clothing.
The thermal resistance of clothing is given by the clo-value. This is a measure of the ratio of
thermal resistance of clothing to a standard 0.155 m2K/W, representative of a business suit.
Temperature and Heat: Sensible Heat versus Latent heat
Comfort is a function of temperature and heat, but temperature and heat are not the same
things.
Sensible heat is heat transported by a body that has a temperature higher than its
surroundings. You can measure it with a thermometer.
Latent heat is the heat required to cause a change of state, most often in the case of
water molecules evaporating to become water vapor. It cannot be measured with a
thermometer.
Units for metabolic heat output are often given in met, where 1 met = 58 W/m2 (ASHRAE
Fundamentals Handbook). The appropriate area is the surface area of the body (approximately
1.9m2 for an adult male and 1.6 m2 for an adult female).[
© 2009 Autodesk
Thermal Comfort
Temperature Definitions
Inside air temperature (qa):
• This is the volume averaged air temperature in the room.
Mean surface temperature (qs):
• The mean surface temperature is the area-weighted average temperature of the internal
surfaces of the room.
Mean radiant temperature (qmrt)
• This is a function of areas, shapes, and surface temperatures as viewed from a specific
point in the room; it varies according to view factors between the object and room
surfaces.
• It is equal to the mean surface temperature at the center of a cubical room in which all
surfaces have the same emissivity. It is often used as a good approximation for other room
shapes.
© 2009 Autodesk
Thermal Comfort
Thermal Indices for Comfort
Thermal indices are used to express comfort in terms of a simple number.
They are useful for designing and assessing the performance of heating systems.
• Air temperature: This is sometimes used but is a poor measure when used in isolation.
• Dry resultant temperature: (qres) is often used as an indicator of thermal comfort. This
index does not take into account humidity.
• Operative temperature: It is equal to the temperature at which a specified hypothetical
environment would support the same heat loss from an unclothed, reclining human body
as the actual environment.
ISO 7730 (1993) recommends light, mainly sedentary activity during winter conditions
(heating period) that the operative temperature should be between 20 and 24°C (that is,
22± 2°C).
For summer conditions (cooling period), the operative temperature should be between 23
and 26°C (that is, 24.5 ±1.5°C).
Operative temperature:
© 2009 Autodesk
Thermal Comfort
Thermal Indices for Comfort
Predicted Mean Vote (PMV)
The Predicted Mean Vote (PMV) is a model developed by ASHRAE that uses a steady-state heat
balance equation to relate six key factors for thermal comfort to the average response of a
survey on indoor thermal comfort. People are asked to “vote” on how comfortable the indoor
environment in question feels to them in terms of thermal comfort, using the following seven
point scale.
• +3 hot
• +2
• +1 slightly warm
• 0 neutral
• -1 slightly cool
• -2 cool
• -3 cold
Predicted Percentage Dissatisfied (PPD)
PPD is the predicted percentage of dissatisfied people at each PMV. As the PMV changes away
from zero in either the positive or negative direction, PPD increases. Unlike PMV, which gives
the average response of a large group of people, PPD is indicative of the range of individual
responses.
© 2009 Autodesk
Thermal Comfort
University of California at Berkeley (UCB) Thermal Comfort Model
The Advanced Thermal Comfort Model was originally developed by the Building Sciences Group
at the University of California at Berkeley for the evaluation of human comfort in automobiles.
Using this model, you can analyze human thermoregulation and comfort responses in nonuniform, transient conditions.
You can also use the model to evaluate the effects of solar gain through windows by calculating
how much radiation is hitting the body and where.
Based on the description of the environment, the model can generate graphic results such as
skin temperature distributions, equivalent homogenous temperatures, and overall comfort
indices.
The UCB Thermal Comfort model integrates
information about:
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Air temperature
Relative humidity
Air movement
Mean radiant temperature
16 body segments
4 layers (core, muscle, fat, and skin)
Transient blood flow
© 2009 Autodesk
The UCB Model also integrates information about
Heat loss by:
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Evaporation (sweat)
Convection
Radiation
Conduction
Clothing model
(including heat and moisture transfer)
Thermal Comfort
Adaptive Comfort
Adaptive Comfort expands on the PMV-PPD model of predicting comfort.
Studies have shown that people’s responses to thermal comfort depend on the outdoor climate
and are different in buildings with central HVAC systems because of other factors such as
people’s expectations, and personal thermal control. (ASHRAE Standard 55).
Research conducted at UC Berkeley concluded that occupants of buildings with centralized HVAC
systems become adapted to a narrow range of temperatures that they define as comfortable.
In contrast, occupants of naturally ventilated buildings not only become more tolerant of a
wider range of temperatures, but they actually seem to prefer the greater range.
© 2009 Autodesk
Thermal Comfort
Modeling Thermal Comfort with Psychrometric Charts
A psychrometric chart is a graph of the physical properties of moist air at a constant pressure.
Understanding psychrometric charts helps in the visualization of environmental control
concepts such as why heated air can hold more moisture, and conversely, how permitting
moist air to cool results in condensation.
A psychrometric chart contains substantial information packed into an odd-shaped graph.
The thermophysical properties found on most psychrometric charts are:
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Dry-bulb air temperature
Wet-bulb temperature
Dew point temperature
Relative humidity
Specific enthalpy
Dry-Bulb
Temperature
© 2009 Autodesk
Wet-Bulb
Temperature
Absolute Humidity
Relative Humidity
Thermal Comfort
Modeling Thermal Comfort with Psychrometric Charts
Psychrometric charts are
particularly useful
because once you know
any three independent
properties of moist air,
one of which is pressure,
you can automatically
determine all of the
other properties on the
chart.
An understanding of the
shape and use of the
psychrometric chart can
help you quickly diagnose
a variety of air
temperature and
humidity problems.
Annual Psychrometric Chart for Vancouver, BC, showing how the normal range of comfort (in yellow) can be extended by a variety of heating, cooling, and
ventilation techniques, Autodesk Ecotect Weather Tool software
© 2009 Autodesk
Human Comfort – An ASHRAE View
ASHRAE Comfort Range
Season
Temperature (deg F)
Relative Humidity (%)
Winter
68 - 76
25 - 80
Summer
74 - 81
20 - 80
ASHRAE Std 55 defines
comfort in
terms of a psychrometric chart
Human Comfort as Represented on a Psychrometric Chart
HOWEVER…adaptive comfort, stretches these bounds and evidence shows that people
actually prefer wider comfort ranges IF they have natural ventilation, control of
windows, ceiling fans, and so on.
© 2009 Autodesk
Air Movement and Temperature
In English, this graph
demonstrates that with
an air movement of
about 150 fpm (1.7
mph), a person will
experience the same
level of comfort with the
air temperature 3-5F
higher than a space
without air movement.
Steepest curve: radiant
surface temperatures are
18F less than air temp.
Flattest curve: radiant
surface temperatures are
18F greater than air.
Source: ASHRAE Standard 55
© 2009 Autodesk
Visual Comfort
Visual comfort calculations are inherently difficult to perform because they depend not only on
the locations and brightness of light sources, but also on the apparent size (that is, solid angle)
of the light sources as seen from a particular viewpoint.
Although there are several different visual comfort metrics in current use around the world,
there is general agreement on the factors that contribute to uncomfortable levels of glare.
In general, these factors are
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the directions of the light sources,
the solid angles of the light sources,
the average luminance of the light sources, and
the background luminance for a particular viewpoint.
Other criteria of visual comfort include:
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Uniform illumination
Optimal luminance
Adequate contrast conditions
Absence of stroboscopic effect or intermittent light
Correct colors
© 2009 Autodesk
Visual Comfort
Color
The color of light that you select can greatly
influence color contrasts. For that reason, the
quality of illumination depends on the color of
the light you choose for an application.
As a result, when selecting light color, you
must carefully consider the tasks that the
building’s occupants will perform.
If the color is close to white, the rendition of
color and the diffusion of light are better.
As light approaches the red end of the
spectrum, color reproduction worsens,
although the environment also starts to
appear warmer and more inviting.
The color appearance of illumination also
depends on the level of luminous intensity.
Each color temperature is associated with a
different form of illumination. The perception
of satisfaction with the illumination of a given
environment depends on this color
temperature.
© 2009 Autodesk
Kruithof curve, relating the illuminance and color temperature of
visually-pleasing light sources,
Kruithof defined, through empirical observations,
a diagram of well-being for different levels of
illumination and color temperatures in a given
environment. In this way, he demonstrated that it
is possible to feel comfortable in certain low-light
environments as long as the color temperature is
also low. An example of this relationship is a
single candle with a color temperature of 1,750 K.
Visual Comfort
Color: Scotopic Lighting
Lighting research suggests that the human eye
perceives cooler temperature lighting (lamps
rated at 5000 K or greater) to be brighter than
standard warmer temperature lamps (3500 K
or less). The lamps containing more blue in the
spectrum (5000 K or greater) will be more
visually efficient than lamps with less scotopic
content (white light with a higher bluish
content) even if they have the same lumen and
efficacy values.
The use of scotopically enhanced lighting can
therefore be used at lower energy levels while
maintaining equal visual effectiveness.
Scotopically enhanced lamps have an energy
savings potential of 17-24% compared to 835
lamps (lamps with a Color Rendition Index of
85%, and a color of 3500K) and 22-30%
compared to 735 lamps (lamps with a Color
Rendition Index of 78%, and a color of 3500K).
© 2009 Autodesk
Kruithof curve, relating the illuminance and color temperature of
visually-pleasing light sources,
An additional advantage of utilizing 5000 K lamps
is the integration of the lamp color with natural
daylight. Daylight, in general, is cool in color
temperature, which gives it a bluish-white
appearance. Noontime sunlight has a color
temperature of approximately 5000 K, this
compares to incandescent lighting at 2800 K,
warm fluorescent at 3000 K, and cool fluorescent
at 4100 K.
Visual Comfort
BIM tools can be leveraged to enable a designer to experiment with and consider the
following aspects of Visual Comfort in their design:
• Experiment with a variety of building massing models and layouts in a variety of
orientations to discover how they affect the penetration of daylight.
• Experiment with a variety of reflective devices, including light shelves.
• Experiment with a variety of wall and ceiling treatments (exposed materials, colors,
shades and tints of paint, tiles, and other surface treatments), and also consider the
psychological impacts of color.
Consider different glazings with varying visible light transmittances and tints.
© 2009 Autodesk
Acoustic Comfort for Sustainable Design
Acoustics is the science that studies the ability to
hear sounds and to accurately interpret their
meanings.
Acoustical engineering and design is applied
acoustics, and it is concerned with the creation of
measures to control the experience of sound,
noise, and vibration.
Architectural acoustics and environmental
acoustics are specific subdisciplines that focus on
controlling these phenomena in indoor and
outdoor environments.
Because of the amazing sensitivity of the human
ear, and the fact that the power in a sound wave is
proportional to the square of the sound pressure
level, the ratio of the maximum power to the
minimum power is incredibly large, above one
trillion. To deal with such a large range, logarithmic
units are useful: the log of a trillion is 12, so this
ratio represents a difference of 120 dB.
© 2009 Autodesk
“Sound pressure level isophones” , from
Acoustics/Fundamentals of Psychoacoustics,
“The perception of sound” from
Acoustics/Fundamentals of Psychoacoustics,
Acoustic Comfort for Sustainable Design
Acoustic comfort has been recognized as
an important criterion of sustainable
design, especially because of the
efficiency and productivity gains that
come with a workplace that is considered
free of noise pollution.
Of central concern to all acoustical
domains is the phenomenon of noise,
which is any sound that is perceived to
interfere with the desired experience of
the listener.
The experience of noise is dependent
largely upon social context and the
subjective psychological state and
preferences of the human listener.
© 2009 Autodesk
The practice of sustainable design requires that
acoustic phenomena be taken into consideration
from the perspective of safety and comfort.
The sound and vibration of surrounding vehicle
traffic, indoor and outdoor machinery, human
foot traffic, door openings and closings, office
equipment, human voices, and recorded music
systems all need to be factored into the design of
the built environment.
Sound, noise, and vibration can reach unsafe
levels of exposure, where human hearing can be
damaged, physiological functions can be
disrupted, and the psychological state of wellbeing can be disturbed.
Acoustic Comfort for Sustainable Design
Designs that can effectively mitigate outdoor noise pollution can range from the
adjustment of aircraft flight paths and highway traffic patterns, to the design and
construction of highway sound barriers in the form of walls, earth berms, and plantings of
sound-absorbing species of trees and shrubs.
© 2009 Autodesk
Highway noise abatement wall in the Netherlands, photo by Michiel1972 (Michiel Gebruiker),
Wikimedia Commons, Creative Commons Attribution ShareAlike 3.0 License,
http://creativecommons.org/licenses/by-sa/3.0/
Acoustic Comfort for Sustainable Design
The mitigation of acoustical problems arising from the interior design of a building presents
a more complex set of challenges.
Three basic acoustical properties of indoor environments determine in large measure
whether a room will function properly:
• The attenuation of sound propagating between the room and adjoining spaces
• The background noise level in the room due to air-handling, plumbing, and mechanical
systems
• The reverberation of sounds within the room
(Quirouette, R.L. and Warnock, A.C.C., Basics of noise control. From the seminar series Building Science Insight 1985, Noise Control in Buildings,
Institute for Research in Construction, National Research Council of Canada, NRCC 27844, pp. 3 – 11. http://www.nrc.ca/irc/bsi/85-1_E.html)
© 2009 Autodesk
Acoustic Comfort for Sustainable Design
Acoustic comfort needs to be considered in any space where:
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Speech intelligibility is important (classroom, courtroom, boardroom).
There is a PA system (airport, gymnasium, public building).
Speech privacy is important (open office, call centers).
Confidentiality is important (doctor's/counselor's office, HR, attorney's office, police
facility, and so on).
Music is important (performance space, concert hall, recording studio).
Both speech and music are important (worship center, ballroom, theater, multi-purpose
room).
A quiet atmosphere is important (library, museum, healthcare facility).
Noise buildup can be problematic (restaurant, lobby, mall).
(“What Does Sustainable Design Sound Like? “http://www.acoustics.com/ra_sustainable.asp)
A survey of “green” office building satisfaction conducted in 2007 by the University of
California Berkeley’s Center for the Built Environment found that over 60% of occupants in
cubicles thought that acoustics interfered with their ability to get their jobs done.
© 2009 Autodesk
Acoustic Comfort for Sustainable Design
Suggested ASTM acoustical criteria for some building occupancies
Recommended Minimum Sound Attenuation
Recommended Range for
Background Noise, dB(A)
ASTC
FIIC
(apparent sound
transmission class)
(field impact insulation
class)
Multi-family homes
55
50
35-40
Bedrooms in residences
55
50
30-35
Private offices
45
40-45
Meeting rooms
50
35-40
Bedrooms in hotels, motels
and hospitals
50
Classrooms up to 300 m3
50
50
Reverberation
Time, seconds
0,5
35-40
35-40
0,6
40-45
0,8
30-35
0,7
Gymnasiums
40-45
1,0
Libraries
40-45
0,7
Cafeterias
Large lecture rooms,
classrooms over 300 m3
50
(From Specifying Acoustical Criteria for Buildings, by A.C.C. Warnock, National Research Council of Canada, June 2001)
© 2009 Autodesk
Summary
Designing buildings with careful attention to parameters of human comfort can contribute
significantly to an energy-efficient, carbon-neutral, and socially engaging approach to
sustainable design.
A variety of models exist that can enable designers to analyze, predict, and simulate the
performance of their designs before they are built.
© 2009 Autodesk
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