INTRODUCTION
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his book provides
charts and tables for estimating our body’s physiological thermal comfort in
response to ambient air temperature and dew point temperature. We employ the PMV
(Predicted Mean Vote) comfort equations of P.O. Fanger.
These equations express physiological
thermal comfort as a simple numeric scale ranging from “-3” (cold) through “+3” (hot) – with “0” denoting neutral (or, ideal) comfort.
This book applies the PMV comfort equations
to the conditions of zero air velocity, sedentary activity and light and
loose-fitting summer clothing.
Most of this book’s charts and tables
pertain to environments shielded from the direct and reflected rays of
the sun (for example, beneath a canopy or shade tree). For shady
areas, thermal comfort
is described by the term: PMVSHADE. The condition of shade implies
that mean radiant temperature (MRT) is equal to the air temperature,
designated as MRTSHADE.
For outdoors environments exposed to direct
rays of the sun (for example, a golf course), thermal comfort is described as
PMVSUN and we denote the corresponding mean radiant temperature
as MRTSUN.
Chapters 8, 9 and 10, describing PMVSHADE
and PMVSUN, are primarily focused on leisure thermal comfort. Mean
radiant temperature, which is an essential PMV variable, is discussed more
completely in Chapters 9 and 12.
Why Another Book On Climate?
Physiological thermal
comfort is influenced by two environmental variables: ambient air temperature
and air moisture content (also called dew point temperature).
Although one or both of these climate
variables are listed in the available literature (for a few regions within the
United States), mental conversion of these raw climate variables into a
meaningful measure of thermal comfort is beyond the ability and motivation of
most of us. A glance at the complex mathematical PMV comfort equations of Appendix
1 – about which most of this book is based
– demonstrates how difficult this conversion is.
Charts and tables included in this book
display leisure thermal comfort values for up to 303 cities and towns within
the United States – enabling an individual to determine how comfortable he or
she is likely to be at a specified location and time of year.
.
A Quick Overview of PMV
We introduce several
important features of the Predicted Mean Vote (PMV) comfort equations in the
following paragraphs. Most charts and tables are based on the Fanger PMV
thermal comfort equations – that were incorporated for many years as part of
the International Standards Organization†.
Although PMV comfort equations can include
various combinations of air velocity, clothing, metabolic rates and mean
radiant temperatures (see Glossary), for this book, we use the simplest set of
conditions: zero air velocity, light summer clothing, sedentary activity and
(except for Chapters 9 and 10) mean radiant temperature uniformly presumed
equal to the outdoors air temperature (designated as MRTSHADE).
From the Laboratory to the
Outdoors
The Predicted Mean
Vote comfort equations are based on rigorously controlled laboratory
conditions. In brief, the physiological comfort of individual test subjects
within a temperature- and humidity-controlled enclosure is assessed for various
groups of people differing in age, sex and nationality. During experimental
calibration of the PMV comfort equations, all surfaces of the experimental
enclosure are maintained at carefully controlled temperatures (mean radiant
temperatures). Air moisture contents of the enclosure are also carefully
controlled.
PMVSHADE for the outdoors implies
that all surfaces of an outdoors fictional enclosure are at the same
mean radiant temperature. A reasonable approximation to the implied equality
between air temperatures and mean radiant temperatures for outdoors PMVSHADE
can be achieved by minimizing the influence of direct and reflected solar radiation
as much as possible.
Example:
a heavily shaded location in a park.
Leisure Is the Thermal Comfort
Baseline
Regardless of
individual activity lifestyles, we each participate in sedentary activity for
at least some portion of the day. Thus, the “leisure” condition (read: sedentary)
is a common and relevant baseline by which to determine our thermal comfort.
Leisure Thermal Comfort for
Different Times of the Day
The leisure thermal
comfort charts and tables in this book are arranged into three city- and
month-specific temperature conditions:
• MAXTMP (average monthly maximum
temperature) commonly occurs at about midday (more precisely: about 3:00 PM
local standard time).
• MINTMP (average monthly minimum
temperature) typically occurs at about sunrise.
• AVETMP*
(monthly average temperature) commonly occurs at about sunset.
Reader Guide and
Chapter Relevance Ratings
Figure 1-1, page 5,
suggests how chapters of this book can most efficiently be read, based on
available time and individual reader interest.
In the paragraphs below, book chapters are
assigned subjective relevance ratings; their order of discussion conforms to
the Table of Contents. Relevance rating codes are:
Best
(most relevant, applies to midday) ☺☺☺☺
Better
(background and explanatory information) ☺☺☺
Good
(relevant, but limited to sunrise or sunset) ☺☺
Fair
(for casual interest) ☺
☺☺☺ A Quick Guide to Basic Climate
Chapters 1 through 3
(Section 1) provide background information (dew point temperature, ambient
temperature, precipitation and snow depth). This information is useful for
vacation planning.
☺☺☺☺ When the Sun Is High Overhead…
Chapters 4 and 5
(Section 2) apply to PMVSHADE at midday (MAXTMP) and these chapters
are most useful for most readers. These chapters show how to estimate leisure
thermal comfort in the shade at midday and represent the core subject matter.
☺☺ When the Sun Is Near the Horizon…
Chapters 6 and 7
(within Section 3) are extensions of Chapters 4 and 5 (within Section 2) but
have lesser application because they respectively refer to conditions of
sunrise (MINTMP) and sunset (AVETMP).
☺☺☺ Do-It-Yourself PMVSHADE
and PMVSUN Estimating
Chapters 8, 9 and 10
in this section (Section 4) are extensions to other chapters, especially
Chapters 4 and 5. Chapters 8 and 9 discuss leisure thermal comfort for shade
and sun, respectively. Chapter 10 is an
application summary of concepts discussed in other chapters.
☺ Topics Off the Beaten Path
The four chapters in
this section (Chapters 11, 12, 13 and 14 within Section 5) discuss peripheral
topics.
Historical Data Are Used
All climate data
displayed in tables of this book derive
from the 1996 ISMCS
Version 4.0 (CDROM) database*.
This database contains about 3.5 gigabytes of data compressed to 580 megabytes;
if printed as hardcopy, it would weigh over seven tons. This database contains
monthly climate data from1946 through 1995.
Climate data are extracted only for
meteorological or weather stations routinely reporting dew point temperatures
(the United States has 303 “First-Order” meteorological stations). Because
these meteorological stations are located throughout the fifty states, we have
good sampling of the U.S. climate.
Figure 1-2, page 6, displays a dot map of
these weather stations within the continental United States, with each dot
representing a weather station location.
Useful Features of the ISMCS Data
The ISMCS climate data
have two useful features:
• Long-term average monthly observations
• The trimmed-down version of the ISMCS
database represents climate throughout the United States without overwhelming
detail. Even this reduced size database yields a large number of tables.
Average Data Are Most Likely
The ISMCS climate data
in this book represent up to fifty years’ worth of averages. Such long-term
climate data help to classify weather as most likely or most probable
and can therefore provide a means to forecast weather for a particular city and
time.
Mega-cities have an urban “heat island”
effect that is roughly proportional to their population. This heat island
effect and information about carbon dioxide and the global warming are
discussed in Chapter 14.
Weather is known to be changeable. Although
we plan for expected weather, the unexpected, extreme event can occur, for example,
flood and heat wave.
Available Data Are Only a Sampling
The level of
sophistication of hundreds of U.S. weather stations varies widely, affecting
the variety but not the quality of data gathered. The data displayed in charts
and tables – from Chapters 1 through 11 – were gathered from 303 U.S. weather
stations (weather stations range from one each in Delaware and New Hampshire to
twenty-five in California, averaging six per state).
Only the Most Basic Climate Data
Are
Displayed
This book attempts to
present only essential information from a minimal set of climate variables.
These few climate variables include monthly averages of minimum and maximum
temperatures, dew point temperatures, precipitation and snow depth. To simplify
the data, physical influences to local weather, such as elevation, proximity to
natural water, prevailing winds, population density, mountain ranges, etc., are
excluded.
Not only is wind velocity excluded, it is
presumed to be zero throughout the discussion of leisure thermal comfort. Zero
wind velocity represents a best-case assumption during the cold winter but
represents a worst-case assumption during the hot summer.
Unfortunately, when we exclude air movement
from consideration, enjoyable summer waterfront breezes are not accounted for
when determining physical comfort.
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