GLOSSARY
Ambient Temperature
Ambient temperature is the current local
temperature of the air.
Average Monthly Maximum Temperature
Abbreviated as “MAXTMP,” this is the late
afternoon temperature, which occurs at around 3:00 PM in the continental United
States. Throughout this book, the time at which MAXTMP occurs is loosely
defined as “midday.” MAXTMP is the long-term (about fifty-year) monthly average
of day-to-day maximum temperatures recorded by a specific weather station.
(Also, see AVETMP.)
Average Monthly Minimum Temperature
Abbreviated as “MINTMP,” this is the early
morning temperature, generally around sunrise in the continental United
States. MINTMP is the long-term (about
fifty-year) monthly average of day-to-day minimum temperatures recorded by a
specific weather station. (Also, see AVETMP.)
Average Monthly Precipitation
Abbreviated as “PRECIP,” this is the long-term
(about fifty-year) monthly average of day-to-day precipitation in all forms
(hail, sleet, snow and rain) recorded by a specific weather station.
AVETMP
This is the average of MAXTMP and MINTMP. All references to AVETMP in this book imply evening
AVETMP, usually one or more hours after sunset (in the continental United
States).
Black Globe Temperature (BGT)
When air velocity is zero, the black globe
thermometer provides a direct measure of Mean Radiant Temperature (MRT). The
BGT is commonly measured with a Vernon globe thermometer, consisting of a
six-inch diameter hollow sphere coated with flat black paint and having a thermocouple
or thermometer at its center.
Climate
Climate is the average course of the weather
over a period of years (long-term) as recorded by weather data; it includes
temperature, wind velocity and precipitation.
Comfort Paradise
Broadly defined as outdoors leisure thermal
comfort, in shade (PMVSHADE) or sun (PMVSUN), with
indices ranging from 0 through ±1.5; and, corresponding to PPD values ranging
from 5 percent to about 50 percent. (See Predicted Mean Vote and Predicted
Percentage Dissatisfied, below.)
Dew Point Temperature
Dew point is the temperature of the air when
condensation occurs. Dew point is an
intuitive measure of the amount of moisture in the air. The larger the amount of moisture in the air,
the higher the dew point temperature. Dew points around 80ºF are almost
intolerable, especially when combined with elevated ambient temperatures.
Arid
and semi-arid regions of the United States usually have low dew points.
Humidity
Relative humidity is the percent saturation of
air with water at a specified temperature. For example, air at ambient
temperature of 91˚F is saturated when moisture vapor pressure is 0.721 psi
(pounds per square inch). If the moisture vapor pressure is reduced to half of
this amount (that is, 0.360 psi), while maintaining the same air temperature,
the relative humidity is reduced to 50 percent.
Tabulated conversions between relative humidity and dew point
temperature are displayed in Table 1-1, page 11 of Chapter 1.
Of the
two concepts, this book favors dew point temperature based on considerations of
comprehensibility and practicality.
Isogram (also, Isoline)
Refers to a line on a map along which the value
is constant (for example, pressure, temperature or elevation).
Isotherm
Refers to a constant temperature line on a
temperature contour map. An isotherm is also an isoline and an isogram.
Leisure Thermal Comfort
Leisure thermal comfort is defined by the P.O.
Fanger comfort equations (see Appendix 1), that include the following
conditions: zero air velocity, light summer clothing, sedentary activity and
three hours of exposure to the environment. Leisure thermal comfort is
expressed in terms of the Predicted Mean Vote (PMV), a scale ranging from “-3”
through “+3” (see Predicted Mean Vote); and is distinguished by the absence or
presence of solar rays, PMVSHADE and PMVSUN,
respectively.
MAXTMP
See Average Monthly Maximum Temperature, above.
Mean Radiant Temperature (MRT)
MRT is the uniform surface temperature of a
black enclosure with which an individual exchanges the same heat by radiation
as the actual environment considered.
As a
practical example, the MRT for any interior room of a home or building, for which
all inner surfaces (walls, floor, ceiling) of the room are at the same temperature,
generally corresponds to the temperature of the room’s surfaces.
When we
conceptualize this example to the outdoors, then the MRT represents the uniform
surface temperature of a fictional enclosure – for which all surfaces of
the fictional enclosure are at the same temperature.
Two
conditions of MRT are dealt with in this book, namely: (1) MRT equal to the
ambient air temperature (see PMVSHADE) and (2) additional heat load
by influence of solar rays (see PMVSUN).
MINTMP
See Average Monthly Minimum Temperature, above.
PMVSHADE
PMVSHADE implies that mean radiant
temperature is equal to ambient air temperature (see Predicted Mean Vote), and
provides a measure of leisure thermal comfort without influence of sunshine.
PMVSUN
PMVSUN implies that mean radiant
temperature is influenced by solar heat load, and provides a measure of leisure
thermal comfort in the presence of sunshine.
Predicted Mean Vote
The Predicted Mean Vote (PMV) is a simple
numeric scale used by P.O. Fanger to designate thermal comfort as shown below:
-3 cold
-2 cool
-1 slightly cool
0 neutral
+1 slightly warm
+2 warm
+3 hot
Predicted Percentage Dissatisfied (PPD)
The symmetrical PPD distribution is expressed as
a function of the Predicted Mean Vote. When PMV is zero, PPD is 5% – meaning
that even under the best conditions, not everyone is satisfied with the condition
of mean neutrality. The following table displays PPD as a function of PMV.
|
PMV |
PPD |
|
0 |
5.0 |
|
±0.5 |
10.2 |
|
±1.0 |
26.6 |
|
±1.5 |
51.5 |
|
±2.0 |
76.1 |
When PMV is either “+1.5” or “-1.5,”
as shown by the table, the Predicted Percentage Dissatisfied is about 50% (actually,
51.5%). On the other hand, this means that nearly one-half of the people are
satisfied.
See page 44 for more discussion of PPD.
Thermal Radiation
Three
forms of thermal radiation are taken into account when calculating leisure
thermal comfort:
• Direct (solar) short wavelength radiation, emitted from the sun during daylight hours.
Example: an environment exposed to full sun.
• Diffuse (solar) short wavelength
radiation, emitted from the sun during daylight hours.
Example: an environment within dense shade or beneath heavy
clouds.
• Long wavelength radiation, emitted from the earth’s surface and terrestrial objects.
Example: heat radiation from the ground, shrubs and trees.
Weather Station
Abbreviations
AFB Air Force Base
AP Airport
FAA Federal Aviation Administration
MCAS Marine Corps Air Station
MUNI Municipal
NAF Naval Air Field
NAS Naval Air Station
NWSFO Naval Weather Service Forecast Office
PMTC Point Mugu Training Center
WSCMO Weather Service Contract Meteorological Observatory
WSFO Weather Service Forecast Office
WSO Weather
Service Office ■