Download Thermal Comfort

THERMAL COMFORT
THERMAL COMFORT
Perception of temperature influenced by:
• Season
• Clothing
• Humidity
• Air Movement
• Presence of heat given off by other
bodies and equipment
THERMAL COMFORT
Body temperature regulated through:
• Skin
• Clothing
• Buildings
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THERMAL COMFORT
Normal Body Temperature:
• 98.6 degrees Fahrenheit
• Few degree variation = distress
www.fnal.gov
THERMAL COMFORT
• Between 1920 and 1970, a period of cheap energy costs,
people developed a preference for year round temperatures in
the range of 72 – 78 degrees Fahrenheit
• Preferred comfortable temperature for most people is 65 – 76
degrees Fahrenheit in the winter
THERMAL COMFORT
Cold Sensitive Areas:
• Upper Lip
• Nose
• Chin
• Chest
• Fingertips
THERMAL COMFORT
Thermal comfort is achieved when a stable, normal body
temperature is achieved
• The result of a balance between the body and its environment
MAINTAINING THERMAL EQUILIBRIUM
…when heat production equals heat loss
THERMAL COMFORT
Building Heating and Cooling Systems:
• Used to control how much heat the human body gives off
• Does not heat/cool the body but adjust the thermal
characteristics of the indoor space to reduce the rate at which
our bodies lose heat
THERMAL COMFORT
Gender Differences
• Men feel warmer than women when first in a space, but later
feel cooler than a woman would
• Men take 1 – 2 hours to feel as warm/cool as a female in the
same space
THERMAL COMFORT
Age Differences
• Elderly and college age students are similar in the responses to
thermal preferences and responses
THERMAL COMFORT
Comfort Conditions
• Independent of the time of day or night
• Individuals are consistent in their thermal preferences
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THERMAL COMFORT
ASHRAE Standard 55-1992: Thermal Environmental Conditions
for Human Occupancy
• Describes the combinations of indoor space conditions and
personal factors that create comfort
THERMAL COMFORT
ASHRAE Standard 55-1992: Thermal Environmental Conditions
for Human Occupancy
Report indicates that our sense of being warm or cool enough is
the result of interactions between:
• Temperature
• Thermal Radiation
• Humidity
• Air Speed
• Personal Activity Level
• Clothing
THERMAL COMFORT
Thermal Sensations – feelings of being:
• Hot
• Warm
• Cool
• Cold
• Range of classifications in-between
THERMAL COMFORT
Indices/Indexes – Integrate environmental factors used to
describe thermal comfort conditions
• Dry-Bulb Temperatures
• Wet-Bulb Temperatures
• Operative Temperature
THERMAL COMFORT
Dry-Bulb Temperatures
Wet-Bulb Temperatures
• The ambient air temperature
as measured by a standard
thermometer
• Estimate the effect of
temperature, humidity, wind
speed and radiation
THERMAL COMFORT
Operative Temperature
• Uniform temperature of an imaginary enclosure in which the
occupant would exchange the same heat by radiation and
convection as in the actual environment
THERMAL COMFORT
Effective Temperature Scale
• Correlated to Physiological Reactions, Comfort and Health
Source: Bradshaw. The Building Environment. Wiley
THERMAL COMFORT
Guidelines for Room Air Temperatures
Source: Bradshaw. The Building Environment. Wiley
THERMAL COMFORT
Principles of Heat Transfer
• Heat always moves from the region of higher temperature to
the region of lower temperature
• Heat flows from an area of active molecular movement to an
area of less movement
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THERMAL COMFORT
Principles of Heat Transfer
• Tendency to decrease the temperature and amount of activity
in the area with the higher temperature, and increase the
temperature and activity in the area with the lowest temperature
• When there is no difference = Thermal Equilibrium
THERMAL COMFORT
Principles of Heat Transfer
Heat energy transferred by:
1.Radiation
2.Conduction
3.Convection
beyondpenguins.ehe.osu.edu
www.physics.smu.edu
THERMAL COMFORT
Principles of Heat Transfer
Heat energy transferred by:
1.Radiation
2.Conduction
3.Convection
THERMAL COMFORT
Principles of Heat Transfer
1.Radiation
•Occurs when heat flows in electromagnetic waves from hotter
surfaces through any medium to detached colder surfaces
THERMAL COMFORT
Principles of Heat Transfer
1.Radiation
•Infrared electromagnetic waves emanate from an object and
carry energy to all bodies within a direct line of sight of that object
THERMAL COMFORT
Principles of Heat Transfer
1.Radiation
•Electromagnetic waves excite the molecules in the objects they
hit, increasing the internal energy, and raising the temperature
THERMAL COMFORT
Principles of Heat Transfer
1.Radiation: How building materials radiate heat
•Reflectance
•Absorptance
•Emittance
THERMAL COMFORT
Principles of Heat Transfer
1.Radiation: How building materials radiate heat
•Reflectance
•Absorptance
•Emittance

Amount of incoming radiation that bounces off a
material, leaving the temperature of the material
unchanged

White paint
THERMAL COMFORT
THERMAL COMFORT
Principles of Heat Transfer
1.Radiation: How building materials radiate heat
•Reflectance
•Absorptance
•Emittance

Opposite of reflectance

Allows thermal energy to enter, raising the
temperature

Stone
THERMAL COMFORT
THERMAL COMFORT
Principles of Heat Transfer
1.Radiation: How building materials radiate heat
•Reflectance
•Absorptance
•Emittance

Ability of a material to radiate absorbed heat
outward

Black surfaces, stone
THERMAL COMFORT
THERMAL COMFORT
Principles of Heat Transfer
1.Radiation: Mean Radiant Temperature
•Air temperature alone does not adequately measure comfort in a
space
•Engineers use a calculation called the Mean Radiant
Temperature (MRT)
•Calculation takes into account heat emitted from surfaces etc
THERMAL COMFORT
THERMAL COMFORT
Principles of Heat Transfer
1.Radiation: Operative Temperature
•Physical measurement
•Average of the air temperature of a space and the average of the
various surface temperatures surrounding the space
THERMAL COMFORT
Principles of Heat Transfer
1.Radiation:
Mean Radiant Temperature and Operative Temperature are used
by engineers to determine the amount of supplementary
heating/cooling needed in a space
THERMAL COMFORT
Principles of Heat Transfer
2.Conduction
•Flow of heat through a solid material
•Represents a small fraction of heat loss from our bodies
THERMAL COMFORT
Principles of Heat Transfer
3.Convection
•Transfer of heat by means of a
moving stream of a fluid (liquid or
gas) rather than another object
•Air movement, water
THERMAL COMFORT
Principles of Heat Transfer
Evaporation
• Process that results from the
three types of heat transfer
• Incorporates both sensible and
latent heat
THERMAL COMFORT
Principles of Heat Transfer
Evaporation:
1.Sensible Heat
•Created by the motion of
molecules
2.Latent Heat
•Heat that is transferred when a
material changes from a solid to a
liquid, or liquid to a gas form
THERMAL COMFORT
Principles of Heat Transfer
Evaporation:
Evaporative Cooling
• Occurs when moisture evaporates and the sensible heat of the
liquid is converted into the latent heat in the vapor
• Air movement increases heat loss caused by evaporation
THERMAL COMFORT
muellerdesignlab.wordpress.com
THERMAL COMFORT
Principles of Heat Transfer
Air Temperature and Air Motion
• Natural convection of air over the body dissipates body heat
without added air movement
• When temperatures rise – air movement must be increased to
maintain thermal comfort
THERMAL COMFORT
Principles of Heat Transfer
Air Temperature and Relative Humidity (RH)
• Ratio of the amount of water vapor actually present in the air to
the maximum amount that air could hold at the same time
THERMAL COMFORT
Ted Talk
http://www.ted.com/talks/wolfgang_kessling_how_to_air_condition_outdoor_spaces.html