All Topics  
Thermal comfort

 

 
   Email Print
   Bookmark   Link
 

 

Thermal comfort
 
 
  Topics Thermal comfort Topic Home

Human thermal comfort is defined by ASHRAE as the state of mind that expresses satisfaction with the surrounding environment (ASHRAE Standard 55). Maintaining thermal comfort for occupants of buildings or other enclosures is one of the important goals of HVAC
HVAC

HVAC is an initialism or acronym that stands for "heating, Ventilation , and air conditioning". HVAC is sometimes referred to as climate control and is particularly important in the design of medium to large industrial and office buildings such as skyscrapers and in marine environments such as aquariums, where humidity and tem...
 design engineers.

Thermal comfort is affected by heat conduction
Heat conduction

Heat conduction or thermal conduction is the spontaneous heat transfer through matter, from a region of higher temperature to a region of lower temperature, and acts to equalize temperature differences....
, convection
Convection

Convection in the most general terms refers to the movement of molecules within fluids . Convection is one of the major modes of heat transfer and mass transfer....
, radiation
Thermal radiation

Thermal radiation is electromagnetic radiation emitted from the surface of an object which is due to the object's temperature. Infrared radiation from a common household radiator or electric heater is an example of thermal radiation, as is the light emitted by a glowing incandescent light bulb....
, and evaporative heat loss. Thermal comfort is maintained when the heat generated by human metabolism is allowed to dissipate, thus maintaining thermal equilibrium with the surroundings.






Discussion
Ask a question about 'Thermal comfort'
Start a new discussion about 'Thermal comfort'
Answer questions from other users
Full Discussion Forum



Encyclopedia


Human thermal comfort is defined by ASHRAE as the state of mind that expresses satisfaction with the surrounding environment (ASHRAE Standard 55). Maintaining thermal comfort for occupants of buildings or other enclosures is one of the important goals of HVAC
HVAC

HVAC is an initialism or acronym that stands for "heating, Ventilation , and air conditioning". HVAC is sometimes referred to as climate control and is particularly important in the design of medium to large industrial and office buildings such as skyscrapers and in marine environments such as aquariums, where humidity and tem...
 design engineers.

Thermal comfort is affected by heat conduction
Heat conduction

Heat conduction or thermal conduction is the spontaneous heat transfer through matter, from a region of higher temperature to a region of lower temperature, and acts to equalize temperature differences....
, convection
Convection

Convection in the most general terms refers to the movement of molecules within fluids . Convection is one of the major modes of heat transfer and mass transfer....
, radiation
Thermal radiation

Thermal radiation is electromagnetic radiation emitted from the surface of an object which is due to the object's temperature. Infrared radiation from a common household radiator or electric heater is an example of thermal radiation, as is the light emitted by a glowing incandescent light bulb....
, and evaporative heat loss. Thermal comfort is maintained when the heat generated by human metabolism is allowed to dissipate, thus maintaining thermal equilibrium with the surroundings. Any heat gain or loss beyond this generates a sensation of discomfort. It has been long recognised that the sensation of feeling hot or cold is not just dependent on air temperature alone.

Factors determining thermal comfort


Factors determining thermal comfort include:
  • Air temperature
  • Mean radiant temperature
    Mean radiant temperature

    Mean Radiant Temperature The net exchange of radiant energy between two objects is proportional to their temperature difference multiplied by their ability to emit and absorb heat ....
  • Air movement / velocity (see wind chill factor)
  • Relative humidity
    Relative humidity

    Relative humidity is a term used to describe the amount of water vapor that exists in a gaseous mixture of air and water....
     (see also perspiration)
  • Insulative clothing
  • Activity levels.


Thermal stress


The concept of thermal comfort is closely related to thermal stress. This attempts to predict the impact of solar radiation, air movement, and humidity
Humidity

Humidity is the amount of water vapor in the air. In daily language the term "humidity" is normally taken to mean relative humidity. Relative humidity is defined as the ratio of the partial pressure of water vapor in a Air parcel of air to the saturated vapor pressure of water vapor at a prescribed temperature....
 for military personnel undergoing training exercises or athletes during competitive events. Values are expressed as the Wet Bulb Globe Temperature or Discomfort Index.

Operative temperature


The ideal standard for thermal comfort can be defined by the operative temperature
Operative temperature

In the study of human Thermal Comfort, the operative temperature is one of several parameters devised to measure the air's cooling effect upon a human body....
. This is the average of the air dry-bulb temperature and of the mean radiant temperature
Mean radiant temperature

Mean Radiant Temperature The net exchange of radiant energy between two objects is proportional to their temperature difference multiplied by their ability to emit and absorb heat ....
 at the given place in a room. In addition, there should be low air velocities and no 'drafts', little variation in the radiant temperatures from different directions in the room, humidity within a comfortable range, and air temperatures in a height of 0.1 m above the floor should not be more than 2 °C lower than than the temperature at the place of the occupant's head. The temperatures should also not change too rapidly across either space or time.

In addition to environmental conditions, thermal comfort depends on the clothing and activity level of a person. The amount of clothing is measured against a standard amount that is roughly equivalent to a typical business suit, shirt, and undergarments. Activity level is compared to being seated quietly, such as in a classroom.

This standard amount of insulation required to keep a resting person warm in a windless room at 70 °F (21.1 °C) is equal to one Clo. Clo units can be converted to R-value
R-value (insulation)

The R value or R-value is a measure of thermal resistance used in the building and construction industry. The bigger the number, the better the building insulation's effectiveness....
 in SI units (K/(W/m²) or RSI) by multiplying Clo by 0.155 (1 Clo = 0.155 RSI). (In imperial units 1 Clo corresponds to an R-value of 0.88 °F ft²hr/Btu.)

Research


These factors were explored experimentally in the 1970s. Many of these studies led to the development and refinement of ASHRAE Standard 55 and were performed at Kansas State University
Kansas State University

Kansas State University, officially named Kansas State University of Agriculture and Applied Science but commonly shortened to K-State, is an institution of higher learning located in Manhattan, Kansas, Kansas, in the United States....
 by Ole Fanger
P. Ole Fanger

Povl Ole Fanger was an expert in the field of the health effects of indoor environments. He was a University Professor at Syracuse University when he died at the age of 72 from an abdominal aortic aneurysm....
 and others. Perceived comfort was found to be a complex interaction of these variables. It was found that the majority of individuals would be satisfied by an ideal set of values. As the range of values deviated progressively from the ideal, fewer and fewer people were satisfied. This observation could be expressed statistically as the % of individual who expressed satisfaction by comfort conditions and the predicted mean vote (PMV)

See also

  • P. Ole Fanger
    P. Ole Fanger

    Povl Ole Fanger was an expert in the field of the health effects of indoor environments. He was a University Professor at Syracuse University when he died at the age of 72 from an abdominal aortic aneurysm....
  • Room air distribution
    Room air distribution

    Characterizing how air is introduced to, flows through, and is removed from spaces is called room air distribution. HVAC airflow in spaces generally can be classified by two different types: mixing and displacement....
  • Psychrometrics
    Psychrometrics

    Psychrometrics or psychrometry are terms used to describe the field of engineering concerned with the determination of physical and thermodynamic properties of gas-vapor mixtures....
  • Air conditioning
    Air conditioning

    An air conditioner is an appliance, system, or Mechanism designed to extract heat from an area via a refrigeration cycle. In construction, a complete system of heating, Ventilation , and air conditioning is referred to as "HVAC." Its purpose, in a building or an automobile, is to provide comfort during either hot or cold...
  • Building insulation
    Building insulation

    Building insulation refers broadly to any object in a building used as insulation for any purpose. Whilst the majority of insulation in buildings is for thermal insulation purposes, the term also applies to acoustic insulation, Fireproofing, and Cushioning ....
  • Mahoney tables


External links