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Exploring Thermal Comfort Factors and Control Mechanisms

Dive into thermal comfort terminology and factors influencing comfort like metabolism, migration, and heat flow. Understand psychrometrics and mechanisms such as convection, conduction, radiation, and evaporation. Learn how clothing can affect comfort levels.

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Exploring Thermal Comfort Factors and Control Mechanisms

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  1. Environmental Controls I/IG Lecture 2 Thermal Comfort

  2. Terminology Abbrev. Units Psychrometrics --- --- Relative Humidity RH (%RH) Dry Bulb Temperature DBT (ºF) Wet Bulb Temperature WBT (ºF) Dew Point Temperature DPT (ºF) Standard Comfort Zone --- ---

  3. Psychrometrics Measurement of moisture content and air temperature.

  4. Relative Humidity Quantity of moisture held in the air relative to the maximum amount that can be held (%). • Warm air holds more moisture • Moisture condenses from the air as it cools Relative Humidity

  5. Relative Humidity What is 100% RH? Fog

  6. Dry Bulb Temperature Air temperature as read from a standard thermometer Dry Bulb Temperature ºF

  7. Wet Bulb Temperature Wet Bulb Temperature Air temperature as read from a moistened thermometer

  8. Dew Point Temperature ºF Dew Point Temperature Temperature at which RH is 100%

  9. Dew Point Temperature ºF Dew Point Temperature For air at 75ºF/60% RH,what is the dewpoint temperature? 60ºF

  10. Standard Comfort Zone [L: p. 61, fig. 4.8a] Conditions where the typical occupant is comfortable for the given intent of a space.

  11. Thermal Comfort Factors Influenced by • Metabolism • Migration • Heat flow • Clothing

  12. Metabolism Metabolism affects perception of thermal comfort • Muscular activity • Digestive process • Daily cycle • Health • Age • Gender

  13. Migration Body attempts to maintain core temperature (98.6ºF) by shifting blood flow • Vasodilation • Vasoconstriction

  14. Heat Flow Multiple mechanisms • Convection • Conduction • Radiation • Evaporation

  15. Heat Flow – Convection Air movement caused by pressure and density changes • Wind is formed by air moving from high to low pressure areas • Warming air rises • Cooling air falls

  16. Heat Flow – Conduction Caused by direct contact between two objects of different temperature • Heat always flows from warm to cool

  17. Heat Flow – Radiation Radiant heat is exchanged by two objects of different temperatures • Heat always flows toward cooler object • Surface temperature controls interaction • Seasonally variable

  18. Radiant Heat Flow Season variations can change direction of radiant heat flow

  19. Mean Radiant Temperature (MRT) MRT approach is used in Europe as a means to lower operating temperatures

  20. Heat Flow – Evaporation Water changes from liquid to gas and this phase change extracts heat • Respiration • Perspiration

  21. Clothing Compounds and/or mitigates the effects of other mechanisms

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