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Environmental Controls

Environmental Controls. Lecture 6 Thermal Comfort. 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 --- ---. Psychrometrics.

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Environmental Controls

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  1. Environmental Controls Lecture 6 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 DBT/65 ºF WBT,what is the dewpoint temperature? 60ºF

  10. Standard Comfort Zone [L: p. 65, 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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