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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 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 Measurement of moisture content and air temperature.
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
Relative Humidity What is 100% RH? Fog
Dry Bulb Temperature Air temperature as read from a standard thermometer Dry Bulb Temperature ºF
Wet Bulb Temperature Wet Bulb Temperature Air temperature as read from a moistened thermometer
Dew Point Temperature ºF Dew Point Temperature Temperature at which RH is 100%
Dew Point Temperature ºF Dew Point Temperature For air at 75ºF DBT/65 ºF WBT,what is the dewpoint temperature? 60ºF
Standard Comfort Zone [L: p. 65, fig. 4.8a] Conditions where the typical occupant is comfortable for the given intent of a space.
Thermal Comfort Factors Influenced by • Metabolism • Migration • Heat flow • Clothing
Metabolism Metabolism affects perception of thermal comfort • Muscular activity • Digestive process • Daily cycle • Health • Age • Gender
Migration Body attempts to maintain core temperature (98.6ºF) by shifting blood flow • Vasodilation • Vasoconstriction
Heat Flow Multiple mechanisms • Convection • Conduction • Radiation • Evaporation
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
Heat Flow – Conduction Caused by direct contact between two objects of different temperature • Heat always flows from warm to cool
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
Radiant Heat Flow Season variations can change direction of radiant heat flow
Mean Radiant Temperature (MRT) MRT approach is used in Europe as a means to lower operating temperatures
Heat Flow – Evaporation Water changes from liquid to gas and this phase change extracts heat • Respiration • Perspiration
Clothing Compounds and/or mitigates the effects of other mechanisms