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 --- --- Mesa Verde: vernacular, passive solar, sun angles, thermal mass
Psychrometrics Measurement of moisture content and air temperature. BH061
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 Air temperature as read from a moistened thermometer Wet Bulb Temperature
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 dew point temperature? Dew Point Temperature ºF 60ºF
Standard Comfort Zone Conditions where the typical occupant [L: p. 65, fig. 4.8a] Conditions where the typical occupant is comfortable for the given intent of a space. BH048
Thermal Comfort Factors Influenced by Metabolism Migration Heat flow Clothing BH040
Metabolism Metabolism affects perception of thermal comfort Muscular activity Digestive process Daily cycle Health Age Gender BH024
Migration Body attempts to maintain core temperature (98.6ºF) by shifting blood flow Vasodilation Vasoconstriction BH024
Heat Flow Multiple mechanisms Convection Conduction Radiation Evaporation BH030
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 BH030
Heat Flow – Conduction Caused by direct contact between two objects of different temperature Heat always flows from warm to cool BH030
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 BH030
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 BH030
Clothing Compounds and/or mitigates the effects of other mechanisms BH049