environmental controls i/ig lecture 6 thermal comfort
TRANSCRIPT
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Environmental Controls I/IGEnvironmental Controls I/IG
Lecture 6Thermal Comfort
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TerminologyTerminology
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 --- ---
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PsychrometricsPsychrometrics
Measurement of moisture content and air temperature.
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Relative Humidity
Relative HumidityRelative 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
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Relative HumidityRelative Humidity
What is 100% RH? Fog
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Dry Bulb TemperatureDry Bulb Temperature
Air temperature as read from a standard thermometer
Dry Bulb Temperature ºF
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Wet Bulb TemperatureWet Bulb Temperature
Air temperature as read from a moistened thermometer
Wet Bulb Temperature
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Dew Point Temperature ºF
Dew Point TemperatureDew Point Temperature
Temperature at which RH is 100%
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Dew Point TemperatureDew Point Temperature
For air at 75ºF/65% RH,what is the dewpoint temperature?
Dew Point Temperature ºF
60ºF
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Standard Comfort ZoneStandard Comfort Zone
Conditions where
the typical occupant is comfortable for the given intent of a space.
[L: p. 65, fig. 4.8a]
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Influenced by Metabolism Migration Heat flow Clothing
Thermal Comfort FactorsThermal Comfort Factors
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MetabolismMetabolism
Metabolism affects perception of thermal comfort
Muscular activity Digestive process Daily cycle Health Age Gender
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MigrationMigration
Body attempts to maintain core temperature (98.6ºF) by shifting blood flow
Vasodilation Vasoconstriction
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Heat FlowHeat Flow
Multiple mechanisms Convection Conduction Radiation Evaporation
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Heat Flow – Convection 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
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Heat Flow – Conduction Heat Flow – Conduction
Caused by direct contact between two objects of different temperature Heat always flows from
warm to cool
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Heat Flow – Radiation 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
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Radiant Heat FlowRadiant Heat Flow
Season variations can change direction of radiant heat flow
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Mean Radiant Temperature Mean Radiant Temperature (MRT)(MRT)
MRT approach is used in Europe as a means to lower operating temperatures
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Heat Flow – Evaporation Heat Flow – Evaporation
Water changes from liquid to gas and this phase change extracts heat Respiration Perspiration
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Compounds and/or mitigates the effects of other mechanisms
ClothingClothing