Environmental Controls I/IGEnvironmental Controls I/IG

Lecture 6Thermal Comfort

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 --- ---

PsychrometricsPsychrometrics

Measurement of moisture content and air temperature.

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

Relative HumidityRelative Humidity

What is 100% RH? Fog

Dry Bulb TemperatureDry Bulb Temperature

Air temperature as read from a standard thermometer

Dry Bulb Temperature ºF

Wet Bulb TemperatureWet Bulb Temperature

Air temperature as read from a moistened thermometer

Wet Bulb Temperature

Dew Point Temperature ºF

Dew Point TemperatureDew Point Temperature

Temperature at which RH is 100%

Dew Point TemperatureDew Point Temperature

For air at 75ºF/65% RH,what is the dewpoint temperature?

Dew Point Temperature ºF

60ºF

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]

Influenced by Metabolism Migration Heat flow Clothing

Thermal Comfort FactorsThermal Comfort Factors

MetabolismMetabolism

Metabolism affects perception of thermal comfort

Muscular activity Digestive process Daily cycle Health Age Gender

MigrationMigration

Body attempts to maintain core temperature (98.6ºF) by shifting blood flow

Vasodilation Vasoconstriction

Heat FlowHeat Flow

Multiple mechanisms Convection Conduction Radiation Evaporation

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

Heat Flow – Conduction Heat Flow – Conduction

Caused by direct contact between two objects of different temperature Heat always flows from

warm to cool

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

Radiant Heat FlowRadiant Heat Flow

Season variations can change direction of radiant heat flow

Mean Radiant Temperature Mean Radiant Temperature (MRT)(MRT)

MRT approach is used in Europe as a means to lower operating temperatures

Heat Flow – Evaporation Heat Flow – Evaporation

Water changes from liquid to gas and this phase change extracts heat Respiration Perspiration

Compounds and/or mitigates the effects of other mechanisms

ClothingClothing