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
Mesa Verde: vernacular, passive solar, sun angles, thermal mass

3. Psychrometrics Measurement of moisture content and air temperature.
BH061

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
Air temperature as read from a moistened thermometer
Wet Bulb Temperature

8. Dew Point Temperature Temperature at which RH is 100%
Dew Point Temperature ºF

9. Dew Point Temperature For air at
75ºF DBT/65 ºF WBT, what is the dew point temperature?
Dew Point Temperature ºF
60ºF

10. Standard Comfort Zone Conditions where the typical occupant
[L: p. 72, fig. 4.8a]
Conditions where
the typical occupant
is comfortable for the
given intent of a
space.
BH048

11. Thermal Comfort Factors
Influenced by
Metabolism
Migration
Heat flow
Clothing
BH040

12. Metabolism Metabolism affects perception of thermal comfort
Muscular activity
Digestive process
Daily cycle
Health
Age
Gender
BH024

13. Migration
Body attempts to maintain core temperature (98.6ºF) by shifting blood flow
Vasodilation
Vasoconstriction
BH024

14. Heat Flow Multiple mechanisms Convection Conduction Radiation
Evaporation
BH030

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
BH030

16. Heat Flow – Conduction
Caused by direct contact between two objects of different temperature
Heat always flows from warm to cool
BH030

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
BH030

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
BH030

21. Clothing Compounds and/or mitigates the effects of other mechanisms
BH049