Chapter 4

Thermal Comfort

Fadi A. Fatayer

What is Thermal Comfort?

- That condition of mindwhich expresses satisfactionwith the thermal environment.ISO 7730

Definition

◦ Thermal Comfort◦ Acoustic◦ Lighting◦ Psychological◦ Ergonomics.

When we talk of human comfort, various aspects are important:

Individual factors

◦Activity◦Clothing

Environmental factors◦Air Temperature◦Relative Humidity◦Air Speed◦Mean Radiant

temperature

“Thermal Comfort” of a human being is influenced by:

Mean Radiant Temperature

The Mean Radiant Temperature is that uniform temperature of an imaginary black enclosure resulting in same heat loss by radiation from the person, as the actual enclosure.

Measuring all surface temperatures and calculation of angle factors is time consuming. Therefore use of Mean Radiant Temperature is avoided when possible.

Actual room Imaginary room

RR’

t1

t2

tr

t3

t4

Heat exchange by radiation:R=R’

Activity Affects the Level of Comfort

r e s t i n g l i g h t i n d u s t r i a l

o f f i c e w o r k h i g h a c t i v i t y

Metabolic Rate Energy released by

metabolism depends on muscular activity.

Metabolism is measured in Met (1 Met=58.15 W/m2 body surface).

Body surface for normal adult is 1.7 m2.

A sitting person in thermal comfort will have a heat loss of 100 W.

Average activity level for the last hour should be used when evaluating metabolic rate, due to body’s heat capacity.

0.8 Met

1 Met

8 Met

4 Met

Met Value TableActivity Metabolic rates [M]

Reclining 46 W/m2 0.8 Met

Seated relaxed 58 W/m2 1.0 Met

Clock and watch repairer 65 W/m2 1.1 Met

Standing relaxed 70 W/m2 1.2 Met

Car driving 80 W/m2 1.4 Met

Standing, light activity (shopping) 93 W/m2 1.6 Met

Walking on the level, 2 km/h 110 W/m2 1.9 Met

Standing, medium activity (domestic work)

116 W/m2 2.0 Met

Washing dishes standing 145 W/m2 2.5 Met

Walking on the level, 5 km/h 200 W/m2 3.4 Met

Building industry 275 W/m2 4.7 Met

Sports - running at 15 km/h 550 W/m2 9.5 Met

Met Value Examples

Walking 3.5 km/h2.5 MET

Jogging8 MET

After 10 MET

Met Value Examples

Influencing Factors

• Other factors affecting comfort:• age

• sensation of old people and younger people

• adaptation• people in warm climates may adapt to hot environment

• sex• women: lower skin temp., evap loss and lower met. rate• clothing and perferrence of temp.

Maintain operative temperature between:

◦ 20.0 to 23.5o C in winter

◦ 22.5 to 26.0o C in summer

Maintaining Rh between 30 to 60%

AIR Speed between 0.1 to 0.35 m/s

Complying with ASHRAE 55 or ISO 7730 would mean:

Four ways the body regulates heat:

• conduction

• convection

• thermal radiation

• evaporation

Space conditions to control:

• surface temperature

• air temperature

• relative humidity

• air motion

Body TemperatureRegulation and Control

Surface

Temperature

Air Motion

Convection

Body Temperature Normal body core temperature:

37 oC. We have separate Heat- and Cold-

sensors.◦Heat sensor is located in hypothalamus. Signals when temperature is higher than 37 oC.

◦Cold sensors are located in the skin. Send signals when skin temperature is below 34 oC.

Heating mechanism:◦Reduced blood flow.◦Shivering.

Cooling mechanism:◦ Increased blood flow.◦ Sweating (Evaporation).

Hot Cold

37 oC 34 oC

The Energy Balance

Thermal Comfort can only be maintained when heat produced by metabolism equals the heat lost from body.

HeatLost

HeatProdu-ced

Comfort Chart

Occupant Satisfaction and Productivity

• 75% of all occupant complaints within buildings are thermal comfort related

• The thermal environment has been shown to have up to a 10% effect on worker productivity

• Energy consumption

• Over $80 billion per year is spent to heat and cool buildings

Why thermal comfort is important?