Thermal Comfort
Arch 140, Lecture #12
Thursday, February 26, 2009
What is Thermal Comfort?
ASHRAE*definition:
“…that condition of mind which
expresses satisfaction with the
thermal environment”
But thermal discomfort is
easier to define and
measure, as a result ….
Engineer’s view:
Comfort
= absence of discomfort
= “neutrality”
* American Society of Heating, Refrigerating, and Air-Conditioning Engineers
Experiential goals –
Thermal neutrality or Thermal delight ??
Thermal comfort & architectural elements
Thermal comfort & the workplace
~ 200 $/ft2-yr
200 -
150 -
$/ft2--year
100 -
~2 $/ft2-yr ~ 20 $/ft2-yr
50 -
0-
Energy Finance Occupants (salaries)
Over the life of a building, occupancy costs substantially
exceed both energy and financing costs
Comfort & the Body’s Heat Balance
Heat Gains & Losses
37 °C = 98.6 ˚F
Physiological Control Mechanisms - Involuntary
Influences our body’s thermoregulatory system
1. Blood flow
- vasoconstriction
- vasodilation
2. Sweating
3. Shivering
4. Goosebumps
Behavioral Control Mechanisms - Voluntary
Environmental Personal
- Turning on/off fan - Changing clothing
- Turning on/off heater - Changing activity
- Opening/closing: - Changing posture,
> windows position or location
> blinds & shades - Eating/drinking
something cold or hot
Major Variables Influencing Thermal Comfort
Measurable factors that influence the body’s
heat balance
Environmental Personal
1. Air temperature 1. Activity
2. Humidity 2. Clothing
3. Air velocity
4. Mean radiant temperature
Air Temperature
Effect of Air Temperature & Heat Loss
A =
Total Body Heat
Gain / Loss
B =
“Dry” Heat Loss
(convection +radiation)
C =
“Wet” Heat Loss
(evaporation)
Humidity
Measures of Humidity
RH Relative Humidity (%)
DP Dew Point temperature (ºF)
WB Wet-Bulb temperature (ºF)
W Humidity ratio (lb,water / lb,air)
Air Velocity
Results: background survey--
air Field Studies:
movement air movement
preference question preference
want less 4%
want less 4%
(n=4)
(n=4)
no change 43% want more 53% no change 58% want more 38%
(n=45) (n=55) (n=55) (n=36)
Summer, n=104 Winter, n=95
People want more air movement,
not less, even in winter
Mean Radiant Temperature
Mean Radiant Temperature
Operative Temperature
combines air & mean radiant temp.
Major Variables Influencing Thermal Comfort
Measurable factors that influence the
body’s heat balance
Environmental Personal
1. Air temperature 1. Activity
2. Humidity 2. Clothing
3. Air Velocity
4. Mean radiant temperature
Activity Metabolic Heat Production
1 MET = 18.4 Btu/ft2-hr, sedentary activity
1 met 1.4 met 3.0 met 4.0 met
Table of activity & met values – See Lecture Handout, p. 25
Clothing Insulation Value
1 CLO = 0.88 (hr-ft2-ºF/Btu), typical 3-piece suit
0.2 clo 0.8 clo 1.0 clo 3.0 clo
Table of clothing & clo values – See Lecture Handout, p. 25
Clothing Insulation Value
1 CLO = 0.88 (hr-ft2-ºF/Btu), typical 3-piece suit
0.2 clo 0.8 clo 1.0 clo 3.0 clo
Table of clothing & clo values – See Lecture Handout, p. 25
0.9 – 1.3 clo
0.7 – 0.8 clo
0.1 – 0.4 clo
0.8 clo 0.5 clo 0.8 clo
1.6 met 2.2 met 2.3 met
70°F 70°F 64°F
7th inning stretch
Research Standards Practice
Thermal Comfort
Standards & Research
How is comfort measured?
• 7-point Thermal Sensation Scale
• “Comfort” or “Satisfaction” is associated
with thermal sensations
+3 Hot
+2 Warm
+1 Slightly warm
0 Neutral Comfortable
-1 Slightly cool
-2 Cool
-3 Cold
Predicted Mean Vote (PMV) and
Predicted Percent Dissatisfied (PPD)
Min = 5% dissatisfied You can’t satisfy
everyone!
ASHRAE* Thermal Comfort Standard
Humidity Ratio
Operative Temperature
Two “comfort zones”
based on assumed
seasonal clo values
* American Society of Heating, Refrigerating, and Air-Conditioning Engineers
Basis for existing standards
• Laboratory experiments, based on:
4 (environmental) + 2 (personal) variables
• Ask people about “thermal sensation”
(cold --- neutral --- hot)
• Develop heat-balance model of the
human body & comfort responses
• “Comfort wisdom” = uniform & steady
Problems with existing standards
• Reality check: Laboratory ≠ Real buildings
• One-size-fits all: Universally applied to all
climates, cultures, and building types
• Energy intensive: Broad application of narrow
setpoints exaggerates the “need” for a.c.
A new approach: “Adaptive” Thermal Comfort
• Based on field data
• 3 types of adaptation:
- physiological
- behavioral
- psychological
• Satisfaction influenced by
expectations & context
• Outdoor climate is an
important influence
Overview of research
• 22,000 sets of raw data from existing studies
- physical and subjective data
- 160 buildings, 4 continents
• Separate analysis for :
- air-conditioned (HVAC)
- naturally ventilated (NV)
• Statistical models
produced a new
standard for NV buildings
SELECTED RESULTS
Observed vs. predicted comfort in
centralized HVAC buildings
indoor comfort temperature, Top (oC)
27
Predicted: Lab-based PMV model
26 Observed: Field-based adaptive model
25
24
23
22
21
20
-5 0 5 10 15 20 25 30 35
o
outdoor temperature index, ET* ( C)
SELECTED RESULTS
Observed vs. predicted comfort in
naturally ventilated buildings
indoor comfort temperature, Top (oC)
27
Predicted: Lab-based PMV model
26 Observed: Field-based adaptive model
25
24
23
22
21
20
-5 0 5 10 15 20 25 30 35
o
outdoor temperature index, ET* ( C)
Design Examples – buildings that have used the Adaptive
Comfort Standard in designing for natural ventilation
• San Francisco Federal Building
• Evergreen Valley College
• Northern Arizona University
• Kirsch Environmental Science Building
• Stanford Science & Engineering Building
• UC San Diego office building
• Rand Corporate Headquarters
• Pier 1 Embarcadero
• IB Tower Lobby Renovation
• Alley 24 speculative office building
• Angola classrooms
New directions in thermal comfort
• Thermal monotony
or thermal delight?
• The role of control?
• Mixed-mode:
the best of
both worlds?
Announcements – Midterm
Midterm Review Session
– Sunday, March 1, 7-9 pm, Room 112
Midterm – next Thursday, March 5
Material covered through this week
See example Midterm on web
Closed book exam.
Equations, property values, etc. provided
Bring: pencil(s), eraser, calculator, LOFSAC
Remember the Building Bioclimatic Chart ??
Temperature (T)
Relative Humidity (RH)
Same Chart – Different Format
“Psychrometric Chart”
Relative Humidity (curved lines)
Dewpoint Temperature
Humidty Ratio or
Temperature
“Psychrometric Chart”
Relative Humidity (curved lines)
Dewpoint Temperature
Humidty Ratio or
Temperature
