1. Philip Demokritou, Ph.D PART I
EH522
INDOOR
ENVIRONMENTAL QUALITY & HEALTH
Lecture 6
PART I
Thermal comfort & Environmental Comfort indices
PART II
Air properties and processes (Psychrometrics)
Philip Demokritou, Ph.D
Harvard School
of Public Health

2. Thermal Environmental Conditions for Human Occupancy
Reading Materials
ANSI/ASHRAE Standard :
Thermal Environmental Conditions for Human Occupancy
CHAPTER 4: Thermal Comfort
From: Lechner N. Heating, Cooling, Lighting, 3rd Edition. Hoboken, NJ: John Wiley & Sons, 2009.

3. Objectives of the Lecture
Discuss Thermal comfort and its environmental indices.
Discuss current standards and guidelines related to thermal comfort (ASHRAE 55 standard)
Discuss health effect issues related to thermal comfort conditions.
Introduce students to air properties and the processes taking place in the indoor environment. (Psychrometrics).

4. PART I: Thermal comfort & Environmental Comfort indices

5. Basic Definitions I: Heat Transfer
Three types of heat transfer
Conduction:
Whenever there is a temperature gradient in a solid medium
Movement of “free electrons” and atom oscillations
Convection:
Heat is transferred by the “bulk flow” of air/liquid medium.
Radiation:
Infrared radiation or thermal radiation. Movement through space from warm to cold surfaces (No medium is required)
Human body obeys the first law of thermodynamics:
Energy balance for human body

6. Thermal Environmental Conditions for Human Occupancy
What is Thermal Comfort ?
That condition of mind in which satisfaction is
expressed with the thermal environment.”
ANSI/ASHRAE Standard :
Thermal Environmental Conditions for Human Occupancy

7. TOTAL COMFORT- IEQ Health Thermal comfort IAQ Physiological Biological
Chemical
IAQ
HVAC Systems

8. Why should we care about comfort?
Health and well-being : many thermal comfort conditions can cause health problems
Optimize performance (for work or leisure)
Improve perceived quality of life
People will do whatever it takes to be comfortable-changing the micro-clima was always a high priority for humans.
CP191: Intro to Healthy Homes

9. Human body: A bio-engine
Our body burns “food” and generate energy through its metabolic activities.
Metabolism: Transformation of chemical energy to heat and work.
Metabolic rate is expressed in met units (1 met: 58.2 w/m2 of human surface (Human surface = 1.8 m2)

10. Metabolic Rates- Depend on activity

11. Thermal Comfort & Health Effects
Human body: Requires constant temp. (96.8F, 36.7C)
Slight body temp. variation can cause stress
+- 20 F body temperature diff. can cause death (hypothermia, hyperthermia)
Hypothalamus in brain –autonomic system responsible to control temperature
Skin contains nerve ends that can sense heat flow and humidity (not temperature!!!)
Autonomic system declines with age but also infants have less developed system

12. Heat dissipation mechanisms
From: Lechner N. Heating, Cooling, Lighting, 3rd Edition. Hoboken, NJ: John Wiley & Sons, 2009.

13. Heat dissipation and Environmental factors
Air temperature ~ Convection
Relative humidity ~ Evaporation
Air velocity near a human body, V ~ Convection
Surface temperature of the enclosure and other objects ~ Radiation
The way heat dissipates depends on EF and what else??? CLOTHING

14. Heat dissipation from human body- 2
Question:
Why are we sweating more in the Summer?
From: Lechner N. Heating, Cooling, Lighting, 3rd Edition. Hoboken, NJ: John Wiley & Sons, 2009.

15. Combined Heath effect: Temperature + Humidity

16. Humidity indoors Indoor humidity is a function of Outdoor humidity
Indoor sources:
Unvented cooking,
Unvented bathrooms
Showering
Number of Occupants
Humidifier use
Air conditioner use
Clothes drying--mechanical or air drying

17. Humidity – Heath Effects
DIRECT
Eye irritation
Respiratory
mucociliary clearance
asthma
Dermal
skin dryness
Comfort perception
INDIRECT
Biological
Dust mites (+)
Molds (+)
Cockroaches (+)
Infectious agents
Bacteria (+/-)
Viruses [+ adenoviruses]
Chemical
Ozone (-)
Formaldehyde, SO2, NO2 (+)

18. Humidity - Health Effects
(from Arundel et al., 1986)

19. Environmental conditions affecting thermal comfort
Primary factors:
Metabolic rate
Clothing insulation
Air temperature
Radiant temperature
Air- speed
Humidity
Personal factors
Non uniformity over body!

20. Energy production – Mechanical work = Heat losses
Can we predict thermal comfort?
Thermal comfort modeling- Energy balance on body :
Energy production – Mechanical work = Heat losses
M - W = Qsk + Qres
M - W = ( Csk + Rsk + Esk ) + ( Cres + Eres )
M - Rate of metabolic heat production (W/m2 body surface area)
W - Rate of mechanical work
Q - Heat losses
C - Convective heat losses
R - Radiative heat losses
E - Evaporative heat losses (sk – Skin, res – Respiration)
What happens if the heat dissipated to the Environment is less than the M-W???
Body thermal load=not dissipated to the environment heat from body !!!

21. Thermal comfort predictive model
Most widely used :
Prof. Fanger’s famous methods:
Comfort equation method (heat balance method)
(Links environmental conditions to body thermal load)
Predicted Mean Vote method (PMV model).
(links body thermal load to a Thermal sensation scale)
Predicted percentage of dissatisfied (PPD).
(Empirically PMV is related to PPD)
Standards:
ASHRAE Standard : “Thermal Environmental conditions for Human Occupancy.”
ISO Standard 7730: “Moderate thermal environments- Determination of the PMV and PPD Indices and specification of the conditions for thermal comfort”.

22. Predicted Mean Vote (PMV)
“Thermal sensation” scale
Predicted Mean Vote (PMV)
+ 3 hot
+ 2 warm
+ 1slightly warm
PMV =0 neutral
-1 slightly cool
-2 cool
-3 cold

23. PPD = 100 - 95 exp [ - (0.03353 PMV4 + 0.2179 PMV2)]
PMV/PPD method
PMV = [0.303 exp ( M ) ] L
L - Thermal load on the body
L = Internal heat production - heat loss to the actual environment
L = M - W - [( Csk + Rsk + Esk ) + ( Cres + Eres )]
Predicted Percentage Dissatisfied (PPD)
PPD = exp [ - ( PMV PMV2)]

24. CP191: Intro to Healthy Homes
PMV
PPD 5%
+- 0.5
20%
+-1.0
50%
+1slightly warm
-1slightly cool
CP191: Intro to Healthy Homes

25. Graphical representation
Thermal comfort zones?
Environmental Factors:
Metabolic rate- activity
Clothing- insulation
Air temperature
Radiant temperature
Air- speed
Humidity
ASHRAE
Based on satisfaction (20% PPD)
Season dependent
For Office buildings- not homes
Operative temperature

26. Operative Temperature
Operative temperature (To):
To = 0.45 Tair Tmrt
Tmrt - Mean radiant temperature
Tmrt = S AiTi / S Ai
Ti - Surface temperature of enclosure i
Ai - Area of surface i
NOTE: Operative temperature is the same as dry bulb temperature if there is no radiant heat!!! ( cos Tair =Tmrt)

27. Graphical representation
Thermal comfort zones?
ASHRAE
Based on satisfaction (20% PPD)
Season dependent
For Office buildings- not homes (specific activity level, clothing level)
Adjusted comfort zones for other conditions (ie. air speed, clothing etc)
Summer
Winter

28. Example: Effect of air motion

29. PART II: Air properties and processes
(Psychrometrics)

30. Air Composition (two components) Moist air = Dry air + water vapor
Moist Air and its Properties
Air Composition (two components)
Moist air = Dry air + water vapor
Dry air composition (volume fraction):
Nitrogen %
Oxygen %
Argon %
Carbon dioxide %
Minor gases %

31. Fundamental Parameters I
Pressure
Temperature (Dry Bulb Temperature), Tdb
Humidity Ratio, W
Relative Humidity RH
pw = partial pressure of the water vapor in the air
ps = partial pressure of the water vapor in a saturated mixture under the same temperature
EXAMPLE:
Dry air: RH=0% Saturated air: RH=100%
Difference between W and RH: W : water content RH: saturation degree

32. Fundamental Parameters II
Dewpoint Temperature, Tdp
Temperature that “air saturation” occurs
(Condensation on window and wall surfaces will occur)
Wet Bulb Temperature, Twb
The temperature measure of moisture content in the air
cloth wick
water
Enthalpy=enthalpy of the dry air + enthalpy of the water vapor
(Enthalpy is energy per unit mass KJ/Kgda)
Sling psychrometer
Enthalpy, h

33. Graphical representation: Psychrometric Chart, Mollier diagram
Moist air properties- Graphical representation
For a given atmospheric pressure, two air properties define ALL “thermodynamic properties” of moist air.
Graphical representation: Psychrometric Chart, Mollier diagram

34. Psycrometric Chart On the P. Chart: STATE is a point,
PROCESS (sequence of states) is a line on the Chart.
From: Lechner N. Heating, Cooling, Lighting, 3rd Edition. Hoboken, NJ: John Wiley & Sons, 2009.

35. Psycrometric Chart

36. Properties of Air on Psycrometric chart
TDB
W, TDP v
TWB RH
RH 100%
RH 100%
RH 100%
RH 100%

37. Example I:
From: Lechner N. Heating, Cooling, Lighting, 3rd Edition. Hoboken, NJ: John Wiley & Sons, 2009.

38. Example II:
From: Lechner N. Heating, Cooling, Lighting, 3rd Edition. Hoboken, NJ: John Wiley & Sons, 2009.

39. Example III: QUESTION: In a room: (condition A)
The windows have temperature of T= 9 C
Water Condensation on the window?
Tdp=12 C

40. HEATING, VENTILATION, & AIR-CONDITIONING (HVAC) SYSTEMS

41. OBJECTIVES OF HVAC SYSTEMS
Temperature Control
Humidity Control
Air Distribution
Air Motion
Building Pressurization (0.05 in. w.)
Indoor Air Quality (IAQ)
Dilution ventilation
Air cleaning (e.g., filtration)
GENERATE/DISTRIBUTE contaminants???

42. Basic Air Conditioning Processes
Sensible Heating / Cooling
Cooling and dehumidification
Heating and humidification
Humidification
Adiabatic Mixing of Air
On the P. Chart:
STATE is a point,
PROCESS (sequence of states) is a line on the Chart.
EXAMPLES:
Sensible Heat (change TDB, constant W)
Latent Heat (constant TDB, change W)

43. h1 h2 DQ(Heat)=Dh (Energy balance) Water vapor (Humidity)
Air Processes
DQ(Heat)=Dh (Energy balance) W1 T1 h1 W2 T2 h2
Water vapor (Humidity)
HEAT & MASS BALANCE

44. Example 1: Sensible heating and cooling2
heating
cooling
W1 = W2 DH

45. Example 2:Latent Heat- Humidification1 2
heating W2 DH W1
Tdb1 = Tdb2

46. Example 3: Heating- Cooling1 2 W2 DH 1 W1 2
Tdb1 Tdb2

47. hC hA hB Example 4: Adiabatic Mixing
The heat balance for the mixture can be expressed as
mA hA + mC hC = (mA + mC)hB         (1)
where 
m = mass flow of the air 
h = enthalpy of the air 
The moisture balance for the mixture can be expressed as:
mA wA + mC wC = (mA + mC) wB        (1)
w = humidity ratio in the air B WC TC hC mC WA TA hA mA WB TB hB A C

48. Example 4: Adiabatic Mixing (P. Chart)hc A C WB DH
When mixing air of condition A and air of condition C, then
mixing point will be on the straight line between the two conditions in point B.
The position of point B depends on the volume of air A to the volume of air C. hB hA Wc B WA
TdbA TdbB
TdbC

49. Thank you for your attention