Thermal Comfort
SNRG 154 – Building Systems
Sustainable Energy and Building Technology Program
Humber College – School of Applied Technology
Dragos Paraschiv, P.Eng.
dragos.paraschiv@humber.ca
Course Outline
Module 1: Introduction and terminology
Module 2: Thermal Comfort
Module 3: Indoor air quality
Module 4: Basics of Heat Loss/Gain and Equipment Sizing
Module 5: Wall and Roof Systems
Module 6: Moisture and Thermal protection
Module 7: Doors and Windows
Mid Term
Module 8: Active climate controls
Module 9: Heating Equipment
Module 10: Cooling Equipment
Module 11: Air Handling Equipment and Systems
Module 12: Piping Equipment and Systems
Module 13: HVAC for Small Buildings
Module 14: HVAC for Large Buildings
Module 15: Plumbing Systems
Module 16: Fire Protection
Final Exam 2
Session Outline
ASHRAE 55-2017
Influencing Factors
o Direct
o Indirect
Indoor Conditions
4
Definition of Thermal Comfort
ASHRAE Standard 55-2017
Thermal Environmental Conditions
for Human Occupancy
o The condition of mind that expresses
satisfaction with the thermal environment; it
requires subjective evaluation.
5
Comfort Air Conditioning
Heats
Humidifies
Cools
Dehumidifies
Ventilates
Filtrates
Circulates
6
Body Temperature Control
Excess heat is rejected by:
o Conduction
o Convection
o Radiation
o Evaporation
7
CLO Unit
The CLO unit is used to specify the insulation
effect of clothing:
o CLO = 0, for the nude body
o CLO = 0.35-0.60, for summer, lightweight clothing
o CLO = 0.8-1.2, for a typical indoor winter ensemble
o 1 CLO = 0.88 (ft2 h ºF) / Btu
o Temperature boundary can be shifted 1 deg. F per 0.1
CLO
8
Mean Radiant Temperature
The uniform surface temperature of an
imaginary black enclosure in which an
occupant would exchange the same
amount of radiant heat as in the actual
non-uniform space.
9
Direct Influencing Factors
Dry-bulb temperature
Wet-bulb temperature
Dew-point temperature
Relative humidity
Air movement
All HVAC systems aim to maintain temperature, humidity
and air movement within an acceptable range
10
Indirect Influencing Factors
Heat stress index
Index of skin wetness
Wind chill index
11
Dry-bulb Temperature
The air temperature as measured by a
thermometer
Referred to as sensible temperature
12
Wet-bulb Temperature
The temperature of the air as measured by
a thermometer with the bulb covered with
a water saturated wick.
Equilibrium temperature of water
evaporating into the air when the latent
heat is supplied by the sensible heat of the
air.
13
Dew-point Temperature
The temperature at which a specified
sample of air, with no moisture added or
removed, would be completely saturated.
The temperature below which air on being
cooled gives up moisture or dew.
14
Air Movement
Supply air should be distributed in such a
way that the occupied zone (floor level to 6 ft
above) has only minor horizontal or vertical
temperature variations.
Air velocity in the space of 15 to 25 fpm is
considered to be still air, while air moving at
65 fpm would be considered a draft to most
people.
A draft may be defined as a noticeable air
current.
15
Air Movement (cont.)
The average air velocity through supply air
diffusers may be 500 to 700 fpm.
In order to heat a conditioned space, the
supply air may be introduced into the space
at 10 deg F to 50 deg F above the design
space temperature and at a velocity
considerably above 15 fpm.
For cooling a conditioned space, the air may
be supplied at 12 deg F to 30 deg F below
the required final space temperature.
16
Non-steady State
Temperature fluctuations
o Rate of change should be less than 4 def. F
per hour
o No restrictions if the peak-to-peak difference
is less than 2 deg F
Humidity fluctuations
o The rate of humidity change should not
exceed 20% per hour
17
Indoor Conditions
The indoor conditions to be maintained
within a building for comfort considerations
are assumed to be the average conditions
at the breathing line, 3 ft to 5 ft above the
floor.
18
Indoor Conditions (cont.)
Examples of typical winter indoor dry-bulb
temperatures (in deg. F):
o Schools
Classrooms 72-74
Gymnasiums 55-65
o Hospitals
Private Room 72-74
Operating Room 70-95
o Home 73-75
o Stores 65-68
o Steam Bath 110
19
Humidity Levels
The humidity level should be maintained
between 30% and 70%
Water vapour originates from activities such
as cooking, laundering, bathing and our
breathing and perspiring
Problems involving moisture may arise from
changes in moisture content, from the
presence of excessive or insufficient moisture
in materials, or from the effects associated
with its change of phase.
20
Humidity Levels (cont.)
The extent to which a building may be humidified
in the winter depends on the ability of the walls,
roof and other elements of the building enclosure
to prevent or tolerate moisture condensation.
The formation of condensed moisture or frost on
surfaces exposed to the building interior, or visible
condensation, can result in deterioration of the
surface finish, mould growth subsequent indirect
moisture damage and nuisance, and reduction of
visibility through windows.
21
Static Electricity
With many materials, relative humidity of
45% or more is usually required to reduce
or eliminate electrostatic effects.
Hospital rooms usually require relative
humidity of 50% or more. It is
recommended for safety and comfort that
hospital operating rooms be maintained at
72 deg F and 55% RH.
22
Prevention and Treatment of Disease
Relative humidity has a significant effect
on the control of airborne infection.
At 50% RH, the mortality rate of certain
organisms is highest.
Example influenza virus loses much of its
virulence.
The mortality rate decreases both above
and below this value.
23
Visible Condensation
Condensation occurs on any interior
surface when the dew-point temperature
of the air in contact with it exceeds the
surface temperature.
In general windows see the first signs
having the lowest thermal resistance and
thereby provide the best guide to the
permissible indoor humidity level for no
condensation.
24
Concealed Condensation
The humidity level that a building can
tolerate without serious difficulties from
concealed condensation may be much
lower then indicated by visible
condensation criteria.
25
End of Session 2
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