# Heating Losses- Infiltration

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```					Heating Losses-
Infiltration and Ventilation
ARCH-432
Attendance
Which civilization
layout whole cities to
passive heating? In
what direction did the
city streets run?
A. Greece
B. Rome
C. Egypt
D. Persia
E. Babylonia
Attendance

“Only primitives and barbarians lacked
knowledge of houses turned to face the
winter sun, dwelling beneath the
ground like swarming ants in sunless
caves.”
Aeschylus
Big Picture Moment
roof

Infiltration   Ceiling
and
Ventilation                      Partition

Glass
conduction

Exterior
wall
Floor
Summary of Heat Losses
Wall
Roof             Envelope Losses
Floor
Windows
Doors
Infiltration
Ventilation
What You Need To Know
The difference between ventilation and
infiltration
Calculation methods for both ventilation
and infiltration
What You Need To Be Able To Do

Be able to reduce/mitigate infiltration
Employ techniques for increasing
ventilation effectiveness
Terms
Infiltration
Exfiltration
Ventilation
Direct Outside Air System (DOAS)
Infiltration

“The uncontrolled
introduction of
outside air into a
building.”
Why Is This Important?
All buildings leak
A tight building will leak
.5 AC/H
A leaky building can
leak 3 AC/H
Regardless of climate,
air leaking into walls
causes problems
Ventilation
The mechanical introduction of outside
air (OA) to:
   Replace Oxygen
   Dilute contaminants
   Pressurize the building
Moisture Load for a Typical Commercial Building

Doors
4%
People
Infiltration                    13%
11%

Permeance
0%

Ventilation
72%
Heating

All sensible (why?)

Q = 1.1 x CFM x (T2 – T1) in BTU/HR
Infiltration Calculation Methods

Crack method
Air Change Method
‘Averaging’ method (‘I don’t know so
I’m going to throw a dart’ method)
Crack Method
Presumes that an accurate estimate can
be obtained by estimating the rate of
infiltration per foot of crack for doors
and windows

CFM = Ft. of Crack x Infiltration Rate

QS = 1.1 x CFM x (T2 – T1) in BTU/HR
Door
Determine Door Usage
   ‫ = ת‬Number of People per Minute
Determine CFM per person (D)

LEED-NC Credit EQ 5 for
CFM = ‫ ת‬x D           providing vestibules.
Infiltration by Crack Method
Add CFM from Crack losses to CFM for
Open Door losses
Mitigate These Losses
How do you reduce
or mitigate these
losses?
Mitigation Strategies
Pressurization

QS = 1.1 x CFM x (T2 – T1)

You own the
Vs.                          variables!

QS = 1.1 x (CFH/ft of crack x ft of
crack)/60 x ΔT
Infiltration Variables
Wind velocity and direction
Stack effects
Corner rooms
Exhaust fans on or off
Pressure zoning
Frequency of use
Maintenance
Stack Effect
Air Change Method
Often used in residential construction
and in large warehouses and similar
buildings

CFM = A.C.H. x Volume (ft3)/60
or
CFM = Volume (ft3)/Frequency (minutes)
Air Change Method
Uses same formula for sensible
Qsens = 1.1 x CFM x T

Equals one room change
Designer will use 0.3 to 2.0 air changes per
hour (ACH)
   Occupancy
   Climatic condition (i.e. winter vs. summer)
   Construction (tight or loose)
Least accurate of the three methods
Table 2-8

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 views: 6 posted: 2/10/2012 language: pages: 24