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Heating Losses- Infiltration

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					Heating Losses-
Infiltration and Ventilation
ARCH-432
Attendance
  Which civilization
  made it a point to
  layout whole cities to
  take advantage of
  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

  Calculate infiltration/ventilation loads
  Be able to reduce/mitigate infiltration
  and ventilation loads
  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
         Moisture Load for a Typical Commercial Building




                             Doors
                              4%
                                             People
              Infiltration                    13%
                  11%

                                                      Permeance
                                                          0%




                               Ventilation
                                  72%
Ventilation/Infiltration Load for
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
Add Infiltration Through Open
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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