Heating Losses- Infiltration

Report
Heating LossesInfiltration 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
The ancient Greeks did
this. What was shown
is Priene (Priēnē); (5th
Century B.C.), which
had all of the streets
laid out in an EastWest fashion, thus
allowing all homes to
point South.
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
Greetings
Capt.
Kirk
Aeschylus
Attendance
Aeschylus pronounced Ess ca less
One of the earliest writer of Greek
tragedy – before him plays had single
actors who could only respond to a
chorus (group of people). Aeschylus
increase the tragedy to two actors with
dialog.
Big Picture Moment
roof
Infiltration
and
Ventilation
Ceiling
Partition
Glass
conduction
Exterior
wall
Floor
roof
Infiltration
and
Ventilation
Glass
conductio
n
Exterior
wall
Ceiling
Five main types of heat loss
1.
2.
3.
4.
5.
Transmission (conduction)
Infiltration (convection)
Ventilation (convection)
Radiation (radiation)
Moisture migration
Floor
Summary of Heat Losses
Wall
Roof
Floor
Windows
Doors
Infiltration
Ventilation
Envelope Losses
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.”
Infiltration
The uncontrolled introduction of fresh air into a building.
1. Most subjective of all losses
2. Oftentimes the largest of all heat losses.
Sometimes comprises up to 30% of the total
heating load.
3. Ends up being an “educated guess”
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%
Infiltration
11%
People
13%
Permeance
0%
Ventilation
72%
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)
CFM = ‫ ת‬x D
LEED-NC Credit EQ 5 for
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?
(Review)
Mitigation Strategies
Pressurization
QS = 1.1 x CFM x (T2 – T1)
Vs.
You own the
variables!
QS = 1.1 x (CFH/ft of crack x ft of
crack)/60 x ΔT
Infiltration Variables
Review
Wind velocity and direction
Stack effects
Corner rooms
Exhaust fans on or off
Pressure zoning
Frequency of use
Maintenance
Stack Effect
Review
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
Heat Loss Due to
Infiltration
Infiltration
Btu H = (.018) x (ACH) x V x (Ti –
To)
ACH
V
Ti
To
= air exchanges per hour
= volume
= inside temperature
= outside temperature
Heat Loss Due to
Infiltration
OR
Heat Loss Due to
Infiltration
Infiltration
Btu H = 1.1 x CFM x (Ti – To)
CFM = (ACH x volume) / 60 min per hour
Heat Loss Due to
Infiltration
Infiltration
Please Note:
For tight construction use 0.5 for ACH.
For medium construction use .85 for ACH.
For loose construction use 1.3 for ACH.
For really bad construction use 2.0 for ACH
For the summer months (cooling) use 70% of the
winter values.
Infiltration & Ventilation
Btu Hour Loss due to
Infiltration Main Area
CFM
Ht.
12
W.
L.
1.10 air exch. vol. In cf
46.66 74.66 1.10
0.5
41,803.63
Temp.
/ 60
Ch.
348.36 76
29,123.19
Btu Hour Loss due to
Ventilation Main Area
Ht.
12
W.
L.
1.10
46.66 74.66 1.10
Occup/
Ra
Rp 1000
0.18
5
10.00
cfm
sf
exchange Occup.
3,483.64 0.180
34.84
Temp.
Ch.
76
66,983.35
Heat Gains Due to
Infiltration
Latent Load
BtuH = 4500 x (air exchanges x (volume)
/60) x
(W Final – W Initial)
(W Final – W
of
Initial)
= Difference Ratio Pounds
Moisture per dry air
Heat Loss Due to
Ventilation
Ventilation
Btu H = 1.1 x [(Ra x square feet of building )
+
(number of people in the building x Rp )]
x
(Ti – To)
Heat Loss Due to
Ventilation
Heat Loss Due to
Ventilation
Ventilation
Ra = Area Outdoor Air Rate
Rp = People Outdoor Air Rate
Example: Pharmacy
Ra = .18
Rp = 5
Heat Loss Due to
Ventilation
Ventilation
Btu H = 1.1 x [ (.18 x 3,632) + (30 x 5)] x 76o
= 67,214
Ventilation
and / or
Infiltration

similar documents