Heating Losses- Infiltration and Ventilation
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Transcript of Heating Losses- Infiltration and Ventilation
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Heating Losses-Infiltration and VentilationARCH-432
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AttendanceWhich civilization made it a point to layout whole cities to take advantage of passive heating? In what direction did the city streets run?
A. GreeceB. RomeC. EgyptD. PersiaE. Babylonia
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AttendanceThe ancient Greeks did this. What was shown is Priene (Priēnē); (5th Century B.C.), which had all of the streets laid out in an East-West fashion, thus allowing all homes to point South.
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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
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Aeschylus
Greetings Capt.
Kirk
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AttendanceAeschylus 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.
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Big Picture Momentroofroof
ExteriorExteriorwallwall
GlassGlassconductioconductio
nn
FloorFloor
Infiltration Infiltration and and VentilatioVentilationn
CeilingPartition
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Five main types of heat loss1. Transmission (conduction)2. Infiltration (convection)3. Ventilation (convection)4. Radiation (radiation)5. Moisture migration
roofroof
ExterioExteriorr
wallwall
GlassGlassconducticonducti
onon
FloorFloor
InfiltratioInfiltration and n and VentilatioVentilationn
Ceiling
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Summary of Heat LossesWallRoofFloorWindowsDoorsInfiltrationVentilation
Envelope Losses
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What You Need To KnowThe difference between ventilation and infiltrationCalculation methods for both ventilation and infiltration
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What You Need To Be Able To Do
Calculate infiltration/ventilation loadsBe able to reduce/mitigate infiltration and ventilation loadsEmploy techniques for increasing ventilation effectiveness
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TermsInfiltrationExfiltrationVentilationDirect Outside Air System (DOAS)
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Infiltration
“The uncontrolled introduction of outside air into a building.”
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Infiltration
The uncontrolled introduction of fresh air into a building.
1. Most subjective of all losses2. Oftentimes the largest of all heat losses.
Sometimes comprises up to 30% of the total
heating load.3. Ends up being an “educated guess”
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Why Is This Important?All buildings leakA tight building will leak .5 AC/HA leaky building can leak 3 AC/HRegardless of climate, air leaking into walls causes problems
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VentilationThe mechanical introduction of outside air (OA) to: Replace Oxygen Dilute contaminants Pressurize the building
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Moisture LoadMoisture Load for a Typical Commercial Building
Ventilation72%
Infiltration11%
People13%
Doors4%
Permeance0%
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Infiltration Calculation Methods
Crack methodAir Change Method‘Averaging’ method (‘I don’t know so I’m going to throw a dart’ method)
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Crack MethodPresumes 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
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Add Infiltration Through Open Door
Determine Door Usage Number of People per Minute = תDetermine CFM per person (D)
CFM = ת x D LEED-NC Credit EQ 5 for providing vestibules.
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Infiltration by Crack Method
Add CFM from Crack losses to CFM for Open Door losses
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Mitigate These LossesHow do you reduce or mitigate these losses?
(Review)
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Mitigation StrategiesPressurization
QS = 1.1 x CFM x (T2 – T1)
Vs.
QS = 1.1 x (CFH/ft of crack x ft of crack)/60 x ΔT
You own the variables!
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Infiltration VariablesReview
Wind velocity and directionStack effectsCorner roomsExhaust fans on or offPressure zoningFrequency of useMaintenance
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Stack EffectReview
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Air Change MethodOften used in residential construction and in large warehouses and similar buildings
CFM = A.C.H. x Volume (ft3)/60or
CFM = Volume (ft3)/Frequency (minutes)
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Air Change MethodUses same formula for sensible
Equals one room changeDesigner 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
Qsens = 1.1 x CFM x T
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Table 2-8
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Heat Loss Due to Infiltration
Infiltration Btu H = (.018) x (ACH) x V x (Ti –
To)ACH = air exchanges per hourV = volumeTi = inside temperature To = outside temperature
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Heat Loss Due to Infiltration
OR
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Heat Loss Due to InfiltrationInfiltration Btu H = 1.1 x CFM x (Ti – To)CFM = (ACH x volume) / 60 min per
hour
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Heat Loss Due to InfiltrationInfiltration 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.
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Btu Hour Loss due to Infiltration Main Area
CFM Ht. W. L. 1.10 air exch. vol. In cf / 60Temp. Ch.
12 46.66 74.66 1.10 0.5 41,803.63 348.36 76 29,123.19
Btu Hour Loss due to Ventilation Main Area
Ht. W. L. 1.10 sfcfm
exchange Occup.Temp. Ch.
12 46.66 74.66 1.10 3,483.64 0.180 34.84 76 66,983.35
Ra RpOccup/
10000.18 5 10.00
Infiltration & Ventilation
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Heat Gains Due to Infiltration
Latent LoadBtuH = 4500 x (air exchanges x
(volume) /60) x(W Final – W Initial)
(W Final – W Initial) = Difference Ratio Pounds of Moisture per dry air
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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)
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Heat Loss Due to Ventilation
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Heat Loss Due to Ventilation Ventilation Ra = Area Outdoor Air Rate Rp = People Outdoor Air Rate
Example: Pharmacy Ra = .18 Rp = 5
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Heat Loss Due to Ventilation
VentilationBtu H = 1.1 x [ (.18 x 3,632) + (30 x 5)] x
76o
= 67,214
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Ventilation and / or Infiltration
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