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Infiltration/Ventilation
HVAC 7a
CNST 305 Environmental Systems 1Dr. Berryman
Infiltration
Types of heat losses?
Types of heat gains?
Calculating Infiltration Crack method Air change method Effective leakage-area method
Sensible
BH = 1.08 x T x CFM
Latent
BH = 0.68 x G x CFM
Equations w/ Air Constants
Air Crack MethodDivide by 60 min for CFM
Lower pressure differentials mean tighter construction
Crack Example (winter)
EXAMPLEGiven:
•3o 5o Double Hung Window
•No added humidification
•IA conditions: DB=75oF
•OA conditions: DB=-5oF
•Medium Construction
How many BTUH are lost due to frame wall infiltration?
Air Change Converts equation to cubic feet
Equals one room change Designer will use 0.3 to 2.0 room changes
per hour Occupancy Climatic condition (i.e. winter vs. summer) Construction (tight or loose)
Least accurate of the three methods
BHsens = 1.08 x T x CF60
Air Change Example
EXAMPLEGiven:
•20’ x 60’ x 10’ room
•Winter - 0.35 RCH
•No added humidification
•IA conditions: DB=75oF
•OA conditions: DB=-5oF
How many BTUH lost due to infiltration?
Ventilation
+ pressure
1600 CFM
200 CFM
1400 CFM
FA
SA
RA
Calculating Ventilation CFM per Person
Use ASHARE chart Room Air Change per Hour
0.5 – 2.0 RCH
Sensible
BH = 1.08 x T x CFM
Latent
BH = 0.68 x G x CFM
Equations w/ Air Constants
Determining Ventilation Requirements
Determinates Building
Application # Occupants
Ventilation - CFM per Person
EXAMPLEGiven:
•2000 SF Coin Operated Laundry
•Winter design
•No added humidification
•IA conditions: DB=75oF
•OA conditions: DB=-5oF
How many BTUH lost due to ventilation?
Ventilation - Room ChangeGiven:
•2000 SF Coin Operated Laundry - 10’ walls
•Winter design 2.0 RCH
•No added humidification
•IA conditions: DB=75oF
•OA conditions: DB=-5oF
How many BTUH lost due to ventilation?
Summer Conditions- CFM per Person
Given:
• 2000 SF Coin Operated Laundry
• 15 CFM/person summer
• IA conditions: DB=75oF 40%RH
• OA conditions: DB= 95oF WB=80oF
How many BTUH gained due to ventilation?
BHsens = 1.08 x T x CFM
BHlat= 0.68 x G x CFM
In Class: Given:
• 2000 SF Coin Operated Laundry 10’ walls
• 1.5 RCH
• IA conditions: DB=75oF 40%RH
• OA conditions: DB= 95oF WB=80oF
How many BTUH gained due to ventilation?
Summer Conditions- Room Change
Next Time Heat Gains Chapter 2.6 – 2.8 (Toa)
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