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Published byZoie Surgener Modified about 1 year ago

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Infiltration/Ventilation HVAC 7a CNST 305 Environmental Systems 1 Dr. Berryman

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Infiltration Types of heat losses? Types of heat gains?

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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

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Air Crack Method Divide by 60 min for CFM Lower pressure differentials mean tighter construction

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Crack Example (winter) EXAMPLE Given: 3 o 5 o Double Hung Window No added humidification IA conditions: DB=75 o F OA conditions: DB=-5 o F Medium Construction How many BTUH are lost due to frame wall infiltration?

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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 BH sens = 1.08 x T x CF 60

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Air Change Example EXAMPLE Given: 20’ x 60’ x 10’ room Winter - 0.35 RCH No added humidification IA conditions: DB=75 o F OA conditions: DB=-5 o F How many BTUH lost due to infiltration?

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Ventilation + pressure 1600 CFM 200 CFM 1400 CFM FA SA RA

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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

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Determining Ventilation Requirements Determinates Building Application # Occupants

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Ventilation - CFM per Person EXAMPLE Given: 2000 SF Coin Operated Laundry Winter design No added humidification IA conditions: DB=75 o F OA conditions: DB=-5 o F How many BTUH lost due to ventilation?

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Ventilation - Room Change Given: 2000 SF Coin Operated Laundry - 10’ walls Winter design 2.0 RCH No added humidification IA conditions: DB=75 o F OA conditions: DB=-5 o F How many BTUH lost due to ventilation?

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Summer Conditions - CFM per Person Given: 2000 SF Coin Operated Laundry 15 CFM/person summer IA conditions: DB=75 o F 40%RH OA conditions: DB= 95 o F WB=80 o F How many BTUH gained due to ventilation? BH sens = 1.08 x T x CFM BH lat = 0.68 x G x CFM

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In Class: Given: 2000 SF Coin Operated Laundry 10’ walls 1.5 RCH IA conditions: DB=75 o F 40%RH OA conditions: DB= 95 o F WB=80 o F How many BTUH gained due to ventilation? Summer Conditions - Room Change

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Next Time Heat Gains Chapter 2.6 – 2.8 (Toa)rooflights equipme nt floor exteriorwall glass solar glass conductio n infiltration people

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