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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