Infiltration/Ventilation

1
Infiltration/Ventilation

• HVAC 7a
• CNST 305
• Environmental Systems 1
• Dr. Berryman

2
Infiltration
Types of heat losses?
Types of heat gains?
3
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
4
Air Crack Method
Divide by 60 min for CFM
Lower pressure differentials mean tighter
construction
5
Crack Example (winter)
BHsens 1.08 x ?T x CFM

• Given
• 3o 5o Double Hung Window
• No added humidification
• IA conditions DB75oF
• OA conditions DB-5oF
• Medium Construction
• How many BTUH are lost due to frame wall
  infiltration?

1.08 x 80oF x (16LF)(21 CF/60)
EXAMPLE
484 BH
6
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

7
Air Change Example

• Given
• 20 x 60 x 10 room
• Winter - 0.35 RCH
• No added humidification
• IA conditions DB75oF
• OA conditions DB-5oF
• How many BTUH lost due to infiltration?

EXAMPLE
BHsens 6,048
8
Ventilation
FA
200 CFM
SA
1600 CFM
RA
pressure
1400 CFM
9
Calculating Ventilation

• CFM per Person
• Use ASHARE chart
• Room Air Change per Hour
• 0.5 2.0 RCH

10
Determining Ventilation Requirements

• Determinates
• Building Application
• Occupants

11
Ventilation - CFM per Person

• Given
• 2000 SF Coin Operated Laundry
• Winter design
• No added humidification
• IA conditions DB75oF
• OA conditions DB-5oF
• How many BTUH lost due to ventilation?

BHsens 1.08 x ?T x CFM
EXAMPLE
(1.08)(80oF)(15cfm)(40 people)
BHsens 51,840
12
Ventilation - Room Change

• Given
• 2000 SF Coin Operated Laundry - 10 walls
• Winter design 2.0 RCH
• No added humidification
• IA conditions DB75oF
• OA conditions DB-5oF

How many BTUH lost due to ventilation?
BHsens 57,600
13
Summer Conditions- CFM per Person

• Given
• 2000 SF Coin Operated Laundry
• 15 CFM/person summer
• IA conditions DB75oF 40RH
• OA conditions DB 95oF WB80oF
• How many BTUH gained due to ventilation?

BHsens 1.08 x ?T x CFM
(1.08)(20oF)(15cfm)(40 people)
BHsens 12,960
BHlat 0.68 x ?G x CFM
(0.68)(80g)(15cfm)(40 people)
BHlat 32,640
BHsummer 45,600
14
In Class
Summer Conditions- Room Change

• Given
• 2000 SF Coin Operated Laundry 10 walls
• 1.5 RCH
• IA conditions DB75oF 40RH
• OA conditions DB 95oF WB80oF
• How many BTUH gained due to ventilation?

15
Next Time

• Heat Gains
• Chapter 2.6 2.8 (Toa)