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74 TRG-TRC014-EN
notes
period five
Application Considerations
Building Pressure Control
Maintaining a slightly positive pressure inside buildings, especially in humid
climates, increases comfort and helps avoid indoor air quality (IAQ) problems
related to microbial growth and outdoor contaminant sources.
Whenever variable quantities of outdoor air are brought into a system, building
pressurization becomes a concern. Resetting the quantity of outdoor air in
response to part-load conditions, or using an outdoor air economizer, may lead
to undesirable changes in building pressure. Varying the quantity of outdoor air
requires the system to exhaust a similar quantity of air to avoid
overpressurizing or underpressurizing the building.
There are several methods used to control building pressure in a VAV system.
The method that is commonly considered the best-suited for VAV applications
is direct control of a central relief fan.
Building Pressure Control
OA
EA
RA
supply
supply
fan
fan
PA
SA
Figure 102
outdoor
static pressure
outdoor
outdoor
static pressure
static pressure
representative
representative
space static
space static
pressure
pressure
OA
EA
supply
supply
fan
fan
relief
relief
fan
fan
RA
Direct Pressurization Control
controllercontroller
controller
PA
SA
Figure 103