Application

Sequence of Operation
Pressurization Control
8
Siemens Industry, Inc.
Application Note, App 2926
140-1308
2015-07-07
Sequence of Operation
The following paragraphs present the sequence of operation for LCM-OAVS
Application 2626: Variable Air Volume Room Pressurization with BTU Compensation,
HW Reheat and Two Venturi Air Valves — One Exhaust, One Supply.
Pressurization Control
The goal of pressurization control is to maintain a fixed difference between the
volumes of total supply air and total exhaust air (see the following figure). The
controller selects supply and exhaust setpoints to balance flows while meeting supply
air requirements, and the supply and exhaust flows are individually controlled by their
respective feedback loops in order to meet the setpoints.
Room Airflow Balance
The difference between total supply flow and total exhaust flow is the room airflow
balance as shown in these calculations:
VOL DIFFRNC = TOTL EXHAUST – TOTL SUPPLY
-or-
VOL DIFFRNC = (HOOD VOL + GEX AIR VOL +
OTHER EXH) – (SUP AIR VOL + OTHER SUP)
The controller uses these calculations to maintain VOL DIFFRNC at the VOL DIF
STPT.
NOTE:
VOL DIFFRNC and VOL DIF STPT are positive numbers in a room that is negatively
pressurized and negative in a positively pressurized room.