Application

Overview

Hardware Inputs

Siemens Industry, Inc.

Application Note, App 2926

140-1308

2015-07-07

Overview

Application 2926 controls pressurization, ventilation, and room temperature in a

laboratory room served by one single-duct supply terminal with a reheat coil, one

general exhaust terminal, and up to six fume hoods (multiple fume hood flow signals

must be averaged using an averaging and scaling module. Pressurization is controlled

by maintaining a selected difference between supply and exhaust airflows.

NOTE:

Application 2926 can be set up to operate without a supply box, or without a general

exhaust box. See the

Application Notes

section for more information.

Application 2926 uses fast-acting electronic actuators for Venturi Air Valve control. A

standard 0 to 10 Vdc actuator is used for the hot water valve.

NOTE:

The LCM controls pressure, ventilation, and temperature. When these functions

conflict, the priorities are:

• Pressurization

• Ventilation (supply minimum may be overridden to maintain negative pressurization)

• Temperature (temperature control is overridden by specified flow limits for the air

terminals)

Temperature control is determined by input from the room temperature sensor. The

discharge temperature setpoint is reset in sequence with the VAV flow to control the

room temperature using a BTU Compensation algorithm. The discharge temperature is

then controlled using the reheat coil.