Application

Overview

Hardware Inputs

Siemens Industry, Inc.

Application Note, App 2928

140-1302

2015-07-07

Overview

Application 2928 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.

This version of the LCM uses conventional supply and exhaust actuation (rather than

high speed actuation). Therefore, it should be used only where rapid room response to

fume hood volume changes is not required. Fume hoods used in conjunction with

these applications should be constant volume or slow actuation.

NOTE:

Application 2928 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 2928 uses slow Venturi Air Valves for both supply and exhaust control. The

Venturi valves are each driven by a 0-10V analog signal. 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.