User Guide

Siemens Building Technologies, Inc. 2-1
Chapter 2–Control Option
Comparisons
Overview
Chapter 2 discusses the following topics:
• Concepts behind some of the major control applications in the
APOGEE Automation System, namely:
— Duty Cycling (DC)
— Enthalpy and Dry Bulb Economizer Control
— Peak Demand Limiting (PDL)
• Procedures the system uses to schedule operations and optimize
system use, namely:
— Start/Stop Time Optimization (SSTO)
— Time-of-Day (TOD)
For specific information on using the PPCL commands identified in
this chapter, see Chapter 3–Syntax.
APOGEE PPCL User’s Manual
2-2 Siemens Building Technologies, Inc.
Duty Cycling (DC)
Most building control systems are designed to meet the expected
maximum system demand. However, the maximum demand is
usually required only a few times per year for short periods of time.
As a result, the system is oversized for the normal load so that it can
meet this exceptional demand.
The duty cycling (DC) function coordinates the operation of all
available equipment to compensate for additional equipment
capacity that is not normally needed. During normal system
operation, some equipment is cycled off for short periods of time to
distribute equipment wear and reduce operating costs.
Applications that can use ON/OFF switching in hourly patterns work
best with a duty cycling program.
CAUTION:
Be careful when designing your programs so that
functions do not conflict. If points used for DC are
also commanded by another application, such as
Time-of-Day (TOD), one program may interfere with
the operation of the other if both functions are trying
to control a point during the same time period.
Example
The following example uses duty cycling in a school building to
control a hall fan, called HFAN.
• In order to conserve energy, the fan will run only during the times
when students are in the hall.
• In this school, classes start on the hour and last for 50 minutes.
• Students are in the hall during a 10-minute period before the next
class.
• Since the hall that HFAN serves has good ventilation, the fan
should run for the last 15 minutes of the hour and for the first five
minutes of the next hour.
• The rest of the time the fan is shut off.