Symbols. Honeywell AUTOMATIC CONTROL SI Edition

AIR HANDLING SYSTEM CONTROL APPLICATIONS

17. PLACE CONTROL VALVES ON THE LEAVING SIDE

OF WATER COILS.

Control valves on the leaving side of water coils leaves pressure in the coil when the valve is closed, thus aiding in eliminating air through the air vent on the leaving side of the coil, and also prevents the possibility of air being induced into the system through the vent if the pump produces a negative pressure in the coil return line.

18. CONSIDER THE ABILITY OF THE HVAC SYSTEM

OPERATOR TO UNDERSTAND THE SYSTEM

WHEN DESIGNING GRAPHICS FOR THE

OPERATOR INTERFACE.

APPLICATIONS-GENERAL

The following applications are presented in a DDC format using notation from the Symbols in this section. In some cases the degree and complexity of control shown is not practical in other forms of control.

Suggested microprocessor data points are shown as they could appear on a color graphic display of a PC operator workstation.

In some cases data points, other than those required for control and operation, are shown to help an operator understand the loading and performance of the HVAC system and related control loops. If a PC station is not required, the data points required for control and operation should still be specified for the operator by listing the points or including a graphic sketch.

Values, setpoints, gains, timings, etc. shown in these examples are general, and actual values should be determined on a projectto-project basis.

The following applications were selected for this section on

Air Handling System Control Applications. Caution should be used in simply combining any of these applications together as a control solution for a more complex system. Application variations may be required depending on the heating, cooling, and pumping configurations, the building use and occupants, the ability of control vendors and related control systems, the ability of local operating and maintenance persons, codes, and weather.

Lines connecting inputs, outputs, values, and control functions have been added to aid in understanding. In many cases these lines would create unacceptable clutter on an actual system graphic display. Graphic display and management function (alarms, records, etc.) concepts are discussed further in the Building Management System Fundamentals section.

Although the control solutions presented are good general recommendations, other solutions are acceptable, and in some cases, may better depending on the job objectives.

206 ENGINEERING MANUAL OF AUTOMATIC CONTROL