Section 4
Controls for HVAC Systems
4.1 Introduction 

4.6.2.1

Operating Premise

4.6.2.2

System Description

4.6.2.3 

Chilled Water Design 

Parameters and Conditions

4.6.2.4

Chilled Water Flow Loops with 

Constant Return Temperature 

and Variable Flow

4.6.2.4.1

Connection to Buildings with 

a Combined (2-Pipe) Pumping 

Scheme

4.6.2.4.2

Connection to Buildings 

with Separate Piping Scheme for 

Heating and Cooling

4.6.2.4.3

Connection to Buildings Not

Requiring Local Pumps

4.6.2.4.4

Retrofit for Building with

2-Pipe System and Local Chiller
4.7 Electrical Pictorial and Ladder

Diagrams

4.7.1

General 

4.7.2

Symbols

4.7.3

Motor Starters

4.7.3.1

On-Off Switch

4.7.3.2

Push Button Start-Stop and 

Holding Contact

4.7.3.3

Hand-Off-Auto Switch

4.7.3.4

Fractional Horsepower

4.7.4 

Diagrams

4.7.4.1

Manufacturing Equipment

4.7.4.2

Chiller

4.7.4.3

Building Heating and Cooling

System

4.8

Typical Control Diagrams

4.8.1

Computer Room Unit

4.8.2

Corridor and Stairs Air 

Pressurization System

4.8.3 

Domestic Hot Water System

4.8.4

Fuel Oil System

4.8.5

Halon Evacuation System

4.8.6

Hot Water Heating System

4.8.6.1

Lead-Lag Boilers

4.8.6.2

Single Boiler

4.8.7

Laundry Room

4.8.8

Mess Hall HVAC System

4.8.9

Tunnel and Vehicle Ventilation

4.8.10

UPS and Battery Room 

Ventilation

4.2 Control System Types and

Energy Sources

4.3 Abbreviations and 

Definitions

4.3.1

Abbreviations

4.3.2

Definitions

4.4 Elementary Control

Systems

4.4.1

Single Zone Heating, Zone

Thermostat

4.4.2

Single Zone Heating, 

Discharge Control with 

Zone Reset

4.4.3

Central HVAC System,

Discharge Control with

O/A Reset and Reheat

Coils in Ductwork

4.5 Components and

Subsystems Control

4.5.1

Coil Capacity Control

4.5.1.1

Water Flow Control to Coil

4.5.1.2

Water Temperature Control

to Coil

4.5.1.3

Varying Air Flow through

the Coil

4.5.1.4

Combination Type Coil  

Control

4.5.2

Air Inlet and Mixing Control

4.5.3

Volume Control, Return and

Relief Air

4.5.4

Fan-Coil Units

4.5.5

Hydronics

4.5.5.1 

Basic Considerations

4.5.5.2

Pumps

4.5.5.3

Hot and Chilled Water 

Systems

4.5.5.4

Water Loop Heat Pump 

Systems

4.6

Larger Control Systems

4.6.1

University Teaching & 

Research Laboratory

4.6.2

A Typical Campus Chilled 

Water Pumping System with

Building Systems and

Connections