Chapter 12

1. Chapter 12 HVAC Controls Pneumatic Control Systems • Air Compressor Stations • Transmitters and Controllers • Pneumatic Thermostats • Auxiliary Components • Switching Relays • Controlled Devices • Actuators

2. Chapter 12 HVAC Controls Pneumatic Control Systems • Air Compressor Stations • Transmitters and Controllers • Pneumatic Thermostats • Auxiliary Components • Switching Relays • Controlled Devices • Actuators

3. Pneumatic controls must operate properly to control the environment.

4. Pneumatic control systems include an air compressor station, transmitters and controllers, additional components, and controlled devices.

5. An air compressor station includes the air compressor and auxiliary components such as the air drier, drains, filters, and pressure-regulating valve stations.

6. A bimetallic element is a sensing device that consists of two metals with different expansion and contraction rates that respond to temperature increase or decrease.

7. Limit thermostats cause a change in a controlled device whenever the set temperature or pressure is reached.

8. Pneumatic humidistats are used to sense and control the humidity in a building space or duct.

9. Pneumatic pressurestats are designed to sense and control the pressure inside a duct or building.

10. Receiver controllers are used for HVAC system control. A receiver controller accepts one or more input signals from pneumatic transmitters and produces an output signal based on the setup of the controller.

11. A single-input receiver controller is designed to be connected to only one transmitter and maintain only one temperature, pressure, or humidity setpoint.

12. A dual-input receiver controller is designed to take the change of one variable and reset the setpoint of the controller to match the changing condition.

13. Switching relays are used to change airflow from one circuit to another.

14. Minimum-position relays are used to provide fresh air ventilation and prevent outside air dampers from completely closing.

15. Pneumatic positioners ensure damper or valve actuators move to a given position.

16. Electric/pneumatic switches enable a pneumatic device such as a damper to respond to the operation of an electrical device such as a fan.

17. Pneumatic/electric switches allow the signal from an outside air transmitter to be used to energize and de-energize a hot water pump.

18. An actuator and linkage control damper regulate the temperature of a building space.

19. Actuators may be damper or valve actuators. Damper actuator components are usually enclosed in the actuator body. Valve actuator components are usually visible from the outside.

20. Direct-coupled actuators are clamped to the damper shaft.

21. Dampers are used to control the flow of air and include parallel, opposed, and round blade dampers.

22. Control valves control the flow of fluids in an HVAC system. Control valve components include the valve body, stem, disc, packing, and actuator.

23. Two-way valves have one inlet and one outlet.

24. Mixing valves and diverting valves have similar designs. Mixing valves have two inlets and one outlet. Diverting valves have one inlet and two outlets.