HVAC Controls

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.