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Chapter 16 Refrigeration

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Chapter 16 Refrigeration & Air Conditioning Technology 5th Edition Advanced Automatic Controls Control Applications Original system controls were manually activated ... – PowerPoint PPT presentation

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Title: Chapter 16 Refrigeration


1
Chapter 16Refrigeration Air Conditioning
Technology 5th EditionAdvanced Automatic
Controls
2
Control Applications
  • Original system controls were manually activated
    and operated
  • Thermostats and other simple controls were added
    to reduce human contact with the equipment
  • Modern automatic control systems require very
    little human attention

3
Control Applications
  • Large buildings can be maintained by a small
    staff of technicians
  • Sophisticated building systems are often used
  • Many staff members do not know how to operate
    these systems
  • There are often areas that are cooler or warmer
    than desired
  • Controls must be understood
  • Technicians need to be educated
  • Should be able to calibrate controls
  • Need to be able to interpret blueprints
  • Need to interpret the intentions of the system
    designer

4
Types of Control Systems
  • First control systems started and stopped main
    system components
  • Newer controls can modulate (start, stop, or
    adjust) the flow or operation of system
    components
  • Three basic components of a control system
  • The sensor measures changes in conditions
  • The controller sends an output signal to the
    device being controlled
  • The controlled device reacts to the controller
    signal to modulate fluid or electrical current
    flow
  • Control systems are often divided into two
    control loops

5
Pneumatic Controls
  • Mechanical systems
  • Use air to transmit signals between the sensor
    and the controlled device
  • Electronic can be integrated into the pneumatic
    systems
  • Advantages of pneumatic systems
  • Simple to install and understand
  • Safe around combustible materials
  • Versatile and reliable
  • Lower installation cost

6
Pneumatic Controls
  • Require a clean and dry permanent air supply
  • Air pressure (100 to 250 psig) generated by an
    air compressor
  • Regulators reduces pressure to working pressure
    (20 to 30 psig)

7
Cleaning and Drying Control Air
  • Pre-filter to the compressor
  • Moisture is removed from the air
  • Local water supply and coil
  • Chilled water coil
  • Desiccant
  • Refrigerated drier (most common)
  • High Density filters
  • Final filtering stage
  • Removes oil vapor and remaining liquid

8
Control Components
  • Control air used to position-controlled devices
  • The pressure on control valves is equal to the
    air pressure multiplied by the cross sectional of
    the diaphragm
  • Air lines are typically ¼ or 3/8
  • Typically controlled components are valves,
    dampers, pumps, compressors, and fans
  • Valves can be normally open or normally closed
    devices

9
Control Components
  • Some heating systems have normally open valves
    (reverse acting)
  • Pilot positioners
  • Use a small volume of air to control a larger
    volume of air
  • Operates an air cylinder that control the valve
  • Fluid flow can be modulated
  • 100 flow through the device
  • 0 flow through the device
  • Partially open to permit intermediate flow
    percentage

10
Control Components
  • Based on sensitivity or gain
  • Pressure and temperature at fully open position
  • Pressure and temperature at fully closed position
  • Sensitivity change in pressure / Change in
    temperature
  • High sensitivity control will hunt
  • Low sensitivity Noticeable difference in space
    temperature
  • Pressure gauges used to measure pressure at the
    controls
  • Gauges have quick connects
  • Different gauges for different manufacturers

11
Control Components
  • Controls adjusted with Allen wrenches
  • Can be used to control electric switches or
    circuits
  • Pneumatic electric (PE) device
  • Similar in operation to a pressure switch
  • Electrical devices can be used to control
    pneumatic devices
  • Electric-pneumatic (EP) devices

12
Direct Digital Controls
  • Referred to as DDC
  • Operate at very low voltages
  • Can be used to open, close, or modulate valves,
    dampers, motor speeds, etc.
  • Systems with DDC can be controlled from remote
    locations via computers and phone lines
    (Internet)
  • Corrective actions can be taken from these remote
    locations

13
Direct Digital Controls
  • Temperature, humidity, motor speed, and other
    system parameters can be observed
  • Can be used for
  • Energy management (load shedding)
  • Night/weekend set-back
  • Lighting circuit
  • Smoke detectors
  • Other building functions

14
Residential Electronic Controls
  • Electronics used on residential systems for many
    years
  • Oil burner control boards
  • Room thermostats
  • Entire board is evaluated, not the individual
    board components
  • Use manufacturers diagnostic systems
  • Boards are often treated with switches
  • Boards often have diagnostic codes for
    troubleshooting

15
Residential Electronic Controls
  • Thermistors are often used
  • Temperature-sensitive devices
  • Resistance changes with changes in temperature
  • Temperature difference point in a system can be
    measured
  • Functions of electronic thermostats
  • Time delay for compressor starting
  • Cycle timer for heating systems
  • Stage timer for two-stage heating systems
  • Heating/cooling set-points
  • Automatic changeover between heating and cooling
    modes
  • Power checks
  • System error codes
  • Smart recovery

16
Residential Electronic Controls
  • Often equipped with DIP switches
  • Allows control to be configured for the equipment
  • Allows user to customize system operation
  • Electronics in heat pump systems
  • Heating or cooling operation
  • High or low speed for multi-speed compressors
  • Status lights indicate mode of operation
  • Discrepancies need to be evaluated
  • Chart on equipment provides status light codes
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