Intro to Chillers : Chiller Condensers

 Condensers for Water Chillers:

• Air-Cooled Condensers:
  • Usage: Up to about 450 tons, typical in residential and commercial air conditioning.
  • Design: Fan and condenser coil, less expensive than cooling towers.
• Water-Cooled Condensers:
  • Efficiency: More energy-efficient, draw lower AMPS due to stable high side pressure.
  • Capacity: Units up to about 1500 tons.
  • Maintenance: Requires water treatment and regular maintenance for efficient operation.
  • Example: Cooling tower that cools water via evaporation, absorbing heat from the remaining water, which then returns to the condenser.

Safety Devices in Chillers:

• Flow Switches: Stop chiller operation if no water flow to prevent freezing.
• Low Temperature or Freeze Protection Cutouts: Set at 34-36°F, trip and turn off the chiller if the temperature drops too low.
• High Temperature Bearing Cutouts: Turn off the compressor if oil temperature exceeds 190°F.
• High Temperature Motor Winding Cutouts: Turn off the compressor if motor temperature reaches 215-225°F.
• Chiller Low Temperature Cutout: Set 5-8°F below the set point, prevents freezing.
• Pressure Relief Devices: Prevent excessive hydrostatic pressure; e.g., rupture discs relieve at about 15 psig above evaporator pressure.
• Lockout Timers/Relays: Prevent short cycling or restarting the chiller until the problem is identified.

Motor Starting Techniques:

• Across-the-Line Start: Used for motors up to 25-30 HP, uses a three-pole contactor for full voltage start.
• Part Winding Start (Star-Delta Configuration):
  • Star Configuration: Draws one-third of normal AMPS, uses a portion of windings to start.
  • Delta Configuration: Switches to full voltage once the motor starts rotating.
• Variable Frequency Drives (VFD):
  • Function: Soft start by reducing voltage and frequency, minimizing inrush current.
  • Example: Lowers motor speed without increasing amperage, displays running capacity percentage and amperage.

Examples and Illustrations:

• Air-Cooled Condenser: Finned coil on rooftops.
• Packaged Air-Cooled Chiller: All components housed in one unit with condenser fans on top.
• Cooling Tower: Water cooled via evaporation, sent back to the condenser.
• Flow Switch: Senses water flow to prevent freezing.
• VFD: Reduces motor frequency and speed, controls output torque and running capacity.