CHILLED WATER BASICS

1
CHILLED WATER BASICS 2-13-2003 Rodolfo Medina
Jr. Christine Mulvey
2
Schematic of Typical Chilled Water System

• 1999 ASHRAE Handbook HVAC Applications

3
Subsystems For Chilled Water Usage

• Condenser Water loop

• Consists of Cooling towers, pumps, piping and
  controls
• Cooling towers reject heat to the environment,
  through heat transfer to ambient air.
• Feedback controller adjusts tower fan speeds to
  maintain a set point for the water temperature
  leaving the cooling tower.
• This temperature is generally referred to as the
  condenser water supply temperature

Cooling towers located on roof of Science Center.
Then connected through pipes to the Central
Utilities Plant in Science Center basement

• 1999 ASHRAE Handbook HVAC Applications

4
Subsystems For Chilled Water Usage

• Chiller Plant

• Chillers arranged in parallel provide primary
  source of cooling.
• 5 chillers in science center utilities plant
  ranging in size from a 5000 ton capacity to a
  1000 ton capacity.
• Chilled Water measure in ton-days which is about
  12,000BTU/hour.
• Individual feedback controllers adjust cooling
  capacity of each chiller to maintain specific
  chilled water supply temperature.

Chiller plant located in the Science Center
Utilities Plant.

• 1999 ASHRAE Handbook HVAC Applications

5
Subsystems For Chilled Water Usage

• Chilled Water Loop

• Consists of pumps, valves, pipes and controls
• Two types of systems Primary and
  Primary/Secondary Chilled Water systems.
• Primary water that flows through the chiller is
  the same water that flows through the cooling
  coils. Single pipe looping.

• Either fixed speed pumps or variable speed pumps
  can be used.
• If fixed speed pumps are used the system requires
  a chilled water bypass valve.

• 1999 ASHRAE Handbook HVAC Applications

6
Subsystems For Chilled Water Usage

• Chilled Water Loop (continued)

• Chilled Water Bypass Valve Maintains constant
  chiller flow rates by maintaining a fixed
  pressure difference between the main and return
  supply lines. Pressure set point is the Chilled
  water loop differential pressure.

• If variable speed pumps are used, they are
  controlled separately to maintain the
  differential set point.

• Primary/Secondary System Designed specifically
  for variable speed pumping.
• Primary loop Fixed speed pump that provides a
  constant flow of water to the chillers.
• Secondary loop Variable speed pumping to
  maintain the differential pressure set point.

• 1999 ASHRAE Handbook HVAC Applications

7
Subsystems For Chilled Water Usage

• Air Distribution System

• Contains terminal units, air handling units,
  ducts, dampers, fan, cooling coils.
• Cooling Coil cools and dehumidifies air.
• Flow of water controlled to maintain a set point
  temperature for air leaving cooling coil.

• Ventilation air is mixed with the return air and
  fed to the cooling coil. The ratio of
  ventilation air to return air is determined by
  the conditions of the outside air.

• 1999 ASHRAE Handbook HVAC Applications

8
Data for Chilled Water usage in WJH
9
Chilled Water Usage in WJH

• Http//www.uos.harvard.edu/reports/uti.shtml

10
Resources Used

• Http//www.uos.harvard.edu/reports/uti.shtml

For utility usage data.

• 1999 ASHRAE Handbook HVAC Applications

For basic overview of the chilled water system.

• Http//www.uos.harvard.edu/reports/uti.shtml