Commercial Energy Systems

Four Pipe System


Four-pipe systems provide two independent water systems - one dedicated to chilled water and one to hot water. Common load systems have a single coil in the air handler while independent load systems have two separate coils.

four pipe system

Four-pipe systems have a high first cost due to the second water system and the need for either two coils or more costly control valves at each terminal unit. They also have a high operating cost due to the two pumps operating, but do provide good flexibility in meeting varying loads.

room unit control

The main advantages are:

  • All year availability of heating and cooling with individual zone temperature control
  • Chilled and hot water are typically only simultaneously supplied during the Spring and Fall seasons
  • Elimination of zoning cost and complexity
  • Simpler changeover decisions
  • The lowest and quietest fan speed is adequate most of the time.

Links to Related Topics

Indoor Air Quality
Outside Air Control
Central Plant System
Central (or Built-Up) System
All-Air Central Systems
All-Air Central Reheat Systems
All-Air Central Dual Duct
All-Air Central Multizone
All-Air Rooftop
Air-Water Central Systems
All Water Central Systems
Two Pipe System
Three Pipe System