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Four Pipe System

General

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

Ventilation
Indoor Air Quality
Filtration
Outside Air Control
Controls
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