This note illustrate the main diferences of pressure direct and reverse return piping arrangement. For simplicity, just consider the pressure drop through piping system, not consider the static pressure.
Direct Return is like a race where the closest person has a shortest track—you have to “slow them down” with balancing valves so everyone finishes at the same time.
Reverse Return is like a race where everyone runs the exact same distance—they naturally finish together without extra help.
Understanding the pressure profile of direct and reverse return will help us select the appropriate piping distribution, control valve (both conventional and PICV), balancing valve, pump control strategy, testing and balancing as well as troubleshooting.
Note:
The basic understanding in this note is for design condition. In partial load condition, more factors shall be considered.
Related notes:
Pressure profile of chilled water system
Pressure profile of condenser water system
Understanding the pressure profile in open-loop water system
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