Quick Reference Guide

6 UNT-PRC015-EN
Know the Riser Design—Design Return versus Reverse
Return
There are two typical methods used for piping a riser column:
Direct return is the most common/popular method.
Advantages of this system are:
• It is cost-effective and simple.
• Straightforward installation.
• Very little confusion about properly sizing the risers.
Disadvantages of this system are:
• The pressure drop is not equal at each unit on the column. A means of balancing water flows
at each floor must be provided. The total pressure drop on the path that the water takes to the
unit on the top floor is much greater than the path to the unit on the lower floors(s) nearer the
pump. If a balance means is not provided, it is possible that there will be no water flow through
the upper units due to its height and friction loss.
Reverse return is less common but is a better arrangement as far as pure piping design is
concerned.
Note: It is not the purpose of this section to make the readers expert piping designers. Rather to
give some familiarity of different piping designs which affect the risers (and pricing) picked
for the job.
Advantages of this system are:
• The system can be designed so the total system pressure drop through each unit is equalized.
• The overall pressure drop is lower—some energy saving potential.
Disadvantages of this system are:
• Water flow balancing at each unit is still required.
Figure 2. System 1—Direct return
BASEMENT
4TH FLOOR
3RD FLOOR
2ND FLOOR
1ST FLOOR
RISERS
MAINS
S
R
CAPPED
SYSTEM 1
DIRECT RETURN
FLUSH/VENT
ROOF
LOOP
SYSTEM 1 – DIRECT RETURN
2-pipe example