Carrier 42C Series Product Data page 19

Application data (cont)
System piping
The following diagrams show some common methods
used to pipe the 42S Series units. Only the 2-pipe systems
are shown; however, the methods would be the same for
4-pipe systems.
System 1, the "direct return" system, is the most com-
mon. It is economical to install since it supplies and returns
the water for a riser column from the same location, at the
top or the bottom of a building. This type of riser arrange-
ment does require more attention to individual unit water
flow balancing. The risers are normally capped at the end
as shown in the diagrams.
System 2, the "reverse return" system, is used to mini-
mize the requirement for individual unit balancing. This
system is usually referred to as the self-balancing system.
The arrangement of the risers allows the water flow for
each unit in a column to be equalized. In the reverse return
system both the supply and return mains are located at the
top or the bottom of a building requiring an additional
return riser to be furnished in the units.
System 3, the "common reverse return" system, typi-
cally has the supply and return mains located remotely
from each other — such as one at the top and one at the
bottom of a building. This eliminates the need for a reverse
return riser in the units.
SYSTEM 1 — DIRECT RETURN
SYSTEM 2 — REVERSE RETURN
SYSTEM 3 — COMMON REVERSE RETURN
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