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TRG-TRC014-EN 45
period three
System Configurations
notes
Similarly, fan-powered terminal units can be used in perimeter spaces that
require seasonal cooling and heating.
In the heating mode, the parallel, fan-powered unit turns on a small fan as the
first stage of heating. Doing so allows it to temper the supply air with the heat
(of the building and lights) that is carried by the return air, rather than using
“new” energy. When activated, the small fan also increases airflow to the
space, improving the mixing of supply air and space air to prevent stagnation.
Series, fan-powered terminal units may also be used in this manner. They offer
the added advantage of supplying constant airflow to the space in both cooling
and heating modes.
Finally, dual-duct VAV terminal units can also be used to heat and cool
perimeter spaces. The specific operation of a dual-duct system was explained in
Period Two.
parallel,
parallel,
fan
fan
-
-
powered VAV
powered VAV
terminal unit
terminal unit
Fan-Powered VAV
heat loss < 250 Btu/hr/ft
heat loss < 250 Btu/hr/ft
[240 W/m][240 W/m]
[240 W/m]
Figure 61
dual
dual
-
-
duct VAV
duct VAV
terminal unit
terminal unit
cool
cool
primary air
primary air
warm
warm
primary air
primary air
Dual-Duct VAV
heat loss < 250 Btu/hr/ft
heat loss < 250 Btu/hr/ft
[240 W/m]
[240 W/m]
[240 W/m]
Figure 62