Units - Trane VariTrane VCCF Installation, Operation And Maintenance Manual

Figure 5. Low height series: LSEF (top) and low
height parallel: LPCF (bottom)
Figure 6. Low height parallel: LPWF (top) and low
height parallel: LPEF (bottom)
The fan on a series unit runs continuously whenever
the main air handler unit is in operation. There are
three (3) methods to start the fan: 1) remotely, 2) by a
duct pressure switch, or 3) by a combination of both.
The particular fan control method may vary from unit
to unit, depending upon job needs.
Typically, heater is off while air valve modulates
primary air and responds to zone temperature. If zone
temperature decreases to the point where a decrease in
primary air will not maintain the desired temperature,
the re-heat will be activated to increase the
temperature of the discharge air.
On a parallel unit, the VariTrane™ air valve delivers
primary cooling air to the unit outlet. When the space
temperature decreases beyond air valve control, the
VAV-SVX08R-EN
fan is turned on as the first stage of heat. The fan
delivers plenum air from above the occupied space to
the unit outlet, which is mixed with primary air and
delivered to the occupied space.
N N o o t t e e : : Either the fan, the air valve, or both can deliver
airflow into the occupied space. In order to
prevent primary airflow from exiting through the
fan when the fan is not running on a parallel unit,
a back draft damper is provided. When the fan is
not running, the efficiency of this system is the
same as a standard single-duct VAV unit.
Typically, the control systems applied to parallel units
cause the air valve to close to zero or a minimum flow
before the fan is activated. After the fan is activated, the
optional heat will be activated upon further reduction
in zone temperature. Therefore, minimal primary air is
mixed with the heated air.
VariTrane™ fan-powered unit fan sizes 02SQ–05SQ,
DS02, PS02 and DS03 were performance tested at .12
in. w.g. and sizes 06SQ and 07SQ were tested at .15 in.
w.g. Units are not designed to operate without ducts
and below these tested static pressures.
N N o o t t e e : : Fan-powered units are available with rectangular
discharge connection only. The optional heater
is mounted on the discharge of the unit. Hot
water coils are connected to either the plenum
inlet or on the discharge on parallel units, and to
the discharge of series units.
Chilled Water Sensible Cooling
Terminal Units
Chilled water sensible cooling terminal units are
available with or without re-heat. Refer to the following
figures.
Figure 7. Chilled water sensible cooling unit
U U n n i i t t I I n n f f o o r r m m a a t t i i o o n n
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