23
STEAM COIL PIPING
Recommendations for Steam Coils
See Fig. 21 and 22.
1. Be sure to provide adequate support for the piping and design
the lines for expansion and vibration.
2. Do not reduce the pipe size on the coil return connection.
Keep the same size through the dirt loop and make any reduc-
tion in the branch to the trap.
3. A vacuum breaker is recommended to prevent condensate
from being held up in the coil. Generally the vacuum break is
connected between the coil inlet and the return main. If the
system has a flooded return main the vacuum breaker should
be open to atmosphere and the trap design should allow for
venting large quantities of air.
4. Do not let steam flow drip through the coil and do not attempt
to have condensate lift when using a two-position or modulat-
ing valve.
5. Size traps in accordance with the manufacturer’s recommen-
dations. Be sure that the required pressure differential is avail-
able. Do not undersize traps.
6. Float and thermostatic or bucket traps are recommended for
low pressure steam. On high pressure use bucket traps. Ther-
mostatic traps should only be used for air venting. Bucket
traps are recommended for use with ON/OFF control.
7. Locate the trap at least 12 in. below the coil return.
8. If a modulating control valve is used be sure to size the valve
properly and do not oversize.
Fig. 21 — Typical Steam Distributing Coil Piping
for Open Gravity Systems with
Steam Pressure Below 10 psig
Fig. 22 — Typical Steam Distributing Coil Piping
for Vacuum-Return Systems with
Steam Pressure Below 10 psig
STEAM COIL CONTROLS
Several methods of control are possible depending on the heating
medium to be used, location and type of thermostatic control and
whether or not modulating or ON/OFF type control is used. Figure
23 shows a typical control scheme for ON/OFF steam coil in
50XCW units.
Install heating thermostat or connect to the heating side of an
available heating/cooling thermostat so that the unit operates the
fan in the desired operation, either continuous or cycling with the
steam coil. The thermostat should provide the required connection
to activate the fan and the cooling and heating should not be able
to be activated simultaneously.
The freeze stat and the heating relay (HR1) are field-supplied and
installed. Refer to Fig. 18 for typical thermostat wiring.
½"
½
