21
Fig. 18 — Typical Thermostat Wiring Connections
Step 9 — Install Piping
HOT WATER PIPING
Recommendations for Water Coils
See Fig. 19.
1. Piping should be in accordance with accepted industry stan-
dards and all components rated for the system pressure
expected. The 50XCW coils are rated for maximum of 400
psig DWP (Design Working Pressure).
2. Coils should be piped such that they will drain. A drain and
vent are provided.
3. Water coils should not be subjected to entering air tempera-
tures below 38°F to prevent coil freeze up. If temperatures
over the coil are below this, glycol or brine solution should be
used. Use a solution with the lowest concentration that meets
the coldest air expected. Excess concentration will greatly
reduce coil capacity.
4. Whenever a hot water coil is subjected to freezing tempera-
tures, some means of adequate freeze protection is required.
A heating coil can be subjected to freezing temperatures by
outside air during the winter. Use of a freeze protection ther-
mostat is recommended.
5. During winter operation, either the outside-air supply must be
closed off or a minimum water flow must be maintained if
freezing outdoor air is admitted. For summer operation, it is
recommended that if possible the hot water coil be closed off,
drained, and residual water blown out. If the residual water
cannot be blown out, an inhibited glycol antifreeze should be
added to the coil.
6. The return air duct system should be carefully designed to get
adequate mixing of the return air and outdoor air streams to
prevent cold spots on the coil that could freeze.
7. Two-position control valves, modulating control valves, or
three-way control valves may be used to control water flow.
Select the valve based on the control valve manufacturer’s
recommendations for size and temperature rating. Select the
control valve based on pressure drop equal to the coil.
8. Pipe sizes should be selected based on the head pressure
available from the pump. It is recommended that the velocity
not exceed 8 ft per second and that the piping system be
designed for approximately a 3-ft loss per 100 equivalent ft of
pipe.
9. Design the piping system to allow for expansion and to mini-
mize vibration between the unit and piping system.
HOT WATER 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
20 shows a typical control scheme for ON/OFF hot water heating
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
heating coil. The thermostat should provide the required connec-
tion 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.
NOTE: Remote sensor is field-installed option.
W1
Y1
G
W
3
CK1
CK2
R
C
W2
Y2
R
S
2
R
S
+5
R
S
1
R
S
GND
UNIT
GROUND
33
C
S
250-01
R
G
Y1
C
Y2
TB2
50XC
(12
S
IZE UNIT AND LARGER)
WIRE NUT
S
HIELD (CUT AND
TAPE BACK)
REMOTE
ROOM
S
EN
S
OR
(P/N ZONECCORR
S
01)
W1
W2
D1
D2
