Product Overview
21 60-2507—3
W7100A-E
Night Setback and Morning Warmup
There are several possible alternatives for controlling
night setback and morning warmup in VAV systems. One
alternative, shown in Fig. 15, makes use of a time clock to
control the unoccupied mode of operation. The time clock
starts the unoccupied mode by de-energizing the W7100,
shutting down the system blower, and driving the econo-
mizer closed. During the unoccupied period, if the building
temperature falls below the setpoint of the night
thermostat(s), both the blower and the heating system will
be energized. When the night thermostat is satisfied, the
blower and heat will cycle off.
The time clock then initiates the morning warm-up,
signaling the daytime or occupied mode of operation. Dur-
ing the morning warmup period, the W7100 remains de-
energized, the system blower starts and the economizer
remains closed. If the return air is below return air setpoint,
heat is energized. The system remains in the morning
warm-up mode until the return air rises above the setpoint
of the return air control. At this point, the system returns to
the day mode of operation. At the start of the day mode, the
W7100 is energized, and the economizer is allowed to
modulate. The system cannot reenter the morning warm-up
mode of operation until the next night cycle.
The night setback and morning warm-up options must
be used only on systems with VAV terminals designed for
night setback. These terminals have built-in thermostats
that cause the box to open if the delivered air temperature is
above the thermostat setpoint, typically 80° F [27° C].
Electric to Pneumatic Interface and Control
The W7100D can control pneumatically actuated sys-
tems by using a Q642A as an interface. The Q642A Output
Module amplifies the W7100D modulating output voltage
from 0.2 to 1.7 Vdc, to a 2 to 10 Vdc level. An input and
output for two separate channels are used to control elec-
tric/pneumatic transducers.
The W7100D can be used to provide heating only,
cooling only, or heating/cooling operation using a T675A
changeover control and a switching relay. A cooling only
hookup with an economizer is shown in Fig. 16. All system
components must be powered from the same control trans-
former to ensure a common electrical ground reference.
The Q642A should have the Y start settings adjusted to
about 5° C [41° F]. This corresponds to a voltage of 0.94
Vdc, which is the midpoint of the economizer output volt-
age range. When the economizer output is 0.2 Vdc, the
Q642A output should be 2 Vdc. The throttling range setting
should be set to 5.5° C [41.5° F] to yield the full 2 to 10 Vdc
output over the W7100 output voltage range.
The Y output of the Q642A Output Module is connected
to the Y input of the RP7507A Electric/Pneumatic Trans-
ducer. The RP7507A converts the 2 to 10 Vdc voltage input
signal to a 3 to 14 psi control pressure on the pneumatic
line.
OPERATION
Reset from Pneumatic Zone System
In most pneumatic systems, the zone dampers are pneu-
matically controlled. Reset of the discharged temperature
can be accomplished from the zone of highest demand by
using an L91B1035 Pressure Transducer and an RP913 Hi/
Lo Pressure Signal Discriminator.
As shown in Fig. 17, representative zone pneumatic
thermostat signals are used as RP913 input signals. The
RP913 selects the highest value signal and outputs a pres-
sure signal corresponding to that of the highest zone de-
mand. The L91B1035 converts the signal to a resistance
value which is used as the reset input to the W7100. The
1715 ohm one percent resistor is used to establish the
proper resistance range.
W7100 RESET SPECIFICATIONS
The W7100 controller can reset the discharge air/water
temperature upward based on space or outdoor air tempera-
ture. This is accomplished by applying a specific resistance
across terminals 6 and 7, 1715 ohms for no reset and
1760 ohms for full reset.
For space reset, use an S963B1037 Manual Potentiom-
eter and a T7047C1025 Space Sensor in series. As the
average space temperature drops below the setpoint of the
reset sensor, the W7100 discharge temperature setpoint is
reset upward by an adjustable amount, 5 to 20 degrees for
cooling and 20 to 80 degrees for heating, until maximum
reset occurs when the average space temperature is three
degrees below the setpoint of the reset sensor or sensors. At
this time, the W7100 setpoint is fully reset (see Fig . 18).
Fig. 18—Space reset.
MECHANICAL SETPOINT
FULL RESET
NO
RESET
ADJUSTABLE RESET
5° - 20° FOR COOL
20° - 80° FOR HEAT
SPACE
TEMPERATURE
-3 BELOW
SETPOINT
SETPOINT OF
RESET SENSOR
M3901
SPACE RESET
For outdoor reset, use a C7031G1016 outdoor sensor
(range -40° F to +110° F). Outdoor reset starts at 90° F
(T-HIGH) and is fully reset at 70° (T-LOW). See Fig. 19.
The No Reset and Full Reset temperatures can be changed
by adding resistors in series/parallel with the C7031G1016
(see Fig. 20). Fig. 20 resistance values can be found in
Table 3 for changing the cooling temperatures and in
Table 4 for changing the heating temperatures.