48 CNT-SVX17G-EN
Sequence of Operations
The factory-installed local electric heater provides two mechanical safeties. The two
safeties are independent of the controller. The controller provides no indication of the
state of the safeties. One safety is an automatic thermal cutout that trips when the
temperature is 140°F (60°C). It resets automatically when the temperature drops. The
other safety is a manual reset cutout that trips when the temperature reaches 160°F
(71.11°C). It requires a manual reset.
Thermostatically controlled electric heat
The controller supports up to three stages of On/Off electric heat with no fan and two
stag
es with a fan. For more information on actuation, refer to “Appendix D: Reheat
Actuation Schedule Tables” on page 97.
PWM electric heat (local stages only)
The amount of PWM electric heat required is calculated by a control algorithm identical
to
the algorithm that calculates the desired airflow for the air valve. It acts like the air valve
control.
It is difficult for the modulating types of reheat
to control to the heating setpoint. The
proportional integral algorithm would normally overshoot slightly and settle in at the
correct amount of heat. However, this overshoot is not allowed for reasons relating to
energy consumption. When the zone temperature reaches the heating setpoint plus 0.5°F
(0.28°C), the reheat is turned Off. This causes the operation with modulating heat to
oscillate over a long time period and not control at the setpoint.
PWM electric heat modulates one, two, or three
local stages. PWM electric heat uses a
hard coded three-minute period and 10-second minimum ON and OFF times. These
values cannot be configured. Each stage of PWM electric heat is an equal percentage of
the total reheat capacity.
Reheat Actuation Schedule with No Fan Present
All types of reheat can be limited by the communicated auxiliary heat enable.
The effect of communicated auxiliary heat enable on reheat is described in the following
ta
ble:
• Table 64 on page 98. Effect of communicated auxiliary heat enable on reheat
The methods of control for the reheat act
uation schedule with no fan present are
described in the following tables:
• Table 65 on page 102. Local heat only with no fan present
• Table 66 on page 102. Remote heat only with no fan present
• Table 66 on page 102. Local and remote heat with local priority and no fan present
• Table 68 on page 103. Local and remote heat with remote priority and no fan present
Reheat Actuation Schedule with a Parallel Fan Present
Fan-powered units have two outputs available for reheat and one output available for the
fan. The parallel fan runs intermittently and is the first stage of reheat. The parallel fan
is not limited by the value in the communicated auxiliary heat enable. All other types of
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