CenCon
17
Applications may require economizer damper control ‘by others’. This requires the CenCon to be programmed
as a MUA, and uses the FbD (Feedback Damper) input to allow the CenCon to adjust and reset the low limit
bypass timer if required during a significant increase in cold outside air.
MINIMUM POSITION
The minimum position setting is preset by design to the setting noted by sales, and may be adjusted using the
display keypad, a computer interface, Modbus or BACnet. This setting corresponds to the actuator output
signal, not the actual air volume.
CALIFORNIA BUILDING ENERGY EFFICIENCY - TITLE 24
This standard dictates that the economizer must be monitored and prove the mechanical operation of the
dampers. This is achieved by a number of methods. Whenever the economizer is in the full open position, a
damper end switch is activated to indicate that the dampers are operating correctly. A mixed air sensor must
be installed to give feedback on the effectiveness of the mixing section and to act as a mixed air low limit.
HIGH AMBIENT LOCKOUT
This feature is required in order to disable the economizer if there is no cooling available from the ambient air.
This can be performed by two different methods. Differential temperature is generally the method used and
compares the ambient temperature to the return temperature. A second method is differential enthalpy.
Humidity sensors are installed in the return and outside air, and enthalpy is calculated based on the humidity
and temperature readings.
LOW LIMIT
Based on discharge air temperature sensing, the low limit will disable unit operation if the temperature falls
below 40°F (4°C). The setpoint is not adjustable. Low limit, or freeze protection, may be enabled or
disabled. The low limit bypass has 2 timers, the main bypass timer that occurs at initial startup of the supply
fan, and an anti-nuisance timer. The anti-nuisance timer has a duration of 30 seconds and resets once the
discharge temperature rises above the low limit setpoint. The main bypass time is 4 minutes for all types of
equipment.
On variable air volume systems the main low limit bypass time is reset if the economizer minimum position is
suddenly increased by over 15%, or if the VFD speed increases by over 20%, both within 10 seconds.
The bypass time is reduced to 2 minutes if the heating has been disabled. The low limit is not active in cooling
mode.
HEATING
The CenCon may control simple fluid based heating devices from the auxiliary heating 0-10Vdc output.
Expansion modules are necessary for gas fired heating to monitor and control the increased complexity and
safety requirements of gas fired equipment.
The MHW (Modulating Hot Water) output is a 0-10Vdc signal, with 0V=no heat and 10V=max heat, typically
associated with a hot water coil. Reversing function must be done at the actuator. A spring return actuator
would be required for applications desiring full open, closed or bypassed when the equipment is off.
