Discharge Air Temperature (Dat) Limiting; Discharge Air Temperature (Dat) Limiting; System Diagnostics; System Diagnostics - Nailor 37S Manual

Discharge Air Temperature (DAT) Limiting
To utilize Discharge Air Temperature (DAT) Limiting, a Discharge Air Temperature (DAT) sensor is required to control VAV units with
reheat. If a DAT sensor is detected and DAT Limiting is enabled, the VAV terminal will be controlled by the DAT loop. The unit will
also limit the Discharge Air Temperature to within 15° F of the Space Temp Reference.
When there is a call for heat and the primary air is cool air, the reheat outputs are directly controlled by the DAT Loop and the
DAT Set point reset based on the output of the Heating loop. As the Heating loop increases from 0% to 50%, DAT Set point is
proportionally calculated between Space Temp Reference and Space Temp Reference + 15° F up to maximum 90° F. This allows the
reheat to be controlled by the DAT loop over the first 50% of a call for heating.
Figure 8-1 DAT limiting operation
ROOM
ROOM TMP
If DAT Limiting is enabled, and a DAT sensor is not connected, the controller will lockout reheat control only in the cooling mode.
The unit will operate this way until a DAT sensor is detected or until the unit is commanded to control to the Active Heating Set
point by a supervisory BMS.
If the unit has detected a DAT sensor and DAT Limiting is not enabled, the unit's reheat is controlled by the Heating loop instead
of the DAT loop.
If DAT Limiting is not enabled, and a DAT sensor is not connected, the controller will satisfy a call for heat with the auxiliary flow
and heating coil.
See also the topics Changeover on page 36 and Input sources on page 34
System Diagnostics
The controller programming includes four system diagnostic indicators in the form of BACnet value objects.
• Need for higher static pressure
• Need for cooler supply air
• Need for warmer supply air
• Need AHU start
These diagnostic indicators or flags are monitored by other BACnet devices connected to the same building automation system as
the controller. How the indicators are used is beyond the scope of these instructions.
Need for higher static pressure The Need Higher Static value object is set to True (1) when the damper is fully open and airflow
cannot reach the required set point value.
Need for cooler supply air The Need Cooler Supply value object is set to True (1) when the damper is fully open and the Cooling
loop is greater than 95% for 30 minutes. The indicator changes to False (0) when the Cooling loop falls below 90%.
Need for warmer supply air The Need Warmer Supply value object is set to True (1) when the damper is fully open and the Heating
loop is greater than 95% for 30 minutes. The indicator changes to False (0) when the Heating loop falls below 90%.
Need AHU start The Need AHU Start value object is set to True (1) for any of the following conditions.
• The system mode is Unoccupied and the Cooling loop or the Heating loop reaches 100%.
• The system mode is Occupied.
• The system mode is Standby.
The Need for AHU Start object changes to False (0) when both loops drop below 5%.
Date: 10-2016 Supersedes: 7-2016
Nailor reserves the right to change any information concerning product or specification without notice or obligation.
Installation and Operation Manual
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