TEC Controller Terminal Box (VAV) - Parallel Fan with Electric Reheat, Application 2026 Application Note 140-1055 2015-10-05 Building Technologies
Table of Contents Overview ............................................................................................................................. 4 Hardware Inputs .................................................................................................................. 6 Hardware Outputs ................................................................................................................ 6 Ordering Notes .............................................................................
Overview Hardware Inputs Overview In Application 2026, the controller modulates the supply air damper of the terminal box for cooling and controls stages of electric reheat for heating. When in heating, the terminal box either maintains minimum airflow or modulates the supply air damper. Application 2026 has a parallel fan that re-circulates the room air in heating mode. In order for the terminal box to work properly, the central air-handling unit must provide supply air.
Overview Hardware Inputs Application 2026 Control Schedule with Minimum Supply Air in Heating Mode. Application 2026 Heating Mode Control Schedule with Modulating Supply Air in Heating Mode. NOTES: 1. See Control Temperature Setpoints. 2. See Heating/Cooling Switchover. 3. The electric reheat is time modulated. This allows it to be controlled proportionally rather than with deadbands. 4. (Optional) The airflow is shown modulating in the entire heating mode. (Default settings must be changed.
Overview Hardware Inputs NOTE: (Optional) The airflow is shown operating parallel with the electric reheat. See Sequencing Logic [➙ 12].
Sequence of Operation Control Temperature Setpoints Sequence of Operation The following paragraphs present the sequence of operation for Application 2026, VAV with Electric Heat and Parallel Fan. Control Temperature Setpoints This application has a number of different room temperature setpoints (DAY HTG STPT, NGT CLG STPT, RM STPT DIAL, and so on.). The application actually controls using the CTL STPT.
Sequence of Operation Room Temperature and CTL TEMP CTL STPT is calculated as follows: With Deadband disabled: CTL STPT = Dial value With Deadband enabled in Heat Mode: CTL STPT = Dial value – 0.5 ∗ Deadband (limited between the value of RM STPT MIN and RM STPT MAX) With Deadband enabled in Cool Mode: CTL STPT = Dial value + 0.5 ∗ Deadband (limited between the value of RM STPT MIN and RM STPT MAX) NOTE: If RM STPT DIAL is failed, it maintains the last known value.
Sequence of Operation Day and Night Modes Day and Night Modes The day/night status of the space is determined by the status of DAY.NGT. The control of this point differs depending on whether the controller is monitoring the status of a wall switch or if the controller is connected to a field panel.
Sequence of Operation Modulating Damper During Heating Mode (Optional) Digital Room Units (2200/2300 Series) The digital room unit will display a graphical bar indicating the number of steps above or below the current operating temperature setpoint. When the controller switches modes (heating to cooling) the span adjustment set will be applied to the new heating/cooling mode center value.
Sequence of Operation Control Loops FLOW STPT and FLOW % are relative to MIN and MAX STPTS of corresponding heating or cooling mode. Example If CLG FLOW MIN = 200 cfm, and CLG FLOW MAX = 1000 cfm, the minimum flow setpoint is (200 cfm/000 cfm) × 100% flow = 20%. When CLG LOOPOUT is 0%, FLOW STPT = 20% flow. [0% × (100% – 20%)] + 20% = 20% This ensures that the airflow out of the terminal box is no less than CLG FLOW MIN. When CLG LOOPOUT is 50%, FLOW STPT = 60% flow.
Sequence of Operation Flow Control in Night Mode HTG LOOPOUT adjusts the value of FLOW STPT differently depending on which flow loop setup is chosen. However, the following rule applies no matter what setup is chosen. In heating mode, FLOW STPT is never set below (CTL FLOW MIN/HTG FLOW MAX) × 100% flow or above 100% flow. In heating mode, CTL FLOW MIN is equal to HTG FLOW MIN. Flow Loop – The flow loop maintains FLOW STPT by modulating the supply air damper, DMPR COMD.
Sequence of Operation Sequencing Logic Sequencing Logic NOTE: Setting FLOW START = 0 and FLOW END = 100, provides modulating supply airflow during heating mode (HTG FLOW MIN to HTG FLOW MAX). NOTE: Sufficient airflow across the heating coil is required whenever it is energized. Ensure that the configuration for the parallel fan and for sequencing the supply flow with the heating coil provides the needed airflow.
Sequence of Operation Sequencing Logic Example 2 (Airflow and Heat Sequenced Together) Assume that your system has electric heat that is to operate in parallel with the flow loop. If: FLOW START = 0% FLOW END = 100% REHEAT START = 0% REHEAT END = 100% then, When HTG LOOPOUT = 0%, FLOW STPT will equal 0% flow. When HTG LOOPOUT = 50%, FLOW STPT will equal 50% flow. When HTG LOOPOUT = 100%, FLOW STPT will equal 100% flow. When HTG LOOPOUT = 0%, the electric heat will be off all the time.
Sequence of Operation Calibration STAGE TIME = 10 minutes If: FLOW START=0% FLOW END=0% (or/and HTG FLOW MIN = HTG FLOW MAX) REHEAT START = 0% REHEAT END = 100% then, When HTG LOOPOUT = 0%, FLOW STPT will equal (170 cfm/1000 cfm) × 100% flow = 17% flow. This will cause the flow loop to maintain an airflow of 170 cfm out of the terminal box. When HTG LOOPOUT = 50%, FLOW STPT will equal 17% flow. When HTG LOOPOUT = 100%, FLOW STPT will equal 17% flow.
Sequence of Operation Parallel Fan Operation This configuration should only be used when the mechanical arrangement is such that the heating coils are in the discharge airflow. CAUTION This fan configuration could cause damage, if the coils are in the return/plenum air path. FAN CONFIGURED TO SUPPLEMENT SUPPLY AIRFLOW FOR THE HEATING COIL.
Sequence of Operation Fail Mode Operation Heating coil located in the return/plenum air duct. NOTE: When a heating coil is external to the terminal unit (perimeter or heated beam/heated floor), the activation of the fan or primary airflow is not a major factor. Fail Mode Operation If the air velocity sensor fails, the controller uses pressure dependent control. The temperature loop controls the operation of the damper.
Sequence of Operation Wiring Diagram Wiring Diagram NOTE: The controller’s DOs control 24 Vac loads only. The maximum rating is 12 VA for each DO. An external interposing relay is required for any of the following: • VA requirements higher than the maximum • 110 or 220 Vac requirements • DC power requirements • Separate transformers used to power the load (for example, part number 540-147, Terminal Equipment Controller Relay Module) Application 2026 – Variable Air Volume Parallel Fan with Electric Reheat.
Application 2026 Point Database Application 2026 Point Database Point Number Descriptor Factory Default (SI Units)2 Eng Units (SI Units) Slope (SI Units) Intercept (SI Units) On Text Off Text 1 CTLR ADDRESS 99 -- 1 0 -- -- 2 APPLICATION 2091 -- 1 0 -- -- {04} ROOM TEMP 74.0 (23.44888) DEG F (DEG C) 0.25 (0.14) 48.0 (8.88888) -- -- {05} HEAT.COOL COOL -- -- -- HEAT COOL 6 DAY CLG STPT 74.0 (23.44888) DEG F (DEG C) 0.25 (0.14) 48.0 (8.
Application 2026 Point Database Point Number Descriptor Factory Default (SI Units)2 Eng Units (SI Units) Slope (SI Units) Intercept (SI Units) On Text Off Text 31 CLG FLOW MIN 220 (103.818) CFM ( LPS) 4 (1.8876) 0 -- -- 32 CLG FLOW MAX 2200 (1038.18) CFM ( LPS) 4 (1.8876) 0 -- -- 33 HTG FLOW MIN 220 (103.818) CFM ( LPS) 4 (1.8876) 0 -- -- 34 HTG FLOW MAX 2200 (1038.18) CFM ( LPS) 4 (1.8876) 0 -- -- {35} AIR VOLUME 0 (0.0) CFM ( LPS) 4 (1.
Application 2026 Point Database Point Number Descriptor Factory Default (SI Units)2 Eng Units (SI Units) Slope (SI Units) Intercept (SI Units) On Text Off Text {77} CTL FLOW MAX 2200 (1038.18) CFM ( LPS) 4 (1.8876) 0 -- -- {78} CTL TEMP 74.0 (23.44888) DEG F (DEG C) 0.25 (0.14) 48.0 (8.88888) -- -- {79} CLG LOOPOUT 0 PCT 0.4 0 -- -- {80} HTG LOOPOUT 0 PCT 0.4 0 -- -- {81} AVG HEAT OUT 0 PCT 0.4 0 -- -- 82 STAGE MAX 90 PCT 0.
Issued by Siemens Industry, Inc. Building Technologies Division 1000 Deerfield Pkwy Buffalo Grove IL 60089 Tel. +1 847-215-1000 Document ID 140-1055 Edition 2015-10-05 © Siemens Industry, Inc., 2015 Technical specifications and availability subject to change without notice.
