TRUE FIT BACnet AAC Airflow Measurement System
Introduction
The TrueFit Airflow Measurement System (AFMS) reliably provides accurate outside, return, and supply airflow data for monitoring and control. The system delivers accurate, repeatable results on any type of equipment, without the traditionally expected mechanical limitations, performance issues, or ongoing maintenance issues.
The system consists of the following components, installed on an AHU, RTU, or unit ventilator:
- One controller with airflow measurement programming
- One inclinometer (included with the controller) mounted on a horizontal out-side or return air damper blade
- If only vertical damper blades, one HLO-1050 Linkage Kit
- At least two airflow pickup tubes installed in a pitot array duct on the supply fan inlet, in the supply air duct
- If a TRF-5901C(E)-AFMS is used, one pressure transducer
- If pressure assist measurements are needed (see Considerations on page 4), one additional pressure transducer, connected to two additional flow pickup tubes that are mounted on both sides of either the outside air damper or return air damper
- Three temperature sensors for outside, mixed, and return air
- One proportional actuator mounted on the damper shaft
Example Diagrams
Standard Application
OAD (Outside Air Damper) PA (Pressure Assist) Application
RAD (Return Air Damper) PA (Pressure Assist) Application
Selecting an AFMS Controller (with inclinometer)
Considerations
Does the unit have any of these non-standard features?:
- A relief fan that is variable speed, or is operating independently of mixed air damp- er position
- A return fan that is not controlled by a supply fan / return fan offset
- A bypass damper utilized to bypass a heat recovery system
- Return VAV boxes
- Supply to return bypass (typically found in zone damper applications, or where a bypass damper is used in place of a VFD)
- Outside and return air dampers that modulate independently
- More than one outside air damper
If yes, the pressure of the unit’s mixed and/or return air sections may change. In that case, select a TRF-5901C(E)-AFMS for (OAD or RAD) pressure assist measurements.
Are there plans to add custom programming?
If there are plans to add custom programming, select a TRF-5901C(E)-AFMS. If additional I/O are needed, select at least one CAN-5900 Series I/O expansion module. (See Adding Custom Programming to a TrueFit AFMS technical bulletin). KMC software is also required.(See Selecting Tools for Configuration and Operation on page 9.)
Where will the controller be mounted?
If the controller will be mounted more than 20 feet from the location of the airflow pickup tubes (see Selecting Flow Pickup Tubes on page 5), select a TRF-5901C(E)-AFMS. A pressure transducer can be mounted closer to the pickup tubes, then wired over a greater distance to the controller. (See Selecting Pressure Transducers on page 6.)
Selecting Flow Pickup Tubes
Options for Installation Location
The array of supply airflow pickup tubes can be installed in one of two places:
- At the supply air fan inlet
- At least six straight duct widths down the supply air duct
If pressure assist measurements are needed (see Considerations on page 4) two additional flow pickup tubes must be installed, one on either side of the outside air damper (for OAD pressure assist) or return air damper (for RAD pressure assist).
Arrangement in Parallel Array
The pickup points must be arranged in a parallel array that evenly covers the area of the supply air duct or fan inlet, similar to what is show below:
Determining the Number of Pickup Points
- Measure the duct or fan inlet:
- For a rectangular or square duct, measure the length of the longest side.
- For a circular duct or the supply fan inlet, measure the diam-eter.
- Consult one of the tables below to determine the total minimum number of pickup points needed:
| FOR A RECTANGULAR OR SQUARE DUCT | |
| If the longest side is less than or equal to: | Total minimum number of pickup points needed is: |
| 4 inches | 2 |
| 15 inches | 3 |
| 24 inches | 4 |
| 35 inches | 5 |
| 48 inches | 6 |
| 63 inches | 7 |
| 80 inches | 8 |
| 99 inches | 9 |
| 100 inches or greater | 10 |
| FOR A CIRCULAR DUCT OR THE FAN INLET | |
| Duct diameter | Total minimum number of pickup points needed: |
| <10 inches | 6 |
| ≥10 inches | 10 |
Selecting the Tubes
Select multiple airflow pickup tubes (at least two) from below that are the maximum length that will fit in the space and total to at least the minimum number of pickup points needed:
SSS-101x models have 3/16” connections for 1/4” OD polyethylene tubing and flat mounting flanges for installation in ducts (or on fan inlets that have struts):
- SSS-1012 One pickup point, 80 mm (about 3”) length tubes
- SSS-1013 Two pickup points, 137 mm (about 5.5”) length tubes
- SSS-1014 Three pickup points, 195 mm (about 8”) length tubes
- SSS-1015 Four pickup points, 252 mm (about 10”) length tubes
SSS-111x models have 3/16” connections for 1/4” OD polyethylene tubing and right-angled mounting feet for installation on the supply air fan bell.
Single mounting foot:
- SSS-1112 One pickup point, 80 mm (about 3”) length tubes
- SSS-1113 Two pickup points, 137 mm (about 5.5”) length tubes
- SSS-1114 Three pickup points, 195 mm (about 8”) length tubes
Dual mounting feet:
- SSS-1115 Four pickup points, five sections*, 315 mm (about 13”) length tubes
- SSS-1116 Five pickup points, six sections*, 395 mm (about 15.5”) length tubes
- SSS-1117 Six pickup points, seven sections*, 457 mm (about 18”) length tubes
*NOTE: The extra section connects the tubes to the second mounting foot, which mounts to the other end of the fan bell (or a midway strut).
Selecting Pressure Transducers
NOTE: Select pressure transducers for a TRF-5901C(E)-AFMS only. TRF-9311C(E)-AFMS have differential air pressure ports, so a pressure transducer is not necessary to connect the flow pickup tubes.
For the standard airflow measurement application, select one pressure transducer.
For airflow measurement applications with pressure assist, select two pressure transducers.
| MODEL NUMBER | INPUT PRESSURE RANGES (SELECTABLE) |
| TPE-1475-21 | –2 to +2” or 0 to 2” wc (–0.5 to +0.5 kPa or 0 to 0.5 kPa) |
| TPE-1475-22 | –10 to +10″ or 0 to 10″ wc (–2.5 to +2.5 kPa or 0 to 2.5 kPa) |
Selecting the Mixed Air Temperature Sensor
Averaging sensors are necessary to minimize errors due to stratification or poor airflow mixing in the mixed air chamber. It is recommended to install the largest averaging sensor that the equipment will accommodate. Copper sensors are recommended when the mixed air section is easily accessible. If not easily accessible, a cable sensor can be used.
|
MODEL |
SENSOR TYPE | PROBE TYPE |
PROBE LENGTH |
ENCLOSURE |
CONNECTIONS* |
| STE-1411 |
Duct, Averaging |
Copper, bend- able |
6 feet (1.8 m) |
Plastic, UL94-V0, IP65 (NEMA 4X) ABS |
FT-6 plenum-rated, 22 AWG wire leads |
| STE-1412 | 12 feet (3.6 m) | ||||
| STE-1414 | 20 feet (6.1 m) | ||||
| STE-1413 | 24 feet (7.3 m) | ||||
| STE-1415 |
Flexible, FT-6 plenum-rated cable |
6 feet (1.8 m) | |||
| STE-1416 | 12 feet (3.6 m) | ||||
| STE-1417 | 24 feet (7.3 m) |
Selecting the Outside Air Temperature Sensor
For units with accessible outside air hoods, select an STE-1412 12-foot bendable copper averaging sensor.
For units with inaccessible outside air hoods, or for outside air ducts, select an STE-1404 duct-mounted 12-inch probe with enclosure. (For sheltered tight fits, an STE-1405 duct-mounted 4-inch probe without enclosure can be used.)
|
MODEL |
SENSOR TYPE | PROBE TYPE |
PROBE LENGTH |
ENCLOSURE |
CONNECTIONS |
| STE-1405 |
Duct, Rigid probe |
1/4-inch OD stainless-steel |
4 inches (100 mm) | None (mounting bracket only) | 10-ft. FT-6 plenum-rated, 22 AWG cable |
| STE-1404 | 12 inches (300 mm) |
Plastic, UL94-V0, IP65 (NEMA 4X) ABS |
PVC insulated, 22 AWG, wire leads | ||
| OA Hoods, Averaging | Copper, bend- able |
12 feet (3.6 m) |
FT-6 plenum-rated, 22 AWG, wire leads |
Selecting the Return Air Temperature Sensor
When possible, select an STE-1404 duct-mounted 12-inch probe with enclosure. For sheltered tight fits, an STE-1405 duct-mounted 4-inch probe without enclosure can be used.
|
MODEL |
SENSOR TYPE | PROBE TYPE |
PROBE LENGTH |
ENCLOSURE |
CONNECTIONS |
| STE-1405 |
Duct, Rigid probe |
1/4-inch OD stainless-steel |
4 inches (100 mm) | None (mounting bracket only) | 10-ft. FT-6 plenum-rated, 22 AWG cable |
| STE-1404 | 12 inches (300 mm) | Plastic, UL94-V0, IP65 (NEMA 4X) ABS | PVC insulated, 22 AWG, wire leads |
Selecting a Proportional Actuator
The unit must have a proportional damper actuator for the AFMS to modulate the damper as needed. If the unit does not have a proportional damper actuator already, select one.
Selecting an HLO-1050 Linkage Kit
The AFMS controller’s inclinometer must be mounted on a horizontal-axis damper blade. For units with vertical-axis damper blades, select an HLO-1050 Linkage Kit. The linkages transfer the damper motion to a surface with a horizontal axis (the kit’s inclinometer crankarm), on which the inclinometer can then be mounted.
The kit’s damper blade crankarm can be mounted to a damper blade or on a jackshaft using the included jackshaft coupler and V-bolt.
If the kit’s axle mount shaft cannot be mounted on a unit’s damper frame (such as when mounting in a duct), select a VTD-0903 right-angle bracket in addition to the kit.
Selecting Tools for Configuration and Operation
The rows in the table below list the processes to set up and operate an AFMS. The columns present the KMC Controls tools that can be used to complete the processes. Consult the table to determine which tools can complete each process and for which AFMS applications.
The user interface and setup requirements of each tool varies. For more information, see each tool’s product pages and documents.
Support
Additional resources for product specifications, installation, configuration, application, operation, programming, upgrading and much more are available on the KMC Controls web site (www.kmccontrols.com). Log in to see all available files.
© 2025 KMC Controls, Inc.
Specifications and design subject t9 o change without notice
AG230816D
Documents / Resources
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TRUEFIT BACnet AAC Airflow Measurement System [pdf] Owner's Manual TRF-5901C-AFMS, TRF-5901CE-AFMS, BACnet AAC Airflow Measurement System, BACnet AAC, Airflow Measurement System, Measurement System |
