Overview:
*LCU Demand Controlled Ventilation (CO2) Set up for 17 SEER and other Multi Speed Fan Products.
Process:
There are 3 fan speed reference points which will be referred to as Low, Medium, and High fan speeds. The DCV set up procedure should be done in test mode. The supply fan test (1st step in test mode) forces the supply fan in the Low fan speed. The compressor stage 1 test (3rd step in test mode) forces the supply fan into the Medium fan speed. The compressor stage 2 test (4th step in test mode) forces the supply fan to the High fan speed.
It is highly recommended to connect the CO2 sensor directly at the unit to LTB4 for convenience. It is much more difficult to verify set points and functionality with the CO2 sensor in the space away from the unit. Breathing on the CO2 sensor simulates a high CO2 concentration in the space.
In addition to the RTEM (ReliaTel Economizer Module) a circuit board called the RTVM (ReliaTel Ventilation
Module) is required for DCV operation on Light Commercial multi speed supply fan and single zone VAV units.
This module is based off of the RTOM (ReliaTel Options Module) but the RTVM has different components and
firmware installed. The RTVM is provided in the DCV accessory kit and is mounted next to the RTOM. See the
accessory kit instructions for installation details.
Initial set up
For damper position adjustment, the Lower Limit (LL) CO2 PPM adjustment potentiometer should be set to the
lowest position (counter clockwise) and the Upper Limit (UL) CO2 PPM adjustment potentiometer should be set
to approximately half way. These can be adjusted later to the required levels. A CO2 sensor should be wired at the unit at LTB4 for the convenience of set up. All three of the Design Minimum adjustment potentiometers (R130 on the RTVM, R136 on the RTVM, and Design Min on the RTEM should be set to the maximum position (fully clockwise) and both of the DCV Minimum adjustment potentiometers (R41 of the RTVM and DCV Min of the RTEM) should be set to the
minimum position as a starting position.
Set up the LOW fan speed damper positions
Enter into the test mode to the supply fan test step (1st step in test mode). Adjust the R130 potentiometer on the RTVM to set the LOW fan speed Design minimum damper position. The Design minimum position set point controls the damper position when there is a high concentration of CO2 in the space and ventilation is required. The damper can be set from 0% open to 100% open during the LOW fan speed. Adjust the R41 potentiometer on the RTVM to set the LOW fan speed DCV minimum position. The DCV minimum position set point controls the damper position when there is a low concentration of CO2 in the space. The damper can be set from 0% open to 100% open in the LOW fan speed. Ensure that the R130 LOW fan speed Design minimum damper position is set greater than the LOW fan speed DCV minimum damper position. Blow on the CO2 sensor to simulate a high concentration of CO2 to confirm the economizer damper responds to the call for ventilation.
Note: This Procedure must also be repeated for the MEDIUM and HIGH fan speeds
Set up the MEDIUM fan speed damper position
Advance to the 3rd step in the test mode (1st stage compressor). This forces the supply fan to the MEDIUM fan
speed. Adjust the R136 potentiometer on the RTVM to set the MEDIUM fan speed Design minimum damper position.
The damper can be set from 0% open to approximately 75% open in the MEDIUM fan speed. There is no DCV Min setup for MEDIUM fan speed. The value from R41 from the previous step is retained for the MEDIUM fan speed. Again blow on the CO2 sensor to simulate a high concentration of CO2 to confirm the economizer damper responds to the call for ventilation.
Set up the HIGH fan speed damper positions
Advance to the 4th step in the test mode (2nd stage compressor). This forces the supply fan to the High fan
speed. Adjust the Design Min potentiometer on the RTEM to set the HIGH fan speed Design minimum damper
position. The damper can be set from 0% open to approximately 50% open in the High fan speed. Adjust the DCV Min potentiometer on the RTEM to set the High fan speed DCV minimum position. Again blow on the CO2 sensor to simulate a high concentration of CO2 to confirm the economizer damper responds to the call for ventilation.
After this procedure is finished adjust the Lower Limit (LL) CO2 PPM adjustment potentiometer and the Upper
Limit (UL) CO2 PPM adjustment potentiometer on the RTEM to the required settings for the application. This is often determined by local codes.
Notes:
- RTVM modules for Light Commercial units are different than RTVM modules for Large Commercial units and
are not interchangeable. - Design minimum position set up is different for Light Commercial multi speed supply fan and single zone VAV
units without DCV. - Communicated BAS set points override any local potentiometer setting.
WARNING:
Information in this article is intended for use by individuals possessing adequate backgrounds of electrical and mechanical experience and who comply with all federal, state, and local laws, rules, orders, or regulations related to the installation, service, or repair of a heating or central air conditioning product. Any attempt to install, service, or repair a heating or central air conditioning product may result in personal injury and/or property damage. The manufacturer or seller cannot be responsible for the interpretation of the information contained herein, nor can it assume any liability in connection with its use.