WebCTRL® system Fault Detection and Diagnostics Phase II


We are excited to announce the release of the WebCTRL® system Fault Detection and Diagnostics Phase II SAL

Initially introduced with WebCTRL v6.0, the latest release of the Automated Logic Fault Detection and Diagnostics (FDD) library can now pinpoint over 100 proven faults in typical HVAC equipment,  including VAV systems, air handlers, fan coils, unit ventilators, water-source heat pumps, and air-source heat pumps.

The logic for the equipment types listed below includes the following types of faults in the FDD alarm category



The logic in this library generates FDD alarms to warn users of problems which may be causing equipment to run inefficiently, wasting energy and/or degrading occupant comfort. The Department of Energy estimates FDD alarming could reduce energy use by up to 15%, and the State of California now requires FDD alarming in the Economizer section of certain rooftop units.

Examples of problems that this logic will detect include:

  • Leaking Heating Valves: A worn valve seat or a misadjusted actuator can cause a heating valve to “leak” hot water to the coil even when it is commanded 100% shut. This wastes heating energy and can bring on additional cooling, which wastes cooling energy. The FDD logic generates an alarm if there is a significant heat rise across a closed coil.
  • Failed DX stage: In a multi-stage DX unit, if one cooling stage fails, the controls will bring on additional stages as needed to provide the required cooling. The user will not even be aware of the failed stage until the weather gets really hot and the unit can no longer provide sufficient cooling without that stage. Then repairing or replacing that stage becomes an emergency. The FDD logic monitors each stage as it is commanded on, and generates an alarm if any one stage fails to provide cooling. Repairs can be undertaken on a routine basis, while the building is still comfortable.
  • Continuous Running: For a typical building, one of the most effective ways to save energy is to make zones “unoccupied” and turn equipment off at night and over weekends when no one is using the building. Unfortunately, a common problem with building automation systems is the existence of “rogue” schedules, locked points, and other overrides which unintentionally cause systems to run even when unoccupied. These problems often go unnoticed because no one is in the building at the time. The FDD logic monitors zone runtime and generates an alarm if it exceeds a certain number of hours per day. By default the trip point is set at 23 hours, but it can easily be changed to a shorter time for zones that should only be occupied fewer hours.