What is Fault Detection and Diagnostics in Buildings?

In essence, Fault Detection and Diagnostics, or FDD, is the process of uncovering errors in physical systems while attempting to identify the source of the problem. In buildings, these physical systems include HVAC&R – systems designed to maintain the indoor environment acceptable to people, products and equipment – as well as lighting, elevators and any specialized equipment residing in the confines of the thousands of buildings all around us.

The term Automated Fault Detection and Diagnostics, or AFDD, has become more prominent lately, particularly in the building industry. In general, the differentiation made is that while FDD commonly refers to the process, AFDD refers to the technologies used to implement FDD processes. An AFDD tool is therefore equipped to implement automated FDD with as little human intervention as possible.

How does Fault Detection and Diagnostics work?

The basic methodology in FDD involves four key processes, fault detection, fault isolation, fault identification, and fault evaluation, as shown in figure 1. Once it has been determined that a fault has occurred in the system, it is isolated and classified based on the fault type, location and detection time. Fault isolation, together with fault identification – which includes determining the fault size and how it behaves at different times – are commonly referred to as fault diagnosis. Fault evaluation is basically an assessment to determine the fault’s impact on system performance, often based on different prioritization categories including energy, comfort, environmental and cost impact.

Four key processes in Fault Detection and Diagnostics