Fault Detection and Diagnostics

Work initially done in California to improve economizers and support fault detection and diagnostics (FDD) on commercial rooftop HVAC units has now been applied at a national level. A recent adoption of the International Energy Conservation Code (IECC) requires economizer FDD on all new and replacement units starting with the 2015 code revision. The measure was proposed to the IECC by NBI and our partners through active participation in the NW Energy Codes Group that includes code stakeholders from Idaho, Montana, Oregon and Washington.The economizer is linked to fan and compressor energy use. Outside air must be drawn into the building through the economizer damper, which could provide ‘free’ cooling’ by reducing compressor operation or eliminating it entirely under the right conditions on a given day. Generally speaking, a working economizer could save as much as 2000 kWh year on a 5-ton rooftop unit.

A 2003 California Energy Commission, PIER, report by NBI on the condition of 215 rooftop HVAC units noted that 62% of the 123 economizers in the sample, were poorly controlled or non-functional at all. It became clear that making economizers work was a significant opportunity to capture energy savings in commercial HVAC equipment.

The FDD measure was initially developed through a collaborative effort in California including NBI, the Western Cooling Efficiency Center (UC Davis, CA), and the California investor-owned utilities Codes and Standards Enhancement (CASE) program. The team developed a code proposal for the 2013 revision of the Title 24 building efficiency standards. The team work resulted in a mandatory economizer FDD requirement for all commercial air conditioners 54,000 Btu/hr (4.5 tons) and larger, including package, split, VRF systems. This was the model for the IECC proposal including the unit size threshold.

The FDD measure is now a virtual national standard. All manufacturers will supply to a national market, not just one state only. There is an efficiency benefit in every part of the country since economizers work everywhere and are required through national standards in more rooftop units. We think this is a good first step