An ASHRAE Level 1 or Level 2 energy audit is like a snap shot of a building, whereas retro-commissioning (RCx) is more like a video of the building. If you have an energy audit performed in the summer, the auditor should be able to identify air conditioning problems, but may not be able to identify heating problems, as the heating equipment may not have been running in the summer.
RCx is more focused on how the equipment operates and how the equipment responds to changes in ambient conditions or occupancy. Trend logs and/or data loggers are used to record temperatures, pressures, power, etc. hourly or in 15 minute intervals. This data is then analyzed to identify problems in how the equipment is working. RCx also typically involves functional testing, which is a systematic way of testing how the equipment responds to changes in ambient temperature, occupancy or schedule. Functional testing might answer questions like: what temperature chilled water is being provided when the outside air temperature is 30°F, 40°F, etc. The inputs to the controls are overridden or simulated in order to document the system’s response.
An energy audit focuses on measures that if implemented, will save energy. Many of these measures involve purchasing and installing new capital equipment, such as new chillers, pumps or boilers. RCx focuses on how the existing equipment is controlled. RCx measures are mostly repairing, recalibrating and reprogramming controls and control devices such as temperature sensors and damper actuators. RCx measures are typically inexpensive to implement and typically offer simple paybacks of two years or less.
An RCx study is typically more expensive than an energy audit, however, when you combine the cost of the RCx study with the cost to implement the measures identified in the report, you will find that RCx is typically less expensive than energy audits, as energy audit measures often have longer paybacks.