What is Retro-Commissioning?
Background: The Unrealized Promise of Building Automation Systems
In the 1980s and 1990s, DDC energy management systems (EMS) were being installed in large buildings throughout the country with claims that they would reduce energy usage. That turned out to be a false claim. An EMS saves energy no better than a hammer builds a house. The EMS is a tool that can be used for good or ill, just as a hammer can be used to build or destroy. With an EMS, an unsophisticated building operator, through use of overrides and poorly chosen setpoints, can waste much more energy than he would have in the past.
For most building operators, the main focus of day-to-day activities is to avoid hot and cold calls. Energy efficiency falls far down the list of concerns. Often this emphasis on avoiding complaints leads to overrides of control settings which may waste significant amounts of energy.
There are other causes that lead to EMS systems not saving energy. Many EMS installers don’t understand energy conservation either. They understand how to install EMS systems, and make them work. However, due to ignorance, poor contract scope, not enough hours budgeted to the job, or value engineering, many energy efficiency strategies are just not programmed into the EMS, which might otherwise have reduced energy usage.
Introducing Retro-Commissioning: The Solution to Underperforming Building Automation Systems
In the 2000s and 2010s Retro-commissioning (RCx) has come along as a popular means to reduce energy usage. Now, all the energy that was supposed to be saved when the EMS was installed, can now be saved because RCx can optimize the EMS, implement missing energy efficient strategies, and reduce energy waste.
According to some authoritative sources, RCx is supposed to get the building back working as it had been originally designed. However, as many in the energy efficiency business know, the original design is often not energy efficient, as it is often the work of architects, whose main focus and area of expertise has not been energy efficiency. A better definition of RCx is to take the building and its controls as they currently are, and to optimize the controls to make the building as energy efficient as is economically feasible, while still maintaining occupant comfort. This optimization is usually done through a combination of repairing control devices (such as economizer dampers), replacing broken components (such as leaky valves, broken VFDs, or faulty sensors), and reprogramming control sequences so that they reduce energy usage.
Whereas energy audits often focus on replacing inefficient equipment with more efficient equipment, RCx focuses on optimizing the control of this equipment.
Typical RCx measures include:
- Replacing temperature and pressure sensors,
- Repairing economizers,
- Scheduling HVAC systems,
- Implementing heating and cooling lockouts,
- Implementing temperature and pressure resets,
- and many more.
RCx studies are more detailed than energy audits. While an energy audit typically involves one visit to a facility, and recommendations are made based on one view of a moving target, RCx employs functional testing, trend logging, and/or data logging to get a better, more in depth, understanding of how the hvac equipment responds to varying conditions. A good RCx study will capture an understanding of how the building operates during the entire year. An RCx study will identify inefficiencies that cannot be found during an energy audit, and RCx will determine the root cause of the problem, so that specific recommendations can be made. Finally, once the recommendations have been made, and the measures have been implemented, RCx often includes a measurement and verification phase, to quantify the savings the measures are actually providing.
RCx is expensive relative to audits, however, the results are usually quite favorable. The building owner can spend the thousands on new equipment, which may or may not work as advertised, or commission an RCx study which not only provides a good return on investment, but also measures and verifies that the savings have actually occurred.