Retrocommissioning with Energy Modeling Software Simulates Building Energy Use

Retrocommissioning (RCx) has become a very ambiguous word with so many different uses that it no longer really means anything. At the heart of a RCx project, a building’s performance is analyzed, and measures to improve the current performance are suggested.

The team of people performing a RCx project have a number of different tools from which to draw. These may include review of existing drawings and energy bills, interviews with building operators, data-logging devices, as well as trends and other information from the building automation system. Another effective tool, often overlooked for this purpose, is an energy model.

Energy modeling is a more well-defined term than RCx: Energy modeling is a physics-based software simulation of building energy use. The original intent of energy models was to provide a way to make apples-to-apples comparisons of different characteristics of a building during design. This allows the design team members to be well informed regarding the energy
impact their decisions would have.

The energy model is capable of providing information in the context of a RCx project, as well. To understand how, it is necessary to first understand the basics of energy modeling.

Primer on Energy Modeling

Energy models manage to be simple and complicated at the same time. All energy models are basically a set of inputs that are run through a mathematical engine that calculates a number of outputs. Most commonly used energy-modeling programs, such as eQuest or Trane Trace 700, act primarily as a graphical front end, displaying the inputs in an easier to understand format and reporting the outputs in a convenient manner.

The mathematical engine used by most energy-modeling programs is produced by the U.S. Department of Energy, Washington, D.C. The code is revised regularly and helps to provide some degree of consistency between different software.

The complication for energy models usually lies in the sheer quantity of inputs required by the software. Every room requires detailed schedules and information about the envelope, lighting, occupant activity, airflows, adjacent shading, mechanical equipment, etc. The quality—and accuracy—of the inputs absolutely determines the quality of the outputs.

Energy models provide very detailed and quite valuable information, including equipment capacities, utility use, system load information and room by room airflows.

About the Author

John Bixler
John Bixler, branch operations manager for Sebesta’s Cedar Rapids, Iowa, office, has 15 years’ experience working with the design and operation of HVAC systems.

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