ASHRAE Journal - December 2012 - 30

can have their performance measured. By using energy modeling analyses to determine the amount of energy a facility should be consuming during a retro-commissioning project, operating adjustments can be made in the facility to fine-tune the building’s operation and reduce operating cost.

Energy Rate Structures
The last piece of the puzzle is to enter the utility rate structures into the modeling software. This information, typically obtained from the building owner, is a document that provides information on previous energy rate structures. It gives information on a utility consumption rate, such as a kilowatt-hour for electrical consumption and hundred cubic feet or cubic meters for natural gas. It also gives a demand charge if one is present. However, in some cases, the building may have purchased chilled water, heating water, or steam in addition to a standard electric or natural gas rate. This information is crucial in determining energy cost savings as well as payback information on various elements of the design. When considering payback periods, the energy modeler will also need to provide an inflation rate to anticipate the rise in utility costs over the study period.3

Energy Modeling in ASHRAE Standard 90.1
ASHRAE Standard 90.1-2007 provides energy modeling information when modeling using certain modeling methods. Section 11 contains the requirements for the energy cost budget (ECB) method, whereas Informative Appendix G contains the requirements for the performance rating method (PRM), which is used by voluntary labeling programs such as LEED.

Verifying Energy Model Accuracy
Energy models produce results that are used for determining design decisions on buildings. In some cases, energy models may be the only tool capable of producing the data required to make these design decisions. But, how do we know the data we are using is accurate? Seasoned energy modeling professionals have typically found a comfort level when reading energy model results. They have been through the process enough times to recognize when they need to throw a red flag, especially those who have been involved in measurement and verification scenarios. This leaves newer, less experienced energy modelers sometimes questioning their results, and they may be given the “That looks about right” quote from their more seasoned peers. So, how do they get the experience they need to become more comfortable? One of the most effective means of verifying energy model accuracy is through actual measured utility data. A building user will need to agree to provide this information to the modeling professional to assist with the comparison. Having measured utility data allows the energy modeler to compare the overall modeled results with actual data, which is beneficial to help people learn how occupancy and operations affect the
30 ASHRAE Journal

overall energy consumption of a facility. The data also provides information on unusual consumption caused by climate peaks and valleys and can assist in determining if there is an operations problem within a facility. However, the downfall of this approach is that for most cases, only total building energy consumption data is available.4 This makes it difficult to break out the energy use for building subsystems such as HVAC, lighting, and receptacle loads. To provide a meaningful exercise, the energy modeler may have to resort to comparing subsystem energy use with typical consumption percentages developed by third-party analysts. This approach will help determine if the model is predicting highly unusual results in a specific area, but will still not produce 100% model accuracy. Installing submetering systems in buildings has given the energy modeling field a terrific opportunity to verify energy model results. Submetering allows the actual measured data to be broken down into subsystem categories. The subsystem energy use can then be compared and analyzed against the model to produce more accurate results in the future, but will still require information from the building user to help determine how the building is being operated. During the energy modeling process, several assumptions have to be made on everything from lighting operation to thermostat set points to occupancy schedules. By obtaining this information, the energy model will be capable of producing results that are closely similar to the actual energy consumption of the facility. Through these exercises, energy modeling professionals can view the accuracy of their energy models and determine what adjustments best fit their modeling approach. The more that is understood about the modeling process and actual building operation, the more accurate predictions can be made, resulting in more informed design decisions in the future.

Conclusion
Energy modeling is complex and incorporates several disciplines to obtain an accurate finished product. The results produced by the energy model will be used to make decisions on the current project as well as future projects. In complex facilities, energy modeling may be the only design tool available for decision making. Using appropriate resources to make as detailed a model as possible will assist in producing an accurate energy model.

References
1. Waltz, James P. 1999. Computerized Building Energy Simulation Handbook, Chap. 6. Lilburn, Ga.: Fairmont Press. 2. California Energy Commission. 2004. “Nonresidential Alternative Calculation Method (ACM) Approval Manual.” http://tinyurl. com/cmwtwsz. 3. COMNET. 2010. Commercial Buildings Energy Modeling Guidelines and Procedures.http://tinyurl.com/cphjluh. 4. Higgins, J.A., S.D. Foster and J.R. Bailey. 2012. “Using Energy Models to Verify Utility Consumption.” ASHRAE Transactions 118(2): 205 – 213. ashrae.org December 2012



ASHRAE Journal - December 2012

Table of Contents for the Digital Edition of ASHRAE Journal - December 2012

ASHRAE Journal - December 2012
Contents
Commentary
Industry News
Letters
Meetings and Shows
Feature Articles
Dual Maximum VAV Box Control Logic
Energy Modeling Basics
Long-Term Commercial GSHP Performance: Part 5: Comfort and Satisfaction
Methods for Effective Room Air Distribution: Part 2
Technology Award Case Studies:
43% Energy Savings
Learning With Nature
Standing Columns
Building Sciences
Special Section
New Product Preview
Refrigeration Applications
Emerging Technologies
IAQ Applications
Washington Report
People
Products
2012 ASHRAE Journal Indices
Classified Advertising
Advertisers Index
ASHRAE Journal - December 2012 - ASHRAE Journal - December 2012
ASHRAE Journal - December 2012 - Cover2
ASHRAE Journal - December 2012 - 1
ASHRAE Journal - December 2012 - 2
ASHRAE Journal - December 2012 - Contents
ASHRAE Journal - December 2012 - Commentary
ASHRAE Journal - December 2012 - 5
ASHRAE Journal - December 2012 - Industry News
ASHRAE Journal - December 2012 - 7
ASHRAE Journal - December 2012 - 8
ASHRAE Journal - December 2012 - 9
ASHRAE Journal - December 2012 - 10
ASHRAE Journal - December 2012 - 11
ASHRAE Journal - December 2012 - Letters
ASHRAE Journal - December 2012 - 13
ASHRAE Journal - December 2012 - Meetings and Shows
ASHRAE Journal - December 2012 - 15
ASHRAE Journal - December 2012 - Dual Maximum VAV Box Control Logic
ASHRAE Journal - December 2012 - 17
ASHRAE Journal - December 2012 - 18
ASHRAE Journal - December 2012 - 19
ASHRAE Journal - December 2012 - 20
ASHRAE Journal - December 2012 - 21
ASHRAE Journal - December 2012 - 22
ASHRAE Journal - December 2012 - 23
ASHRAE Journal - December 2012 - 24
ASHRAE Journal - December 2012 - 25
ASHRAE Journal - December 2012 - Energy Modeling Basics
ASHRAE Journal - December 2012 - 27
ASHRAE Journal - December 2012 - 28
ASHRAE Journal - December 2012 - 29
ASHRAE Journal - December 2012 - 30
ASHRAE Journal - December 2012 - 31
ASHRAE Journal - December 2012 - Long-Term Commercial GSHP Performance: Part 5: Comfort and Satisfaction
ASHRAE Journal - December 2012 - 33
ASHRAE Journal - December 2012 - 34
ASHRAE Journal - December 2012 - 35
ASHRAE Journal - December 2012 - 36
ASHRAE Journal - December 2012 - 37
ASHRAE Journal - December 2012 - Methods for Effective Room Air Distribution: Part 2
ASHRAE Journal - December 2012 - 39
ASHRAE Journal - December 2012 - 40
ASHRAE Journal - December 2012 - 41
ASHRAE Journal - December 2012 - 43% Energy Savings
ASHRAE Journal - December 2012 - 43
ASHRAE Journal - December 2012 - 44
ASHRAE Journal - December 2012 - 45
ASHRAE Journal - December 2012 - Learning With Nature
ASHRAE Journal - December 2012 - 47
ASHRAE Journal - December 2012 - 48
ASHRAE Journal - December 2012 - 49
ASHRAE Journal - December 2012 - 50
ASHRAE Journal - December 2012 - 51
ASHRAE Journal - December 2012 - Building Sciences
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ASHRAE Journal - December 2012 - 58
ASHRAE Journal - December 2012 - New Product Preview
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ASHRAE Journal - December 2012 - 126
ASHRAE Journal - December 2012 - Refrigeration Applications
ASHRAE Journal - December 2012 - Emerging Technologies
ASHRAE Journal - December 2012 - 129
ASHRAE Journal - December 2012 - 130
ASHRAE Journal - December 2012 - 131
ASHRAE Journal - December 2012 - IAQ Applications
ASHRAE Journal - December 2012 - 133
ASHRAE Journal - December 2012 - Washington Report
ASHRAE Journal - December 2012 - 135
ASHRAE Journal - December 2012 - People
ASHRAE Journal - December 2012 - Products
ASHRAE Journal - December 2012 - 138
ASHRAE Journal - December 2012 - 2012 ASHRAE Journal Indices
ASHRAE Journal - December 2012 - 140
ASHRAE Journal - December 2012 - 141
ASHRAE Journal - December 2012 - 142
ASHRAE Journal - December 2012 - Classified Advertising
ASHRAE Journal - December 2012 - Advertisers Index
ASHRAE Journal - December 2012 - Cover3
ASHRAE Journal - December 2012 - Cover4
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