Exceptional Calculations (EC)

90.1 2016, 2019 and 2022 ECB

When the simulation program does not model a design, material, or device in the proposed design, an exceptional calculation method must be used. Where there are multiple designs, materials, or devices that the simulation program does not model, each must be calculated separately, and exceptional savings determined for each. The following documentation must be submitted for each exceptional calculation method:

1. Theoretical and empirical information verifying the method’s accuracy, and step-by-step documentation of the exceptional calculation method performed, detailed enough to reproduce the results.
2. Copies of all spreadsheets used to perform the calculations.
3. A sensitivity analysis of energy consumption when each of the input parameters that are estimated is varied from half to double the value assumed.

90.1 2016, 2019, and 2022 PRM

Either the actual rates for purchased energy or state average energy prices published by U.S. Energy Information Administration (EIA) for commercial building customers may be used, but rates from different sources may not be mixed in the same project.

1. Step-by-step documentation of the exceptional calculation method performed, detailed enough to reproduce the results.
2. Copies of all spreadsheets used to perform the calculations.
3. A sensitivity analysis of energy consumption when each of the input parameters is varied from half to double the value assumed.
4. The calculations must be performed on a time-step basis consistent with the simulation program used.

Review Tips

1. Exceptional calculations are listed in Table 1 of the Exceptional Calculations tab of the Compliance Form. Prioritize review of exceptional calculations that are expected to generate the greatest savings based on the information provided in Table 2 of the tab.
2. Refer to Submittal Checklist #35 for the list of files and documents substantiating the exceptional calculations. Locate the material and confirm that the provided details meet 90.1 requirements quoted above for each exceptional calculation.
3. Common mistakes
   1. Submittal includes screenshots or printouts of the calculations but not the spreadsheet files where formulas can be examined.
   2. Savings are estimated using proprietary calculators from the vendor of specified system and equipment.
   3. Calculation methodology not based on peer-reviewed reference or fundamental principles of physics or thermodynamics.
   4. The whole building simulation tool used on the project must be able to explicitly model all systems and components of the baseline/budget design (Section G2.2.1 b, Section 11.4.1.1/12.4.1.1 h), thus exceptional calculations may only apply to the proposed design.

90.1 2016, 2019, and 2022 The Energy Cost Budget and Performance Rating Methods

Each exceptional calculation is subject to approval by the authority having jurisdiction or rating authority.

Review Tips

1. The Energy Cost Budget and Performance Rating Methods require that all building systems and equipment are modeled identically in the baseline/budget and proposed design except when specifically allowed to be different (see Table 11.5.1 No 1 (12.5.1 No 1 in 90.1 2022) and Table G3.1 No 1. Confirm that system or equipment that is the subject of exceptional calculation method is an allowed trade-off opportunity.
2. Verify methodology used for the exceptional calculation methods to confirm that it is acceptable
3. Confirm that calculation inputs reflect properties of the relevant systems and equipment specified in the design documents.
4. Ensure that operating conditions assumptions and other inputs not inherent in system design are conservative and do not exaggerate savings.
5. Verify that applicable interactive effects are accounted for.

90.1 2016 and 2019/2022 ECB

There is no limit on the contribution of savings documented via exceptional calculations toward compliance.

90.1 2016, 2019 and 2022 PRM

Section G2.5: When the simulation program does not model a design, material, or device associated with the proposed design, an approved exceptional calculation method may be used. The total Exceptional Savings must not account for more than half of the difference between the baseline building performance and the proposed building performance.