ASHRAE Standard 90.1 Performance Based Compliance (Section 11 and Appendix G)

Training webinars available!  BECP is hosting two webinars on forms for performance-based code compliance:

  • Performance-based Compliance Documentation for ASHRAE 90.1 Section 11 and Appendix G — September 29,2020.  Learn more
  • Performance-based Compliance for Submittal Reviewers — December 8, 2020.  Learn more

Performance Based Energy Codes

Commercial building energy codes such as ASHRAE Standard 90.1 typically include two types of approaches for demonstrating compliance; prescriptive and performance paths.

  • The prescriptive path establishes criteria for energy related characteristics of individual building components such as minimum R-values of insulation, maximum U-factors and solar heat gain coefficients of fenestration, maximum lighting power allowance, occupancy sensor requirements for lighting control, and economizer requirements for HVAC systems.
  • The two performance-based approaches in Standard 90.1 are the Energy Cost Budget (ECB) method found in Section 11 and the Performance Rating Method (PRM), commonly referred to by its location in the Standard, Appendix G. These methods provide more flexibility by allowing a designer to "trade off" compliance by not meeting some prescriptive requirements if the impact can be offset by exceeding other prescriptive requirements. This is demonstrated using computer simulation to compare a proposed building design to a reference building design commonly referred to as a baseline.

The main differences between the ECB and PRM approaches in Standard 90.1 are the characteristics of the baseline building design.

ECB

  • The baseline is essentially a clone of the proposed design with most of the building components adjusted to “just meet” current prescriptive requirements.
  • A building is deemed in compliance with ECB when the annual energy cost of the proposed design is no greater than the annual energy cost of the baseline building design. This approach is referred to as a dependent baseline.

Appendix G

  • Appendix G uses a more independent baseline where many of the characteristics of the baseline design are based on standard practice, meaning credit is available not only for exceeding prescriptive requirements in the code, but also for exceeding standard practice that is not regulated by the code. For example, in Appendix G credit is available for strategies not credited in ECB such as optimized window area and orientation, selection of more efficient HVAC and service water heating equipment type, right sizing HVAC equipment, efficient use of thermal mass, etc.
  • Appendix G uses a stable baseline approach with efficiency levels set at values that are not intended to be updated with each new addition of the code. Instead, the proposed building energy performance needs to exceed that of the baseline by an amount commensurate with the code year being evaluated.

Tools

Compliance Forms Proper enforcement of performance-based compliance submittals is necessary to ensure consistency and confidence in modeling results, yet, enforcement is a notoriously difficult process. This spreadsheet-based compliance form meets the documentation requirements of Standards 90.1-2016 and 2019 Section 11 Energy Cost Budget Method and Appendix G Performance Rating Method. It helps the modeler establish simulation inputs for the baseline/budget and proposed design models and includes a submittal checklist to ensure that all necessary supporting documentation is included in the submittal. It standardizes compliance documentations and simplifies submittal reviews by code officials and administrators of above code program implementers.

For questions about use or customization of the form please contact the Building Energy Codes Help Desk

Performance Rating Method Reference Manuals (PRM RM). These documents are intended to be a reference manual for the Appendix G PRM of Standard 90.1-2016. The PRM can be used to demonstrate compliance with the standard and to rate the energy efficiency of commercial and high-rise residential buildings with designs that exceed the requirements of Standard 90.1. The procedures and processes described in this manual are designed to provide consistency and accuracy by filling in gaps and providing additional details needed by users of the PRM. PNNL has created PRM RMs for Standard 90.1 2010 and 2016.

Total System Performance Ratio (TSPR). TSPR is an approach for rating the efficiency of the entire HVAC system. Unlike a component based prescriptive approach, a system efficiency approach accounts for the interactions between the different components of a system. However, unlike whole-building performance it does not allow tradeoffs between different building systems (i.e., HVAC, lighting, envelope). TSPR evaluates the resources required for an HVAC system to fulfill the function for which it is intended – meeting building sensible and latent loads. TSPR in its most basic form, is calculated as the ratio of the sum of a building’s annual heating and cooling loads to the sum of the annual energy used for the whole HVAC system including heating, cooling, fans, pumps, heat rejection, and energy recovery.

TSPR equation

As demonstrated by simplified energy modeling, the TSPR of a proposed building design must be greater than the TSPR of a baseline building design to comply. The baseline system configuration used to represent energy use can be customized to meet any desired level of performance. Washington State’s new energy code uses cycling air source heat pumps with a DOAS with heat recovery as the baseline system (WSEC 2018). The denominator representing energy use can be customized to meet any policy goal. Site energy use, source energy, energy cost, and CO2 emissions are all valid metrics. Washington State uses carbon emissions in the denominator to promote the states policy goal of zero carbon emissions from buildings. A tool created by PNNL to implement Washington State's new TSPR requirement can be found here