1.3 Performance Rating Method Compliance Calculations

The modeling procedures in the 2019 standard build upon the ‘fixed-baseline’ approach added for the 2016 edition of the standard.  The baseline building is fixed to be roughly equal in stringency to Standard 90.1-2004 and compliance is determined through a metric called Performance Cost Index (PCI). Section 4.2.1 of Standard 90.1-2019 specifies the process to calculate the target PCI to demonstrate compliance with the Standard. Building Performance Factors (BPF) are defined in this section that are used to calculate a target PCI (PCI_t). Building Performance Factors for a particular edition of Standard 90.1 are calculated as a ratio of the prototype building regulated energy cost for a given building prototype, climate zone and edition of Standard 90.1 to the proposed building regulated energy cost for the 2004 edition of Standard 90.1. BPF for all prototypes and climate zones are specified in Standard 90.1-2019.

where:

Prototype Building Regulated Energy Cost year x = The portion of annual energy cost due to regulated energy use from the PNNL prototype buildings for a given building prototype, climate zone and edition of Standard 90.1.

Prototype Building Regulated Energy Cost 2004 =    The portion of annual energy cost due to regulated energy use from the PNNL prototype buildings for a given building prototype, climate zone and the 2004 edition of Standard 90.1.

N_p                                                                       =      Number of prototype buildings of a particular building type

The target PCI for 90.1-2019 code compliance is a function of the building type, the climate zone and the proportion of regulated to unregulated energy projected to be used by the baseline building (Table 1). Unregulated energy use (defined in Section 2.2.4 of this document) is neutral for 90.1 code compliance. In order to demonstrate compliance with Standard 90.1-2019, the PCI of the proposed building is required to be less than or equal to the PCIt, when calculated using the equation below (Rosenberg & Hart 2016). PCI targets can also be associated with performance levels for beyond code programs. On-site renewable energy generated by systems included on the building permit that is used by the building shall be considered free and is not included in the proposed design energy cost. However, for the determining compliance with the standard only renewable energy up to a limit of 5% of the baseline energy cost can be credited towards complying with the PCI_t. The following rules apply for on-site renewable energy, site-recovered energy and on-site electricity generation systems. Applicability of the rules depends upon whether the building owns the on-site renewables, a lease agreement or a renewable purchase contract. This is discussed in further detail in Section 3.10 of this document.

1. On-Site Renewable Energy Systems
   1. Energy produced by an on-site renewable energy system that is part of a separate building permit may not be used. Credit can be taken for on-site renewable energy systems owned by the building owner.
   2. Energy produced by an on-site renewable energy system that is used by another building may not be included.
   3. Credit can be taken for on-site renewable energy systems where the building owner has signed a lease agreement for the on-site renewable energy system for at least 15 years.
   4. Credit can be taken for on-site renewable energy systems where the building owner has signed a contractual agreement to purchase energy generated by the on-site renewable energy system for at least 15 years.
2. On-Site Power Generation Systems
   1. Where the proposed design includes on-site electricity generation systems other than on-site renewable energy systems, the baseline design shall include the same generation systems excluding its site-recovered energy.
   2. Site-recovered energy shall not be considered purchased energy and shall be subtracted from the proposed design energy consumption prior to calculating the proposed building performance.

Both the proposed and baseline building are required to include all end use load components when calculating the PCI. Where a building has multiple area types, the required BPF shall be equal to the area-weighted average of the building area types.

PCI        = Performance Cost Index calculated in accordance with Equation (2).

BBUEC = Baseline Building Unregulated Energy Cost.

BBREC = Baseline Building Regulated Energy Cost

BPF       = Building Performance Factors

BBP       = Baseline Building Performance (BBUEC + BBREC)

PBP       = Proposed Building Performance accounting for the reduced annual purchased energy cost associated with all on-site renewable energy generation systems

PBP_nre    = Proposed Building Performance without any credit for reduced annual energy costs from on-site renewable energy generation systems.

When,

( PBP_nre – PBP ) / BBP > 0.05

new buildings, additions to existing buildings and/or alterations to existing buildings shall comply with the following:

PCI + [( PBP_nre – PBP ) / BBP] - 0.05 < PCI_t

Regulated energy cost is calculated by multiplying the total energy cost by the ratio of regulated energy use to total energy use for each fuel type. Unregulated energy costs are calculated by subtracting regulated energy cost from total energy cost. For a complete description of regulated and unregulated cost, refer to Section 2.2.4 of this document.

For building area types not listed in Table 4.2.1.1 use “All others.” Where a building has multiple building area types, the required BPF shall be equal to the area-weighted average of the building area types.

Table 1. Building Performance Factors (BPF)

Prior to 2016, the Appendix G baseline building stringency changed with each version of Standard 90.1 and sometimes with each addendum. This created much confusion for software developers, energy modelers and program administrators. For many use-cases, an excessive amount of time was spent creating the baseline building and verifying its correctness. With the new procedure, the intent is that the baseline building stringency does not change. Instead, as the standard becomes more stringent, a greater level of improvement over the stable baseline is required. The 2004 version of the standard has been used for defining the baseline performance. This version of the standard has been used as a benchmark by ASHRAE and the US DOE for evaluating the stringency of more recent versions of Standard 90.1 and now it is used as a stable baseline for all performance calculations. Each consecutive version of the Standard would update the target PCI without modifying the stringency of the baseline building requirements.

The modeling procedures in the 2022 standard build upon the ‘fixed-baseline’ approach added for the 2016 edition of the standard.  The baseline building is fixed to be roughly equal in stringency to Standard 90.1-2004 and compliance is determined through a metric called Performance Cost Index (PCI). Section 4.2.1 of Standard 90.1-2022 specifies the process to calculate the target PCI to demonstrate compliance with the Standard. Building Performance Factors (BPF) are defined in this section that are used to calculate a target PCI (PCI_t). Building Performance Factors for a particular edition of Standard 90.1 are calculated as a ratio of the prototype building regulated energy cost for a given building prototype, climate zone and edition of Standard 90.1 to the proposed building regulated energy cost for the 2004 edition of Standard 90.1. BPF for all prototypes and climate zones are specified in Standard 90.1-2022.

where:

Prototype Building Regulated Energy Cost year x = The portion of annual energy cost due to regulated energy use from the PNNL prototype buildings for a given building prototype, climate zone and edition of Standard 90.1.

Prototype Building Regulated Energy Cost 2004 =    The portion of annual energy cost due to regulated energy use from the PNNL prototype buildings for a given building prototype, climate zone and the 2004 edition of Standard 90.1.

N_p                                                                       =      Number of prototype buildings of a particular building type

The target PCI for 90.1-2022 code compliance is a function of the building type, the climate zone, prescriptive renewable energy requirements according to Section 10.5.1, and the proportion of regulated to unregulated energy projected to be used by the baseline building (Table 1). Unregulated energy use (defined in Section 2.2.4 of this document) is neutral for 90.1 code compliance. In order to demonstrate compliance with Standard 90.1-2022, the PCI of the proposed building is required to be less than or equal to the PCIt, when calculated using the equation below (Rosenberg & Hart 2016). PCI targets can also be associated with performance levels for beyond code programs. On-site renewable energy generated by systems included on the building permit that is used by the building shall be considered free and is not included in the proposed design energy cost. However, for the determining compliance with the standard only renewable energy up to a limit of 5% of the baseline energy cost can be credited towards complying with the PCI_t. The following rules apply for on-site renewable energy, site-recovered energy and on-site electricity generation systems. Applicability of the rules depends upon whether the building owns the on-site renewables, a lease agreement or a renewable purchase contract. This is discussed in further detail in Section 3.10 of this document.

1. On-Site Renewable Energy Systems
   1. Energy produced by an on-site renewable energy system that is part of a separate building permit may not be used. Credit can be taken for on-site renewable energy systems owned by the building owner.
   2. Energy produced by an on-site renewable energy system that is used by another building may not be included.
   3. Credit can be taken for on-site renewable energy systems where the building owner has signed a lease agreement for the on-site renewable energy system for at least 15 years.
   4. Credit can be taken for on-site renewable energy systems where the building owner has signed a contractual agreement to purchase energy generated by the on-site renewable energy system for at least 15 years.
2. On-Site Power Generation Systems
   1. Where the proposed design includes on-site electricity generation systems other than on-site renewable energy systems, the baseline design shall include the same generation systems excluding its site-recovered energy.
   2. Site-recovered energy shall not be considered purchased energy and shall be subtracted from the proposed design energy consumption prior to calculating the proposed building performance.

Both the proposed and baseline building are required to include all end use load components when calculating the PCI. Where a building has multiple area types, the required BPF shall be equal to the area-weighted average of the building area types.

PCI        = Performance Cost Index calculated in accordance with Equation (2).

BBUEC = Baseline Building Unregulated Energy Cost.

BBREC = Baseline Building Regulated Energy Cost

BPF       = Building Performance Factors

PRE       = PBP_nre - PBP_pre

BBP       = Baseline Building Performance (BBUEC + BBREC)

PBP       = Proposed Building Performance accounting for the reduced annual purchased energy cost associated with all on-site renewable energy generation systems

PBP_nre    = Proposed Building Performance without any credit for reduced annual energy costs from on-site renewable energy generation systems.

PBP_pre    = Proposed building performance, excluding any renewable energy system in the proposed design and including an on-site renewable energy system that meets but does not exceed the requirements of Section 10.5.1.1 modeled following the requirements for a budget building design in Table 12.5.1, row 15. See Section 3.10.1.4 for detail.

When,

(PBP_pre – PBP ) / BBP > 0.05

new buildings, additions to existing buildings and/or alterations to existing buildings shall comply with the following:

PCI + [(PBP_pre – PBP ) / BBP] - 0.05 < PCI_t

Regulated energy cost is calculated by multiplying the total energy cost by the ratio of regulated energy use to total energy use for each fuel type. Unregulated energy costs are calculated by subtracting regulated energy cost from total energy cost. For a complete description of regulated and unregulated cost, refer to Section 2.2.4 of this document.

For building area types not listed in Table 4.2.1.1 use “All others.” Where a building has multiple building area types, the required BPF shall be equal to the area-weighted average of the building area types.

Table 1. Building Performance Factors (BPF)

Prior to 2016, the Appendix G baseline building stringency changed with each version of Standard 90.1 and sometimes with each addendum. This created much confusion for software developers, energy modelers and program administrators. For many use-cases, an excessive amount of time was spent creating the baseline building and verifying its correctness. With the new procedure, the intent is that the baseline building stringency does not change. Instead, as the standard becomes more stringent, a greater level of improvement over the stable baseline is required. The 2004 version of the standard has been used for defining the baseline performance. This version of the standard has been used as a benchmark by ASHRAE and the US DOE for evaluating the stringency of more recent versions of Standard 90.1 and now it is used as a stable baseline for all performance calculations. Each consecutive version of the Standard would update the target PCI without modifying the stringency of the baseline building requirements.

Improvements in 90.1 2022

Modifications to Prototype Models used to Develop BPFs

The 2022 edition of Standard 90.1 PRM used an improved methodology for determining the BPFs. As discussed, BPFs represent the minimum improvement in regulated energy use of the proposed design relative to the baseline design that projects must demonstrate to comply with the energy code. The BPFs included in the 2016 and 2019 editions of 90.1 were based on the 90.1 2004 commercial building prototype models, which followed several but not all the modeling rules prescribed for the Appendix G baseline building. For example, heating, ventilation, and air conditioning (HVAC) system types modeled for some occupancies deviated from the baseline PRM system types. Starting with 90.1 2022, a new set of commercial building prototypes that more closely follow the Appendix G baseline modeling rules were created and used to establish BPFs. This group of models will be used to establish BPFs for subsequent editions of 90.1.

Guidance for using Compliance Metrics other than Energy Cost

The 90.1 PRM currently uses energy cost as the compliance metric. Using energy cost as the compliance metric in jurisdictions with a high electricity cost relative to natural gas puts projects that use electricity for space and service water heating at a disadvantage compared to projects that use fossil fuels for these end uses. Informative Appendix I in 90.1 2022 provides sample language for using the PRM in conjunction with site energy, source energy, and greenhouse gas emission metrics to support local policies and goals, such as promoting electrification and decarbonization. Appendix I also includes a table with BPF values to be used with each alternative metric.

Inclusion of Limits on Envelope Tradeoffs

Another improvement in 90.1 2022 compared to earlier editions of 90.1 is the inclusion of rules that limit trade-offs between envelope and building systems for new buildings following the PRM. The backstop requires that the specified envelope does not increase whole building energy cost of the proposed design by more than 15% for multifamily, hotel/motel, and dormitory occupancies, and by more than 7% for all other occupancies compared to a design with the envelope minimally compliant with the prescriptive envelope requirements in 90.1 Section 5. The backstop margins are based on designs with opaque surfaces and fenestration minimally complying with prescriptive requirements but with fenestration area up to 70% of above grade wall.

Addition of New Rules for Alterations

Lastly, 90.1 2022 PRM includes updated modeling rules for alterations. The prescriptive path of compliance with 90.1 includes special rules for project alterations. In contrast, Appendix G modeling rules were the same for new construction and alteration projects, with no differences in the methodology used to establish compliance based on the simulation results for the baseline and proposed design model. As a result, alterations were held to the same standard as new construction projects and were penalized for having existing systems that are less efficient than the current requirements for new construction projects. 90.1 2022 addresses this issue. For substantial alteration projects, the modeling rules are the same as for new construction, but the BPF increased by 5%, resulting in a corresponding reduction in stringency. New construction and substantial alterations projects follow the modeling rules in Standard 90.1-2022 Section G3.2. For limited alterations (i.e., minor alterations), the modeling rules are similar to the Energy Cost Budget method, requiring that the energy use of the proposed design does not exceed the energy use of the baseline design where all retrofitted systems are modeled as minimally complying with the applicable prescriptive and mandatory requirements of the Standard. Projects follow the modeling rules in Standard 90.1-2022 Section G3.3. Alterations modeled following Section G3.3 use BPF = 1.