1.3 Standard 90.1-2019 Performance Rating Method Compliance Calculations

1.3 Standard 90.1-2019 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 (PCIt). 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.

Np                                                                     =    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 PCIt. 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 System
   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

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

When,

( PBPnre – PBP ) / BBP > 0.05

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

PCI + [( PBPnre – PBP ) / BBP] - 0.05 < PCIt

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.