ASHRAE 90.1 Appendix G 2022 - Understanding the Performance Cost Index (PCI)
1. Introduction
The Performance Rating Method (PRM), described in Normative Appendix G of ASHRAE Standard 90.1, provides a whole-building approach to evaluating energy efficiency. Instead of checking every wall assembly and chiller against a prescriptive checklist, the PRM uses computer simulation to compare the annual energy cost of your proposed building design against a standardised baseline building. One number in, one number out. Conceptually simple, even if the modelling effort to get there is anything but.
The primary metric produced by this method is the Performance Cost Index (PCI): a dimensionless ratio that expresses the proposed building's annual energy cost as a fraction of the baseline building's annual energy cost. Lower is better. Think of it as a fuel economy sticker for a building.
In 90.1-2022, a new building has three compliance paths (Section 4.2.1.1): the prescriptive path of Sections 5 through 11 (note that Section 11, "Additional Efficiency Requirements," is new in this edition), the Energy Cost Budget Method of Section 12, or Normative Appendix G. The PRM can be used for compliance with the standard, for documenting beyond-code performance (LEED certification, utility incentive programmes, impressing your client), or both. It applies to new buildings, additions, and alterations, provided the building has a mechanical system and an envelope design. If your building has neither, you've got bigger problems than Appendix G.
2. Key Concepts
2.1 Baseline Building vs. Proposed Building
Two energy models are created using the same simulation program, climate data, purchased energy rates, and schedules of operation. The proposed building is modelled as actually designed and built. The baseline building is a hypothetical variant of your design, developed following the prescriptive rules of Table G3.1. It substitutes standardised, less efficient options for envelope, HVAC, lighting, and other regulated systems while retaining your building geometry, schedules, and process loads.
The comparison is deliberately apples-to-apples. Same weather file, same rate structure, same occupancy schedules. The only variable is your design decisions.
Important change carried forward from 90.1-2016: the baseline building is intentionally less stringent than the prescriptive requirements of the standard. It does not itself comply with the standard. This catches people off guard. Compliance requires achieving a specified improvement over the baseline, as defined by the Performance Cost Index Target. The baseline is the starting line, not the finish line.
2.2 Regulated vs. Unregulated Energy
The baseline building's annual energy cost splits into two components:
Baseline Building Regulated Energy Cost (BBREC): Energy used by systems the code actually governs (Sections 5 through 10): HVAC, lighting, service water heating, motors, transformers, vertical transportation, refrigeration, computer-room cooling, and other regulated systems.
Baseline Building Unregulated Energy Cost (BBUEC): Everything else. Process loads, plug loads, kitchen equipment, server racks. The code doesn't set efficiency requirements for these, so it would be unreasonable to penalise you for them.
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 cost is calculated by subtracting regulated energy cost from total energy cost. The total baseline building performance is:
BBP = BBUEC + BBREC3. Calculating the Performance Cost Index
The PCI itself is straightforward:
Where:
PBP = Proposed Building Performance, the annual energy cost of the proposed design including the reduced annual purchased energy cost from all on-site renewable energy generation systems.
BBP = Baseline Building Performance.
A PCI of 0.72 means your building costs about 72% of what the baseline costs to operate. A PCI above 1.0 means you've somehow made the building worse than the baseline, which is a conversation nobody wants to have with the building official.
4. The Performance Cost Index Target and Building Performance Factor
4.1 Compliance Criterion
You don't just need a PCI below 1.0. You need to beat a specific target, the PCIt:
The target is calculated as:
Where PRE = prescriptive renewable energy = PBPnre - PBPpre (defined in Section 6).
Note on the 2022 formula: the target now subtracts the prescriptive renewable energy term (PRE) in the numerator. This reflects the fact that on-site renewable energy is, for many buildings, prescriptively required in 2022 (Section 10.5.1.1), so the standard expects it rather than rewarding it. Where a building has no prescriptive renewable requirement, PRE = 0 and the formula reduces to the familiar
(BBUEC + BBREC x BPF) / BBP.
This formula applies the improvement requirement only to the regulated portion of the energy cost. Unregulated energy cost passes through at its full value. The reasoning is sound: if 80% of your building's energy goes to process loads you can't touch, the standard shouldn't demand you cut your total energy bill in half.
4.2 The Building Performance Factor (BPF)
The BPF is the mechanism that makes this work. It's a value pulled from Table 4.2.1.1 of the standard, and it depends on two things: building area type and climate zone. In 90.1-2022 the tabulated values span 0.19 to 0.76.
The BPF represents the fraction to which the regulated energy cost must be reduced. A BPF of 0.50 means the standard requires your regulated energy cost to hit 50% of the baseline value, a 50% improvement in regulated energy performance. A BPF of 0.70 is more forgiving: you only need a 30% cut.
For mixed-use buildings, the BPF is calculated as the area-weighted average of the BPFs for each building area type, based on gross floor area. For types not listed in the table, use "All others." Where a project includes an existing building and an addition, the required BPF is the area-weighted average of the existing-building BPF (Section 4.2.1.3) and the addition BPF from Table 4.2.1.1.
The complete BPF values from Table 4.2.1.1 of ASHRAE Standard 90.1-2022 follow. Note the structural change from the 2019 edition: climate zones that were previously paired (for example 0A/1A) are now listed as individual columns.
Table 1: Building Performance Factor (BPF), ASHRAE 90.1-2022 Table 4.2.1.1
Multifamily
0.69
0.68
0.71
0.70
0.72
0.72
0.71
0.76
0.63
0.69
0.76
0.71
0.66
0.72
0.71
0.65
0.67
0.65
0.67
Healthcare/hospital
0.69
0.69
0.70
0.68
0.67
0.65
0.65
0.66
0.64
0.64
0.66
0.63
0.67
0.65
0.65
0.66
0.67
0.68
0.70
Hotel/motel
0.66
0.66
0.69
0.65
0.65
0.64
0.64
0.65
0.65
0.63
0.65
0.63
0.62
0.63
0.62
0.61
0.62
0.59
0.58
Office
0.54
0.54
0.53
0.52
0.52
0.52
0.50
0.54
0.48
0.48
0.53
0.48
0.49
0.52
0.48
0.48
0.49
0.46
0.48
Restaurant
0.62
0.59
0.57
0.57
0.57
0.53
0.57
0.53
0.51
0.55
0.54
0.54
0.57
0.56
0.55
0.59
0.58
0.61
0.64
Retail
0.51
0.49
0.48
0.48
0.44
0.43
0.43
0.43
0.44
0.42
0.43
0.46
0.43
0.42
0.47
0.43
0.43
0.41
0.44
School
0.52
0.57
0.57
0.56
0.52
0.53
0.52
0.49
0.50
0.46
0.47
0.47
0.47
0.46
0.46
0.46
0.44
0.45
0.45
Warehouse
0.26
0.26
0.22
0.25
0.21
0.22
0.25
0.21
0.19
0.25
0.22
0.22
0.28
0.24
0.22
0.31
0.28
0.29
0.32
All others
0.62
0.60
0.62
0.59
0.55
0.51
0.53
0.52
0.55
0.53
0.52
0.55
0.53
0.53
0.56
0.54
0.54
0.54
0.54
Interpreting the BPF Table
Warehouses now carry the lowest BPFs in the table by a wide margin (0.19 to 0.32), a dramatic tightening from the 2019 edition, where warehouse values ran from roughly 0.38 to 0.57. The standard now demands that warehouse regulated energy be cut to somewhere between a fifth and a third of the baseline. The logic: warehouse regulated energy is dominated by lighting and relatively light HVAC, where LED retrofits, occupancy and daylighting controls, and envelope measures deliver very deep savings very cheaply. The values still generally increase toward colder climate zones, from a low of 0.19 in the mild 3C zone up to 0.32 in Zone 8, since deep savings in extreme cold cost more and deliver less, though the trend is not perfectly monotonic.
Multifamily buildings sit at the top of the table (0.63 to 0.76). Individual dwelling units with distributed systems simply don't offer the same optimisation opportunities as a centralised commercial building, so the standard gives them more room.
Healthcare/hospital facilities are comparatively relaxed in 2022 (0.63 to 0.70), noticeably higher than the 2019 range. Continuous operation, high ventilation requirements, and process-intensive medical systems limit what's achievable.
Schools, which held the lowest BPFs in the 2019 table, now land in the middle of the pack (0.44 to 0.57). Offices (0.46 to 0.54) and retail (0.41 to 0.51) are among the tighter building types, reflecting the depth of cost-effective savings available in those stock.
5. Practical Application of the BPF
Consider a data centre where 80% of energy goes to servers (unregulated) and only 20% goes to HVAC and lighting (regulated). A data centre falls under the "All others" area type, whose 2022 BPFs run from about 0.51 to 0.62. If the applicable BPF requires a 47% reduction in regulated energy, that reduction applies only to the 20% regulated share. That's roughly a 9 to 10% reduction in total energy cost. Without the BPF mechanism separating regulated from unregulated, the data centre would face an impossible whole-building target. The split is what makes this system workable across fundamentally different building types.
6. Renewable Energy Systems and Compliance
The most significant change in 90.1-2022 is how the standard treats on-site renewable energy. On-site renewables (typically PV panels, but potentially other types) are now, for many buildings, a prescriptive requirement under Section 10.5.1.1 rather than a purely optional compliance tool. The Appendix G framework accommodates this by distinguishing three levels of proposed building performance:
PBPnre = proposed building performance with no credit for on-site renewable energy at all.
PBPpre = proposed building performance with prescriptive renewable energy only, that is, an on-site system that meets but does not exceed the requirements of Section 10.5.1.1, modelled per Table 12.5.1, row 15.
PBP = proposed building performance including all on-site renewable energy generation actually in the design.
The prescriptive renewable energy contribution is:
Prescriptive renewables lower the PCIt target (via the - PRE term in Section 4.1) because the standard expects them. Renewables in the actual design lower PBP, which lowers PCI. The compliance credit for renewables installed beyond the prescriptive minimum, however, is still capped.
6.1 The Renewable Credit and the 5% Cap
The compliance credit from renewables beyond the prescriptive requirement is capped at 5% of the Baseline Building Performance. The quantity that matters for the cap is the renewable generation beyond the prescriptive minimum, expressed as a fraction of baseline cost:
Note the shift from the 2019 edition: the capped quantity is now measured from PBPpre (with prescriptive renewables already in place), not from PBPnre. Only renewable generation in excess of the prescriptive requirement counts against the cap.
The intent is clear. You can't slap an oversized solar array on a poorly insulated building with undersized equipment and call it compliant. The building itself has to be reasonably efficient. Solar can get you over the finish line, but it can't run the whole race.
6.2 Compliance Rules
When (PBPpre - PBP) / BBP <= 0.05: the standard PCI <= PCIt check applies as normal. The PCI naturally decreases as renewables offset cost.
When (PBPpre - PBP) / BBP > 0.05, an Adjusted PCI applies:
The Adjusted PCI produces the same value regardless of how much additional renewable capacity you install beyond the 5% threshold. You could triple the size of your PV array and the compliance math wouldn't budge. Additional panels still save money on energy bills, of course, but they won't buy you any more compliance credit.
7. Worked Example
An office building in Climate Zone 3A produces the following simulation results. For clarity this example assumes no prescriptive renewable energy requirement applies, so PRE = 0 and PBPpre = PBPnre.
From Table 4.2.1.1, the BPF for an office in Climate Zone 3A is 0.50 (down from 0.53 in the 2019 edition).
Since PCI 0.74 > PCIt 0.70, the building does not comply without renewables. Not ideal, but not uncommon. Here's what happens as PV is added:
Table 2: Impact of Renewable Energy System Size on Compliance
Renewable Production
$500
$750
$1,000
$1,250
$2,000
Capped Renewable Fraction
0.02
0.03
0.04
0.05
0.08
Proposed Building Perf. (PBP)
$18,000
$17,750
$17,500
$17,250
$16,500
Performance Cost Index (PCI)
0.72
0.71
0.70
0.69
0.66
Adjusted PCI
N/A
N/A
N/A
N/A
0.69
Complies? (PCIt = 0.70)
No
No
Yes
Yes
Yes
The building first complies at roughly $1,000 of renewable production. Once the excess renewable fraction passes 0.05 (beyond the $1,250 system), the Adjusted PCI locks at 0.69, which is PCInre - 0.05 = 0.74 - 0.05. Both the $1,250 and $2,000 systems achieve compliance, but there's no point oversizing purely for compliance reasons.
Worth noting how much tighter the 2022 target is: the drop in BPF from 0.53 to 0.50 pushes the target from 0.718 down to 0.70. Had the proposed building performance been the $19,000 used in the older edition of this example (PCI 0.76), the Adjusted PCI would have floored at 0.71, above the 0.70 target, and renewables alone could not have delivered compliance. Under 2022's tighter targets, the envelope and systems have to do more of the work before PV can finish the job.
8. Calculating Percentage Improvement
For beyond-code applications (LEED, utility incentive programmes, green building certifications), the percentage improvement is:
If the building includes renewable energy and the rating authority applies the 5% cap, use the higher of PCI or the Adjusted PCI in the formula. Different rating authorities may treat renewables differently, so check the specific programme requirements before assuming.
9. Simulation Requirements
To keep the comparison honest, all simulation runs for the proposed and baseline buildings must use the same:
Simulation program, climate data, purchased energy rates, and schedules of operation (except adjustments needed to account for energy-efficiency features).
These rules prevent extraneous differences from contaminating the results. If you used different simulation engines, part of the cost difference would just be algorithmic disagreement. If you used different rate structures, you'd be optimising for a tariff that might not exist in five years. The standard wants a clean comparison of building design, nothing else.
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