ASHRAE 90.1 Appendix G 2019 PRM
Performance Rating Method Scope
ASHRAE 90.1 Appendix G provides an alternative compliance path for meeting the minimum standards in Section 4.2.1.1. It can also be used by rating authorities to quantify performance that exceeds the standard's requirements, though not for minimum compliance purposes under Section 4.2.1.1.
Appendix G can be used to evaluate all proposed designs, including alterations and additions to existing buildings, except for designs without mechanical systems. When a building official uses this appendix solely to determine compliance with Section 4.2.1.1, substitute "building official" wherever "rating authority" appears in the text.
The proposed building design must comply with Sections 5.2.1, 6.2.1, 7.2.1, 8.2.1, 9.2.1, and 10.2.1. Interior lighting power must not exceed the allowance determined using either Table G3.7 with the Section 9.6.1 methodology or Table G3.8 with the Section 9.5.1 methodology.
All installed components and systems must meet or exceed the energy efficiency levels used to calculate the proposed building's performance. The verification, testing, and commissioning requirements in Section 4.2.5 must be met.
For any proposed building systems, controls, or envelope elements documented in Section G1.3 (c) that lack criteria in Sections 5 through 10, verification or testing must document proper installation and operation according to Section 4.2.5.
Performance Rating Calculation
Calculate the proposed design's performance using this formula:
Performance Cost Index = Proposed building performance / Baseline building performance
Both the proposed and baseline building performance must include all end-use load components within and associated with the building when calculating the Performance Cost Index.
Exception: Energy used to recharge or refuel vehicles for off-site transportation purposes should not be modeled in either the baseline or proposed building performance.
Simulation General Requirements
Performance Calculations
Calculate both the proposed building performance and baseline building performance using the same simulation program, weather data, and energy rates.
Simulation Program
Use a computer-based program for analyzing energy consumption in buildings, such as EnergyPlus. The simulation program must include calculation methodologies for all building components being modeled. For components that cannot be modeled by the simulation program, follow the exceptional calculation methods requirements in Section G2.5.
The rating authority must approve the simulation program, which must be able to explicitly model the following: 8760 hours per year with hourly variations in occupancy, lighting power, miscellaneous equipment power, thermostat set points, and HVAC system operation, defined separately for each day of the week and holidays. The program must model thermal mass effects and ten or more thermal zones.
It must also model part-load performance curves for mechanical equipment, capacity and efficiency correction curves for mechanical heating and cooling equipment, air economizers with integrated control, and the baseline building design characteristics specified in Section G3.
The simulation program must be able to either directly determine the proposed building performance and baseline building performance or produce hourly reports of energy use by energy source suitable for determining the performance using a separate calculation engine.
The simulation program must also be capable of performing design load calculations to determine required HVAC equipment capacities and air and water flow rates in accordance with generally accepted engineering standards and handbooks (such as ASHRAE Handbook—Fundamentals) for both the proposed and baseline building designs.
The simulation program must be tested according to ASHRAE Standard 140, excluding Sections 7 and 8. Post the test results and modeler reports on a publicly available website along with the results of other simulation programs included in ASHRAE Standard 140, Annexes B8 and B16. Complete the modeler report in Standard 140, Annex A2, Attachment A2.7 for any results exceeding the maximum or falling below the minimum of the reference values, or for missing results.
Climatic Data
The simulation program must use hourly values of climatic data, such as temperature and humidity, from representative climatic data for the site where the proposed design will be located. For cities or urban regions with multiple climatic data entries, or for locations where weather data are not available, the designer must select available weather data that best represent the climate at the construction site. The rating authority must approve the selected weather data.
Renewable, Recovered, and Purchased Energy
On-Site Renewable Energy and Site-Recovered Energy
Site-recovered energy is not considered purchased energy and must be subtracted from the proposed design energy consumption before calculating the proposed building performance. On-site renewable energy must also be subtracted from the proposed design energy consumption before calculating the proposed building performance, provided the building owner either owns the on-site renewable energy system, has signed a lease agreement for the system for at least 15 years, or has signed a contractual agreement to purchase energy generated by the system for at least 15 years.
Annual Energy Costs
Determine the design energy cost and baseline energy cost using either actual rates for purchased energy or state average energy prices published by USDOE's Energy Information Administration (EIA) for commercial building customers. Do not mix rates from different sources in the same project.
When on-site renewable energy or site-recovered energy is used, base the baseline building design on the backup energy source, or the baseline system energy source in that category if no backup has been specified. When the proposed design includes on-site electricity generation systems other than renewable energy systems, the baseline design must include the same generation systems excluding site-recovered energy.
Exceptional Calculation Methods
When the simulation program does not model a design, material, or device in the proposed design, use an exceptional calculation method as approved by the rating authority. Where multiple designs, materials, or devices cannot be modeled, calculate each separately and determine exceptional savings for each. The total exceptional savings must not exceed half of the difference between the baseline building performance and the proposed building performance.
All applications for approval of an exceptional method must include step-by-step documentation of the calculation method detailed enough to reproduce the results, copies of all spreadsheets used, and a sensitivity analysis of energy consumption when each input parameter is varied from half to double the assumed value. Perform the calculations on a time-step basis consistent with the simulation program used and provide the performance rating calculated both with and without the exceptional calculation method.
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