# ASHRAE 90.1 Energy Standard ## Table of Contents - [[#Overview]] - [[#Scope and Applicability]] - [[#Climate Zones]] - [[#Compliance Paths]] - [[#Prescriptive Path]] - [[#Performance Path Appendix G]] - [[#Building Envelope Requirements]] - [[#Opaque Envelope U-Factors]] - [[#Fenestration Requirements]] - [[#Lighting Power Density LPD]] - [[#HVAC Efficiency Requirements]] - [[#Service Water Heating]] - [[#Power and Other Equipment]] - [[#Appendix G Performance Rating Method]] - [[#Relationship with LEED]] - [[#Version History]] - [[#Practical Notes for Architects]] - [[#References and Standards]] --- ## Overview ASHRAE Standard 90.1, *Energy Standard for Buildings Except Low-Rise Residential Buildings*, is the primary energy code standard in the United States and is referenced or adopted globally. Published by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE), it establishes minimum energy efficiency requirements for the design and construction of new buildings and major renovations. ASHRAE 90.1 is a foundational reference for the [[International Building Code IBC]] (through the International Energy Conservation Code), [[LEED Certification System]] energy performance credits, and numerous international energy codes. --- ## Scope and Applicability - Applies to all buildings except low-rise residential (3 storeys or fewer above grade). - Covers: building envelope, HVAC systems, service water heating, power distribution, lighting, and other equipment. - Excludes: single-family houses, multi-family buildings ≤3 storeys (governed by IECC Residential). - Applies to new construction, additions, and alterations to existing buildings. --- ## Climate Zones ASHRAE 90.1 defines 8 climate zones (0 through 8) based on heating degree days (HDD) and cooling degree days (CDD), with moisture sub-classifications (A = moist, B = dry, C = marine): | Zone | Description | Representative Cities | |------|--------------------------|----------------------------------------------| | 0A | Extremely hot humid | Singapore, Kuala Lumpur | | 1A | Very hot humid | Miami, Mumbai | | 2A | Hot humid | Houston, Cairo | | 2B | Hot dry | Phoenix, Riyadh | | 3A | Warm humid | Atlanta, Sydney | | 3B | Warm dry | Los Angeles, Lisbon | | 3C | Warm marine | San Francisco, Cape Town | | 4A | Mixed humid | New York, Beijing | | 4B | Mixed dry | Albuquerque | | 4C | Mixed marine | Seattle, London | | 5A | Cool humid | Chicago, Berlin | | 5B | Cool dry | Denver, Salt Lake City | | 6A | Cold humid | Minneapolis, Helsinki | | 6B | Cold dry | Helena, Astana | | 7 | Very cold | Duluth, Moscow | | 8 | Subarctic/Arctic | Fairbanks, Yakutsk | Climate zone determines prescriptive envelope requirements, HVAC sizing conditions, and baseline parameters for the performance path. --- ## Compliance Paths ### Prescriptive Path The prescriptive path requires each building component to meet or exceed the prescriptive requirements for the applicable climate zone: - Envelope insulation and fenestration values per Section 5 tables. - Lighting power density per Section 9 tables. - HVAC equipment efficiency per Section 6 tables. - Service water heating efficiency per Section 7. - No trade-offs between building systems allowed. The prescriptive path is straightforward but does not allow optimisation or credit for innovative strategies. ### Performance Path Appendix G The Performance Rating Method (Appendix G) provides flexibility by comparing the proposed design against a code-minimum baseline building through energy simulation. See [[Energy Modeling for Buildings]] for modelling methodology. --- ## Building Envelope Requirements ### Opaque Envelope U-Factors Maximum U-factors (W/(m²K)) for opaque envelope components by climate zone (selected zones, non-residential): | Component | Zone 2A | Zone 4A | Zone 5A | Zone 7 | |-----------------------|----------|----------|----------|----------| | Roof, insulation above deck | 0.184 | 0.184 | 0.153 | 0.119 | | Metal building roof | 0.167 | 0.065 | 0.065 | 0.055 | | Mass wall (above grade)| 0.580 | 0.433 | 0.365 | 0.278 | | Steel-framed wall | 0.352 | 0.247 | 0.210 | 0.184 | | Wood-framed wall | 0.292 | 0.210 | 0.170 | 0.142 | | Mass floor | 0.322 | 0.137 | 0.107 | 0.087 | | Below-grade wall | 0.678 | 0.340 | 0.340 | 0.245 | | Slab-on-grade (unheated)| NR | NR | 0.84 F | 0.52 F | NR = No requirement. F-factor values are in W/(mK) for slab perimeter. Values are from ASHRAE 90.1-2019; check the applicable edition. ### Fenestration Requirements Maximum fenestration values by climate zone (non-residential, 0–40% WWR): | Parameter | Zone 2A | Zone 4A | Zone 5A | Zone 7 | |---------------------|----------|----------|----------|----------| | U-factor (W/(m²K)) | 3.69 | 2.27 | 2.27 | 1.82 | | SHGC | 0.25 | 0.36 | 0.38 | 0.49 | - **U-factor**: Thermal transmittance of the entire fenestration assembly (frame + glazing). - **SHGC**: Solar Heat Gain Coefficient, the fraction of incident solar radiation admitted through the window. - **Window-to-wall ratio (WWR)**: Prescriptive path limits vertical fenestration to 40% of gross above-grade wall area. Skylight area limited to 5% of roof area. - North-facing fenestration may have higher SHGC allowances in heating-dominated climates. --- ## Lighting Power Density LPD ASHRAE 90.1 limits installed lighting power by two methods: ### Building Area Method | Building Type | LPD (W/m²) | LPD (W/ft²) | |---------------------------|-------------|--------------| | Office | 8.8 | 0.82 | | Retail (general) | 12.4 | 1.15 | | School/University | 9.8 | 0.91 | | Hospital | 10.8 | 1.00 | | Hotel/Motel | 9.4 | 0.87 | | Warehouse | 6.6 | 0.61 | | Multifamily residential | 5.8 | 0.54 | | Religious building | 10.0 | 0.93 | ### Space-by-Space Method Allows more precise calculation using LPD values for individual space types: | Space Type | LPD (W/m²) | LPD (W/ft²) | |---------------------------|-------------|--------------| | Open office | 7.5 | 0.70 | | Private/enclosed office | 9.7 | 0.90 | | Conference/meeting room | 11.8 | 1.10 | | Corridor | 5.0 | 0.47 | | Lobby (office) | 8.6 | 0.80 | | Restroom | 8.6 | 0.80 | | Stairway | 5.7 | 0.53 | | Mechanical/electrical room| 7.5 | 0.70 | | Active storage | 5.7 | 0.53 | Values are from ASHRAE 90.1-2019. The space-by-space method generally yields higher total allowances than the building area method. **Mandatory lighting controls**: - Automatic shut-off (occupancy sensors or scheduled) in all spaces. - Daylight-responsive controls in daylit zones (primary: within 4.5 m of fenestration; secondary: 4.5–9 m). - Exterior lighting controls (photosensor + time clock). --- ## HVAC Efficiency Requirements ASHRAE 90.1 specifies minimum equipment efficiencies for all HVAC equipment categories: ### Selected Minimum Efficiencies | Equipment Type | Capacity Range | Minimum Efficiency | |-----------------------------------|-----------------------|----------------------| | Air-cooled unitary AC | < 19 kW | SEER 14.0 | | Air-cooled unitary AC | ≥ 19 kW, < 40 kW | EER 11.2 | | Air-source heat pump (heating) | < 19 kW | HSPF 8.2 | | Water-cooled chiller (centrifugal) | All capacities | COP 6.1 (full load) | | Air-cooled chiller | All capacities | COP 2.8 (full load) | | Gas-fired furnace | < 66 kW | AFUE 80% | | Gas-fired boiler (hot water) | ≥ 88 kW | Et 82% | ### Mandatory HVAC Provisions - Economiser required for systems above specified capacity thresholds (varies by climate zone). - Simultaneous heating and cooling limitations (reheat restrictions). - Variable speed drives on fans and pumps above specified power thresholds. - Duct and pipe insulation requirements. - Energy recovery ventilation (ERV) required when outdoor air exceeds specified flow rates and operating hours. - Demand-controlled ventilation (DCV) for spaces with design occupancy > 25 persons per 93 m². --- ## Service Water Heating - Minimum equipment efficiency for water heaters (gas, electric, heat pump). - Pipe insulation requirements for hot water distribution. - Solar water heating system sizing for certain building types (prescriptive option). - Heat recovery from HVAC condenser water for service hot water pre-heating. --- ## Power and Other Equipment Section 8 (Power) addresses: - Voltage drop limits for feeders and branch circuits. - Automatic receptacle control (50% of receptacles in offices must be controllable). - Transformer efficiency requirements. - Motor efficiency requirements (referencing NEMA Premium efficiency standards). --- ## Appendix G Performance Rating Method The Performance Rating Method (PRM) compares a proposed building design against a baseline building to calculate percentage improvement: ### Baseline Building Rules | Element | Baseline Rule | |---------------------------|-------------------------------------------------------| | Envelope | Prescriptive values from Section 5 for the climate zone| | WWR | 40% (if proposed exceeds 40%) | | Lighting | LPD from Section 9 (building area method) | | HVAC system | System type per Table G3.1.1 (based on building type, size, and heating source) | | Service water heating | Same fuel as proposed, code-minimum efficiency | | Orientation | Four rotations (0°, 90°, 180°, 270°), averaged | ### Baseline HVAC Systems | System No. | Description | Application | |------------|------------------------------------------------|----------------------------------| | 1 | PTAC (packaged terminal AC) | Residential ≤ 3 storeys | | 2 | PTHP (packaged terminal heat pump) | Residential ≤ 3 storeys (electric)| | 3 | PSZ-AC (packaged single-zone AC) | Non-residential < 2,300 m² | | 5 | Packaged VAV with reheat | Non-residential 2,300–14,000 m² | | 7 | VAV with reheat (chilled water) | Non-residential > 14,000 m² | | 8 | VAV with PFP boxes | Non-residential > 14,000 m² (electric) | | 11 | SZ-VAV | Non-residential < 2,300 m² (2019+) | | 12 | SZ-CV-HW (single-zone, constant volume) | Heated-only systems | ### Performance Calculation ``` % Improvement = (Baseline Cost - Proposed Cost) / Baseline Cost × 100 ``` Costs are calculated using virtual energy rates (not actual utility rates) specified in the standard or by the rating authority. --- ## Relationship with LEED ASHRAE 90.1 serves as the baseline standard for [[LEED Certification System]] energy performance credits: | LEED v4.1 BD+C | Minimum Improvement | Maximum Points | |------------------------|---------------------|----------------| | Prerequisite | 5% (new), 3% (major renovation) | — | | Optimize Energy Performance | 6% improvement | 1 point | | | ... | ... | | | 50% improvement | 18 points | - LEED references a specific edition of ASHRAE 90.1 (currently 90.1-2016 for LEED v4.1). - The Appendix G methodology is mandatory for LEED energy modelling. - Additional LEED points are available for advanced energy metering, demand response, and on-site renewable energy. --- ## Version History | Edition | Key Changes | |---------|----------------------------------------------------------------| | 2004 | First edition widely adopted by LEED | | 2007 | Tighter envelope, expanded lighting controls | | 2010 | Major update: mandatory economisers, DCV, ERV, 30%+ improvement over 2004 | | 2013 | Enhanced envelope, variable speed drives, exterior lighting | | 2016 | Further tightening, referenced by LEED v4/v4.1 | | 2019 | Latest published: tighter LPD, additional HVAC restrictions, new baseline systems | | 2022 | In development: anticipated further envelope and HVAC improvements | Each edition is approximately 30% more stringent than the edition published 10 years prior. --- ## Practical Notes for Architects - Confirm which edition of ASHRAE 90.1 is adopted by the jurisdiction and which is referenced by the targeted LEED version; they may differ. - Prescriptive envelope values should be treated as a starting point, not a target. High-performance buildings typically require U-values 30–50% better than prescriptive minimums. - Window-to-wall ratio is a critical design lever: each percentage point above 40% WWR triggers mandatory performance path compliance with increasing difficulty. - Specify lighting power density targets early and coordinate with the electrical engineer. Space-by-space method allows more flexibility than building area method. - Mandatory lighting controls (occupancy sensors, daylight dimming) must be coordinated in the electrical layout from Stage 3 onward. - For LEED projects, commission the energy model at schematic design stage. The Appendix G analysis requires detailed HVAC system specification, so early M&E coordination is essential. - Climate zone determines most prescriptive requirements. For international projects, map the project location to the appropriate ASHRAE climate zone using the CDD/HDD data. - Consider cost-of-energy when evaluating design alternatives: ASHRAE 90.1 uses virtual rates for compliance, but actual project economics may differ significantly. --- ## References and Standards - ASHRAE, *Standard 90.1-2019: Energy Standard for Buildings Except Low-Rise Residential Buildings* - ASHRAE, *90.1 User's Manual* - ASHRAE, *Standard 62.1: Ventilation for Acceptable Indoor Air Quality* - ICC, *International Energy Conservation Code (IECC)* - [[Energy Modeling for Buildings]] - [[LEED Certification System]] - [[Net Zero Energy Buildings]] - [[Passive House Standard]] --- #codes #energy #ASHRAE #envelope #LPD #HVAC #climateZones