Understanding ASHRAE 90.1 Energy Standard for Buildings: The Guide for HVAC Engineers & Contractors

Technical Quick-Reference

Is ASHRAE 90.1-2022 mandatory? It is mandatory only if adopted by your local jurisdiction; check the local adoption date as some states lag behind the latest version.
What is the new TSPR path? The Total System Performance Ratio (TSPR) is a new Mechanical System Performance Path that evaluates entire HVAC system efficiency rather than just individual components.
Does 90.1-2022 require renewable energy? Yes. Unlike previous versions, the 2022 edition introduces a minimum prescriptive requirement for on-site renewable energy.
What are Section 11 Energy Credits? A new mandatory requirement in the 2022 version where buildings must achieve a specific number of energy credits (often 50 or more) by choosing from various efficiency measures.

Introduction

ASHRAE 90.1, titled “Energy Standard for Buildings Except Low-Rise Residential Buildings,” sets the minimum energy efficiency requirements for commercial, institutional, and high-rise residential buildings. It’s the primary standard referenced in building codes across the U.S., including IECC and state codes, and is crucial for LEED and energy compliance.

1. Scope and Site-Wide Applicability

The standard applies to new construction, renovations, and major retrofits.

Expanded Scope (2022 Update): The scope has expanded from the “building” to the entire building site. This includes energy used for exterior parking lot lighting and on-site renewable energy production.
Broad Coverage: Covers heating, cooling, ventilation, lighting, building envelope, service water heating, and energy monitoring.
Applicability: Applies to commercial, institutional, and high-rise residential buildings (not single-family homes, which are under 90.2 or residential codes).

Exemptions:

Industrial processes not related to comfort.
Equipment not serving conditioned space.
Temporary structures under certain conditions.

Major Changes: ASHRAE 90.1-2019 vs. 2022

The transition from the 2019 to the 2022 edition introduced over 80 addenda aimed at achieving nearly 9% more energy cost savings.

Feature	90.1-2019	90.1-2022
Primary Scope	Limited to the building only.	Expanded to the entire Building Site (e.g., parking lot lighting).
Renewable Energy	Encouraged but not mandated.	Mandatory prescriptive requirement for on-site renewables.
Efficiency Measures	Standard prescriptive path requirements.	New Mandatory Energy Credits (Section 11) point system.
Mechanical Path	Component-based individual ratings.	New TSPR (Total System Performance Ratio) system-wide path.
Building Envelope	Focus on U-factors and R-values.	New strict requirements for Thermal Bridging and air leakage.
Testing/Commissioning	Basic commissioning verification.	Enhanced mandatory testing, documentation, and reporting.

2. Key Compliance Paths

ASHRAE 90.1 allows multiple compliance approaches:

2.1 Prescriptive Path

Provides specific requirements for:

Building envelope (walls, roofs, windows)
HVAC systems (efficiency, controls, fan power)
Lighting (power density, controls)

Easy for standard designs and common building types, but must meet all listed minimum requirements.

2.2 Performance Path (Energy Cost Budget Method)

Model the proposed building vs. a baseline building using energy simulation.
Allows flexibility in materials or systems as long as total energy use ≤ baseline.
Often used for complex designs, unique building types, or LEED projects.

2.3 Advanced Energy Design Guides (AEDG)

Published by ASHRAE in collaboration with other organizations.
Provides easy-to-follow, cost-effective strategies for 30%, 50%, or 90% energy savings over baseline.

3. Building Envelope Requirements

The building envelope is the first line of energy conservation.

3.1 Walls, Roofs, and Floors

Must meet minimum R-values based on climate zone.
Insulation must be continuous or cavity-fill.
Air barriers and vapor barriers are required for high-performance walls.

3.2 Windows and Glazing

Maximum U-factor and solar heat gain coefficient (SHGC) per climate zone.
Mandatory air leakage limits for windows and doors.
Consider daylighting strategies for energy efficiency.

3.3 Doors and Openings

Exterior doors must be insulated or weather-stripped.
Vestibules required for large entrances.

4. HVAC Requirements

ASHRAE 90.1 provides detailed requirements for HVAC systems:

4.1 Equipment Efficiency

Minimum COP, EER, SEER, AFUE, or IEER ratings depending on system type.
Encourages high-efficiency chillers, boilers, heat pumps, and packaged units.

4.2 System Design

Proper sizing (avoid oversizing).
Controls: thermostats, zoning, and economizers are required.
Automatic shutoff for fans and pumps during unoccupied hours.

4.3 Ventilation

Must comply with ASHRAE 62.1 minimum OA.
Must use energy recovery for large systems in some climate zones.

4.4 Fan Power Limits

Maximum fan power per CFM to limit electrical consumption.
Encourages high-efficiency motors (ECM, premium efficiency).

5. Lighting Requirements

Lighting is a major energy consumer; ASHRAE 90.1 sets:

5.1 Power Density Limits

Maximum watts per square foot by building type and space function.
Encourages LEDs and high-efficiency fluorescent.

5.2 Controls

Occupancy sensors for intermittently used spaces.
Daylight-responsive dimming in naturally lit areas.
Automatic shutoff or scheduling.

5.3 Exterior Lighting

Limits wattage for parking, landscape, and security lighting.
Encourages cutoff fixtures to reduce light pollution.

6. Service Water Heating (SWH)

Minimum efficiency for water heaters and boilers.
Controls for circulation pumps and temperature setpoints.
Encourages heat recovery from process or HVAC systems.

7. Energy Metering and Commissioning

Meters for electricity, gas, chilled water, and hot water are required in large buildings.
Commissioning ensures HVAC systems operate efficiently, lighting controls work, and outdoor air/economizers function correctly.

8. Renewable Energy Integration

ASHRAE 90.1 encourages on-site renewables; however, note that the 2022 update introduces prescriptive mandates for certain projects.
The performance path can credit solar PV, solar thermal, or geothermal systems.

9. Compliance Documentation

Contractors and engineers must provide:

Design submittals showing prescriptive or modeled compliance.
Equipment schedules and efficiency ratings.
Airflow, lighting, and envelope calculations.
Commissioning reports verifying installed systems meet requirements.

10. Common Mistakes and Pitfalls

Oversizing HVAC systems beyond loads.
Ignoring climate zone-specific envelope requirements.
Using low-efficiency lighting or failing to install controls.
Neglecting air leakage and sealing in the envelope.
Failing to coordinate HVAC and envelope for energy performance.
Not performing commissioning or measurement verification.

11. Updates and Climate Zones

ASHRAE 90.1 is updated roughly every 3 years. While the 2019 version is widely adopted, the 2022 version is the latest edition.
The standard includes 17 U.S. climate zones with specific envelope and system requirements.
Engineers must check the local adoption date, as jurisdictions often lag behind the latest published version.

12. Practical Tips for Engineers and Contractors

Use software modeling (e.g., EnergyPlus, TRACE, HAP) for performance path compliance.
Design for modular compliance: envelope, HVAC, lighting, and controls as integrated systems.
Document everything for permitting and LEED credits.
Coordinate early with architectural, structural, and mechanical teams for envelope, penetrations, and daylighting.

13. Key Takeaways

ASHRAE 90.1 is mandatory for code compliance in most commercial projects.
The prescriptive path is simpler, while the performance path allows flexibility and optimization.
Envelope, HVAC efficiency, lighting power/controls, and commissioning are critical components.
Early coordination and modeling save time, money, and compliance headaches.