ASHRAE 90.1 vs NECB

Two documents dominate energy efficiency requirements for larger commercial and institutional buildings in Canada: ASHRAE Standard 90.1, Energy Standard for Sites and Buildings Except Low-Rise Residential Buildings, and the National Energy Code of Canada for Buildings (NECB). Depending on the province and the project, a designer may be required to use one, allowed to choose between them, or asked to use one for code compliance and the other for a green building rating.

They aim at the same goal and cover similar ground, but their structure, climate definitions and modelling rules differ in ways that matter to HVAC design.

Who publishes them and how often

Because NECB editions come out less often and provinces adopt them later still, the editions in force in Canada may lag the newest versions of either document by several years.

Where each applies in Canada

• Provinces adopting the NECB: many provinces, including Alberta, use the NECB for buildings outside the scope of Part 9.
• British Columbia: the BC Building Code allows compliance with either the NECB or ASHRAE 90.1 edition it references, or through the performance-based Energy Step Code.
• Ontario: Supplementary Standard SB-10 sets compliance paths based on ASHRAE 90.1 or the NECB, with Ontario-specific modifications.
• Green building programs: LEED projects in Canada have historically been able to use ASHRAE 90.1 Appendix G or a Canadian alternative compliance path based on the NECB for energy performance credits, depending on the rating system version.

See provincial building codes and HVAC for more on how each province applies them.

Structure

Both documents follow similar subject divisions:

Both contain mandatory provisions that apply regardless of compliance path, plus prescriptive requirements that can be traded off or replaced with a performance approach.

Climate zones

The documents define climate differently.

• NECB assigns climate zones 4 through 8 based on heating degree-days below 18 C. Zone 4 covers the mildest areas, such as coastal BC, with fewer than 3,000 HDD; zone 8 covers the far north with 7,000 HDD or more. Requirements tighten as HDD increases.
• ASHRAE 90.1 uses climate zones 0 through 8 with moisture subtypes, based on heating and cooling degree-days and humidity. Canadian locations generally fall in zones 4 through 8.

The same city can land in a numerically similar zone in both systems, but the requirements attached to each zone are not identical.

Compliance paths

Both documents offer three broad routes.

Prescriptive path

Each component meets its own requirement: envelope U-values, lighting power density, equipment efficiencies, economizers, energy recovery, fan power limits, controls and so on. This is simplest for straightforward buildings.

Trade-off path

Limited trade-offs within a single system are allowed, most commonly between envelope components. For example, more glazing area can be offset by a better wall or roof. Both documents have envelope trade-off procedures.

Performance path

A computer energy model of the proposed building is compared with a reference or baseline building. This is where the two documents differ the most:

Appendix G's stable baseline lets one model show both code compliance and how far beyond code a design goes. The NECB's approach resets the reference with each edition. See building energy modelling for HVAC design.

HVAC provisions compared

Both documents address similar HVAC topics:

• Minimum efficiencies for chillers, boilers, rooftop units, heat pumps and other equipment.
• Economizer requirements, with thresholds and exceptions.
• Energy or heat recovery on ventilation exhaust above certain airflows and outdoor air fractions.
• Fan power limits, fan control and variable speed requirements.
• Pump control and piping insulation.
• Controls such as setback, shutoff, zone isolation and reset strategies.
• Limits on simultaneous heating and cooling and on reheat.

The thresholds and specific requirements differ between documents and between editions. Designers should not assume a design that complies with one will automatically comply with the other.

NECB 2020 tiers

The 2020 NECB introduced performance tiers, giving provinces a way to require progressively better energy performance over time on the path toward net zero energy ready buildings. Tier 1 corresponds to the baseline NECB, and higher tiers require measured percentage improvements over the reference. See NECB 2020 and HVAC compliance.

Choosing between them

When a choice exists, the decision often comes down to:

1. Project goals: if a LEED or similar certification is planned, using the same standard for code and certification can avoid duplicate modelling.
2. Building type: some designs fare better under one document's prescriptive rules or baseline assumptions.
3. Familiarity: the design team and the authority having jurisdiction may be more comfortable reviewing one approach.
4. Local requirements: some municipalities set their own targets that override the choice.

Early energy modelling can compare compliance under both where allowed.

Key takeaways

• ASHRAE 90.1 and the NECB cover similar ground but differ in structure, climate zones and modelling rules.
• The NECB defines climate zones by heating degree-days; 90.1 uses heating, cooling and moisture.
• Appendix G compares energy cost against a fixed baseline; NECB Part 8 compares energy use against a reference built from the same edition.
• Which document applies depends on the province, and some provinces allow either.
• Compliance with one does not guarantee compliance with the other.