6.6 ASHRAE 90.1-2016 Fundamentals
Key Takeaways
- ANSI/ASHRAE/IES Standard 90.1-2016 is the energy-efficiency reference standard for LEED v4/v4.1 BD+C; it sets minimum requirements for envelope, HVAC, service water heating, power, lighting, and other loads
- Appendix G defines the Performance Rating Method (PRM) used to compare a proposed design against a fully prescriptive baseline for the Optimize Energy Performance credit
- Envelope requirements are organized by ASHRAE climate zone (1–8, A-moist/B-dry/C-marine) and set maximum U-factors and SHGCs for opaque and fenestration assemblies
- Lighting Power Density (LPD) tables limit installed lighting power either by Building Area Method (whole-building W/ft²) or by Space-by-Space Method (per-room W/ft²)
- HVAC equipment minimum efficiencies are expressed in EER, IEER, COP, and AFUE for cooling and heating equipment, with values that vary by size, configuration, and condenser type
Why Candidates Need to Know ASHRAE 90.1-2016
Every EA prerequisite and credit either directly references ANSI/ASHRAE/IES Standard 90.1-2016 or uses it as the baseline against which performance is measured. The exam does not require you to recite specific table values, but you must recognize the standard's structure, climate-zone framework, and key terms.
Quick Answer: ASHRAE 90.1-2016 sets minimum energy requirements for buildings except low-rise residential. Its prescriptive sections cover envelope, HVAC, service water heating, power, and lighting. Appendix G provides the Performance Rating Method used by LEED's whole-building simulation path.
Performance Rating Method vs. Prescriptive
| Compliance Path | What It Does | LEED Use |
|---|---|---|
| Prescriptive | Comply line-by-line with envelope, lighting, HVAC, and SWH tables | Minimum Energy Performance Option 2 / prescriptive credit path |
| Energy Cost Budget (ECB) — Section 11 | Cost-based simulation, but baseline mirrors proposed system type | Historical method; not used as primary path in LEED v4 |
| Performance Rating Method (PRM) — Appendix G | Cost-based simulation; baseline system type assigned by Table G3.1.1-1 | Required for LEED v4/v4.1 Optimize Energy Performance simulation path |
Appendix G is the more aggressive method because the baseline can differ from the proposed design (e.g., baseline electric resistance heat in a small building), exposing proposed-design choices to a more meaningful comparison.
Climate Zones (Section 4 / Figure 5.1.2)
ASHRAE divides the U.S. (and the world via ASHRAE Standard 169) into eight climate zones numbered 1 (hottest) through 8 (coldest), each subdivided by humidity:
- A — Moist
- B — Dry
- C — Marine
| Zone | Examples | Heating Degree Days |
|---|---|---|
| 1A | Miami, Honolulu | Very low |
| 2A | Houston, Orlando | Low |
| 3B | Los Angeles, Phoenix | Mild, dry |
| 4A | Baltimore, Kansas City | Moderate |
| 5A | Chicago, Boston | Cold |
| 6A | Minneapolis, Burlington | Very cold |
| 7 | Duluth, Fairbanks (subarctic) | Subarctic |
| 8 | Barrow, Yellowknife | Arctic |
Envelope, fenestration, and many HVAC requirements scale with zone number.
Building Envelope (Section 5)
Section 5 sets maximums for U-factor (heat transfer) and SHGC (Solar Heat Gain Coefficient) for opaque and fenestration assemblies. Selected illustrative values for nonresidential walls:
| Climate Zone | Mass Wall U-Factor (Btu/hr·ft²·°F) | Vertical Fenestration U | Fenestration SHGC |
|---|---|---|---|
| 1A | U-0.580 | U-0.50 | 0.25 |
| 4A | U-0.090 | U-0.38 | 0.36 |
| 6A | U-0.080 | U-0.36 | 0.40 |
| 8 | U-0.052 | U-0.29 | NR |
U-factor caps decrease (envelope improves) as climate gets colder; SHGC caps rise with colder zones because solar gain is increasingly desirable.
Lighting Power Density (Section 9)
Lighting Power Density (LPD) is the installed interior lighting power per unit floor area (W/ft²). The standard offers two compliance methods:
- Building Area Method (Table 9.5.1) — single whole-building LPD by occupancy type (office, retail, warehouse, etc.).
- Space-by-Space Method (Table 9.6.1) — individual LPD per space type (open office 0.79 W/ft², conference 1.23 W/ft², corridor 0.66 W/ft², etc.).
The Space-by-Space Method usually allows a slightly higher total but requires room-by-room documentation. Either way, automatic lighting controls (occupancy sensors, daylight responsive controls, time-clock scheduling) are mandatory.
HVAC Equipment Efficiency (Section 6)
Minimum efficiencies in ASHRAE 90.1-2016 are reported in the metric that matches the equipment:
| Equipment | Metric | Notes |
|---|---|---|
| Air-cooled DX cooling ≤ 65,000 Btu/h | SEER | Seasonal (residential-style) |
| Air-cooled DX cooling > 65,000 Btu/h | EER, IEER | Full-load and part-load |
| Water-cooled chillers | kW/ton, IPLV | Lower is better |
| Heat pumps (cooling) | EER | Plus heating COP |
| Heat pumps (heating) | COP | Coefficient of Performance |
| Furnaces and boilers | AFUE, Et, Ec | Annual Fuel Utilization Efficiency |
Minimum values rise with equipment capacity and condenser type; e.g., a 100-ton water-cooled centrifugal chiller has a different minimum from a 50-ton air-cooled scroll chiller.
Service Water Heating (Section 7) and Receptacle/Process Loads (Section 10)
Section 7 sets minimum efficiencies for water heaters (Energy Factor, Thermal Efficiency) and requires insulation on storage tanks and recirculation piping. Section 10 (Other Equipment) sets minimum motor, transformer, and elevator efficiencies and limits receptacle (plug) loads that must be modeled identically in baseline and proposed Appendix G runs unless a documented reduction has been negotiated.
Which ASHRAE 90.1-2016 appendix or section is the basis for the whole-building energy simulation method used by EA Credit: Optimize Energy Performance?
An engineer is designing lighting for a new office. Which ASHRAE 90.1-2016 method allows individual W/ft² limits for each room type rather than a single value for the whole building?