Energy Codes
ASHRAE 90.1 and IECC govern the energy efficiency of buildings. Lighting power density, HVAC efficiency, controls, metering — all are mandatory minimums. Many jurisdictions add stretch codes (Title 24 in CA, NYStretch in NY).
Energy Codes — The Two That Matter
| Standard | Scope | Adoption |
|---|---|---|
| ASHRAE 90.1 | Energy Standard for Buildings Except Low-Rise Residential. The commercial/industrial energy code. | Adopted by most US states (sometimes via IECC reference). Updated every 3 years (2019, 2022, 2025). |
| IECC (International Energy Conservation Code) | Includes residential + commercial chapters. References ASHRAE 90.1 for commercial as alternate. | Adopted by many states. |
| California Title 24 | California-specific energy code. Stricter than ASHRAE 90.1. | California only. Often the most aggressive code. |
| ASHRAE 90.4 | Specific energy standard for data centers (since 2016) | Adopted with caveats by some jurisdictions for data center energy compliance. |
ASHRAE 90.1 Coverage Areas
| Topic | Key requirements |
|---|---|
| Lighting Power Density (LPD) | Maximum W/sq ft by space type. Office: ~ 0.7 W/sf. Warehouse: ~ 0.3 W/sf. Patient room: ~ 0.5 W/sf. |
| Lighting controls | Mandatory: occupancy sensors, daylight harvesting (perimeter zones), automatic shutoff, multilevel switching. |
| Receptacle controls | 50% of receptacles in offices must auto-shutoff (NEC 406.4(D) + 90.1 coordinate) |
| HVAC efficiency | Minimum efficiency for chillers, boilers, fans, pumps, heat pumps |
| Building envelope | Minimum insulation, fenestration U-factor + SHGC |
| Service water heating | Minimum efficiency for water heaters, pipe insulation |
| Energy metering + monitoring | Submeters required for buildings > 50,000 sf or 25,000 sf in some adoptions |
| Renewable energy provisions | Some adoptions require PV-ready or PV install |
| Transformer efficiency | NEMA TP-1 / DOE 2016 minimum efficiency for distribution transformers |
| Motor efficiency | NEMA Premium efficiency required for new motors |
Lighting Power Density (LPD) by Space Type
| Space type | ASHRAE 90.1-2022 LPD (W/sf) |
|---|---|
| Office (open) | 0.59 |
| Office (private) | 0.81 |
| Conference room | 0.87 |
| Classroom | 0.71 |
| Lobby | 0.87 |
| Restroom | 0.61 |
| Storage | 0.42 |
| Warehouse (medium-bulky) | 0.31 |
| Mechanical room | 0.43 |
| Patient room (hospital) | 0.55 |
| Operating room (hospital) | 2.20 |
| Server room (data center) | 0.39 |
| Retail | 0.84-1.62 (sales area type-specific) |
| Parking garage (open) | 0.13 (interior); 0.04 (exterior) |
Mandatory Lighting Controls
| Control type | Where required (ASHRAE 90.1) |
|---|---|
| Occupancy sensors | Most spaces. Auto-off when unoccupied (15-30 min delay typical). |
| Manual on / partial on | Many private spaces — must turn on manually or to ≤ 50% automatically. |
| Daylight responsive controls (DRC) | Within 15 ft of windows — daylight zones must reduce lighting based on natural light. |
| Automatic shutoff | All buildings — automatic time-based shutoff (after hours). |
| Multilevel control | Most spaces — minimum 3 levels (off, ~ 50%, full). |
| Egress lighting controls | Always-on emergency lighting per life-safety code (independent of energy code). |
| Exterior lighting controls | Photocell + curfew controls. Multi-level for parking lot. |
Energy Metering Requirements
| What's metered | When required |
|---|---|
| Whole building | Always — utility meter |
| Lighting subsystem | Buildings > 25,000 sf (some adoptions) |
| HVAC subsystem | Buildings > 25,000 sf |
| Receptacle subsystem | Buildings > 25,000 sf |
| Process loads (kitchen, lab, manufacturing) | Buildings with significant process loads |
| Tenant submetering | Often required for multi-tenant — allows tenant accountability |
| Renewable energy | Always — track production separately |
ASHRAE 90.4 — Data Center Energy
Data centers consume so much energy that they got their own ASHRAE standard. ASHRAE 90.4 addresses the energy efficiency of the data center components themselves, not just the building shell.
| ASHRAE 90.4 metric | Description |
|---|---|
| MLC (Mechanical Load Component) | Cooling system efficiency relative to IT load. Lower is better. |
| ELC (Electrical Loss Component) | Electrical distribution losses (UPS, transformers, conductors) relative to IT load. |
| PUE (Power Usage Effectiveness) | Total facility power / IT power. Industry metric (not officially in 90.4). |
| Climate-zone-specific limits | MLC + ELC limits vary by climate zone (warmer climates = higher MLC allowed). |
Worked Example 1 — Atlas DC1 Energy Compliance
Example 01 · Atlas DC1 spine2.5 MW data center — ASHRAE 90.1 + 90.4 compliance
Building energy compliance
- Lighting (ASHRAE 90.1): Server rooms 0.39 W/sf, mech 0.43 W/sf, office 0.59 W/sf. All compliant with LED lighting.
- Lighting controls: Occupancy sensors in all unoccupied DC areas (server rooms, mech rooms, electrical rooms). Daylight controls in office perimeter. Manual override only in occupied spaces.
- Receptacle controls: 50% of office receptacles auto-off. (Not applied in IT halls — every server is critical.)
- Transformer efficiency: All transformers spec'd to NEMA TP-1 / DOE 2016 efficiency.
- Motor efficiency: All motors NEMA Premium.
- Submetering: Each PDU + each chiller + each major mech equipment.
Data center energy (ASHRAE 90.4)
| Metric | Atlas DC1 | Target |
|---|---|---|
| PUE | 1.4 (typical for 2N-redundant) | < 1.5 for modern, < 1.3 for hyperscale |
| MLC | 0.20 (chiller plant efficient) | Per ASHRAE 90.4 climate zone |
| ELC | 0.16 (UPS double-conversion + 2N) | Per ASHRAE 90.4 |
Trade-off: 2N redundancy increases PUE (more conversion losses) but reduces downtime risk. ASHRAE 90.4 acknowledges this trade-off.
Worked Example 2 — Office Building LPD Compliance
Example 02 · Alternate context50,000 sq ft office — verify lighting power compliant with ASHRAE 90.1
- Building total LPD allowance (whole-building method):Office buildings: 0.61 W/sf × 50,000 sf = 30.5 kW total lighting power
- Designed lighting: 30,000 sf open office × 0.59 = 17.7 kW. 5,000 sf private office × 0.81 = 4.05 kW. 5,000 sf circulation × 0.66 = 3.3 kW. Etc.
- Total designed: ~ 28 kW. Within 30.5 kW allowance. ✓
- If over limit: Reduce LPD. Switch from fluorescent to LED (40-60% reduction). Or use space-by-space method which can be more flexible.
Drill — Quick Self-Check
Work each problem mentally; reveal to check. Goal: reflex, not deliberation.
Drill 1 · ASHRAE 90.1
Commercial energy code standard?
ASHRAE 90.1
ASHRAE 90.4 specifically for DCs.
Drill 2 · Office LPD
Open office LPD per ASHRAE 90.1-2022?
0.59 W/sf
Whole-building method or space-by-space.
Drill 3 · Receptacle controls
% of office receptacles must auto-off?
50%
Per ASHRAE 90.1.
Drill 4 · PUE
Power Usage Effectiveness for modern DC?
< 1.5; hyperscale < 1.3
Atlas DC1 = 1.4 (typical 2N).
Drill 5 · Daylight harvesting
Required within how many ft of windows?
15 ft
ASHRAE 90.1 mandatory control.
Illumination Calculations — Lumen Method + Point Method
Lighting design has two layers: meeting the energy code limit (LPD W/sf, ASHRAE 90.1) AND meeting the illuminance requirement (footcandles, IES). Both must be satisfied simultaneously.
Footcandle Requirements by Space (IES Lighting Handbook)
| Space type | Recommended (fc) | Notes |
|---|---|---|
| Office (general) | 30-50 fc on work plane | Higher for reading-intensive tasks |
| Office (computer-only) | 20-30 fc | Reduce glare on screens |
| Conference room | 30-50 fc | Dimmable for video presentations |
| Corridor / lobby | 10-20 fc | Lower than work areas |
| Restroom | 10-20 fc | — |
| Storage / warehouse | 10-30 fc | Higher in active picking aisles |
| Operating room (hospital) | 1,000-2,000 fc on patient | Special task lighting |
| Server room (data center) | 20-30 fc | Per ASHRAE TC 9.9 — minimal lighting; off when unoccupied |
| Retail (sales floor) | 50-100 fc | Higher for merchandise display |
| Parking garage (interior) | 5-10 fc minimum | Per IES RP-20 |
| Parking lot (open) | 2-5 fc minimum | Per IES RP-20 |
| Stair / egress | 10 fc minimum (NFPA 101) | Continuously lit |
Lumen Method — General Lighting Design
Used to determine the number of fixtures needed for general illumination of a uniformly-lit area.
Number of fixtures required
N = (E × A) / (L × CU × LLF)
N = number of fixtures · E = required illuminance (fc) · A = area (sq ft) · L = lumens per fixture · CU = coefficient of utilization (geometry-dependent, ~ 0.5-0.8) · LLF = light loss factor (~ 0.7-0.85, accounts for dirt + lamp depreciation)
Worked Example — Office Lighting Design
Example · 5,000 sq ft open officeLumen method — fixture count + LPD compliance
Inputs
Area
5,000 sq ft
Required illuminance
40 fc on work plane (general office)
Fixture
2×4 LED troffer, 4,500 lm output, 30 W
CU
0.65 (10×10 grid spacing, 80% reflectance walls)
LLF
0.80 (clean office, modern LED)
Calc
- Fixture count:N = (40 × 5,000) / (4,500 × 0.65 × 0.80) = 200,000 / 2,340 = 85 fixtures
- Connected lighting load:85 × 30 W = 2,550 W = 0.51 W/sf
- ASHRAE 90.1-2022 LPD limit (open office):0.59 W/sf maximum.
0.51 ≤ 0.59 → COMPLIANT ✓
i
Why LED won the energy code race
10 years ago this same office would have needed ~ 45-watt T8 fluorescent fixtures, totaling ~ 3,825 W = 0.77 W/sf — exceeding the 0.59 W/sf limit. LED converted the lighting industry overnight by enabling code compliance without sacrificing footcandles.
Point Method — for Specific Locations
Used when you need to verify illuminance at a specific point (operating table, security camera location, parking garage corner). Computed using inverse-square law for direct light + lumen method for reflected.
Illuminance from a single source (point method, direct only)
E = (I × cos θ) / d²
E = illuminance (fc) at point · I = candela toward the point · θ = angle from normal · d = distance (ft). Sum across all fixtures contributing to the point.
If You See THIS, Think THAT
| If you see… | Think / use… |
|---|---|
| "ASHRAE 90.1" | Commercial/industrial energy code. Universally relevant. |
| "IECC" | Building energy code. Often references ASHRAE 90.1. |
| "Title 24" (CA) | California-specific. Strictest. Distinct from NEC. |
| "ASHRAE 90.4" | Data center-specific energy standard. |
| "LPD" (Lighting Power Density) | Watts per sq ft limit by space type. Mandatory cap. |
| "PUE" (Power Usage Effectiveness) | Data center metric. Total / IT power. 1.0 = perfect, 2.0 = inefficient. |
| "Daylight harvesting" | Reduce artificial lighting based on available daylight. Required within 15 ft of windows. |
| "Occupancy sensor" | Auto-off when unoccupied. Required in most spaces by ASHRAE 90.1. |
| "NEMA Premium efficiency" | Highest efficiency tier for motors. Required by DOE for new motors. |
| "NEMA TP-1" / "DOE 2016" | Distribution transformer efficiency standards. Required. |
| "Submetering" | Per-tenant or per-subsystem electrical metering. Required for buildings > 25,000 sf often. |
| "Performance path" vs "Prescriptive path" | Two ways to comply with ASHRAE 90.1: meet specific limits (prescriptive) or demonstrate equivalent overall energy use (performance, more flexible). |