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Energy Codeconcept

Energy code basics: lighting power density, ASHRAE 90.1, and Energy Star

One-line orientation

The energy code governs how efficiently a building uses energy — envelope, lighting power, and HVAC — with ASHRAE 90.1 as the common commercial benchmark; the exam mostly tests what each named standard is rather than specific numbers.

Key points

  • Purpose: energy codes limit energy use in new construction through requirements for the envelope, lighting, mechanical systems, and related building systems.
  • Lighting power density (watts per square foot) — caps the maximum lighting wattage per square foot, steering design toward efficient sources (LED, fluorescent) over incandescent.
    • Example framing: a ~380 sq ft space might be limited to roughly 380 watts of lighting.
  • ASHRAE 90.1 — sets benchmarks for heating, cooling, and overall energy use in commercial buildings; standards tighten over time, and compliance can earn LEED credit.
  • ENERGY STAR: includes building-performance programs and efficiency labels for products and equipment. It is not the adopted building code.
  • Building-type applicability — common for offices and retail; specialized uses (stadiums, theaters) may be excepted; single-family applicability varies by municipality.
  • Where to look — energy codes typically have sections for lighting/LPD, HVAC efficiency, the envelope, and building-type-specific requirements.

IECC, ASHRAE 90.1, Energy Star, and LPD are different kinds of things

Edition-neutral

Three institutions, three roles; lighting power density is a metric inside compliance.

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Three-card role comparison of IECC, ASHRAE 90.1, and Energy Star with a separate lighting-power-density metric Three equal cards compare commonly confused energy names. IECC is labeled Code and paired with a building glyph. ASHRAE 90.1 is labeled Standard and paired with a benchmark gauge. Energy Star is labeled Certification and paired with an equipment glyph. A separate full-width lower band states that lighting power density is lighting watts per square foot, one metric inside energy-code compliance rather than the whole code. IECCCODEModel energy codeadopted by a jurisdictionASHRAE 90.1STANDARDCommercial benchmarkcompliance path + LEED referenceEnergy StarCERTIFICATIONEfficient products + equipmentnot the building energy codeft²LPD = lighting watts per square footone metric inside energy-code compliance—not the whole energy code

Do not memorize one universal LPD number—allowances vary by building or space type and by code edition.

Confusions / comparison

What it isApplies toRole
IECCModel energy codeBuildings (as adopted)Often the adopted law
ASHRAE 90.1Energy-efficiency standard/benchmarkCommercial buildingsBenchmark + LEED reference
ENERGY STAREfficiency program and labelBuildings, products, and equipmentRecognizes energy performance; not the adopted code
LPD (W/sf)A metric in the codeLighting designCaps lighting wattage per area

→ HVAC efficiency (Systems): the equipment side the energy code regulates · Lighting (Systems): fixture/source efficiency behind LPD limits · Sustainability / LEED (this/ProPractice): where ASHRAE 90.1 compliance earns credit.

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