Energy Efficiency in Buildings
Energy Efficiency in Buildings
This domain covers envelope, HVAC, lighting, service hot water and building controls, with ECBC and EPI as core references. The exam tests load calculations, U-values, SHGC, window-to-wall ratio, LPD, chiller efficiency and commissioning.
Core rules
- ECBC applies to commercial buildings above the notified connected load and conditioned area thresholds; check the current state adoption and version.
- EPI = annual site energy use ÷ conditioned or carpet area, in kWh/m²/year. Compare like-for-like building type and climate.
- Envelope heat gain depends on U-value, area and temperature difference; solar gain depends on SHGC, orientation and shading.
- Chiller efficiency may be expressed as COP, kW/TR or IPLV. 1 TR = 3.517 kW cooling; COP = cooling kW ÷ input kW.
- Daylighting and occupancy controls save lighting energy, but also reduce internal heat gain and cooling load.
Worked example
A 10,000 m² carpet-area office uses 1,200,000 kWh/year. EPI = 1,200,000 ÷ 10,000 = 120 kWh/m²/year. If the applicable ECBC benchmark is 100, the building is 20% above benchmark. A retrofit cuts lighting from 12 W/m² to 8 W/m² over 8,000 m² for 2,500 hours: saving = 4 × 8,000 × 2,500 = 80,000 kWh/year. At INR 8/kWh that is INR 640,000/year; if the retrofit costs INR 1.6 million, payback is 2.5 years. The reasoning separates site energy from the benchmark and states operating hours.
Traps
Using gross floor area when the benchmark uses carpet area; comparing EPI across climates; ignoring plug loads; and claiming chiller COP without stating full-load or part-load conditions.