Building Energy Waste Detector: engineer's guide
Most operating buildings waste 15 to 30% of their energy on preventable issues: over-cooled unoccupied zones, incandescent legacy lighting, uncorrected power factor, and idle standby loads.
Open the Building Energy Waste Detector →
What this calculator does
The calculator scores an existing building on eight common waste categories and returns a prioritised action list with typical payback periods.
Formulas used
- Waste ratio:
W = (Eactual - Ebenchmark) / Ebenchmark - Payback:
t = Capex / Annual saving
Variables
- Eactual = measured annual kWh/m²
- Ebenchmark = ASHRAE 100 or CIBSE TM46 target
Worked example
Scenario: 5000 m² office at 250 kWh/m²/yr; benchmark 180 kWh/m²/yr.
- Waste ratio = (250 - 180) / 180 ≈ 39%
- Categories: HVAC scheduling (10%), lighting retrofit (5%), PF correction (8%), plug-load management (4%)
- Combined typical payback under 4 years
Common mistakes to avoid
- Comparing without weather normalisation
- Missing occupancy pattern effect
- Chasing lighting first when HVAC dominates (60 to 70% of energy)
- Ignoring low-cost operational fixes before capex investment
Frequently asked questions
Where to start?
BMS scheduling and setpoints — typically 5 to 10% savings at zero capex.
Sub-metering?
Essential to isolate the actual waste category. Rule of thumb: sub-meter anything > 5% of building load.
Standards and references
ASHRAE 100, CIBSE TM46, LEED O&M
Related tools on this site
Open the calculator that pairs with this guide: Building Energy Waste Detector.
Verification note
This guide is planning support only. Final design must be verified against the applicable project specification, authority requirements, manufacturer data, and the standards cited above. Consult a licensed engineer for construction-issue calculations.