Energy Efficiency and Demand Management
This domain tests whether you can quantify savings honestly and design demand-side programmes that deliver them. The recurring theme is the difference between instantaneous power reduction and annual energy, and the discipline of baseline adjustment.
Core rules and concepts
- Energy versus power. Kilowatt reductions are demand savings; kilowatt-hours are energy savings. A load shifted from afternoon to night saves demand at the peak but may save no energy at all, or even lose energy through storage round-trip efficiency.
- Normalisation before comparison. Buildings must be weather-normalised using heating and cooling degree-days, and industrial sites normalised for production volume, before year-on-year or peer benchmarking. Energy use intensity metrics such as kWh/m², kWh/t or kWh/unit are only meaningful within a normalised peer group.
- Measurement and verification. IPMVP options A (retrofit isolation, key parameter measurement), B (retrofit isolation, all parameter measurement), C (whole facility) and D (calibrated simulation) differ in cost and rigour. Baselines must be adjusted for changes in weather, occupancy, production and building use.
- Demand response types. Peak clipping, valley filling, load shifting, strategic conservation and flexible load. Programmes are procured as capacity, energy, or ancillary services, and priced through time-of-use rates, critical peak pricing or direct control.
- Economic tests. Simple payback ignores asset life; life-cycle cost and the total resource cost test do not. Programme evaluation must also correct for free-ridership, spillover, rebound effect and persistence of savings.
- Motor affinity laws. For variable-speed drives, flow scales with speed, pressure with speed squared, and shaft power with speed cubed.
Worked example
A 100 kW fan runs 6,000 hours a year at full speed. Fitting a variable-speed drive allows it to run at 80% speed for half those hours. Power at 80% speed = 0.8³ = 0.512, so 51.2 kW, a saving of 48.8 kW. Energy saved = 48.8 kW × 3,000 h = 146,400 kWh, about 146 MWh per year. A damper would cut flow by the same amount but reduce power only slightly, so the affinity law, not the flow reduction, is the source of the saving.
Traps that cost marks
- Reporting a peak kW reduction as an annual kWh saving, or vice versa.
- Claiming savings without adjusting the baseline for weather or production.
- Ignoring interactive effects: lighting savings also cut cooling load and raise heating load.
- Inflating programme savings by ignoring free-ridership, or overstating persistence beyond the measure life.