Variable Load, Timed Schedule (VLTS)

VLTS includes equipment with varying load and constant hours-of-use, as depicted below. While the total number of operation hours is constant, the equipment may spend a fixed number of hours at different loads; this is the basis of the multiple percentage load bins in the load frequency distribution (chart on right-hand side). The load curve (chart on left hand side) may be obtained from engineering models, manufacturer’s performance curves or data, or empirical relationships (regressions) developed from monitored data. The energy use rate (kW) is a function of the load and the load itself may be a function of other parameters.

Examples of equipment with CLVS operating characteristics include:

1. Elevators

2. Lighting under occupancy-sensor control

3. Constant-speed cooling tower fan operation (schedule varies with temperature)

4. Hot water or chilled water pumping, no VFD (schedule varies with boiler/chiller


5. Auto factory paint-shop exhaust fans

Source: BPA’s Verification by Equipment or End-Use Metering Protocol