Metering approaches vary depending on facility design and intended purpose (e.g., administrative offices, laboratory, warehouse, etc.). No one approach fits all applications. In fact, different approaches are often needed at different times.
For example, a different approach is needed depending on whether the program is trying to verify utility rates, implement demand response or load management programs, or support Leadership in Energy and Environmental Design (LEED®) certification efforts.
Four predominant approaches exist:
One-time measurements are useful in many baseline activities to understand instantaneous energy use, equipment performance, or loading. These measurements become particularly useful in trending equipment performance over time.
For example, one-time measurements are useful when an energy-efficiency project results in a finite system performance change. A measurement of electric motor or lighting system efficiency is taken before and after a retrofit to quantify system savings – assuming similar usage (hours of operation) before and after.
Equipment useful in making one-time measurements include clamp-on amp probes, contact and non-contact temperature devices, non-intrusive flow measurement devices, and a variety of combustion-efficiency devices.
Most one-time measurements are obtained and recorded in the field.
Run-time measurements are made when hours-of-operation are the critical variable, such as when an energy efficiency project has impacted the use of a device. Run-time measurements do not capture energy use. Because of this, they are often taken in conjunction with one-time measurements.
Appropriate applications for run-time measurements include the run times of fans and pumps, or the operational characteristics of heating, cooling, or lighting systems.
Equipment useful in making run-time measurements includes standalone (battery-operated) data loggers providing run-time records. Most of these devices do not impact metering process or systems and are either optically triggered or take advantage of the electromagnetic characteristics of electrical devices.
Run-time measurements are usually obtained in the field by the device, recorded to memory, and then downloaded at a later date.
Short-term monitoring combines one-time and run-time measurements into a time-series record of energy or resource use. It is typically used to verify performance, initiate trending, or validate energy efficiency improvement. Monitoring length is usually less than one year.
In the case of energy efficiency improvement validation, these measurements may be made for two-weeks before and after installation of an efficiency improvement project. The data is then extrapolated over the year to report the annual impact.
Equipment useful in short-term monitoring includes portable, standalone data loggers capable of multivariable time-series data collection and storage. Most of these data loggers accept a host of sensors (including temperature, pressure, voltage, current flow, etc.) and have standardized input communications. These loggers are capable of recording at user-selected intervals from fractions of a second to hourly to daily recordings.
Short-term monitoring typically relies on in-field manual downloading or network connections if available.
Long-term monitoring uses time-based recording of energy resource consumption over a long duration to develop trending or performance verification. The time period is typically more than a year and is often a permanent installation.
Useful applications for long-term monitoring include systems influenced by variances in weather, occupant behavior, or other operating conditions. Other applications include reimbursable resource allocation, tenant billing activities, or cases where the persistence of energy or resource savings over time is an issue.
Equipment useful in long-term monitoring includes data loggers, utility-grade meters, or fixed data acquisition systems. In most cases these systems communicate via a network connection to a host computer.