NorthWrite’s Utility Bill Management, Monitoring and Energy Expert Tools support all 3 of the monitoring-based approaches specified in the IPMVP.  Below is a summary of these approaches.

Extracted from:

Department of Energy’s Continuous Commissioning Guidebook for Federal Energy Managers

Measuring Energy Savings

The process for determining savings as adopted in the International Performance Measurement and Verification Protocol IPMVP [2001] de­fines energy savings, Esave, as:

ESave = Ebase – Epost

where Ebase is the “baseline” energy consumption before energy savings measures were implemented and Epost is the measured consumption following implementation of the measures.

The IPMVP includes four different techniques or options. These options may be summarized as Option A: some measurements, but mostly stipulated savings; Option B: measurement at the system or device level; Option C: measurement at the whole-building or facility level; and Option D: determination from calibrated simu­lation. Each option has advantages for certain applications.  Options A through C are discussed in more detail below.

Option A - Stipulated Savings (Involving some measurements)

The stipulated option estimates savings by measuring the capacity or the efficiency of a system before and after energy savings measures are implemented and multiplying the difference by an agreed upon or “stipulated” factor such as the hours of operation, or the load on the system. This option focuses on a physical determination of equipment changes to ensure that the installation meets contract specifications. Key performance factors (e.g. lighting wattage) are determined with spot or short-term measurements. Operational factors (e.g. lighting operating hours) are stipulated based on historical data or spot measurement. Performance factors are measured or checked yearly. This method provides reliable savings estimates for applications where the energy savings are independent of weather and occupancy conditions (for most loads that are constant).

For example, during a retrofit, the fan pulley was decreased from 18” to 16” for a constant volume AHU. The fan power savings can be determined using the following method:

·         Measure the fan power consumption before changing the pulley and the power consumption after changing the pulley

·         Determine the number of hours the fan operates

·         Determine the fan power savings as the product of the hourly fan power energy savings and the number of hours

If the energy consumption varies with occupancy and weather conditions, this op­tion should not be used. For example, the minimum air flow was adjusted from 50% to 0% for 100 VAV terminal boxes at night and during weekends. Since the air flow depends on both internal and external loads, the air flow may not be 0% even if the minimum flow setting is 0%. This method cannot be used to determine savings. If the goal of the measurement is for savings determination, option A should be con­sidered first. If it can provide the required accuracy, option A should be used.

Option B - Device/System Level Measurement

Within Option B, savings are determined by continuous measurements taken throughout the project term at the device or system level. Individual loads or end-uses are monitored continuously to determine performance and long-term persis­tence of the measures installed. The base line model can be developed using the measured energy consumption and other parameters. The energy savings can be determined as the difference of base model energy consumption and the measured energy consumption. This method provides the best savings estimation for the de­vice or system.

Since measure­ments are taken throughout the project term, the cost is higher than option A.

Option C - Whole Building Level Measurement

Option C determines savings by analyzing “whole-building” or facility level data measured during the baseline period and the post-installation period. This option is required when it is desired to measure interaction effects, e.g. the impact of a lighting retrofit on the cooling consumption as well as savings in lighting energy. The data used may be utility data, or sub-metered data.

The minimum number of measurement channels recommended for performance assurance or savings measurement will be the number needed to separate heating, cooling and other electric uses. The actual number of channels will vary, depending on whether pulses are taken from utility meters, or if two or three current transform­ers are installed to measure the three phase power going into a chiller. Other chan­nels may be needed, depending on the specific measures that are being evaluated.

Option C requires that installation of the proper systems/equipment and proper operating practices be confirmed. It determines savings from metered data taken throughout the project term. The major limitation in the use of Option C for savings determination is that the size of the savings must be larger than the error in the base­line model. The major challenge is accounting for changes other than those associ­ated with the ECMs, or commissioning changes implemented.

Accurate determination of savings using Option C normally requires at least 9 months of continuous data [Reddy et al, 1992, Ruch et al, 1992, and Katipamula et al., 1995] before a retrofit, and continuous data after retrofit. However, for commis­sioning applications, a shorter period of data, during which daily average ambient conditions cover a large fraction of normal yearly variation, is generally adequate.

Note that monthly bills may be used to estimate the energy savings. This method is one version of Option C described above. It is typically the least expensive method of verification. It will yield reliable results under the following conditions:

1.    Significant savings are expected at the utility meter level

2.    Savings are too small to cost-justify metered data

3.    There will be no changes in:

a.    Equipment

b.    Schedules

c.    Occupancy

d.    Space utilization