(first in a three-part series)
Mike Opitz PE, LEED AP
Certification Manager, LEED for Existing Buildings
U.S. Green Building Council
Introduction
Saving energy to lower utilities costs has been an effective facilities management strategy for decades, and has clear benefits for the environment as well. Rising energy prices are now inspiring building operators to dust off their energy management plans and take a fresh look to see if they can be doing even more. Much is known about the best ways to assess savings and to select and implement the most cost-effective projects, but after project completion skeptical owners and site managers often wonder, “How much did we really save? How close is our actual savings to what we expected, and if we’re off the mark, why? How can I learn these answers without spending too much money?”
What M&V is and what it can do for you
Enter energy savings measurement and verification (M&V), an industry standard way of answering these questions. M&V is basically a set of procedures and protocols you can follow to determine energy use or peak electric demand of a single mechanical system, a group of systems, or an entire facility. This is done using standardized, replicable methodologies that will allow you to compare the results to other time periods in your own building—like before and after an energy project—or even to other buildings (see “Benchmarking” in this column, April 2005, for an overview of how to do that).
Viewed more broadly, a robust M&V program overlaps substantially with commissioning, or inspections and testing to ensure the building operates as the owner and designer intended. This is helpful in ensuring a building provides the best possible services to its occupants at the lowest possible operating cost. Building teams pursuing the USGBC’s LEED for Existing Buildings certification will find several M&V- and commissioning-related prerequisites and credits under the Water Efficiency and Energy & Atmosphere sections.
Standard M&V offers several options for assessing energy use, including dedicated metering with data loggers, specialized software that analyzes patterns in utility bills, or even full-blown computer energy modeling. The best approach for a given facility and project depends on how much accuracy is desired, the size of the M&V budget, and how much M&V expertise staff has or is willing to acquire. M&V techniques are equally useful whether projects are done in-house or contracted out, and as a rule they apply equally well to determining water usage.
The remainder of this article will focus on M&V as applied to energy-saving projects. In that context, M&V will provide three basic indicators of the project’s performance:
- An estimate of how much energy or peak demand it saved
- How accurate that estimate is, and how much confidence you should have in it
- How long the savings persist over time (if the M&V is continued)
Careful comparison of energy use before and after project implementation yields the energy savings, but it’s not as easy as performing a simple subtraction.
Energy savings—a surprisingly complex notion
Occasionally a facility’s energy bills go up after completing an energy project. Does this mean the project failed? Not necessarily, for two basic reasons clear to trained energy managers but obscured to casual observers:
- The price of the energy or peak demand may have risen, raising costs even if raw energy use was stable or fell
- Changed conditions in the facility may have caused the raw energy use to rise for reasons unrelated to the energy project
Both of these complications suggest that energy savings is best viewed as avoided use or cost, not a literal drop in the energy bill. In other words, a successful energy project means your future energy costs will be lower than they otherwise would have been, given the same set of assumptions (i.e., continuation of business-as-usual with no surprises). Of course, all this can work in reverse too, with changes in price or conditions causing energy bills to go down more than expected. Believe it or not this is also troublesome, as it can mislead you into thinking your energy project saved more than it really did, possibly biasing your choices about future projects.
It’s easy enough to correct for known price changes, but properly discovering, tracking, and accounting for changes in facility conditions is much more challenging because of the enormous number of factors causing variations in energy use. Here are common examples, listed according to how much the facility staff can typically influence them:
| cause of variation | ability to influence | typically part of energy project? |
| Weather | none | no |
| utility service interruptions | none | no |
| occupant behavior | low | rarely |
| service provided to occupants | ||
| system “enabled” hours/day | medium | yes |
| occupied space temperatures | medium | sometimes |
| light levels | medium | sometimes |
| ventilation levels | medium | sometimes |
| building alterations | ||
| space reconfigurations or renovations | medium | no |
| additions or demolitions | medium | |
| fuel type | medium | sometimes |
| new equipment selection | high | yes |
| upgrades & repairs of existing equipment | high | yes |
| control strategies | high | yes |
| unoccupied space temperatures | high | yes |
| maintenance (preventive & corrective) | high | sometimes |
It’s the basic apples/oranges problem: the before and after energy use must be measured relative to the same set of conditions. Said another way, the effects of all significant changes unrelated to the energy project must be removed from the savings calculation. M&V provides a way to do this, and in the world of M&V the resulting corrections are called savings adjustments. You can see now that M&V is really a philosophy for defining exactly what the term “energy savings” means—which changes in raw energy use count in the savings calculation, and which don’t. Only when this has been sorted out will you know your project’s true savings.
We’re now ready to define energy savings more precisely: “the reduction in energy use resulting from an energy project, relative to the use the site would have experienced without the project, assuming no other changes occur.” Or, in mathematical form,
Energy savings = (energy use before project) – (energy use after project) +/- (savings adjustments)
Coming up in part II
M&V is such a complex enterprise that good planning and rigorous execution are essential for success. Next month we’ll get into setting goals, dealing with uncertainty, living within the M&V budget, choosing the best M&V options to suit your needs, and real-world M&V examples.
Resources
International Performance Measurement and Verification Protocol (www.ipmvp.org)
Offers free downloads of several voluntary M&V standards representing consensus of global experts. Volume I includes an excellent introductory, non-technical overview of M&V concepts.
Federal Energy Management Program’s M&V Resources (www.eere.energy.gov/femp/financing/superespcs_mvresources.cfm)
Free download of the Department of Energy’s FEMP M&V Guidelines for federal government facility managers to use in planning and implementing M&V on energy projects, plus many other M&V planning resources.
American Society of Heating, Refrigeration, and Air Conditioning Engineers (www.ashrae.org)
Publishes ASHRAE Guideline 14: Measurement of Energy and Demand Savings. Highly technical, but a good resource for engineers responsible for executing or overseeing M&V work.
U.S. Green Building Council (www.usgbc.org)
The USGBC’s LEED for Existing Buildings program addresses M&V issues in several of its requirements and credits.
