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What's Ailing the EMS?
Unlike straightforward energy upgrades like lamp and ballast replacements that require little human involvement once installed, energy management systems (EMS) often need close attention to ensure they produce expected savings. Among energy consultants, it is a well-known “secret” that many new or upgraded EMS are not fully checked after installation, leaving significant savings untapped.
One reason for this failure is the extra cost of independently verifying the many parts of the EMS, which most facility executives simply assume should be working once installed. In an effort to win bids and contain costs, some EMS installers quote commissioning separately or exclude that charge from their bids. The end result may be a gold-plated system delivering tin-plated results.
For example, here is what one professional commissioning service found:
- Some outside air flow scheduled to pull 100 percent when not needed.
- Summer/winter humidity limits were reversed, causing too much cooling and heating.
- Damper linkages installed but never wired, dumping conditioned return air.
- Variable speed drives set at full 24/7.
- Failed temperature sensors causing chronic complaints.
- Sensors located outside the air stream, yielding spurious results.
- Control wiring disconnected by personnel unable to correctly address a problem.
These problems resulted in tenant grievances, some of which were raised when it came time to renew leases. A few began looking for more comfortable accommodations, with one large tenant noting an increase in absenteeism that it attributed to the building’s increasingly poor air quality. These errors and problems were also increasing energy costs by almost 20 percent.
A typical EMS consists of a central computer and many measurement and control points that activate or modulate fans, dampers, pumps, coils, chillers, boilers and other HVAC equipment. Programmed into that system are many schedules, sequences of operation and control schemes designed to maintain comfort while trimming energy costs. For savings to occur, however, not only must the programming be correct (without conflicts, such as simultaneous heating and cooling) but all measuring devices (e.g., temperature sensors) and actuators (e.g., motorized valves, damper linkages) must be working as designed. As with links in a chain, failure at one level makes the rest essentially irrelevant.
When an EMS is installed it is usually tested to ensure it will deliver comfortable conditions, but its operation may not be verified with regard to optimal energy efficiency. To ensure an EMS will deliver promised savings, it needs to be commissioned upon installation or retrocommissioned thereafter.
Time for an EMS to be Retrocommissioned?
An EMS and its control points need to be retrocommissioned if you find:
- Unusually high energy usage on a unit per square foot basis.
- Chronic failures of building equipment, the control system, or both.
- Numerous and growing comfort complaints.
Retrocommissioning may not make sense where:
- Systems are old and slated for replacement in the near future.
- A system was not designed properly and never worked from day one.
- Large systems (e.g., chillers) are failing and require replacement.
Costs and Savings
Due to variations among buildings and systems, costs for commissioning or retrocommissioning services vary widely, from $.03 to $.43 a square foot, with $.20 a square foot being a generally accepted average. That cost typically encompasses review of all EMS programming, testing of all measurement and control points, identification of all problems, minor repairs, and a short-term verification of savings.
Savings from proper commissioning or later retrocommissioning will also range widely, depending on how well systems were designed, installed and maintained prior to review. Independent studies have shown cuts in energy costs ranging from 2.5 percent to 49.4 percent with paybacks for commissioning ranging from 3 months to 4.6 years. (See chart.)
To cover the cost of this process, some facility executives pursue it under a performance contract in which the service provider guarantees energy cost savings, or else pays the customer for savings not found during the contract term. In some areas, utilities or state energy agencies may also provide low-cost or subsidized commissioning services as part of a demand-side management program.
Where systems (e.g., a chiller plant) are sub-metered so that their operating cost and savings may be measured separately, it may be possible to address them individually. But it pays to be mindful of the incremental costs involved once a commissioning practitioner is in the building. Leaving some stones unturned may also miss major savings.
Energy waste is often distributed in a variety of locations. It may result from the interaction of several systems (e.g., a faulty temperature sensor and an erroneous sequence of operation), such that fixes at only one level may fail to secure savings. One can never be sure where the biggest bang for the buck may be hidden. A large system may have a small inefficiency that is less worth correcting than a small system with a large inefficiency. Unless there is good reason to avoid involving all aspects of EMS operations, it makes sense to take a comprehensive approach.
Pitfalls to Avoid
Not all commissioning is the same. During the bid process, it pays to secure and compare commissioning forms and procedures that will be used by potential commissioning practitioners. If possible, examine a deliverable for a known customer, and then match both the forms and the deliverables against their proposals. Failure to do so may result in a good price for a less-than-sufficient product.
Commissioning also requires careful planning with building and operations staff, possibly including off-hour activity requiring coordination with security and HVAC personnel. The usual insurance and liability issues that pertain to any on-site contract work also apply.
Once the work is complete, don’t be surprised if the deliverable looks like a large volume of seemingly repetitious forms requiring close examination by a controls specialist to be understood. More than one commissioning customer has complained about paying big bucks for a big book without any ability to be sure what the organization got for its money.
If no performance contract is involved, it may pay to involve an independent energy consultant to ensure that the work is complete, that savings do indeed occur, and that they are clearly demonstrated via post-commissioning measurements and utility bills. In some cases, savings may not show up until the next heating or cooling season because fixes of those systems occurred outside of those seasons.
Studies and retrocommissioning practitioners suggest starting with benchmarking to assess the present level of energy use and costs. One of the quickest and cheapest ways to get a handle on where a facility stands relative to similar buildings in a given area is the ENERGY STAR Portfolio Manager system. By inputting energy and building data to this free online system, a building is ranked on a percentile basis (e.g., uses more energy per square foot than X percent of similar facilities within a geographic area), providing a glimpse of possible savings opportunities.
Quantifying those savings in dollars requires a more rigorous effort, however, with attention paid to any eccentricities (e.g., gas-fired chiller, thermal storage system) that could skew costs or usage. In most cases, it pays to have an energy professional perform an analysis that takes such details into account. Once overall potential savings are ballparked, it’s essential to separate out savings that may require major investment (e.g., chiller replacement) from those attainable through tweaking and minor repair of EMS and controls. Involvement of an energy professional is again suggested to derive a realistic savings number.
Such a review may also involve a brief walk-through, especially where system documentation or operator knowledge is lacking. That combination of services is typically accomplished through a low-cost scoping study that is done in a few days versus the weeks that a full retrocommissioning may entail. Scoping studies may cost only a few cents per square foot but are well worth the investment. They may also be essential to securing buy-in from upper management to justify the cost of a full commissioning. In a complex, such as a campus or industrial park, a scoping study may highlight which facilities could benefit from full commissioning.
In a 300,000-square-foot building, a retrocommission charge of $.20 per square foot yields a $60,000 bill, roughly the annual cost of a small cleaning crew. Fortunately, a properly maintained and operated EMS and its attendant mechanical systems should not require a new retrocommission for several years. Some studies recommend a four- to five-year interval between retrocommissioning efforts, with annual benchmarking of energy use and costs to watch for any aberrations requiring special attention.
Others suggest an ongoing commissioning process to maintain systems at optimal performance at all times. The Federal Energy Management Program (FEMP) has, for many federal facilities (such as labs), been pushing this method through its Continuous Commissioning program. FEMP claims this process “has produced typical savings of 20 percent with payback under 3 years (often 1-2 years) in more than 130 large buildings.”
Who Performs Commissioning?
While commissioning may be performed in-house, the need for uninterrupted detail work usually requires a level of rigor more appropriate to outside expertise. Much may also be said for having an independent eye reviewing systems that may have been poorly installed or operated.
— Lindsay Audin
Retrocommissioning Case Studies: Savings and Payback
Source: J. Gregerson, “Cost Effectiveness of Commissioning 44 Existing Buildings,” in Proceedings of the National Conference on Building Commissioning (Huntington Beach, Calif., April 28–30, 1997) as summarized by Thorne and Nadel in “Retrocommissioning: Program Strategies To Capture Energy Savings in Existing Buildings,” June 2003.
Lindsay Audin is president of EnergyWiz, an energy consulting firm based in Croton, NY. He is a contributing editor for Building Operating Management.