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Building Operating Management

How to Squeeze More Savings From the EMS





By Lindsay Audin   Building Automation

OTHER PARTS OF THIS ARTICLEPt. 1: This PagePt. 2: EMS/BAS Products

Energy management systems (EMS) are common in many medium-to-large buildings, and practically mandatory at campus-based facilities. Facility managers depend on them to maintain comfort and control energy costs. But while the former is routinely achieved, the latter often is not.

Getting energy savings out of an EMS involves a multipronged approach that includes commissioning, ongoing staff training, routine verification of settings, and pursuing options for improving existing EMS capabilities.

An EMS could be as simple as a group of time clocks that automatically turns on and off lighting, HVAC and other equipment. In many cases, it is a computerized system that monitors multiple variables at a variety of locations, controlling conditions based on settings and algorithms in pre-programmed software. A building automation system may encompass the above while also handling non-energy functions.

A well-operated EMS is an exercise in data management. It may, for example, monitor all of the following variables affecting an air handler: temperature, humidity, flow and pressure of incoming air; return air and mixed air damper settings; discharge temperatures at preheat, heating, cooling and reheat coils; temperatures/pressures of chilled and hot water flows to those coils, plus kW and run time of fans. Through sequences of operations, schedules and other presets, an EMS would react to some of those variables and control others.

Such information allows trending of temperatures, humidity, occupancy, etc. When analyzed, that data may point to opportunities to reduce or shut down services when not essential. Data collection also allows tracking and benchmarking of a facility’s performance against prior years, or comparable buildings in the same climate zone. In the hands of a skilled energy manager, data may help to set goals for energy use and peak demand, and sniff out opportunities for cost-effective upgrades, such as a poorly performing chiller.

Some EMS are also used to gather and store energy use data from meters and submeters. Depending on meter location and the sophistication of EMS software, such capability may be used to generate invoices for departmental or tenant energy use.

Why Problems Arise

Since the 1970s, EMS have been integral in efforts to minimize the cost to run equipment while maintaining comfort. Many EMS were bought based on the notion that they would pay off their million dollar price tags over time by cutting energy waste. And that’s often true — but not always. Some EMS owners have been disappointed with their systems, often pointing fingers at manufacturers, contractors and energy service companies (ESCOs).

What goes wrong? EMS practitioners generally divide the problems into three categories:

  • Failure to properly commission a system at startup. If it’s providing comfort when first put into operation, there is often a reluctance to “fool with success,” or to pay the extra for commissioning, which in a new building could be $1 per square foot.
  • Disinterest in retrocommissioning on a regular basis (e.g., every 2 years). Over the years, sensors go out of calibration or fail, leading to errors like excess reheat, overcooling/dehumidifying or a lack of response. When odd readings appear, they may be ignored or the problematic sensors and controls disconnected. Schedules may be overridden for a one-time event, and then remain overridden.

    In one instance at a well-operated laboratory, chillers ran on natural gas. A bump in monthly summer natural gas consumption was seen that did not correlate with weather conditions, but the gas-fired chillers were found to be performing efficiently. When hourly gas usage logs maintained by the EMS were checked, however, a major (but brief) nightly increase was found during late hours, even when the building was empty. Outside air dampers had — once — been set to fully open for an hour, probably to flush out odors, but the damper schedule was never reset. Each time the dampers re-opened, the system sensed the humid night air entering the building, and started the chillers to dehumidify it, consuming gas in the process.
  • Insufficient training and retraining of operating personnel. When experienced personnel leave or retire, replacements may lack necessary knowledge and background to run the system properly, or successfully troubleshoot problems. Some systems may be too complicated to be maintained properly by such personnel without additional training.

    Some of these problems feed off each other, with operating staff blaming the equipment or installer, and the vendor accusing the staff of not knowing what they are doing. If there’s no budget or will to correct the situation, an EMS may gradually turn into a very expensive time clock.

Obsolescence can also cause problems. At a large university, an EMS kept in operation well beyond its useful life lacked sufficient storage memory to handle more than a year’s worth of meter data. Once the first year had passed, it began to purge the oldest data in its memory one month at a time. When its hard drive failed, all data was lost because there was no automated backup system that routinely stored it elsewhere. By the time these problems were noticed, a great deal of data had been lost, making trending and benchmarking impossible.

Steps to Take

One way to get more savings from the EMS is to assess present building energy use and systems. Start by benchmarking against past years’ use at the facility and, if possible, against comparable nearby facilities. Focus on energy use, not cost. Due to changes to utility rates and fuel prices, cost may change significantly even when use doesn’t.

If use on a per-square-foot basis is more than 20 percent greater than prior years (which is more than typical weather and minor facility changes will cause), pursue retrocommissioning — or at least verify that all major schedules and control points are within spec. If a pre-owned facility lacks at least two years of use data, push for a full retrocommissioning. If a building’s air system has not been balanced to ensure proper distribution and temperatures in the last 10 years, that should be part of the commissioning process to address changes in occupancy and use of the building that may have occurred.

Commissioning averages about $.25 to $.30 per square foot, but may be higher for labs or other smaller or complex facilities, or if other services, such as air balancing, are included. Recouping that investment in two to three years (sometimes less) is not unusual. When equipment schedules have been disabled, for instance allowing fans or lights to run all night, or where sensors or controls have failed or been bypassed, quick paybacks may be achieved.

Once all systems are operating properly, start logging energy use data for that ideal condition at major locations — chillers, plant auxiliaries, lighting panels — at least monthly to record their disaggregated use. That information forms a baseline against which future performance may be measured.

To stay on top of this effort, take advantage of an EMS’s ability to collect and correlate large quantities of data without human involvement. Many “canned” functions, like benchmarking, come standard in EMS software while others, like diagnostics, may require an upgrade. Dedicate a knowledgeable staff member to oversee such capabilities on a daily or weekly basis (not just when energy bills arrive), and report anomalies for timely investigation.

Facility managers might also consider performance contracts that involve off-site monitoring and EMS maintenance. With performance contracts, the contractor has to maintain savings or else pay for lost savings, so the contractor will return to a facility and correct problems as part of the service.

OPPORTUNITIES
More Places to Look For Savings

Energy management systems (EMS) have a multitude of capabilities, and many cost-cutting options may be available using existing equipment and staff, such as:
  • Optimized start/stop
  • Zonal night setback
  • Monthly check (and correction) of overrides
  • Preset dispatch of multiple chillers and auxiliaries
  • Deadband settings: temperature ranges during which neither heating nor cooling occurs, but air flow continues
  • Compatible sequences of operations — no simultaneous heating and cooling, for example
  • Maximizing use of variable speed drives (VSDs) on fans and pumps
  • Pre-cooling using low enthalpy outside air during night ventilation
  • Monitoring peak electric demand and implementing steps to limit it.
New ways to cut energy use and cost continue to appear, sometimes through merely changing operations of existing equipment. An annual review of such options — typically by an ESCO or consultant — may find major opportunities. Various optimization routines (e.g., for chillers and their auxiliaries) and hardware may be added to an EMS to that end.Some EMS improvements may require the addition of measuring/control points. When linked to the EMS via an existing LAN or fiber optic network, their installation costs may be greatly reduced, yielding quick paybacks.
— Lindsay Audin

 

Lindsay Audin, CEM, LEED AP, CEP, is president of EnergyWiz, an energy consulting firm based in Croton, N.Y. He is a contributing editor for Building Operating Management.


Continue Reading: Showcase: EMS/BAS

How to Squeeze More Savings From the EMS

EMS/BAS Products

posted on 5/31/2010

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