Building load profiles: the basics

Store Equipment & Design, June, 2000 by G. Russell Brown

Buildings tend to operate in much the same way every day. Changes in their operation tend to be gradual unless there is a radical change in the type and/or level of business being done there. For this reason, a building load profile is generally an excellent indicator of future energy use. Furthermore, in this age of deregulated energy, building load profiles can be invaluable in negotiating power contracts and keeping utility costs under control.

Building load profiles offer other benefits as well. Just as the medical profession relies on X-rays, EKGs, ECGs and lab tests for diagnosing illnesses, facility and energy managers rely on building load profiles to set benchmarks, establish best practices and determine if equipment is working up to design parameters.

Building load profiles are frequently expressed as charts; this makes interpretation easier. In fact, many experienced energy managers can analyze a chart in seconds.

Of course, very little is perfect in the real world, and building load profiles are no exception: There tend to be day-to-day deviations. Examples of these deviations include: emergency generator test; power failure; refrigerator cycling at night; peak-load generator operating to shed loads; multistage compressor cycling on or off; utility meter being replaced; early arrival of an unauthorized employee; someone forgetting to turn the lights off at the end of the day.

Each of these deviations may have an impact on the electric bill so they should be avoided whenever possible. To that end, issues and possible causes must be constantly explored. For example:

* Was the deviation planned?

* Was the utility cost of staying late taken into consideration when the decision was made to do so?

* Does the applicable utility tariff have peak, off-peak and mid-peak rates? Is the facility operating with this in mind?

* Can something be done about the deviation without compromising customer and employee service levels?

* Should the peaking generator start 50 kW sooner or later?

* Will this change impact the budgeted dollars for the month?

* Will unnecessary refrigeration and/or cooling cycling (sawtooth pattern) add wear that will eventually shorten the equipment's natural life, thereby necessitating a new compressor every five or 10 years?

* Did the building equipment react to yesterday's weather as expected?

* Did a "spike" cause an undue peak kW in the bill?

* How great a load did the emergency generator take on?

* Was it a full-load test?

* Was last year's demand exceeded this year? Was it because equipment was added or because the "pre-cool or post-cool" program is not working?

* Did all the lights and equipment go off as intended, or is that the real nighttime load?

If any of these questions are relevant to the building load profile, a trained tactician should be able to answer them quickly and then respond in the appropriate fashion. That may be to send an e-mail, phone call or page to his field staff to make the appropriate correction before it shows up on the upcoming utility bill.

For many companies, obtaining a load profile is as simple as going to the local utility. The cost for this may include a meter upgrade, telephone line and an on-going nominal administration charge. However, the expenditure will typically be very worthwhile as the payback may be measured in months, if not days. *

Russ Brown has 20 years of experience in energy and maintenance, and is a well-known speaker in both areas.