IAEEL newsletter 2/94

Loggers Give the Answer

Lighting loggers answer questions about when and how often individual luminaires are used. And since they don't require hard-wire installation, they provide these data at a low cost.

Energy professionals involved in energy efficient lighting retrofits have long known that estimates of kWh savings are questionable when based on engineering assumptions, rules of thumb, and the occupants' best guess about current lighting usage.

Obtaining actual usage data on a before-and-after lighting retrofit basis has traditionally been either a dream or a very expensive proposition involving hard-wired electrical meters. In addition to the high cost of hard-wired electrical metering, the extra time required to hire a licensed electrician to perform the work often led to unacceptable project delays.

Now the dilemma of questionable data vs. the high cost of metering has been resolved by a class of devices called lighting loggers. They are small, usually about 2.5x5x10cm (1x2x4 inches) or less, battery-powered instruments capable of detecting when a given luminaire is activated and of storing a variety of data concerning the luminaire's usage.

Lighting loggers come with various capabilities and built-in functions. Knowing the types of data required for analysis in advance is fundamental in selecting the right lighting logger. For instance, if the utility has time-of-day pricing, lighting loggers with time-of-day usage recording capabilities would be appropriate. If, on the other hand, the primary financial savings will result from a decrease in kWh usage, then a meter that records only elapsed on-time might be more appropriate and certainly less expensive. Lighting loggers are most cost-effective when used to obtain information about lighting usage in many different rooms of a building. To measure the lighting usage of a whole building, other methods may be more cost-effective.

Lighting loggers are less suited for systems equipped with dimmable ballasts.

Lighting loggers can record four types of data concerning lighting use:

Runtime data-the total time the luminaire was on during the monitoring period.Runtime loggers are the simplest and cheapest type of loggers. They present one single number-the amount of time lights were on during a monitoring period.
Event tallying data-the number of times the luminaire was turned on.
Time of use-the complete data set. Time-of-use (TOU) loggers record the times of day at which luminaires are turned on and off, and give the complete usage pattern of a monitored luminaire or room. They require special software for processing the gathered information.
Occupancy data-the number of hours a luminaire was on while a given room was unoccupied.Occupancy loggers are more sophisticated and expensive, and are made in both runtime and time-of-use versions.

In addition to the variety of data that lighting loggers can record, a wide range of features are important to consider in order to get the logger most suitable for a given purpose:

Battery life: Depending on the power draw of the logger and the battery system, the loggers currently on the market will provide between 6 months and 10 years of active use. A battery failure in the middle of a monitoring period is frustrating and expensive and may result in project delays.
Sensitivity adjustment: The level of the light required to trigger the lighting logger can be a very sensitive variable. Rooms with large picture windows are particularly hard to monitor because of "stray" ambient light triggering the meters. The ability to adjust the on-trigger is an important design feature that can enable the monitoring of luminaires that otherwise could not be monitored.
Fiber optics: Some loggers are shipped with fiber optic cables that enable installation some distance away from the luminaire. Fiber optics can also help overcome the problem with ambient lighting, since the logger's "field of vision" is much narrower with a fiber optic cable that can be attached directly to the lamp wall.
Method of data recording: Data can be acquired from lighting loggers in three basic ways. The simplest way is to read the LCD on the face of the logger and record the data by hand. This method is required with most meters that only record total runtime. The more sophisticated type of meter acts as a data recorder, tracking usage until downloaded into a computer. One manufacturer utilizes an infrared scanner to download information. Information from the scanner is then downloaded to a computer. This feature allows quick data collection in the field and does not require the removal (and replacement) of the lighting logger.

Choosing the lighting logger best suited for a project's needs is crucial if the value of these instruments to the analysis of lighting retrofits is to be maximized. Knowing the type of data needed, the features desirable for the project needs, and, of course, the project budget all play an important role in selecting lighting loggers. The true value of lighting loggers is their ability to provide accurate data for use in analyses of lighting retrofits in a timely and cost-effective manner.

Bruce Manclark
Nils Borg

Bruce Manclark is an energy conservation consultant at:
Delta-T, Inc.
P.O. Box 11622,
Eugene, Oregon 97440, USA
Fax: +1 503 995 2254

TABLE
Finding Loggers: Manufacturers

Results From the Real World

A current project in the Pacific Northwest area of the US is taking advantage of the flexibility and low cost of lighting loggers. Six public utilities with funding from the Bonneville Power Administration are undertaking the task of determining residential lighting usage.

The "Baseline Residential Lighting Energy Use Study" is using over 1 200 lighting loggers in 51 single-family homes in a year-long survey-an average of almost 24 loggers per house. This type of intensive data collection was simply not possible with hard-wired electrical meters. The compact design of lighting loggers allows them to be placed inconspicuously in most cases. In addition, the very nature of residential wiring allows for very few "clean" lighting circuits. Most residential electrical circuits comprise a variety of load types, including lighting and small appliances, making lighting-only metering impossible from the panel box.

Preliminary results from the first 6-month metering period are available. The calculated annual lighting usage per household varied widely, from 79 to 7 750 kWh/customer, the average annual use being 2 282 kWh per customer. The data were adjusted for unusable readings and extrapolated over a year without regard to seasonal adjustment.

The proportional distribution of annual lighting energy usage was as follows (percentage of households within parentheses):

<1 000 kWh/year (20%)
1 000-1 999 kWh/year (31%)
2 000-2 999 kWh/year (27%)
>3 000 kWh/year (22%)

These preliminary estimates of lighting energy usage are much higher than energy professionals' traditional estimates. It also appears as if lighting usage patterns vary widely, thus making our rules of thumb even more inaccurate. According to the first results, there is no correlation between energy-use for lighting and either the number of occupants or the floor space of the homes. It is clear that lighting loggers represent the only technology available that will allow energy professionals to move beyond best guesses and rules of thumb to an analytical approach based on solid data.

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