This column features helpful information, innovative equipment, systems and applications utilities around the nation can use to save energy and improve service.

Determining savings with micro-loggers

“Our gadget will save you 20 to 40 percent of your energy bills!”  How many times have we read or heard something like that?  Most resource conservation managers hear it all the time.  Often the savings are “guaranteed.”  Suppose you bite and install the new product or technology—how do you tell whether the savings really happen? 

If the new product affects a component or system that operates on the same schedule and at the same load from day to day, you can do “before” and “after” metering using one or more micro-loggers.  Micro-loggers are pocket-sized devices with ample memory and energy-miser circuits that can operate for months or years on a small internal battery.  

Simple to complex

Micro-loggers are usually one of three types:

• Running-time meters, the simplest units, tell the number of operating hours a particular load has accumulated since the logger was installed and initiated.  To detect operation, various models sense light, magnetic fields, voltage, vibration or current.  Use running-time meters to assess a product or technology that purports to reduce the operating time of something.
  
  
• Time-log meters are a step beyond the running-time meter.  They produce a data file that records the date and time of each change of state, e.g.: ON/OFF.  Use these if you need to know the schedule of operating time as well as the total operating time, for example to evaluate water heater time clocks intended to mitigate peak demand.
  
  
• Magnitude loggers record the actual magnitude of a parameter like temperature, current or power with respect to date and time.  Use these when the product or technology is expected to reduce power during operation, rather than just shorten or reschedule operating times.

Most manufacturers make all three types.

The battery life of a micro-logger usually exceeds the time needed for monitoring and evaluating equipment.  Some micro-loggers have internal modems or network cards so they can be read remotely.  At least one manufacturer sells a data-fetching device barely larger than a book of matches. It can be taken into the field to download the data and then reset the loggers.  This device saves you from dragging around a laptop or removing the loggers to take them to a desktop computer.

Choose right unit for data to be measured

Directly measuring electrical consumption is one of the most important applications for micro-loggers.  You can get by with cheaper and simpler loggers if you just measure current, but beware.  Current loggers can suffice when energy reductions come from changing the loading on individual components (such as fixing compressed air leaks). You can establish the kW-versus-amp relationship with a portable power meter before installing a current logger. 

If a single load is monitored and that load is driven by an induction motor, the motor can be entered into MotorMaster+ software’s “Inventory” module. A range of currents plugged into the “Field Measurements” tab to generate a kW versus amp curve. 

Carefully consider whether you need direct power monitoring rather than just current monitoring.  The issue is that utilities bill in kilowatthours, not kVAR-hours.  When loads are reduced, and especially when power conditioners are installed, kW often does not drop in proportion to kVA. 

Some power conditioners are mostly capacitors and can dramatically reduce kVA with almost no reduction in kW.  When a power conditioner is implemented as the energy saving device, the logger must be attached on the line side of the conditioner and there is no reliable way to convert current data to kW.

Manufacturers of micro-loggers include ACR Systems, Onset Hobo and Dent Instruments.  All have diverse models including electrical current loggers.  Dent has a higher-end model that can record three-phase real and reactive power in a very small battery-powered package.  When selecting a micro-logger to record electrical data, consult the manufacturer and carefully review the specifications if you have to measure high harmonic current or voltage.  Products vary in how accurately they read in the presence of high harmonics.

Depending on what you must measure, the appropriate micro-logger and sensor(s) can cost anywhere from less than $150 to about $1,000.