Battery-powered data loggers incorporate a microprocessor, memory and sensors into a single compact package. (Feature photos courtesy of Onset.)

Low-cost data loggers can provide contractors and building managers with information that helps save thousands of dollars in energy costs, while helping ensure that IAQ and occupant comfort are maintained throughout properties.

By monitoring and recording simple variables like temperature, rh, CO2, and light or motor on and off, data loggers can help detect and document whether “too hot or too cold” comfort complaint conditions are real, whether the property is threatened by conditions suitable for mold growth, and whether energy savings can be realized through ensuring that lights are off when areas of the building are unoccupied.

More sophisticated measurements (ac current, voltage, power demand [kW], energy consumption [kWh], pressure, and differential air pressures) provide valuable information for troubleshooting HVACR systems, submetering, building commissioning, and measurement and verification of energy savings.


Data loggers are battery-operated, standalone measurement tools containing a microprocessor, memory, and sensors for measuring and recording one or more variables over time. They are typically quite small, enabling them to be deployed almost anywhere throughout a building or complex, with some packaged to work in outdoor environments.

Some data loggers have internal sensors, so measurements are made only at the logger location. Others utilize sensors on external cables that allow for monitoring at some distance from the data logger itself. A logger may offer a combination of internal and external sensors, as well as external channels accepting pulse, 4-20mA or dc voltage inputs from other sensors for even greater flexibility. The loggers operate unattended for hours, days, or months at a time. Specialized software is used to configure the logger (select sampling intervals, synchronize logger and computer clocks, etc.) and to offload the recorded data from the logger to a PC for graphing and analysis.

Temperature is the most common measurement required for most environmental monitoring applications, as it is important in monitoring the human environment as well as equipment operation and efficiency. CO2 and rh are two other common measurements for IAQ and comfort complaint investigations.

Combined temperature and rh measurements are also critical indicators of conditions that may be conducive to mold growth, which is an important concern for today’s building managers and occupants.

In addition to stand-alone data loggers, Web-based remote monitoring systems are available which not only measure and record a range of environmental parameters, but also make the data available on the Internet on a 24/7 basis. Typically, these systems incorporate some type of wireless communications technology - including GMS cellular or WiFi - and offer Web-based software that enables all logger management and retrieval functions to happen over the airwaves.

Web-based energy and environmental monitoring systems can provide real-time HVACR system performance data on the Internet.


HVACR troubleshooting:Airflow pressure, monitored with an external airflow pressure sensor mounted within an air duct, or attached to heating coils or pipes, can provide valuable insight into heating distribution or air balance problems. Multiple airflow points may be used to evaluate a larger section of an air distribution system for larger-scale analyses, along with temperature readings (at supply and return vents).

In addition, time-of-use data loggers can be used to monitor HVACR equipment to detect short cycling of, for example, a compressor or blower, or other equipment runtime in order to evaluate potential failures for scheduling repairs or replacements.

Chiller system efficiency is easily and accurately monitored by logging outdoor temperatures, water temperatures, and flow rates at supply and returns, and when pumps are turning on.

Energy management:Data loggers can be used to track energy usage in various parts of a building, to verify equipment operating efficiencies, and to identify areas where energy costs can be reduced.

Light usage monitoring:Total light usage in a building complex can gobble up a good share of power, especially if they are left on unnecessarily for long periods of time. Light intensity (loggers that have built-in photo sensors) or state on-off data loggers can be placed as close as possible to individual light sources, or on ceilings or walls, to record when lights are on over various times.

Data should be logged for a period long enough to cover various times of day and night, as well as occupied and unoccupied periods. The data gathered will not only detect direct light usage, but can also help in deciding whether the expense of permanently installed occupancy light sensor/switches or some other remediation is justified.

If changes are made to reduce light use (or wattage reduction), the same loggers can be redeployed in the same spaces later on to generate data to verify that the changes were successful.


Portable data loggers are inexpensive and easily deployed measurement-recording tools that can have a positive impact on containing building energy costs without sacrificing occupant comfort levels.

With so many possible uses in a building - energy usage monitoring, verifying comfort, and IAQ conditions, etc. - they are primary measurement and recording tools for balancing and managing a building’s energy usage and environmental qualities.

Publication date:08/17/2009