Application Story

Onset HOBO® Data Loggers are playing a key role in a landmark national weatherization study to gauge the success of a $5 billion federal assistance program that provides funds for energy efficiency improvements in low-income houses.

Called the National Weatherization Assistance Program Evaluation, the effort marks the first time in two decades the federal government has gathered technical data on energy consumption and other energy efficiency factors in homes treated under the federal weatherization program. The objective is to evaluate the impact of weatherization on household energy usage and characterize other effects of weatherization on indoor air quality.

HOBO Data Logger

An Onset state logger monitors heating system operating cycles.

Not only will the weatherization study help calibrate federal strategies for low-income homes, but it will also provide insight into best practices for the larger energy efficiency industry.

Managed by Oak Ridge National Laboratory, the study looks at efficiency improvements funded through the Weatherization Assistance Program (WAP). Information is being gathered from homes served by more than 900 local weatherization agencies and hundreds of utilities.

One part of the evaluation is a field study investigating heating energy savings in homes that rely on non-metered fuels (propane and fuel oil).

The Energy Center of Wisconsin, a Madison-based research and education firm, is part of the team chosen to perform the evaluation. The Energy Center has installed several hundred Onset HOBO® data loggers in homes that use bulk fuels, such as propane and oil. This includes state loggers for monitoring heating system run time, temperature-relative humidity loggers to characterize space conditioning, and thermocouple temperature loggers to monitor secondary heating systems.

The study focuses on low-income homes in the Midwest, Northeast and South, where testers hope to determine if homes heated with propane and oil achieve comparable energy savings to those heated by natural gas.

In the fall of 2010, the Energy Center installed HOBO data loggers in selected homes to record heating system operation for 8 to 12 weeks before the houses were weatherized. The Energy Center also will record data over a similar time period after weatherization. A number of control homes, not subject to weatherization, were also included. The data loggers will be retrieved in the spring of 2011 and the data analyzed to establish heating energy savings in the homes.

Data loggers are crucial to the weatherization study because it is difficult to measure heating energy use in homes that use bulk fuels. These homes do not receive monthly utility bills showing consumption patterns as homes do that use metered natural gas. Analyzing fuel deliveries, alone, can create skewed results. For example, one household may fill its oil tank to the top for the winter; another may fill it only partially and then use a wood-burning stove to supplement.

In going into the homes, the Energy Center's main objective is to determine heating system run-time. Researchers installed data loggers with current sensors on primary heating systems, and temperature data loggers on any space heaters or wood stoves that are used often. In addition, they placed temperature and relative humidity loggers at central thermostats.

The Energy Center is also using HOBO U9-001 State Loggers to record each operating cycle of the primary heating system in each home.

"We're interested in knowing when fuel is being consumed, which is not the same as monitoring heating calls or fan operation," said Dan Cautley, Energy Center senior project manager. "To get burner on-time, we're watching the power wire to the gas valve in propane systems, and in oil systems we are monitoring either the oil solenoid valve power, or when there is no solenoid valve, the burner power. In each case, we install a current switch on the appropriate wire, and connect this switch to the state logger with the usual stereo jack cable." The state logger records the actual time to one-second resolution when the current switch closes and opens, providing a time-stamped record of fuel consumption.

"To be sure the current switch would be triggered with a single pass of the power wire, we asked Onset to price out a more sensitive current switch (Veris H300) than the items usually stocked," he added. "The H300 triggers at 0.15 A, and has a clip-on split core, so it can be installed without disconnecting any wiring, a must for our project."

In addition to state loggers, the Energy Center installed a HOBO U10-003 temperature/RH logger at the main thermostat in each home. This gives information on the actual space temperature setting over the study period, which can be used to improve the variable-base degree day analysis used in the study.

"We try to filter out homes that have significant supplemental heating sources such as wood stoves or free-standing space heaters, but it's not possible to do so completely," Cautley said. "Since supplemental heaters may not have electric valves or burners, we couldn't rely on state loggers to monitor them. Instead, we decided that periodic readings on a temperature logger would give us a snapshot of how much the supplemental system operates on average. Along with an estimate of its input, we can at least roughly account for its contribution to the heating load."

APPRISE, a Princeton, NJ-based research institute, is serving as the lead contractor for the weatherization evaluation, with partners ECW, Blasnik & Associates, and Dalhoff Associates.