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Research Highlights

October 2015

Cooling off the Energy Impact of Rooftop Units

Smart Monitoring and Diagnostic System field demonstration finds energy saving potential

Cooling off the Energy Impact of Rooftop Units
12.5-ton, two-stage RTU at an office building in Beltsville, MD, after installing the Hardware SMDS (outlined in red)

Packaged air conditioners and heat pumps—referred to as rooftop units (RTUs)—frequently operate well below peak efficiencies. Most RTUs are aged and not well maintained—a major issue for the 2.1 million buildings in the United States that use them. RTUs consume the equivalent of enough energy to power nearly 17 million homes each year.

New technology called the Smart Monitoring and Diagnostic System (SMDS) can continuously monitor the performance and condition of RTUs, a capability that did not exist until now. Integrating SMDS reduces operating costs by up to 30 percent and extends the RTU lifetime by several years.

Smart Solution

Developed by PNNL for DOE's Building Technologies Office, in collaboration with NorthWrite, Inc. and Universal Devices, the SMDS is a low-cost, retrofitable technology that can be applied to new and existing RTUs. It provides meaningful information on performance degradation and energy consumption so that building owners can make informed decisions regarding when to have the equipment serviced.

To test detection capabilities, the SMDS prototypes were installed at field locations in Maryland, New York, and Puerto Rico. The prototypes successfully identified both degradation and operational faults, and were able to quantify electricity use associated with the performance degradation, as documented in the DOE report. The field demonstrations found 4,200 kWh of energy losses due to RTU performance, and $511 in utility costs over the study period (61-121 days at the various sites).

There are two SMDS types:

  • Hardware SMDS—consists of a hardware package that is installed on each RTU. It provides data collection, detection of performance degradation and operational faults, and local wireless communication to a wireless router and Internet access point, which communicates results to a network operations center.
  • Cloud SMDS—uses off-the-shelf components for sensing and data collection and a commercially available cell modem to transmit the raw sensor measurements to a Cloud service. Data are stored and managed in the Cloud, where the SMDS algorithms process the data, and a web server makes the results available to authorized users.

The SMDS detects issues and alerts building owners, staff, and authorized maintenance providers through a web-based interface. Authorized users can access information about their RTUs from any computing device with a web connection, staying informed on RTU condition and the impact of faults and degradation, including the energy cost.

Next Steps

PNNL and DOE are further developing the SMDS technology, and seeking partners for further testing and deployment. For more information, visit the Better Buildings website.

PNNL Research Staff: Michael Brambley, Danny Taasevigen, Lucy Huang, Robert Lutes, Spencer Gilbride, and Linda Sandahl

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