Conservation Minnesota

Multifamily Buildings: Locking in Savings

Posted by Helen Booth-Tobin
CEE’s research team explores and identifies cost-effective energy efficiency measures to improve utility programs and related policy efforts. We conduct field research in buildings ranging from homes to high-rise office towers, analyzing valuable data on the energy savings and performance characteristics of energy upgrades. Among our recent research projects, CEE’s team has been looking closely at a relatively new approach to cut energy waste and improve comfort for thousands of Minnesota families.

In recent years, Minnesota has seen a boom in multifamily housing, which includes all residential buildings that provide separate living spaces for more than one family (i.e., apartments and condos). Multifamily housing is inherently energy efficient, using about half the energy of single-family housing — but there is still room to reduce air leakage that wastes energy due to excessive heating and cooling.

A building’s “envelope” is the divider that separates the conditions inside from the conditions outside. Tight exterior envelopes have become standard for modern single-family homes, but these construction practices have not yet reached the multifamily sector. Multifamily buildings have many of the same pathways for leakage as houses, plus additional paths hidden in walls or other cavities that are difficult to seal with conventional methods. Fortunately, a new aerosol sealant method provides a cost-effective way to generate energy savings and reduce envelope air leakage in multifamily buildings.

Built on established approach, sealing does more for multifamily

The aerosol technology has been used for more than 15 years for duct sealing. UC Davis Western Cooling Efficiency Center (WCEC) staff modified the duct sealing technology for building envelope sealing. Building on their successes with single-family structures, the team at WCEC developed a system specifically for multifamily envelope applications. The approach shows potential to be more effective and convenient than traditional sealing methods, because it requires less time and effort to seal a larger area more quickly. The method can be used both in new construction and in existing buildings with finished surfaces.

In addition to energy benefits from better managed heating and cooling, aerosol sealing also reduces the air-flow transfer of “contaminants” between units — meaning a reduction both in odors and in sound transfer, significantly improving the comfort level of tenants. If you’ve ever lived in an apartment building, you know firsthand that this side-benefit is a major value-add.

Energy saving in action

This year, CEE and WCEC’s field team completed extensive sealing and testing of two newly constructed multifamily buildings. The results illustrate noteworthy successes. One of the buildings reduced leakage by about 78% after aerosol sealing, resulting in the sealed building measuring 87% to 94% tighter than the EPA’sENERGY STAR Multifamily High Rise Program requirement for new construction. (The ENERGY STAR designation was created specifically to improve building quality and occupant comfort while lowering energy demand and reducing air pollution.)

Given the important benefits to tenant comfort, CEE’s researchers also performed tests to document the side effects on sound reduction. Results showed a notable decrease in sound across both interior and exterior walls — particularly for higher frequencies, where human voices typically register.

As a new technology, the aerosol method may be difficult to visualize in action. To help demonstrate how the approach works so well, CEE’s researchers took UV photos (seen in the above image) that capture the volume of small leaks being sealed and those that otherwise would not be seen or reached by caulk or foam sealant. In future, the team also plans to produce a time-lapse video of leakage sites during the sealing process to show how sealant particles build up to seal gaps; in the meantime, they created this helpful animation of the sealing process.

Next steps, from new construction to existing buildings

Aerosol sealing promises positive impacts for utility program managers, contractors, developers, and building owners and managers — not to mention about a million Minnesotans living in multifamily settings.

CEE’s findings of high-savings potential coupled with the low-cost of materials indicate aerosol sealing could be an extremely cost-effective way to reduce air leakage and save energy in multifamily buildings. The reduced air transfer between units will also improve indoor air quality by keeping cooking and smoking odors from permeating other units. And the success of this technology could even change how architects and building developers plan, allowing for reduced “conventional” envelope sealing and potentially cutting overall construction costs without decreasing occupant comfort.

CEE will wrap up its testing of new construction with a third and final property in late September 2015. After that, CEE’s researchers will turn their attention to Minnesota’s existing multifamily dwellings, scheduling several existing properties for sealing and testing later this fall.

Stay tuned for an upcoming video documenting this work, and additional results as they become available!

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