Reducing Energy Loss in B-Huts

Pressure-sensitive air sealing tapes have the potential to keep the building enclosure sealed and could reduce the operational energy needed to heat and cool when used on plywood-toplywood building envelope seams on temporary U.S. Army shelters in theater.

 

 By Megan Kreiger, Jedediah Alvey and Dahtzen Chu

 


 

B-Hut taped

B-Huts are wood-framed shelters used by the U.S. Army in contingency environments. Researchers at the U.S. Army Engineer Research & Development Center – Construction Engineering Research Laboratory evaluated how eight types of pressure sensitive air sealing tapes sealed building seams to reduce air leakage. PHOTOS COURTESY ERDC-CERL


  

Temporary wood-framed structures or shelters used by the U.S. Army, such as B-Huts, experience significant air leakage.

This, in turn, causes many issues associated with drafts, occupant comfort and building energy performance. 

The problem of air leakage is not new. Air leakage in residential buildings within the United States accounts for up to 40 percent of energy costs, depending on the climate zone. An effective solution to the problem of air infiltration is to use air-sealing tapes rated for interior or exterior use to seal and reduce the air leakage in a building. When applied to shelters in theater, this can similarly improve operational energy use.

Reducing heating and cooling energy demand over an entire forward operating base would potentially change the amount or size of generators required for power generation, reduce the amount of fuel being shipped to the site, and reduce the cost of operation. Added benefits of mitigating air leakage include improving the quality of living, reducing dust and pests entering the shelter, and curtailing water penetration (depending on the type of tape used).

 

ADDRESSING THE ISSUE

Air, like a fluid, will exit a building through the path of least resistance, which would be any holes in the enclosure. After sealing these holes, the next concern would be to keep this fluid from penetrating into the wall surface. The solution to this would be house wrap. However, plywood fills this role as it only requires a thickness of 0.374- in to have a non-measurable amount of airflow through the material.

Often, when evaluating buildings and energy, the emphasis is on insulation. Unfortunately, insulation many times is impractical in temporary structures due to the short building life (three to five years) and shipping and disposal issues in theater. The absence of insulation leads to air leak­age playing an even larger role in energy demand. Air-sealing tapes require a very small amount of shipping and disposal volume. Many tapes are packaged with shrink-wrap and liners on the adhesive side to reduce destruction during shipping.

While building seams may be an obvi­ous source of air leakage, any places where infiltration occurs need to be sealed, such as where utilities enter, or through the light fixture opening. In fact, some of the largest infiltration areas may be hidden by light fixtures or other objects that need to be moved before applying tape. Depending on the type of tape chosen for air sealing, it may be used on the structure’s interior occupied space or exposed exterior side.

 

TESTING THE TAPES

Researchers with the U.S. Army Engineer Research & Development Center – Construction Engineering Research Laboratory (CERL) conducted testing from September 2013 through May 2014 to evaluate the performance of which tapes would perform well on the exterior side of a shelter. Researchers tested exte­rior air-sealing tapes for performance in sealing joints between plywood panels in temporary wood-framed structures used by the Army. Outdoor exposure testing was performed in conjunction with in-lab accelerated aging and pressure chamber tests at CERL. Out of the eight initial tapes, two were selected as the top performers under the exposure conditions.

 

Many of the tapes tested, including the top performers, were suitable for both inte­rior and exterior application. The recom­mended type of tape for this application has a polymer backing and an acrylic adhesive, which has the added benefit of a low volatile organic compound level.

B-Hut test shelter

B-Huts have a high amount of air leakage, which can cause issues associated with drafts, comfort and energy performance. Using pressure-sensitive air sealing tapes in interior or exterior plywood-toplywood seams can help to raise the quality of living for soldiers, keep the building enclosure sealed, and reduce the operational energy or fuel required to heat and cool temporary buildings in theater.


 

EXPERIMENTAL SHELTER

At the Experimental Forward Operating Base at CERL’s campus in Champaign, Ill., a shelter modeled after B-Huts was sealed to show the reduction of air leakage using air barrier tapes. It was built by contrac­tors using materials within the continental United States and was assumed to have air tightness greater than those constructed in the limited conditions of an actual forward operating base. It had no vents and was heated using a mini-split heat pump, which re-circulates the air—a mechanism often used in Afghanistan. Since the tapes show­ing the least degradation also were suitable for internal use, to reduce their amount of environmental degradation, the internal seams and infiltration areas of the structure were taped, and the structure was subjected to blower door tests. The B-Hut, measuring 16-ft by 32-ft by 8-ft, was completely taped for $500 in supplies. The taping was done by researchers with no previous experience taping building enclosures; they relied on manufacturer guidelines and instruction from online resources. The blower door tests were done according to U.S. Army Corps of Engineers air leakage test protocol for building enclosures.

The tape was applied in three steps and tested for air leakage after each one. The first areas taped were around the light fixture penetrations, 90˚ edges, utility penetrations, door frame and outlets, with a resulting air leakage of 0.313 cfm/ft². This initial step took the longest, with two people working for three hours, in addition to an extra 1.5 hours required to remove and reattach the light fixtures (tape was applied post-construction) for a total of 10 work hours. Ceiling-ceiling seams and wall-wall seams were sealed next, reducing an air leakage to 0.124 cfm/ft². Despite the large amount of surface area covered during this step, it only took three hours to complete. The last areas sealed were the floor-floor seams, which dropped the air leakage down to 0.041 cfm/ft². The entire time it took to tape the shelter was 14.5 hours of work, a duration that would likely be reduced through experience and taping during construction of the shelter.

 

EVALUATING RESULTS

Applying tape reduced total air leak­age from 0.615 cfm/ft² to 0.041 cfm/ft². The majority of the remaining air leakage occurs along the only seam left unsealed: the door. Since these doors are made on site, they have a high amount of air and water infiltration as they are unable to seal well.

To reduce air infiltration through the doors, pre-hung doors should be used for the entrances. The air leakage coefficients were incorporated in building energy performance simulation software (Energy Plus). The simulation results showed that sealing the structure with tape can have an estimated savings of up to 79 percent of the energy consumed by heating and cooling, depending on the structure and climate. The building is so air-tight that the shelter, after fully taping, would require proper ventilation considerations.

Use of pressure-sensitive air sealing tape in plywood-to-plywood seams has the potential to dramatically reduce air leak­age in a building. This not only applies to temporary Army structures but to more sophisticated structures as well.

 

EFFECTIVE AND APPLICABLE

Implementing air sealing tapes on tempo­rary wood-framed structures is inexpen­sive. It requires only a small amount of time and no previous training or experience.

Pressure-sensitive air sealing tapes in interior or exterior plywood-to-plywood seams have the potential to raise the qual­ity of living for soldiers, keep the building enclosure sealed, and reduce the opera­tional energy or fuel usage required to heat and cool temporary buildings in theater. 

   


 

Megan Kreiger is a Materials Research Engineer, Jedediah Alvey is a Graduate Research Assistant, and Dahtzen Chu is a General Engineer, U.S. Army Engineer Research & Development Center – Construction Engineering Research Laboratory. They can be reached at 217-373-4564, or This email address is being protected from spambots. You need JavaScript enabled to view it." target="_blank">This email address is being protected from spambots. You need JavaScript enabled to view it.; 217-373-4564, or This email address is being protected from spambots. You need JavaScript enabled to view it." target="_blank">This email address is being protected from spambots. You need JavaScript enabled to view it.; and 217-373-6784, or This email address is being protected from spambots. You need JavaScript enabled to view it." target="_blank">This email address is being protected from spambots. You need JavaScript enabled to view it., respectively. 

J. Lake Lattimore contributed to the research effort at CERL.