Description:
Today, there are an estimated 8 billion square meters of commercial building space in the U. S., which consume 19 % of the energy used in the U. S. [1]. A report by the U. S. Department of Energy estimates that reducing air leakage through the exterior envelope of commercial buildings could result in energy savings of over 800 TBtu U. S.-wide by 2030 (5 % of the energy consumed by commercial buildings in 2014) [2]. Leaky building exteriors also lead to moisture issues inside wall cavities and building interiors, which can affect the integrity of the building envelope and the health of the occupants [3, 4]. However, barriers to making improvements in building envelope airtightness include not knowing a building’s current airtightness and thus not knowing how much energy (and thus money) one could save by investing in airtightness improvements. The current primary technique for determining building envelope airtightness is the building pressurization test, which is standardized in the American Society of Testing and Materials (ASTM) Standard E779-10 [5]. However, many building owners, tenants, and other stakeholders choose not to conduct this test because of the cost, time, and disruption to day-to-day building operations. It has also been shown that building envelope airtightness does not correlate to building age or construction characteristics [6].
Another method to determine building envelope airtightness is to use building energy models calibrated by utility data. Changes to equipment operation and efficiency, and to occupant usage are made in the model to reflect differences between design assumptions and operating conditions (e.g. [7]). When significant differences still exist after these changes are made, they are attributed to unknowns in the input parameters, such as building envelope airtightness. This value may be then adjusted using engineering expertise. However, it is difficult to know whether the airtightness value identified during the calibration process is the actual value or merely one that matches the modeling results and utility data.
Thus, a novel method is needed to determine building envelope airtightness that would be attractive to building owners and tenants. Such a method should be lower in cost, time, and effort and be less disruptive than the current best available technology, i.e., building pressurization testing. It should also provide a building envelope airtightness value with more confidence than calibrating energy models to coarse utility data. The new method should be accessible to the entire building industry. A commercial product that can deliver envelope airtightness values to clients would be crucial when faced with choosing whether or not to make capital investments to increase of airtightness. It would also allow building energy modelers to increase the confidence in their model results since infiltration is the one of the largest sources of the uncertainty [8].
The adoption of such a method has the potential to improve the airtightness and energy usage of innumerable commercial buildings. In addition, improved airtightness can prolong the life of buildings reducing or eliminating moisture migration into the building. The development of a method to easily determine building envelope airtightness would serve NIST in satisfying its goal by advancing the measurement science in this field. It would also serve the U. S. in reaching its goals to reduce reliance on oil and improve energy security [9].
The method developed to determine building envelope airtightness should be lower in cost, time, and effort and be less disruptive to normal operations compared to currently available technology. It should also provide a building envelope airtightness value with more confidence than calibrating to coarse utility data. It should be a method that can be used in a variety of building types including, but not limited to, stand-alone, those with shared walls, single story, and skyscrapers. The airtightness values determined by such a method should include bounds of uncertainty and be validated with pressurization test results. The method should be demonstrated in actual commercial buildings, with both multizone airflow and energy models of the buildings developed to support future research.
Phase I expected results:
Develop a literature review or market research demonstrating their knowledge of the state of the art in sensors and approaches to determining building envelope airtightness that could be commercialized. Present the details of the proposed feasibility study (or studies) that have high potential to address the need for novel methods to determine building envelope airtightness in commercial buildings. Report the results of their study (or studies), including sensitivity and uncertainty analyses in the Phase I final report.
Phase II expected results:
Provide a schedule to the NIST technical expert on how the method will be developed from Phase I to a final product. Select 3 or more commercial buildings for field testing (to be approved by the NIST technical expert) and obtain written consent to perform building envelope airtightness testing in order to validate the method developed. Identify plans to bring the method to the commercial marketplace and demonstrate that it is lower in cost, time and effort, and less disruptive to normal operations, compared to currently available technology. Provide a building envelope airtightness value with more confidence than calibrating to coarse utility data.
The NIST technical expert will be available for consultations and discussions to answer questions and clarify any other technical aspects of this effort.
References:
[1] DOE. Building Energy Data Book. 2011 [cited 2014; Available from: http://buildingsdatabook.eren.doe.gov/
[2] DOE, Windows and Building Envelope Research and Development: Roadmap for Emerging Technologies. 2014, U. S. Department of Energy: Washington, D. C.
[3] Bomberg, M., Kisilewicz, T. and Nowak, K. “Is there an optimum range of airtightness for a building?”, Journal of Building Physics, 2015.
[4] IOM, “Damp Indoor Spaces and Health”, I.o. Medicine, Editor. 2004, The National Academies Press: Washington, D.C.
[5] ASTM, ASTM E779-10 Standard Test Method for Determining Air Leakage Rate by Fan Pressurization. 2010, American Society of Testing and Materials: Philadelphia.
[6] Emmerich, S.J. and Persily, A.K. “Analysis of U. S. Commercial Building Envelope Air Leakage Database to Support Sustainable Building Design”, International Journal of Ventilation, 2014. 12(4): p. 331-343.
[7] Raftery, P., Keane, M. and Costa, A. “Calibrating whole building energy models: Detailed case study using hourly measured data”, Energy and Buildings, 2011. 43(12): p. 3666-3679.
[8] Hopfe, C.J. and Hensen, J.L.M. “Uncertainty analysis in building performance simulation for design support”, Energy and Buildings, 2011. 43(10): p. 2798-2805.
[9] Obama, B., “The President's Climate Action Plan”, 2013: Washington, D. C.
