Effect of Thermal Bridging on Buildings' Energy Performance

Comparison of Area-Weighted vs. Additive Thermal Resistance in Facades

Overview

Authors

Photo of Mahsa Farid Mohajer

Mahsa Farid Mohajer

Ph.D. Candidate & Teaching Assistant

University of Massachusetts Amherst

mahsafarid@umass.edu

Photo of Ajla Aksamija

Ajla Aksamija

Associate professor

University of Massachusetts Amherst

aaksamija@umass.edu


Abstract

Heat transfer through building facades can occur by any combinations of conduction, convection, and/or radiation. Conductive heat transfer depends on materials’ thermal conductivity (λ) and thickness (d), which influence building envelope’s thermal resistance (R-value). The most common approach for calculating R-value of building facades is based on the additive method, where material components of the facade in sectional view, their relative thickness and thermal conductivity are considered. However, in order to account for thermal bridging caused by framing, area-weighted approach should be used to determine more accurate R-value. This approach also considers plan view of building facade, and the properties of framing components. The main objective of this research was to investigate the effects of facades’ thermal resistance (additive vs. area-weighted R-values) on buildings’ energy performance. Research methods included data collection, modeling, simulations and comparative analysis of results. An existing Campus Recreation Building on UMASS Amherst campus was used as a case study building. First, the original construction documentation was reviewed to create a 3D model in Revit. Facade material components and specifications were used to determine properties of the opaque facade system, consisting of brick cavity wall with steel stud framing. R-values for this facade system were calculated using additive and area-weighted methods. Then, a building energy analysis simulation program Green Building Studio was used to calculate annual and monthly energy consumption for the case study building, where one energy model was created to analyze the impacts of two different R-values on the overall energy consumption of this building. Other inputs, such as building geometry, occupancy schedules, glazing materials, etc. were identical in both simulation scenarios. Energy modeling results were compared to actual energy consumption data, collected over a period of one year. Simulation results showed that energy consumption, cost, energy usage intensity, carbon emission, and heating loads were higher with area-weighted method, and lower with additive approach.

Introduction

Heat transfer through buildings’ facades significantly impacts buildings’ thermal performance, their energy consumption, energy costs, and carbon emissions. Therefore, it is essential to provide an appropriate level of insulation, thus

Members Only

Background

Heat transfer mechanisms include conduction, convection, and radiation. In conduction, heat travels through solid materials. In convection, heat circulates within the building through liquids and gases, and in radiation, heat

Members Only

Research Questions and Methods

The research objectives of this study were to compare area-weighted vs. additive R-values of a facade assembly, and to quantify their effects on various performance aspects of the building. The

Members Only

Analysis Results and Comparison

Analysis model was extracted as gbXML file from Revit, and uploaded into GBS in order to prepare for the simulation runs. The first simulation design alternative captured monthly and annual

Members Only

Conclusion and Future Work

Actual energy consumption data was a representation of energy usage based on weather data specific to only one-year cycle. In contrast, simulation results captured energy consumption based on typical metered

Members Only

Rights and Permissions

Aksamija, Ajla. 2013. Sustainable Facades: Design Methods for High-Performance Building Envelopes. Hoboken, NJ: John Wiley & Sons, Inc.

ASHRAE. 2013a. ANSI/ASHRAE Standard 62.1 Ventilation for Acceptable Indoor Air Quality. Atlanta: ASHRAE.

ASHRAE. 2013b. ASHRAE Handbook: Fundamentals. Atlanta: ASHRAE.

ASHRAE. 2016. ANSI/ASHRAE Standard 90.1 Energy Standard for Buildings Except Low-Rise Residential Buildings. Atlanta: ASHRAE.

Berggren, Björn, and Maria Wall. 2013. “Calculation of Thermal Bridges in (Nordic) Building Envelopes - Risk of Performance Failure Due to Inconsistent Use of Methodology.” Energy and Buildings 65: 331–39. https://doi.org/10.1016/j.enbu... Mohajer, Mahsa, and Ajla Aksamija. 2019. “Integration of Building Energy Modeling (BEM) and Building Information Modeling (BIM): Workflows and Case Study.” In Building Technology Educators’ Society Conference. Amherst, MA.

Grondzik, Walter T., Alison G. Kwok, Benjamin Stein, and John S. Reynolds. 2015. Mechanical and Electrical Equipment for Buildings. Edited by Eleventh. Hoboken: John Wiley & Sons, Inc.

Hens, Hugo, Arnold Janssens, Wim Depraetere, and Jan Carmeliet. 2007. “Brick Cavity Walls: A Performance Analysis Based on Measurements and Simulations.” Journal of Building Physics 31 (2): 95–124. https://doi.org/10.1177/1744259107082685.

Kotti, Stella, Despoina Teli, and P.A.B. James. 2017. “Quantifying Thermal Bridge Effects and Assessing Retrofit Solutions in a Greek Residential Building.” Procedia Environmental Sciences 38: 306–13. https://doi.org/10.1016/j.proenv.2017.03.084.

Lawton, Mark, Patrick Roppel, David Fookes, Anik Teasdale, and Daniel Schoonhoven. 2010. “Real R-Value of Exterior Insulated Wall Assemblies.” Proceedings of the BEST2 Conference: Building Enclosure Science and Technology, 26.

Parliament, European. 2010. “Directive 2010/31/EU of the European Parliament and of the Council of 19 May 2010 on the Energy Performance of Buildings.” Journal of the European Union, 13–35.

Theodosiou, Theodoros G., and Agis M. Papadopoulos. 2008. “The Impact of Thermal Bridges on the Energy Demand of Buildings with Double Brick Wall Constructions.” Energy and Buildings 40 (11): 2083–89. https://doi.org/10.1016/j.enbuild.2008.06.006.

Theodosiou, Theodoros G., Aikaterini G. Tsikaloudaki, Karolos J. Kontoleon, and Dimitrios K. Bikas. 2015. “Thermal Bridging Analysis on Cladding Systems for Building Facades.” Energy and Buildings 109: 377–84. https://doi.org/10.1016/j.enbuild.2015.10.037.