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APPLICATION OF INFRARED THERMOGRAPHY ON THE IN-SITU MEASUREMENT OF BUILDING ENVELOPE THERMAL PROPERTIES
Abstract
Building energy consumption accounts for about 40% of the total energy consumption in the U.S., and therefore approaches that can reduce building energy demand are of great interest. The building envelope system is one of the main elements in buildings that can be improved for better building energy performance, and it also plays a significant role in building energy simulation. The thermal resistance, i.e., the R-value, is the key thermal parameter for building envelope systems contributing to the whole building energy performance. While the R-value has been long introduced in the building science field, however, there is still a lack of sufficient research work in understanding its influence on the whole building energy simulation process and results. In particular, there is serious need for experimental methods to determine the real R-values for existing buildings in order to obtain the actual building performances instead of the theoretical values.
The primary goal of this proposed research is to develop a quantitative infrared thermography approach to measure the R-values for building envelope systems on site. Achieving this would provide the industry with a more practical and faster alternative to measure the R-values for existing buildings. Traditionally, to measure the real R-value of building envelope systems, Hot
Box Test Method is used in laboratory to measure building envelope mock-up assemblies. However, the Hot Box Test Method requires large testing facilities and also an envelope component to test, which will not be practical when measurements of existing buildings are of concern. Compared to new construction, for existing buildings, in-situ measurement of the building envelope thermal properties may be essential since in most cases drawings and details may not be known. The Heat Flow Meter Method is the generally known technique for in-situ
measurement, which involves the use of a number of sensors and portable data acquisition systems. However, due to the unsteady natural conditions, the accuracy of Heat Flow Meter Method is not completely understood yet. To consider the influence of unsteady environmental conditions, some dynamic methods have been developed. The dynamic methods are so far not widely known or commonly used for in-situ measurement as their accuracies and performances are not completely explored.
The infrared thermography has long been used for building diagnosis purposes to detect surface imperfections, moisture issues, air leakage and thermal bridge locations. Even though it has served as a powerful diagnosis tool for years, its application still remains qualitative and the interpretation of the image results can be somewhat confusing. However, the capability that infrared camera can catch the temperature distribution on the entire surface gives us the potential to use it as a quantitative tool for in-situ measurement of building envelope thermal properties. This research is focused on the development and validation of a quantitative methodology using infrared thermography for in-situ measurement. Several key difficulties, such as the exterior radiation and convection model, interpretation of infrared images and measurement of environmental conditions are discussed and explored. The results of this study can serve as a quick and effective tool for engineers and researchers to measure thermal properties of existing buildings, and therefore provide appropriate inputs for building energy simulation and energy retrofit.
This research has been carried out through accomplishing several objectives. Initially, the influence of R-values for building envelope systems in the whole-building simulation process was studied, especially the detailed modelling approaches for several common techniques to improve the building envelope performance such as adding insulation materials and using advanced building envelope system types. This initial study helped better understand the importance of obtaining the realistic R-values instead of the “design values”. The next objective was to explore the existing methods to measure the building envelope R-values, using both the Hot Box Test Method and the Heat Flow Meter Method. By comparing the existing test methods and models, the most appropriate one can be used for on-site application to validate the results of infrared thermography method developed in this research. The final objective was to develop a quantitative infrared thermography testing method and calculation model that can be used for in-situ R-value measurement as a quick and practical tool.
Table of Content
List of Figures……………………………………………………………………………………………………………… xiii
List of Tables………………………………………………………………………………………………………………. xvii
Acknowledgement…………………………………………………………………………………………………………. xx
Chapter 1. Introduction ……………………………………………………………………………………………………. 1
1.1 Overview of the Research Work ………………………………………………………………………………. 1
1.2 Scope and Limitations…………………………………………………………………………………………….. 4
1.3 Organization of the Dissertation ………………………………………………………………………………. 5
Chapter 2. Literature Review ……………………………………………………………………………………………. 7
2.1 The Importance of R-values …………………………………………………………………………………….. 7
2.2 Measurement of R-values ……………………………………………………………………………………….. 8
References ………………………………………………………………………………………………………………… 10
Chapter 3. Objectives and Tasks ……………………………………………………………………………………… 12
3.1 Introduction …………………………………………………………………………………………………………. 12
3.2 Objectives and Tasks Outline ………………………………………………………………………………… 13
3.3 Further Explanation of the Tasks ……………………………………………………………………………. 14
3.3.1 Tasks for Objective #1 ……………………………………………………………………………………. 14
3.3.2 Tasks for Objective #2 ……………………………………………………………………………………. 16Chapter 4. Building Insulation Materials ………………………………………………………………………….. 18
4.1 Introduction …………………………………………………………………………………………………………. 19
4.2 Literature Review…………………………………………………………………………………………………. 20
4.2.1 Cellulose Fiber ………………………………………………………………………………………………. 20
4.2.2 Mineral Wool Insulation …………………………………………………………………………………. 21
4.2.3 Rigid board insulation …………………………………………………………………………………….. 21
4.2.4 Vacuum Insulation Panels……………………………………………………………………………….. 22
4.2.5 Phase Change Materials ………………………………………………………………………………….. 23
4.2.6 Aerogel …………………………………………………………………………………………………………. 23
4.2.7 Life Cycle Assessment ……………………………………………………………………………………. 24
4.3 Energy Performance Simulation …………………………………………………………………………….. 25
4.3.1 Model Characteristics …………………………………………………………………………………….. 25
4.3.2 Insulation Properties ………………………………………………………………………………………. 26
4.3.3 Wall Section ………………………………………………………………………………………………….. 27
4.3.4 BEopt Result and Discussion …………………………………………………………………………… 29
4.4 WUFI Analysis ………………………………………………………………………………………………… 33
4.4.1 Introduction to WUFI Analysis ……………………………………………………………………….. 33
4.4.2 WUFI Results and Discussions ………………………………………………………………………… 34
4.5 Life Cycle Assessment ………………………………………………………………………………………….. 38
4.5.1 Introduction to Life Cycle Assessment ……………………………………………………………… 38
4.5.2 Results of Life Cycle Assessment …………………………………………………………………….. 39
4.6. Discussions and Conclusions ………………………………………………………………………………… 40
References ………………………………………………………………………………………………………………… 42
Chapter 5. Advanced Building Envelope Systems …………………………………………………………….. 45
5.1 Introduction …………………………………………………………………………………………………………. 46
5.2 Literature Review…………………………………………………………………………………………………. 46
5.2.1 Energy Performance of Residential Building Envelope Systems ………………………….. 46
5.2.2 Selected Innovative Building Envelope Systems ……………………………………………….. 51
5.3. Methodology ………………………………………………………………………………………………………. 58
5.3.1 Model Characteristics …………………………………………………………………………………….. 58
5.3.2 Wall Assemblies ……………………………………………………………………………………………. 60
5.3.3 Energy Simulation Model ……………………………………………………………………………….. 70
5.4. Result and Analysis……………………………………………………………………………………………… 72
5.4.1 Results and Discussions (Boston) …………………………………………………………………….. 72
5.4.2 Validation of Results………………………………………………………………………………………. 82
5.5. Life Cycle Assessment …………………………………………………………………………………………. 86
5.6. Summary and Conclusions …………………………………………………………………………………… 90
Reference …………………………………………………………………………………………………………………. 93
Chapter 6. Measurement of R-value in Laboratory: Hot Box Test……………………………………….. 97
6.1 Introduction …………………………………………………………………………………………………………. 98
6.2 Literature Review…………………………………………………………………………………………………. 98
6.2.1 Hot Box Test Method……………………………………………………………………………………… 98
6.2.2 Dynamic Calculation Models ………………………………………………………………………… 102
6.3 Experimental Setup …………………………………………………………………………………………….. 105
6.3.1 BETL Hot Box Chamber ………………………………………………………………………………. 105
6.3.2 Specimen Construction …………………………………………………………………………………. 106
6.3.3 Data Acquisition System (DAQ) ……………………………………………………………………. 107
6.3.4 Example of Temperature and Heat Flux Measurement ……………………………………… 107
6.4. Methodology …………………………………………………………………………………………………….. 109
6.4.1 Anderlind’s Multiple Regression Model …………………………………………………………. 109
6.4.2 R-C Network Model …………………………………………………………………………………….. 111
6.5 Results and Discussion ……………………………………………………………………………………….. 114
6.5.1 Example of R-C Network Model ……………………………………………………………………. 115
6.5.2 Calculation of R-value ………………………………………………………………………………….. 117
6.6 Summary and Conclusion ……………………………………………………………………………………. 125
Reference ……………………………………………………………………………………………………………….. 127
Chapter 7. The Dynamic Models for R-value Determination…………………………………………….. 131
7.1 Introduction ……………………………………………………………………………………………………….. 132
7.2 Dynamic Models ………………………………………………………………………………………………… 134
7.2.1 The Average Model ……………………………………………………………………………………… 136
7.2.2 Pentaur Model ……………………………………………………………………………………………… 137
7.2.3 R-C Network Models ……………………………………………………………………………………. 138
7.3 Experimental Setup …………………………………………………………………………………………….. 141
7.4 Result and Discussion …………………………………………………………………………………………. 144
7.5 Summary and Conclusions ………………………………………………………………………………….. 153
Reference ……………………………………………………………………………………………………………….. 155
Chapter 8. Measurement of the Convective Heat Transfer Coefficient ……………………………….. 158
8.1 Introduction ……………………………………………………………………………………………………….. 159
8.2 Literature Review……………………………………………………………………………………………….. 160
8.3 Methodology ……………………………………………………………………………………………………… 165
8.4 Experimental Setup …………………………………………………………………………………………….. 170
8.4.1 The Tested Building ……………………………………………………………………………………… 170
8.4.2 Equipment …………………………………………………………………………………………………… 172
8.5 Results and Discussion ……………………………………………………………………………………….. 174
8.6 Summary and Conclusions ………………………………………………………………………………….. 185
References ………………………………………………………………………………………………………………. 187
Chapter 9. Development and Validation of An Innovative Outdoor Infrared Thermography Method
to Measure the Building Envelope R-values …………………………………………………………………… 191
9.1 Introduction ……………………………………………………………………………………………………….. 192
9.2 Literature Review……………………………………………………………………………………………….. 194
9.3 Methodology ……………………………………………………………………………………………………… 205
9.3.1 Testing Site and Facilities ……………………………………………………………………………… 205
9.3.2 Measurement of Convective Heat Transfer Coefficient …………………………………….. 207
9.3.3 The Night Sky Cooling Effect ……………………………………………………………………….. 210
9.3.4 Measurement of Surface Emissivity ……………………………………………………………….. 212
9.3.5 Infrared Thermography Model Basis ………………………………………………………………. 214
9.3.6 Measurement of Interior and Exterior Air Temperatures …………………………………… 216
9.3.7 Determination of Reflected Temperature ………………………………………………………… 218
9.3.8 HFM Method Validation……………………………………………………………………………….. 219
9.4 Results and Discussions ………………………………………………………………………………………. 221
9.5 Conclusions ……………………………………………………………………………………………………….. 227
References ………………………………………………………………………………………………………………. 229
Chapter 10. Validation of the Indoor Infrared Thermography Method to Measure the Building
Envelope R-values ………………………………………………………………………………………………………. 235
10.1 Introduction ……………………………………………………………………………………………………… 236
10.2 Literature Review……………………………………………………………………………………………… 238
10.3 Methodology ……………………………………………………………………………………………………. 242
10.3.1 Model Characterization ……………………………………………………………………………….. 242
10.3.2 Testing Site and Facilities ……………………………………………………………………………. 244
10.3.3 Measurement of the Surface Emissivity and the Reflected Temperature ……………. 245
10.3.4 HFM Measurement …………………………………………………………………………………….. 247
10.4 Results and Discussion ……………………………………………………………………………………… 248
10.5 Recommended Step-by-Step Procedure for Indoor IRT Method …………………………….. 251
10.6 Conclusions ……………………………………………………………………………………………………… 252
References ………………………………………………………………………………………………………………. 254
Chapter 11. Summary and Conclusions ………………………………………………………………………….. 258
11.1 Outcomes ………………………………………………………………………………………………………… 258
11.2 Further Discussion on Practical Aspects and Limitations ………………………………………. 264
11.3 Research Conclusions and Contributions …………………………………………………………….. 265
11.4 Potential Future Research Work …………………………………………………………………………. 267
Chapter 1. Introduction
1.1 Overview of the Research Work
The energy consumption of the U.S. residential buildings accounts for 22% of the total energy use, with about 42% due to heating and cooling loads. With increasing demand for energy saving in the building sector in recent years, any technique that can demonstrate a reduction in building energy consumption is highly desirable. One of the effective ways to decrease the energy used by space heating and cooling is to improve the performance of building envelopes, which account for 36% of the overall building energy consumption due to heat gain and loss.
There are many solution methods applicable to building envelope systems to enhance energy efficiency. Using more advanced building insulation materials and high-performance building envelope systems seem to be the two most effective approaches. To better understand the performance of building insulation materials and different types of building envelope systems, building energy simulation is necessary to quantify their effectiveness. The insulation materials explored in the initial part of this study include conventional materials such as Cellulose Fiber, Mineral Wool, Rigid Board Insulation, and innovative materials such as Vacuum Insulation Panel, aerogel and Phase Change Materials. The building envelope systems discussed in this study include standard wood frame wall, Advanced Framing, Insulated Concrete Forms, Structural Insulated Panels and Exterior Insulation and Finish System. Building energy simulation tools such as BEopt and DesignBuilder were used to compare the results.
For the building energy simulation process, the thermal resistance (R-value) of the building envelope systems is one of the most important parameters in modeling. The difference in R-value
inputs can result in significantly different energy simulation results. Therefore, for more accurate simulation results, the real properties of building envelope systems are of great interest. However, the theoretical R-values of building envelope systems available from the manufacturer documentation can be very different from the real R-values. To obtain the real R-values, it is essential to measure the building envelope thermal resistance instead of just using the documented values.
Hot Box Test Method has been used as a reliable method for measurement of thermal properties of building materials and envelope assemblies in the U.S. for decades. By using two environmental chambers to simulate both the indoor and outdoor conditions, the tested building envelope assemblies located in the middle of the two chamber can be measured under quasi steady-state conditions. Hot Box Test Method can provide accurate results; however, it also has apparent limitations. The use of such method requires large testing facilities and building envelope mockup assemblies. When measurements of existing buildings are desired, such limitation can cause great difficulties. Also, this method generally requires relatively long testing periods.
When building energy simulation or energy retrofit is required for existing buildings, in-situ measurement of the building envelope thermal properties is needed. The Heat Flow Meter Method can be used by mounting a number of temperature and heat flux sensor on both surfaces of the wall. Unlike laboratory conditions, the environment on site is usually far from being steady-state. To solve this issue, several dynamic methods have been developed such as the Anderlind’s Method and the R-C Network Method. It should be noted that as the Heat Flow Meter Method is based on point measurement, the measured R-value may not represent the overall building envelope performance, as the existence of thermal bridges will lower the clear-wall R-value. Moreover, the Heat Flow Meter Method involves the use of portable data acquisition systems, and the user should be careful about the measurement of heat flux measurement due to the high sensitivity of the heat flux sensors.
The infrared thermography has long been used in building sector for diagnosis purposes to detect thermal bridge locations, air leakage, moisture issues and cold spots. It is mostly used as a qualitative tool to help engineers and researchers find where the problem is in the building envelope systems during field measurement. However, as the infrared camera provides a complete temperature profile for the entire surface, it also has the potential to be used as a quantitative tool to measure the building envelope thermal properties on site. The final goal of this study is then focused on the development and validation of a quantitative approach to measure building envelope thermal properties by infrared thermography.
The multiple areas of study and research for this work include building insulation materials, building envelope system modeling, laboratory testing, field measurement, data acquisition, heat transfer analysis in building envelope systems and building energy simulation. Hence, the following topical areas are selected for detailed study in order to identify state-of-the-art advances and related shortcomings and issues.
- Building insulation materials
- Advanced building envelope systems
- Measurement of R-value in laboratory by hot box test and the dynamic models for Rvalue determination
- In-situ measurement of R-value by infrared thermography
Detailed introduction of each topic including the respective literature review is provided in the corresponding chapters.
1.2 Scope and Limitations
It is essential to define the scope and limitations of this research for appropriate understanding and implementation of the results. The scope and limitations of this research are described as follows.
- The focus of this research is on low-rise residential buildings, and therefore results and conclusions may not necessarily apply to other building types such as medium-rise or highrise buildings.
- The final goal of this research is to develop an in-situ, quantitative infrared thermography method that can be used to measure the building envelope R-values for existing buildings. This method can serve as a quick and effective tool for engineers and researchers to determine the building envelope R-values in a more practical way. The purpose of developing this infrared thermography method is to aid the building envelope diagnosis, performance evaluation and energy retrofit process.
- Chapter 4 and Chapter 5 include the whole-building energy simulation results for different insulation materials and different building envelope systems in different climate regions. Therefore, the results in these two chapters can be regarded as generalized.
- Results in Chapter 8-10 are obtained specifically from the on-site measurements in State College, Pennsylvania. Therefore, further validation may be needed to apply the models and correlations proposed in these chapters in a different climate region.
1.3 Organization of the Dissertation
This dissertation is in the format of Thesis by Publication (Journal Articles). The first chapter is an overview of the overall research work including the general scope and limitations of this study. Chapter 2 provides a basic literature review on the main areas of this research, while chapter 3 describes the methodology followed for this study consisting of main objectives and tasks. Chapter
4-10 consist of 7 journal papers. Three of these papers presented in Chapter 5, Chapter 6 and Chapter 8 have already been published respectively in “ASCE Practice Periodical on Structural
Design and Construction”, “Energy and Buildings” and “Advances in Building Energy Research”. Two other papers presented in Chapter 4 and Chapter 7 have been accepted for publication (in press), respectively in “International Journal of Architecture, Engineering and Construction” and “Journal of Green Building”. The remaining two papers have been submitted and still in the review process for publication.
The first two papers (Chapter 4 and Chapter 5) serve as the fundamentals for this research to understand the whole-building energy simulation process and the influence of R-value on this process, including detailed discussions about the modeling techniques for building envelope systems in building energy simulation. The papers in Chapters 6 and 7 are the prerequisites for this research exploring the Hot Box Test Method to measure the building envelope R-values in laboratory and several existing dynamic models. The paper in Chapter 8 studies a necessary parameter (the convective heat transfer coefficient) used to develop the quantitative infrared thermography measurement approach. Chapter 9 and Chapter 10 propose the main results of this research including the outdoor and indoor infrared thermography methods. The last chapter (Chapter 11) summarizes the outcomes and contributions of this research and the potential future research work.
