Tag Archives: Infrared Imaging

Simulating geometric thermal bridges using Energy2D

Fig. 1: IR image of a wall junction (inside) by Stefan Mayer
One of the mysterious things that causes people to scratch their heads when they see an infrared picture of a room is that the junctions such as edges and corners formed by two exterior walls (or floors and roofs) often appear to be colder in the winter than other parts of the walls, as is shown in Figure 1. This is, I hear you saying, caused by an air gap between two walls. But not that simple! While a leaking gap can certainly do it, the effect is there even without a gap. Better insulation only makes the junctions less cold.

Fig. 2: An Energy2D simulation of thermal bridge corners.
A typical explanation of this phenomenon is that, because the exterior surface of a junction (where the heat is lost to the outside) is greater than its interior surface (where the heat is gained from the inside), the junction ends up losing thermal energy in the winter more quickly than a straight part of the walls, causing it to be colder. The temperature difference is immediately revealed by a very sensitive IR camera. Such a junction is commonly called a geometric thermal bridge, which is different from material thermal bridge that is caused by the presence of a more conductive piece in a building assembly such as a steel stud in a wall or a concrete floor of a balcony.

Fig. 3: IR image of a wall junction (outside) by Stefan Mayer
But the actual heat transfer process is much more complicated and confusing. While a wall junction does create a difference in the surface areas of the interior and exterior of the wall, it also forms a thicker area through which the heat must flow through (the area is thicker because it is in a diagonal direction). The increased thickness should impede the heat flow, right?

Fig. 4: An Energy2D simulation of a L-shaped wall.
Unclear about the outcome of these competing factors, I made some Energy2D simulations to see if they can help me. Figure 2 shows the first one that uses a block of object remaining at 20 °C to mimic a warm room and the surrounding environment of 0 °C, with a four-side wall in-between. Temperature sensors are placed at corners, as well as the middle point of a wall. The results show that the corners are indeed colder than other parts of the walls in a stable state. (Note that this simulation only involves heat diffusion, but adding radiation heat transfer should yield similar results.)

What about more complex shapes like an L-shaped wall that has both convex and concave junctions? Figure 3 shows the IR image of such a wall junction, taken from the outside of a house. In this image, interestingly enough, the convex edge appears to be colder, but the concave edge appears to be warmer!

The Energy2D simulation (Figure 4) shows a similar pattern like the IR image (Figure 3). The simulation results show that the temperature sensor placed near the concave edge outside the L-shape room does register a higher temperature than other sensors.

Now, the interesting question is, does the room lose more energy through a concave junction or a convex one? If we look at the IR image of the interior taken inside the house (Figure 1), we would probably say that the convex junction loses more energy. But if we look at the IR image of the exterior taken outside the house (Figure 3), we would probably say that the concave junction loses more energy.

Which statement is correct? I will leave that to you. You can download the Energy2D simulations from this link, play with them, and see if they help you figure out the answer. These simulations also include simulations of the reverse cases in which heat flows from the outside into the room (the summer condition).

The National Science Foundation funds large-scale applications of infrared cameras in schools

We are pleased to announce that the National Science Foundation has awarded the Concord Consortium, Next Step Living, and Virtual High School a grant of $1.2M to put innovative technologies such as infrared cameras into the hands of thousands of secondary students. This education-industry collaborative will create a technology-enhanced learning pathway from school to home and then to cognate careers, establishing thereby a data-rich testbed for developing and evaluating strategies for translating innovative technology experiences into consistent science learning and career awareness in different settings. While there have been studies on connecting science to everyday life or situating learning in professional scenarios to increase the relevance or authenticity of learning, the strategies of using industry-grade technologies to strengthen these connections have rarely been explored. In many cases, often due to the lack of experiences, resources, and curricular supports, industry technologies are simply used as showcases or demonstrations to give students a glimpse of how professionals use them to solve problems in the workplace.

Over the last few years, however, quite a number of industry technologies have become widely accessible to schools. For example, Autodesk has announced that their software products will be freely available to all students and teachers around the world. Another example is infrared cameras that I have been experimenting and blogging since 2010. Due to the continuous development of electronics and optics, what used to be a very expensive scientific instrument is now only a few hundred dollars, with the most affordable infrared camera falling below $200.

The funded project, called Next Step Learning, will be the largest-scale application of infrared camera in secondary schools -- in terms of the number of students that will be involved in the three-year project. We estimate that dozens of schools and thousands of students in Massachusetts will participate in this project. These students will use infrared cameras provided by the project to thermally inspect their own homes. The images in this blog post are some of the curious images I took in my own house using the FLIR ONE camera that is attached to an iPhone.

In the broader context, the Next Generation Science Standards (NGSS) envisions “three-dimensional learning” in which the learning of disciplinary core ideas and crosscutting concepts is integrated with science and engineering practices. A goal of the NGSS is to make science education more closely resemble the way scientists and engineers actually think and work. To accomplish this goal, an abundance of opportunities for students to practice science and engineering through solving authentic real-world problems will need to be created and researched. If these learning opportunities are meaningfully connected to current industry practices using industry-grade technologies, they can also increase students’ awareness of cognate careers, help them construct professional identities, and prepare them with knowledge and skills needed by employers, attaining thereby the goals of both science education and workforce development simultaneously. The Next Step Learning project will explore, test, and evaluate this strategy.

SimBuilding on iPad

SimBuilding (alpha version) is a 3D simulation game that we are developing to provide a more accessible and fun way to teach building science. A good reason that we are working on this game is because we want to teach building science concepts and practices to home energy professionals without having to invade someone's house or risk ruining it (well, we have to create or maintain some awful cases for teaching purposes, but what sane property owner would allow us to do so?). We also believe that computer graphics can be used to create some cool effects that demonstrate the ideas more clearly, providing complementary experiences to hands-on learning. The project is funded by the National Science Foundation to support technical education and workforce development.

SimBuilding is based on three.js, a powerful JavaScript-based graphics library that renders 3D scenes within the browser using WebGL. This allows it to run on a variety of devices, including the iPad (but not on a smartphone that has less horsepower, however). The photos in this blog post show how it looks on an iPad Mini, with multi-touch support for navigation and interaction.

In its current version, SimBuilding only supports virtual infrared thermography. The player walks around in a virtual house, challenged to correctly identify home energy problems in a house using a virtual IR camera. The virtual IR camera will show false-color IR images of a large number of sites when the player inspects them, from which the player must diagnose the causes of problems if he believes the house has been compromised by problems such as missing insulation, thermal bridge, air leakage, or water damage. In addition to the IR camera, a set of diagnostics tools is also provided, such as a blower-door system that is used to depressurize a house for identifying infiltration. We will also provide links to our Energy2D simulations should the player become interested in deepening their understanding about heat transfer concepts such as conduction, convection, and radiation.

SimBuilding is a collaborative project with New Mexico EnergySmart Academy at Santa Fe. A number of industry partners such as FLIR Systems and Building Science Corporation are also involved in this project. Our special thanks go to Jay Bowen of FLIR, who generously provided most of the IR images used to create the IR game scenes free of charge.

Comparing two smartphone-based infrared cameras

Figure 1
With the releases of two competitively priced IR cameras for smartphones, the year 2014 has become a milestone for IR imaging. Early in 2014, FLIR unveiled the $349 FLIR ONE, the first IR camera that can be attached to an iPhone. Months later, a startup company Seek Thermal released a $199 IR camera that has an even higher resolution and is attachable to most smartphones. In addition, another company Therm-App released an Android mobile thermal camera that specializes in long-range night vision and high-resolution thermography, priced at $1,600. The race is on... Into 2015, FLIR announced a new version of FLIR ONE that supports both Android and iOS and will probably be even more aggressively priced.

Figure 2
All these game changers can take impressive IR images just like taking conventional photos and record IR videos just like recording conventional videos, and then share them online through an app. The companies also provide a software developers kit (SDK) for a third party to create apps linked to their cameras. Excited by these new developments, researchers at several Swedish universities and I have embarked an international collaboration towards the vision that IR cameras will one day become as necessary as microscopes in science labs.

To test these new IR cameras, I did an easy-to-do experiment (Figure 1) that shows a paradoxical warming effect on a piece of paper placed on top of a cup of (slightly cooler than) room-temperature water. This seemingly simple experiment actually leads to very deep science at the molecular level, as blogged before.

I took images using FLIR ONE (Figure 2) and SEEK (Figure 3), respectively. These images are shown to the right for comparison. As you can see, both cameras are sensitive enough to capture the small temperature rise caused by water absorption and condensation underside the paper.

The FLIR ONE has a nice feature that contextualizes the false-color IR image by overlaying it on top of the edges (where brightness changes sharply) of the true-color image taken at the same time by the conventional camera of the smartphone. With this feature, you can see the sharp edges of the paper in Figure 2.

The time of infrared imaging in classrooms has arrived

At the Consumer Electronics Show (CES) 2014, FLIR Systems debuted the FLIR ONE, the first thermal imager for smartphones that sells for $349. Compared with standalone IR cameras that often cost between $1,000 and $60,000, this is a huge leap forward for the IR technology to be adopted by millions.

With this price tag, FLIR ONE finally brings the power of infrared imaging to science classrooms. Our unparalleled Infrared Tube is dedicated to IR imaging experiments for science and engineering education. This website publishes the experiments I have designed to showcase cool IR visualizations of natural phenomena. Each experiment comes with an illustration of the setup (so you can do it yourself) and a short IR video recorded from the experiment. Teachers and students may watch these YouTube videos to get an idea about how the unseen world of thermodynamics and heat transfer looks like through an IR camera -- before deciding to buy such a camera.

For example, this post shows one of my IR videos that probably can give you some idea why the northern people are spraying salt on the road like crazy in this bone-chilling weather. The video demonstrates a phenomenon called freezing point depression, a process in which adding a solute to a solvent decreases the freezing point of the solvent. Spraying salt to the road melts the ice and prevents water from freezing. Check out this video for an infrared view of this mechanism!