Thermal Mass & Buoyancy Ventilation Research Project

Insulation and Other Sensations

Oh hi, didn’t see you there behind my giant block of Geofoam insulation! Let me explain. Recently, Thermal Mass and Buoyancy Ventilation Research Project Team has been designing their first experiment, the desktop scale experiment known as “the chimney,” and building a mock-up of it.

The team used the data obtained from the thermal conductivity testing in Auburn University’s material testing lab along with their test concrete panel making experience to choose which concrete mix to use. They are going with Quikcrete Pro-Finish 5000, a high strength, smooth finish mix. Next, the team poured nine new concrete panels at the adjusted thickness. The thickness of the panels increased slightly due to inputting the exact thermal properties of the concrete mix into the code of the optimal tuning application.

The desktop experiment takes the form of a 3″ x 1″ x 1″ chimney with the thermal mass panels facing the interior. The desktop experiment needs to operate in nearly ideal conditions which means eliminating as many variables as possible. It is important to remember this is a scientific experiment of an unproven theory of how an internal thermal mass can be sized for a space to control temperature and promote proper ventilation. Therefore, to eliminate the variable of heat loss or gain from the exterior to the interior, and to understand how the thermal mass panels themselves are working, the chimney needs to be highly insulated.

When you need R50 insulation, even for such a small structure, it can get expensive and big. Their creative solution to getting the proper insulative value without spending hundreds of dollars per test was combining Geofoam and Rockwool! EPS Geofoam is much like rigid insulation but is typically used for earthwork such as building up underneath highway on-ramps. It is very dense giving it more insulative value per inch. Rockwool is a rock-based mineral fiber insulation. Thankfully, Rural Studio had extra R30 from a previous donation. The Geofoam was also donated, the Breathing Wall Mass Timber team got in touch with a construction operation that had extra and transported it to Newbern. In the drawing above you can see the concrete panels screwed onto a piece of 1/2″ OSB and 2″ Geofoam which is then surrounded by 9″ of Rockwool then encased by another layer of 2″ Geofoam. This combination of materials results in R50 insulative value.

The Geofoam comes in giant 8″ x 4″ x 3″ blocks because they are typically stacked underground. So another creative solution was needed, how to cut it down to the size we need. The TMBV team did not have to think too hard on that one because their big sister research team, the Breathing Wall Mass Timber squad, had already built a hot wire cutting system for their own Geofoam needs. A copper wire was spanned at the desired height above a table and heated using cables and an external power source.

Next, the Geofoam block was slid across the table and cut through by the hot wire. Once the Geofoam is at a more manageable size it can be cut using a hack saw. Shout out to the best big sister research team ever, Fergie, Jake, Preston, and Anna, the TMBV team appreciates you!

Whew, that was a lot of insulation talk! To ease everyone’s mind here is a beautiful Newbern sunset. See you next week!

In the field trip

The Thermal Mass and Buoyancy Ventilation Research Project Team got out of Newbern last week and into the field, sawmill, and lab!

The first field trip of last week was to Charlie’s sawmill. Charlie is a retired engineer, woodworker, and long time friend of Rural Studio, having helped with the Greensboro Animal Shelter. The team met Charlie at the Animal Shelter during neckdown week, where he was leading the project to revamp the kennels.

Charlie has a “hobby mill” he has been building up over the past years. He works mainly with salvaged wood and timbers making furniture and folk art. After the team got a tour of Charlie’s sawmill, he treated them to lunch and a brief presentation on wood. Even more than lunch, Charlie has offered the team use of his sawmill. Charlie has a passion for helping others and great deal of building knowledge, the team feels very lucky to have met him! Thank you Charlie!

Next, the TMBVRP team met up with Professor David Kennedy in the material testing lab at Auburn University’s College of Mechanical Engineering to test the thermal properties of their concrete samples. These samples were made using three different concrete mixtures, high finish, fiber-reinforced and 100% Portland cement. The objective was to find the exact heat capacity, thermal conductivity, and effusivity of each mixture. Knowing the specific thermal properties will help eliminate variables in the math when evaluating how the Optimal Tuning Theory is working.

David gave the students a crash course in scientific testing procedure. When conducting such tests, everything needs to be documented. The samples were marked, 10 of each mixture, measured for thickness and diameter, and weighed. The specific volume and density were then calculated for each sample before testing. The sample was again weighed after the test had run. Everything needs to be documented!

Next, the team will analyze the data and recode the Thermal Mass and Buoyancy Ventilation proportioning application with the specific thermal conductivity results. We’ll talk to you soon!

When it rains, it pours!

After a very rainy neckdown week, the Thermal Mass and Buoyancy Ventilation Research Project team is back and pouring concrete panels.

First, the team had to make molds for 18″ x 18″ panels to test for the Habitable Structure, 12″ x 12″ panels for the Desktop Experiment, and concrete samples for material thermal conductivity testing. They used melamine covered OSB, which is reusable, for the panel formwork and PVC pipe siliconed onto rigid insulation for the sample molds. The samples or “biscuits” are small cylinders of the three different concrete types they are considering; fiber-reinforced, high finish, and pure cement. These samples will be taken to Auburn University’s engineering lab to test their thermal properties. This information will help sharpen scientific experiments!

When the formwork was done, the team was ready to pour their panels and samples. However, due to the extremely low temperatures this week the team got to work in the Plug-in House! Don’t worry though, they taped down tarps and the Plug-in is staying clean. You can read all about the Plug-in House and what it’s doing underneath the Rural Studio Fabrication Pavillion here: http://ruralstudioblogs.org/2019/09/18/the-plugin-house/

The TMBVRP team prepped the panels by taping and oiling them. Vegetable oil helps prevents the concrete from sticking in the mold. Next, the team mixed the concrete with shovels in a wheelbarrow adding small amounts of water at a time. They think, for next pour, they will use a hand mixer attachment for a drill and a bucket to mix the concrete. Part of this process was figuring out a better way to complete this process.

Finally, the pour! The team used trowels and a bladeless reciprocating saw to smooth and vibrate the panels. It is important that concrete is vibrated to remove air trapped within. The panels and samples will stay in their forms for three days until they are cured. Next, the team will test its panel attachment system and work on their Desktop Experiment mock-up.

You will have to check in next week to see how our concrete turned out and maybe you’ll get a sneak peek into the testing at Auburn University’s engineering lab!

Panel Making

This week the Thermal Mass and Buoyancy Ventilation Research Team got to use the largest skill saw they’ve ever seen and we’ll tell you why!

In the technical workshop Sal last week, the team decided to narrow the number of materials they will test throughout the experimental cycle from four to two. The lucky two will be concrete and softwood! Concrete is often used as a thermal mass material while softwood is not which will make comparing the data collected from the separate experiments all the more interesting. The Optimal Tuning Theory calls for the thermal mass to be externally insulated which allows the thermal mass material to be much thinner than a typical thermal mass. Therefore, the concrete and wood need to be panelized.

The thermal properties of wood act most efficiently as a thermal mass when the cross grain is exposed to the air. This means that panelizing the softwood is more like creating giant cutting boards. To practice this process the team used 8″ x 8″ Cypress timbers and their matching 16″ diameter skill saw leftover from the Newbern Town Hall project. The team learned that 6″ x 6″ timbers would be ideal for their project, that way they can cut the cross-grain pieces in one cut with their 16″ skill saw without having to rip down the timber.

The concrete panels are far more straightforward, build a mold, pour the concrete, let it cure. However, the team has to think about how the panels would be attached to a larger structure. To solve this they cast PVC into the panel which will allow it to be screwed into a structure.

Voila! We have much refining to do of the panel making process, but the first two turned out well. We also have here a rendering of the habitable structural with the separate concrete and wood panel rooms. Our next step is to apply what we learned working with these materials to designing and building our first experiment. Thermal Mass and Buoyancy Ventilation Research Team out.

The Experimental Cycle

The team with the longest name possible is back this week diving deep into the science behind the Optimal Tuning Theory with its author, engineer, Sal Craig. Sal, along with his colleague, architect Kiel Moe at Mcgill University in Montreal, Canada, are our partners in the Thermal Mass and Buoyancy Ventilation Research Project. The team has weekly meetings via Skype with Sal and Kiel to discuss the project, but this week they had an in-depth technical workshop.

Behind our simple understanding of the Optimal Tuning Theory, there are very intricate scientific equations that Sal has written, solved, and published in his peer-reviewed paper, The optimal tuning, within carbon limits, of thermal mass in naturally ventilated buildings. Although the student team does not need to obtain an engineering degree to work on the project, it is important they grasp the basics so the project is truly a collaboration. They need to be able to have a conversation with Sal about the possibilities of the project instead of asking his permission. 

The team studied up for their technical session with Sal


Thankfully, Sal is a wonderful teacher and the students were able to reach a deeper understanding of the theory with him during their day-long technical workshop. Afterward, they were able to make a couple of important decisions about the project together one of which was defining the undergraduate phase of the project as an experimental cycle.

The experimental cycle will be comprised of testing the Optimal Tuning Theory at three different scales they are calling Desktop, Human, and Habitable. These scales are important because the theory is meant to be proportional. The Desktop experiment will resemble a small chimney made of thermal mass material, the Human scale experiment a full-sized thermal mass wall, and the Habitable experiment will be a full structure i.e. the pod where the interior walls will be entirely thermal mass. 

Livia with her beloved schedule

Defining the experimental cycle has allowed the team to start scheduling and setting deadlines, something Livia has been dying to do. Completing this cycle in the undergraduate phase of the project will allow freedom for the graduate phase. Thanks for tuning in!