Thermal Mass & Buoyancy Ventilation Research Project

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!

How do we build that?

Now that the pods have been given forms, it’s important to figure out how we can make them stand up. To accomplish this, we are comparing three different structural systems to find the best method. We are considering Cross Laminated Timber (CLT), Structural Insulated Panels (SIPs), and more conventional stick framing systems.

All of these systems require slightly different assemblies, and we drew many wall sections to begin to understand them.

These forms also require unconventional joints at odd angles, so we did studies of how to join corners, whether with panelized systems such as CLT and SIPs, or stick framing.

By the end of these studies, and with the help of a review from Hank and Julie of KoningEizenberg Architecture, we began to realize that these forms were too complex, and could be simplified without forgetting our experimental requirements. This led us to a form we’re calling the “Rowhouse”. 

We will continue investigating structural systems using the Rowhouse form. We are currently investigating using the SIPs systems, as they offer a high insulating value while integrating structure. Our next steps will be designing the thermal mass panels that will live in these structures.

Grain Silos to Air Silos

Welcome back to another round of Thermal Mass and Buoyancy Ventilation! Now that you’ve seen what we looked like in our presentation, here’s some of what we were actually talking about.

Our project relies on the testing of materials to observe how they work as thermal masses according to the Optimal Tuning Theory. To be able to do this scientifically, we need spaces in which we can test our four materials. These four spaces need to be identical so that they can be directly compared to each other. In each of the four spaces, one material will be tested, either timber, concrete, brick, or earth. These four spaces will be arranged into a “foursquare” configuration, housed under one roof.

Once we decided on a layout for the four spaces, pod forms could begin to be generated. For this, inspiration was drawn from the silos that surround us. In order to gather our airflow into a measurable point, the pods will take on a funnel shape, both on the top and bottom. This is because the ventilation cycles will function both in updraft and downdraft. After creating this funnel shape, we iterated on the basic shape to create options for the pod forms.

From here, we’ll be evaluating these forms, and researching structural systems to support them. Eventually, we will select one form to house our experiments.