wood grain

Wood you believe we did it?

Timber pun prepared and deployed? Scientific apparatus built? Yes to both! Live from HomeLab, the Thermal Mass and Buoyancy Ventilation Research Project team is proud to present to you, the Wood Chimney Experiment! No science lessons today folks, just photos.

Students posing with their test chimneys.

SPOILER ALERT! On the left, you see our tried and true, the one who taught us so much, the Concrete Chimney Experiment. On the right, the Thermal Mass and Buoyancy Ventilation family welcomes their newest member, the Wood Chimney Experiment. Now let’s look at the building process.

The top and bottom insulation blocks are created by adhering two 6″ x 3′ 7″ x 3′ 7″ to make them 1″ thick. If you would like a reminder on why this insulation is necessary for the experiment phase and not necessarily for an actualized building you can read this post. The airflow cones are carved out so that they align with the airflow opening of the chimney interior chamber.

Here we’ve got the chimney walls coming together! Four sandwiches of ZIP sheathing, GeoFoam, and Wood Thermal Mass Panels all attached to create an interior chamber.

Three walls up, the fourth needs its sensors! The TMBVRP team thinks it would be absolutely wonderful to be in a space surrounded by edge grain wood that is also naturally ventilated.

The Sensirion airflow sensors will also be in this experiment. Incorporating how sensors can be attached within the chimney and their cords can make it out of the chimney without being squished is a crucial part of the design.

Before the Wood Chimney Experiment interior chamber is sealed, the fourth wall containing the temperature signal sensors must be attached. The temperature signals, read about temperature signals here, will be sensed with thermocouples and heatflux sensors. Next step in the process will be building up the insulation surrounding the interior chamber.

The Thermal Mass and Buoyancy Ventilation team is aware they used to refer to these scientific apparatus as “Desktop Experiment’s”. Technically the inner chamber could stand on a desk, but a more appropriate name might be Carport Experiments or Taller than the Team Experiments. Let’s just call them the Chimney Experiments for clarity. These experiments are still the first and smallest experiments for the scalable Optimal Tuning Strategy. And look, the Wood Chimney Experiment is done! Batt insulation and 2″ GeoFoam walls encase the interior chamber and ZIP tape is used to seal the entire experiment.

Students posing with their test chimneys.

Thank you to all who have encouraged and supported the Thermal Mass and Buoyancy Ventilation team! The team is very excited to have reached this point, but the work is no where near over. It will take time to learn a new data retrieval and analysis workflow for the new sensors. The team is excited to get to it, but first we are going to celebrate our Wood Chimney Experiment! Cheers y’all and STAY TUNED!

Preparing a Timber Pun for a Post Title

Live from HomeLab, it’s Wood Chimney Experiment preparation. The Thermal Mass and Buoyancy Ventilation Research Project team members are continuing their efforts to refine a passive cooling and ventilation system which can be deployed to public buildings in the rural South. Due to the fantastic results from the Concrete Chimney Experiment, the team is starting the Wood Chimney Experiment. They have developed an experimental method for designing and building chimneys which test the Optimal Tuning Strategy. They also have honed their data collection workflow and analysis. Now they can move on to testing how timber can work as a thermal mass. You can read about why we are using mass timber as a thermal mass here.

The first step in Wood Chimney Experiment preparation is gathering materials. The team collected sensors that the Mass Timber Breathing Wall team is no longer using. Rural Studio has been growing its scientific equipment stock which allows for reuse between research projects.  The TMBVRP team is inheriting data loggers, heat flux sensors, thermocouples, power supply, and airflow sensors. They will be using different temperature sensors, thermocouples and heat flux sensors, then are used in the Concrete Chimney Experiment. These sensors, like the GreenTeg Go Measurement System, will still deliver the proper temperature readings. This equipment is flexible and adaptable making it easily reusable between projects.

Sensors and power source for wood chimney experiment.
Reduce, Reuse, Re-sense!

Next, you might remember the team’s good friend, GeoFoam. GeoFoam is a type of dense expanded polystyrene foam usually used for earthwork under roadways. Both research teams have been able to use it as insulation for their experiments after the geofoam was donated to the Studio from a construction site. Remember, the team must cut smaller sections of GeoFoam from a huge 8’ x 4’ x 4’ block using a hot wire. The team was able to do so underneath the Morrisette Campus Fabrication Pavilion for a designated time and with faculty approval to ensure safety during the pandemic. They collected the rest of the batt insulation from storage in Brick Barn as well as materials for the structure of the experiment. Everything was hauled back to HomeLab for construction.

Next, the Thermal Mass and Buoyancy Ventilation team continued cutting down and shaping openings in the Geofoam. The top and bottom pieces of the chimney are made of two 6” thick pieces of GeoFoam that are adhered together as 1’ of insulation is needed for the proper U-Value for testing. The top and bottom pieces have cones carved out to ensure proper airflow. Resident King of Precision, Jeff Jeong, double and triple checks each piece of foam. This way the Chimney comes together like an airtight puzzle.

The base for the chimney is constructed out of 2” x 4” lumber and plywood. The legs of this base are taller than the Concrete Chimney Experiment to match its height after being raised. Another difference in the design of the experiments is the walls of the interior chimney which the wood panels will be attached to. The walls for the Concrete Chimney Experiment are, from the chimney chamber outward, concrete panels, insulation, plywood, and then more insulation. The walls of the Wood Chimney Experiment will be pine panels, insulation, ZIP sheathing, and then more insulation. Notice Dijon doing his best to help in the photos below.

Last, but not least, is pre-drilling holes for the concrete panels. The concrete panels will be screwed to the insulation, ZIP sheathing wall. There will be four walls to complete the chimney. Notice the grain direction of the panels. This edge grain allows for parallel heat transfer between the air within the chimney chamber and the pine panels. Not only is the Thermal Mass and Buoyancy Ventilation Research Project testing if timber works as a thermal mass but how the grain direction affects its efficiency as a thermal mass.

The Thermal Mass and Buoyancy Ventilation Team is excited for the Wood Chimney Experiment to come together. So are the kittens! The team would not leave you without a HomeLab mascot update. While Dijon mostly naps, Rosemary is trying to get some construction experience to build her resume. They’ve had to tell her she is not OSHA certified, but she is fine napping a safe distance from construction now. It was not a hard sell. Stay Tuned to see the completed Wood Chimney Experiment!

Zoom Roast

Unfortunately, due to COVID-19, Rural Studio had to cancel the Pig Roast celebration hosted at the end of each spring semester to acknowledge the work happening in Newbern. To conclude the team’s two years of research, the team presented to a wide range of reviewers in a “Zoom Roast.” This celebration/critical review allowed the team to share their work as well as receive feedback on how to continue moving forward. Thank you to the Rural Studio faculty, Auburn University faculty, and our project collaborators from McGill University and Auburn University for spending the morning reviewing the project on Zoom. Also a huge thank you to Michael Jemtrud from McGill University, Z Smith from Eskew Dumez Ripple, Billie Faircloth from Kieran TImberlake, and Jonathan Grinham from the GSD at Harvard University for coming in as guest reviewers to critique the research project.

Zoom Roast with reviews from Auburn University, Rural Studio, McGill University, Harvard University, New Orleans, and Philadelphia.
Overview of experiments the team conducted in their two year research project.

The team is currently working on a draft of their first peer reviewed paper (!!!) to be published in Energy and Buildings. The “zoom roast” was an opportunity to analyze the experimental set ups before beginning the peer review process. The team has been working closely with Salmaan Craig in the past few months to finalize a draft focusing on three experiments the team completed in the past year. The paper explores a method of integrating ventilation and heating into a mass timber envelope, allowing for a mono-material building that is able to sequester carbon and reduce greenhouse gases while also reducing the need for mechanical ventilation systems. The experiments in the paper lays out 1) how to optimize panel geometry and identify the design space for this system, 2) how the system could be synchronized with natural ventilation flows to obviate conventional HVAC, and 3) how transient behaviors affect the system. 

The team is also working on writing up the results and testing method for the thermal conductivity testing they completed in the engineering lab at Auburn University to be published in an architectural journal. 

The team tested a variety of pine samples measuring the thermal conductivity of each.

Stay tuned for links to both of these papers once published and available to the public! 

From Builders to Writers,

The Jubilant Journalists 

Soundtrack: Paperback Writer  |  The Beatles

Wood Wise

An important part of the Thermal Mass and Buoyancy Ventilation Research Project is investigating whether, if properly sized, mass timber can be used as a thermal mass. To do so, the team will build a Wood Chimney Experiment to run in parallel with the Concrete Chimney Experiment. As they work to compare the thermal mass performance of concrete and softwood, they must learn more about the thermal and structural properties of the materials. A material’s anatomy affects how it absorbs, transfers, and offloads heat. Concrete has been used as a thermal mass for ages and therefore has widely known and defined thermal properties. However, there is far less information on the thermal properties of wood. Let’s take a closer look at the composition of timber as taught to the team by colleague David Kennedy, a self-proclaimed, “Wood Anatomist Fanboy.”

The first consideration for wood is the difference between isotropic and anisotropic materials. Isotropic materials, like concrete, have consistent properties in all directions. Anisotropic materials, like wood, have orientation dependant properties. Wood has an anisotropic, cellular structure that provides its strength and its the ability to move water and minerals to the outer reaches of the branches. A tree’s main job is to transfer water and nutrients from the ground to the sky and vice versa. Therefore, wood cells can be visualized as bundles of straws, with some acting as pipelines while others store nutrients. These cells consist of tracheids, parenchyma, and epithelial cells. Tracheids are actually dead cells that function as water transporters. Parenchyma store starches that give nutrients for the tree. Epithelial cells take on the job of building the tree. These cells act vertically, while ray tracheids, ray parenchyma, and ray epithelial cells work in the horizontal direction.

As trees grow their structural properties change based on what they need. This is why different parts of the tree are composed of different types of wood depending on their age. If a cross-section is examined, two important types of wood will be present, juvenile wood and heartwood. Juvenile wood is a weaker less dense outer ring and is usually distinguished by a lighter color. This wood makes up the early growth and is not evenly distributed throughout the tree. Often, the tops of trees will be 100% juvenile wood, while the lower parts of the tree are more mature heartwood. Heartwood, the mature, older wood, is produced by converting stored chemicals that are produced by the dying parenchyma cells that have been sent to the center of the tree. This area of the tree is typically darker and denser. These different cells and wood types can result in different characteristics throughout the same tree, which must be carefully considered. 

Timber mapping diagram
Different cuts of wood result in different grain condition which cause different construction systems

The performance of thermal mass is heavily influenced by the thermal conductivity of materials. The thermal conductivity of materials is heavily influenced by the density of materials. With the variety of conditions that are possible all within the same tree, it is important to consider how the material is cut and oriented. This is also important because of the grain directions present in the wood. Just like water flows through the tree along cellular pathways, heat will follow the grain of the wood. Therefore, the cut of the wood must be selected so that the grain in the same direction as the preferred heat transfer.

How heat transfer is affected by grain orientation and construction.

Now that we have learned more about the structure of wood and how that affects its heat transfer we can understand how the wood should be cut and oriented. Initially, the team’s wood test panels utilized the timber end grain. This end grain direction would be parallel to heat transfer. However, depending on the size of the tree and how blocks were cut, the types of wood in the panels could become inconsistent. This meaning they could be made of different mixtures of juvenile wood and heartwood. They were also pretty inefficient to make.

To find a better way, the team investigated the different ways timber is milled into boards. The TMBVRP team found that different cuts of wood could produce different grain directions. The most efficient grain direction for our panels would be to have the grain running perpendicular to the wide face of the boards. This allows the board to cover the area most efficiently, and the board thickness can be controlled to work with the app results. This grain direction can result from several milling, but we believe quarter sawing will produce the most favorable boards with the least waste. The team then made their own version of these boards, but as panels for their wood chimney.

Wood is a far more complex than the Thermal Mass and Buoyancy Ventilation Research Project Team realized! They too are now “Wood Anatomist Fanboys” and hope you’re on you’re way to becoming one. Now, Give your brain a break and look at Rosemary and Dijon being mischievious! Thank you again to David Kennedy for all the help and as usual stay tuned to see what theTMBVRP Team learns next!