buoyancy ventilation

Concrete Content

Live from—wait, is that a 3′ x 4′ concrete panel? Lately, Thermal Mass and Buoyancy Ventilation Research Project Team has been delving into the interior of the test buildings. Inside, Wood and concrete thermal mass line the walls of the test buildings. The thermal masses thickness and surface area are optimally proportioned based on the thermal properties of the materials, size of the room, and ventilation required. This proportioning makes the whole passive temperature and ventilation control strategy tick. Therefore, the TMBVRP team must figure out an elegant solution for hanging the thermal mass to create a beautiful interior which also operates optimally. Let’s take a look at how they are tackling this task. Hint: it involves very big concrete panels …

Typically, designers think of concrete as the go-to material used in passive thermal mass strategies. This is why the TMBVRP team is testing it in the Testing Buildings alongside the more surprising material; Southern Yellow Pine. If you remember from previous posts when the materials are proportioned properly using the Optimal Tuning Strategy they can be equally effective at cooling and creating buoyancy ventilation cycles.

However, when it comes to hanging the two materials on the SIPs walls, Pine is obviously much more straight forward. The pine boards attach to the SIPs panel walls with a simple screw. Well, multiple simple screws. On the other hand, the team will have to get much more creative to secure the concrete panels.

To start, the team tested two strategies hanging concrete panels; masonry anchors and cone form ties. First, they cast the masonry anchors and cone form ties into two 12″ x 12″ concrete panels. Similar to the panels in the Concrete Test Box in size, but different in the attachment system as the security of the panels in the test box is far less crucial as no one will be sleeping in it. Both test panels are attached at all four corners to shear walls in the Red Barn.

Masonry anchors are fluted plastic chambers that adhere to the concrete and are screwed through tp attach concrete to wall. They allow for a connection point that looks as if the screw passes directly through the concrete. However, for the sake of durability, the team would include a washer in this scheme to keep the screw from bearing into the concrete.

Likewise, the cone form ties act the same as the masonry anchor, but are larger in diameter and thickness. Also, they are able to set into the concrete to create a nice reveal. While the team liked the effect of this reveal, team collaborator Professor Salmaan Craig revealed a possible hurdle for the experiment. Revealing edges at the attachment points could slightly disturb the direction of heat transfer. The direction of heat transfer is integral to the strategy which is why the panels are insulated on the back. And, while this is a very small area that could be affected it is multiplied enormously by the number of panels and screws. We call this problem, fastener effect loss. Fastener effect loss assumes, very conservatively, that the small area around the reveal is ineffective to the system.

Next, the team ran the numbers and if all the panels were 12″ x 12″ with four form ties each, 6% of the thermal mass would be lost to faster effect. Now, that’s not bad at all for a real building, and again that’s an extremely conservative estimate. However, for an experiment establishing the most ideal situation for a small building, 6% is not negligible enough. Going forward, if the team prefers the cone form ties, they will need to lessen the amount of panels therefore lessening the number of form ties. Fewer form ties means less fastener effect loss. Fewer form ties also means bigger panels. The team sketched out many different possible panel arrangements but decided they needed to test just how large they could cast a concrete panel. Above on the far right, you will see their biggest panel possible design. This design consists of 3′ x 4′ panels in a running bond pattern.

Next, Jeff and Rowe got to work creating the panels for biggest panel possible design. The estimated weight for these panels is 200 lbs. While this is fairly difficultl for construction, the size of panel cuts down on the number of panels needed from 128 to 39. So while it may be hard to lift, the team would have to make far fewer panels. And the fastener effect loss shrinks exponentially as the design goes from using over 500 screws and form ties to under 200. The question still remains, however, will the panels crack at this size?

To address the issue of cracking concrete panels, the team tested two different mixes for their large panels. If you remember from their blog post on concrete thermal property testing, the team obtained the thermal property data from three different standard concrete mixes. They ended up using the Quikrete Pro-Finsh for the Concrete Test Box, but thought for the large panels they should also try the Quikrete Fiber-reinforced mix. The fiber-reinforced mix is increased in structural integrity which will be beneficial for larger panels by reducing possible cracking. Jeff and Rowe built two form works to test both mixes at the 3′ x 4′ panel size.

Look at that! Both the fiber-reinforced and smooth finish concrete mixes came out great! Very smooth with zero cracks, but very heavy. Above you see the fiber-reinforced panel which turned out just as good as the professional finish and would be much stronger. This does not mean that the team will be using the enormous panels, most likely they will cut them in half. However, the team now knows their largest limit on size is possible. The team will continue to weigh their options between attachment method, panel size, and panel arrangements as they solidify their design. Keep tuning in to see where these crazy kids and their crazy concrete end up!

Lab to Barn, Science to Design

Live from Rural Studio Red Barn, it’s the Thermal Mass & Buoyancy Ventilation Research Project Team! The team, though they might come to miss the cat interns and the AC, is so excited to be back on campus. For health safety measures, the team has an entire studio room to themselves which also acts as a convenient hiding place from Andrew Freear. The TMVRP Team is being as safe as possible as they sorely missed Newbern and the Rural Studio staff and faculty. This week the team will cover their pod design process while bombarding you with design iteration images. Enjoy!

As the Wood and Concrete Chimneys chug along, quite literally, the TMBVRP team have been designing their test buildings. Like the Mass Timber Breathing Wall team’s nearly completed test buildings, the TMBV test buildings apply their research at a small building scale. After some initial testing, the TMBV test buildings can be used as 3rd-year accommodations. The Studio calls the funky dorm rooms for 3rd-years on Morrisette campus “pods.” In true Rural Studio fashion, the design of these pods is an iterative process, but must always be grounded in what is necessary for the experiment. Now, science experiments are not only driven by the hard data we might get out of them. Many experiments are experience-based, especially when trying to describe a phenomenon to the public. Think about going to a science museum, touching the electrified ball and your hair shooting up from your head. Static electricity makes a lot more sense to you when you experience it rather than if you had read data and looked over graphs explaining it. The design of the Thermal Mass & Buoyancy Ventilation pods revolves around both data and experience production. A main objective of the Thermal Mass & Buoyancy Ventilation Research Project, while being rigorously tested for data currently, is for inhabitants to experience the comfort of the cooling and ventilation effects. Let’s journey through TMBV Pod design as the team tries to focus on both experiment and experience!

When massing the general size of the pods, the team can use the Optimal Tuning Strategy app. From the app the team knows the amount of surface area needed for the thermal mass, the thermal mass thickness, and the size of the ventilation openings based on the information they input which is how much ventilation, temperature change, and height the pods need. General massing schemes are quickly generated from these design parameters. The team is creating massing schemes for two to three pods, one with concrete thermal mass walls and one or two with wood ones. These massing schemes also explore whether to share walls in a multi-unit pod or separate the pods to highlight the material difference within. As long as these massings can fit the app outputs, a 3rd-year, a bed, and the sensors we need for testing that’s all of the design work to be done, right? Nah. While these are sleeping quarters for students, they are also examples to the public of how spaces that utilize thermal mass and buoyancy ventilation can feel.

To create a peak TMBV experience, the team is elevating the pods! This will allow for a gathering space underneath the pods where anyone can sit and enjoy the cool air being naturally pumped out of the spaces above. The TMBVRP team calls it, the “Cooling Patio.” Here, students, faculty, or clients interested in the system can experience the effects of TMBV without lingering too long in a 3rd-years dwelling. It also highlights one eventual goal of the work; naturally cooled public spaces enjoyed in the Black Belt. The Cooling Patio is located underneath the buildings because the TMBV system operates in downdraft during the day. This means during the day the air is pushed out of the lowest opening as opposed to at night when the air is pushed out of the highest opening. Therefore in a typical building, you would not need to elevate the structure above the ground, you simply need a low and a high ventilation opening. The TMBV Pods’ ventilation “top and bottom” openings are so literal for both the quality of the experiment and the Cooling Patio.

Why the pod is elevated may now be clear, but why do some of these drawings have such tall chimneys? The exaggerated Chimneys are an experiential detail like the elevation of the spaces. They are not necessary for the experiment or the TMBV strategy to work. A typical building would not need tall Chimneys to utilize Thermal Mass and Buoyancy Ventilation, just as they would not need to be elevated. The tall chimneys are specific to the Thermal Mass and Buoyancy Ventilation Research Project Pod as they highlight the ventilation created by the passive strategy. This is another detail, like the cooling patio, that will work as an experiential demonstration of the research. Increasing the overall height of the structure, beyond what surface area is needed, highlights the ventilation aspect of the system. The elongated chimneys do not increase the amount of air ventilated through the spaces, it does increase the speed of the air as it exits the spaces. The faster the air exits the interior space into the cooling patio, the cooler the patio space will feel. Think of it as the difference between being hot with a fan and without. Moving air always increases the cooling effect and therefore the cooling experience. This increased airspeed will help with explaining how Thermal Mass and Buoyancy Ventilation works as visitors and users will be able to clearly feel the cool air rushing out. Now, the design is focused on three main outcomes: replicating the experiment so TMBV works effectively at building scale; providing a comfortable and useful space for sleeping and demonstrating; and creating a space below the buildings in which people can gather and experience the strategy working for long periods of time. What comes next is siting and about 1,000 other details.

Siting began by looking at various locations around the Super Shed and the existing pods. The Team began exploring the pods as stand-alone buildings. Next, the team explored how they could utilize the roof and structure of the Super Shed. While investigating stand-alone sites, the team also did some surveying of the Super Shed. Both options have benefits. A stand-alone structure would allow for greater height, not being capped by an existing roof, so a more generous cooling patio space and higher airspeed into that space. The existing roof of the Super Shed, however, would provide constant shade and rain protection making it a very similar environment to the Chimney Experiments in the carport at HomeLab. Both have experiential and experimental benefits that the team is still exploring.

The Thermal Mass and Buoyancy Ventilation Team has a lot of hard work ahead, but nothing makes it better than being back in the Red Barn. Seeing the old and new faces of Newbern, even from a social distance, is exciting and motivating. Thanks for Tuning in!

New Cat, New Data, New Designs

Live from HomeLab it’s the newest member of the Thermal Mass and Buoyancy Ventilation Research Project team, Sonic! More on our scrappy, little intern later, we’ve got fresh Wood Chimney Experiment results.

Longhaired black kitten shining in the sun

TMBV Research Project’s last post discussed equalizing the environment of HomeLab to improve the accuracy of the Concrete and Wood Chimney Experiments. While the screen on the eastern side is blocking direct solar radiation, the team discovered a new heat source. The roof of the carport is significantly hotter, even on the underside, than the team thought. This was discovered while trying to understand the Chimney’s airflow data. To show how trapped heat can affect the experiments we will take a look at the long-awaited Wood Chimney Experiment Data.

The above airflow data was taken from the first week the Wood Chimney was up and running and shows both updraft and downdraft. Automatically, the Optimal Tuning Strategy is validated for wood, as well as concrete, by the existence of both airflow directions within the experiment. Go, Wood Chimney, Go! However, the updraft is nearly twice as strong as the downdraft which did not quite make sense. The team looked back to their thermal imaging photos for an answer as to why there is such a large difference between the updraft and downdraft.

The thermal imaging photos show that the top of the Wood Chimney Experiment is much, much hotter than the side of the chimney. This can cause a build-up of hot air at the top of the chimney which explains why downdraft is so much lower. While in downdraft, the air is brought in from the top and expelled out of the bottom of the chimney. It works the opposite in updraft, bringing air in from the bottom and expelling out of the top of the chimney. If there is much more hot air at the top of the chimney, that causes turbulence, making it harder to bring in air during downdraft and too easy in updraft. So what is causing this heat at the top? The HomeLab ceiling!

The team learned, from the thermal images above, that the ceiling of the carport was nearly 120 degrees Fahrenheit, which clearly was the reason for the heat build-up at the top of the Wood Chimney Experiment. To combat this the team stapled a radiant barrier to the rafter of the carport to insulate and reflect heat away from the tops of the chimney, trapping it at the ceiling. The radiant barrier is made of Reflectix insulation which looks like shiny bubble wrap. In the thermal images, you can see the radiant barrier lowers the temperature above the chimney by nearly 10 degrees.

The radiant barrier works! Both the thermal images and data show that the excess heat at the top of the chimney was increasing the updraft and making the downdraft more turbulent. The top surface of the chimney also dropped 8 degrees. The amount of air per second is now mirrored in updraft and downdraft at about 0.05 l/s.

in the last post, the team left y’all with thoughts on a “Human Scale” experiment, to test the Optimal Tuning Strategy and App at a larger scale that can be experienced. After a discussion with the entire Thermal Mass and Buoyancy Ventilation Research Project team, including partners at McGill University and Rural Studio faculty, everyone found the Human Scale experiment is not necessary to validate the Optimal Tuning Strategy. The data from the Chimney Experiments is primo and the team can move on to designing a permanent, Inhabitable Structure. The Inhabitable Structure will be a usable example of the effects of coupling thermal and buoyancy ventilation in a building as well as being a mechanism for producing data. Rural Studio will be able to use the spaces on the day-to-day, but it will also show people the system works and can be applied in the community. While the team has thoroughly enjoyed learning about design through crafting an experiment, they are excited to get back to architecture! There is still plenty of science to come, don’t be fooled.

Balancing science and design seemed like too big a job for 4 students, 2 cats, and a Copper so the team hired a new pet intern. Meet Sonic! He was found at just 4-weeks old out on a county road with only his thoughts and half a tail. As you can see, he is getting along great with the other interns and doing some great sketching. Stay Tuned for updates on Inhabitable Structure design and the teams myriad of four-legged friends.

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!

Raising Chimney

Live from HomeLab, it’s the Graduate Program! The Thermal Mass and Buoyancy Ventilation Research Project team members are officially Rural Studio master’s students. The team’s summer semester has started off hot with ventilation opening calibration.

Even with the latest ventilation opening adjustment, described in our airflow post, the data from the Concrete Chimney Experiment reveals the airflow is still choked. As you can see in the temperature signal graph below, the thermal mass surface temperature never rises above the interior air temperature as it should in an optimally tuned space. If we then look at the airflow graph below, we see that the updraft, bulk airflow during the night, is nearly double the downdraft, bulk airflow during the day. When the blue line is above zero, the system is in updraft and when below zero it is in downdraft. Both of these graphs allude that the thermal storage cycle and the buoyancy ventilation cycle are out of sync. This is due to a lack of air. Air drives the cycles as it brings warm air into the chimney to be absorbed and offloaded by the thermal mass.

The team examined their previous math for calculating the total area for the ventilation opening. They’ll spare you the gory details, but the predicted bulk air flow rate they were using to calculate the size was too small resulting in a ventilation opening that was too small. Thanks to the airflow sensors they no longer needed to use a predicted air flow rate and instead used the actual average airflow rate coming from the Concrete Chimney Experiment. After this recalculation the ventilation opening nearly doubled from 3/4” to 1 1/8”. The team then let the chimney do her thing for a week.

a graph showing two days of temperature signals, where the air temperature falls below the panel temperature
Black = Exterior Air
Dashed Gray = Interior Air
Orange = Thermal Mass Surface,
Dashed Orange = Thermal Mass Interior

The data is in and it is as hot as the Alabama asphalt. The team, along with their colleagues were correct in their assumption that the flow was being choked AND the new ventilation opening size is allowing the chimney to operate optimally! In the temperature signal graphs, the thermal mass surface temperature and the interior air temperature properly oscillate. Therefore, the thermal mass is absorbing the heat properly allowing it to be warmer than the interior air at times.

a graph showing two days of airflow data, where the downdraft is larger than the udraft
Blue = Bulk Air Flow

As you can see from the airflow graphs, the bulk airflow of the updraft and the down draft has equalized and is becoming more symmetrical. Both outcomes, in temperature and airflow, reveal there is now a proper amount of air moving through the chimney. The downdraft is still a bit more turbulent than the updraft however and the team wondered if this was due to the concrete pad underneath the chimney releasing heat it absorbed throughout the day. To combat this heat, the team jacked up their Concrete Chimney Experiment… literally!

To raise the chimney, in order to give it some more height via cinder blocks, the Thermal Mass and Buoyancy Ventilation Research Project used car jacks. The team will see if this helps with the heat interference and its possible effects on the air flow. 

two small white dogs in a car

As you can see Wolfie is still in town on his summer vacation! He and Copper like to observe the team work. To insure their safety as the chimney was being raised they watched from inside the car. They really love the car. For more science, design, and cute pets, stay tuned!