Thermal Mass and Buoyancy Ventilation

Breaking News: We’re Breaking Ground!

This just in: there’s is a big hole in the Thermal Mass and Buoyancy Ventilation Research Project site!

Thanks to C & T Excavation Inc. the TMBV Test Buildings have broken ground. Local and Rural Studio excavation efficiando, Tyler, completed the initial site grading and the foundation dig. Let’s take a look at how the TMBV team prepped the site for this momentous day.

Newbern’s Newest Crater

plan view drawing showing batterboard arrangement
Plan of Batter Board layout, this drawing guided students in find the foundation limits

Before you can dig a hole, you’ve got to know where to dig! This is where the superheroes of construction, batter boards, come into play. Batter boards are quintessential for starting construction so they must be precise. To clarify, batter boards are temporary frames, set beyond the corners of planned groundwork at common elevations.

Typically, batter boards consist of two stakes driven into the ground with a horizontal member held between them. Next, once you’ve assembled and leveled the batter boards, you use construction string to “pull” layout lines. The layout lines are then secured to the batter boards. Layout lines cross the site either east to west or north to south, between batter boards, to indicate the foundation limits at their intersections. It’s important to note the elevation of the top of each batter board must match so when strings are pulled across the strings intersect.

The TMBV team pulled their first layout line west to east from the Supershed columns. From this line, all other layout lines are set. When all lines’ distances and intersections’ squareness are triple-checked, the team marked the initial grading limits on the ground with spray paint. The end result, with string crisscrossing about like laser beams, feels a bit like a scene from an action movie. Especially if you practice jumping over and rolling under the strings. But, of course, none of these very professional research graduate students took part in such conduct.

At the end of a long day pulling strings, the team marked their initial grading and detached all the layout lines from one side. The layout lines positions are marked on the batter boards so they can be put up and down as needed. Obviously, you can’t build with a bunch of strings in your way. After the initial site grading, the students re-pulled the strings which indicated the foundation limits, marked the corners, and Tyler began digging again. In about 6 hours time, Morrisette Campus had a brand new swimming pool and the TMBV team had a real project site.

Mock-up Progression

In parallel with site groundwork, the TMBV team worked across campus on their mock-up. To mimic the SIPs walls of the test buildings, the mock-up uses 2″ x 12″ stud walls. Due to the angle of the roof and the chimneys, there was much mitering to complete and even more mitering math to figure out. The team built all the stud walls and are ready to assemble. All the especially funky parallelograms you see below are the chimney pieces. With the kit of parts complete, the team awaits columns to build upon.

Cooling Patio Design

True to the design-build spirit, the team is still designing as they’ve started building. The ground plane of the cooling patio was the subject of this week’s design charrette. The team has used, concrete side-walk pieces they intend on using as pavers. However, it is not decided yet how those pavers are arranged.

The team wants to eliminate any excessive cutting of the pavers, especially exact cutting, so they ruled out a linear pattern. They are pursuing a mosaic-like pattern that minimizes concrete cuts. However, without a full inventory of all the concrete pieces, it’s difficult to produce a realistic design. Therefore, in the coming weeks, the team will be taking stock of their recyclable materials. After this, they can start laying out patterns using a steer skid loader to move concrete pieces around.

Welcome to Winter

a dirt roads lead to to silos both surround by frosted grass

As mentioned in the Thermal Mass and Buoyancy Ventilation Research Project Team’s last blog post, the chill has rolled into Hale County. There is never a shortage of beautiful scenery in these parts as proven by these frosty silos. By next post the TMBV team hopes to have another gorgeous view for you; a freshly poured foundation! Here’s hoping and thanks for tuning in!

The Structure at the End of the Rainbow

double rainbow over Morrisette campus storehouse

Live from a double-rainbow kissed Morrisette Campus, It’s the Thermal Mass and Buoyancy Ventilation Research Project team! Recently, as the chill rolls into Newbern, the students and faculty witnessed this heart-warming phenomenon. And if you came for the rainbows, you should stay for the structure. Hang tight to learn how the TMBVRP team is supporting the Test Buildings eight feet off the ground.

One more thing before we get on to the structure, a quick look at the Horseshoe Courtyard. During this semester the TMBV Research Project team has enjoyed working on the Horseshoe Courtyard site. Every Tuesday, project teammates Caleb and Claudia are wonderful and patient teachers to the TMBV team. The team certainly appreciates the construction experience and the time away from their computers. Go check out all of the beautiful work the Horseshoe Courtyard project team has done on their blog!

Column Conundrums

First, a quick reminder of how and why the Test Buildings are up on stilts. Because the Optimal Tuning System uses thermal mass to create airflow, the Test Buildings will expel cooled air. In the Summertime, that cooled air could be a benefit to more than just the Test Building dwellers. Therefore the Test Buildings design was lifted in order to create a Cooling Patio underneath. Here, anyone can enjoy an outpouring of chilled air. The team chose steel columns to do the heavy lifting to keep the focus of the space on the solid Downdraft Chimneys. As seen in previous blog posts, the column’s placement is dictated by the relationship to the Downdraft Chimney’s and the seating arrangement. However, the column arrangement can not just look good on paper and feel right in the mock-up, it’s got to actually, safely stand up.

Thankfully, structural engineer Joe Farruggia approved the column placementnow it was time to size the columns. Through a series of hand calculations, the team tested the stiffness of 3.5″ – 6.0″ diameter steel columns to see which ones could handle the weight of the pods. Then, Rowe took this work into Intercalc, an engineering software. Intercalce allowed him to test structural loads such as gravity loads, wind loads, live loads, and overturning forces. It turns out a 5″ O.D. steel column will be more than safe. Now, onto bracing!

Three of the four columns, per test building, are braced to eliminate excessive drift caused by wind loads on the tall faces of the buildings. Similarly, bracing the columns reduces possible deflection and improves stiffness. The column bracings, hidden in the berm walls surrounding the Cooling Patio, are 4″ x 4″ x 3/8″ steel angles. The six braced columns appear 5′ tall as they disappear into the berms while the other two are the full height of the occupiable space at 8′ tall. These taller, unbraced columns act as entrance markers.

Foundation Demystification

Originally, the team believed a concrete ring beam foundation would be sufficient for fixing the steel columns, and thus the buildings, solidly to the ground. As seen in the drawing above, the ring beams would extend to catch bracing. However, the team needed to consider overturning moments, or overturning forces, due to the height and the aforementioned wind loads of the Test Buildings. Overturning moments are those applied moments, shears, and uplift forces that seek to cause the footing to become unstable and turn over. This means they needed to make sure the foundations were strong enough to keep the columns and bracing in the ground during bad storms.

Before these moments could be properly designed for, the team needed to do some soil testing. The quality, based on its compaction, of the soil is another factor in determining the necessary size, and strength, of the foundation. Jeff and Cory dug some holes and then used a penetrometer to test the soil. And who would have thoughtthe site has some pretty decent soil! Unfortunately, Jeff has been stuck in that hole for weeks… We miss you Jeff!

To counteract the overturning forces, the foundation changed from a ring beam to a buried slab foundation which increases its weight. Each Test Building will have its own foundation. The slab foundations secure all columns and bracing to each other as well as the ground. Below are currents drawings of the foundation, column location, and bracing connections.

The Thermal Mass and Buoyancy Ventilation team will be jumping into drainage and ground material master planning next. Translating research into design into construction has been an arduous journey. However, the pay off will be worth it when designers anywhere can use the Optimal Tuning Strategy to make building materials work as air conditioners. Thanks for reading and stay tuned!

Getting Down to the Details Episode II: Attack of the Drawings

diagram of Test Building showing all details the team must draw

Live from behind multiple stacks of full-scale detail drawings, it’s the Thermal Mass and Buoyancy Ventilation Research Project Team! The team has continued their pursuit to draw every detail of the Test Buildings. These drawings have cemented aspects of the building such as cladding, roofing materials, and entryway design. Certainly, there is still much more to decide and conquer. Let’s check out what the team’s got so far.

Concrete Barrier Bargains

First up, a much-needed win for the TMBVRP team; they got concrete barriers! The Cooling Patio, a space for literal chilling underneath the Test Buildings, uses recycled concrete barriers as a retaining wall and seating. Road work being done on Highway 61 in Newbern revealed many of these stackable, concrete barriers just asking to be reused. The construction team doing the roadwork donated and delivered all of the extra concrete barriers straight to Morrisette Campus. However, this generous gift was not the only score for the team. Next, the team found more concrete barriers at the Greensboro Highway Department Office just 10 miles down the road. The Greensboro Highway Department has 40 more barriers and the team can have them if they can move them. Time to start the powerlifting team!

Cladding Conclusions

Meanwhile, as the team solidified the material of the Cooling Patio seating, they also came to exterior cladding conclusions. The last post touched on how the team committed to using timber for their open-joint cladding system. Now they have decided on wood species and size. The team chose Cypress in both 6″ and 8″ boards to clad the Test Buildings.Cypress is a locally available and weather-resistant cladding option.

Pod cross section showing cypress cladding system

The variation in board sizes allows for more flexibility around complex details. For example underneath the walkway, attached underneath the door, 6″ inch boards come up too short. On the other hand, 8″ boards overhang too much and interfere with the cladding on the Cooling Patio ceiling and Chimney. The mix of boards also allows for board spacing to differ slightly without drawing attention. Uniform board sizes make it easier to spot mistakes and the team is keen on hiding those from you.

A Smattering of Details

Because it would be entirely boring to describe each of these details; the TMBV team will just hit the highlights for you. First, the roofing material will be 1/4″ corrugated metal. While Rural Studio is no stranger to corrugated metal, this is a less common type. Being just 1/4″ in depth, this material has the advantages of durability and low price of normal corrugated metal, but with a more subtle profile. Below, you can see just how that ventilated roof and corrugated metal interact with the cypress clad chimneys and drip edge flashing. These were definitely some of the most complicated details due to the aerodynamic shapes of the chimneys and roof.

cut section through door showing door frame and walkway connection
full door section showing walkway connection

Next up is the door. Although the Test Buildings will be used as quasi-dorm rooms for 3rd-year students, the team does not want them appearing too residential. Just in case the polygonal shape and hovering nature of the Test Buildings don’t shout, “Experiment!” loud enough the door has got to be different too. The door acts as a punch through the SIPs wall and Internal Thermal Mass to emphasize that one is entering into an active system. This is done by highlighting the depth of the wall with a thin 13″ aluminum frame, slightly thicker than the wall. This detail was unabashedly stolen from the beloved Newbern Library project, the smart detail treasure trove.

And from the Details, a Mock-up is Born

After drawing and redrawing all those tricky details, Steve Long and Andrew Freear suggested the team practice building them before attempting them on the real deal. This is a time-old tradition at Rural Studio known as the mock-up. A mock-up is a condescended version of a building, or a small part of it, that allows students to practice and visualize construction. For example and as seen above, 20k Ann’s Home Project team built a wonderful mock-up where they tested all their cladding and roofing details to scale. The Thermal Mass and Buoyancy Ventilation Research Project team used this mock-up as inspiration when designing their own. You can take a look at the TMBVRP Test Building mock-up construction document set (CD set) below!

Axon and Axon section drawings of the pod mock ups

Every detail the team solved can be seen in the mock-up. The entire structure will end up being approximately 6′ x 6′ x 10′. The height is a bit substantial for a mock-up but practicing detailing the chimneys at full scale is very important. The team is making framed walls to the same thickness as the SIPs (Structural Insulated Panels) instead of building with SIPs for the mock-up. This will save a lot of time and money. The team finds the mock-up rather cute on paper though it won’t seem so miniature in person. They plan to start building the mock-up soon, but first, need to gather all the real materials they would use on the Test Buildings. It’s important they practice on something as close to the Test Building design as possible.

The Thermal Mass and Buoyancy Ventilation Research team is happy to be down in the weeds of detailing as their research becomes real. Thanks for Tuning in!

Getting Down to the Details

Live from behind a stack of full-scale detail drawings, it’s the Thermal Mass and Buoyancy Ventilation Research Project Team! Lately, the team has been investigating all details inside and out. Starting out with material pallet and ending up at chimney flashing, the team is kicking it into high gear.

Cladding Material

Unsurprisingly for a project so focused on the interior systems, it was difficult to make decisions regarding cladding. Initially, as seen in previous models shown above, the team experimented with separate cladding systems for the chimneys, Cooling Patio ceiling, and exterior walls. For iteration 1 of the test building design included a timber open-joint cladding system wrapping every surface. Next, for iteration 2, the cladding system wrapped only on the exterior wall faces of the buildings and the adjoining chimney faces. However, thin sheet metal covered the roof, cooling patio ceiling, and the chimney faces which touch those surfaces.

The consistent cladding of iteration 1 appealed better to the monolithic nature of the SIPs structure. It also reinforced the importance of the chimneys to the buildings as a whole from the exterior. From there the team began to test if the timber was the correct mono-material for the test buildings. Seen above are renderings testing different materials for the cladding, columns, retaining walls, and benches. It is important to view these materials as they interact in the Cooling Patio. While sheet metal and polycarbonate cladding options may look more monolithic, timber is a low carbon material that better represents the heart of the project. In some cases, timber as a building material acts as a carbon-sink meaning it stores and processes more carbon than it produces. This of course relates strongly to the passive goals of the Thermal Mass and Buoyancy Ventilation Research.

Recycled Retaining Wall

Now the team is settled on the timber cladding, but they are not convinced of the retaining wall and bench materials. These aspects want to be a more earthen material as they rise from the ground towards the test buildings. After investigating rammed earth and concrete, the team wanted to find something more stackable. Concrete and rammed earth are beautiful, but they require formwork which requires more time. Something stackable will give the team more flexibility as well as members are movable.

Thankfully, down here on Highway 61 road work is being done to remove a load of 8″ x 8″ x 8′ stackable concrete barriers. The TMBVRP team is getting their hands on some of these reusable members and are calling around to local highway departments to find more similar materials. If they find enough, they will have a durable, stackable, and reusable material for their Cooling Patio. They can also use the old sidewalk pieces as a mosaic, ground material for the Cooling Patio. Above are drawings showing the use of these recycled materials.

Structure and Detailing

For the past three weeks, the team has been meeting consistently with Structural engineer Joe Farrugia. He is guiding the team through lots of math to size their columns. While the gravity load on the columns is extremely manageable, the wind load is more difficult. The test buildings height means they will face more wind load than a structure this size typically experiences. However, Joe is confident that the structural system the team has chosen is doable with the correct column sizing.

While the team is attempting to draw every detail of the test buildings, they’ve found the trickiest spots to be around the chimneys. Making sure water moves off the roof consistently and air moves behind the ventilated screen is crucial. The TMBVRP will spare you the pain of walking through each flashing bend and board cut. Struggles emerge when the chimneys converge with the angled roof, but it’s very doable with lots of thinking, drawing, and redrawing. Then Andrew Freear and Steve Long, come in to save the day because how you’ve redrawn it five times is still wrong. Lots of covered wall reviews later and the TMBVRP team is on their way to compiling all the details in a digital model and drawing set.

Looking forward to keeping this momentum going, the TMBVRP can be found in Red Barn from dawn to dusk. Feel free to bring by some late-night snacks but for now thanks for TUNING in!

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!