passive strategies

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!

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!

Calibrate and Graduate

Team is posing with their new outfit

Exciting things have been happening at HomeLab lately! First, the Thermal Mass and Buoyancy Ventilation Research Project (TMBVRP) Team were able to install airflow sensors into the Concrete Chimney Experiment. Second, the chimney has brought in some impressive data. And third, the TMBVRP team participated in an end of the semester presentation and round table discussion with their big sister team, the Mass Timber Breathing Wall Research Project, and a cast of professionals in the architecture and building science research field.

This week the team received their Sensirion differential pressure air flow sensors. The sensors record a difference in dynamic and static pressure which the team uses to calculate bulk flow. Bulk flow is the total airflow at the sensor location. The team installed two sensors into the Concrete Chimney Experiment, one at the bottom and one at the top, to measure updraft and downdraft ventilation created by the thermal mass.

Just to refresh your memory, updraft occurs during the night when the cool, night air is brought in the bottom ventilation opening, warmed by the thermal mass, and exhausted out the top. Downdraft occurs during the day, the warm, exterior air is drawn into the top ventilation opening, is cooled by offloading heat to the thermal mass,  and vents out the bottom.  Being able to measure the direction and amount of ventilation is critical to understand if the Concrete Chimney Experiment is performing as expected.

And the results are in, our initial measurements from the airflow sensors do show that during the day the chimney is operating in downdraft and during the night it operates in updraft. This gives us proof of concept, that thermal mass is able to alter the atmosphere inside the chimney so that it goes against the exterior environment.

graph showing airflow in the test chimney

The GreenTeg temperature sensors have also brought in proof of concept data, showing that the thermal mass is having a damping effect on the interior air. It is important that the temperatures of the thermal mass and interior air cycle with the daily swing in temperature so that heat is absorbed by the mass during the day and offloaded during the night. This shows that the internal thermal mass is effectively moderating the temperature in the chimney and causing continuous ventilation. We are continuing our testing to further calibrate the amount of ventilation to achieve the most efficient and effective heat transfer between the internal thermal mass and air.

Temperature signal graph comparison

To wrap up our undergraduate work, we had a roundtable presentation via Zoom to give an update on where our work is and share our exciting results with Auburn, our collaborators at McGill, and professionals in the architecture and building science research field.  This panel included Billie Faircloth, a partner and research director at the architecture firm Kieran Timberlake in Philadelphia, PA.  Second, we were joined by Jonathan Grinham, who is a Lecturer in Architecture and Research Associate at the Harvard University Graduate School of Design.  Last but not least, is Z Smith.  Z is a Principal and the Director of Sustainability & Performance at Eskew Dumez Ripple in New Orleans, LA.  

It was a privilege to be able to present and have a productive discussion with such esteemed professionals.  We gained valuable insight on how to best relay the work we are doing do both those in the research field and the common person. In addition, their backgrounds led to an intriguing discussion on how The Optimal Tuning Strategy could be implemented at the building scale. It was especially awesome to discuss the successful data the team recently got form the Concrete Chimney Experiment. Both the data and the discussion gave the Thermal Mass and Buoyancy Ventilation Research Project Team a boost of confidence and pride in their work. It not always easy for these architecture students to wrap their heads around the science, but the hard work paid off. Thank you to Rural Studio, Salmaan Craig, Kiel Moe, David Kennedy, and the reviewers for a positive end of the undergraduate phase of the Thermal Mass and Buoyancy Ventilation Research Project.

Final shout out to the incredible Mass Timber Breathing Wall Research Project Team. As they complete the paper on their research and graduate from the Master’s program they still had time to do something very sweet for their little sister team. They passed along their Rural Studio lab coats, crossing out their names and writing the names of the TMBVRP team members. Their work, dedication, and attitude could not be a better example for the TMBVRP team to emulate. From one research project team to the other, thank you for helping us whenever we needed and being the best big sister team imaginable. We hope to live up the legacy! Well, everyone, stay tuned (optimally tuned) this summer for the start of the graduate program at HomeLab.

Temperature Swings

Now that the Concrete Chimney Experiment is built, let’s take a look at what should be going on inside! To understand if the Optimal Tuning Strategy is cooling and ventilating the space within the chimney, we compare four temperature signals. Quick reminder, the Optimal Tuning Strategy refers to the set of mathematical scaling rules that proportion thermal mass and buoyancy ventilation to act together in a natural feedback loop. The Thermal Mass and Buoyancy Ventilation Research Project team prefer nicknames, typing their project name is enough work.

Let’s take a look at these four temperature signals which identify how effectively the Optimal Tuning Strategy is operating with the Concrete Chimney Experiment. The temperature signals are; exterior air temperature, interior air temperature, thermal mass surface temperature, and thermal mass interior temperature. These temperatures are taken within the chimney using GreenTeg sensors. The exterior air temperature is the temperature of the air outside, like the temperature you read on a forecast. The interior air temperature is the temperature of the air within the chimney, like the temperature you read on your thermostat in your home. The thermal mass surface temperature measures the temperature of the surface of the concrete panel. This surface interacts with the interior air. The thermal mass interior temperature is the temperature inside the mass. We can use a melting ice cube to understand the difference in the thermal mass temperatures. When an ice cube melts, the surface melts first while the center of the cube remains frozen. So, the surface and interior temperatures of the thermal mass can differ just as the outdoor and indoor temperatures can.

Theses four temperature signals describe if the thermal mass is absorbing and offloading heat from the air which should, in turn, drive conveyance ventilation cycles. The times of day the mass is absorbing and offloading heat should be relatively consistent day-to-day due to the diurnal cycle. The diurnal cycle is the variation between a high temperature and a low temperature that occurs during the same day. In other words, for most days the temperature rises until a peak typically in the afternoon and then falls again until reaching a low before the sun begins to rise again.

Each day the cycle repeats. Though the time of day of the high and low can vary. Here, you can see the diurnal cycle for a typical summer day in Hale County. We can then normalize that temperature swing into a Sin Wave for mathematical analysis. This is the exterior air temperature.

To see how all these temperatures should compare to each other throughout the day we can look at this graph. Notice the axis of temperature and time are simplified radially, but we are still looking at a full day with a typical temperature swing. This graph represents an Optimally Tuned space where the proportions of thermal mass and buoyancy ventilation are ideally balanced. The solid black line represents the exterior air temperature. The dotted gray line represents the interior air temperature. The solid orange line represents the thermal mass interior temperature. The dotted orange line represents the thermal mass surface temperature. As you can see, the interior air temperature is never hotter or cooler than the exterior air temperature. It is dampened by the thermal mass absorbing and offloading heat from the interior space. The thermal mass surface and interior temperatures show the mass warming by the absorption of heat from the air and cooling when the heat releases back into space. When the thermal mass and buoyancy ventilation proportions are not balanced the graph looks drastically different.

On the left, you see what it would be like if there were a lot more ventilation and a lot less thermal mass. Too much ventilation causes the interior environment to act just like the exterior environment and there is not enough thermal mass to affect the space. This would be like being in a tent. On the right, you see what it would be like if there were a lot less ventilation and a lot more thermal mass. Too little ventilation does not bring in enough heat for the thermal mass to absorb. The thermal mass is also so large it takes too much heat to fill up, which means it takes longer for the mass to start offloading it into the space. This is like being in a cave.

temperature signal graph
Temperature signal data graphed to compare to ideal Optimal

Finally, here is some of the data we have pulled from our sensors so far! Although the Concrete Chimney Experiment is definitely damping the temperature within the space the thermal mass temperatures are essentially the same. This means we may not have enough ventilation, not enough heat being brought in with be absorbed and offloaded. We are working on getting airflow sensors to see if this could be the case. The team is also recalculating the size needed for the ventilation openings.

If you stuck around until the end of this one, big thanks! Here’s a picture of Cory’s kittens Rosemary and Dijon to ease your mind. As always, we will be back soon with more rural science so stay tuned…. optimally tuned.