P16486: Test Rig to Characterize Biochar Housing Materials

James Reitano, Lakeishia Brown, PrasannaParthiban, Kimberly Eklund, Domenico Colati, Sari Houchaimi

The Ithaka Institute wants a credible method that will help to validate if biochar could be a healthier choice for housing materials. By testing the material, it is possible to see how it can withstand natural climates, as well as, normal living conditions. If biochar succeeds in coping with the various changes, it could help to reduce the amount of carbon dioxide in the atmosphere which would significantly improve environmental conditions.

An environmental test chamber (ETC) is modified in a way that would test the durability of the biochar. The modification includes a heating bar for increasing the temperature, as well as a humidifier to test the humidity of the biochar. The ETC is set up in such a way that other housing materials can be tested in place of the biochar. Eventually, the results of biochar would be extracted from the test, and compared with other housing materials. This would help to determine if the biochar is better suited than its competition.

Background

The Ithaka Institute is a non-profit organization based on the research of carbon sequestration through the use and treatment of biochar, a coal substitute now being looked at as a possibility in housing materials [5].

Biochar is created by the thermochemical decomposition of organic materials at elevated temperatures in the absence of oxygen, a process known as pyrolysis [6]. It can be made from many types of biomass, including agricultural wastes. Biochar also has unique characteristics due to its composition and physical structure including low density, high porosity, and a high pH level [1]. Due to its stability, it has potential for sequestering carbon taken from the atmosphere as a remediation for climate change [1].

One of the more novel uses of biochar is as a component in building materials [4]. Researchers are beginning to experiment with biochar amended concrete and plastic composites that could result in lighter weight and lower cost building materials with enhanced insulating, filtering, cooling, and humidity control characteristics [4]. Some recent attempts include biochar-concrete panels, biochar-lime bricks, indoor and outside insulating plasters [4].

As this field progresses, the Ithaka Institute would like to be able to test the properties of building materials made with biochar. The goal of this project is to develop a test rig which can adjust the humidity and temperature outside a biochar “building” and measure changes inside the building over time. The test rig must be transferable to real environmental conditions (outdoors).

Process

Requirements

Prior to the designing phase of the project, the customer had asked for specific requirements to be met. These requirements were vital in collecting the correct results, as well as, being able to compare the different housing materials. The customer requirements included, but not limited to: the ability to record and store the changes in temperature and humidity over time, applying airflow to the ETC, accommodating indoor and outdoor test conditions, the ability to control, adjust, and hold external temperatures and humidity, and being able to accommodate different wall types.

The engineering requirements were constructed by team P16486. This requirement outlined

the elements that are considered to be add-ons to the ETC. This includes: the heating element, temperature sensors, humidity sensors, microcontroller, fans, and drawe. The heating element had an ideal value of 60W, the sensor accuracy +/- 2%, the power had an ideal value of 120 Vac, and the fan required 0.05 m^3/s. Further, the inner diameter of the cylinder should be nearly 3 inches, included with a slight clearance, an outer diameter of 5 inches and height of 7 inches. Further, the half sphere required an inner diameter of 5.5 inches and an outer diameter of 6 inches.

Using the customer and the engineering requirements, a flowchart was designed to show how the ETC would operate as a whole. The flowchart is shown below in Figure 1. When analyzing the flowchart, it is possible to see how each of the subsystems within the ETC would communicate with each other.

Functional Decomposition

As the main goal of this project is to test biochar as a housing material and compare it to standard housing materials, biochar must be accessible, appropriate tests must be conducted on the biochar to determine its abilities, and lastly the data from said tests must be analyzed. Part of acquiring biochar requires that it is made into a suitable housing material. After which, the material must be secured to the test chamber that will be implemented. Further, after the material is secured, multiple tests will be ran to characterize the materials; i.e. to record the change in temperature and humidity. Lastly, after an appropriate number of tests, a data storage device used in the test chamber can then be retracted and analyzed.

Concept Screening/Selection

To access material, a drawer was decided to be the most practical method to expose the test sample to ambient conditions. Further, a computer fan would be utilized to produce airflow. Specific sensors would be chosen in order to provide necessary accuracy, have recording capability, and would be practical in size and weight in relation to the testing apparatus. In addition, a USB was chosen to store the data from tests performed; it is the most common and is the least likely to have compatibility issues with users' computers. Finally, a graphical spreadsheet such as Excel would be used to analyze all data and an LCD controller would be used as the user interface, all powered by an AC supply.

System/UI Flow

The controller flow diagram shown above represents how the microcontroller would operate in order to successfully power and run the Environmental Test Chamber (ETC). When analyzing the diagram, the process that is takes to run a full test is shown in detail.

The purpose of the user interface is to guide the user in setting up the ETC to test the biochar. Upon powering up the ETC, the interface displays “Biochar Testing; Press Enter”. Using the keypad, the button labeled “Enter” would be pressed to input the required values. After pushing the button, the option to complete a thermal test, or a humidity test will be provided. There are left and right buttons on the keypad that would allow the user to choose between the two tests. To complete a humidity test, the “Humidity” option would be selected using the keypad. To complete a temperature test, the “Thermal” option would be selected. If the “Humidity” option is selected, then the user would then be asked for the maximum humidity percentage. The up and down buttons on the keypad can either increase or decrease the percentage of humidity that is wanted. Once the desired percentage is selected, then the interface will ask for the test time. The user would first input the hour, followed by the minute. After selecting required time, the interface will display the timer for the user to know how much longer until the test is completed. Once the timer is done, the microcontroller will beep, and the green LED will turn on. Then interface will then display “Done; Connect PC; then press print”. This gives the option of printing out the values of the humidity test once you connect a USB to the microcontroller. The thermal testing is similar to the humidity test as far as the process goes, however, you will input different values. The thermal testing asks for the maximum temperature, the width of the sample you want to test, and then it displays the internal and outer temperature while the test is running. When the test is complete, it will display “Test Complete” and then show the K and R value.

Heat Transfer Model

To properly assume one dimensional heat transfer with minimal errors, a cylindrical model would be utilized.

The overall objective is to determine the k value (thermal conductivity) of the biochar cement cylinder to quantify its insulation abilities. To do this, an electric heater will be placed in the center of an aluminum cylinder, with the top and bottom thermally insulated, to ensure that uniformly heat power is applied. The model will then be calculated backwards for k (thermal conductivity) and R (thermal resistance). In this case, the refrigeration system can be eliminated thereby resulting in decreased complexity and cost while producing a scientific result simultaneously.

In order to experimentally determine the k and R values, the following mathematical model is used:

Q = Total Heat Transfer (heat supplied) L = Length of the cylinder

k = Thermal conductivity R = Thermal Resistance

T1 = Inner Temperature r1 = Inner Radius

T2 = Outer Temperature r2 = Outer Radius

Humidity Analysis Model

In quantifying biochar as a housing material, its capabilities of controlling varying humidity levels in the ambient air needed to be tested. The most appropriate model to ensure uniform modelling was a half sphere with a uniform thickness.

Testing

Test Plan

In testing the overall system, subsystems were tested first for feasibility and general usability. The components tested included: the Microcontroller (S1) and its ability to hold data (S2), the interface and corresponding buttons to control it (S3), the humidifier (S4), the fan and airflow production (S5), the heater (S11), temperature and humidity sensors (S6, S7), a calibration test for thermal conductivity (S8), overall thermal conductivity of biochar (S9), and a humidity test on biochar (S10).

Please refer to go to “Integrated System Build and Test” and refer to the link for an overview of the test plan.

Procedure for Testing System

Using molds and varying recipes of cement (with or without the use of biochar), create cylinder and/or half hollow sphere shapes for testing.
Thermal Conductivity Test
Place sample over aluminum cylinder and secure sensor using allocated sensor arm.
Follow steps for interface in the User Manual
Test for Relative Humidity
Place hollow half dome on neoprene on tray, ensuring coverage of the humidity sensor.
Follow steps for interface in the User Manual

Results/Discussion

In testing the microcontroller, that would be use to control settings and tests on the environmental test chamber, functionality, storage, and the interface were all tested. It was found in a simple coding test, in junction with the sensors, that the Dragonboard-HC12 will suffice. Further, in performing a trial and error test, it was solidified that the microcontroller will hold 56kB of data, 48kB would be designated for recording samples, allowing for 3000 sample with space to store code. Lastly, the interface was coded two times over. The first, original, code had simple usability. However, the new code featured a more sophisticated math library added allowing for double precision floating point values, which would help with accuracy and rounding errors.It also added user input of sample thickness in order to accommodate future expandability by allowing different sample thickness.

Additionally, three humidifiers were tested for functionality for a successful humidity test. Humidifier 1, a 12 LED fountain pond humidifier, failed to mist and humidify; ergo, two different humidifiers were purchased. Humidifier 2, an Aluminum mist maker fog maker, splashed excessively, however worked sufficiently and formed humidity in ETC. Finally, humidifier 3 is 5V water bottle mister and worked sufficiently. Additionally, a humidity sensor setup accordingly to test relative humidity (please see Humidity Sensor plot below). One humidity sensor read up to a value of approximately 95% after nearly 5 minutes of running both the humidifier and fan. Humidity sensors should suffice for test. Finally, a computer fan was tested in combination with the humidifier and worked sufficiently in both high and low speeds.

Lastly, the heater was given power and produced sufficient heat to show temperature readings from the sensors that successfully displayed on the interface (please see Temp Sensor plot below). Ergo, the water heater should suffice in one dimensional heat transfer analysis on the biochar cylindrical model. Further, the heater was connected to temperature sensors and read up to approximately 250 °F. Therefore, sensors can read increasing temperature from heater which will aid in deriving a thermal conductivity value.

In calibrating the heat transfer model, Owen’s Corning R250 Insulation was made into a cylinder and implemented into the system. This R250 insulation has a characteristic R value of R5 per inch, so with a thickness of 1.4 inches, the expected R value would be 7. The actual R value received was approximately 7.5, with a percent error of 7.7%.

Further, in extracting the thermal conductivity of biochar, an R value was found to be approximately 1.7, whole concrete has a value of 1.5.

Conclusion and Recommendations

In conclusion, 5% biochar cement mix compares closely with high end concrete and can therefore qualify as a housing material. Due to time constraints, the humidity control characteristics are still unknown. However, biochar by nature is lightweight and more porous. It can be assumed that while porous, it will control changes in ambient humidity fairly well.

In utilizing the test rig created by this project, it is recommended that the user only use molds provided that integrate easily with the test chamber and that they closely follow the user manual. Further, it is strongly suggested that the user implements a vibration table in the mixing of the concrete to mitigate heat loss in thermal conductivity testing and to decrease the amount of pores for humidity testing.

Acknowledgements

We would sincerely like to acknowledge Kathleen Draper for her support and guidance, as well as for sharing her knowledge of Biochar. We would also like to thank Sarah Brownell for the amount of information she has provided as well as explaining exactly what needed to be done. Additionally, we want to acknowledge George Slack for making us always ask "Why" to obtain all of the information we needed to undergo this project successfully. Lastly, we want to thank the MSDII team that clarified for us how biochar can be used to making housing materials!

References

[1] "Biochar : USDA ARS". Ars.usda.gov. N.p., 2016. Web. 10 Nov. 2016.

[2] "Ithaka Institute - 55 Uses Of Biochar". Ithaka-institut.org. N.p., 2016. Web. 10 Nov. 2016.

[3] "Ithaka Institute - Biochar Production". Ithaka-institut.org. N.p., 2016. Web. 10 Nov. 2016.

[4] "Ithaka Institute - Building Material". Ithaka-institut.org. N.p., 2016. Web. 10 Nov. 2016.

[5] "Ithaka Institute - Home". Ithaka-institut.org. N.p., 2016. Web. 10 Nov. 2016.

[6] "Pyrolysis". Cpeo.org. N.p., 2016. Web. 10 Nov. 2016.