An-Gels of Insulation
|Sponsor||University of Idaho Mechanical Engineering Department|
|Advisor||Dr. Behnaz Rezaie|
|Duration||Fall 2017 - Spring 2018
|Team Name||An-GELs of Insulation|
This team’s project was sponsored by the University of Idaho, which allowed for a great deal of freedom in the scope of what the project entailed. The project was centered on testing the insulative properties of a variety of different insulation materials, as well as designing the proper equipment required to test them. It was also determined that the equipment and procedure could be replicated and improved upon for an ME 430 Senior Lab project. This opportunity allowed for a vast amount of research on similar studies, methods for collecting data and interpretation of the results.
In 2015, about 40% of total U.S. energy consumption was consumed in residential and commercial buildings. Most existing buildings in the US were built before building energy efficiency was a concern, and most of these buildings will still be in use for quite some time. They are not built with energy savings in mind. It is of great interest to decrease their heat loss in the least intrusive and least expensive way possible. A probable, and perhaps inexpensive way to lower the heat loss of buildings is to retrofit them with improved insulation. The alternative is to overhaul a buildings HVAC network, which can be expensive and intrusive.
This team aimed to characterize the performance of various types of insulation. A simulated building insulation envelope was designed in an attempt to replicate real world situations. The team designed testing equipment that could enclose the insulation as well as an internal heat source, similar to a building. An experimental procedure to accurately measure the performance of each type of insulation was required. The testing equipment required several design options before finding the most effective option. The testing equipment needed to be able to properly house several different types of insulation. Additionally, it was required for the types of insulation to be easily changed. Making the insulation easier to change would reduce the efforts for each test and allow for more testing to be performed.
Insulation materials are often accompanied by an R-value, which corresponds to the effectiveness of the insulation. However, it is not always easy to see how these different R-values affect the performance of an insulating envelope. Experimental data is required to directly compare the operation of different insulation's. This team’s project revolved around designing testing equipment and performing an experiment on different types of insulation. Gathering experimental data allows for further exploration into the effectiveness of different insulation's. Increased understanding of insulation properties allows for more informed design choices.
Common insulation used in buildings are shown below in the table.  Not all of these types were used during the project due to time constraints.
|Glass Fiber||Glass fiber is a woven glass with extremely fine fibers. Most buildings in the United States use glass fibers for insulation. Typical R values range from 11 in low density fibers, to 21 in higher quality ones.|
|Mineral Wool||Contains of natural minerals such basalt or diabase. Commonly comes in blankets and is composed of 75% recycled content. It is flame resistant. |
|Cellulose||Primarily composed of recycled newspaper. Can be used as a loose-fill insulation in building cavities. 
|Polystyrene||Themroplastics that is colorless and transparent. Used to make foam board insulation of beadboard insulation.|
|Aerogel||Aerogel is a lightweight, porous substance created by evaporating a solvent from a silica base. Aerogel contains around 50%-99.8% air while maintaining a rigid structure.The end result is a material that has very low thermal conductivity.|
Other types of insulation are shown in the table. They each have various pros and cons that enable them to be used in different applications. Common applications include wall insulation, roof insulation, piping insulation, as well as insulating of valves and other piping components. This project featured aerogel and polystyrene foam board insulation types. Both were easily available and could be found in the required sizes.
The majority of design work was centered on the testing equipment.
The testing equipment needed to be easily transported through various building doorways while still providing a stable testing environment. The idea was to have a two cubic foot enclosure that was suspended several feet in the air. Each side panel of the box would be removable, allowing for various insulation types to be attached to the interiors for easy installation. Sensors would then be placed on both the interior and exterior or the box walls to measure the temperature profile for later calculations. Costs for construction would entail plywood, screws, wood framing, hinges, and wheels.
Instead of constructing a testing environment from scratch, the team instead purchased an 18”x18”x18” shipping create from an online company. This saved a significant amount of funding which was used later on to upgrade the create to perform as required. Construction time was able to be disregarded as the setup of the testing equipment took little time. Similar to the previous design, a thermocouple was placed on the interior wall surface along with an air temperature sensor. On the exterior surface another thermocouple was also be attached in order to get a temperature profile through the walls. There is also an ambient air temperature sensor that measures any fluctuation in the environment to ensure consistency. The testing equipment is lightweight, which makes it easily transported. It also is able to be easily assembled and disassembled on site.
Temperature gradients were observed in a simulated room model using aerogel, R max thermosheath, and simple carpet. Hobo temperature sensors were used to measure and record the temperature at several points both within and without the simulated wall.
Measurements will be taken in 5 second intervals. The time could have been reduced to get better validity, but the storage capabilities of the HOBO sensors were limited. The beginning of the experiment consists of lighting two simple candles within the testing enclosure to provide a source of heat.
Once the candles have been verified to be lit, the box will be sealed. The box has several air holes in order to provide enough oxygen for the candles to remain lit. This is a source of uncertainty, as the ventilation allowed for more heat to leave. However, each type of insulation was faced with an identical setup, thereby mitigating the holes effects.
A waiting period of 30 minutes was used to allow the testing equipment to reach steady state conditions. Once steady state conditions were reached, the holes were covered with aluminum tape.The tape cut off the oxygen and extinguishes the candles. Another waiting period of 60 minutes was observed. During this time, the heat would leave the testing enclosure. At the conclusion of the experiment, the data was plotted to establish a temperature profile over time. These temperature profiles were compared for the various insulation materials.
Curve fits were established using fitting commands within excel to generate an equation relating temperature versus time. The derivative of this empirical equation was then used to compare the time rate of change of temperature. The time rate of change of temperature provided insight on how quickly the temperature declined within the box for various materials.
The table below outlines the specification for the project. They define the type of equipment required and outlines the expectations of all parts of the project.
|Sensor Temperature Accuracy||+/- 1 Degree C|
|Data Logging Capability||Able to log and record reading every minute for 90 minutes, or duration of test.|
|Test Specimens||All test insulation must be equal thickness, or as close to equal thickness as possible
|Temperature Measurement Locations||Temperatures will be recorded in three locations. One temperature sensor will record the ambient air temperature in the center of the box, Another temperature will be recorded on the inside of the walls and on the surface of the test insulation. A third temperature measurement will be taken on the surface of the box.|
|Model Material||Model will be constructed using plywood and 2X2 wood framing. The goal is to replicate a residential home as closely as possible.|
|Size of Model||Model will be a cubic structure with an internal volume of approximately 8 cubic feet.|
Shown below is a temperature versus time plot of aerogel and R max Thermosheath. The temperatures rise until steady state conditions are reached. Once the candles are extinguished, the temperature begins to decline towards room temperature. The rate at which this decline occurs is what is important. A slower rate of decline indicates that an insulation is better suited to keeping heat inside a space.
The maximum temperature was higher for the thermosheath than for the aerogel. This is likely due to fluctuations in candle output. Many other tests result in fairly different maximum temperatures. The ambient room conditions were constant for the most part. The different candle outputs can be rectified by analyzing data from within a common range of temperatures. For example, the maximum temperature reached in all tests was 100 degrees Fahrenheit, therefore the temperature decay from 100 degrees and below were used for analysis.
The internal wall temperatures were found to increase in temperature more quickly than the air inside the box. One possible reason is radiative effects from the light of the candle. The light from the candle hits the inside surface of the box where its energy is then absorbed and the surface warms. This effect is only temporary. Once steady state conditions are reached, the difference in temperatures between the walls and the box air become negligible.
Once the candles are extinguished, the wall temperatures are shown to decrease faster than the air temperature. This was expected due to the walls being exposed to a temperature gradient from the outside air. This temperature gradient drives heat from the higher temperature inside wall towards the colder air within the room. Heat from the air within the box then moves towards the walls.
To account for different maximum temperatures within the box, data was selected from 100 degrees and below. This allows for different types of material to be compared on a more equal footing.
Conclusion and Future Work
The team has provided all of its deliverables. First, a reusable testing apparatus was obtained. This box allows for insulation to be easily changed. Second, temperature data was obtained for several types of insulation. Several trials were administered for each type of insulation. Third, graphs showing temperature distribution and temperature decay were created using temperature data.
Several trends were identified during testing. The interior surface of the box reached a steady state temperature more quickly than the internal box air temperature. This was likely due to radiation effects from the candle. Once steady state conditions were reached and the candles extinguished, the internal surface temperature began to decrease more quickly than the internal air temperature. This was expected as the temperature gradient between the internal and external surfaces was high, meaning a higher rate of heat transfer would occur.
Once the candles were extinguished, the temperature began to decay as expected. The team was interested in comparing how quickly the temperature dropped for each type of insulation. A comparison was made between 100 ℉ and room temperature. These graphs can be seen in appendix B. It was observed that the temperature dropped more quickly in the R_max foam board. The carpet was found to have the slowest decline in temperature.
The team compared the slopes of the temperature decay to get a closer look at how quickly the temperature dropped per second. Once again, the carpet had the slowest temperature decay while the R_max foam had the highest, with aerogel being in between.
The R-value of aerogel tested is around 3.79 [h-ft^2-F/Btu] while the R_max was listed as 3.2 [h-ft^2-F/Btu]. Therefore it was expected that the aerogel outperform the R_max. The caret, however, did not come with an R-value. Based upon the results of the aerogel and R_max. The R value of the carpet is likely higher than the aerogel. The carpet was also thicker than the other two materials, therefore making it difficult to accurately determine how effective an equal thickness of carpet would be.
The experiment can be improved through the use of a more consistent heat generation source. A hair dryer or portable resistance heater placed inside the box would likely provide a more consistent result, which would allow for easier comparison. Many additional materials can be tested to widen the scope of the project. Another source of improvement could be the implementation of additional thermocouples located in between the different layers of insulation. Knowing the temperature in more locations would increase the amount of knowledge available on the heat transfer.
Continuation of this project would allow future students to become familiar with thermocouples and air temperature sensors as well as improving coding skills through MatLab or other computational programs. This would be an excellent project for ME 430 senior lab.
Austin Anderson is a senior in mechanical engineering at the University of Idaho. His interests include thermal energy systems and power generation. Following his graduation in May 2018, Austin plans on attending the University of Idaho to earn his Masters of Science in Mechanical Engineering.
Cameron Moore is a senior in mechanical engineering at the University of Idaho. His interests are in clean energy resources and fluid mechanics of which he hopes to start a career in.
Nick Chen is a senior in biological engineering at the University of Idaho.
Yue Yu is a senior in electrical engineering at the University of Idaho.
- About Aerogel|url=http://www.zerogaerogel.com/aboutaerogel.html