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. A general method for testing the insulative properties of a variety of materials was desired. The possible use for the Senior Lab course in later semesters was another possibility. This opportunity allowed for a vast amount of research on similar studies, methods for collecting data and interpretation of the results.

Problem Definition
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 in order to provide experimental data from a simulated building insulation envelope. In order to reach the goal, the team designed testing equipment that could enclose the insulation as well as an internal heat source. An experiment 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 for testing. 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.

Background
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.

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 other various equipment insulation. This project featured aerogel and polystyrene foam board insulation types. Both were easily available and could be found in the required sizes.

Concepts Considered
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 would be used to later on upgrade the base model. 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 would 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. It was able to provide all the necessary functions required without the construction time costs.



Methodology
Temperature gradients will be observed in a simulated room model using aerogel, R max thermosheath, simple carpet, and plywood. Hobo temperature sensors will be 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 beginning of the experiment will consist of lighting two simple candles within the box.

Once the candles have been verified to be lit, the box will be sealed. The box will have several air holes in order to provide enough oxygen for the candles to remain lit.

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 cuts 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.

Specifications
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.

Test Results
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.

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