The following results highlight the hottest days of this past summer. Thermocouple readings are plotted against time in a graphical representation of heat transfer through each roof matrix.
TC High, the sensor located beneath the membrane, values for all figures showed the greatest fluctuation in temperature. All graphs depict a diurnal heating and cooling cycle of the roof matrix. Heating occurs for twelve hours and subsides for the following twelve hours.
The following images may be difficult to read - follow this key for interpretation OR you can view the attached document at the bottom of the page.
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Comparison: Admin White R-48 & Engineering Black R-36
Figure 1. Administration roof (White, R-48). Heat Flux and Thermocouple Readings in degrees Celsius over time in UTC. June 21 - 23, 2012.
Figure 2. Engineering roof (Black, R-36). Heat Flux and Thermocouple Readings in degrees Celsius over time in UTC. August 8 - 10, 2012.
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Comparison: LSB White and Black R-24
Figure 3. LSB White roof (R-24). Heat Flux and Thermocouple Readings in degrees Celsius over time in UTC. August 8 - 10, 2012.
Figure 4. LSB Black roof (R-24). Heat Flux and Thermocouple Readings in degrees Celsius over time in UTC. August 8 - 10, 2012.
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Figure 5. Theory roof (R-21). Heat Flux and Thermocouple Readings in degrees Celsius over time in UTC. August 8 -10, 2012.
Roof Membrane Color: White vs. Black
* White membranes absorb significantly less heat at upper levels of the roof matrix; consider that black roofs reached temperatures ~30 ͦC greater than white roofs.
* White roofs show little to no heat transfer to the lowest levels of the roof matrix, therefore reducing the heating impact on the interior environment.
* Black membranes absorb more heat & release it quicker than white membranes over the same period of time.
Insulation Thickness
* 8” of insulation, on a white roof, is found to have little to no recognizable heat transfer into the indoor atmosphere.
* 0.5” Plywood and 5/8” DensDeck do not seem to provide any insulation value on the ENGIN & LSB roofs.
* ≤3.5” insulation led to visible heat transfer to the metal roof deck; however, 5.25” insulation was sufficient to prevent this heat transfer to the metal roof deck.
* There is greater heat transfer to interior levels of the roof matrix in values ≤R-24.
* The precense of thicker insulation slows heat transfer to the interior plenum airsapce.
* There is immediate heat fluctuation observed by the Plenum air thermocouple, experiencing no lag between temperature increases at the surface and termperature increases in the interior plenum air.
Further Investigation
* Acquire & analyze data for winter months.
* Study the building envelope & compare to heating/cooling loads, total heat loss and gain, & roof sensor data.
* Consider tradeoffs between maintenance & cost-benefits.
* Generate an interactive model to portray different roof designs and the associated heat transfer - to be used as a model for different climatic regions.
