The primary objective of this study is to determine the best combination of roof characteristics (insulation thickness, membrane color) that prove to be the most energy efficient. Researchers are interested in observing heat transfer occurring within the matrix of a roof and have been able to do so with two types of sensors - heat flux and thermocouples. Heat flux sensors measure the rate of heat energy transfer and thermocouple sensors measure the temperature at given locations. The data drawn from these sensors can provide a visual picture of the path solar energy travels as it passes through the roof, and sometimes, penetrates the building itself. Researchers will be able to share this knowledge with the commercial roofing industry in efforts to retrofit and optimize roofing designs, and ultimately influence energy efficiency in the commercial sector.
The sensors were strategically placed at different levels within the roof to observe temperatures at different thicknesses. Heat flux sensors were installed at the surface below the membrane and at the base of the insulation against the roof deck. Thermocouples were installed at different thicknesses of insulation to observe temperature variations. They were also placed within the air plenum above the suspended ceiling to observe any penetration of heat to the interior environment. The locations of sensors varied slightly among the five roofs in the study, depending on the structure and design of the roof.
Administration Building (R-48, white)
The Administration roof was the first roof to have sensors installed. Three heat flux sensors were placed at equal depths within the insulation. Thermocouples accompanied the sensors and an additional two sensors were mounted to the roof deck and placed in the plenum air space above the suspended ceiling. This setup allows for thorough and complete analysis of how heat is transferred throughout the matrix. This roof design has a R-48 value at this location and a white membrane. It is the thickest insulation value studied.
Engineering Building (R-36, black)
The Engineering roof has a layer of plywood located above the insulation and below the membrane. This roof is unique in that none of the other roofs in the study are constructed with plywood. Heat flux sensors were placed at the surface beneath the membrane and at the bottom of the insulation resting on the roof deck. These locations are ideal for observing differences in heat flux between extremes. Thermocouple sensors accompanied the heat flux sensors and were additionally placed beneath the plywood, in the center of the insulation, and in the plenum air space above the suspended ceiling. The distribution of sensors within the roof matrix generates valuable data to depict heat transfer from one layer to the next. Data acquired from thermocouples above and below the layer of plywood can be comparatively studied to determine if there are any insulating properties of plywood itself. The Engineering roof has a R-36 value at this location and a black membrane.
LSB Extension (R-24, black section & white section)
The LSB Extension roof is the newest roof on PPPL's campus. It was installed in the summer of 2012 and is primarily white; however, for the purpose of this study, a black membrane was also used on a portion of the roof. The black section was studied alongside the white section; both study sites had identical sensor locations within the roof matrix. The uniqueness of this roof is the apparent DensDeck layer immediately below the membrane. This material is denser, thicker, and much stronger than a material such as plywood. These characteristics enable it to potentially support alternative forms of energy such as solar panels; plywood and other common building materials do not have this functionality. The thermocouples are strategically placed at almost every layer within the matrix, providing comprehensive temperature range data. The black and white sections of this roof share one weather station with independent surface temperature technology. In the locations that are being studied, the roof has a R-24 value.
Theory Wing (R-21, black)
The Theory Wing roof is the oldest roof that researchers are studying. The purpose of studying this roof was to observe an older roofing design against those of modern design. The Theory roof, constructed in 2002, is representative of this type of design at nearly over a decade in age. Developing research and increasing knowledge of insulating techniques have helped to progress the roofing industry over the decade. Advancements in the roofing industry have led to enhanced roof designs, greater energy efficiency, and the testing of new concepts. The roof is constructed with a single layer of 3.0" insulation and a black membrane, for a R-value of R-18. Due to the adhesive properties of the design, it was not possible for researchers to install sensors without replacing the installation first. Consequently, existing insulation was replaced with two layers of insulation for a total thickness of 3.25" and a R-value of R-21. Although the improvised design is not identical to existing conditions it remains an accurate representation of aged roofing designs with minimal insulation and a black membrane.
