Note: This is the second article of a three-part series covering green building plastics (1) trends, (2) material/process advances and (3) applications.
Green building technology redefines how we make and live in buildings. From a plastics material and processing perspective, we can both reduce a building's energy consumption and simultaneously provide for a building's energy production.
These plastic material and process advances "disrupt" an existing market by displacing earlier technology. Let's delve into some emerging green building technologies that involve plastic material and processing aspects.
Energain, developed by DuPont, is a long-lasting thermal mass sheet solution for environmentally sustainable buildings based on an innovative phase-change material. The extruded sheet stock shape — length x width x thickness is 1198 millimeters (mm) x 1000mm x 5.26mm — is composed of 60 percent polyolefin copolymer and 40 percent paraffin wax, with aluminum sheet facing on all surfaces.
The phase-change paraffin wax increases the thermal inertia of a building. As the internal temperature of the building rises, Energain absorbs and stores the heat, which it releases back as the temperature drops in the evening. The panel must be cooled at night, in order to work again the next day.
The aluminum facing protects against fire, rigidifies the panel for easier installation, and protects against wax migration. Typical heat storage capacity of Energain is 143 watt hours per square meter or 45 BTU per square foot.
This sheet building product can help improve summer comfort by stabilizing effects on room temperature by up to 7 degrees C. Energain was field tested in cooperation with the EDF (Electricité de France) in identical structures with and without Energain. The peak temperature was reduced an average of 4.5 degrees C during the validation period up to a maximum of 6.7 degrees C.
DuPont
Energain panel installation (left) and a look at concrete/other materials vs. Energain energy comparison (right).
Continuing in exterior construction, "cool roof" coatings are advancing rapidly into the market place. Rooftops and other artificial surfaces absorb heat from the sun, creating an urban island heat effect that can raise city temperatures 1-3 degrees C or more compared to rural surroundings.
If all rooftops were painted white, this urban island heat effect could be reduced by 33 percent. In addition, white roofs significantly reduce temperatures within buildings. Adding a layer of specialized white coating on flat or low-slope rooftops provides these main benefits:
- Extends the life of the roof — Cool roofs are typically 50-80 degrees degrees F cooler than typical asphalt roofs
- Increases heat reflectivity reducing annual air conditioning costs by up to 25 percent
- Decreasing annual CO2 emissions by 5 metric tons for every 10,000 square feet of commercial roof space
Dow Chemical sees huge market potential for its acrylic-based elastomer coatings for ThermoPlastic Olefin (TPO) rooftops in the U.S. Dow estimates that there is between 5 and 10 billion square feet of installed TPO rooftops in the U.S. just waiting to be coated.
Dow and the Oak Ridge National Laboratory are collaborating to advance cool roof technology with a focus on advanced reflective know-how. Dow has commercialized new "Cool Roof" coatings, which are widely considered a cost-effective means of improving the energy efficiency of both new and existing buildings.
A focus will be on technologies with the potential to improve the long-term resistance to dirt pickup and microbial growth in white elastomeric roof coatings. This is a key consideration for widespread commercial adoption of cool roof technology. Currently, after three years of exposure to the elements, today's cool roof coatings may lose as much as 45 percent of their reflectance.
The U.S. Department of Energy (DOE) has implemented a series of initiatives to more broadly advance cool roof technologies on DOE facilities and across the federal government. As part of that effort, all DOE offices have been directed to install cool roofs whenever cost effective over the lifetime of the roof, when constructing new or replacing old roofs.
Finally, ground-loop heat exchange systems are coming of age with respect to plastics material and process. Geothermal heat pump systems take advantage of the moderate and relatively constant ground temperatures to provide renewable energy for heating, cooling and domestic hot water.
According to the DOE, geothermal systems are "the most energy-efficient, environmentally clean and cost-effective space conditioning systems available today." Because they use electricity only to move energy, rather than to generate it, geothermal heat pumps are significantly more efficient than conventional systems. They typically use only one unit of electricity to move three to four units of energy from the earth.
A great example of this is the Raugeo ground-loop heat exchange system from Rehau. A high-efficiency geothermal energy source for home heating and cooling, the Raugeo system incorporates advanced high-performing components including PEXa (crosslinked polyethylene trade named Raupex) pipe, double U-bends and geothermal manifolds.
The durable PEXa provides superior resistance to impact, rock impingement and the stresses of earth movement. Unlike high density polyethylene (HDPE) pipes that require sand-bedding, PEXa pipes can use natural backfill, which is lower in cost and provides superior thermal conductivity.
The superior flexibility of PEXa pipe allows a continuous length of pipe to be bent into a tight 180-degree radius for U-bend fabrication. The PEXa's high degree of crosslinking results in a durable, yet flexible pipe with enhanced temperature capability and long-term strength.
Rehau
Raugeo ground loop heat exchange system. Two U-bends per borehole achieve up to 20 percent more energy extraction.
