Monday, July 27th, 2015
Imagine a home that produces its own electricity. At times it may use some energy from the power grid, and at times it may give some back. But in the end, the give and take balance out.
We actually do not have to imagine, because these homes already exist. And plastics play a fundamental role.
Zero Energy Homes
They are known as “zero energy” homes. Zero energy does not mean the homes use no energy for heating, cooling, and electricity. It simply means that the homes’ own energy supply is equal to the homes’ energy use. As noted, the homes at times may use energy from the community power grid and at other times may provide energy to the grid, but over time the home is net energy neutral, which is why they sometimes are called “net zero-energy.”
Homes that actually produce more energy than they consume over time are called “positive energy” or “net positive energy” homes.
These homes now are a reality, through a combination of passive energy sources such as solar and geothermal and a proper design with modern plastic foam insulation and other materials.
Nearly 40 percent of our nation’s energy is consumed in our homes and buildings, and heating and cooling account for most of the energy use in a typical U.S. home, according to the U.S. Energy Information Administration (EIA). Unfortunately, much of it is wasted due to outdated building practices. In addition, EIA estimates that six percent of energy is lost in transmission over power lines. Wasted energy not only hurts our environment, it hits our wallets, as well.
Zero energy homes can contribute significantly to our nation’s efforts to improve energy efficiency in two ways—by providing passive electricity on site and eliminating long distance transmission power loss.
How do we know this really works? The National Institute of Standards and Technology (NIST) built a “Net Zero Energy Residential Test Facility” near Washington, DC, in 2013. On its July 1 one-year anniversary, NIST announced that the home produced more energy than it used, enough to “power an electric car for about 1,440 miles.”
NIST found that “instead of paying almost $4,400 for electricity—the estimated average annual bill for a comparable modern home in Maryland—the virtual family of four residing in the all-electric test house actually earned a credit by exporting the surplus energy to the local utility.”
The house achieved this “despite five months of below-average temperatures and twice the normal amount of snowfall.”
What Role Do Plastics Play?
Insulation obviously is key to reducing energy loss in any home, zero energy or not. While each building is unique, zero energy homes typically rely on modern plastic foam insulation systems under and around the foundation, in the walls, and in the roofing, which can dramatically decrease the amount of energy needed to heat and cool a home. Many of these insulation products do not simply increase R-value—they also help reduce leaks and air loss to seal the building envelope.
And these are not novel or unique insulation systems—they all are available to homebuilders.
- Sheets of polystyrene foam under and around the home’s foundation create a barrier and insulate the floors and walls. Foundations are poured directly onto the insulation sheets, which also are attached to below-grade foundation walls.
- Insulated concrete forms—usually expanded polystyrene forms that stack and are filled with concrete and rebar to create walls—provide excellent insulating properties and create a very solid building.
- Structural insulated panels typically sandwich large sheets of expanded polystyrene foam between oriented strand board (OSB), creating large wall systems with few seams, greater R-value, and improved strength.
- Polyiso or polyurethane foam installed under the roof system instead of in the attic floor helps seal the building against leaks and increase the R-value of the roofing system. The NIST home used this method to achieve an R-value of 75 in its roofing system, which is about twice the typical R-value. In addition, since the attic is tempered space, ductwork doesn’t shed its cool or hot air in un-tempered space.
- The NIST building used six-inch instead of four inch-studs to increase the space for insulation between studs, plus a plastic air moisture barrier and four inches of polyiso on the exterior, which virtually eliminates thermal bridging (the transfer of heat between the interior and exterior caused by non-insulating materials).
- While not used in all the above insulation systems, plastic house wrap significantly reduces the infiltration of outside air, helping to reduce the energy required to heat or cool the home.
- Finally, plastic sealants (caulks, mastics, foams, tape) are applied to any remaining gaps that may exist between floors, walls, roofs, and windows, as well as around ductwork joints.
NIST estimates that its home is almost 70 percent more efficient than the average area home.
“The most important difference between this home and a Maryland code-compliant home is the improvement in the thermal envelope—the insulation and air barrier,” says NIST mechanical engineer Mark Davis. “By nearly eliminating the unintended air infiltration and doubling the insulation level in the walls and roof, the heating and cooling load was decreased dramatically.”
To actually reach zero energy, many other energy saving products made with plastics are used, such as plastic piping for radiant heat and efficient water delivery, insulated window frames clad in plastics, highly energy efficient refrigerators, and even plastic roofing tiles that incorporate solar cells in the tiles themselves instead of having to install both tiles and panels.
How much does plastic insulation and other building products contribute to energy efficiency of zero energy homes—or typical suburban homes? A one-year study by Franklin Associates found that the use of plastic building and construction materials saved 467.2 trillion Btu of energy over alternative construction materials. That’s enough energy saved over the course of a year to meet the average annual energy needs of 4.6 million U.S. households.
While zero energy homes are still outside the norm, numerous events and trends are driving efforts to dramatically improve energy efficiency, from concerns over climate change impacts to substantial upgrades in building codes.
To encourage greater energy efficiency, NIST plans “to develop tests and measurements that will help to improve the energy efficiency of the nation’s housing stock and support the development and adoption of cost-effective, net-zero energy designs and technologies, construction methods and building codes.”
And according to NIST, some “states are taking steps toward encouraging or even requiring construction of net-zero energy homes in the future. For example, California will require that, as of 2020, all newly constructed homes must be net-zero energy ready.”
That is going to require help from a lot of plastics.
Previously published in Plastics Engineering and posted with permission from the Society of Plastics Engineers.