Billed as the first green home built in a typical suburban neighborhood, the goal of the Mainstream GreenHome is to be a model for environmentally focused construction. The home features a range of technological innovations to minimize impact on the environment. The home primarily uses a unique passive solar thermal hot water system that operates underneath the shingles on the roof and avoids all aesthetic distractions of traditional roof-applied solar thermal panels. On an annual basis, the GreenHome's solar thermal system has the ability to harvest more than 41 million Btu of solar energy for space and water heating, saving the equivalent of 440 gallons of oil or 570 therms of gas each year.
RALEIGH, N.C. - Those collaborating to build a first-of-its-kind green home here hope the project will encourage contractors to adopt sustainable homebuilding practices nationwide.
Billed as the first such home built in a typical suburban neighborhood, the goal of the Mainstream GreenHome is to be a model for environmentally focused construction.
John Delafield, president of Landmark Solar in Apex, N.C., said he thinks the home also will spark an interest among contractors who want to learn more about green homebuilding.
"One of the things that contractors bring to a project like this is a series of preconceived notions," Delafield said. "Once you begin to get the guys on site and begin to show them what's going to go into it, what we find is there is a significant reservoir of interest and curiosity. The guys really want to learn about this stuff and they're really intrigued by the way it works."
The home, which broke ground in the spring of last year, features a range of technological innovations to minimize impact on the environment.
According to Delafield, the home has a geothermal system that uses the earth's relatively consistent year-round temperature of 56°F in North Carolina as a heat source in the winter and a heat sink in the summer.
Designed and installed by TRC Energy Solutions, the system has five wells that are 6-in. in diameter, run 300-ft. into the ground and circulate water in a closed-loop system to absorb the earth's heat during the winter and return the heat in the summer. The wells connect to a Florida Heat Pump geothermal unit that acts as a heat exchanger and condenser that then ties to a traditional duct ventilation system.
"The wonderful thing about ground source heat pumps is that they don't have to run a compressor," Delafield said. "They're just running cool liquid through a coil, and that's why they're so wonderfully energy efficient."
The system contributes to heating hot water in the summer by channeling some heat collected in the home to a heat exchanger within the hot water tank.
The home primarily uses a unique passive solar thermal hot water system that operates underneath the shingles on the roof and avoids all aesthetic distractions of traditional roof-applied solar thermal panels.
Half-inch high-density PEX tubing runs along the roof decking on the southern and western exposures of the rooftop, Delafield said. An antifreeze/water solution circulates through the tubing and collects heat throughout the year. The Dawn Solar system connects to a large solar thermal storage tank in the basement that transfers heat to a radiant floor system and the incoming cold-water line just before entering the hot water tank.
Delafield said heat collected by the storage tank can go toward several uses, such as domestic hot water or radiant floor heat.
"That flexibility is above and beyond what you would find in a normal solar hot water heating system," he said. "This was a bit of an experiment to see how we could collect the heat of the sun for domestic hot water purposes as well as heating purposes."
The home's kitchen and master bathroom have Warmboard radiant floor underlayment. The system receives heat through a heat exchanger connected to the solar thermal storage tank, which in turn receives its heat from the Dawn Solar system and the Florida Heat Pump ground-source heat pumps. Warmboard fuses an aluminum coating onto a plywood sheathing that includes preset grooves for the radiant tubing.
Pex-Al-Pex radiant tubing includes an aluminum interior and easily lays in the preset grooves. An antifreeze/water solution transports heat efficiently through the aluminum coated tubing, which quickly disperses through the aluminumbacked flooring throughout the kitchen and bathrooms. Radiant floors warm up quickly and evenly without cement and require significantly less floor elevation.
On an annual basis, the GreenHome's solar thermal system has the ability to harvest more than 41 million Btu of solar energy for space and water heating, saving the equivalent of 440 gallons of oil or 570 therms of gas each year.
The home also features Marathon's 105-gallon electric water heater insulated with a highly efficient and non-ozone depleting foam product, according to Delafield. The solar thermal tank preheats the water heater's incoming cold water.
If the solar thermal system cannot provide enough hot water, the Marathon tank first relies on heat available from the ground source heat pump desuperheater and then from a conventional electric heating backup.
The home's "structured plumbing" system captures the cold water typically lost from faucets and showerheads while waiting for hot water to arrive and returns it to the water heater. A Metlund Hot Water D'MAND System circulates the ambient temperature water in the hot water pipes back to the water heater.
As the ambient temperature water in the cold water line travels toward the water heater, the system fills the hot water line with hot water. When the hot water reaches the system, a thermal sensor detects a temperature rise and quickly closes the zone valve to shut off the pump. This results in hot water reaching the fixtures four to five times more quickly. The reduced wait time saves water and energy, according to Delafield.
"Some on-demand hot water systems simply pump in a loop that circulates on a continuous basis," Delafield said. "With this system, you only run the pump when there is a call for hot water."
A waste drain heat exchange system in the home also preheats incoming city water with the outgoing heat from hot water running down the drain. According to GFX Technology, the system captures up to 60% of the energy used for hot showers and baths.
The system taps into a significant, though hidden, source of energy exchange given that 33% of a home's energy use goes into producing hot water and 80% of that water goes down the drain. The Energy Information Agency estimates that such devices can help residential users reduce the energy used to heat water by 34% and pay back the cost of the exchange system in two to five years.
Delafield said a system that incorporates many of these green design features mainly resembles a standard plumbing system.
"One of the greenest parts of green building is the design and intellectual work that goes into the integration of the various features," he said. "Once you do that, most any plumbing contracting firm can install and connect what at first appear to be disparate systems."
Other water efficiency efforts in the GreenHome include a rainwater catchment system that collects, filters, stores and delivers rainwater for certain nonpotable uses in the home and landscape irrigation.
The GreenHome features a unique solar system (left) and a stormwater management system (right).