PEX pipe helps heat, cool Texas community

The largest net-zero ready housing development in the United States is tapping into the sun two ways: using solar power to create thermal and electrical energy for the 7,500 homes and apartments under construction in Austin, Texas.

A geothermal system of cross-linked polyethylene (PEX) pipe loops underneath the $2 billion development to reduce energy consumption for heating and cooling by up to 65 percent compared with traditional heating methods.

The plans call for the community of Whisper Valley to be able to meet the carbon-neutral standards adopted for Austin's municipal building code. The city's goal is to reduce carbon emissions to zero by 2050.

The first 237 houses built in Whisper Valley are equipped with a double U-bend PEX pipe and a heat pump that take advantage of the fairly constant ground temperature to create renewable energy for heating and cooling. So far, 313,000 lineal feet of Rehau Raugeo-brand pipe called PEXa has been used.

Based in Leesburg, Va., Rehau has been manufacturing its PEX pipe with a high-pressure peroxide method of cross-linking that it pioneered in 1968. The company says the method gives its pipe better flexibility, strength, and chemical and corrosion resistance.

With $178 million in sales, Rehau is the No. 30 pipe, profile and tubing extruder in North America based on Plastics News' latest ranking.

In Whisper Valley, all builders are required to hook up to a 5-mile loop of underground distribution piping that links the homes to a geo-exchange network. The system uses the earth's relatively steady temperature range of 45° - 75° F in Austin to heat and cool structures.

At all lots, boreholes are drilled to depths of 335 feet and the Rehau pipe loops are inserted. Each PEX vertical pipe loop connects to a system of horizontal pipes. In the winter, a fluid with antifreeze and water circulates through the ground loop system. It absorbs stored heat that originated from the sun and carries it indoors.

In the summer, the heat pump works in reverse. It draws heat from the house and carries it through the loop system back into the earth. When needed on really hot days, the so-called "geo loop" is augmented with two 250-ton cooling towers for meeting peak cooling loads. Homeowners will pay an estimated monthly service fee of $60 for access to the system.

The project shows how PEX pipe in a geo-exchange application can help reduce carbon footprints by minimizing the energy required to heat and cool homes, according to Tony Radoszewski, president of the Plastics Pipe Institute (PPI), an Irving, Texas-based trade group.

"The developer providing the geo-exchange network and requiring builders to connect to it, is game changing," Radoszewski said in a news release. "It removes the primary barrier that prevents more widespread adoption of geo-exchange systems."

The trade group recognized Whisper Valley as its 2019 PPI Project of the Year for its building and construction division. When completed, the community will have seven separate villages, a fire station and two schools for up to 30,000 residents.

The Whisper Valley development model is expected to be duplicated elsewhere as more cities set net-zero targets.

"Not only is this project a unique application for PEX pipe, it is also at the forefront of community geothermal technology," Radoszewski said.

PPI established a geothermal steering committee to support the use of these technologies. The group says other benefits of ground-source systems include better reliability and building resiliency without any exposed outdoor components.

The geothermal committee also supports efforts to update geothermal standards and codes, publishes documents about the use of plastic piping systems for these applications and serves as a technical resource for geothermal system designers.

In addition, the U.S. Bipartisan Budget Act of 2018 reinstated the tax credit for fuel cells, small wind and geothermal heat pumps. The act provides a 30 percent federal tax credit for geothermal systems, and some states also offer rebates.