Zero Net Energy (ZNE), an alternative sustainable building movement, continues to grow as more formalized initiatives with ambitious goals come online around the globe. For the Parris Island Marine Corps Recruit Depot in South Carolina, KCI engineers worked as part of a design-build team to construct a child development center (CDC) that is U.S. Green Building Council (USGBC) Leadership in Energy & Environmental Design (LEED) certified and meets net zero objectives, a first for the base.
The 25,775-square-foot Parris Island facility was originally slated to meet LEED-silver certification requirements. When additional funding became available during design, the Naval Facilities Engineering Command began working with contractor Sauer Inc., architect VOA Associates Inc. and engineers Van Wagenen and Beavers Inc. and KCI (then Redding Linden Burr) to expand the proposed solar array and incorporate additional conservation measures.
As opposed to LEED, which recognizes holistic green building successes, ZNE focuses only on a facility’s power demands. By combining energy generation via solar panels (and in some cases wind turbines) with targeted conservation measures like geothermal heating and cooling, ZNE or net zero buildings can produce enough power on an annual basis to offset their overall demand. Energy conservation and efficiency are substantial aspects of the LEED verification process, encompassing up to one-third of the possible prerequisite credits available at the different certification levels. Only a fraction of USGBC certified buildings meet ZNE goals, yet most net zero buildings achieve some type of sustainable certification.
Practice Leader Gregory M. Tinkler, CGD, was called in to model the CDC’s energy profile, which outlines estimated power consumption by month. “Everything about the building is built virtually so that it responds,” he said. “People come in and out, lights go on and off.” Critical components include window placement and thermal functionality, wall orientation and insulation values, roof type, lighting and HVAC controls as well as their expected settings, the number of occupants, and their equipment like computers, printers and copiers.
If developed during the conceptual stage, energy modeling can help identify opportunities for potential cost savings and determine return on investment for additional expenses as the design schedule progresses. Engineers also use the data to calculate the number of photovoltaic panels (and/or wind turbines) needed to meet net zero. Once peaks in the energy model—most often summertime air conditioning or mid-winter heating—are identified, the design team works to normalize demands over the entire year by incorporating conservation measures, including geothermal heating and cooling.
Tinkler also led the design for the geothermal system, which encountered some unusual challenges. During installation of the multiple 250-foot-deep boreholes required to support the Parris Island facility, drilling technicians discovered caverns under the site. These karst formations occur when landscapes made of limestone and other soluble rocks come into contact with underground water. Using sonar, geotechnical engineers determined the general size and footprint of the caverns in order to identify which well sites would be affected. The subterranean voids ranged in height from two to 40 feet, sitting approximately 60 feet beneath the surface. “Drilling through that and maintaining circulation in the geothermal system was challenging,” said Tinkler. “We avoided the larger caverns, but where they were smaller, we put the loop in and accounted for the void.” Geothermal systems are designed for heat exchange using exact calculations for the length of underground piping in contact with earth. To ensure expected functionality, engineers had to add more boreholes at the end of the project to account for the sum of the loop sections within the voids.
Sinkholes presented another unexpected complication. “When we first started drilling into one of those large voids, all the sand on top ran through the hole like an hourglass,” Tinkler explained. “Following installation, we had to drill back in at an angle toward each well and inject epoxy to reseal the top of the cavern.” Once completed, the variable flow geothermal closed-loop system with its 76 vertical boreholes was capable of supporting the CDC’s heating, cooling and even some of the domestic hot water for the next half-century.
In addition to the solar panels and geothermal system, the facility features a host of other sustainable measures including conservation-minded product choices for high-efficiency electric appliances, LED lighting and water saving plumbing fixtures. Designers also considered sustainability when selecting materials that contain high percentages of recycled content or were manufactured locally.
These design and construction components combined to allow the Parris Island CDC to generate all of the power it needs to support its staff of 65 as well as nearly 250 children. Operating since 2011, the facility earned a LEED gold certification and was recognized by the USGBC North Florida Chapter with the organization’s Global Green Award. The building also supports the Department of Defense Education Activity’s (DoDEA) target for energy independence at all of its facilities by 2030 as well as the Navy’s goal of using renewable energy to meet at least 50 percent of its power demand by 2020.