INDUSTRY NEWS Greenbuild, From Page 6 2015 to Oct. 31, 2016, allowing projects to continue to register under the less stringent LEED 2009 during this time. The USGBC cited a survey conducted at this year’s Greenbuild in which 61% of respondents said they needed more time to prepare for LEED v4. Projects can continue to be registered under the more rigorous LEED v4, but fewer than 400 projects have been registered under LEED v4 since it was introduced. “LEED v4 created a certain amount of chaos with transparency and disclosure,” said Dwayne Fuhlhage, who attended an educational session related to evaluating the risk of chemicals in building products. Fuhlhage is Sustainability and Environment Director for PROSOCO, a building product manufacturer based in Lawrence, Kan. “It’s not all been resolved. We’re seeing a gradual maturing.” “It is triggering the transformation it is intended to trigger,” Fuhlhage said. “Materials are coming along the way with net zero.” At the Expo, many exhibitors offered environmental product declarations and third-party certifications. The Expo also featured a focus on net zero energy, including a net zero energy house and a portion of the expo space that operated on a net zero energy basis. Attendees toured the 2014 Greenbuild PHOTO: ATELIERS JEAN NOUVEL CHICAGO—A residential building in Sydney has been named the “Best Tall Building Worldwide” by the Council on Tall Buildings and Urban Habitat (CTBUH). One Central Park beat 87 other international entries, and was commended for its visible use of green design. Key features include hanging gardens, a cantilevered heliostat, an internal water recycling plant and a low-carbon trigeneration power plant. The building’s most visible feature, the hanging gardens, use a remote-controlled, dripper irrigation system and a special process in which the roots of each plant are attached to a mesh-covered felt, and soaked with mineralized water. This allows the plants to grow without soil along the faces of the building envelope. One Central Park in Sydney Australian Tower ‘Best Tall Building’ 8 A S H R A E J O U R N A L ashrae.org D ECEM BER 2014 LETTERS Return Fans in VAV Systems Your description of airflow tracking and direct pressure control in October’s “Return Fans in VAV Systems” was very good. Would you recommend this approach for an air-handling system that serves areas where space to space pressure relationships are critical? If so, what steps would you recommend to ensure that the static pressure in the return duct is appropriate for the proper operation of return air VAV boxes? I’ve seen buildings with critical spaces and with multiple AHU’s attempt to convert all of their systems over to direct pressure control only to have space pressure relationships become a problem. Brian Rose, P.E., Member ASHRAE, Guilford, Ind. The Author Responds You are correct and my example a) for Airflow Tracking is misleading. Systems that have return air VAV boxes essentially have pressure control at the zone level, typically by zone level airflow tracking (tracking the return airflow rate with the supply airflow rate), but occasionally with zone level direct pressure control (controlling return airflow rate to maintain zone pressure using a zone pressure sensor). Either way, the return airflow rate is determined by the return air VAV boxes, not directly by the return fan, similar to a VAV supply air system. So, the return fan simply needs to be controlled like a supply air fan on a supply air VAV system: maintain enough negative static pressure in the return air duct to allow all return air VAV boxes to meet their airflow setpoints. In other words return fan speed should be controlled by return duct pressure and not be controlled based on system level supply/return airflow differential as my article suggests. Sorry for the confusion! Steven Taylor, P.E., Fellow ASHRAE, Alameda, Calif. LivingHome throughout both days of the Expo. The modular net zero home that featured the latest sustainable building techniques was relocated and permanently placed in New Orleans’ Lower 9th Ward after the conference. The Net Zero Pavilion, which included 11 exhibitors in 1,500 ft2 of exhibit space, was powered by an on-site microgrid including alternate energy generation, storage and distribution. The space was designed for the hybrid use of alternating current and direct current and was designed to demonstrate the efficiency, reliability and resiliency of hybrid microgrids, which can operate in combination with the local utility grid or in isolation from it.