Sustainable Transparency: Sustainable Design and Performance Verification of an Integrated Tower

Abstract

Building envelopes fulfill many functions: structure, climate control, energy savings and generation, aesthetics, psychological well-being, and occupant comfort. Building envelopes are closely interdependent to building service systems and can further reduce building energy consumption by 7 to 20% depending on building type and size. As contemporary buildings increase to use high quantities of glazing in building envelopes, challenges exist in not only economic viability but also energy code compliance and environmental stewardship. A highly glazed building requires performance-based design, employing an integrative design and comprehensive whole building performance verification process. The primary objective of this presentation is to address the sustainability of contemporary building envelopes and to establish a performance assessment methodology. The case study building is New York Times Building (NYT) in New York, USA designed by Renzo Piano Building Workshop and Fox & Fowel Architects. The NYT building is located in a climate zone 4 in accordance with ASHRAE 90.1, which is mixed and humid climate. The curtainwall has approximately 75% WWR (window-to-wall ratio) and utilizes low-e coated insulated glass unit (IGU). The ceramic coated rod in front of the curtainwall blocks unwanted solar heat while maximizing daylighting performance. The building mass and ceramic rods of the NYT building were built in Revit Massing platform and exported a 3D model as Green Building xml (gbxml). Once the gbxml file was imported in DesignBuilder, the gbxml file transferred information about building mass, ceramic rods, WWR, and thermal and perimeter zones. DesignBuilder is a building energy simulation program performed on hourly-recorded weather data mainly consisting of sub-hourly weather data and illumination data. The vision curtainwall was set to provide an assembly U-factor of 0.45, SGHC-0.31 and VLT-0.56. These values are calculated based on VE13-2m low-e coating which is also conforming to ASHRAE 90-1 building envelope requirements. Three sustainability indicators in this presentation focus on 1) solar gain through a curtainwall system 2) daylighting contribution and 3) solar energy potential. Solar gain through vision curtainwall is important in that it contributes to internal heat gains and affects interior cooling load. In order to understand the shading effect of ceramic rods, the building energy simulation was carried out for the building without ceramic rods and with ceramic rods. The result shows that the ceramic rods reduce the solar gain through vision curtainwall (26.4kBtu/hr) by 50% compared to the solar gain without ceramic rods (42.4kBtu/hr). Further, daylighting benefits were measured by applying the daylighting control function in DesignBuilder. The analysis reveals that daylighting control can reduce artificial lighting load by 40%, measuring a lighting load of 55kBtu/hr with daylighting control and 85kBtu/hr without daylighting control. Lastly, the annual solar energy potentials were estimated to be 184kBtu/hr based on 5% electricity efficiency of a thin film photovoltaic system, which equates to annual electricity saving of ~$8,000. It can be concluded form the energy analysis that building envelopes of an integrated tower in an urban setting provide opportunities to enhance building energy savings and solar energy generation. Further, integration of BIM and energy simulation tool provides timely efficient energy verification process that could solve many problems in building sustainability.