ID#2626 made on
EAp2 - Minimum energy performance
LEED BD+C: Core and Shell
At over 2 million GSF, Beijing Parkview Green (PVG) is one of China's largest sustainable architecture projects. PVG is made up of four buildings, including two 11-story and two 20-story towers (Block...
At over 2 million GSF, Beijing Parkview Green (PVG) is one of China's largest sustainable architecture projects. PVG is made up of four buildings, including two 11-story and two 20-story towers (Blocks A-D) that house a retail area, offices and a six-star hotel - all of which are encased in a "Microclimatic Envelope" (ME) composed of glass and plastic (ETFE - ethylene-tetrafluoroethylene). As a separate, non-structurally tied edifice, we ask that the ME be treated as an example of an Energy Conservation Measure (ECM). The buildings in and of themselves are fully functional, independent entities, designed to meet or exceed ASHRAE 90.1-2004 standards. Each of the buildings' exterior walls was designed as if it were to have no benefit from the ME. The ME's microclimate saves energy by reducing annual average temperature difference between the buildings' average indoor temperature and the "outdoor" temperature represented by the atrium space. The ME also reduces excess solar heat gain. The atrium has been designed to allow for wider temperature fluctuations than in the individual buildings; it is passively ventilated and spot-heated or cooled as a process load. We are requesting confirmation that our modeling strategy of the ME, outlined below, conforms to the Appendix G modeling protocol as required by EA Prerequisite 2 and EA Credit 1: Baseline Building Model: The ME will not be included in modeling the four fully-conditioned buildings. Each will have the appropriate envelope properties and mechanical systems as required by ASHRAE 90.1-2004. The four buildings would be directly exposed to the Beijing weather file. Vertical glazing will be modeled as fixed and the building interiors will be 100% heated and cooled mechanically. Facade and plaza area lighting will be modeled as process loads in the baseline building, but not the supplemental spot cooling or heating equipment. Proposed Design Model: The ME will be modeled using the glass and ETFE wall and roofing properties as installed. The Beijing weather file will be applied as the exterior condition of the ME. Within the ME, the atrium will be modeled as an open area so that airflow can occur freely within the space. In EnergyPlus, virtual partitions will be created to represent the temperature gradient within the vertical space. Using this information in conjunction with a CFD model, we will be able to create an hourly schedule for when natural ventilation from atrium air can be used in the office spaces at each elevation to satisfy the cooling and heating loads. We will model the proposed building as a "hybrid system" where "cooling is provided by natural ventilation when conditions are acceptable and by the default mechanical cooling system (AHUs and chilled ceiling in this case) when natural ventilation is inadequate to provide thermal comfort." The envelope of four buildings will be modeled as the exterior of the conditioned space, which faces the "weather" inside the atrium. The presence of the exoskeleton will require the windows of Buildings A-D to be modeled as interior windows. EnergyPlus will allow the use of a full interior and exterior window option, which will allow for solar radiation penetration through both the exoskeleton glazing and the fenestration on Buildings A-D. Mechanical equipment and lighting within the four buildings will be modeled as built. Plug loads and equipment and lighting in the atrium area will be modeled as process loads: including supplemental spot cooling and heating units on the plaza level; facade, exoskeleton and area lighting, and vertical transportation loads.
The project team is asking for clarification regarding energy modeling protocol for buildings within a secondary enclosure. The modeling methodology for the proposed case consisting of combining CFD analysis with analysis of the projected temperature of the interstitial space between the building skin and the secondary microclimatic enclosure is acceptable. Provide documentation verifying the enclosure is a part of the project. Baseline Model: It is acceptable to model the baseline without considering the ME and the buildings directly exposed to the Beijing weather file. The process energy for the ME should be accounted for in the baseline case and should be identical to the proposed case as per Appendix G. Please note the process energy should follow the ASHARE 90.1 definition. As such, the energy that is consumed for conditioning spaces, maintaining comfort and amenities for the occupants of the building cannot be considered as process energy. Exterior lighting, including the facade and plaza area lighting is regulated by ASHRAE 90.1 and it is not acceptable to model this as process energy. Baseline exterior lighting should be modeled according to Appendix G protocol. In addition, as the baseline model does not consider the existence of the ME shell structure, the baseline model should not account for any lighting attributed to the ME shell structure e.g. canopy or overhang. Proposed design model: It is acceptable to combine different modeling methods and create iterative models to demonstrate savings. The approach towards modeling a hybrid system by developing hourly schedule when natural ventilation from atrium air can be used in the office spaces at each elevation to satisfy the cooling and heating loads seems appropriate. Indoor conditions/setpoints should be the same for Proposed and Baseline when the Proposed is operating under natural or hybrid mode. Provide documentation supporting the classification and/or sub-classification of ME as conditioned or unconditioned space as per ASHRAE 90.1 definitions. The model should demonstrate that the four buildings perform better on account of the presence of the ME. As such, energy used in maintaining the thermal comfort conditions in the ME should be reflected in the proposed case energy. Process energy for ME should follow the ASHRAE 90.1 definition. It is not acceptable to consider spot heating, spot cooling, lighting or any mechanical ventilation energy in the ME as process loads. In addition, please note any daylighting credits for this project should be supported with a daylight simulation model to correctly account for the optical properties of the ME and the interior glazing. If the ME and the buildings are modeled as two separate models, the heating, cooling, lighting and ventilation energy and other non-process energy for the ME should be entered as negative savings in Section 1.7 - Exceptional Calculation Methodology. The process energy for the buildings and the ME can be entered in its entirety in Table 1.8.2. At the minimum, following documentation should be provided during the application in addition to the input and output summaries of the baseline and proposed case:
Related Addenda (Corrections & Interpretations)