Energy Modeling in Architectural Design by Hemsath Timothy. & Kaveh Alagheh Bandhosseini

Author:Hemsath, Timothy. & Kaveh Alagheh Bandhosseini
Language: eng
Format: epub
Publisher: Taylor & Francis (CAM)

Materials

Moving beyond the generic or specific window definition in the BEM is the definition of building materials. Early on in design, we may not know which specific materials will be used, but BEM can simply understand the materials by their U-factor or R-value. Defining the R-value of the building envelope and its elements (roof, walls, and floors) is a necessary input into any BEM. This can be specific or generic, depending on the information you have available at the time.

After the material definition of the building envelope comes the definition of the building’s HVAC system. Many BEM programs focus on the design of a building’s mechanical and ventilation systems; however, within architectural design these aspects are usually handled by mechanical engineers. Without their expertise, one could use typical system templates or inputs to establish the system’s efficiency for the BEM.

HVAC systems typically have a significant impact on the total building’s energy use. Involvement of the engineering team and careful attention to the HVAC systems throughout the design process is critical to a successful building project. Furthermore, in defining the building system comes another critical point in the creation of the BEM. Building spaces have certain needs and associated zones for a specific HVAC system, and a larger building may have many zones with different specifications for these systems. However, in an early application of BEM in design, specific spaces may or may not yet have been laid out. BEM tools therefore offer a choice between a single-zone analysis or using perimeter and core zones.

Single-zone analysis treats the whole building as one thermal zone and calculates energy needs based on maintaining the building set points uniformly across the entire zone. This is acceptable for some building types such as residences, warehouses, and small retail buildings, among others.

Perimeter and core zones are typical for larger buildings (especially offices), where the heating and cooling demands are different for the building façades around the perimeter and for the core. Heating and cooling around the exterior is typically more variable than that of the core.

Following the input of the HVAC system into the BEM, definition of the basic space uses, occupancy loads, schedules, lighting power densities, and equipment plug loads round out the initial basic building inputs. These final items could be entered first; however, in early BEM we often do not yet know enough about the design to use specifics. Therefore, basic defaults are necessary early on in the BEM, and as the design develops these inputs can be changed based on project details and priorities.

Figure 4.11 Required inputs for a beginning BEM. The specific order of entry is less relevant than ensuring that all inputs are accurate and complete.

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