Utah Engineers Journal 2021 Issue

38 Early Design Phase Energy Modeling and Multiobjective Optimization I n the U.S., buildings have an average life span of 70-75 years (DOE, 2011) and represent 40% of the country’s annual energy use (Energy Information Administration, 2012). Consequently, design choices related to new buildings have a significant and long- lasting impact. In general, it is important to consider energy consumption and cost for the design of every building. However, when buildings are part of a larger campus, a single-building perspective can fall short of identifying how the buildings can interact to reduce their overall energy consumption, cost or emissions. This reduction is only achievable through a multibuilding analysis simulation. One difficulty of performing a multibuilding simulation is that each building is probably only defined conceptually during the early design phase of a large campus. This article will go through one way to simulate, analyze and optimize the mechanical system types for a campus when only building function type, quantities of buildings, and size is known. A good starting point, and excellent overall resource, for modeling building energy consumption from a high-level perspective are the DOE Prototype Building models (Commercial Prototype Building Models, 2021) created by researchers at Pacific Northwest National Laboratory (PNNL). There are 16 commercial building types available for 19 different climate locations that represent 75% of the commercial building stock in the U.S. The prototypes were created using data from the Commercial Buildings Energy Consumption Survey (CBECS, 2015), which in 2003 included data from 5,215 buildings. The CBECS database is thorough and includes information such as floor area, occupancy, and envelope construction. For information not readily available in the CBECS survey, the PNNL prototype buildings use guidelines outlined in ASHRAE 90.1 for criteria such as operating schedules, infiltration, and lighting power densities. The prototypes are available for efficiency requirements outlined in ASHRAE 90.1 and the International Energy Conservation Code from 2004 through 2019. These prototypes are specifically designed for use with EnergyPlus, a building energy analysis and thermal load simulation program developed by the Department of Energy. EnergyPlus is free to download and use. It may be accessed here: https://www.energy.gov/eere/buildings/downloads/ energyplus-0. Even though these prototype models won’t be an exact match for every project, they are a very useful template. They can be used as a consistent starting point for evaluating design choices such as the HVAC system type. For example, consider a project where a developer would like to construct a six-office building campus. They intend to have two 580,000 square-foot, 14-story office buildings with data centers and four 110,000 square-foot, 6-story office buildings. Countless possibilities can be considered, but for the sake of this exercise, the following options will be evaluated: typical HVAC systems, all-electric HVAC systems, a blend of any system, and then a central plant that services the entire campus. The central plant’s underlying purpose is to capture the waste heat from the data centers to heat office spaces in the winter. The overall procedures for evaluating these different scenarios are listed below: 1. R eview the DOE building prototype database and select buildings of similar functional use. 2. Select the building template file for the correct code version and correct climate zone and download the appropriate TMY3 (Typical Meteorological Year) weather file. 3. Adjust room multipliers and floors to align the template building file with the campus’s proposed functional usage. 4. M odify and/or add HVAC systems to align with the different mechanical systems considered in the assessment. 5. Run the simulations and normalize energy use and emissions on a square foot basis. 6. E valuate the solution set to select the system types that best align with the project objectives. ASHRAE