End-Use Savings Shapes Measure Documentation: Economizers

Building on the successfully completed effort to calibrate and validate the U.S. Department of Energy's ResStock™ and ComStock™ models over the past 3 years, the objective of this work is to produce national data sets that empower analysts working for federal, state, utility, city, and manufacturer stakeholders to answer a broad range of analysis questions. The goal of this work is to develop energy efficiency, electrification, and demand flexibility end-use load shapes (electricity, gas, propane, or fuel oil) that cover a majority of the high-impact, market-ready (or nearly market-ready) measures. "Measures" refers to energy efficiency variables that can be applied to buildings during modeling. An end-use savings shape is the difference in energy consumption between a baseline building and a building with an energy efficiency, electrification, or demand flexibility measure applied. It results in a time-series profile that is broken down by end use and fuel (electricity or on-site gas, propane, or fuel oil use) at each time step. ComStock is a highly granular, bottom-up model that uses multiple data sources, statistical sampling methods, and advanced building energy simulations to estimate the annual subhourly energy consumption of the commercial building stock across the United States. The baseline model intends to represent the U.S. commercial building stock as it existed in 2018. The methodology and results of the baseline model are discussed in the final technical report of the End-Use Load Profiles project. This documentation focuses on a single end-use savings shape measure - economizers. Economizers act to increase outdoor ventilation air during periods when the system requests cooling and the controls determine the outdoor air is cold enough to be beneficial. The measure adds economizer controls to air handling units (AHUs) that do not already have this functionality. The prevalence of economizers in ComStock baseline AHUs is based on the governing energy code for each specific model. The type of economizer control added is based on the guidelines of the ASHRAE 90.1. Furthermore, a common fault that is prevalent in economizers (i.e., outdoor air damper fully closed fault) are added with certain prevalence: less than 35% of random buildings with economizers and fault present for a month randomly chosen. The economizer measure applies to buildings that cover 61% of total building stock floor area and demonstrates 0.3% total site energy savings (14 trillion British thermal units [TBtu]) for the U.S. commercial building stock modeled in ComStock. The economizer measure demonstrates 1 million metric tons (MMT) of greenhouse gas emissions avoided (0.2-0.4% reduction depending on the three grid electricity scenarios presented).