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As described in Part 1 of this guide, an unmet load hour is any hour of any day of the year when one or more zones in the building are outside of their temperature control range. This control range includes both the zone temperature setpoints and associated throttling ranges. The UMLHs test uses the cooling and heating setpoints plus tolerances to account for the extension of throttling ranges above and below the cooling and heating setpoints, respectively. Part 2 described the determination of which spaces, dates, and hours are subject to UMLH tests.
Part 3 of the IES Unmet Load Hours guide delves into the specifics of how UMLHs are determined for those spaces within the IES Virtual Environment software. The focus is on relevant user inputs in the setup of the model and HVAC systems, and how these inputs are used in automated UMLH analysis for ASHRAE 90.1 Appendix G, CA Title-24, and other performance rating and energy code compliance tools. This will help you understand the mechanics of UMLH tests within the IES Virtual Environment.
Related topics previously covered in Part 1: Understanding Unmet Load Hours
Related topics previously covered in Part 2: Spaces, Dates, and Hours subject to Unmet Load Hours tests
Topics covered in Part 3
Part 4 will describe the use and application of manual UMLH checks for performance assessment, tracking down sources of UMLHs, and identifying problematic HVAC zoning. Subsequent parts of the guide will present various additional strategies for minimizing UMLHs and addressing particular situations.
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You can view our other Understanding and Minimizing Unmet Load Hours articles by clicking HERE.