![]() ASHRAE Standard 90.1 defines two baselining procedures, “Energy Cost Budget” and “Performance Rating Method,” the latter commonly known as Appendix G.īaseline-driven performance rating is the basis for green certification. ![]() This is done by starting with a model of the proposed building and applying a set of mechanistic transformations to it. The key procedure is the creation of a baseline model that represents a theoretical version of the building built to minimum prescriptive requirements. Performance path compliance relies on BEM. For instance, the ASHRAE 90.1 prescriptive limit for window-to-wall ratio is 40%, yet some buildings essentially have 100% glass façades! These buildings comply with code by exceeding minimum requirements in other areas such as window performance, lighting, or HVAC. They also have performance compliance paths that provide designers and engineers with flexibility, enabling them to exceed prescriptive limits in one area by compensating for them elsewhere. The typical question here is “how much more energy-efficient is this building than it is minimally required to be?”īuilding energy-efficiency standards like ASHRAE Standard 90.1 have prescriptive compliance paths that specify minimum and maximum values for building aspects like insulation levels and equipment efficiencies (electric lighting levels and window-to-wall-ratios). In other applications, the comparison is not between two buildings but rather between one building and a theoretical version of itself. These EUIs are weather-normalized and mapped to building-type specific “technical” scales created by simulating a range of configurations-from efficient to inefficient-under the same standard weather and operating assumptions, to obtain 1-10 scores that can then be directly compared.Ĭomparing A Building to an Alternate Version of Itself These values represent typical use and were extracted from large building surveys such as the Energy Information Administration’s (EIA) Commercial Building Energy Consumption Survey (CBECS).ĭOE’s Asset Score uses these standard values to calculate energy use intensities (EUIs). These inputs cover occupancy, occupant activity, plug-loads, and lighting levels at hourly resolution, along with ventilation rates and thermostat settings. The American Society of Heating Refrigeration and Air Conditioning Engineers (ASHRAE) defines standard modeling inputs for different space (offices, corridors) and building types (hospitals, schools). ![]() These comparisons are easy to conduct with BEM using standard values for weather, occupancy, and use. These comparisons are nearly impossible to conduct in a controlled way in the physical world-ratings based on measured data like ENERGY STAR ® are useful but do not fully isolate inherent performance from weather, occupancy, and use. ![]() Comparing Buildings to One AnotherĪsset ratings such as DOE’s Energy Asset Score compare the inherent energy-efficiency of different buildings. Inherent performance rating is the basis of procedures such as compliance-demonstration for codes like ASHRAE Standard 90.1, green certification via programs like USGBC’s LEED, the calculation of asset ratings such as DOE’s Energy Asset Score, and performance documentation for tax credits and utility incentives. Building energy modeling (BEM) can isolate inherent performance by controlling for exogenous variables. A building’s inherent energy performance is attributed to the building itself rather than to weather, occupancy, or use.
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