Review space type percentages

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The proportion of areas used for different activities in a building will impact its energy performance. Mixed-use buildings (e.g. combination of building types such as retail, office, multifamily residential, or others) will perform differently than single-use building types. Additionally, two buildings of the same type will perform differently if they have a different mix of space types. For example, an office building with a fitness center or a data center will perform differently than an office with no specialty spaces.

Review the building program's space type percentages as soon as they are available to improve the accuracy of the early stage models.

Relevance to BEM Practitioner During Early Stages

During the early stages, space programming information may be sparse, so modeling the space uses explicitly may not be possible immediately. The approaches below are listed in order from "least availability of data" to most. Of course, more available data will lead to a better representation of the project.

Prototype Approach

At the very earliest stage, before space programming occurs or any architectural massing studies have been performed, all that is know is the desired building type. If you are asked what design strategies may make sense for the project, you could get some insight by analyzing prototype models. Bear in mind that the space type assignments in these models are very simplified and unlikely to represent your project's final design. Nonetheless, they can provide valuable guidance on measures that may appropriate for your project's building type.

  • If there are specific design features that are being considered (or are often considered) by the design team, you could modify the prototypes by applying these features. Analyzing a set of options on the prototypes would help you understand the relative magnitude in energy impacts for the set of options. Of course, this analysis can be time consuming if you wish to look at a large set of measures, but if your firm or clients often work on similar building types, this analysis could be useful across multiple projects.
  • Many modeling studies have been performed using the prototypes as the basis for analyzing the relative magnitude of energy savings for different building types and climate zones. It is likely that these resources can help you develop a short list of measures that will be appropriate for your project. See the Additional Resources section below for some example studies.

Whole-Building Approach

If architectural massing is underway, but no programming information is available yet, then using modeling assumptions based on a "whole-building" approach would be appropriate. In this scenario, create a simple box model and assign assumptions (loads, schedules) that represent a whole-building average of all the space types combined.

For mixed-use buildings, you would assign differing whole-building assumptions to different floors (or areas) of the building for each building type.

Space-by-Space Approach

In this scenario, architectural massing is underway, and space programming information exists (even if only in draft form). Here, you would create a simple box model, and be sure to divide it into zones that allow you to assign the proper proportions of each space type. Given the early state of the design, you may not know the locations of each space type, so focus on getting the percentages right and don't worry too much about the locations (for mixed-use buildings, at least get the building story assignments correct). However, there may be an opportunity to test the impacts of placing a certain space type in different locations (e.g. impact of south facing conference rooms vs. north facing).

Additional Resources

  • PNNL Commercial Prototype Models - Here you can find links to download prototype models for 16 building types in 19 climate zone locations. The models were developed by PNNL and are constructed to meet the code minimum requirements. There are versions of the prototypes for multiple vintages of ASHRAE 90.1 dating back to 2004.
  • ASHRAE Advanced Energy Design Guides - The AEDGs are based on the analysis of a large set of prototype models. Each AEDG is focused on a specific building type and the document provides guidance on packages of measures that may achieve a specific percentage savings compared to a code minimum. There are versions of the AEDGs for 30% savings targets, 50% savings targets, and for achieving zero net energy.
  • COMNET Reference Appendices - These docs provide detailed tables with assumptions for whole-building and space-by-space loads, schedules, and other model features.
  • California Title 24 NACM Appendices - These documents also provide detailed tables with assumptions but are focused on application to CA's Title 24 energy code. These assumptions are automatically used by CA compliance software tools, but may also be useful for building early stage models.

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