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Virtual Energy Efficiency Software

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Virtual Energy Efficiency

Glimpse Calculator Technical Methodology

Glimpse Calculator is a software technology developed by the Constellation Navigator Virtual Energy Efficiency Team. The technology combines building energy modeling processes, building information on the U.S. building stock, and current technology information from manufacturers who produce equipment that implements or enables energy efficiency in buildings. The technology uses this data to analyze the energy savings of Energy Improvement Measures (EIMs) in buildings.

  Intro

The calculator provides insights into EIM impact that traditionally can only be calculated with manual processes, typically executed by consultants, that take large amounts of resources to complete for a single building and are very difficult to deploy for a whole building stock or portfolio.

  Methodology at a Glance

The Glimpse Calculator uses live building energy models created and simulated in the industry-standard energy modeling software, EnergyPlus1. These energy models are representations of every energy-using process in a building. Each one simulates the interactions between the building and its environment at an hourly or sub-hourly level. They include specific and verbose geometry, construction assemblies, lighting, appliances, occupancy levels, HVAC system configurations and control, and domestic hot water system configuration and control.

The Glimpse Calculator structures calculations at the building level. For each building, a user goes through an input process to enter the necessary information to represent the building in question. In the case of the Glimpse API, the input process can happen through other software tools, which interact with the Glimpse Calculator in the background and receive and display the typical output metrics. In the case of the Glimpse Platform, the input process and output viewing process is directly in the software.

For any information not provided by the user, the building information necessary to create a representation is taken from various building stock data sources, using inferences from the data provided. After creating the building representation, this model is dubbed the “Baseline” scenario, representing the as-is operation of the building. The specified EIMs are then applied to the baseline building, creating different versions of the building representation, each with the EIM changes applied. The results of these models are dubbed the “EIM” scenarios. All models are then simulated for a year in a weather environment represented by a Typical Meteorological Year (TMY). The TMY environment used is the closest out of over 1,000 weather measurement stations in the U.S. and Canada.

  Post-Simulation Outputs

After simulation, a variety of energy, cost, and emissions-related outputs are available for analysis. The first output section is the baseline results, representing the annual energy usage, utility cost, and emissions from the building as-is. The second output section is the EIM impact results, representing the impact that each scenario has on the annual energy usage, utility cost, and emissions of the building. Additional analyses are optionally available, producing other output sections such as investment required for each scenario, life cycle impact of each scenario, rebates available for the completion of each EIM, benchmarking the baseline building as compared to similar buildings, and analysis of any applicable state or municipal building performance standards that may impact the building.

  Public Data Sources

Building energy models are complex, requiring many inputs to adequately represent a building. When not input by the user, the Glimpse Calculator supplements certain building parameters with averages of its class. A building’s class is determined by its age or date of last major renovation, function, climate, and main heating fuel. Overall, the Glimpse building information database consists of over 500 attributes affecting energy usage in a building, each with specific values for the major energy model parameters.

Data Category Usage Details
Building Datasets & Fuels Making up a majority of the database are the DOE Commercial Reference Buildings2 and the PNNL Residential Prototype Building Models3. These rich datasets are based on large U.S. surveys, a full set of applicable building codes, and other national lab research. EIA’s CBECS4 and RECS5 models are used for further refinement. Industry-leading efficiency technology manufacturers’ equipment specifications are used to model performance of different pieces of HVAC equipment included in the EIMs. The American Community Survey’s Home Heating Fuel data6 is used to help understand what type of fuel is used for heating in residential buildings in the U.S.
Weather & Climate Data Weather and climate data has a large impact on building energy performance and subsequently on energy improvement measure performance. It is therefore important to have a granular dataset with which to simulate each building representation. Glimpse sources TMY weather data from the official EnergyPlus weather database7, and only uses the most updated datasets, dubbed TMY3 data.
Future Weather Scenarios In custom cases, the Glimpse Calculator can simulate buildings with future weather, which is constructed using TMY3 datasets and climate change model outputs from the World Climate Research Programme’s CMIP5 multimodel dataset8.
Utility Rates & Emissions While energy models calculate energy usage at intervals across the year, external data is needed to convert this information to subsequent utility charges and emitted CO2e. Utility rates can come from a number of proprietary sources, but in some cases, the electric utility rate may come from the OpenEI United States Utility Rate Database9. If the rate is not found in either the OpenEI database or the proprietary data sources, the building’s state and industry, commercial or residential, is used to get the average rate from EIA electricity10 and natural gas11 datasets. Emissions factors for electricity and all combustible fuels come from Constellation Navigator’s Carbon Accounting API12.