Welcome to the public engineering documentation site for the Home Energy Saver (HES), the first Internet-based tool suite for calculating energy use in residential buildings.


The Home Energy Saver project provides a family of interactive web sites, as well as the Application Programming Interfaces (APIs) that underlie them, designed to help residents and home energy professionals make decisions about energy use in their homes. The aims of the project are to increase consumer interest in energy efficiency and to foster market activities that capture those opportunities. HES is developed and maintained by the Lawrence Berkeley National Laboratory with sponsorship (past and/or present) from the U.S. Department of Energy (DOE), U.S. Environmental Protection Agency (EPA), and the California Energy Commission.

The major products of HES are:

  • The Home Energy Saver consumer website
  • The Home Energy Saver professional website
  • The Home Energy Saver pro/consumer (legacy) API
  • The Home Energy Scoring Tool website
  • The Home Energy Single Family API
  • The Home Energy Saver Multifamily API

Links to these projects are in the sidebar. The main technical documentation site for the APIs that underlie the websites and enable replication of their functionality in third-party applications is: http://developers.buildingsapi.lbl.gov.

Project Background

Development of the Home Energy Saver began in 1994, and the first site went on-line in 1996[1], originally sponsored by the Energy Star program, operated by EPA and DOE (Mills 1997; Mills et al. 2007)[2] [3]. The Home Energy Saver uses state-of-the-art data and models to support the Federal energy mission by helping to build national recognition of  energy efficiency programs and by enabling consumers to quantify the energy savings and environmental benefits that can be achieved by improving the energy efficiency of their home. The sites are also used periodically by researchers, designers and contractors as a tool for analyzing residential energy performance issues, and for learning from actual homeowners about their experiences with implementing energy-saving upgrades. Finally, through the Energized Learning module, science educators at the high school and college level regularly use HES as part of their science curricula. Based on a user-feedback form, submitted thus far by approximately 1100 users, approximately 80% of users are homeowners or renters, with the balance made up of those who visit for professional/educational reasons, such as building professionals, educators, contractors etc.

The Home Energy Saver websites provides two basic services:

  • A calculation of energy consumption by end use, for the entire household
  • Estimate of energy bills and greenhouse-gas emissions based on end use consumption, and a comparison of consumption to a “typical” household and subsequent recommendations for bill reduction.

This wiki provides a description of the method for calculating energy consumption, and the levels of input detail available to the user and the output reported to the user. It also outlines calculation of energy bills based on consumption, and documents the presentation by which consumers can compare results for their household to households typical in their geographical area, and which suggest possibilities for energy bill reduction.

The goal in developing the Home Energy Saver web sites has been to provide diverse audiences with a simple way to use state-of-the-art residential energy calculation tools and energy data. The site integrates a variety of models, algorithms, and data sources developed over several decades at Lawrence Berkeley National Laboratory, other DOE National Labs, utilities, and elsewhere in the energy community. Historically, access to and use of such materials has required more extensive expertise and knowledge of energy and building technologies than that possessed by consumers. Making these tools and information available via a web-based interface, enables lay users to obtain energy use and savings estimates tailored to their particular home, climate, lifestyles, etc. While not discussed further here, the site also provides “decision-support” information to accompany the analytical results.

Consumer-oriented home energy calculators are most effective if they combine careful energy analysis with energy cost information in a fashion that yields meaningful energy bills. Energy tariffs (particularly those for electricity) are becoming increasingly complex, as they are redesigned to encourage efficient use of energy at the margin and management of peak demand. For example, the so-called “inverted block tariffs” present the user with an increasing per-unit electricity price as consumption rises. “Time-of-Use” tariffs present the user with high electricity prices at times when the utility system is likely to be facing peak demands (e.g. weekday afternoons during summer), and correspondingly low prices at off-peak times. Most energy calculators utilize highly stylized prices (e.g. a flat cents-per-kilowatt-hour value), which fail to capture the real-world conditions facing consumers. To address this void, the Home Energy Saver site includes a process to model electricity bills using actual utility tariffs.

Limitations and Advantages of Web-based Energy Modeling

  • State – Unlike a computer based application, the web based environment does not maintain a constant connection between a user and the application. For each new action, the web server must be given information to connect a user with their particular session, in the form of cookies or a session ID. If this information expires, the user is required to start the process over.
  • Network Latency and Errors – the internet is a conglomeration of servers, routers and transmission paths that are largely independent of each other. Delays or lack of service in any part can make it appear to a user that our site is unavailable or slow. To a great extent, the internet compensates for outage and bottlenecks by re-routing traffic to areas with greater capacity, but some bottlenecks can’t be avoided, such as the link from the user’s computer to their ISP.
  • User comprehension – energy modeling is a complex process, and has its share of technical language. We’ve attempted to use common language in parsing inputs and results, but misunderstandings and confusion can still occur. The lack of a trained professional on hand to assist may limit some users experience.

Advantages include ease of distribution, version control, platform independence and the ability to locate computation-intensive simulation engines such as DOE-2 on a central (free to the public) server, rather than requiring users to install and administer them on home personal computers.

[1] An earlier version developed at LBNL in the early 1990s was called WebCalc.

[2] In 2000, the Energy Star program sponsored the development of a simplified consumer web site derived from the HES, called Home Energy Advisor. In most cases, Advisor used the same data and calculation methodologies as HES, but employed a more constrained building description and provided different outputs.

[3] A companion report (Warner 2005) describes the use of the DOE-2.1E simulation model for handling space conditioning.