Are your Facilities Energy Efficient?

Written By: Gabriel Sanchez, Client Data Manager

How to Measure Energy Efficiency, Cost, and Consumption

Buildings and the occupants inside them use energy for processes like cooling, heating, and lighting. Building energy consumption accounts for nearly half of all energy consumption in the United States, at a cost of more than $200 billion per year; more than any other industry sector (Energy Star). Surprisingly, about 30% of the total energy consumed by buildings is wasted through inefficient practices and behaviors! Energy costs have been steadily rising and will likely continue to rise in the future. Although new technologies and renewable energy sources are becoming more available, improving energy efficiency is a simple, low cost approach to reduce energy use and cost.

Understanding how to measure energy use in buildings can help your organization set and track energy efficiency goals. Facilities vary greatly in size, type, and function, so how can you accurately measure the energy use and efficiency of your buildings? One measurement tool that can be used to compare energy use for all building types and various types of energy is Energy Use Intensity (EUI) (Energy Star).  Energy Use Intensity is defined as the energy used per square foot per year. To calculate the EUI, the amount of energy must be converted to a uniform metric for energy units known as British Thermal Units (BTUs) (Architect's Technical Reference). Different conversions are used for different units of energy like kWh of electricity and therms of natural gas. The BTUs are then divided by the total square feet of the building, resulting in the EUI of the building! In general, a low EUI is associated with an efficient building and good energy performance. When comparing EUIs, it is important to remember that certain building types will always use more energy than others. For example, a warehouse facility uses relatively little energy compared to a hospital. Take a look at the example below to learn how to calculate a building’s EUI.

Calculating a Building's Energy Use Intensity – Example

  • A retail clothing store has a total area of 35,000 sq. ft.
  • The store used 950,000 kWh of electricity and 1,500 therms of natural gas during the year.
  • kWh is converted to kBTUs by multiplying by 3.412 (1 kWh = 3.412 kBTU).

950,000 x 3.412 = 3,241,000 kBTUs

  • Therms are converted to kBTUs by multiplying by 99.9 (1 therms = 99.9 kBTU).

1,500 x 99.9 = 149,850 kBTUs

  • kBTUs are divided by the total sq. ft. of 35,000.

3,390,850 / 35,000 = 96.8 EUI (kBTU/sq. ft.)

Two other metrics that can be used to measure the energy performance of a building are the energy cost per sq. ft. ($/sq. ft.) and the kWh consumption per sq. ft. (kWh/sq. ft.). These metrics are practical because it is not necessary for the energy to be converted to kBTUs. However, they only consider the electricity consumption of a building in kWh, so if the building uses other forms of energy like natural gas or steam, these other energy types would not be included. Despite its limitations, calculating cost and kWh consumption per sq. ft. are useful methods to monitor the energy performance of your buildings over time, and can also help your organization to set and reach energy conservation goals. See below for an example of how to calculate cost ($/sq. ft.) and consumption (kWh/sq. ft.).

Calculating a Building's Electricity Cost ($/sq. ft.) & Electricity Consumption (kWh/sq. ft.) – Example

  • A retail clothing store has a total area of 35,000 sq. ft.
  • The retail store used 950,000 kWh of electricity and spent $115,000 in electricity costs during the year.
  • To calculate cost per sq. ft. ($/sq. ft.), divide the total amount spent in electricity costs by the sq. ft. of the building.

$115,000 / 35,000 sq. ft. = $3.29/sq. ft. 

  • To calculate kWh per sq. ft. (kWh/sq. ft.), divide the total kWh by the sq. ft. of the building.

950,000 kWh / 35,000 sq. ft. = 27.1 kWh/sq. ft.

Saving energy translates into saved dollars! To maximize savings and the success of an energy conservation program, it is important to closely measure and monitor energy costs and consumption over time. Using different metrics like a building’s Energy Use Intensity, cost per square foot ($/sq. ft.), and kWh consumption (kWh/sq. ft.) are great ways to evaluate the performance of your buildings and success of your energy program. After all, you can’t manage what you don’t measure!

Do you want to cut energy costs and consumption but don’t know where to begin? Pierce Energy Planning can help you get started on your energy conservation program!