Lighting, HVAC equipment, water heaters, and appliances all consume energy in the form of either electricity or fuel. All of these things are important to understand and optimize for high performance building design, and are important inputs for whole building energy analysis simulation.
The equipment, lighting, and plug loads described below are determined by the building’s intended use, its occupancy, and its scheduling. In short: its program.
Lighting Loads
Lighting loads are the energy used to power electric lights; they make up nearly a third of US commercial building energy use, but for residential buildings they are generally only 10 – 15%. Lighting loads in a building are often referred to in terms of a “Lighting Power Density” that is measured in watts per square foot or square meter.
When deciding which lighting products to use, look at the efficiency (or luminous efficacy) of the products. More efficient light sources and fixtures not only reduce lighting loads, but also reduce cooling loads for the same visible brightness.
Plug loads
Plug loads are the electricity used for other equipment, like computers and appliances; they make up 20 – 30% of energy loads in US commercial buildings, and 15 – 20% of home energy, though these numbers are growing as electronics become more pervasive.
Plug loads are sometimes included in “Equipment Power Density” (EPD) and sometimes they are separated. When doing building analysis, it’s important to know which value you’re inputting.
| Equipment | Rated Power (watts) |
| Desktop computer | 120 |
| Notebook computer | 45 |
| 17” LCD Display | 75 |
| Desktop laser printer | 120 |
| Office laser printer | 250 |
| Office copier | 750 |
| Refrigerator | 750 |
| Dishwasher | 1,200 |
| Television | 100 |
| Commercial refrigerator | 1,000 |
| Commercial fryer | 10,000 |
| Clothes washer | 350 |
| Clothes dryer | 2,000 |
| Plug loads for specific items (Source: USGBC and EnergyStar) |
Equipment Loads
Equipment, like HVAC systems and water heaters, is the other main internal load. This is typically separated from plug loads and is given in terms of an “Equipment Power Density,” which is measured in watts per square foot or square meter .
When deciding which equipment to use, look at third-party quantitative reviews, or read the maximum power use listed on product specification sheets (average power use data is usually not available because it can vary greatly by usage.)
Example Internal Loads for Different Space Types
| Lighting Power Density | Equipment Power Density | Plug Loads (Peak) | Occupancy | ||||
| W/m2 | W/ft2 | W/m2 | W/ft2 | W/m2 | W/ft2 | People/100m2 | |
| Assembly | 17 | 1.6 | 10 | 0.9 | 2.2 | 0.2 | 75 |
| Classroom | 13 | 1.2 | 11 | 1.0 | 10 | 0.9 | 25-35 |
| Food Service | 15 | 1.4 | 9 | 0.8 | 13 | 1.2 | 15-40 |
| Office | 11-30 | 1.0-2.8 | 14 | 1.3 | 27 | 2.5 | 3.5-5 |
| Retail | 16 | 1.5 | 10 | 0.9 | 4.5 | 0.4 | 10-20 |
| Residential (single family) | 5 | 0.5 | 5 | 0.5 | NA | NA | 1 |
| Residential (multi family) | 8 | 0.7 | 11 | 1.0 | NA | NA | 2.5 |
| Warehouse | 9 | 0.8 | 5 | 0.5 | 2.2 | 0.2 | 1.5 |
Note that this information can vary greatly based on the design and use of the space. Use more precise and specific estimates when available. (Sources: United States Department of Energy (1 and 2), and Mechanical and Electrical Equipment for Buildings by Grondzik et al.)
Links and References
Energy Star DatabaseA database of more energy efficient appliances and equipment. Includes really helpful reference information about basic metrics and efficiency standards.