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

Incandescent and compact fluorescent bulbs emit similar output of visible light, but the incandescent emits far more heat (infrared light), causing higher lighting loads and cooling loads. (From Pacific Energy Center)

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.

EquipmentRated Power (watts)
Desktop computer120
Notebook computer45
17” LCD Display75
Desktop laser printer120
Office laser printer250
Office copier750
Commercial refrigerator1,000
Commercial fryer10,000
Clothes washer350
Clothes dryer2,000
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 
Food Service151.490.8131.215-40
Residential (single family)50.550.5NANA1
Residential (multi family)80.7111.0NANA2.5

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.