Plug load

Last updated

Plug load is the energy used by products that are powered by means of an ordinary AC plug (e.g., 100, 115, or 230 V). [1] This term generally excludes building energy that is attributed to major end uses (HVAC, lighting, water heating, etc.) [1]

Energy quantitative physical property transferred to objects to perform heating or work on them

In physics, energy is the quantitative property that must be transferred to an object in order to perform work on, or to heat, the object. Energy is a conserved quantity; the law of conservation of energy states that energy can be converted in form, but not created or destroyed. The SI unit of energy is the joule, which is the energy transferred to an object by the work of moving it a distance of 1 metre against a force of 1 newton.

Lighting deliberate use of light to achieve a practical or aesthetic effect

Lighting or illumination is the deliberate use of light to achieve a practical or aesthetic effect. Lighting includes the use of both artificial light sources like lamps and light fixtures, as well as natural illumination by capturing daylight. Daylighting is sometimes used as the main source of light during daytime in buildings. This can save energy in place of using artificial lighting, which represents a major component of energy consumption in buildings. Proper lighting can enhance task performance, improve the appearance of an area, or have positive psychological effects on occupants.

Water heating thermodynamic process that uses an energy source to heat water above its initial temperature

Water heating is a heat transfer process that uses an energy source to heat water above its initial temperature. Typical domestic uses of hot water include cooking, cleaning, bathing, and space heating. In industry, hot water and water heated to steam have many uses.



Plug loads are often synonymous with terms such as "receptacle loads", "miscellaneous loads", "unregulated loads", or "process energy/loads." While many building codes/standards haven't defined "plug loads" specifically, they have defined these related terms, which are usually broader energy use categories.

"Process energy" is defined as energy consumed in support of a manufacturing, industrial, or commercial process other than conditioning spaces and maintaining comfort and amenities for the occupants of a building. [2] It typically includes office and general miscellaneous equipment, computers, elevators and escalators, kitchen cooking and refrigeration, laundry washing and drying, lighting exempt from the lighting power allowance, and other energy uses. [3]

Elevator Vertical transport device

An elevator or lift is a type of vertical transportation device that moves people or goods between floors of a building, vessel, or other structure. Elevators are typically powered by electric motors that drive traction cables and counterweight systems like a hoist, although some pump hydraulic fluid to raise a cylindrical piston like a jack.

Escalator moving staircase

An escalator is a type of vertical transportation in the form of a moving staircase which carries people between floors of a building. It consists of a motor-driven chain of individually linked steps on a track which cycle on a pair of tracks which keep them horizontal.

Refrigeration Process of moving heat from one location to another in controlled conditions

Refrigeration is a process of removing heat from a low-temperature reservoir and transferring it to a high-temperature reservoir. The work of heat transfer is traditionally driven by mechanical means, but can also be driven by heat, magnetism, electricity, laser, or other means. Refrigeration has many applications, including, but not limited to: household refrigerators, industrial freezers, cryogenics, and air conditioning. Heat pumps may use the heat output of the refrigeration process, and also may be designed to be reversible, but are otherwise similar to air conditioning units.

"Receptacle loads" has been defined as equipment loads normally served through electrical receptacles, such as office equipment and printers, but does not include either task lighting or equipment used for HVAC purposes. [4]

Energy use

In 1999, the US Department of Energy projected that office equipment would be the fastest-growing commercial end use between 1998 and 2020. [5] The Commercial Buildings Energy Consumption Survey (CBECS), a national sample survey project of the US Energy Information Administration, reported that based on 2003 data, 19% of the total energy of US office buildings is attributed to plug load energy use (office equipment, computers, and other energy use). [6]

United States Department of Energy Cabinet-level department of the United States government

The United States Department of Energy (DOE) is a cabinet-level department of the United States Government concerned with the United States' policies regarding energy and safety in handling nuclear material. Its responsibilities include the nation's nuclear weapons program, nuclear reactor production for the United States Navy, energy conservation, energy-related research, radioactive waste disposal, and domestic energy production. It also directs research in genomics; the Human Genome Project originated in a DOE initiative. DOE sponsors more research in the physical sciences than any other U.S. federal agency, the majority of which is conducted through its system of National Laboratories. The agency is administered by the United States Secretary of Energy, and its headquarters are located in Southwest Washington, D.C., on Independence Avenue in the James V. Forrestal Building, named for James Forrestal, as well as in Germantown, Maryland.

Energy Information Administration government agency

The U.S. Energy Information Administration (EIA) is a principal agency of the U.S. Federal Statistical System responsible for collecting, analyzing, and disseminating energy information to promote sound policymaking, efficient markets, and public understanding of energy and its interaction with the economy and the environment. EIA programs cover data on coal, petroleum, natural gas, electric, renewable and nuclear energy. EIA is part of the U.S. Department of Energy.

One confounding factor with estimating plug load energy use is the discrepancy between the rated or nameplate energy power consumption and the actual average power consumption, which can be as little as 10-15% of the nameplate value. [7]

Office equipment and other plug loads emit heat which may require the building to supply additional cooling, a side-effect which contributes to total energy consumption. However, when heating is needed, waste heat from plug loads also supplies part of the energy requirement for heating. Heating a space with electric heating is environmentally less effective than using the electricity for heat pumps, however if the electricity is being consumed anyway this is not a factor.

Electric heating process in which electrical energy is converted to heat

Electric heating is a process in which electrical energy is converted to heat energy. Common applications include space heating, cooking, water heating and industrial processes. An electric heater is an electrical device that converts an electric current into heat. The heating element inside every electric heater is an electrical resistor, and works on the principle of Joule heating: an electric current passing through a resistor will convert that electrical energy into heat energy. Most modern electric heating devices use nichrome wire as the active element; the heating element, depicted on the right, uses nichrome wire supported by ceramic insulators. A warning that these can go to very high temperatures and create excruciating burns

Heat pump a device that transfers thermal energy in the opposite direction of spontaneous heat transfer

A heat pump is a device that transfers heat energy from a source of heat to what is called a heat sink. Heat pumps move thermal energy in the opposite direction of spontaneous heat transfer, by absorbing heat from a cold space and releasing it to a warmer one. A heat pump uses external power to accomplish the work of transferring energy from the heat source to the heat sink. The most common design of a heat pump involves four main components – a condenser, an expansion valve, an evaporator and a compressor. The heat transfer medium circulated through these components is called refrigerant.

Plug load energy efficiency

In general, although total plug load energy use is increasing, the actual plug load equipment stock is getting more efficient; technical advances such as low power consumption by LCD monitors, more effective sleep modes and the uptake of the notebook laptop computer in lieu of a desktop computer have produced lower plug load power levels. [8]

Plug load energy efficiency programs such as Energy Star help distinguish energy efficient plug load/office equipment products to consumers. Energy Star labeled computers, fax machines, scanners, and printers have demonstrated over 50% energy savings as compared to standard equipment. [9]

User behavior and power management

Although the efficiency of this equipment category is improving, many studies have indicated that user behavior may be a factor for its overall increasing energy use. In one study of 11 after-hours walk-throughs of offices in San Francisco and Washington DC, "only 44 percent of computers, 32 percent of monitors, and 25 percent of printers were turned off at night". [10]

Additionally, equipment power management adds some uncertainty to estimating plug load energy use. While most plug load products have "off" and "on" states, the "sleep" or "low power" states can represent a wide range of power savings, from 55% in desktop computers to 94% in CRT monitors. [11]

See also

Related Research Articles

Heating, ventilation, and air conditioning Technology of indoor and vehicular environmental comfort

Heating, ventilation, and air conditioning (HVAC) is the technology of indoor and vehicular environmental comfort. Its goal is to provide thermal comfort and acceptable indoor air quality. HVAC system design is a subdiscipline of mechanical engineering, based on the principles of thermodynamics, fluid mechanics and heat transfer. "Refrigeration" is sometimes added to the field's abbreviation, as HVAC&R or HVACR or "ventilation" is dropped, as in HACR.

Energy Star certification mark

Energy Star is a program run by the U.S. Environmental Protection Agency (EPA) and U.S. Department of Energy (DOE) that promotes energy efficiency. Energy Star provides information on the energy consumption of products and devices, using standardized methods. The Energy Star label, can be found on more than 75 different product categories, new homes, commercial buildings and industrial plants.

Building automation branch of automation

Building automation is the automatic centralized control of a building's heating, ventilation and air conditioning, lighting and other systems through a building management system or building automation system (BAS). The objectives of building automation are improved occupant comfort, efficient operation of building systems, reduction in energy consumption and operating costs, and improved life cycle of utilities.

Underfloor heating and cooling is a form of central heating and cooling which achieves indoor climate control for thermal comfort using conduction, radiation and convection. The terms radiant heating and radiant cooling are commonly used to describe this approach because radiation is responsible for a significant portion of the resulting thermal comfort but this usage is technically correct only when radiation composes more than 50% of the heat exchange between the floor and the rest of the space.

Energy recovery ventilation (ERV) is the energy recovery process of exchanging the energy contained in normally exhausted building or space air and using it to treat (precondition) the incoming outdoor ventilation air in residential and commercial HVAC systems. During the warmer seasons, the system pre-cools and dehumidifies while humidifying and pre-heating in the cooler seasons. The benefit of using energy recovery is the ability to meet the ASHRAE ventilation & energy standards, while improving indoor air quality and reducing total HVAC equipment capacity.

Infiltration is the unintentional or accidental introduction of outside air into a building, typically through cracks in the building envelope and through use of doors for passage. Infiltration is sometimes called air leakage. The leakage of room air out of a building, intentionally or not, is called exfiltration. Infiltration is caused by wind, negative pressurization of the building, and by air buoyancy forces known commonly as the stack effect.

Efficient energy use Energy efficiency

Efficient energy use, sometimes simply called energy efficiency, is the goal to reduce the amount of energy required to provide products and services. For example, insulating a home allows a building to use less heating and cooling energy to achieve and maintain a comfortable temperature. Installing LED lighting, fluorescent lighting, or natural skylight windows reduces the amount of energy required to attain the same level of illumination compared to using traditional incandescent light bulbs. Improvements in energy efficiency are generally achieved by adopting a more efficient technology or production process or by application of commonly accepted methods to reduce energy losses.

Miscellaneous electric loads (MELs) in buildings are electric loads resulting from electronic devices not responsible for space heating, cooling, water heating, or lighting. MELs are produced by hard-wired and “plug-in” electrical devices, including home entertainment centers, kitchen electronics such as microwaves and toaster ovens, bath items such as hair dryers and electric hot tubs, and others such as security systems and ceiling fans. MELs are gaining greater importance as home electronics become more sophisticated and more widespread, and miscellaneous electric use is expected to rise.

Voltage optimisation is a term given to the systematic controlled reduction in the voltages received by an energy consumer to reduce energy use, power demand and reactive power demand. While some voltage 'optimisation' devices have a fixed voltage adjustment, others electronically regulate the voltage automatically.

Energy Management Software (EMS) is a general term and category referring to a variety of energy-related software applications which may provide utility bill tracking, real-time metering, building HVAC and lighting control systems, building simulation and modeling, carbon and sustainability reporting, IT equipment management, demand response, and/or energy audits. Managing energy can require a system of systems approach.

Energy conservation in the United States

The United States is the second-largest single consumer of energy in the world. The U.S. Department of Energy categorizes national energy use in four broad sectors: transportation, residential, commercial, and industrial.

HVAC is a major subdiscipline of mechanical engineering. The goal of HVAC design is to balance indoor environmental comfort with other factors such as installation cost, ease of maintenance, and energy efficiency. The discipline of HVAC includes a large number of specialized terms and acronyms, many of which are summarized in this glossary.

A Deep energy retrofit can be broadly categorized as an energy conservation measure in an existing building also leading to an overall improvement in the building performance. While there is no exact definition for a deep energy retrofit, it can be defined as a whole-building analysis and construction process that aims at achieving on-site energy use minimization in a building by 50% or more compared to the baseline energy use making use of existing technologies, materials and construction practices. Such a retrofit reaps multifold benefits beyond energy cost savings, unlike conventional energy retrofit. It may also involve remodeling the building to achieve a harmony in energy, indoor air quality, durability, and thermal comfort. An integrated project delivery method is recommended for a deep energy retrofit project. An over-time approach in a deep energy retrofitting project provides a solution to the large upfront costs problem in all-at-once execution of the project.

Dedicated outdoor air system

A dedicated outdoor air system (DOAS) is a type of heating, ventilation and air-conditioning (HVAC) system that consists of two parallel systems: a dedicated system for delivering outdoor air ventilation that handles both the latent and sensible loads of conditioning the ventilation air, and a parallel system to handle the loads generated by indoor/process sources and those that pass through the building enclosure.

ANSI/ASHRAE/IES Standard 90.1: Energy Standard for Buildings Except Low-Rise Residential Buildings is an American National Standard published by ASHRAE and jointly sponsored by the IES that provides minimum requirements for energy efficient designs for buildings except for low-rise residential buildings. The original standard, ASHRAE 90, was published in 1975. There have been multiple editions to it since. In 1999 the ASHRAE Board of Directors voted to place the standard on continuous maintenance, based on rapid changes in energy technology and energy prices. This allows it to be updated multiple times in a year. The standard was renamed ASHRAE 90.1 in 2001. It has since been updated in 2004, 2007, 2010, 2013 and 2016 to reflect newer and more efficient technologies.

Variable refrigerant flow (VRF), also known as variable refrigerant volume (VRV), is an HVAC technology invented by Daikin Industries, Ltd. in 1982. Like ductless minisplits, VRFs use refrigerant as the cooling and heating medium. This refrigerant is conditioned by a single outdoor condensing unit, and is circulated within the building to multiple indoor units.

Radiant heating and cooling Systems using temperature-controlled surfaces to exchange heat with their surrounding environment through convection and radiation

Radiant heating and cooling systems are temperature-controlled surfaces that exchange heat with their surrounding environment through convection and radiation. By definition, in radiant heating and cooling systems, thermal radiation covers more than 50% of heat exchange within the space. Hydronic radiant heating and cooling systems are water-based. It refers to panels or embedded building components. Other types include air-based and electrical systems. Important portions of building surfaces are usually required for the radiant exchange.

ASHRAE global society advancing human well-being through sustainable technology for the built environment

The American Society of Heating, Refrigerating and Air-Conditioning Engineers is a global professional association seeking to advance heating, ventilation, air conditioning and refrigeration (HVAC&R) systems design and construction. Founded in 1894 it now has more than 50,000 members worldwide, composed of building services engineers, architects, mechanical contractors, building owners, equipment manufacturers' employees, and others concerned with the design and construction of HVAC&R systems in buildings. The society funds research projects, offers continuing education programs, and develops and publishes technical standards to improve building services engineering, energy efficiency, indoor air quality, and sustainable development.

Cooling load is the rate at which sensible and latent heat must be removed from the space to maintain a constant space dry-bulb air temperature and humidity. Sensible heat into the space causes its air temperature to rise while latent heat is associated with the rise of the moisture content in the space. The building design, internal equipment, occupants, and outdoor weather conditions may affect the cooling load in a building using different heat transfer mechanisms. The SI units are watts.

Sensitivity analysis of an EnergyPlus model identifies how uncertainty in an output can be allocated to uncertainty in the input parameters of a process model. Sensitivity analysis is useful for identifying which parameters need more attention during model design and which input parameters influence simulation results the most. Influence of the construction materials and number of people, so-called occupancy, on the room temperature and incoming air ventilation temperature of a house can be obtained by sensitivity analysis. Performing a crude sensitivity analysis that shows the impact of the uncertainty with respect to changes of individual values for these parameters identifies the most significant individual contributors to variability in results.


  1. 1 2 Nordman, Bruce; Marla McWhinney (2006). "Electronics Come of Age: A Taxonomy for Miscellaneous and Low Power Products". ACEEE Summer Study on Energy Efficiency in Buildings. Washington, D.C.: ACEEE.
  2. ASHRAE (2010). ANSI/ASHRAE Standard 90.1-2010: Energy Standard for Buildings Except Low-Rise Residential Buildings. Atlanta, GA: American Society of Heating, Refrigerating and Air-Conditioning Engineers.
  3. U.S. Green Building Council (October 2007). LEED for New Construction & Major Renovation Version 2.2 Reference Guide (Third ed.). U.S. Green Building Council. ISBN   978-1-932444-11-7.
  4. COMNET (2010). Commercial Buildings Energy Modeling Guidelines and Procedures. Oceanside, CA: Commercial Energy Services Network.
  5. Energy Information Administration (1999), Annual Energy Outlook 2000 with Projections to 2020, U.S. Department of Energy
  6. "Commercial Buildings Energy Consumption Survey". U.S. Energy Information Administration. Retrieved 28 November 2011.
  7. Hosni, M. H.; Beck, B. T. (2009), Update to Measurements of Office Equipment Heat Gain Data, Final Report, ASHRAE Research Project RP-148
  8. Wilkins, Christopher K.; Mohammad H. Hosni (2011). "Plug Load Design Factors". ASHRAE Journal. 53 (5): 30–34.
  9. Webber, C. A.; R. E. Brown; J. Koomey (2000). "Savings Estimates for the ENERGY STAR® Voluntary Labeling Program". Energy Policy. 28 (15): 1137–49. doi:10.1016/s0301-4215(00)00083-5.
  10. Webber, C. a. (2001). "Field Surveys of Office Equipment Operating Patterns". Draft Report, LBNL-46930.
  11. Webber, C. a. (2006). "After-Hours Power Status of Office Equipment in the USA". Energy. 31 (14): 2823–38. doi:10.1016/