Plug loads (computers, monitors, printers, projectors, etc.) are estimated to use between 20% to 50% of building energy use. They have evolved to become a larger percentage of a building’s overall heat.

Two factors are responsible for that increase, according to Glenn Friedman, chair of the Standard 203 committee.

“First, over time, computer use has continued to increase, resulting in a much larger number of personal computers in buildings,” he said. “Second, advances in building techniques have improved envelopes and reduce that portion of load/energy use.”

Engineers optimize HVAC equipment selections by performing cooing load calculations. Internal heat gains from plug loads are a significant portion of those calculations.

“Most plug loads operate at a fraction of their nameplate electrical load, so, as a result, produce significantly less heat load than engineers may use in their cooling load calculations based on those nameplate values,” said Friedman. “This can result in oversizing of air-conditioning equipment, resulting in extra initial cost for that equipment as well as higher operating cost.”

Friedman noted that engineers face several challenges when it comes to determining heat gain of equipment. Since there are no standards for establishing how the power consumption or heat rejection data or various plug loads is determined, it is difficult for engineers to accurately use this data in their cooling load calculations. ASHRAE has funded research to develop a test method and measure plug load type equipment heat rejection. In addition, plug load type equipment is an ever evolving market, so equipment design changes frequently and requires new testing for power consumption and generation of heat rejection data for cooling load calculation use.

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