Inside a building, heat is generated by people, processes, equipment, and lighting — factors that constitute the internal load. Outside, the climate and thermal performance of the building’s exterior — including the amount of insulation, number of windows, and whether the building is north or south facing — comprise the external load.
The trouble is, most buildings experience internal and external loads that vary throughout the day. Consequently, buildings with systems optimized only for full-load operation are wasting energy when the loads fall below 90 percent.
In recent years, the HVAC industry has witnessed the evolution of three distinct approaches to advancing energy efficiency. For decades, the industry focused on improving full-load efficiency before the current shift to part-load efficiency standards for equipment. Today, new part-load rating methods better account for how equipment operates at off-design conditions when loads vary hour by hour. The next stage in the evolution of building energy efficiency will focus on whole building efficiency for facilities.
Given the progress to date, Part One of this article will examine the evolution of equipment-efficiency standards from full to part load and their relationship to whole-building efficiency.
Part Two will look at how HVAC technologies are advancing to modulate capacity to match variations in building loads, a major factor in improving whole-building energy performance.