Energy Savings Modeling of Standard Commercial Building Re-tuning Measures: Large Office Buildings

Abstract

Today, many large commercial buildings use sophisticated building automation systems (BASs) to manage a wide range of building equipment. While the capabilities of BASs have increased over time, many buildings still do not fully use the BAS's capabilities and the BASs are not properly commissioned, operated or maintained, which leads to inefficient operation, increased energy use, and reduced lifetimes of the equipment. This report investigates the energy savings potential of several common heating, ventilation and air-conditioning (HVAC) system re-tuning measures on a typical large office building prototype model, using the Department of Energy's building energy modeling software, EnergyPlus. The baseline prototype model uses roughly as much energy as an average large office building in the existing building stock, but does not utilize any re-tuning measures. Individual re-tuning measures simulated against this baseline include automatic schedule adjustments, damper minimum flow adjustments, thermostat adjustments, as well as dynamic resets (set points that change continuously with building and/or outdoor conditions) to static pressure, supply air temperature, condenser water temperature, chilled and hot water temperature, and chilled and hot water differential pressure set points. Six combinations of these individual measures have been formulated -each designed to conform to limitations to implementation of certain individual measures that might exist in typical buildings. All of these measures and combinations were simulated in 16 cities representative of specific U.S. climate zones.The modeling results suggest that the most effective energy savings measures are those that affect the demand-side of the building (air-systems and schedules). Many of the demand-side individual measures were capable of reducing annual HVAC system energy consumption by over 20% in most cities that were modeled. Supply-side measures (chiller, cooling tower and pump measures) affecting HVAC plant conditions were only modestly successful (less than 5% annual HVAC energy savings for most cities for all measures). Combining many of the re-tuning measures revealed deep savings potential. Some of the more aggressive combinations revealed between 35% and 75% reductions in annual HVAC energy consumption, depending on climate and building vintage.iv Executive SummaryToday, many large (>100,000 sf) commercial buildings use sophisticated building automation systems (BASs) to manage a wide range of building equipment. While the capabilities of BASs have increased over time, many buildings still do not fully use the BAS's capabilities and are not properly commissioned, operated or maintained, which leads to inefficient operation, increased energy use, and reduced lifetimes of the equipment.Periodic re-tuning of building controls and heating, ventilation and air conditioning (HVAC) systems helps to reduce inefficient and faulty operations and improve building efficiency. Re-tuning is a systematic, semi-automated process of detecting, dia...

Development of control quality factor for HVAC control loop performance assessment—II: Field testing and results (ASHRAE RP-1587)

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