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Impacts of relaxing humidity constraints on chilled water demand in a commercial building.

Number: 3352

Author(s) : GREKIN R., CHALENDAR J. de, BENSON S.

Summary

In 2018, commercial building space cooling alone consumed 9% of the world’s electricity, and the median age of the U.S. commercial building stock was 37 years. Heating, Ventilation, and Air Conditioning (HVAC) systems in older buildings often have limited controls and are expensive to upgrade. Current HVAC operational rules of thumb are outdated and do not prioritize energy efficiency. Here, we explore opportunities to reduce energy consumption in existing commercial buildings by explicitly considering both indoor and outdoor relative humidity (RH) in HVAC operational decision making through real-world experiments.
Air handling unit (AHU) set point temperatures are generally very low (50-55°F/10-12.8°C), to condense excess water from the outside air to maintain indoor RH below 50-60%, well below the maximum RH limits set by ASHRAE Standard 55 for occupant comfort. The air is then often reheated to maintain a comfortable indoor temperature. Relaxing indoor space RH constraints is thus expected to save energy. To quantify these energy savings, experiments were conducted in a commercial building at a corporate campus in Texas (IECC climate zone 2A, Hot Humid). Over the course of three weeks, the AHU Supply Air Temperature (SAT) set point was repeatedly increased from a baseline of 55°F (12.8°C) or 57°F (13.9°C) to 59°F (15°C). There are three main findings from these experiments: indoor RH increased from 55% to 65%, cooling load was reduced by up to 10%, and zone-level temperatures were minimally impacted (+0.45°F/0.25°C). Experimental conditions met ASHRAE Standard 55 comfort levels and maintained no risk of mold growth. We also measured secondary system effects, including the impacts on total air flow and reheat activity. The system was modeled using enthalpy calculations and good agreement was found between measured and calculated chilled water loads. This indicates that a simple model for estimating chilled water load can be created to understand how demand responds to changes in set points if accurate air flow estimates through the system are available. Our results indicate that relaxing RH constraints could significantly reduce cooling loads and provide a lever for demand flexibility, applicable in existing buildings with limited HVAC controls across the U.S.

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Pages: 10 p.

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  • Original title: Impacts of relaxing humidity constraints on chilled water demand in a commercial building.
  • Record ID : 30032939
  • Languages: English
  • Source: 2024 Purdue Conferences. 8th International High Performance Buildings Conference at Purdue.
  • Publication date: 2024/07/15

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