HVAC system cleaning can boost building energy efficiency and ventilation performance and improve indoor air quality for occupants, researchers at the University of Colorado-Boulder and University of Pavia in Italy suggest.
HVAC cleaning is crucial for improving and maintaining energy efficiency, with cleaned systems saving an average of 41% to 60% on fan and blower energy in all but one case they examined, the researchers say in a paper summarized in the Feb. 1 issue of Energy and Buildings.
“This research demonstrates how a new generation of low-cost HVAC system monitors can … show immediate energy consumption benefits associated with cleaning HVAC components and their associated ductwork serving relatively high occupancy commercial and educational spaces,” the researchers said.
Until now, researchers have rarely considered building operations practices’ impact on both energy efficiency and indoor air quality, the paper states. “The advent of post-pandemic indoor air quality guidelines suggests that building hygiene will gain increased attention as [a] systematic part of building maintenance portfolios,” however, it states.
To that end, the study evaluates HVAC energy consumption and ventilation performance before, during and after routine HVAC cleaning in four buildings operating in cooling mode in four different climate zones. The buildings are in Johnson, Vermont; Pearl, Mississippi; Boulder, Colorado; and Pavia, Italy. The sites have nearly identical HVAC systems serving similar architectural features and occupational loads. The systems were segregated so researchers could compare the performance of cleaned systems with systems that weren’t cleaned.
Following cleaning, the HVAC systems used significantly less energy and delivered higher airflows compared with their uncleaned counterparts, the researchers say.
The greatest change from the previous cleaning phase was an 89% increase in conditioned supply airflow at the Pavia site and 76% improvement in the Pearl site following duct cleaning. In Boulder, the most significant effect was observed after coil cleaning, which resulted in a 110% increase in conditioned supply airflow compared with the previous phase, followed by a 20% increase after blower cleaning.
“The coils in Colorado were visibly soiled,” the researchers said. “Cleaning these coils led to a notable increase in supply airflow compared to the control system, highlighting the importance of maintaining clean coils for optimal system performance.”
Only the Johnson site did not show significant reductions in energy compared with the uncleaned control. At that site, researchers said, “both the ducts and coils were relatively clean.”
The primary issue in the Johnson system was the presence of leaves and large debris in the air handling unit, located outside the building. Cleaning the AHU box during the final stages of the cleaning process improved the supply airflow, the paper said.
The study supports comments in an October National Institute of Building Sciences webinar by experts from ASHRAE, the U.S. Green Building Council and the International WELL Building Institute that indoor air quality can be enhanced without compromising on energy efficiency.
Other strategies to improve IAQ while managing energy use include right-sizing outdoor air filters, implementing demand-controlled ventilation, adopting displacement ventilation and using ultraviolet irradiation to combat mold growth in central air handling units, said Nathan Stodola, chief engineer at the International WELL Building Institute, in another presentation during the webinar.
