Is Duct Cleaning the New Answer for Building Decarbonization?

A new study published in the “Energy and Buildings Journal” suggests that regular, maintenance-level cleaning of ducts and fans can have a significant effect on the energy consumption and air flow in non-residential public buildings.

“Impacts of HVAC cleaning on energy consumption and supply airflow: A multi-climate evaluation” by Nasim Ildiri, Emma, Biesiada, Tullio Faccinetti, Norma Anglani, Nouman Ahmded, and Mark Hernandez of the University of Colorado and the University of Pavia, is one of the first studies to provide integrated analysis of building energy consumption and indoor air quality in response to building hygiene habits.

While numerous studies emphasize the importance of HVAC operation and maintenance for improving building energy performance, there is a lack of research investigating the effectiveness of building hygiene practices, in particular HVAC cleaning, on immediate and long-term energy savings potential for higher occupancy buildings.

While this study focused on HVAC performance in cooling mode before, during and after cleaning, it provides many results that could translate to building heating efficiencies and emissions. For instance, they found that while fouling affects both air conditioner and furnace energy use, anticipated energy savings are minimal for single-family residential buildings and may be negative for small office buildings based on fouling levels reported in the literature.

The experiment entailed selecting two “nearly identical Air Handling Units” at each site. The properties needed to be in immediate proximity and serve similar architectural space, and the systems had to be free of excessive variables like numerous reheat coils. To maintain consistency, existing filters were replaced with identical new filters before the cleaning protocols began. The cooling capacities ranged from 10 tons in Vermont to 30 tons in Italy.

“During the cleaning process, the supply and return duct systems, including registers, were thoroughly cleaned, ensuring that any dampers were left in their pre-cleaning positions. All HVAC system components, including fans/blowers, heat exchangers, and evaporator/ condenser coils, were cleaned following industry standards.”

Results:

The tests results were remarkable, though they differed widely between sites.

The conclusion reported that, across the different stages, “the average relative increase in supply airflow (CFMs) were as follows: 46 % for the Italian site; 35 % for Colorado site; 19 % for Mississippi site; and 10 % for the Vermont site. Comparative analysis suggests that the larger cleaned duct area, correlates with a greater relative increase in supply airflow. The two sites with the largest improvements, Italy and Colorado, had the greatest duct surface areas cleaned and the highest duct surface-to-serving area ratios. They also had the largest cooling capacities.”

It also noted that in systems where Variable Air Volume (VAV) controls are enabled, cleanings improved stability and the range of pressure fluctuations was smaller in the intervention system for several months after cleaning.

Overall, net energy consumption decreased in all locations, although they varied by site and system size. “Examination of all cleaned HVAC systems suggests that a larger cleaned duct area is associated with a greater relative increase in supply airflow. In smaller systems, the larger relative energy benefit is realized from coil cleaning, as cleaner evaporative coils enhance heat exchange efficiency by increasing the effective area for heat transfer. Additionally, clearing the limited flow passage area within coils can further improve flow rates.”

The liquid fuels industry already knows that annual tune-ups and system maintenance can reduce energy use, but we are unaware of any similar, recent, side-by-side before and after comparisons in residential or commercial buildings. It could be worthwhile to have current assessments of energy use, emissions, and air quality results from simple and cost-effective preventive maintenance.

Source: Ildiri, Biesiada, Faccinetti, Anglani, Ahmed, and Hernandez; “Impacts of HVAC cleaning on energy consumption and supply airflow: A multi-climate evaluation” Energy & Buildings Journal, https://www.sciencedirect.com/science/article/pii/S0378778824012635

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