Bubbles for Energy Savings

The Stanford Facilities Energy Management (FEM) team recently conducted a pilot study on air handling systems, investigating a potential way to reduce energy use. FEM tested a new coil-cleaning product that uses an enzyme-infused foam formula to reduce air resistance and improve thermal transfer in coils for increased energy efficiency of heating and cooling systems. 

Chilled water and hot water coils are copper tubes with bins at the end. Like radiators, they act as heat transfer mechanisms. Over time, dirt and debris accumulate in the coils, reducing air flow and lowering air quality. While they are typically cleaned through pressure washing, a process that involves shutting down the air handlers and closing the building for the day (and is consequently rarely performed), this new technology offers an alternative cleaning solution. The foam formula includes a non-toxic enzyme to break down biological matter in the coils and can be run at any time while the building is still in operation. 

Based in the Mitchell Earth Sciences Building, the FEM study tested the energy-saving capabilities of this product by measuring the gallons per minute (GPM) flow of chilled water entering the building’s coils as well as the supply and return air temperatures to calculate the amount of chilled water used to meet cooling demands. This data was recorded for three days prior to cleaning and for four days after using the cleaning product. 

FEM found an improvement in coil thermal efficiency post cleaning, with a reduction in GPM needed to achieve specific tons of cooling. However, there was no improvement measured in fan speed of the coil, and there was only a 9% overall change in coil heat transfer performance. Considering the small electrical savings and the high cost of purchasing equipment for cleaning, FEM has not determined whether they will progress with the project in other buildings. 

Previous reports show improvement in fan speed and greater electricity savings after using the cleaning solution. It is possible that the difference in performance stems from the size and structure of coils used in the various studies, meaning that the product could potentially have a greater sustainability benefit for other campus buildings with different coils. 

Should FEM continue with the study, the next step in its plan is to install a pressure port to measure the differential air pressure across coils in the Physics and Astrophysics Building and then perform the cleaning service. These coils have recently been pressure washed, so measuring the air pressure drop before and after using the new solution could indicate whether this treatment is better than pressure washing. 

If future trials in different buildings yield improved results, this cleaning process could become a part of regular building maintenance and could help the university improve sustainability efforts by cutting back on energy consumption.