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Air Quality in Transit Buses (2023) / Chapter Skim
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Day 1 Session 3
Pages 21-25

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From page 21...
... The new fleet of the future DNE class car has a better cooling capacity, with two HVAC units per car with a cooling capacity of 16 tons and total airflow of 4,300 CFM. The supply ducts are on the ceiling for better airflow and better cooling for standees, and there is an improved design against refrigerant leakage and a switch from an ozonedepleting refrigerant to a new, environmentally friendly refrigerant.
From page 22...
... With a MERV 11 filter, which is somewhere in that 0.3-to-1 micron range, about 40% would be clean air. Sound Transit conducted carbon dioxide tracer gas sampling to measure how much outside air was being changed over in the vehicles and found that the bus fleet had low outside ACH and low filtration, with the result that the total dilution ventilation rate was low.
From page 23...
... The airflow through the filter was measured with thermal anemometers, which measure the flow rate by using one or more simple temperature sensors to monitor the amount of heat removed from a surface. The shape of this filter has a lot of complex curves, and there was not sufficient depth for the MERV 13 filter area to hit the airflow rates that were needed to not exceed the appropriate static pressure drop.
From page 24...
... Regarding supply chain issues, Piedmont noted that the filters themselves have not been the issue, but the items sourced to customize the fit of the filters have been. Wagner added that sometimes the minimum quantity allowed from a manufacturer is still a large quantity for an individual agency to order.
From page 25...
... Food and Drug Administration notes that although UV-C light has a very low ability to penetrate skin, it can efficiently damage the eye and generate cytotoxic ozone gas; see https://www.fda.gov/radiation-emitting-products/tanning/ultraviolet-uv-radiation.]


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