PRO’S AND CON’S OF CONSIDERATIONS FOR ALTERATION TO 100% FRESH AIR AND MERV13+ FILTERS AS IS EXAMPLE HVAC SUGGESTED 100% FRESH AIR SUGGESTED HEPA FILTERS FRESH AIR EXHAUST AIR FRESH AIR EXHAUST AIR FRESH AIR EXHAUST AIR (NO VIRUS?) (NO VIRUS?) (N0 VIRUS?) (NO VIRUS?) (NO VIRUS?) (NO VIRUS?) MIXING MIXING MIXING A DAMPERS B A DAMPERS B A DAMPERS B MIXED AIR C MIXED AIR C MIXED AIR C PLENUM (NO VIRUS?) PLENUM PLENUM (N0 VIRUS?) EXISTING EXISTING MERV13+ FILTERS FILTERS FILTERS SUPPLY RETURN SUPPLY RETURN SUPPLY RETURN FAN “X” HP FAN FAN “X” HP FAN FAN “X +” HP FAN HEATING HEATING HEATING FUNCTION FUNCTION FUNCTION D E D E D E “W” “X” “Y” VIRUS F G H I ONLY F G H I F G H I “G” TO “E” NOTE: red arrows are virus travel range. All other arrows are HVAC airflow paths. According to case studies in the “COVID-19 Scientific Advisory Group Rapid Evidence Report, prepared for the Alberta Health Services, the virus can only travel up to 6m with wind speeds of 4km/h to 15km/h. (Alberta Health Services, Dbouk and Drikakis 2020 Page 11.207) and another case study states a maximum of 4m travel in patient rooms. (Alberta Health Services, Guo et al 2020 Page 11.206). Common knowledge accepts that the virus can travel no more than 2m, respecting social distancing. It seems unlikely the virus can travel from the occupied space to the mixed air plenum of the fan system. As the supply air enters the room at “D”, If it carries no virus, there is no virus contamination threat from that point to the person at “H”. As the air from “D” passes over the virus carrier person at “G”, the air may pick up virus and carry it to the person at “H”. If “G” to “E” is more than 6m, current studies indicate that the air from “E” to “C” will contain no virus. Better filtration or more fresh air will not alter this outcome. Altering from scenario “W” to “X” will provide no additional virus protection if the virus content is the same at “A” as it is at “B”. With no added virus protection, the system will consume much more energy, produce much more GHG emissions, have increased risk of freezing a coil, experience more low limit shut downs and will likely not be able to heat the space in severe winter weather. If MERV13+ filters are installed with scenario “X” and the virus content in the fresh air is considered to be virus-free, the virus content in the air before and after the MERV13+ filters will be equal, with no virus. The extra pressure drop of the MERV13+ filters over the existing filters will cause the fan’s air volume to be decreased. If MERV13+ filters are installed as per scenario “Y”, the air entering the filters will likely be virus-free, as the fresh air at “A” and the return air “C” are likely both virus-free. The fan horse power will require increasing to produce the same airflow as scenario “W”. With no added virus protection, the system will consume more energy and produce more GHG emissions. An additional concern is that excessive fresh air supply in cold weather tends to lower the relative humidity in the occupied space, benefitting the virus and is detrimental to the human occupants. We require a study identifying the virus presence at locations A, B, C, D, E and F. Current studies appear to assess the virus content from G to H. If the virus cannot travel from G to C, the alterations increasing the percentage of fresh air in the supply air at “D” and the change to MERV13+ filters will achieve nothing in addressing the virus transmission issue. Both changes will cost a lot of money that could be applied to other relevant solutions. 11.203
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