Ship Ventalation systems

[chengkp75]

1 hour ago, ovccruiser said:

With all respect, "we don't know", is exactly what I have said and the smoke screen of the Brownian motion is irrelevant.

 

Apart form that, I would almost certainly say that air con on ships was not designed to use hepa filters and god know the cost of improving the system to adopt them. It is not just a case of putting them inline, to achieve their current air changes and air flow would mean increasing the output of the fans and probably increasing the size of the ducting.

One thing you don't take into account is that filter performance improves as it becomes more fouled.  This reduces the pore size due to the collection of particulates, and results in better performance.  And, according to the EPA:

 

"HEPA is a type of pleated mechanical air filter. It is an acronym for "high efficiency particulate air [filter]" (as officially defined by the U.S. Dept. of Energy).  This type of air filter can theoretically remove at least 99.97% of dust, pollen, mold, bacteria, and any airborne particles with a size of 0.3 microns (µm). The diameter specification of 0.3 microns responds to the worst case; the most penetrating particle size (MPPS). Particles that are larger or smaller are trapped with even higher efficiency. Using the worst case particle size results in the worst case efficiency rating (i.e. 99.97% or better for all particle sizes)."

 

Note the portion that I bolded and underlined.

 

As for installing HEPA filters, you are right that you just can't install them, but the challenges are not that great.  Unlike home HVAC systems, and many older building systems, ship HVAC systems tend to use variable frequency drives to adjust the speed, and therefore the airflow of the fans in the systems, and are designed not to run at full speed under normal conditions, so these can be ramped up in speed to meet the 7-11% reduction in airflow that high MERV HEPA filters would present, and still maintain airflow.

 

While I still maintain that installing HEPA filters would be an expensive exercise with no known or proven benefits with regards to covid at this time, if a study does show that there is a significant, viable, viral load at the filter inlet, then HEPA filters would remove them, and provide a measurable benefit.

Edited August 10, 2020 by chengkp75

[ldubs]

8 hours ago, chengkp75 said:

One thing you don't take into account is that filter performance improves as it becomes more fouled.  This reduces the pore size due to the collection of particulates, and results in better performance.  And, according to the EPA:

 

"HEPA is a type of pleated mechanical air filter. It is an acronym for "high efficiency particulate air [filter]" (as officially defined by the U.S. Dept. of Energy).  This type of air filter can theoretically remove at least 99.97% of dust, pollen, mold, bacteria, and any airborne particles with a size of 0.3 microns (µm). The diameter specification of 0.3 microns responds to the worst case; the most penetrating particle size (MPPS). Particles that are larger or smaller are trapped with even higher efficiency. Using the worst case particle size results in the worst case efficiency rating (i.e. 99.97% or better for all particle sizes)."

 

Note the portion that I bolded and underlined.

 

As for installing HEPA filters, you are right that you just can't install them, but the challenges are not that great.  Unlike home HVAC systems, and many older building systems, ship HVAC systems tend to use variable frequency drives to adjust the speed, and therefore the airflow of the fans in the systems, and are designed not to run at full speed under normal conditions, so these can be ramped up in speed to meet the 7-11% reduction in airflow that high MERV HEPA filters would present, and still maintain airflow.

 

While I still maintain that installing HEPA filters would be an expensive exercise with no known or proven benefits with regards to covid at this time, if a study does show that there is a significant, viable, viral load at the filter inlet, then HEPA filters would remove them, and provide a measurable benefit.

 

While I've never used one, I used to hear folks talk about the need to "pre-load" fabric/felt dust collector filters. Of course a filter for dust removal is not the same as a HVAC system.   When I last purchased a HEPA canister filter for my cyclone collector, it cost about 75% more than the standard canister.  And, it has basically the same spec's you provided -- 99.97% eff at 0.3 microns.    I figure my lungs would be happy getting rid of all the fines so it was worth it to me.   But for covid, IDK.   

 

 

[SRF]

On 8/7/2020 at 12:44 PM, chengkp75 said:

Even more problematical is the change to 100% fresh air (no recirculation), which will increase the heat load on the AC system by 5 times, and the vast majority of ships do not have this much reserve cooling capacity.

 

Bottom line is, they are SYSTEMS, and you cannot just make changes and have them still work.

 

 

[SRF]

On 8/9/2020 at 2:32 PM, ovccruiser said:

You have confirmed what I said. 0.3 microns or larger, viruses are much smaller and if you are relying on the Brownian motion, which states erratic not linear, you cannot guarantee the filter will stop viruses, you would be better blanking off the outlet altogether.

 

You do not have just a virus in the air.  You have a virus particle in a droplet.

 

 

[jojo453]

Hi,

I'm researching the relationship between Covid-19 transmission and fresh air intake on cruise ships. I have struggled to find specific information on the typical volume of fresh air per hour which flows into cabins and public areas on ships. I know there are a few engineers on this site who might have some information or links to articles with more details.

 

In particular, I am trying to find out the typical fresh air intake in proportion to the total volume of a room, or whole occupied spaces of the ship (the air changes per hour), and how much this varies depending on whether the ship's air conditioning is cooling or heating air because the fresh air intake may be reduced in cold or hot conditions.

Kind regards

Joe

 

@chengkp75 (I have seen some places where you have posted about this)

 

 

Edited August 13, 2020 by Host Kat
Threads merged.

[ovccruiser]

54 minutes ago, SRF said:

 

You do not have just a virus in the air.  You have a virus particle in a droplet.

 

 

And your proof is where? Viruses can live alone for a few hours, the droplet bit is what we are told with coughing and sneezing. "We know the coronavirus primarily spreads through person-to-person contact when an infected person coughs or sneezes. But live particles that cause COVID-19 can survive on some surfaces for days or weeks, and remain in the air for hours." San Fransisco Chronicle

Edited August 12, 2020 by ovccruiser

[2wheelin]

2 hours ago, ovccruiser said:

And your proof is where? Viruses can live alone for a few hours, the droplet bit is what we are told with coughing and sneezing. "We know the coronavirus primarily spreads through person-to-person contact when an infected person coughs or sneezes. But live particles that cause COVID-19 can survive on some surfaces for days or weeks, and remain in the air for hours." San Fransisco Chronicle

Those live particles would need the droplet for survival in an infectious form and droplets dry up. Dead virus particles, while measurable are generally considered non infectious.

As for remaining in the air, again if in a droplet, they are heavier than air and will fall.

[jojo453]

On 8/10/2020 at 2:19 PM, chengkp75 said:

One thing you don't take into account is that filter performance improves as it becomes more fouled.  This reduces the pore size due to the collection of particulates, and results in better performance.  And, according to the EPA:

 

"HEPA is a type of pleated mechanical air filter. It is an acronym for "high efficiency particulate air [filter]" (as officially defined by the U.S. Dept. of Energy).  This type of air filter can theoretically remove at least 99.97% of dust, pollen, mold, bacteria, and any airborne particles with a size of 0.3 microns (µm). The diameter specification of 0.3 microns responds to the worst case; the most penetrating particle size (MPPS). Particles that are larger or smaller are trapped with even higher efficiency. Using the worst case particle size results in the worst case efficiency rating (i.e. 99.97% or better for all particle sizes)."

 

Note the portion that I bolded and underlined.

 

As for installing HEPA filters, you are right that you just can't install them, but the challenges are not that great.  Unlike home HVAC systems, and many older building systems, ship HVAC systems tend to use variable frequency drives to adjust the speed, and therefore the airflow of the fans in the systems, and are designed not to run at full speed under normal conditions, so these can be ramped up in speed to meet the 7-11% reduction in airflow that high MERV HEPA filters would present, and still maintain airflow.

 

While I still maintain that installing HEPA filters would be an expensive exercise with no known or proven benefits with regards to covid at this time, if a study does show that there is a significant, viable, viral load at the filter inlet, then HEPA filters would remove them, and provide a measurable benefit.

 

Do you know approximately what the volume of fresh air entering cabins, rooms, public spaces etc., in relation to the volume of the room? In other words, what is the number of fresh air changes per hour typically throughout the occupiable parts of the ship?