Ship Ventalation systems

[bobnfl]

Will cruise companys ever install hepa filter systems in their ships ventalation systems. I believe it would help stop or slow down the transfer of virus through out the ship. What do you think? Do the cruise lines care enough about their customers to do what is right to protect them.

[ProgRockCruiser]

Your question is phrased a little pejoratively, but:

 

The primary factors, IMHO, are cost, practicality, and actual effectiveness.

 

Cost: If each cabin requires an individual filter (I'm using the cabin as an example, because that is where pax can be isolated), and they must be changed every cruise, and they cannot be reused after some form of cleaning, then cost is going to be significant - both in materials and labor (the filters don't just magically change themselves).  But maybe they can use longer-lasting clean-able filters.  Might be more expensive, but might be palatable.  Remember, whatever the cost increase, you, the cruiser, will pay it in the end.

 

Practicality: is it logistically possible to insert a removable filter segment for each cabin?  I sure can't answer that.

 

Effectiveness: what does it matter if there are HEPA filters on each cabin if you have to pass by your fellow passengers in the hallways, in the MDR, along the Promenade deck?  The virus isn't going to just be in the air going into your cabin.  It will be "everywhere".  And HEPA filters in those public areas will not stop it swirling around in those areas.

 

Will it happen?  :shrug:  I don't think so, but maybe they'll do it as a feel-good move.

 

Edited August 6, 2020 by ProgRockCruiser
clarity

[Shmoo here]

1 hour ago, bobnfl said:

Will cruise companys ever install hepa filter systems in their ships ventalation systems. I believe it would help stop or slow down the transfer of virus through out the ship. What do you think? Do the cruise lines care enough about their customers to do what is right to protect them.

Sounds like a question that @chengkp75 could answer.

[chipmaster]

Just tear apart the HVAC, yeah right.... 

 

 

[bafinegan]

I read they are considering placing those HEPA filters on room designated as isolation rooms.  That is what hospitals do.  Surgical suites and isolation rooms have them.

 

But that would only work once a person has been identified as being Covid 19 +.  Wouldn't do squat for those "silent/symptom-less" people.  SO masks and social distancing would still be required.

 

baf

[Roger88]

2 hours ago, bobnfl said:

Will cruise companys ever install hepa filter systems in their ships ventalation systems. I believe it would help stop or slow down the transfer of virus through out the ship. What do you think? Do the cruise lines care enough about their customers to do what is right to protect them.

Why would  you need such an advanced ventialtion system when you spend most of your time outside your cabin? Moreover, these systems will most likely eat up all the energy on board the ship and might cause problems to the overall electrical navigation of the ship. I think its better to stick to the systems they have right now 

[Ashland]

Just changing the regular filter's a bit more often...I've seen pictures posted on this board of some dirty disgusting filters some have seen when they have check their cabin's. I would never think to check the filter but some did and revealed a dirty little secret some of us never would think of.

[mammajamma2013]

2 hours ago, Shmoo here said:

Sounds like a question that @chengkp75 could answer.

He has on a couple of other threads on the same subject.  If OP does a search for them, s/he'd find good information.

[chengkp75]

2 hours ago, Shmoo here said:

Sounds like a question that @chengkp75 could answer.

 

7 minutes ago, mammajamma2013 said:

He has on a couple of other threads on the same subject.  If OP does a search for them, s/he'd find good information.

Yes, I have.  Too lazy to search up a link right now.  I will just give a short answer.

 

While it has been shown that airflow in a space (room) can spread the virus further than the accepted "sneeze/cough" radius of 6 feet, this is the airflow in the room (from the supply air register, around the room, and to the exhaust register.  This is nothing that a HEPA filter can help with, since it is airflow outside the ducting system.

 

There has been no study done of what the viral load is at the filter inlet in any central HVAC system, let alone a ship's system, so to say that a HEPA filter would help is without factual basis, since merely saying that the filter can remove the virus does not say that it actually is, if there is no virus in the ductwork to begin with.  Even the aerosolized virus cannot stay airborne forever, and even if it did manage to travel all the way up the return duct, through the filter, fan and cooling coil, and then back down the supply duct, it would likely not be in a viable state, as it was outside the host for too long.

 

Finally, cruise ship cabins get their air from two sources:  fresh outside air (low likelihood of viral load) and air that is recirculated within that one cabin.  So, an infected person in a cabin, would not be spreading the virus around the ship via the HVAC system, just to those who enter that cabin.

 

Until I see a peer reviewed study that shows a significant, living viral load at an HVAC filter inlet, I consider installing HEPA filters to be at best a "well, anything can help" situation, and at worst a PR exercise.

[Shmoo here]

18 minutes ago, chengkp75 said:

I will just give a short answer.

Thank you.  Even your short answers are educational.

[ldubs]

Interesting discussion.   I would imagine the cost of a HEPA filter rated to capture viruses would be very high.       

[nosapphire]

I really doubt that the air circulation system on a ship where people are mingling in various locations has as much effect on a ship as people think.

Example - new ship, all balcony, maiden season, entirely fresh-air circulation.

2 cruises that we were on:

- September, a nasty cough that travelled rapidly around the ship. Not everybody caught it - but a lot did.

- December, a really vicious chest infection that went round like wildfire, several people ill enough to be put on antibiotics by the ship's doctor, plus so much cough medicine needed that they ran out of supplies shortly after restocking.

Then 4 cruises that we were (fortunately) not on - each with a serious outbreak of norovirus.

None of these are unusual on a ship - most cruises have something or other going around.

What WAS unusual is that on the old ships operated by the same line (without the modern fresh-air circulation, and with plenty of inside cabins) outbreaks were small - some people caught whatever was going round, most did not - but on the new ships the percentage of infected people was considerably larger.

So relying on a ship having 100% fresh air circulation, or special filters, to reduce the likelihood of catching something is not going to be the answer.

[SRF]

It is also not as simple as just putting a HEPA filter into the duct.

 

The higher the level of filtration, the higher the pressure drop and flow drop.  So the system may only be able to move 1/2 to 1/3 the air it did before.  Which means, the AC does not work well, so the entire ship is very hot and humid.

 

Also, high back pressures can cause issues with the fans and motors.

 

Systems need to be designed from scratch for HEPA filtration.

 

And again, it does not help when in a the MDR or theater and you are close to people.

 

[sunonfire]

Here is link to a related solution. It sounds really promising.

 

https://www.seatrade-cruise.com/news/integra-fragrances-launches-bespoke-scent-sanitizer-solution-shipboard-hvac-systems

[chengkp75]

3 hours ago, SRF said:

The higher the level of filtration, the higher the pressure drop and flow drop.  So the system may only be able to move 1/2 to 1/3 the air it did before.  Which means, the AC does not work well, so the entire ship is very hot and humid.

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.

[Bgcruising]

UV lighting is used in ducts where I work.

[ovccruiser]

Problem with Hepa filters, they are normally designed to stop particles of 0.3 microns, coronavirus is 0.06 - 0.14 microns so would still pass through

[2wheelin]

1 hour ago, ovccruiser said:

Problem with Hepa filters, they are normally designed to stop particles of 0.3 microns, coronavirus is 0.06 - 0.14 microns so would still pass through

But a “naked” virus particle cannot survive so would be not problem. Any viable virus would be much larger than that as in a droplet. Still not necessary to install filters as the virus is still short lived in the air.

[chengkp75]

1 hour ago, ovccruiser said:

Problem with Hepa filters, they are normally designed to stop particles of 0.3 microns, coronavirus is 0.06 - 0.14 microns so would still pass through

This is not correct.  HEPA filter rating says that it will stop 99.7% of particles of 0.3 microns or larger, but it does not rate how it does against smaller particles.  And, with Brownian motion and diffusion of small particulates, which causes the small particles to impact the filter material anyway, the HEPA filter is found by NASA to trap nearly 100% of all particulates, regardless of size.

44 minutes ago, 2wheelin said:

But a “naked” virus particle cannot survive so would be not problem. Any viable virus would be much larger than that as in a droplet. Still not necessary to install filters as the virus is still short lived in the air.

This is the big point.  Until someone shows that there is a significant, viable, viral load at the filter inlet (not just at the register in the room or rooms), no one can tell if a HEPA filter is doing anything at all.

[ovccruiser]

2 hours ago, 2wheelin said:

But a “naked” virus particle cannot survive so would be not problem. Any viable virus would be much larger than that as in a droplet. Still not necessary to install filters as the virus is still short lived in the air.

Naked corona viruses survive on surfaces for up to 72 hours, if they are short lived in the air, why are we being asked to wear masks?

[ovccruiser]

1 hour ago, chengkp75 said:

This is not correct.  HEPA filter rating says that it will stop 99.7% of particles of 0.3 microns or larger, but it does not rate how it does against smaller particles.  And, with Brownian motion and diffusion of small particulates, which causes the small particles to impact the filter material anyway, the HEPA filter is found by NASA to trap nearly 100% of all particulates, regardless of size.

 

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.

Edited August 9, 2020 by ovccruiser

[Shmoo here]

27 minutes ago, ovccruiser said:

Naked corona viruses survive on surfaces for up to 72 hours, if they are short lived in the air, why are we being asked to wear masks?

"Short lived"  - they can last a while.  And you can't see them.  How do you know whether you've walked through a cloud of them that someone left hanging around there?  Aerosolized particles can hang in the air for up to 3 hours before landing on a surface.

[chengkp75]

1 hour ago, 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.

This is a woeful misunderstanding of what a performance standard is.  Yes, the filter stops 99+% of particulates over 0.3 micron, but what percentage of smaller particles does it stop?  We don't know, because the testing lab only looks at what the standard requires.  Why test to a smaller size, when the filter meets the larger size which is what is required.  Many HEPA filter manufacturers claim much better performance than the HEPA standard, but even those who don't make this claim, actually do very well with smaller particles.  As for Brownian motion, I guess NASA didn't attend that day in physics.

[chengkp75]

1 hour ago, ovccruiser said:

Naked corona viruses survive on surfaces for up to 72 hours, if they are short lived in the air, why are we being asked to wear masks?

Not wanting to get into the mask debate, let me just say that a mask prevents droplet spray transmission, and once the droplets break down and the virus becomes aerosolized, it can travel even further than the "6 foot cough/sneeze radius" and still be viable, as is shown in the Chinese restaurant study, where the airflow from the AC vent moved the virus to adjacent tables, even when they were over 6 feet apart.  But coronavirus in air, is subject to low humidity, low temperature, and UV light, so it tends to either drop out of the airflow, or begin to break down.  I'm not sure that the covid viruses that were found to be viable on surfaces after 72 hours were deposited as "naked" virus (single viruses in aerosol) or from droplets (with accompanying moisture for extending "life"), and I haven't seen any data one way or the other on this.

[ovccruiser]

15 hours ago, chengkp75 said:

This is a woeful misunderstanding of what a performance standard is.  Yes, the filter stops 99+% of particulates over 0.3 micron, but what percentage of smaller particles does it stop?  We don't know, because the testing lab only looks at what the standard requires.  Why test to a smaller size, when the filter meets the larger size which is what is required.  Many HEPA filter manufacturers claim much better performance than the HEPA standard, but even those who don't make this claim, actually do very well with smaller particles.  As for Brownian motion, I guess NASA didn't attend that day in physics.

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.