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Are cruise ships able to re-route HVAC/Air? Why they re-circulate air?

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so given the current situation, it's interesting to me that most cruises re-circulate air and does not get any significant air that's fresh. which is a big factor making people sick. i do understand why they re-circ and it is all due to cost. but out of curiousity for mild waether places such as right now in most places , wouldn't it make more sense to re-route the HVAC to get all fresh air, and if its too cold, ask people to wear more clothes?

 

or can they simply not do that , tech wise? it would seem to make sense to help reduce the spread of contaminated air

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Our resident Chief Engineer (of cruise ships) has said that very little air is recirculated and that what is, is heavily filtered.

 

Covid19 is spread by droplets that as far as can be known, are not carried through air ducts, anyway.

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As is the case with most buildings on land, the standard is that 80% of the air in a space is recirculated, and 20% is exchanged for fresh air, every minute.  For public spaces, this air is somewhat co-mingled, since the spaces are generally open to each other, but spaces each have their own recirculation circuit, and no, there is no way to change this over to all fresh air exchange, as the ducting just isn't there.

 

In cabins, while there is "recirculated air", it is merely recirculated within that cabin.  There is a fresh air inlet, to get the 20% of fresh air into the cabin, and the bathroom exhaust takes away the 20% of exhaust to the outside.  The 80% is recirculated by a small fan and cooler unit that takes the air from the cabin and passes it over the cooler, and then back to the same cabin.  This is the system that is controlled by the cabin thermostat.  Further, the fresh air supply provides a slightly greater volume of air than the bathroom exhaust takes out, so that the cabin is maintained at a slight positive pressure compared to either the outdoors or the passageway.  This means that air from the cabin will flow out of the cabin under the door into the passageway, and not the other way.  This is why isolation is done in the cabins, and exposure to public spaces is limited.

 

Both the fresh air supply ducts and the public space and cabin recirculation systems have filters in them, and the large air handlers for the public space recirculation have sanitizing pads in the drains to kill bacteria and viruses that may have fallen out of the air with the condensation caused by cooling the air.

 

As noted, CDC does not believe at this time that covid-19 can be transmitted via air ducts.

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Another insightful answer as usual, Chief.

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3 hours ago, chengkp75 said:

As is the case with most buildings on land, the standard is that 80% of the air in a space is recirculated, and 20% is exchanged for fresh air, every minute.  For public spaces, this air is somewhat co-mingled, since the spaces are generally open to each other, but spaces each have their own recirculation circuit, and no, there is no way to change this over to all fresh air exchange, as the ducting just isn't there.

 

In cabins, while there is "recirculated air", it is merely recirculated within that cabin.  There is a fresh air inlet, to get the 20% of fresh air into the cabin, and the bathroom exhaust takes away the 20% of exhaust to the outside.  The 80% is recirculated by a small fan and cooler unit that takes the air from the cabin and passes it over the cooler, and then back to the same cabin.  This is the system that is controlled by the cabin thermostat.  Further, the fresh air supply provides a slightly greater volume of air than the bathroom exhaust takes out, so that the cabin is maintained at a slight positive pressure compared to either the outdoors or the passageway.  This means that air from the cabin will flow out of the cabin under the door into the passageway, and not the other way.  This is why isolation is done in the cabins, and exposure to public spaces is limited.

 

Both the fresh air supply ducts and the public space and cabin recirculation systems have filters in them, and the large air handlers for the public space recirculation have sanitizing pads in the drains to kill bacteria and viruses that may have fallen out of the air with the condensation caused by cooling the air.

 

As noted, CDC does not believe at this time that covid-19 can be transmitted via air ducts.

But the myth of its the fault of the air conditioning is not going to go away anytime soon. Facts may be facts, but people are going to believe what they want to believe.

 

But as always, thank you for laying out the facts.

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Yes well this current farce has proven many people are ridiculously stupid. So giving them facts isn't going to help them. 

 

They are too busy stocking up on toilet rolls and tinned beans ready for the apocalypse.

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3 hours ago, That sinking feeling said:

Yes well this current farce has proven many people are ridiculously stupid. So giving them facts isn't going to help them. 

 

They are too busy stocking up on toilet rolls and tinned beans ready for the apocalypse.

And its not going to stop. I just read a post from less than 10 minutes ago on the Carnival board, the Carnival corona virus thread and it speaks of the recirculating air on the cruise ships  being one of the problems with travel by cruise ship.

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I certainly thought that air was circulated throughout at least parts of the ship so thank you for a good explanation of how it actually works.

As an aside to just above do you think the toilet paper and beans related???  🙂

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4 hours ago, Cee_Jay said:

I certainly thought that air was circulated throughout at least parts of the ship so thank you for a good explanation of how it actually works.

As an aside to just above do you think the toilet paper and beans related???  🙂

 

Yeah, if you stock up on the latter, stocking up on the former seems advisable.

 

What I don't get are the people stocking up on water.  Our taps will not run dry and I've heard nothing about the virus spreading via the water supply.  It is as if they are operating off a list of what to stockpile for an anticipated hurricane.

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I honestly believe too many people have watched too many zombie movies. Its completely crazy behaviour from what you would have assumed were sane people.

 

We had it in the uk with brexit. People are so stupid its almost impossible to explain.

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Focusing on the wrong, thing, if I was on a ship, I'm not,  but even on the airplane I worry very little about the air but the passenger that walks by me, touching everything, or the one that sat in my seat before me.  

 

Pay attention to what you touch, and then touch on yourself, I would say surface transfer is fare more likely than everyone on a plane getting sick, as we already know based on how things are going that can't be the case.

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Good hygiene practices start before you go on your trip. You are not going to stop bad habits, just because you are on a trip.

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1 hour ago, Mike981 said:

Good hygiene practices start before you go on your trip. You are not going to stop bad habits, just because you are on a trip.

And one of the things we are being told to not do is touch your face. I know I do that. And I see in your picture you are doing that!

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22 hours ago, ontheweb said:

And one of the things we are being told to not do is touch your face. I know I do that. And I see in your picture you are doing that!


Nope, there is a good half inch between my chin and my hand. 😆

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On ‎3‎/‎8‎/‎2020 at 8:15 PM, crystalspin said:

Our resident Chief Engineer (of cruise ships) has said that very little air is recirculated and that what is, is heavily filtered.

 

Covid19 is spread by droplets that as far as can be known, are not carried through air ducts, anyway.

 

There are some alternative views about such as this:

 

https://www.purdue.edu/newsroom/releases/2020/Q1/cruise-ship-ac-systems-could-promote-rapid-coronavirus-spread,-prof-says.html

 

"“It’s standard practice for the air conditioning systems of cruise ships to mix outside air with inside air to save energy. The problem is that these systems can’t filter out particles smaller than 5,000 nanometers. If the coronavirus is about the same size as SARS, which is 120 nanometers in diameter, then the air conditioning system would be carrying the virus to every cabin."

 

 

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14 minutes ago, KnowTheScore said:

 

There are some alternative views about such as this:

 

https://www.purdue.edu/newsroom/releases/2020/Q1/cruise-ship-ac-systems-could-promote-rapid-coronavirus-spread,-prof-says.html

 

"“It’s standard practice for the air conditioning systems of cruise ships to mix outside air with inside air to save energy. The problem is that these systems can’t filter out particles smaller than 5,000 nanometers. If the coronavirus is about the same size as SARS, which is 120 nanometers in diameter, then the air conditioning system would be carrying the virus to every cabin."

 

 

Please see post #3 regarding recirculation of air.  Currently, the CDC does not feel that the covid-19 virus can stay viable during the time it would be in the air ducts.  Air ducts for recirculation can reach several hundred feet on a good sized cruise ship (counting the ducting from the space to the cooler and then back to the space).  Also, please note that air conditioning is not recirculated from multiple cabins to multiple cabins.

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On 3/9/2020 at 11:46 AM, Toofarfromthesea said:

 

Yeah, if you stock up on the latter, stocking up on the former seems advisable.

 

What I don't get are the people stocking up on water.  Our taps will not run dry and I've heard nothing about the virus spreading via the water supply.  It is as if they are operating off a list of what to stockpile for an anticipated hurricane.

Just saw a post on Twitter that areas of London are experiencing problems with the water not flowing or flowing very poorly. Apparently a pump station of some sort is down according the the tweet. Mind you I would think just an unexpected equipment failure unrelated to the virus, but what happens when a lot of people in an area are ill and there aren't enough trained workers on duty to make an emergency repair of this nature?

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9 hours ago, TravelinGert said:

Just saw a post on Twitter that areas of London are experiencing problems with the water not flowing or flowing very poorly. Apparently a pump station of some sort is down according the the tweet. Mind you I would think just an unexpected equipment failure unrelated to the virus, but what happens when a lot of people in an area are ill and there aren't enough trained workers on duty to make an emergency repair of this nature?

 

Stocking up on water in anticipation of something like this is the very definition of panic, IMO.

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14 minutes ago, bluesea321 said:

This is how RCL does it.  Please note their comments on recirculation.

 

https://www.rclcorporate.com/a-chill-in-the-air/

This is a prime example of a non-technical person writing about a technical matter.  I have always said that the air in public spaces has been recirculated, and this has been done for decades, I don't know what ship this guy is speaking about of once through AC, but I digress.  He also does not understand how a heat recovery wheel works.  Where is the heat "caught"?  Heat can only be "caught" by something cooler than what you are trying to capture heat from.  The air that is drawn out of an air conditioned space for recirculation is almost always cooler than the outside air, and warmer than the air being supplied as AC.  So, you can't transfer the heat from the recirculation air to the outside, and if you transfer it to the AC air, you are just heating the air you just cooled by the AC.  Nope.  Note that the description of the heat recovery wheel is not a quote from the technical expert quoted elsewhere in the article.  The heat recovery wheel takes the air that is being exhausted to the outside (typically 20% of air volume per minute), and which is cooler than the outside, and this air, which you don't care about, is heated by cooling the incoming fresh air (again 20% of air volume per minute), and since you now have cooler fresh air coming into the ship, you need less energy to cool that air to the proper temperature.

 

They do not specify what the "fan coil" units are set up for.  For public spaces, these are large fan coil units that cool the recirculation air, but for cabins, each cabin has it's own fan coil unit, where the fan takes the air from the cabin, passes it over the cooling coil, and returns the air to the cabin.  This is the AC that is controlled by the cabin thermostat.  There is another AC system supplying cool fresh air to the cabin, and that cannot be controlled by the cabin thermostat.

 

The only real change that this RCI article speaks about over what I have worked on aboard ships for the past 30 years, is the use of CO2 measuring to adjust the cooling load of a public space to the heat load of the number of people in the space.

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Posted (edited)
20 minutes ago, chengkp75 said:

This is a prime example of a non-technical person writing about a technical matter.  I have always said that the air in public spaces has been recirculated, and this has been done for decades, I don't know what ship this guy is speaking about of once through AC, but I digress.  He also does not understand how a heat recovery wheel works.  Where is the heat "caught"? .....

 

Why don't you contact RCL and tell them their official documents are "incorrect"?

Edited by bluesea321

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36 minutes ago, chengkp75 said:

The only real change that this RCI article speaks about over what I have worked on aboard ships for the past 30 years, is the use of CO2 measuring to adjust the cooling load of a public space to the heat load of the number of people in the space.

 

In building systems, CO2 levels are used to adjust make up air, along with incoming air temp.

 

As outside air normally needs to be heated or cooled or dehumidified, you want the minimum makeup air.  But for personal comfort, you want higher makeup air. 

 

So modern, computer controlled systems look at several factors.

 

If the CO2 levels go up (more people) it increases the makeup air.  If CO2 levels go down, they reduce makeup air.  

 

If the outside air is cool, it is better to bring in cool air, than to cool recirculated air.  So some systems can go to 100% make up air (single pass) to reduce energy use. Same for heating.

 

I have not seen a heat recovery wheel that cooled.  The ones I have seen take heat out of the warm exhaust air, to heat the incoming colder air.  

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1 hour ago, bluesea321 said:

 

Why don't you contact RCL and tell them their official documents are "incorrect"?

Because that's not an "official" document, it's a PR document.

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10 minutes ago, chengkp75 said:

Because that's not an "official" document, it's a PR document.

 

The document comes from RCL Corporate.  How more official can it get!!!  

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