Accomodation Air conditioning/ ventillation in Oil Tankers 2

[prkumar]

During cargo operations on oil tankers safety inspectors insist that accomodation ventillation put on recirculation and all intakes and natural vents to be kept shut. Recently I was on 6 months old tanker and when in port Air condition is put  on recirculation and all intakes were shut.Crew complained of vaccum in accomodation,disconfort in the ears and carbon dioxide levels going up. We found that this is caused by sanitary and gally exhaust blowers exhausting air from accomodation and no replenishment as all intakes were shut. Did any one face  similar situation and what methods are employed to overcome this problem?    

 

[metoo]

Keeping all intakes and natural vents to be kept shut sound like a strange request.&nbsp;&nbsp;&nbsp;You could look at some kind of valve turning on air inlets for the sanitary and galley exhaust blowers exhausting air.<br><br>&nbsp;&nbsp;On Submarines they absorbents to deal with carbon dioxide odors.&nbsp;&nbsp;They add Fresh oxygen made from seawater. <br>

 

[jonralph]

It does seem like a strange request.&nbsp;&nbsp;An alternative could be to install gas detectors at your air intake connected to your dampers etc.&nbsp;&nbsp;if gas/vapors are detected your dampers shut and your hvac shuts down.

 

[AndyA]

I have recently returned from a ULCC &quot;Sew World&quot; Built in 1978,where I have spent two years seatime. The ship is 500,000 dead weight tonnes, with Two Air-con fan units in seperate rooms.These have been a major problem to us as the capacity is very under rated. These units were designed to run air with an outside air temp of 29c and drop it to 23c. As our trading area is normally Floating Storage at Kharg Island where the outside air is 48c,you can imagine the problems we had with heat 35-36c in the accomadation.This problem was looked into,and quotes of $250,000 for a new system were given.With freight rates down,this was not an option. Our recirc system was a 2/3 damper to an outside vent,so even with the cargo ops in progress you could not have a full recirc,and infact it would be dangerous with carbon di-oxide build up over a 7 day discharge(As mentioned by yourselves).
As the engine room temp is 60c and 68c at the feed pumps,something had to be done as the engineering staff were not willing to work hot--sleep hot.
Solution:- As the design for a not full recirc,I believe you must have intrinsically safe motor driving the fan.This illeviates putting blanks on the outside air vents.We permantely run with this on recirc as mentioned about the temp.With outside air in use only ,we were supplying air at 39c,but on recirc 32c so inorder to get more cold air into the cabins this was done:
We uprated to a bigger pulley on the motor end and a smaller pulley on the fan end to increase air flow in the accomadation,as you could just about feel air comming out of your cabin vents.This done,it was almost impossible to get the fan room doors open,(meaning of coarse that there was a lack of flow of air through the fan),to counter this it was tried to let more outside air in.This defeats the purpose as you are then fighting air flow against humidity (98%).Once again this was put back to recir.The gas axe was then brought in and we burned holes between the accomadation and the fan rooms, as well cutting a hole into the sanitary exhaust system to supply the fan room.A nice job for the fitters,and fitting fire flaps to the New recircs.This dropped the ai temp supplied by us 10c and upon sealing the outside suction it was dropped down 12c.
So now with &quot;freezing&quot; air supplied,is every one happy NO!
As you have mentioned you create a slight vacuum in the accomadation due to other losses(i.e. galley exhaust fans,hospital extraction fans,etc.etc...)Now another trick was required,how to stop doors banging and ears popping,now we all know Pressure = Force/Area. After extensive deckhead removal we found that all of our recircs and extractions were on deck 1 including the two big ones we cut.On this deck is the C/E office,Capt office,C/O office, coffeerooms, CCR, messrooms,conferencr rooms,computer rooms, hospital,dirty messrooms etc.etc...(trust me they all fit on that deck as it's the widest ship in the world with a beem of 80M )So we decided to increase the area,by replacing cable trunking doors with open fire doors (cable trunking runs top to bottom of the accom. and has plenty of space around them to let air be extracted from the different decks, all seven of them).Only the galley door has to be permanetly shut while we run total recirc, which stops the biggest air loss. Other air is supplied into the accom.by normal air leaks.Now those working on deck 1 don't have banging doors and there ears popping every thim some one opens the stairwell.And with the outside air cracked open a little there is no difference in pressure.

I havn't gone into the problems involving the refrigeration, side of the air con system,as you can believe it wasn't easy, Bigger expansion valves , compressor motor re-rated, trying to reduce F.W. cooling temp to the condensers when S.W. temp is 35c.I could go on.. At least I didn't have to change a freeon 12 system to a freeon 22 ..

Any comments post them.

Thanks,and good sailing ,
Andy

 

[xltsport]

There is a big misconception that the A/C must be on 100% recirc when on the terminal. The actual rule, as per the ISGOTT Guide(which should be in the mate's and/or the Old Man's office states that no flammable or toxic vapours should be allowed to enter the accommodation. This is to be achieved by either recirculation or shutting down the A/C unit. A poitive pressure is also supposed to be maintained in the accommodation to prevent the ingress of flammable/toxic vapours
If you put the unit on 100% recirc it will ice up and could self destruct. Our last set of newbuilds out of Korea 3 years ago were designed for Arabian Gulf, so that meant 38 deg sea temp, 55 deg outside air temp. We could cool down a large hotel in normal conditions. Unfortunately they don't like recirc so we have lost a total of 14 compressors in 3 years on two ships.
Also on recirc you do create a vacuum because of the exhaust fans.
You can't shut the system down because:-
a) You will fry the crew - and the electronics.
b) The terminal will most probably throw you off because
it is too hot for their supercargo.

We are trying to find a solution, but no joy as yet.

 

[MASE81]

An alternative ..install gas detectors at your air intake if gas/vapors are detected your dampers shut and your hvac goes into recirc mode.
Is the gas problem related to H2S?
Is a refit/relocation/increased height of your existing IG mast risers needed?