Hot Water - literally.....

[A2Mich]

Hoping for an answer from chengkp75 or BruceMuzz here, but does anyone know how the ships heat water for domestic use? Wife and I were talking the other night about how much we enjoy the relatively limitless hot water on board, and being a technical type of person, was curious how ships heat water these days. Boilers? Heat recovery from engines, HVAC equipment? Just curious.....

[iheartbda]

Just read that it's heat from the engines.

[Khsh08]

I believe I read about hot water being generated from engines or equipment, but it may have been referring to laundry? I can't remember...I will see if I can find the article.

[Khsh08]

I found it!

" Engine heat is used to heat laundry room water and showers; air-conditioning condensation is also used as a source for laundry water."

http://www.nytimes.com/2015/03/22/business/a-luxury-liner-docks-and-the-countdowns-on.html

[A2Mich]

Thank you both! Kind of figured the ships would use some sort of heat recovery system, yet wondered if they would be able to produce enough heat for the amount of water used daily.

[chengkp75]

Thank you both! Kind of figured the ships would use some sort of heat recovery system, yet wondered if they would be able to produce enough heat for the amount of water used daily.

 

Most of the engine heat in the cooling water is used for the evaporators. The ships have boilers (most oil fired, but some also have exhaust gas waste heat boilers) that generate steam. This steam is used to heat domestic hot water, and laundry water, but this is just really a secondary use. The major use for the steam is to heat the fuel for the engines. Since the residual fuel needs to be heated to 130-140*C (260-280*F), only steam has enough heat to do this.

 

To heat one pound of water one degree, requires 1 BTU (British Thermal Unit). So, one pound of engine cooling water would give up 1 BTU for every degree it is cooled. However, to condense one pound of steam gives up 144 BTU, so steam heating of water is far more efficient (smaller equipment, less energy input) than water heating of water. Another means of increasing efficiency is that both the hot and cold water is constantly recirculated, so the hot water is continually "topped up" to temperature, rather than waiting for demand (some home systems do this as well).

 

The 90*C (194*F) engine cooling water is sufficient to boil water at 100% vacuum as is done in flash evaporators.

Edited March 21, 2015 by chengkp75

[A2Mich]

Most of the engine heat in the cooling water is used for the evaporators. The ships have boilers (most oil fired, but some also have exhaust gas waste heat boilers) that generate steam. This steam is used to heat domestic hot water, and laundry water, but this is just really a secondary use. The major use for the steam is to heat the fuel for the engines. Since the residual fuel needs to be heated to 130-140*C (260-280*F), only steam has enough heat to do this.

 

To heat one pound of water one degree, requires 1 BTU (British Thermal Unit). So, one pound of engine cooling water would give up 1 BTU for every degree it is cooled. However, to condense one pound of steam gives up 144 BTU, so steam heating of water is far more efficient (smaller equipment, less energy input) than water heating of water. Another means of increasing efficiency is that both the hot and cold water is constantly recirculated, so the hot water is continually "topped up" to temperature, rather than waiting for demand (some home systems do this as well).

 

The 90*C (194*F) engine cooling water is sufficient to boil water at 100% vacuum as is done in flash evaporators.

 

Thank you, as usual, for your detailed technical explanation. I am an HVAC service tech by trade, so am intimately familiar with BTU's and heat transfer. My wife and I were talking the other night after taking nearly cold showers thanks to our daughter, and we were talking about how much we enjoyed the nearly limitless hot water on board cruise ships, and was just curious how the ships were able to heat enough water (not to mention keep it hot, which it sounds as if water is constantly heated, as opposed to stored, like typical residential water heaters) to meet the huge demand. I had no idea that the fuel had to be heated to a certain temperature for either storage or just before combustion. Thanks again!

[chengkp75]

Thank you, as usual, for your detailed technical explanation. I am an HVAC service tech by trade, so am intimately familiar with BTU's and heat transfer. My wife and I were talking the other night after taking nearly cold showers thanks to our daughter, and we were talking about how much we enjoyed the nearly limitless hot water on board cruise ships, and was just curious how the ships were able to heat enough water (not to mention keep it hot, which it sounds as if water is constantly heated, as opposed to stored, like typical residential water heaters) to meet the huge demand. I had no idea that the fuel had to be heated to a certain temperature for either storage or just before combustion. Thanks again!

 

Residual fuel needs to be heated to 35-40*C just to efficiently pump it from the storage tanks. It is then stored in a "settling" tank at 75*C, then heated to 98*C for centrifuging on its way to the "service" or ready use tank. The final heating to 130-140*C is done in a loop from the service tank to the engine and back. It is necessary to heat the fuel to this temperature and raise the pressure to 300 bar (4500psi) before it can be injected into the engine.

 

You always ask for technical details, so this is a bit more detail than I'd normally give. But since you are the OP, this can go wherever you want.

[A2Mich]

Residual fuel needs to be heated to 35-40*C just to efficiently pump it from the storage tanks. It is then stored in a "settling" tank at 75*C, then heated to 98*C for centrifuging on its way to the "service" or ready use tank. The final heating to 130-140*C is done in a loop from the service tank to the engine and back. It is necessary to heat the fuel to this temperature and raise the pressure to 300 bar (4500psi) before it can be injected into the engine.

 

 

 

You always ask for technical details, so this is a bit more detail than I'd normally give. But since you are the OP, this can go wherever you want.

 

 

Awesome!!! I also didn't realize that fuel injection pressure was quite that high on a low or medium speed diesel. You are such a wealth of information and I learn a lot from your posts! I'm absolutely fascinated by some of the technology that is incorporated into ships, aircraft, trains, etc. It's truly amazing how technical many things can be yet so many don't appreciate all of the engineering and development that goes into building things like this, the incorporation of various systems, safety systems, integration, redundancy, etc.

[heziggy]

wish we had unlimited hot water, heck even warm, for our cruise in october on explorer. no matter what time we showered, morning, afternoon, night, even at like 2am, we had tepid to down right icy water!!! :eek:

[A2Mich]

wish we had unlimited hot water, heck even warm, for our cruise in october on explorer. no matter what time we showered, morning, afternoon, night, even at like 2am, we had tepid to down right icy water!!! :eek:

 

 

Wow. I'm sorry to hear that. I've always had hot water on all of my cruises. So hot it could scald you! Never ever came close to not having hot water.