1400 KW DX Plant for Offshore Platform

[biddu]

Friends

This for an offshore drilling rig application. Brief specifics are as follows

1. Application : Offshore Drilling Rig
2. Location: Tropical
3. System : AHU’s with DX coil serving mechanical areas and Living quarters (approx 15 AHU’s)
4. Ambient : 35 deg C, 80% RH
5. Total Cooling Load : App 3000 KW

My question is

Client want to use central DX plant in 3 x 50% (Basically assembly of compressors and water cooled condensers) configuration located centrally on the project. The length of pipes to the AHU's could be as long as 50m and may be much more depending on the pipe layout.

Please advice:
1. Is this a practical system.
2. We have proposed chilled water systems as we feel this it as a more reliable and simple system but owner want to go for DX.
3. Any idea how much refrigerant charge would be required.
4. Is there any limit on the maximum cooling capacity available for water Cooled DX plants.
5. Is pressure drop and heat gain in tubes could be an issue.
6.Is VRV a possible soilution for such an application.
7. Any other issue with DX system for such application

It would be great if someone can advice on merits and demerits on these systems.

Thanks

 

[MintJulep]

I agree with you. Chilled water sounds like a much better option.

 

[EAJ82]

>50m DX tubing is a hampering agent and a real issue, it makes the unit lose a lot of its capability.
Refrigerant Charge: A LOT
Limitations for water cooled DX systems: i'm afraid i never see a limit in it, but don't have enough experience in this subject.
Chilled water system : Definitely

 

[marcoh]

1 - Technically it is possible, but you need someone who is experienced in designing built up refrigeration systems.

2 - I agree that going for a chilled water system would be much simpler with off the shelf components and much less change of operational issues.

3 - A lot of refrigerant is required! Need to piping schematic and do a take-off, similar to calculating water volume in a chilled water system.

4 - Water cooler chilled are water cooled DX plant, but talk to someone like Bitzer who can give guidance on compressors (and system design)

http://www.bitzer.de/home/index.php

5 - Pressure drop, heat gain etc are all fundamental issues and hence require an experienced designer.

6 - Doubt VRV (ie Daikin style) is applicable. You can get large VSD controlled compressors which may be applicable or use unloading on reciprocating style compressors.

 

[imok2]

If you have a concern for cost,labor,engineering, simplicity of installation and the environmentI would urge you to go with chilled water

 

[biddu]

Thanks friends

I think damage to environment should be the biggest concern. We talked to some of our suppliers for the quantity of refrigerant. It is huge (5~6 Tonnes???). We are not sure if this is correct. Is there any rule of thumb to calculate approximate quantity of refrigerant charge?

Imagine how much damage this system can cause to environment if there is a small undetected leak in the system and if we multiply this with the life time of rig (25 years)...

 

[absrbrtek]

You will have a system that no one will be able to service properly and will be broken constantly. If I had to take a guess, depending on the reciever size I would say your in the 3000 to 5000 pounds of refrigerant charge range. No way would I put my name on a design like that. This design would challange even the most seasoned engineer. Central chilled water plant is definitly the way to go. Have them do it properly or let someone else design it. JMHO

 

[simsd]

Chilled water.

Think of the maintenance of the DX system in those conditions - it would end up being full time. Also, no flexibility.

How much is a rig worth? $ 500 million? 1 billion? What's the chilled water system worth relative to that and the daily production costs?