water cooled ammonia systems

[Dossat]

Hi All

I have a customer who is insisting on water cooled condensers (plate heat exchangers) connected to a cooling tower.
If my Wet bulb is 21C & water avaialble on to condenser is 25C what would a sensible target discharge temperature be (for my compressor selection)?
I dont want the plate heat exchanger too large & expensive but on the other hand I want to get my COP as best as I can. Refrigerant is ammonia.

Any assistance would be appreciated
cheers

[Sandro Baptista]

Dossat,

First at all welcome to RE.

If you have +25ºC inlet temperature ate condenser and supposing +29ºC outlet I would say +34ºC of condensing temperature it's a good compromise between condenser economics and COP of the refrigerant plant.

[Dossat]

Sandro

Many thanks for your help!

[RANGER1]

From what I have heard ,I don't know why people want to use PHE condensor on ammonia?
Maybe someone can suggest why.

You still have water treatment & tower cleaning as well as it uses a lot more power to run it.
ie cooling tower pump is much bigger for PHE to perform

[Magoo]

I agree with Ranger1, generally prefer Evap/condensers

[Josip]

Hi, RANGER1,

From what I have heard ,I don't know why people want to use PHE condensor on ammonia?
Maybe someone can suggest why.

You still have water treatment & tower cleaning as well as it uses a lot more power to run it.
ie cooling tower pump is much bigger for PHE to perform

first reason ... It is easy to install it, with EC you have more job to do for the same money .... thus less profit ... PHE are available in the same moment, for EC there is some waiting time ...

second reason .... installation companies would inform client/s (very rare) that solution is going to use more energy and sometimes causing more problems due to bad water treatment (for second reason I cannot give explanation .... maybe kind of ignorance)

third reason .... maybe need to use PHE to recover heat ... good reason to use PHE ...but this is much better when use PHE as desuperheater with closed circuit of cooling medium (brine or water) and then again EC ....

it is possible to be more reasons too.....


Best regards, Josip

[McFranklin]

The use of a PHE (or shell and tube condenser) allows some reduction of the ammonia charge, and the ammonia piping. It is very common in ice rink installations. And if the customer has a maritime background, they could be going back to a system they know works.
If you ground loop the water side you eliminate make up water, bleed water and tower maintenance.
Or you can install a heat recovery system.

[TXiceman]

PHE condenser on a water cooled system is going to be a disaster if they do not stay on top of water treatment. They make great crud filters.

Ken

[Jason NH3]

PHE condenser on a water cooled system is going to be a disaster if they do not stay on top of water treatment. They make great crud filters.

Ken

I second that, I am not a degreed engineer- only a lowly technician but I still wonder that if over a given time, say 10 years, if the intense water treatment requirements and the potential headache if lack of water treatment exists, if the benefits of a plate chiller over an evaporative condenser still wins out? On one system I service one bad year of water treatment has led to 4 years of less than desirable condenser performance and has led to multiple disassemble/ manuall cleaning jobs on the plate & frame condensers as well as the shell & tube oil coolers. Ten's of thousands of dollars in maintenance all because of improper water treatment.

[RANGER1]

Gaskets are not cheap either

[McFranklin]

As far as a PHE being a disaster if the water treatment is not kept up, what equipment will work as designed if it is not maintained?

[D.D.KORANNE]

1) besides, high isentropic index of ammonia makes it compulsory that water fed to condensers ( phe or s & t ) is of top quality. Salt formation accelerates .
2) moreover , total suction superheat limitation for nh3 is max 10k .

Both these factors will contribute to high dis end temps & condensers will be affected due to ca & mg salt formation

[aham]

plate heat exchangers are more susceptable to infilitration than are EC. The design of EC should not require a cooling tower and thus will have less chance for outside particles to make its way into the water system.

All very good points and informative discussion

[Sandro Baptista]

plate heat exchangers are more susceptable to infilitration than are EC. The design of EC should not require a cooling tower and thus will have less chance for outside particles to make its way into the water system.

All very good points and informative discussion

Well, about this point you can always use a closed tower (closed circuit between PHE and the tower coil). Of course this closed tower will much more expensive.