Air Separator Location - CHW System

[ChasBean1]

Greetings:

My application is a chiller and chilled water system with a standard primary/secondary loop and a flow decoupler.

The design shows the air separator and associated bypass valve (with expansion tank and make-up water line at the top connection of the air separator as commonly seen) on the primary loop CHW return side of the decoupler.

The installation currently has the air separator and associated connections on the secondary loop side, in the CHW return pipe.

The net result will be that the primary CHW (that runs through the chillers) will not continuously pass through the air separator but the secondary loop water will. Other than the fact that this is not installed as designed, will this present problems?

Hopefully I stated this clearly enough. Your thoughts are appreciated. -CB

 

[Cooky]

Having thought about your application, I can't see any real problem. Regardless of the air separator's location, the water will eventually pass through it.

If your concerned about air entering the system and causing damage, you should ensure the chilled water recieves proper chemical treatment. A system pressure of 1.5 to 2.0 Bar should ensure no air enters the system.

 

[KenRad]

CB,

Should be no problem at all. In fact, assuming that your secondary flow will be less than primary flow almost all of the time, then one advantage to this arrangement is that the air separator is in the highest temperature part of the system, so air separation efficiency will be maximized.

---KenRad

 

[quark]

CB!

If the locational height of the air separator is more than that of any point in your primary loop, you will not have any problem. Generally as the flow through secondary loop is varying as per the load, I personally feel it is the right place to keep air separator.

If your primary loop height is more, then there is a possible chance of airlock but as you are maintaining full and nonvariable flow in this loop chances of air entering the system are low.

Regards,

 

[cme]

You could throw an auto air vent on the primary side, located at the high point or at the end of the pump suction line run. That should vent entrained air.

 

[ChasBean1]

Thanks for your input. I reviewed this with the design engineer and they felt the same so I guess this configuration will stay. -CB

 

[Blackstick]

The air control experts in our region advise against using automatic air vents in a closed hydronic system. Automatic air vents have a reputation for getting trash (rust, scale etc.) in their ports and sticking in the open position thereby turning your closed system into an open system with air problems. Air is introduced into a closed chilled water system primarily through the make-up water. The system as designed had the air separator in the optimum position. The air separator in its present location will remove what air it can from the water that passes through it but obviously that is a reduced volume from that of the primary loop (assuming your secondary loop is variable volume). My question is why not have the installers pipe the system as designed. Essentially the installers are asking the design engineer to accept responsibility (liability) for their error.

 

[briand2]

Blackstick,

I know this is getting a little way off the original subject, but I'm a design engineer and I often accept responsibility for changes made to my design by the installers. As long as it makes no real difference to the operation/safety/etc then I just say "OK" and effectively adopt it as my own. This is the real world (to me anyway). If it was not like that, then I would not be able to take advantage of the design improvements that the installers often suggest to me!!

Brian