Desuperheater from R134 to domestic hw

[svetski]

We have existing 280t (R134, twin screw compressors, two of them, 30HXA model) Carrier's chiller with two separate refr. circuits and air cooled condenser, roughly, 100' away and 3 floors higher then the chiller.
We would like to install desuperheater to capture some of the heat to preheat domestic hot water.
Carrier installation manual requires separate refrigeration pipes to practically two air cooled condensers.

It would be easy to install desuperheater (heat exchanger) beside the chiller, but how can we control head pressure with two condensers (desuperheater and existing air cooled condenser) in series and make sure no liquid is going back to the chiller?

Carrier will not provide support for this, our thoughts are that must be a way to recover some of 4000MBH available in the peak time.

Thanks for help.
Svetski

 

[chilled]

"Carrier will not provide support for this, our thoughts are that must be a way to recover some of 4000MBH available in the peak time."

Have you calculated the energy actually available to a desuperheater? Considering R-134A refrigerant which already runs at a low discharge temperature and Carriers specs of 90 to 135*F Saturated Discharge Temperature, there might be a lot less energy available than you might thing. Plot the cycle on a Mollier Chart and determine if it is worth it.

 

[absrbrtek]

With that far of a piping run and adding desuperheaters I think you'll have oil seperation and oil return issues. JMHO

 

[svetski]

We have realized that we don't have high temperature of hot gas, so we will preheat the cold water directly. As long as we can count on 1600MBH for example we can have a reasonable payback.

We are not sure how to make sure liquid does not enter gas pipe and have two condensers ion series.

Thanks guys for help.

 

[BronYrAur]

This link provides some good basic information:

http://www.alabamapower.com/energy_knowhow/desuperheaters.asp

 

[svetski]

Thanks BronYrAur, good link.
We had a presentation today about Multistack modular chillers and in air cooled version each module has its own circuit-air condenser. I guess there must be complicated to control head pressure for some reason. Carrier does not allow combining two refr. circuits into one air cooled condenser.
Does anybody know how desuperheaters are controlled to stay vapor area?