effect of lowering chilled water supply

[hvacers]

guys,

is there any effect on the system (disadvantage/advantage) by lowering the setpoint of the chiller from 44F to 42F?

from what i know...

by lowering the chilled water supply;

ADVANTAGE: Less amount of chilled water required to be supplied throughout the system therefore less pump energy


DISADVANTAGE: More compressor power required to pull down the temperature of the chilled water down to 42F.



please share some ideas on this...

thanks

 

[Zesti]

You say:

"ADVANTAGE: Less amount of chilled water required to be supplied throughout the system therefore less pump energy"

This is only true if the return temperature stays the same.
It is the difference between supply and return temperature that results in the flow needed to deliver the required cooling power to the system.

If it is lowering of pump-energy you are after, lowering the supply temperature is not the way to go. Raising the return temperature is better (more energy efficient) for both pump and chiller.

 

[Cooky]

Lowering the chilled water temperature will result in an increase in the latent cooling effect.

 

[hvacers]

does lowering the LCHW really increase the chiller consumption?? by how many percent??

i was arguing with someone because he keeps his setpoint at 42F but his delta t ranges from 5-7 F..

i was thinking if we could increase the setpoint to 44 the delta t will start ranging to 10F.

 

[Zesti]

Depends how you look at it: it actually lowers the chillers performance on the cooling side. So you get less kW output for your kW electric input.

Pull up the data for any Trane or Carrier chiller and you will see the specs for different temperatures (also ambient temperature to which the chiller has to reject the heat).

What type of system are we talking about here?
Most systems will be designed for specific temperatures and flows so playing around with those parameters might mess things up.

To me, changing the water temperature and the delta T of the flow are two separate things.

- What (average) temperature do you really need?
- Do you want to minimize flow and pipesize etc.?
- Find a cost-effective balance of both...

 

[hvacers]

actually the system is actually a constant flow chilled water with only a primary pump. i noticed that the delta T is ranging from 5-7 F and the chiller operator setpoint for LCHW is 42F.

If i increase the LCHW to 44F will my delta T increase having my chilled water flow constant.??/

 

[Zesti]

I guess this depends on what types of equipment is using the chilled water and how this reacts to the higher temperature of the chilled water.

Raising the temperature from 42F to 44F will likely decrease the heat transfer of the equipment and so the delta T of the chilled water decreases rather than increases when raising the chilled water temperature.

It all depends on what the equipment using the chilled water is doing, how it is controlled etc.