Dry Cooler (Free Cooling) vs Chiller 1

[engineers_eyes_and_ears]

Hi Guys

I am bit unsure on how to run the dry cooler and the chiller.

I have attached the setup.

The idea is to cool the water using the dry cooler (as much as possible).
When the ambient temperature is high and the dry cooler no longer can hold the temperature, a chiller is used to help or fully cool down the water.


My idea was to do the following:

The temperature at TT4 must always be lower than than a given setpoint (SP).
So we could say:

TT4 > Setpoint

If the TT4 is higher than setpoint then start the chiller and maintain setpoint.


In addition, IF

TT2 > TT1 then fully close port B

That would enable us to directly go to chiller operation if the dry cooler can no longer hold the temperature.


The issue is only, if the ambient temperature falls again, then I want to go back to using the dry cooler.
However, as I see it, there is no flow through TT2, then how will I pick it up?

Please let me know if there any smart way to do this!

 

[EnergyProfessional]

You need an ambient temperature sensor. If TT@ is outside by the DC, it would get close to ambient when there is no flow. But TT2 is only an ambient sensor when there is no flow, so better to get a dedicated ambient sensor.

you could do above control and open the valve any time ambient (separate sensor) is below TT1. I assume this is glycol and you don't have freezing problems?

 

[BronYrAur]

How would TT2 be greater than TT1? Also, you should put a bypass around the chiller when it is not in use.

 

[EnergyProfessional]

If ambient temperature is high, the DC would heat up the fluid and TT2 would be higher than TT1.
the DC only is like an economizer, it will work against the desired economics if ambient is high.

Not sure if it is worth isolating the chiller. You would save the chiller pressure drop, but you add a diverting valve pressure drop (and another point of failure or not working correctly).

If you need cooling in winter, but can cool with DC during winter, you could have manual bypass for the chiller so chiller service can be performed in winter while the system is running on DC. Not enough information given on the system and planned operation and climate to make a good decision.

 

[BronYrAur]

Ok, but you should turn off the dry cooler long before TT2>TT1 because you are just wasting fan energy.

 

[EnergyProfessional]

You can determine a dT to turn off the DC fans. Good point, if there is only 1F dT, the fans may use more energy than you gain from saved cooling. Also account for some sensor inaccuracy. A 5-10F dT may work. it depends.

 

[MintJulep]

The performance of the dry cooler as a function of ambient temperature, fluid temperature, fluid flow and cooler fan speed (if variable) can be calculated.

Decisions about using the dry cooler should be made based on the result of that calculation.