Air cooled chilled water plant with freecooling in openstudio

asked 2019-05-09 18:52:52 -0500

HJOJOA's avatar

updated 2020-01-28 10:59:14 -0500


In a simulation of chilled water plant, one chiller of 320 Kw cooling and 10 C degrees chiller water outlet temp, the simulation run as i spec and leaving chiller water is 10C like we spect, but when adding a dry-cooler in a parallel loop that provide free-cooling to the chilled water plant trying to simulate a free cooling air cooled chiller, something happen

This is the chilled water plant, the plant use a heat exchanger in series with chiller to give the free-cooling characteristic.


This is the freecooling parallel loop

C:\fakepath\FC Plant.JPG

When using an ideal heat exchanger, the result shows strange numbers because checking leaving chilled water temp is not near set point (10 C degress), the result is more than 2 C degrees vs setpoint.

C:\fakepath\Temperature comp.JPG

The hourly cooling energy is wrong because when compare cooling coil rate vs (evaporator cooling rate+drycooler cooling rate) is lower than than the first.


Blue curve is Cooling coil rate Orange is evaporator cooling rate Red is freecooling capacity

in my opinion the numbers should close, cooling coil capacity equal sumatory of other two

My questions are?

1- Why the supply chilled water temp is not equal to setpoint? if chiller is oversized and heat exchanger is cooling setpoint modulated, how to to solve it? 2- Can we use heath exchanger in series with chiller like in the pictures? 3- How is the right set for the heat exchanger arrange, uncontrolled, cooling setpoint on/off or modulated?

Testing other configuration the results in zone temperatures are modified and the chiller water temp also modified (increase in every case)

Can somebody share a template model to compare?


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