Chiller mass flow strange peak at low temperatures in EnergyPlus

edit

Hi all,

I am simulating a data center in OpenStudio for my thesis. The HVAC system consists of:

• Air loop with the IT equipment to be cooled
• Chilled water loop to transport heat
• Condenser water loop to reject heat to the outdoor air

The model seems to behave fine, however, when the temperature becomes quite cold (<10 C), the mass flow rate of the chilled water loop suddenly increases a lot, then makes a steep drop and stays constant for a while at a lower mass flow rate than before. After a while (1 or 2 days mostly) the mass flow suddenly jumps up again and then steadily decreases until it is at the value it was at before the cold temperature. This is my first post ever, so unfortunately I cannot upload a picture to make it a bit clearer yet :(

Does anyone know what could cause this behaviour? I think it is very strange especially since there are no large fluctuations in the parameters of both the Air Loop and the Condenser Water Loop when it occurs.

Thank you in advance!