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Free Cool HX with HeatExchanger:FluidToFluid

asked 2018-03-01 11:41:17 -0500

jt1234's avatar

updated 2018-03-01 14:08:08 -0500

I'm modeling a basic chilled water free-cooling setup that has worked in past versions of OpenStudio:

image description

Now with V2.4.0, as soon as the HX is added to the loop, the loop no longer maintains the setpoint defined in the SetpointManager (all types). Setpoint is 6.66deg-C:

image description

The HX appears to be working properly and predictably reduces the chilled water temperature as a function of the outdoor wb (top HX EWT, bottom HX LWT), but the chiller does not appear to be recognizing the setpoint and only brings the water temp down to 21deg-C (see screenshot above): image description

Adding individual SetPointManagers after the HX, Chiller, and at the loop supply node seems to completely correct the issue when the HX is in parallel, but only partially fixes the issue when in a series arrangement (series screen shot below). The series arrangement still seems to lose the setpoint at random intervals: image description

Any thoughts on why this has become an issue in v2.4? And, is there any way to mitigate this issue when the HX is in series with the chillers? This same issue has been replicated on multiple projects with the same configuration. The SetpointManager and supply node references for the loop, chiller, and HX appear to have all been correctly translated to the IDF. Note that this sample project is a standard office with typical night shutoff.

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answered 2018-08-23 14:20:01 -0500

Brett M's avatar

I was ran into a similar issue in v2.6 but adding the "Follow System Node Temperature" set-point manager after the integrated plate heat exchanger resulted in expected operation for me with the chilled water set-point met. I am hard-sizing the plate and chillers and simulating a plant with 24-hr operation.

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Asked: 2018-03-01 11:41:17 -0500

Seen: 400 times

Last updated: Mar 01 '18