Howdy,

I'm trying to simulate a four pipe fan coil system with a DOAS ERV providing outdoor air in DOE 2.3 and getting some errors I haven't been able to figure out, I'm hoping someone here knows the answer!

The fan coil system runs by itself, connected to a campus CHW and steam loop, though I get the following error in my sim file:

***ERROR***********************************************************************
Heat-Exchanger: L1West Perim Zn (G.W1) UA calculation
failed to converge.

This seems to be a random zone and switches every time I run it. Besides defining OA flow at the zone, there are no other custom inputs at this time on the zone. When I add the DOAS (without the ERV) to the "OA From" field in the fan coil system, I get an aborted simulation and the following errors:

***NOTE************************************************************************
Convergence issues in Design-Day mode 14
Hours Slow: 3209; Hours Failed: 0

***ERROR***********************************************************************
Heat-Exchanger: HENE Perim Zn (M.ENE16) UA calculation
failed to converge.

***ERROR***********************************************************************
Heat-Exchanger: HSouth Perim Zn (Mb.S22) UA calculation
failed to converge.

***ERROR***********************************************************************
Fatal HVAC simulation errors.

Adding the ERV to the DOAS gets me a new set of errors:

***NOTE************************************************************************
Convergence issues in Design-Day mode 14
Hours Slow: 3384; Hours Failed: 1834

***ERROR***********************************************************************
Heat-Exchanger: HNorth Perim Zn (M.N17) UA calculation
failed to converge.

**WARNING**********************************************************************
PredictX parabolic solution failed. Please
send this input and weather file to program developers 3015
***ERROR***********************************************************************
Heat-Exchanger: HEast Perim Zn (T.E39) UA calculation
failed to converge.

***ERROR***********************************************************************
Fatal HVAC simulation errors.

Same notes and warnings as before but it adds the PredictX warning around 50 times (I edited the above).

I tried stepping back to DOE 2.2 but of course you can't define a DOAS in that engine and in 2.2 and 2.3 I'm unable to put an ERV on a fan coil system type.

So then, can anyone shine a light on what's going on?

[TBCx]

Matt Garlick, CxA, CEM, BEMP
Building Efficiency Engineer | TBCx

E-mail: msg at tbcxinc.com
Mobile: 801-907-5654
Direct: 801-401-9492

324 S. State Street, Suite 400
Salt Lake City, UT 84111
www.tbcxinc.com