[TRNSYS-users] Type927 source outlet temperature fluctuations when control signal is zero

Jeff Thornton thornton at tess-inc.com
Mon Mar 5 11:15:49 PST 2018


Your work-around is clever but shouldn't be necessary.  In most cases, 
this behavior is caused by too large of a timestep, a poor component 
calling order, or not having any mass in your flow loop (pipes, tanks 
etc.).  I would suggest that you check these carefully first.  Using the 
TRACE command/tool can also point out where your convergence problems 
are occurring and often lad to an "A HA" moment.


Jeff Thornton
President - TESS LLC
22 N. Carroll Street, Madison WI USA 53703
Office: (608) 274-2577  Fax: (608) 278-1475
E-Mail: thornton at tess-inc.com

On 03/05/2018 6:53 am, Eric Peterson via TRNSYS-users wrote:
> Hello there more experienced TRNSYS 17 Simulation Studio users,
> I am finding some wildly oscillating outlet temperatures on the source
> side of heat pump type 927 provided in TESS GHP Library.  These have a
> huge computational cost to attempt convergence, and have caused me to
> increase the allowable errors on the control cards.
> Several degrees of fluctuations occur during time steps when the
> cooling control signal is zero that I send to both the  ground loop
> circulation pump and the type 927 heatpump (that I using like a
> chiller).
> I have found a work-around by using an equation in Trnsys 17
> Simulation Studio Assembly to force the temperature going out of the
> type927 to my circulation pump.  So I assume the pump closely
> approaches ambient when the control signal is zero.
> I would appreciate a more elegant approach, but if others have the
> same problem then I am happy to share by equation:
> 	CondOUT = GT(coldGO,0)*ChillerOUTsource + (1-GT(coldGO,0))*ambient
> Where my input control signals is "coldGO", the type927 source outlet
> temperature is " ChillerOUTsource ",  and "ambient" is from the hourly
> TMY file reader.
> Eric Peterson, PhD, PE, RPEQ, M-ASHRAE TC4.2 Climatic Data
> Research Fellow in Geothermal Systems Modelling
> School of Civil Engineering, University of Leeds
> Leeds, West Yorkshire LS2 9JT United Kingdom
> Telephone +44 (-0) 11334 31957
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