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

[Eric Peterson]

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