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

Eric,
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

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