[TRNSYS-users] Convergence problems when mass flow drops to zero ??

[Santeri Siren <santeri.siren1@gmail.com>]

Dear Trnsys users,

I am simulating a large combined cooling/heating system witch includes multiple heating and cooling loads, storage tanks, chillers and heat pumps. The system works fine exept for certain situations. 

I am trying to conrol a source side and a load side pump of a heat pump in a following way: When a storage tank (source side) temperature is lower than 0 C, the pumps stop. When the storage tank temperature is higher than 0 C, the pumps are controlled by a Type2 aquastat. Problems occur when the storage tank temperature drops lower than 0 C. In this case the pumps stop (so the control function is fine), but the simulation starts to get real slow and it takes a very long time for TRNSYS to calculate even a few hours of simulation time in this situation. Also convergation errors start to appear.

Could it be possible that TRNSYS has problems to solve the equations numerically when the pumps stop and the mass flows drop suddendly to zero? I have had similiar problems seweral times in other situations when a large mass flow drops suddendly to zero in a large system...

Does anyone know how to get rid of this problem so that TRNSYS could handle this kind of situations?

best regards,

Santeri Siren