Division D - NotesDivision D - Notes

Division D - Notes

Pump cycling and simulation stability

 For pumped SWHs the pump controller may cycle the pump on/off if the ratio Ton/Toff is too small. See Duffie & Beckman, "Solar Engineering of Thermal Processes", Section 10.4 Controls for more detail [1] and how to calculate the required Ton/Toff ratio to avoid pump cycling.

 Modelling an in-tank coil heat exchanger for the solar circulation loop using the Type 60 tank model can lead to convergence problems in TRNSYS 15, particularly for glycol-water mixtures. Using water as the HX fluid instead and/or artificially increasing the collector flow rate may overcome this problem. Changing the heat transfer fluid and/or flow rate will introduce an error, and the increase in flow rate should be kept as small as possible.

Batching multiple TRNSYS rating Calculations

 Running multiple TRNSYS decks can be automated by using a Windows batch file. For example, four decks (deckfilenameZ1 to deckfilenameZ4) can be run successively by writing the following lines into a Notepad file (note the spaces) and saving the file with .bat extension.

C:\Trnsys15\trnsys.exe deckfilenameZ1.dck /N

C:\Trnsys15\trnsys.exe deckfilenameZ2.dck /N

C:\Trnsys15\trnsys.exe deckfilenameZ3.dck /N

C:\Trnsys15\trnsys.exe deckfilenameZ4.dck /N

Right-clicking the batch file allows to one to edit it, left clicking or double clicking will run it.

References

[1] Duffie, J. A. and Beckman, W. A., Solar Engineering of thermal processes, 3rd ed., Wiley, New York, 2006.