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[EnergyPlus_Support] Impact of Heat Balance Algorithm



I know this has been touched on before but it seems to me that no satisfactory conclusion was ever reached...

changing from Conduction Transfer Function (CTF) to Conduction Finite Difference (CondFD) seems to have an inordinate impact on the model results. the CondFD results change a little bit as the number of time steps per hour is increased but the results never converge onto the CFT results obtained with 6 time steps per hour. frustratingly as the time steps increase the cooling loads get closer and the heating loads further away. i took the example file:

RefBldgSmallOfficeNew2004_ChicagoCondFD.idf

that ships with E+ 6.0 and changed only the heat balance algorithm and the number of time steps (10, 20, 30, 40, 50, and 60 per hour).


annual difference in the cooling ranged from 28% to 14% and the heating from 9% to 19%.

it this to be expected? do i need to make any other changes when switching heat balance equation types?

i woudl very much like to hear about others' experience with the CondFD algorithm and, more specifically, any issues that arose when modeling phase change materials.




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