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[EnergyPlus_Support] Re: CTF vs. CondFD results

Hello. 
That part is hard to understand without studying the algorithm in Energyplus.

The timestep/hr that you input(it is called zonetimestep) is different from the time step(CTFtimestep) used for CTF calculation when the zonetimestep is smaller than CTFtimestep.

If the mass of the construction is thick and heavy weight, the
CTFtimestep is incrased until 4 hr until it meets the internal standard.

It is very powerful and accurate when internal air temperature is
constant, but it sometimes gives inaccurate results when indoor environment is unconditioned or the indoor air temperature is fluctuated much for a short time. In these cases, Energplus may not perceive the change of indoor temperature with a big zonetimestep. 

Here is a tip.

If you want to use ConFD, check the stability condition of explicit 
finite difference method (Fourier number<1/2) and use the time step that meets this condition.

I think the result from ConFD is more reliable for the cases of heavy weight and thick construction. If the results are different each other, I suggest to use the result of ConFD for heavy weight constructions.




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