Re: [EnergyPlus_Support] Impact of Heat Balance Algorithm

[Linda Lawrie <linda@xxxxxxxxxxxxxx>]

Some of this is a known condition and we have at least two
changes in the development version to "fix" it.  But it's
not all the way there yet.

At 05:45 PM 2/2/2011, wgorrissen wrote:
> 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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