RE: Time base transfer function

[Michaël Kummert <kummert@xxxxxxxxxxxxxxx>]

Marco,

I think that what this sentence means is that the simulation start time must
be an integer multiple of the wall timebase. You are right that the wall
timebase must be an integer multiple of the TRNSYS time step. The simulation
start time must also be an integer multiple of the time step. That probably
explains the sentence you mention.

The warning which says that the TRNSYS time step is not equal to the wall
timebase is not an error. It does not mean that the results will be
affected. Please keep in mind, however, that most TRNSYS types were not
designed which small time steps (as 0.01h) in mind. You should check your
results carefully (check energy balances and use your common sense) when
using such small time steps.

FYI, Here is a copy-paste of one of the FAQ's on the TRNSYS website about
the Timebase and simulation start time:

>The simulation START time must be an integer multiple of the
>wall TIMEBASE in BID or the program WILL NOT run correctly.
>For example, if the wall timebase is 0.5 hours, the simulation
>start time must be 0.0, 0.5, 1.0, 1.5 etc., or the program will
>not produce correct results. In fact, it will produce extremely
>strange results. If you find this hard to believe, change the
>restaurant example provided with purchase. I changed the
>timebase to 0.5 and the simulation start times to
>0,0.25,0.5,0.75, and 1.0. The results were different for all
>but the 0,0.5, and 1 cases.

Regards,

Michaël Kummert
_________________________________________________________

Michaël Kummert

Solar Energy Laboratory - University of Wisconsin-Madison
1303 Engr Res Bldg, 1500 Engineering Drive
Madison, WI 53706

Tel: +1 (608) 263-1589
Fax: +1 (608) 262-8464
E-mail: kummert@sel.me.wisc.edu

SEL Web Site: http://sel.me.wisc.edu
TRNSYS Web Site: http://sel.me.wisc.edu/trnsys




-----Original Message-----
From: owner-trnsys@relay.doit.wisc.edu
[mailto:owner-trnsys@relay.doit.wisc.edu] On Behalf Of Marco Sangiorgi
Sent: Wednesday, October 09, 2002 05:44
To: Trnsys
Subject: Time base transfer function


Dear Trnsys user,

I have a doubt reading the Prebid manual. What does it mean that "the start
time in the TRNSYS input file (*.DCK) must match to the time base of the
transfer function"? (Pag 12, 3.2 Outputs)

Maybe it refers to the simulation time step that should match the time base.
Now I'm using a simulation time step (0.01) smaller than the wall TimeBase
(1) and so I get a warning in the .LST file. May I get unaffordable results
in my simulations using a simulation time step smaller than the wall
TimeBase?

Thank you,

Marco Sangiorgi