Thanks again for your answer. However,
since my solution is known only for Ti and Tf and nowhere between, any
attempt at integrating numerically over the time step and dividing by the
time step length will result in a linear approximation for Tavg as before.
I can of course solve the equation to find T at the midpoint of the time
step, and then use a three-point numerical integration rule. I can't think
of anything else at the moment.
Kind regards,
Knut Erik
From:
"Jeff Thornton" <thornton@tess-inc.com>
To:
knut.erik.enerstvedt@niva.no
Cc:
trnsys-users@engr.wisc.edu
Date:
08/31/2009 07:04 PM
Subject:
Re: [TRNSYS-users] "Average value
over time step" in TRNSYS Types
<If I solve the model equation for the time t(i-1/2),
would this be a
correct approach to find Tavg? I can then solve for both Tavg and Tf, and
use Tf as Ti in the next time step. Is this how it's done in the
standard/TESS TRNSYS components? >
No - in the TRNSYS components that have mass we solve for the average
temperature over the timestep and don't approximate it with a linear
solution or a solution at the midpoint of the timestep.
Take your solution for the temperature and integrate it over the timestep
and then divide by the timestep to get the average value. Refer to
the
Programmers guide in the section for differential equations for a more
detailed explanation when you have a simple linear DiffEq.
Jeff
Jeff Thornton
President - TESS, LLC
22 North Carroll Street - Suite 370
Madison WI 53703 USA
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