Re: [TRNSYS-users] Mistake in type 33i

Hi David,

Great idea! Tightening the tolerance did make the result more accurate (not on point, but better). As always, thanks a lot for your help.

Best regards,

Yose Wandy

Von: David BRADLEY [mailto:d.bradley@tess-inc.com]
Gesendet: Donnerstag, 5. November 2015 20:54
An: TRNSYS users mailing list at OneBuilding.org; y.wandy@ostfalia.de
Betreff: Re: [TRNSYS-users] Mistake in type 33i

Yose,
The psychrometrics routine has to use some iterative methods in order to solve for all the air properties when it is given certain combinations for which the properties cannot be determined directly. When RH and w are specified it has to iterate to find a drybulb temperature that has the same saturation pressure as the saturation pressure that can be computed directly from knowing RH and w. There are tolerances on the iterative calculations and with your two input values (RH=60% and w=0.006) the iteration continues until the saturation pressure for the guessed dry bulb temperature is within 0.01 kPa of the saturation pressure computed from RH and w. Tightening the tolerance on that iteration (which is one of a few iterations) causes the recomputed RH to come out closer to the starting value but I suspect that simply tightening the iterative tolerance would not always result in the recomputed value being equal to the starting value.
kind regards,
David

On 11/05/2015 03:55, Yose Wandy wrote:

Hello TRNSYS experts,

There seems to be a mistake in the type 33i, it modified the Inputs that I gave, resulting on wrong value (e.g. dry bulb temperature, enthalpy, etc.)
I attached a small example that shows the difference between the relative humidity input & output, in this case, it shows a difference by 0.09%.
Does it supposed to do that? Anybody have any idea how to fix it or get around it? Any help would be appreciated.

Thanks in advance.

Best regards,
Yose Wandy

--------------------------------------------------------------------------------
Yose Wandy B.Sc.
Wissenschaftlicher Mitarbeiter

Ostfalia Hochschule für angewandte Wissenschaften
Hochschule Braunschweig/Wolfenbüttel
Fakultät Versorgungstechnik
Institut für energieoptimierte Systeme (EOS)
Prof. Dr.-Ing. Lars Kühl

Salzdahlumer Straße 46-48
D - 38302 Wolfenbüttel

www.ostfalia.de/v

Tel. 0049 - 5331 / 939 – 40 550
Fax 0049 - 5331 / 939 – 40 552
y.wandy@ostfalia.de
_______________________________________________
TRNSYS-users mailing list
TRNSYS-users@lists.onebuilding.org
http://lists.onebuilding.org/listinfo.cgi/trnsys-users-onebuilding.org

--

***************************

David BRADLEY

Principal

Thermal Energy Systems Specialists, LLC

22 North Carroll Street - suite 370

Madison, WI  53703 USA

P:+1.608.274.2577

F:+1.608.278.1475

d.bradley@tess-inc.com

http://www.tess-inc.com

http://www.trnsys.com