Hi Wirich, we had a master thesis running some years ago on this topic (comparing TRNSYS with DesignBuilder which actually uses Energy+ as calculation engine). Though it was some years ago maybe it helps a little (find the work attached). As far as I can remember there were also different models used for solar radiation (diffuse radiation calculation and also for interpolation). Some ideas: - Is there a window in your building model? If yes remove it and do your comparison again. Thus you can find out if the difference comes from the window. - Have a closer look at the energy balance (Transmission, solar gains, ...); maybe you can find the causing influence - Simplify your model and switch on the different aspects (infiltration, ventilation, gains ...) step by step. Hope this helps, Hermann. _______________________________________________________________ DI Dr. mont. Hermann Schranzhofer Institut fuer Wärmetechnik / Institute of Thermal Engineering TU Graz / Graz University of Technology Inffeldgasse 25 / B, A-8010 Graz Tel.: +43 316 873 7314 mobil: +43 664 60 873 7314 Fax : +43 316 873 7305 http://www.iwt.tugraz.at/ _______________________________________________________________ -----Ursprüngliche Nachricht----- Von: TRNSYS-users [mailto:trnsys-users-bounces@lists.onebuilding.org] Im Auftrag von FREPPEL Wirich Gesendet: Donnerstag, 28. August 2014 11:56 An: David BRADLEY; TRNSYS users mailing list at OneBuilding.org Betreff: Re: [TRNSYS-users] solar absorptance of walls David, I took your advice into account and modified the convective heat coefficients so that they are the same in both programs. As a results, the air temperature has exactly the same behaviour for both curves. Hovewer there still is a difference by around 3 degrees between both, TRNSYS being below E+. Do you think this difference is due to the different method of calculation of the two programs? I wouldn't mind if the difference temperature was less than 10°C or let's say 2°C. I'm not using the BESTEST since I was just trying to be more familiar with Energy+ and compare the two programs, but I'll have a look on it, it seems to be quite usueful for my needs. Thank you very much Wirich FREPPEL Doctorant Recherche & Developpement Noirot 8 rue Ampere, 02000 Laon 03 23 27 31 99 Le 04/09/2014 18:25, David BRADLEY a écrit : > Wirich, > It could be the outside (or inside) convection coefficient > assumption is different between TRNSYS and EnergyPlus. If your test > case is the BESTEST / ASHRAE140 building then they give an equation > that you are supposed to use for the outside convection coefficient. > In Standard 140, it is listed in Informative Annex B4. I don't have > the BESTEST documentation so don't know where it might be in there. > Best, > David > > > On 8/27/2014 03:59, FREPPEL Wirich wrote: >> Thank you David for your quick reply, >> >> Indeed the floor is a boundary wall, however I fixed it at 18°C >> annually, it's the default setting for Energy plus. It means that all >> the year, the outside temperature of the Ground floor is 18°C. >> I checked the inside temperature of the ground floor, its varies, >> according to the air temperature of course. >> Actually, I checked all the inside surface temperatures of the box, >> they are all below those of Energy plus calculations (by around 4°C >> in summer). About the outside surface temperatures, the amplitude is >> smaller in TRNSYS compare to Energy+. Which makes me think that >> Energy+ takes something into account that TRNSYS doesn't for the >> outside temperature of the surfaces, but I don't know what it could be. >> >> If the temperature difference was only less than 1or 2°C, I would >> think that the cause is the calculation method of the 2 programs. But >> here I think the temperature difference is too big to be only that. >> Do you have any clue? >> >> King regards >> >> Wirich FREPPEL >> Doctorant Recherche & Developpement >> Noirot >> 8 rue Ampere, 02000 Laon >> 03 23 27 31 99 >> >> Le 03/09/2014 15:34, David BRADLEY a écrit : >>> Wirich, >>> If you are using Trnsys17 then there is almost certainly an >>> automatic connection of solar radiation between the weather data >>> reader and the building because in TRNBuild the default selection is >>> that those connections will be made for you. >>> >>> I would guess that the difference lies in how you have treated the >>> floor of your zone. If you created a BOUNDARY wall for your floor >>> then Type56 is expecting you will provide a temperature on the back >>> side of the floor (i.e. the interface between the floor and the >>> soil). If you did not make a connection to the boundary temperature >>> Type56 input then it is probably set to a constant value of 0 C, >>> which would keep your zone temperature quite low throughout the year. >>> Regards, >>> David >>> >>> >>> On 8/28/2014 03:30, FREPPEL Wirich wrote: >>>> Hello everyone, >>>> >>>> I'm running some tests in order to compare TRNSYS to another >>>> software, which is Energy+. >>>> >>>> My model is simple, a 3 meters long cube, with the same composition >>>> for all the faces, without windows. >>>> What I did in first place, was to create a new multizone project >>>> using an idf file created from sketch up. Then I runned the >>>> simulation in order to observe the evolution of the air temperature >>>> inside the box. >>>> Comparing it to Energy+ results, I noticed that in summer, the >>>> temperature is far below those of Energy+. So I looked at the >>>> connections in simulation studio to see if there was a problem on >>>> the solar radiation on the walls, and I noticed that initially, >>>> there are not any connection which give the solar radiation on the >>>> walls. >>>> >>>> My conclusion is that to take account of the solar radiation on >>>> walls, we have to link it by ourself at the beginning, is it right >>>> or did I miss something?. >>>> >>>> Furthermore, in the "wall type manager", there's a tab called >>>> "Solar Absorptance of wall". When I change the value, nothing >>>> change regarding the temperature inside the box. So when is this >>>> value used exactly? >>>> >>>> Thank you in advance. >>>> >>>> King regards >>>> >>> >> >> > _______________________________________________ TRNSYS-users mailing list TRNSYS-users@lists.onebuilding.org http://lists.onebuilding.org/listinfo.cgi/trnsys-users-onebuilding.org
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