[TRNSYS-users] solar absorptance of walls

Fri Sep 5 06:35:20 PDT 2014

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 at 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 at lists.onebuilding.org
http://lists.onebuilding.org/listinfo.cgi/trnsys-users-onebuilding.org
-------------- next part --------------
A non-text attachment was scrubbed...
Name: MA_Karitnig-TRNSYS vs DesignBuilder.pdf
Type: application/pdf
Size: 1845576 bytes
Desc: MA_Karitnig-TRNSYS vs DesignBuilder.pdf
URL: <http://lists.onebuilding.org/pipermail/trnsys-users-onebuilding.org/attachments/20140905/dde18279/attachment-0001.pdf>