[TRNSYS-users] solar absorptance of walls

[FREPPEL Wirich]

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
>>
>