[TRNSYS-users] Type 34, again ...

[David Bradley]

Christophe,
   I have seen the same phenomenon; essentially, Type34 makes an 
isotropic sky assumption when it calculates the diffuse radiation on 
the receiver so you have to use that same assumption in your weather 
data / radiation processor. The isotropic sky model gives a somewhat 
conservative estimate of solar radiation than does Perez. That means 
that your building heating loads will be higher, your cooling loads 
lower, and the effects of shading devices will be less important. 
Both models (isotropic and Perez) are certainly well within the 
uncertainty of other modeling assumptions.
Kind regards,
  David


At 10:50 4/19/2007, Enertech wrote:
>Dear TRNSYS Users,
>
>When I want to simulate a building, the biggest difficulty is to take into
>account the good insolation. For a big building with a lot of balconies,
>it's impossible to be accurate in calculation of shading masks, without
>using hundreds of type 34. So we have to simplify the phenomena.
>
>I find a new problem (for me) with Type 34 : I simulate a building without
>any overhang and wingwall and I find a certain quantity of Qheat = Qheat1
>(for example). I want to test wingwall, so I add a type34. At first, I test
>a type 34 with all overhang and wingwall lengths equal to 0. The problem is
>that I don't find the same quantity of Qheat (Qheat2) for my building.
>Qheat1 is bigger than Qheat2.
>
>To refind the same Qheat in the 2 cases, I have to change the Sky Model for
>diffuse radiation in the type 109 Wheather data, from the Perez Model to
>the Isotropic sky model.
>
>So, what should I think about that ? What is the impact of the Isotropic
>sky model on the accuracy of a building simulation ? Is there a way to keep
>the Perez Model and to refind the same Qheat in the 2 cases (with and
>without type34).
>
>Thanks for your help.
>Christophe.
>
>
>===========================
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