I went through the previous discussions on this topic, but since some posts are from 5 years ago, it seems some of the solutions used previously have been surpassed by the new features in Delphin 6. Therefore, I decided to post this as a new question in an attempt to clarify the best current practices when using Delphin 6.
Context: A vertical wood cladding facade (with open edges) and a ventilated cavity with battens and counter-battens (summing to an 80mm air gap) fixed on an OSB with Tyvek foil or a Pavatex bituminized wood fiber board, followed by: a wood stud cavity insulated with mineral wool; OSB; and a gypsum board.
According to ISO 6946, we have two approaches:
1. Neglect the air gap and wood cladding, and add a surface resistance to the remaining outer layer. (Not intended for our case)
2. Add an air material and assign a source air exchange with the ambient environment, plus a long-wave radiation exchange in the cavity, and a surface resistance on both sides of the air material to account for convection and long-wave radiation.
Therefore, following option 2, we created:
a. Material - Air Material 80mm vertical with properties (created using the Excel file provided by Fechner):
- ρ = 1.3 kg/m³,
- cp = 1050 J/(kg·K),
- λ = 0.138 W/(m·K),
- μ = 0.18,
- KG = 0.1 s;
- Wsat = 1000 kg/m³,
- W80, Aw, and Kleff remain undefined.
c. Source - Long-wave radiation exchange in the cavity [LongWaveRadiation] – X-Direction emission coeff. Left = 0.9 / Right = 0.9 (Calculated according to ISO 6946 §6.8 - Table 7 - see notes).
d. Contact Condition – Additional resistances between material layers [AdditionalResistance] – Heat transfer resistance = 0.14 m²·K/W (Calculated according to ISO 6946 Annex C).
Where:
- Tmn (thermodynamic temp. of the surface and its surroundings) in K = 10°C + 273.15 (Potsdam external temperature ave.)
- σ (Stefan-Boltzmann constant) = 5.67 × 10⁻⁸ W/(m²⋅K⁴)
- ε is the hemispherical emissivity of the surface = 0.9
- hr0 = 4 ⋅ σ ⋅ Tmn³ => 4 * 5.67E-08 * (10 + 273.15)³ => 5.15E+00 W/(m²·K)
- hr = ε ⋅ hr0 => 0.9 * 5.15E+00 => 4.63E+00 W/(m²·K)
- hc = hci (according to Table C.1 – for horizontal heat flow) => 2.5 W/(m²·K)
- Rs = 1 / (hc + hr) => 0.14 m²·K/W
1. Are the settings above correct?
2. Did I miss something, or are the numbers wrong?
3. Since the surface resistance is temperature-dependent, how does Delphin handle this constant value?
4. For a 2D simulation, should I also add a pressure difference at the top and bottom openings, or is the source air change rate sufficient?
5. As the cladding joints are open, how can we set an additional water source on the surface of the cavity's external layer? If I am correct, it accounts for 1% by default, but we would like to evaluate scenarios for 3%, 5%, and 10%.
Thank you in advance for your attention.
Best Regards,
Thomaz