Solar absorption of building envelope elements

def Solar_absorption_of_element(cls, building_object) -> solar_absorption_elements

Inputs

Name	Type	Description
building_object	dict	Building data structure that contains a list of surfaces under building_surface. Each surface must define ISO52016_type_string and optical parameters (solar_absorptance or g_value).

Required Fields in building_object["building_surface"]

Each element in building_surface should include:

Field	Description
ISO52016_type_string	OP = Opaque element • W = Transparent (window) • GR = Ground-contact • AD or ADJ = Adjacent wall
solar_absorptance	Solar absorptance coefficient (0–1) for opaque elements.
g_value	Solar energy transmittance (0–1) for transparent elements.

Purpose

Computes the solar absorption coefficients for each building envelope element in accordance with EN ISO 52016-1 solar heat gain modeling.
The result is a 5×N matrix a_sol_pli_eli assigning solar absorption values to the nodal structure of each surface.

How it works

Note

The type of the surface has been mapped in the calculation using the following code:

• OP: Opaque element
• W: Transparent element
• GR: Ground-contact element
• AD: Adiabatic element
• ADJ: Adjacent element

...
for i, surf in enumerate(building_object["building_surface"]):
    if surf["type"] == "opaque":
        if surf["sky_view_factor"] == 0:
            typology_elements[i] = "GR"
        else:
            typology_elements[i] = "OP"
    elif surf["type"] == "adiabatic":
        typology_elements[i] = "AD"
    elif surf["type"] == "transparent":
        typology_elements[i] = "W"
    elif surf["type"] == "adjacent":
        typology_elements[i] = "ADJ"
    surf["ISO52016_type_string"] = typology_elements[i]

1. Determine number of envelope elements

   el_list = len(building_object["building_surface"])
   

   Creates an empty coefficient list solar_abs_elements of length N.

2. Extract solar properties

   • For each surface:
     • If "solar_absorptance" is defined and the element is not "AD" or "ADJ", use its value.
     • If "solar_absorptance" is missing, use the "g_value" (for transparent elements).
     • If the element type is "AD" or "ADJ", set absorptance = 0.0 (no solar gain through adjacent walls).

3. Create absorption matrix

   a_sol_pli_eli = np.zeros((5, el_list))
   a_sol_pli_eli[0, :] = solar_abs_elements
   

   Only the first node (external surface) receives the solar absorptance value; deeper nodes remain zero.

4. Return result

   return solar_absorption_elements(a_sol_pli_eli=a_sol_pli_eli)
   

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Outputs

Type	Description
solar_absorption_elements	Wrapper containing the 2D array a_sol_pli_eli (shape 5×N), where N = number of elements in building_surface.

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Example

# Expected result:
a_sol_pli_eli = np.array([
    [0. , 0.6, 0.6, 0.6, 0.6, 0.6, 0. , 0. , 0. , 0. ],
    [0. , 0. , 0. , 0. , 0. , 0. , 0. , 0. , 0. , 0. ],
    [0. , 0. , 0. , 0. , 0. , 0. , 0. , 0. , 0. , 0. ],
    [0. , 0. , 0. , 0. , 0. , 0. , 0. , 0. , 0. , 0. ],
    [0. , 0. , 0. , 0. , 0. , 0. , 0. , 0. , 0. , 0. ],
])

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Notes

• Only external surfaces (node 0) receive solar absorption values, as solar radiation is applied to the outermost layer.
• Adjacent elements ("AD" or "ADJ") are excluded from solar absorption (set to zero).
• Transparent elements ("W") use g_value instead of solar_absorptance.
• The 5×N output format is consistent with the 5-node thermal network defined in ISO 52016-1.

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References

• EN ISO 52016-1:2017 – Energy performance of buildings – Calculation of energy needs for heating and cooling. - Section 6.5.7 – Definition of solar absorptance and its application to surface nodes.