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temperatures due to solar load


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What is the response of the thermal mass of a construction to the solar gains upon exterior and interior wall surfaces (combined with other boundary conditions) ?


Previous page: solar load through windows

Boundary conditions
The absorbed solar radiation on exterior and interior wall surfaces are converted to node powers in the surface nodes
The absorbed solar radiation on a transparent wall is converted to node powers in the nodes behind the transparent wall surface (i.e. mass absorption)
These solar boundary conditions are added to the other boundary conditions (e.g. outside air temperature as a function of time, heating or cooling power, ventilation flows)

Material properties
The thermal conductivity, specific heat, material density, solar reflection factor, solar transmission factor are entered in the Colours window

3D building simulation
Suppose the construction has initially a uniform temperature of 20C and there are no other boundary conditions than the solar radiation
What is the impact of the solar radiation throughout the day on the temperature distribution in the construction ?
The figures below show the surface temperatures at 10:30 am (10 June, climate of Uccle, south oriented exterior wall with window)

Exterior view of south oriented wall

Top view (ceiling clipped off)
The direct solar radiation causes an important temperature increase (10C and more) on the direct sunlit part of the floor

The hot spot follows (with some hysteresis) the movement of the sun and is most pronounced just after noon
After sunset the accumulated heat in the construction will be further cooling down

Figure below: temperature distribution at 5:00 pm (no more direct sun infiltration through the south oriented window from about 4:00 pm)

Sunroom effect
A veranda is placed in front of the window to study the thermal effect
The figure below (ceiling cut off) shows the shaded and sunlit wall surfaces at 10:30 am

The figure below shows the corresponding temperature distribution at 10:30 am
The temperature scale is increased up to 60C

The chart below shows the balanced air temperatures in both cases (10 June, solar radiation of Uccle):
- Room 1 (i.e. without veranda)
- Room 2 + veranda

Adding natural ventilation for cooling
Suppose the air temperature is ventilated with the outside temperature (at 20C)
The applied ventilation rate is 1/h (for the room) and 5/h (for the veranda)
The corresponding ventilation flows (in m3/s) are entered in the Ventilation window
The chart below shows the resulted tempered air temperatures

VOLTRA enables dynamic 3D thermal simulations embedding a 3D solar processor
The shadow patterns, solar radiation calculation, diffuse reflection, transmission, absorption are automatically determined and added to other dynamic boundary conditions

See also animation examples