HVAC
VENTILATED
FACADE
Thermo-fluid dynamic performance
of a high-efficiency building envelope
CLIENT
Developer of high energy performance ventilated facade systems
CHALLENGE
Predict the real air flow through the facade, its pressure losses and how well it sheds heat
RESULT
A pressure loss curve for sizing the ventilation, a quantified heat exchange and an estimate of wall transmittance
01
CHALLENGE
A ventilated facade is a complex system whose behaviour depends on a great many variables at once — the geometry, the ambient conditions and the mode of ventilation.
At the design stage three things are hard to predict: the real air flow rate through the facade, the pressure losses of the system, and how effectively the heat is actually carried away.
Without a proper analysis the risk runs both ways: over- or under-sizing the ventilation system, or failing to exploit the benefits of natural ventilation that the facade was built to provide.
02
SOLUTION
We built a three-dimensional CFD model of the ventilated facade from the real geometry supplied by the client.
The model covers both modes. Under forced ventilation, a range of air flow rates was imposed to trace out the pressure loss curve. Under natural ventilation, the convective motion generated by the temperature differences between the wall, the outside air and the internal environment was analysed on its own terms.
Heat exchange between the surfaces and the fluid was included throughout, in scenarios representative of both summer and winter conditions — the facade does a different job in each.
03
RESULTS
The simulations characterised the facade completely. The relation between air flow rate and pressure loss was established, which is what a ventilation system has to be sized against.
The thermal analysis showed the ventilation to be effective at reducing thermal loads, particularly in summer, and produced an estimate of the transmittance of the wall.
It also showed how much natural ventilation alone contributes to shedding heat — improving the overall energy performance of the system without any fan running.
