Internal/HVAC CFD

Internal CFD can model the airflow within a space in microscopic detail and is therefore an excellent tool to be used in assessing the performance of a building HVAC system. With CFD you can quickly study the variation in flow patterns due to the space conditions which means consideration such as occupant comfort, air mixing, age of air and pressure distribution for diffuser selection can all be assessed. The CFD model can be constructed to include the specifics of the space environment such as furniture arrangements which will have a direct effect on airflow direction along with capitalising on surface boundary data, temperatures and flow rates, available from an energy model to enhance the model quality.

For example things get a tricky when the space size increases and ventilation strategies are non-traditional. Take the example of a large auditorium which are now typically designed to have underfloor plenums and swirl diffusers with the overriding assumption the flow will be uniformly distributed across the various swirl diffusers. Time and again the design team will fail to account for the stratification caused by the inclined shape of the auditorium due to uniform distribution of flow through the diffusers. The audience near the speaker will report the seating to be cold whereas those at back will report it too warm.

Sometimes there is limited space to ‘package’ the underfloor plenum and could cause unfavourable non-uniform distribution of flow across the diffusers due to unexpected pressure variation in the plenum. The quick solution is to reduce the size of opening of the swirl diffusers in the front of the auditorium and increase it at the back. However if the diffusers are non-adjustable then it becomes a difficult conundrum to solve but completely avoidable if modelled beforehand.

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