SimTec performed CFD simulations for “INSTA Consultants Engineers” to calculate the flow and temperature fields inside and around the “Piraeus Tower” (Commercial–Shipping Center of Piraeus), the second tallest building in Greece to the “Tower of Athens”. The building’s height is 88m, it has 24 floors (including two basements) and a total built area of 34,600m2. Atmospheric conditions in the simulations corresponded to a hot summer day with ambient temperature of 38 [oC].

All mechanical equipment for each floor is hosted in a single engine room, located in the north face of the building. The scope of the study was to verify that the hot air rejected by the heat pumps (HP) in each floor (at 55 [oC]) is not sucked by the fresh air venting intakes of the floors above, and that the inlet air of the HP is at adequately low temperature.

The complex architectural form of the façade, consisting of decorative horizontal and perpendicular fins, frames with louvers and mesh panels, as well as the complicated geometric configuration of the equipment (HVAC devices and ducts) in the engine rooms, rendered simulation necessary for the estimation of buoyant air flow caused by large thermal gradients and the interaction of wind pressurization with under–pressure effect at the fresh air suction vents and the breathing HP grills.

For the description of the HP breathing grilles and the decorative mesh panels, the porous jump model was utilized, whereas for the frames with louvers, the porous medium model was employed. These tools are available in Ansys Fluent and can be used for the accurate determination of pressure drop and flow direction without the need to discretize the actual geometric form, which would require a huge number of computational cells.

The concerns of INSTA engineers were confirmed after the initial design configuration was simulated, returning HP inlet temperatures significantly higher than those stated in the specifications for efficient operation. The inspection of the CFD results and the direct interaction between SimTec and INSTA experts led to a series of design steps of the following parameters: (a) number and power of HP, (b) positioning of HP, fresh air intakes and related ductwork inside the engine rooms, (c) internal sealing of a portion of frames with louvers, aiming at guiding the hot rejected air away from the inlet ports of the same floor, as well as the adjacent ones (mainly above). Each modification was followed by a new CFD simulation, until the temperature field at the fresh air inlets and HP breathing grilles satisfied the requirements for various scenarios of either absence of or weak wind conditions.

Ansys Fluent enabled the experienced SimTec analysts to decisively help INSTA engineers in solving a difficult and multi–parametric technical puzzle in a complex building. The most important benefit of the CFD project was that a solution was provided when there is plenty of flexibility; at design stage instead post–construction, when margin for changes is limited and cost is orders of magnitude higher.