Our customer is a large construction group with specific interest in design and development of ultra-luxury living apartments. For cooling requirements Out Door Units (ODUs) are used with high cooling capacity. In the summer season, it is experienced that the cooling provided is below the comfort level. This is presumed to be attributed to two problems (1) Stack effect i.e. hot exhaust of one ODU going into inlet of upper one (2) Location of the ODU, hindrance to the fresh air.
Two pronged strategy was used for the simulation. First the entire elevation of the 40 storey building was simulated along with inlets and outlets of the ODUs. ODUs of two manufacturers were considered with the first one having the inlet and exhaust in the same plane and the other at 90 deg to each other and having twice the power of the first. CFD simulation was carried out by modeling the whole building elevation without the internals. Studies were done for various wind conditions derived from Met data. In the second part, studies were done for typical floor to find the flow path of air for different seasons.
The studies concluded that the type 2 ODU was better due to higher power and orientation of the exhaust. It was also found that for the flats in the middle the stack effect of much higher compared to lower and upper flats as observed by customer. This was explained due to fresh air at the bottom and quick dissipation of hot air at the top. It was found that leeward chajja received much less fresh air and hence got derated soon. Grills were found to cause considerable pressure loss. To solve the problem, increase in capacity of ODU and change in direction of exhaust was suggested and the simulations redone to prove the concept.