CFD Analysis to Study the Wind and Heat-Island Effect due to Outdoor A.C. Units in an High Rise Building

Objective: To study the airflow around the project building & other buildings due to the effect of wind and effect of heat generated by outdoor air conditioners installed in high rise project building on other surrounding buildings in worst case scenario.For wind flow analysis the predominant wind direction of SW with average wind velocities of 3 m/sec in Mumbai is considered based on the ISHRAE weather data. Hence, in worst case scenario all 30 floors with 20 outdoor AC units in each floor were considered for total heat dissipation from the project building. The worst case conditions were simulated for 21st March at 22:00 which is assumed to be a condition when all the ACs were working. At that moment as per ISHRAE weather data the ambient temperature in Mumbai is 26.9 C, same was considered in the CFD analysis.

Modelling and Analysis: Based on the provided CAD drawings details of the “Kahprideo project building & surrounding buildings”, the 3D CFD model was prepared. The area of interest for the project building & its surrounding building is 305m width, 340m length & 125.5m height. After preparing the 3 D geometry, the high quality mesh with different hexagonal & tetrahedral mesh was generated with total mesh cells of 8.8 million cells were obtained. The meshed geometry was used for solving the flow & energy equations in “project building & surrounding buildings” with applying the suitable boundary conditions in worst case conditions to see the effect of wind flow around buildings and heat dissipated by outdoor air conditioners on other buildings.

Conclusion: Thus CFD Analysis was carried out to study the airflow around the project building & other buildings due to the effect of wind and also the effect of heat generated by outdoor air conditioners installed in high rise project building on the other surrounding buildings in worst case scenario. From the analysis it was found that the temperatures created due to outdoor air conditioners located in project building were reaching at lower levels to other buildings, however the temperature of this heat wave is 0.8 C above the ambient temperature & this temperature difference is very negligible. However while closely observing all the temperature results it reveals that just few meters away from the project building the temperature dropped to 27.6 C, then after 45m of distance the temperature is dropped to 27.2 C and then after 480m of distance the temperature  dropped to ambient conditions. Hence it was concluded that the outdoor air conditioning units placed in the building were slightly affecting the surrounding buildings however it was almost negligible.

An Introduction to Fire Simulation

In real world, it is never acceptable to set fire inside iconic and large commercial buildings or facilities. But if you are working at Mechartés, you will come across buildings & facilities that are set on fire routinely to simulate real and potential fire scenarios on computers to assess their impact and methods of controlling these fires.

The destruction caused by fire in urban establishments is known to human civilization since the time in antiquity when Rome burned for six days continuously. But in modern times, fire engineering practices have reduced causalities & infrastructure damage exponentially. Today, the scope of fire safety is not only limited to extinguishing fire but covers wide variety of disciplines like early fire detection, smoke management, provision for escape facilities; even during building space & layout planning and last but definitely not least, proactive use of dynamic fire modeling to assess risks to life and property and to develop effective fire protection & evacuation strategies for scenarios that cannot be predicted by conventional wisdom.

Even with modern engineering and safety practices, the threat of accidental fire cannot be negated in modern building and industrial infrastructures. This threat brings the necessity of fire modeling to the forefront of large building and industrial facility design & development. With advances made in computer hardware performance and numerical algorithms, Computational Fluid Dynamics (CFD) software are routinely used by engineers to come up with ingenious & effective solutions to minimize damage to life and property.

Fire Dynamics Simulator (FDS) is one such CFD software actively developed by National Institute of Standards and Technology (NIST), to simulate fire driven fluid flow in situations of varying complexities. The hydrodynamic model, combustion model, thermal radiation model, sprinkler model etc, that are incorporated in FDS are continuously verified and validated by the active community of academic, scientific and professional interest group. This community effort has developed FDS into a robust and reliable software to model and simulate fire & smoke propagation inside buildings and facilities. Apart from dynamic fire modeling, numerical simulation methods are also actively used to simulate evacuation and predict indoor air quality inside buildings. Modern evacuation modeling software have reached the capability to incorporate psychological responses of human beings to fire inside enclosed spaces. With software like CONTAM, important information about exposure of occupants to airborne contaminants can be modeled and simulated for eventual risk assessment.

Modern design practices for fire safety are increasingly adopting numerical simulations to study the behavior of a fire protection system without building it. The results are accurate in general, compared to analytical model, especially when applied in complex situations. These simulations are also helping fire engineers to find unexpected phenomenon, behavior of the system and easily perform “What-If” analyses. Mechartés has been enabling our customers to address the following design & safety concerns:

• What locations inside a building can be described as the “worst” location for a fire incident?
• What is the minimum response time required during evacuation in a given “worst” condition?
• With the proposed fire safety & evacuation methodology, what changes can reduce loss of life and property?
• What is the effectiveness of smoke extraction fans and equipments?

Finally, do take out 5 minutes to view our presentation on how fire simulation services can be used to engineer your buildings and facilities for fire safety.

Thermal Analysis of a Data Center

Objective: To perform the thermal analysis of a data center and predict the temperature distribution and air flow movement for minimizing computer room air conditioning units (CRAC’s).  Using above-floor CFD modeling, we monitor and view the entire life cycle of the airflow through the data center. We track the air from the point at which it leaves the computer room air conditioning (CRAC) unit into the sub floor, as it travels from the sub floor through the perforated tiles into the ambient room, and as the air travels through the server racks and back to the CRAC unit.

Engineering Solution: The analyzed data center is rectangular with an area of 516 m sq. and height of 3.35m. Cooling is to be provided using raised flooring layout and demarcation is done for cold aisle and hot aisle. The source of heat from exterior wall according to thermal resistance of wall & heat source from 154 server racks are 1.26MW with each racks emitting 8kw of heat. Three fans of about 500CMH were assumed to transport air from cool aisle to hot aisle in each rack unit.

Figure: Image showing temperature profile (in ^oC ) inside data center

Conclusion:

• The Average temperature on the rack surface at the 0cold aisle side is 15^oC.
• The temperature at cold aisle is varies from 12 to 17^oC.
• The Average temperature on the rack surface at the 0hot aisle side is 27^oC.
• The temperature in hot aisle is varying from 18^oC to 32^oC.
• The simulation shows that a good number of servers are experiencing temperatures well above and below the ASHRAE recommended temperature levels.
• Short circuiting of cold air is clearly visible in the simulation.
• Using Computational Fluid Dynamics the system was designed to reduce the capital cost of the data center design by  10% of the original design.
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Pulsation Analysis For High Pressure Petroleum Pipelines

Objective: Piping systems are a central part of numerous engineering installations. A number of sources such as pumps generate vibrations which can propagate along the pipes and excite other structures. These vibrations can cause two main problems, namely mechanical fatigue and acoustical noises. Further, interaction of the dynamic flow generated by the pump plungers with acoustical resonances in piping systems can result in high pressure pulsation levels pump and piping, cavitation, excessive vibrations and failures. Moreover, higher frequency fluid borne noise can be generated from flow perturbations associated with elbows, valves or cross section changes in the pipe. This design approach in conjunction with pulsation simulation is required to couple technical analysis of piping system to ensure that the piping will have adequate supports and clamps to maintain mechanical natural frequency of major acoustical energy.

Modeling and Analysis: The first design approach involved pulsation and vibration control through the use of good piping layout and support principles, adequate suction pressure and use of pulsation control devices such as dampers, accumulators, preventers, hydraulic isolators, inhibitors, suppressors, stabilizers, acoustic filters and selected piping configurations.The acoustical simulation techniques predict the potential of cavitations and the  required minimum suction to prevent cavitations, based on amplitudes of the pulsations. The results obtained from the analysis proved that the pulsation levels at the suction end were considerably reduced and the pulsation levels were found to be under API 674 standards. Based on the pulsation amplitudes at various frequencies harmonic loads acting on the pipelines were calculated. These harmonic loads were applied at respective nodes and a FEM based harmonic analysis was done to determine the natural frequency of the system and response of the system to harmonic loads arising from pressure pulsations.

Conclusion: From the analysis the pipeline was first tested for the given set of pulsation damping equipments and reciprocating pumps. It was observed that the old configuration did not provide the desired pulsation control in the system. We observed amplification in pulsation in the suction side which was much above the values accepted by API and cavitations were observed at the suction end of the plunger. To reduce the pulsation it was therefore suggested that an additional pressure dampening equipment of size 1 liter must be installed 0.55 m from the suction end of the reciprocating pump. Further the analysis done on the pipeline with the additional dampening accumulator shows considerable reduction in pressure pulsation and the pulsation amplitudes were much below the allowable limits