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.

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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Ventilation Design verification of Car Park basement – CFD Analysis

Objective: The objective of this project was to verify the  design of a ventilation system for the basement car parking area using CFD. The specific aim is to find the optimal locations, number & configuration of the induction fans required for the ventilation of the car parking lot, for the given positions of inlets and exhaust, and given configuration of the Supply air fans & exhaust fans, such that it meets requirements of CO exposure limit set by health & safety regulations and also to check whether it meets the sufficient visibility & temperatures in case of fire.

CO PPM Without Jet fans at 1.7 m

Technical Challenge: The acceptance contaminant level criterion for parking garages is specified in ASHRAE 2007 handbook. According to ASHRAE, the main criterion for car parks is that the carbon monoxide levels should remain below a designated peak value.

 

CO PPM with Jet fans at 1.7 m

Engineering Solution: The mathematical modelling using CFD can be developed which would simulate the actual behavior of the system. At first the analysis was done without placing any jet fans. This provides an indication of the stagnant areas in the car park. The subsequent analysis is done with jet fans operating so as to remove the stagnant areas , to reduce the concentrations of CO and to remove smoke in case of fire.

Velocity Vectors at 1.7 m without Jet fans

 

Results and Conclusion: 

• The CO concentrations from the CFD simulations, without using induction fans has been obtained as 167.5 ppm which is higher than the safe CO limit for human beings.
• After conducting CFD analysis by placing and optimizing the jet fans in the car park area, maximum CO level found to be as 27.8 ppm (33.36 mg/m3), which is with in safe CO limit for humans.
• Ventilation System in the car park area has been designed optimally to reduce the CO level within the acceptable limits.

  

  Velocity Vectors with Jet fans at 1.7 m

Heat Transfer Analysis in Hot Water Generator

Objective: The objective of the project was to verify the hot water generator design by ensuring that the operation conditions are met based on actual experimental results of combustion, heat transfer and fluid flow through the combustion chamber and pipes. CFD Analysis was done to simulate  the combustion and flow of hot flue gases through the combustion chamber, hot water generator and economizer till the exhaust and to calculate the temperature of water passing through the heat exchanger pipes as it comes out of the water outlet. Suggestions were given based on the simulation result to enhance turbulence in the fluid flowing inside the tube.

Model of Hot Combustion Chamber

Modeling and Engineering Solutions:  The proposed design uses the Lamont type hot water generator. The hot water generator has a rectangular box type construction which has an economizer over the top and it finally connects to the exhaust draft tube. The meshing scheme is used to distribute the mesh uniformly in the outer region and  a very fine mesh in the central core region is used. The figure shows the geometry created and the meshing scheme used for this geometry.

Fig. Showing the Meshing scheme used for the Generator

Conclusion: After the analysis was done it was verified that the operating conditions of the hot water generator was similar to the actual experimental results of combustion, heat transfer and fluid flow through the combustion chamber and pipes. The total volume flow rate of water entering the hot water generator is 900 GPM. The economizer is designed to ensure that the water enters the inlet drums located at the bottom of the hot water generator at 160 F – 180 F. The temperature in the core combusting region is high and progressively reduces through the heat exchange region as it is carried away by the water and the flue gases. The positions of the baffles were clearly understood from the flow.

Temperature contours inside the Generator