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End of Semester Report: CFD Model Optimization for Building Thermal Management

This report outlines the progress made by the STP Team in optimizing the CFD model for the EAB building's thermal management during the semester. Focused on simplifying the previous model and expanding it to encompass the entire floor, we investigated various configurations to enhance heat removal from critical areas. Our modeling assumptions and validation efforts led to significant insights, notably a reduced time to reach critical temperatures. The report includes a detailed analysis of various cases tested under different airflow configurations, with recommendations for future optimization.

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End of Semester Report: CFD Model Optimization for Building Thermal Management

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  1. Members: Ryan Bigelow, MEEN Sr Adam Tallman, CVEN So Iris Hill, ISEN So Andrew Ingram, MEEL Fr Ricky Palacios, CHEL Fr Graduate Mentor: James Hardy, MEEN STP TeamEnd of Semester Report

  2. Presentation Outline • Model Description • Modeling Assumptions • Model Validation • AnalyticalResults • Recommendations

  3. Introduction • This semester attention was focused on simplifying the previous model, and expanding the model to the entire floor. • CFD efforts were focused on prioritizing techniques used to remove thermal energy from critical rooms on the floor.

  4. Model Description • Model of floor 0 in SolidWorks • Floor 0 modeled as one part • Accurate dimensions per STP data • Each room contains: • A centrally located heat block that uses a specific heat generation rate provided by STP

  5. Floor 0 Model Can we describe here each room where we have a heat source? How about showing the block where the heat source is applied? We need to describe here our modeling approach -what is included in our model ( all rooms and corridors? -where are the heat sources -are there any fans to bring in external air? Overall, this is a good picture to use to explain our modeling approach Penetration room Figure 1. “Floor 0” Model of EAB Building

  6. CFD • Simulations were performed using various door and fan configurations to investigate the effect on room temperature. • A parametric analysis was carried out to determine the variables that had the greatest effect on room temperature. • Model assumptions were tested against results of the parametric analysis to produce a more accurate simulation.

  7. ModelingAssumptions • Various assumptions were made in the following areas: • Adiabatic Wall Boundary Conditions • Heat Source Location and Size • Equipment Volumes • Fan Specifications

  8. Boundary Conditions • Walls, Floor & Ceiling • Adiabatic walls (no heat loss through the internal/external walls, ceiling, and floors) • Frictionless walls • Penetration Room (adjacent to EAB room) • Ambient pressure & 68˚F

  9. Heat Source Location and Size • Each heat source is modeled as a block that has a total surface area of 1 m2 on the five surfaces that have contact with the fluid • Each heat source is centrally located within each room

  10. Last Year’s CFD Results • CFD model from last semester included thermal mass from equipment in SGR. • Time to reach critical temperature was found to be 22.5 minutes.

  11. This Year’s Validation Run • The door lids were shut in the SGR and a 85700W heat load was applied to the room to mimic conditions of last semester’s model • This semester, CFD model did not include thermal mass from equipment. • Time to reach critical temperature was found to be 10.5 minutes

  12. Analytical Verification of CFD Model • Switch Gear Room • Analytical Approach - Expected time to reach 104F • CFD Results - Time for model to reach tcrit: 10.5 min • Difference between CFD and analytical : 3%

  13. Comparison of Results Spring 2009 Tc: 22.5 minutes Fall 2009 Tc: 10.5 minutes Percent Difference: 53%

  14. CFD Analysis Case Descriptions • Case 1 – “Sealed Floor” Model. No air flow in from penetration room (PR) or flow out from stairwells. All internal doors open, no fans active. • Case 2 – “Sealed Floor” Model. No air flow in from PR or flow out from stairwells. All internal doors open, 6 fans with 6000CFM flow rate placed as per STP procedure. • Case 3 – Air flow is introduced into the EAB from the PR by assigning the PR lid a volumetric flow rate of 6000CFM. All internal doors open, 6 fans with 6000CFM flow rate placed as per STP procedure. • Case 4 – Air flow is introduced into the EAB from the PR by assigning the PR lid a ambient pressure, 68°F boundary. A 6000CFM fan was placed directly in front of lid to provide flow. All internal doors open, 6 fans with 6000CFM flow rate placed as per STP procedure. • Case 5 – Same as Case 4 with additional 6000CFM fan added at Switchgear Room (SGR) doorway. Fan blows air from hallway into SGR. • Case 6 – Same as Case 5, all fans now have 15,000CFM flow rates. • Case 7 – Same as Case 6, additional 15,000CFM fan added to SGR at other doorway. Fan blows air from SGR to hallway.

  15. Sealed Floor SimulationsCases 1 & 2 • Initial conditions: All air is at initial temperature of 64°F • No penetration room air flow in • Case 1 – no fans • Case 2 – six identical fans (6000CFM) placed in model as shown on right.

  16. Sealed Floor Simulations • Case 1- Time to reach 104°F (average room) with no forced circulation (no fans): 8.22 minutes • Case 2- Time to Reach 104°F with six fans configured as per STP procedure: 8.62 minutes • 5% Difference

  17. Case 2 Results

  18. Critical Rooms • Case 2- ( with fans) From the sealed heat up analysis, the following rooms showed fastest temperature rise SGR heated up 60% faster than any other room

  19. Cases 3 & 4Introducing Flow From Penetration Room Case 3 - Air flow from penetration room was modeled in two ways. A specified volume flow rate boundary condition was established at the lid as seen in figure below. Fan placed in front of lid Time to reach 104°F: 8.66 min Case 4 - In second method, lid was assigned ambient pressure and temperature (68°F). A fan was placed directly in front of the lid. Differences were negligible. Second method was used in subsequent tests. Volume flow rate assigned to lid Time to reach 104°F: 8.60 min

  20. Case 4 - Results • Introducing flow from the penetration room did not have great effect on the heat up rate. • Time to reach 104°F with no PR flow: 8.62 min • Time to reach 104°F with PR flow: 8.60 min • 8.60 minutes is the estimated time to reach critical temperature with current “Loss of EAB HVAC Response Improvements” document procedures. • It was found that there was minimal air exchange in the SGR

  21. Case 4 Results @ 5.7 Min: No Fan at SGR

  22. Case 5 - Adding a Fan to SGR • Although not in the current procedure, the team investigated adding a fan to the entrance of the SGR. It was found that the heat up rate was decreased by approximately 15% • Time to 104°F without fan in front of SGR: 8.66 min • Time to 104°F with fan in front of SGR: 10.05 min • Strong correlation was found between air velocity and fluid temperature

  23. Case 5 Results @ 5.7 Min: 1 Fan at SGR

  24. Case 6 - Increasing Fan size Case 6 investigated increasing all fan sizes to 15,000 cfm Case 5 - Time to reach 104°F with 6,000 cfm fan: 10.05 min Case 6 - Time to reach 104°F with 15,000 cfm fan: 10.37 min Increasing fan size reduced heat up rate by 3% Velocity profile of EAB floor with 15,000 cfm fan

  25. Case 7 - Adding Second Fan to SGR • A second fan was added that pulled air from SGR. • Time to 104°F fan in front of SGR: 10.37 min • Time to 104°F with fan in front and at exit of SGR: 11.12 min • Time to reach critical temperature was increased by 7%

  26. Case 7: Results Figure on left shows velocity profile with all fans set to 15,000 cfm. Figure on right shows an additional fan added to draw air from switchgear room.

  27. Combined Results

  28. Conclusions • Current fan placement by STP procedure had minimal effect on SGR heat up rate. • Addition of fans to Switch Gear Room produced greatest effect on heat up rate of critical rooms. • Modeling approach is very conservative. However results can be used to update the safety procedures.

  29. Future Work • Future work will focus on improving the accuracy of the model • Evaluate more case studies • Conduct further sensitivity analyses on parameters • Add thermal mass to the rooms. • Accurate equipment volumes and weights are needed

  30. Special Thanks • Matt King, STP • Mrs. Lagoudas, SEI • Ernie Kee, STP

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