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Stack Effect and Ventilation System Design

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Understanding stack effect is extremely important for building design, as it creates natural ventilation and air infiltration. In this webinar, you will learn how the SimScale cloud-based simulation platform enables HVAC engineers to leverage the potential of CFD for their own projects by using a standard web browser.

You can check the official webinar page here: http://ow.ly/c8bM30oC97R

Published in: Engineering
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Stack Effect and Ventilation System Design

  1. 1. STACK EFFECT AND VENTILATION SYSTEM DESIGN JON WILDE and JESUS VILAR
  2. 2. JON WILDE VP Customer Success 15+ years of experience in CFD, application engineering and team management. Before joining SimScale, he worked with many other CFD solutions and managed a team of technical support engineers.
  3. 3. JESÚS Application Engineer Aerospace Engineer specialised in CFD. First experience in industry with SimScale. (Responsible for this webinar and all the awesome stuff within).
  4. 4. 1. Benefits of Using Simulation 2. Introduction to SimScale 3. Stack Effect 4. Setup 5. Live Demonstration 6. Results Summary 7. Q & A
  5. 5. ACCELERATE YOUR DESIGN PROCESS Easily test performance, optimize durability or improve design efficiency with cloud-based simulation.
  6. 6. ALL-IN-ONE Structural mechanics, fluid dynamics, and thermodynamics. REAL-TIME SUPPORT Chat, phone and email. Consultancy, webinars, and training. COLLABORATION Join the community, benefit from public projects, and share know-how. FAST & EASY Get results faster on any device thanks to cloud technology. COST-EFFICIENT Start risk-free without an upfront investment. SECURE High security with government-approved Advanced Encryption Standard (AES).
  7. 7. STACK EFFECT
  8. 8. STACK EFFECT FOR VENTILATION SYSTEM DESIGN OVERVIEW ● Stack effect describes the natural ventilation that occurs due to a difference in indoor-to-outdoor temperature and air density. ● It can aid fireplace plumes and direct smoke propagation, therefore it is crucial to evaluate your design’s ventilation systems. Source: https://www.servprokitsapcounty.com/blog/post/68733/building-services/stack-effect-chimney-effect
  9. 9. WINTER ● Temperature difference generates a buoyancy effect that drives the flow inside the house at the low level and expels it at the top level. SUMMER ● Reverse effect is experience in summer conditions. It is usually weaker due to lower temperature difference. Source:http://www.blackmoldmildewremoval.com/wp-content/uploads/stackeffect_wintersummer.jpg DIRECT AND REVERSE STACK EFFECT
  10. 10. STACK EFFECT VARIABLES ● Variables that have a direct impact in the buoyancy forces provoking the stack effect are height and temperature gradients. ● Ventilation design will affect air flow distribution and will be critical to control this phenomena. Where ● ΔP = pressure drop. ● C = 0.0342 K/m (constant). ● a = atmospheric pressure. ● h = height. ● To , Ti = outside/inside temperature. Stack effect in chimneys
  11. 11. CONVECTIVE HEAT TRANSFER ● Convective Heat Transfer (CHT) is used when temperature changes in the fluid lead to density variations and movement of the fluid due to gravity. ● This solver can be used for natural convection but also for forced convection, when air movement is induced by external forces, such as wind, pumps or fans.
  12. 12. SETUP
  13. 13. CAD IMPORT Upload your CAD model or import it from other cloud services into SimScale. SIMULATION SETUP All steps to define and run a simulation are done within SimScale. DESIGN DECISION Use the simulation insights to make better and faster design decisions.
  14. 14. OUR CASE: ENGLISH COTTAGE IN WINTER/SUMMER CONDITIONS Objectives ● Simulate the standard and reverse Stack effects. ● Detect ventilation patterns due to temperature differences. ● Become familiar with CHT in SimScale, and how the platform can help designing ventilation systems. Source: https://wallpapersafari.com/w/iHtGpQ
  15. 15. CAD MODEL A simplified CAD model of an old English Cottage is created with some interesting elements for the simulation: ● Two floors ● Chimney ● Windows ● Ventilation above the windows ● Air conditioning
  16. 16. CAD Import Enclosure operation to simulate both internal and external domain. Mesh Generation Automatic + Refinement ● Edges, air conditioning, windows and chimney refinement. ● 8.5 million cells. GENERAL SETUP Wind direction
  17. 17. GENERAL SETUP Analysis type ● CHT analysis. ● Steady state. ● K-omega SST turbulence model. ● Compressible flow. Boundary conditions ● Velocity inlet (1 m/s). ● Pressure outlet. ● Zero-gradient walls for far field. ● Adiabatic wall for the ground and the house. Wind direction
  18. 18. WINTER/SUMMER SETUP WINTER ● 10°C outdoor temperature. ● 22°C indoor temperature. ● 300 kW heat source (fire). ● Floor heating at 25°C. SUMMER ● 40°C outdoor temperature. ● 20°C indoor temperature. ● Inlet cooling at 20°C.
  19. 19. WINTER ● Air enters the room through the ventilation ducts. ● Higher convection at low height. GROUND FLOOR VENTILATION - VELOCITY ● Air exits the room through ventilation ducts. ● Air enters the room through frontal ventilation. SUMMER
  20. 20. ● Air enters the room through all ventilation. ● Air exits through the chimney. GROUND FLOOR VENTILATION - VELOCITY ISOVOLUMES ● Weak convection through stairs. ● Recirculation area in the corner. SUMMERWINTER
  21. 21. WINTER ● Cool air entering the house. ● Smooth transition into room temperature. GROUND FLOOR VENTILATION - TEMPERATURE ● Low amount of hot air entering the house. ● High temperature area due to recirculation (ventilation design). SUMMER
  22. 22. WINTER ● Air exits the room through ventilation. ● Air enters at the front due to external flow velocity. FIRST FLOOR VENTILATION - VENTILATION ● Air enters the room through all ventilation. ● Higher convection at high height. SUMMER
  23. 23. WINTER ● Cool air enters through frontal house side. ● Uniform temperature distribution. FIRST FLOOR VENTILATION - TEMPERATURE ● Hot spot in the corner (ventilation design). SUMMER
  24. 24. High flow acceleration due to large temperature gradient (peaks at 10 m/s). WINTER CHIMNEY - VELOCITY
  25. 25. SUMMARY ● With SimScale, we are able to carry out a complete natural ventilation CFD study. ● Different heat/cooling sources can be modeled. ● Stack effect is captured at different heights and external temperature conditions. ● These features can help to optimize and improve ventilation systems design.

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