Stack Effect and Ventilation System Design

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

1. STACK EFFECT AND
VENTILATION SYSTEM DESIGN
JON WILDE and JESUS VILAR

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. 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. 1. Benefits of Using Simulation
2. Introduction to SimScale
3. Stack Effect
4.Setup
5. Live Demonstration
6. Results Summary
7. Q & A

9. ACCELERATE YOUR
DESIGN PROCESS

Easily test performance, optimize
durability or improve design efficiency
with cloud-based simulation.

10. ALL-IN-ONE
Structural mechanics,
fluid dynamics, and
thermodynamics.

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Chat, phone and email.
Consultancy, webinars,
and training.


COLLABORATION
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benefit from public projects,
and share know-how.

FAST & EASY
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on any device thanks
to cloud technology.

COST-EFFICIENT
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an upfront investment.


SECURE
High security with
government-approved
Advanced Encryption
Standard (AES).

11. STACK EFFECT

12. 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

13. 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

14. 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.
●T
o
, T
i
= outside/inside temperature.



Stack effect in chimneys

15. 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.

16. SETUP

17. 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.

18. 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

19. 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

20. 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

21. 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

22. 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.

24. 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

25. ●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.























SUMMER
























WINTER

26. 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

27. 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

28. WINTER






















●Cool air enters through frontal house side.
●Uniform temperature distribution.











FIRST FLOOR VENTILATION - TEMPERATURE










●Hot spot in the corner (ventilation
design).























SUMMER

29. High flow acceleration due to large temperature gradient (peaks at 10 m/s).























WINTER












CHIMNEY - VELOCITY

30. 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.