Renewable Energy Systems

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Renewable Energy Systems
Natural Ventilation Using Wind Towers or Chimneys
John Seryak
4/24/2002
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Why is a Wind Tower Useful?

• A wind tower uses natural ventilation to
  displace the need for air-conditioning equipment
  and energy consuming fans.

How Does a Wind Tower Work?

• A wind tower utilizes pressure differences to
  create a draft. There are four ways a pressure
  differential can be created
• Temperature differences between inside and
  outside air
• Pressure difference from stack height
• Bernoulli effect of wind on a sloped roof
• Venturi effect of constricted airflow through
  chimney exhaust opening

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What Does a Wind Tower Look Like? Do They Really
Work?
Yes! They Do! Check out the Queens Building of De
Montfort University
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Model for Simulation
Ft Ac x (Pi Po) Ac x h x ?o x g
Fst Ac x h x ?i x g
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Model for Simulation
Fnet Ac x h x g x (?o ?i)
? P / (R x T)
Student Project Equation
Pnet h x g x Pbar x (1/To) (1/Ti) / R
ASHRAE Published Equation
Pnet ?i x g x h x (Ti/To 1)
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Model for Simulation
Velocity v(2 x Pnet/ ?)   Volume Flow Rate
(VFR) Velocity x Ac
Ti (Qgain) / (Aw/Rw Ac/Rc VFR ? Cp)
To
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Model for Simulation
Qgain Qwalls Qventilation Qceiling 0
Qgain Aw/Rw x (Ti To) VFR x ? x Cp x (Ti
To) Ac/Rc x (Ti To) 0
Ti (Qgain) / (Aw/Rw Ac/Rc VFR ? Cp)
To
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Results

• Velocity
• Student Project 0.61 m/s
• ASHRAE 0.61 m/s
• Physical Experiment 0.43 m/s

• Temperature
• Student Project 305.1 K
• ASHRAE 305.1 K
• Physical Experiment 304.2 K

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Results Auditorium Simulation

• With No Ventilation, Internal Temperature
  reaches 323 K (121 F).

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Results Auditorium Simulation

• Temperatures decrease asymptotically, 294 K (69.5
  F) can be Obtained Inside by Using a Chimney Stack

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Results Auditorium Simulation
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Results Auditorium Simulation
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Results Auditorium Simulation
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Results Auditorium Simulation
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Recommendations

• Add Bernoulli and Venturi effect algorithms to
  simulation.
• Add algorithms for chimney placement and number
  of chimneys.
• Rerun physical experiment to calibrate to
  simulation. Run physical experiment in wind
  tunnel to calibrate to Bernoulli/Venture model.
• Use Esim and year round simulation to calculate
  a simple payback.

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