Flashcards
Natural Ventilation 2: envelope flow model
Cards in this deck (23)
- 1What else does stage 3 envelope flow model require/do? It uses the explicit method. - weather conditions - ventilation - openings- internal and external temperatures
- wind speed
- determine required ventilation rates
- calculate areas of openings to give required ventilation rates using envelope flow model - 2In stage 4 off-design calculations, for given openings, it determines flows using implicit method. What needs to be determined?• Fix opening sizes
• Choose off-design weather conditions
– Internal and external temperatures
– Wind speed
• Determine ventilation rates using envelope flow model
• Iteration of flow model required for solution - 3What are the 3 design conditions?1. Buoyancy only
2. Wind only
3. Buoyancy and wind combined - 4Buoyancy flow: - What does it use/include?- Hydrostatic pressure acting across surface.
- Openings allow air to flow into and out of the space
- Change in neutral height with opening sizes
- Identical openings NPL mid- point
- Different opening sizes shifts NPL vertically - 5Buoyancy flow: What is the pressure acting on the external surface (equal to the hydrostatic equation):
- 6Buoyancy flow: If is the internal temperature is uniform (hydrostatic equation acting on interl surfaces):
- 7Buoyancy flow: What is the pressure difference acting on the ith of j openings at height z, is:
- 8Wind driven flow: - Pressure? - Windside, leeward? - Roof?- Pressure distribution across surface of building
- Windward side: +ve
Leeward side: –ve
- Roof may produce +ve and –ve pressure distributions - 9Wind driven flow: Uniform density pressure on surface is sum of hydrostatic equation is? What is the internal pressure? Density is assumed as?
- 10Wind driven flow: What is Cp equal to? What is delta p equal to?
- 11Combined flow: What is the pressure difference acting across ith of j openings at height z? Or?
- 12Flow equation: Air flow through ith of j openings??
- 13What is the continuity equation Why is it needed? What does it state?This equation is fundamentally important to the prediction of a ventilation rate.
It states that the volume of air that enters a building must equal that leaving the building.
- 14What equations must openings have?
- 15See notes for example...
- 16Envelope flow models: For building with more than 3 opennings what must be used? What are the difference between the models?Method 2 is more accurate than method 1.
- 17See notes for explicit example...
- 18See example for explicit buoyancy method...
- 19See notes for example of explicit method for wind....
- 20See notes for combined explicit method....
- 21Implicit method: - Flow? - Neutral height? - Can envelope model be used? - Flow rate?
- 22Example of implicit method?- The Implicit method must be used to predict airflow through adventitious openings because airflow rates cannot be specified in advance.
- Areas can be estimated and so the airflow forgiven weather conditions is estimated. - 23Adventitious air leakage: - What is it? - How does it occur? - Airflow through small openings can e shown through what equation?Cracks and small openings, typically less than 10mm and usually much less.
Occur in joints between the building envelope and components such as windows, doors, through wall ducting and porous walls.
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- Architectural Engineering Flashcards on Natural Ventilation 2: envelope flow model, created by Alice K on 22/10/2019.
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- Alice K
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