Passive Strategies: Natural Ventilation (b)

Last week we started our series on Passive Strategies in Buildings. We kicked off with Natural Ventilation (a)Why it’s needed, What needs to be doneHow and Factors important for it.

This week we look at Strategies and related Issues for Natural Ventilation.

  1. Zoning
  2. Orientation and Form
  3. Building Depth
  4. Fenestration
  5. Advanced Strategies

(1) Zoning

Building functions can be zoned according to the ventilation strategy for effective management and energy conservation. This is seen in Akshay Urja Bhavan1 where spaces are divided into zones according to setpoints – Apex, Controlled and Passive. Only around 12% of the area is air-conditioned. Mist cooling systems are used for the Controlled and Passive zones.

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(2) Orientation and Form

Buildings should preferably be oriented between 0o and 30o with respect to the prevailing wind direction2. The building form can incorporate courtyards or verandahs (transitions zones between inside and outside) for increased ventilation and thermal comfort. These features temper down the harshness of the exterior environment, providing shade and cool breezes in summer.

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(3) Building Depth

unit thick principle
Unit Thick Principle in 2 projects by WOHA

A building depth of around 15 meters or less would enable Natural Ventilation and Daylighting. This is an assumption based on our research of many buildings by WOHA applying their Unit thick Principle. Some buildings may not be able to achieve less depth due to larger functions such as Industrial labs.

Solution | Fragmentation of Form – Such buildings could employ courtyards or atriums to break the overall form, thus enabling light to penetrate or air to flow better. (eg. Cleantech One) Fragmentation of form is also seen in Indira Paryavaran Bhavan3, where two North-South oriented blocks are separated by a centrally running  public spine.

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(4) Fenestration

  • Location, Sizing, Area – The location and size of windows, should take into account the wind direction and the ‘Living Zone’. The total area of openings should be a minimum of 30% of floor area2.
  • Window to Wall Ratio – The Window to wall ratio (WWR) should fall between 20-40% for Commercial buildings. In any case, it should not exceed 60%4.
  • Operable windows – The windows should preferably be operable with a staggered alignment. Operable windows may present certain issues. In the case of hotels for example, people might leave windows open when the air-conditioning is on, which would affect energy costs. Operable windows could also have safety implications.

Solution 1 | Sensors – Some hotels install sensors that automatically shut off air-conditioning when windows are opened.

Solution 2 | Individual Project Detailing – Safety concerns would need to be addressed in projects individually, through railing design details, selective openings or special locking mechanisms.

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(5) Advanced Strategies

(i) Air Earth tunnels

neemrana

A 16 km (once campus completed) tunnel network of Air Earth tunnels, will be running 4 m below the ground in NIIT University, Neemrana Campus. Surface temperature and seasonal variations do not penetrate below this depth, keeping air temperature constant throughout the year. Fans will pull cool air through these tunnels. This would then be taken through precipitators to eliminate dust and would be supplied to the building through ducts. The result! – Pleasant 25oC temperatures indoors, without the use of air-conditioning, when temperatures outside are nearing 50oC5.

(ii) Wind Tower

These are utilized widely in desert climates (eg. Iran, Saudi Arabia). Tall towers are built with openings facing the prevailing wind direction. The openings are narrow and the towers may contain misters or other moisture creating devices. As the tall tower catches winds, air moves down the tower, cooling on the way and is used in the building. A similar system using Shower Towers is used at DPR Office, Phoenix.

(iii) Stack effect

According to the principle, warm air from an area would rise, making space for cooler air. This would generate a loop of air circulation. This effect can be seen at building scale or even at room level. In Indira Paryavaran Bhavan, the central courtyard spine coupled with well placed building punctures, generates the ‘Stack Effect’ at the building scale. The IRRAD Building, although using air-conditioning, is utilizing a similar principle. The vents are placed near the floor, instead of the ceiling. Cool air enters the room at a lower level and it rises as it become warm6.

(iv) Displacement Ventilation

In Neemrana University, the cool air from ducts is introduced at lower levels in rooms. This pushes warm air in the room upwards, which is then exhausted through openings in higher parts of the spaces. It is similar to the stack effect, but here an additional push is being provided by the introduced cool air, to get the circulation loop going.

(v) Wind Scoops

Wind Scoops like the one used in CapitaGreen can channel air into a ‘Cool Void’. This brings cool air from a higher altitude, deeper into a high-rise building. Air flow, such as that channeled by CapitaGreen maybe blocked by surrounding buildings in a different scenario.

Solution | City Planning and Studies – This leads to the need for city planning and studies like Computational Fluid Dynamics (CFD) to ensure these strategies are workable at a city level. This would help avoid “dead air zones”, wind canyons and other undesirable wind related events. This becomes especially important in city centers with greater density and multiple high-rise structures.

(vi) Solar Chimney

The DPR Phoenix Regional Headquarters in Pheonix, Arizona use solar chimneys to exhaust warm air from the building.

(vii) Evaporative cooling

This technique utilizes the latent energy used to convert liquid to gas. As water evaporates, its phase changes, which results in a cooling effect. This technique has been used widely in desert coolers.

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That’s all for this week. Hope this was useful! As always, please let us know your thoughts, suggestions, queries, opinions. Your views will make this exploration richer!

Thank you!

 


References

  1. BEE, USAID, PACE-D. Case Studies – Akshay Urja Bhawan. NZEB. http://www.nzeb.in/case-studies/detailed-case-studies-2/akshay-urja-bhawan-case-study/.
  2. BEE, USAID, PACE-D. Knowledge Centre – Natural Ventilation. NZEB. https://bit.ly/2QhxxoD. Accessed September 9, 2018.
  3. CA(NDR), CPWD. Sustainable Architectural Built Environment.
  4. GRIHA, TERI. GRIHA V-2015.; 2015. http://www.grihaindia.org/files/GRIHA_V2015_May2016.pdf. Accessed September 9, 2018.
  5. Bhandari P. Let buildings breathe. Times of India Jaipur. https://bit.ly/2MH0kzV. Published 2009.
  6. Somvanshi A. Simply creative. DownToEarth. https://www.downtoearth.org.in/coverage/simply-creative-39818. Published 2015.