How effective is double skin façade in preventing building heat loss
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How effective is double skin façade in preventing building heat loss

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How effective is double skin façade in preventing building heat loss How effective is double skin façade in preventing building heat loss Document Transcript

  • T: +65 6722 9388 F: +65 6720 3804 E: enquiry@iqpc.com.sg W: www.facadechina.com HOW EFFECTIVE IS DOUBLE-SKIN FAÇADE IN PREVENTING BUILDING HEAT LOSS DARWIN JAYSON MARIANO Developing high performance building facades requires implementing efficient design, engineering techniques and material technologies to be effective. Certainly, one of the most talked about concept lately is the use of double-skin facades. There are several types of skins: Insulated Glass Unit or IGU Wall This is technically a double-skin because there are two layers of glass. However this is the basic window component in all projects that strive for any sustainability. It is the base case for all exterior walls built today. The Cavity Wall The Cavity Wall is where there is more than 1.0m between the two skins. The inner skin is an IGU and the outer skin is single or laminated glass. The Vented Wall The Vented Wall is where there is less than 300mm between the two skins. Either inner skin is an IGU and the other skin is single or laminated glass. The Double-skin facade (Cavity type) is a system of building consisting of two skins placed in such a way that air flows in the intermediate cavity. The ventilation of the cavity can be
  • T: +65 6722 9388 F: +65 6720 3804 E: enquiry@iqpc.com.sg W: www.facadechina.com natural, fan assisted or mechanical. Apart from the type of the ventilation inside the cavity, the origin and destination of the air can differ depending mostly on climatic conditions, the use, the location, the occupational hours of the building and the HVAC strategy. THE GOOD The last few years have seen an uptick in the use of double-skin facades, or what others call a “skin within a skin”, throughout the world. This can be attributed to the fact that it provides key advantages such as durability, ecology, easy circulation of fresh-air and use of natural resources. One important factor to note is that the type of double-skin façade determines the type of air circulation. In fact, the most remarkable systems are those designed in such a way that it permits natural air circulation while also using solar energy, converting it into electrical energy. These are some of the most popular benefits of doubleskin facades: • • • • Natural ventilation Better acoustic insulation improve noise protection Reducing heating energy requirements Reducing cooling energy requirements THE BAD However, many critics of this system also point out that the advantages of double-skin facades are not so clearcut. Many argue that similar insulative objectives can be met by using conventional high-performance, low e-windows. In addition, the construction of a second skin could induce significant increase in materials and design costs. From a technical point of view, it can also be said that building energy modelling of double skin facades is inherently more difficult due to varying heat transfer properties within the cavity. Some of the disadvantages are: • • • • • Twice the area to build, repair, and clean High first investment cost payback period is 5+ years More material in the building Requires fire separation in some cases Not every climate is fit for a double skin cavity wall. The climate requires a 40 deg. C change from winter to summer to achieve the benefits Putting advantages and criticisms aside, many architects and engineers consider this option for some of the most iconic buildings today – seemingly proving that the benefits far outweigh the possible drawbacks. One such project is the Shanghai Tower, a supertall skyscraper in China which, once completed in 2014, will be the tallest building in China and the second tallest in the world.
  • T: +65 6722 9388 F: +65 6720 3804 E: enquiry@iqpc.com.sg W: www.facadechina.com THE BEST To get some perspective about the effectiveness of double-skin facades, especially in the context of preventing building heat loss, we spoke with Marshall Strabala, Shanghai Tower’s chief architect: “Once finished, the Shanghai Tower will be the world’s tallest double-skin building. And so from the beginning, we try to minimize the amount of façade on the building in order to decrease the cost and increase the value of the façade. ç ç “With regard to one of its key benefits, it’s not only just about preventing heat loss; it’s also about limiting heat gain. We all know that temperature usually goes from a higher state to a lower state. This is called entropy. In the summer, you cool the inside of the building through these steps: 1. 2. 3. 4. 5. Bring the air into the building, and then Dehumidify the air Cool the air to the desired temperature Push the air to the desired location. Then expel the air to the outside and start again Repeat this process about 2-5 times an hour depending on the location. “The latent heat of the this cool air wants to migrate to the outside in the summer. This is controlling heat gain. In the winter, it’s the opposite. It’s the hot air on the inside that wants to migrate out of the building where it is cold. The air temperature wants to equalize state of energy with the larger mass of nearby air. “What you’re trying to do is keep the temperate from passing through the façade. In the case of Shanghai Tower, what we do is normally done, as described above: we dehumidify it, then we cool it, then we push it through the fans to the office. Then instead of throwing that air out, and starting the process all over again, we use it a second time by “spilling” or diverting the cool air into the interstitial atrium space. We use it a second time, and why not? It already has embodied energy that we can use. And we then use it a third time in a hydronic heat exchanger that pre-dehumidifies the incoming air. “For example, we take air that is say, 35 degrees outside, we bring it in, we dehumidify it to about 30deg C. Then cool it down from 30 to maybe 18. We pump that through the fans, we deliver it to the office and by the time it gets to the office it is back up to 20. Then as it sits in the office for 30 or 40 minutes, it’s back up to about 22/24deg C. Then instead of throwing that out, because we have a lot of embodied energy, we use it a second time in the atrium. And we spill it at the top and the bottom so we actually allow the atrium to mix the air by natural convection. “So you can have a situation where the outside temperature is 35, the atrium might be 30/28 and the inside temperature of the office is 24. So there’s a temperature gradient across the facade. This temperature gradient is what gives us a very high insulative value in the façade.”
  • Marshall Strabala AIA AFAAR LEED ap. is the co -Founder and Design Partner of 2DEFINE Architecture. He is an American architect, living in Shanghai, who has lead the design team of three of the ten tallest “constructed” buildings in the world. For the last three years, Strabala has been the principal of his own architectural firm, with over 30 years of combined experience. He was an Associate Partner in Chicago at SOM, and the only Director of Design M. Arthur Gensler Jr. & Associates, Inc. Hear more from Marshall Strabala and other distinguished speakers at the 3rd Annual Facades Design and Engineering China 2013, happening on 18-21 June at Shanghai, China. www.facadechina.com About the Author: Darwin Jayson Mariano is the Online Content Manager and Regional Editor - Asia for International Quality & Productivity Center (IQPC), a leading producer of events and conferences for business leaders around the world. Connect via LinkedIn sg.linkedin.com/in/whoisdarwin or email darwin.mariano@iqpc.com.sg Disclaimer: Please note that we do all we can to ensure accuracy and timeliness of the information presented herein but errors may still understandably occur in some cases. If you believe that a serious inaccuracy has been made, please email darwin.mariano@iqpc.com.sg. This article is provided for information purposes only. IQPC accepts no responsibility whatsoever for any direct or indirect losses arising from the use of this report or its contents.