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Simple Steps for a Thermally Comfortable House That Everyone Can Adopt

Saswati is the Senior Programme Officer at Greentech Knowledge Solutions Pvt. Ltd and an architect by training who works on building design. She has previous experience with an architectural firm (Deependra Prashad Architects & Planners) and is a certified GRIHA trainer and evaluator. Saswati specialises in energy efficient building design, program management, building energy code development, and day-light analysis. She has a B. Arch from NIT, Bhopal and M. Plan from SPA, Delhi.

The phrase “a roof over our head” often conjures up an image of a house as something that protects us. While traditional achitecture did focus on keeping a house comfortable by keeping the elements – like sun, winds, and rain – out, over time, the focus on thermal comfort has waned as architechture became generic and outdoor elements had less influence on the design of homes.
This can clearly be seen in the case of air-conditioning. With air-conditioners getting more and more affordable, we forget to design our homes in response to our climate. Most homes today are not inherently designed for thermal comfort, leaving residents to “deal” with the heat or resort to air-conditioning.
But, we do need to remember that most of India still cannot afford air-conditioning. At the same time, making ACs affordable is not a viable option for an energy-efficient future. With this reality, we need to return to the forgotten focus on building design and the building envelope as the means to provide thermal comfort to the extent possible in the given climate.
For this to happen, buildings need to be designed to do 2 things:

  • Reduce heat gains into the house (in hot climates), and reduce heat loss from the house (in cold climates)
  • Allow for adequate natural ventilation when needed

Without getting into specific design details, these 2 requirements can boil down to a few simple design guidelines:

  • Orient your home considering the sun-path and wind direction. For e.g.
    • In hot-dry and composite climates, longer faces of the building, including most windows, should preferably face north–south direction, to minimise solar exposure on walls. East and west faces get high solar radiation is summer.
    • In warm-humid climates, longer facades, and windows, should generally be oriented at an angle (usually ±45 degrees) to the most prevalent wind direction. This is done to reasonably strike a balance between minimising solar exposure and improving air movement.
    • In cold climates, longer facades of the building should preferably face north–south direction, to allow the low winter sun in winters while cutting off high summer sun.
  • Insulate your roof. In hot areas, insulation will reduce the sun’s heat from coming into the living spaces from the roof. In cold areas, roof insulation will reduce heat loss from the space to the outside.
  • Additionally, in hot areas, shade your roof or put a high reflective roof finish. Shading will reduce solar radiation falling on your roof. A reflective finish helps by reflecting off much of the sun’s radiation.
  • An insulative wall will help in hot-dry, composite and cold climate zones of India. You can do this by using insulation material on conventional walling materials like brick walls and RCC walls; or use masonry blocks with better insulative properties, like Autoclaved Aerated Concrete (AAC) blocks to build your walls.
  • In warm-humid regions, highly insulative walls are not very helpful as the day-night temperature difference is not much. Here, it would be better to have larger window openings to let in more breeze.
  • Optimise your window sizes to allow enough daylight and ventilation. In hot areas, do not go overboard with your window glazing as they let in a lot of heat too.
  • Shade your windows to cut off solar radiation in hot areas. For most of India, north and south faces can be adequately shaded in summer by a horizontal overhang or “chhajja”. For east and west faces, external shades that can moved (think bamboo “chiks” outside your window) work best.
  • Seal your windows properly, especially in the cold climate where cold drafts enter homes.
  • Use casement windows (or windows with hinges) instead of sliding windows. For the same window size, casement windows have more openable window area than sliding windows. Hence better ventilation potential.

While thermal comfort is an essential requirement for any home, these simple rules are often overlooked for other superficial comforts. Keeping these points in mind next time you buy or rent a home, or while designing your home, can not only give you thermal comfort but can also help you save on your electricy bill.

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On the way to easy accessible calculation methods with Computational Fluid Dynamics (CFD) freeware for optimisation of natural ventilation in dense urban context in India

Pierre Jaboyedoff has more than 30 years of experience in energy-efficient buildings and solar energy applications. He is a partner in Effin’Art Sarl and is an expert in the development and application of high-performance, innovative, and climate-responsive solutions ranges from industry to data centres. Pierre was instrumental in the establishment of the Rolex Learning Centre, one of Europe’s lowest energy consuming buildings. Pierre has also worked extensively in India, to implement projects related to energy efficiency and renewable energies in various economic sectors since the early 1980s.

Majority of the residential buildings in India are not air-conditioned and rely on natural ventilation. Due to population pressure and high land cost, most of the new housing construction in urban areas, is in the form of multi-storey apartment buildings, located close to each other. The natural ventilation (particularly the cross-ventilation) inside these buildings is greatly influenced by the access to wind (air velocity and pressure) on the façade of these buildings. Thus, proper massing of residential buildings, that ensures good access to wind on the facades is important for cross-ventilation to work. It is possible to simulate the air flow around a building using Computational Fluid Dynamics (CFD) software, which can help the building designer in assessing natural ventilation potential. However, commercial CFD software are expensive. BEEP aims at developing a freely available (open-source) CFD software for simulating air flow around buildings. This blog reports initial work done under this initiative.

 The Swiss PMTU (EffinArt) has initiated a collaboration with the University of Applied Science of Sion (HES-SO Valais, Dr. Jean Decaix) to develop a freeware CFD with a dedicated interface for the analysis of the building massing alternatives in large multi-storeys project. Beside this collaboration, EffinArt has got successively two interns (final master year students of ETHZ Praharsh Pai Raikar , and EPFL, Grégory Duthé, with CFD background). These two internships have been directed to get first useful new knowledge gains for the student and at the same time to get some useful results for BEEP. The two interns contributed in exploring and checking the feasibility of the development of an easy to use CFD freeware for natural ventilation which could be eventually distributed to a large audience for residential large projects. Both the interns also interacted with Dr. Jean Decaix, from HES-SO, Sion. We present here few of results of their work as interns.

The interns worked on comparing the simulation results using a free software (OpenFOAM) which BEEP plans to use for the development of the freeware, with the experimental results from a wind tunnel and a commercial CFD (Flovent) software.

Figure 1 shows the arrangement for the wind tunnel test. It shows a 25 m tall building located in the wind flow. Figure 2 shows the results of the wind tunnel tests and the results from simulation using the two software. The results are shown in terms of wind velocity at a plane located on the front façade of the building (façade facing the wind flow) and the building height.


Figure 1: view of the single building in the wind tunnel with 1000 sensors in perspective and elevation

Figure 2: wind velocity (u) just before the windward façade as a function of the height (z), the building is 25 m high at x=-11.4 m

Figure 3: perspective and top view of a real project in Indore (1700 dwellings)

Figure 4: Velocity magnitude contours in the z = 10 plane. Top: simulated with FloVENT. Bottom: simulated with OpenFOAM

One can see that there is a good agreement between measured velocities and simulation by the two CFD. A further comparison between the commercial and free CFD is shown above.

One can see that the velocities are in good agreement for a first comparison.

As mentioned earlier, through a collaboration with the University of Applied Sciences (Dr. Jean Decaix, HES-SO Sion) BEEP intends to develop a methodology and a tool to be available by 2020 end as a freely distributable software allowing a large audience of non CFD specialists to compute wind and pressure distribution on facades of building allowing to assess the natural ventilation potential with a much better accuracy than practiced today.

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Shading Options You Can Consider if You Live in India

Prof. Ashok B. Lall is an eminent architect and principal of Ashok B Lall Architects in Delhi. The firm has executed several well-known projects in India, including the headquarters of Development Alternatives in New Delhi. Prof. Lall is a strong advocate of low energy sustainable architecture. He also engages in architectural education and is a visiting professor at Guru Gobind Singh Indraprastha University, New Delhi.

This is the second part of a 2-part series on using shading to keep your home naturally cool.  You can read the first part titled External Shading Should be Used More Often to Keep Your Home Naturally Cool here.

When we talk about using shading for thermal comfort, we need to go back to the basics to understand that keeping a building cool in hot climates is about how you let daylight in without letting the sun in directly. For this we focus on the fact that the sun moves in a particular trajectory across the sky depending on where you live. As seasons change and the time of day changes, the intensity of the sun will also change. So how shading in used in your building design needs to respond to this trajectory and changes in movements.

A very effective solution to deal with this is the use moveable shades. An External Moveable System, or what we call external movable shading system (EMSYS), works for buildings with any orientation, at any time of the day, and at any location. However, EMSYS is not as easily available in Indian markets as they are in more developed countries. BEEP is working with innovators and technical experts to come up with options that fit the Indian context. It is expected that there will be significant development on what kind of EMSYS homeowners can opt for in the future.

Depending on your requirement you can also strike a happy balance between static and moveable shade. In India, this will be more cost effective and better from a durability and maintenance point of view. A great example of a combination of moveable and static shades is the chiks that are used in many Indian homes. They are easy to install, roll up and down as needed, and are not too heavy on the pockets.

Unfortunately, this kind of information, more often than not remains with the architects, the building industry, and those with technical knowhow.  Using shading to make homes more thermally comfortable is not a new idea. But it is not being used as much as it should be, given the weather conditions we usually have in India. For this to change, those who are designing and building homes will have to be more creative and take a lead in making homes more thermally comfortable, which also being energy efficient. Once this happens homeowners will also experience that simple solutions, such as using shades to keep homes cool, are options that benefits their pocket as well as the environment.

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