Paint the town white!

Summers are getting hotter. Air Conditioners are expensive. So are energy bills - which makes ACs un-affordable for many. Painting the roof white is a low cost solution to beat the heat relatively. This is for rooms and spaces where the roof is exposed to direct Sun light. A little bit of tech gyan first. Heat and light from the Sun travel together. A body is black in color because it absorbs all light falling on it. Hence it absorbs all heat too. A white body on the other hand reflects all light (and so heat) falling on it. In simple words, white is coolest, black is hottest. A dark concrete roof absorbs and transmits a lot of heat during daytime and also radiates during the evening. On the other hand a reflective surface like white painted roof reflects away the light and heat and is often several degrees cooler. Indoors can become 10-15 degrees (Celsius) cooler after being coated with white paint. The hot oven-like feeling on entering rooms during afternoon and evening can be eliminated using this technique. For buildings having air conditioning, energy bills will reduce as it takes lesser energy(also less power plants, less CO2) to cool a cooler room than a hot one. 

White roofs can also help reduce global warming too. According to a research by Department of Energy, USA, white roofs not only reduce air conditioning loads of a building but also help reflect back the solar irradiation back to space. Darker surfaces on the other hand absorb the heat during Sun shine, and radiate it afterwards making cities and the surroundings hot. This is urban heat island effect. These radiations being in different wavelength than the ones incident are not rejected back to space. Studies suggest that if roofs of all buildings in the whole world are painted white, global warming can be reverted. Yes, lower energy bills, a comfortable interior & also saves the environment.

The options:

White paints come in different forms. Traditionally limestone(choona) mixed with adhesive is available commercially in India. Lime is cheap and easy to apply. Other alternative is white cement paint, which is affordable and also is slightly better in resisting rains than lime. Do note that these two paints have to re-coated every year. Another alternative is elastomeric paints. Some Indian brands like ICI Dulux and Berger Paints sell it. These paints form a rubber like stretchable membrane on the surface and are highly resistive to rains. It can last 3-5 years. The downside is that it costs a lot, generally 20 rupees per square feet area. In contrast, lime and cement paint come at around just 1-2 rupees per sqft including labor charges.  

A permanent but expensive alternative is white ceramic tiles. They come at 50-60 rupees per sqft at the least. They can last a lifetime and are much easier to clean, and your terrace looks beautiful too. The roof can be water proof too if grouted properly. It provides an all year cooling as paints are usually washed after rains, and in our tropical climate, we often need air conditioning for more than 6 months in the year. Any white surface (both paints and tiles) provide a longer life to the roof, as expansion and contraction due to heat is greatly reduced. Crack formations are minimized too. Solar Reflectance Index (SRI) values on commercial products are a good way to compare - higher the better. For tiles, vitrified variety is better suited to outdoors due to lower water absorption capacity. 

White is the new green. Cars too in white color save fuel as compared to black ones. Yes your walls and everything exposed to Sun is better off in white. We do white cement paint every year and it is a big relief in this sultry Odisha heat. We have temperatures touching 45 degrees Celsius every summer. White paint works beautifully here. Let us know if you have done it, your experience or any questions if you have - we will be happy to answer them. So cool interiors, climate change arrest, longer roof life – when are you going white?

Electric buses - ideal for our cities

BYD K9 electric bus in London

The Bangalore Metropolitan Transport Corporation has recently started trial runs of Electric Buses for its vast public transportation network. Electric Buses are slowly gaining acceptance and have been adopted in few cities around the world. The most popular of these buses is the E9 – manufactured by BYD – a popular Hong Kong based battery and automobile company. Electric buses are commercially in use at various places in China. They are in trial at Utah, Chile, London, South Korea.

The batteries that BYD uses are Lithium Iron Phosphate, developed in-house. These give a range of 250km per charge, which is quite respectable for a day’s intra-city route. They can be charged in 6 hours at normal rate and 3 hours for a quick charge. Ideally electric city buses can be fully charged overnight or given short bursts of high speed charging during terminal stops. Another possibility is wireless induction charging. Read more about that here. It consumes 100 kWh in an hour and that translates to just Rs.4 per km, as compared to Rs.20 per km in diesel buses. The battery is expected to last 6000 recharging cycles or 1.5 million kms, thereby capable of saving nearly a crore of rupees before a battery swap. This is considering the fact that there are hardly any maintenance costs in electric vehicles. Unlike petroleum operated vehicles, they do not have filters, oil changes, turbochargers, etc. These expenses are a lot in heavy vehicles like buses, and the time taken to service also accounts for revenue loss. In fact there is only one moving part in the electric motor.   

Electric buses are an ideal choice for cities with dense traffic and otherwise too. They are very silent. A V8 roar may be appreciable in a sports car, but an old bus noisily accelerating and blowing soot on your face is never charming.  Apart from that, electric buses have regenerative braking. This is a technology that helps vehicles recover the kinetic energy of motion that is otherwise lost during braking. What happens is when the foot is left off the accelerator, the motor acts in reverse as a generator using the motion to top up the excess energy into the batteries. This also reduces the need of brakes in predictable situations (Bus routes = more predictable), thereby elongating the life of brake pads and shoes by a huge margin. This technique is very useful in stop-start situations which are very high in dense city traffic. Going downhill, a Mahindra Reva e2o (an electric car from India) has been able to recover 20% more range on the return journey on a particular trip to hilly region.  

Then there is the usual electric advantage of not wasting fuel at traffic stops – they use energy when the accelerator is pressed. Hence there is no wastage of energy like internal combustion engines which have to kept on during idling and consume fuel in that process. This is particularly beneficial in dense cities and typically for buses as they stop for loading and unloading of people. This frequent dis-acceleration also helps in regenerative braking. Also electric motors produce 100% torque at 0 rpm. This high torque nature is more suited to heavy vehicles like buses and trucks.

With rising costs of polluting petroleum, the operating cost difference will widen further for sure. Electric buses at present scenario are able to recover the initial investment fast too. A proper charging infrastructure is highly necessary. The grid needs to get greener. Dirty coal needs to be replaced with renewable sources like hydro, solar and wind energies. Karnataka produces a fair share of green electricity. These low floored, air conditioned electric buses will go head-on with the red Volvo city buses and are expected to be even more comfortable than them. They will also make the Bangalore air more breathable. We hope this model is a success and it is replicated in more cities throughout the country.