Cooling homes…heated pockets
Several parts of India are sizzling in extreme heat conditions. Delhi’s power demand is touching near to 5000 MW even on Saturdays, when several offices are closed and home energy consumption puts pressure on the grid. With temperatures soaring to as high as 46 deg C, use of air-conditioners is almost unavoidable in offices and urban homes. Good old desert coolers can do the magic at one tenth energy and cost, but water is a scarce commodity, and saving water is perhaps more pressing than saving energy. The brunt of the rising energy consumption falls on the high end consumers , such as hotels/offices, but the cumulative impact of saving energy in homes is much higher than by a handful of high end consumers. Residential sector accounts for about 24% of electricity consumption in India, and is a sector that is not under the radar of the Energy conservation Act 2001.
Lighting and air-conditioning are largest load centres in residential sector. Urban India faces equal challenge of housing shortage and increasing energy consumption in homes due to rising aspirations and lifestyles. Continuing in business as usual scenario, residential energy consumption is expected to grow by 5 times in 2020 compared to 2010 levels. Standards and Labelling programme of the government for appliances such as air conditioners/ refrigerators is the only instrument through which we can influence the sector’s energy consumption.
As per the recent census ,National Capital Territory of Delhi has more than 32 lac household., with more than 36 % being 3 room tenements. With reasonable assumptions, daily electricity consumption by air conditioners in Delhi’s residential sector on a peak summer day can be as high as 16 million units (kWh), which is a significant percentage of our daily electricity requirement.
Running one air conditioner (AC) of BEE(Bureau of Energy Efficiency) 1 star level for 8 hours a day requires 9-10 units of electricity which would cost us about Rs 60 per day and Rs 1800-Rs 2000 per month. If the AC is 5 star labelled the cost can be halved. Hence, choice of higher labelled appliance gives direct benefit to consumers. Now a days, invertor controlled ACs are available that can further cut costs. However, it is equally important to pay attention to design and choice of materials and finishes of a building to get maximum energy saving.
In a study conducted by TERI for the National Housing bank, it was calculated that upto 20% energy saving is possible through good design and choice of materials. More than 20,000 apartments were analysed to determine various energy efficiency options that may be incorporated in residential premises. Analysis proved that on an average an apartment can save about 20 units of electricity per sqm (in Delhi like climate). This translates to about saving Rs 10,000 annually in electricity bills for a two bed room apartment using two air conditioners in summer. Insulated light colour walls allow less heat to be absorbed and transmitted indoors. Insulation in wall can be provided by use of light weight aerated concrete blocks (that also use flyash),or use of insulating materials such as extruded polystyrene or mineral wool .
Light colors reflect heat and should be preferred over dark coloured finishes. Roof attracts maximum heat; it should be insulated and have light color finish to reflect heat. Cool roof techniques should be deployed as much as possible. TERI’s experiment on cool roof shows that there can be upto 30 deg C difference in surface temperature between conventional roof and cool roof. If the surface temperature of roof is reduced, lesser heat ingress to space occurs, thus reducing load on air conditioners or other cooling equipment. High albedo paints are commonly available in market that can be easily applied on roof . This measure has major impact on homes that have exposed roof. Roof garden or shading the roof can also have significant cooling impact. Windows are very critical part of any home and care should be taken to avoid leaking windows and use of glass with solar control coatings should be preferred. Windows should be shaded and orientation towards west should be avoided. Light colors should be preferred indoors and daylight use can save enough energy. Often the common area lighting such as lights for staircases/lift lobbies or external spaces are not energy efficient. Since a resident pays the regular maintenance costs, which includes charges for common area lighting as well, it is equally crucial to use efficient lighting using T5 fluorescent lights , LEDs etc for common areas. Provisions through use of automatic controls such as timers should be provided to switch them off when not required .
Choosing the right size of air-conditioner is important. An oversized air-conditioner does not cool room more, and can potentially increase energy consumption. A smaller unit running for an extended period operates more efficiently and is more effective than a large unit that cycles on and off too frequently. AC thermostat settings should be set at 25-26 deg C. AC uses 3 to 5 percent less energy for each degree higher set point above 22°C. Smaller the difference between the indoor and outdoor temperatures, lower will be the electricity consumption. Using an interior ceiling fan in conjunction with AC helps better distribution of cool air. Energy efficient ceiling fans should be preferred.
Cities around the country are dotted with multiple high rise residential buildings. Passing through any prominent airport of the country , I am often intrigued by numerous eye catching advertisements by builders promising lifetstyles ,to lure customers ,that are totally unsustainable and absurd. None of the hoarding and bill board talks about homes being sustainable or having lower cost of operation and maintenance through energy and water saved.
With rising electricity tariffs and gradual reduction of subsidy on diesel, home owners have to pay much higher prices to meet the electricity needs. We tried talking to a few prominent developers from different parts of India, on steps being taken by them to reduce energy consumption in homes constructed by them. Most of them are not aware of the useful measures and are under incorrect impression of high initial cost. Studies show that in order to affect 25-30% operational energy savings, the incremental cost may by 1-4% of cost of construction, but the lifetime savings are enormous. The payback period of energy efficiency measures is maximum 2 years with assured lifelong savings.
Builders and developers often charge premium for apartments that are on lower floors/penthouses/ or that have premium views. Consumers often pay premium on property for reasons that have no connect with any tangible benefit. It is worth trying charging premium for energy efficient homes that actually have tangible benefits through energy saved.
My advice to prospective home buyers would be to ask the developer on energy efficiency aspects that have been provided. Check out the thickness and composition of the wall and evaluate the insulation level, ask for better windows that do not leak and have high performance glass, see if the windows are shaded adequately, check out if the builder is providing star labeled appliances (and ask for higher stars) , see if the place for installation of air conditioners/outdoor units are adequately ventilated and devoid of obstruction. Check out the daylight levels and prefer light color interiors for better light reflection.
If you opt for top floor, ask for roof insulation or cool roof. Solar water heaters can bring down water heating costs significantly and it is mandated by law in several states of India including Haryana and Delhi. Demand moves supply…It is high time that we start demanding better and efficient homes ,as well.
source- The Economic Times