Surprised by high electricity bills despite having bought that air-conditioner with a 5-star energy efficiency rating? Blame the hot summers for it.

A recent study by Delhi-based Centre for Science and Environment found that split AC's having five-star ratings become worse than air conditioners with lower ratings when the temperature is above 40 degree celsius. The study was conducted after 5-star rated split room air conditioners (RACs) of three popular brands, Voltas, LG and Godrej were tested by National Accreditation Board for Testing and Calibration Laboratory under normal and maximum temperature conditions.

Here are some of the findings of the study:

A representational image | Source: Reuters

  • With the increase in the outdoor temperature, the energy performance drops. It means a 5-star rated air conditioner performs worse than a 1-star rated one when the external temperature reaches 45 degree celsius.
  • When the outdoor temperature increases, power consumption also increases. In peak summers with afternoon external temperatures in the 45-50 degree Celsius range, an RAC unit consumes 10-28 percent more power.
  • Cooling capacity of an AC decreases when the outside temperature increases. An 8-21 percent drop has been measured when the temperature reaches 40-50 degree Celsius.
A representational image | Source: AFP

  • When users lower the temperature more that it is required, the efficiency also gets affected. The performance of a 5-star rated AC becomes equivalent to that of a 2- or 3-star rated AC when the internal temperature is lowered below 27 degree celsius, which is the prescribed thermal comfort level according to the National Building Code.

Anumita Roychowdhury, executive director-research and advocacy at CSE, says that the findings undermine the claims of energy savings and monetary benefits.

"In monetary terms, running a 5-star RAC for a couple of hours in the afternoon during summers under normal conditions should cost about Rs 490 a month. But with worsening of its energy performance, it can cost anywhere between Rs 660-780 (based on Delhi’s non-subsidised tariff rate of Rs 5.8 per unit). It will also cool about 30 percent less," adds the report.

A representational image | Source: Reuters

The CSE study has also come up with solutions which can address the issue. Here are some of the suggestions:

  • An additional energy saving test by the Bureau of Indian Standards (BIS) based on multiple higher temperature range relevant for different climatic zones for testing and rating of ACs. The result of the tests should be made public and star ratings should be based on them
  • Declaration of the annual energy consumption based on cooling capacity tests by manufacturers
  • Promotion of buildings having architectural designs that reduce thermal load on buildings

You can read the full report here.

(Feature image source: WikiCommons)