New study by Centre for Science and Environment shatters the myth of star-rated ACs

July 27, 2016

New study by Centre for Science and Environment shatters the myth of star-rated ACs

Your so-called ‘5-star’ rated split AC becomes energy-inefficient as soon as the temperature soars over 40oC. In fact, it becomes worse than a 2- or 1-star rated AC – show results of study

  • When the outdoor temperature increases to 40oC, a 5-star rated room air conditioner (RAC) starts performing like a 2-star rated RAC; at above 45oC, it is worse than a 1-star RAC  

  • A 5-star RAC is supposed to save 20-22 per cent of your energy cost compared to a 1-star RAC, claims the Bureau of Energy Efficiency (BEE). But the CSE study shows in peak summers, when temperatures are in the 40-50oC range, a 5-star RAC can start consuming 10-28 per cent more power than its declared capacity 

  • Cooling capacity of room ACs also drops by about 30 per cent in peak summers, which means a 1.5-tonne AC acts like a 1-tonne AC  

  • Energy efficiency further deteriorates when users lower the room temperature artificially to levels below 27oC 

  • Bureau of Indian Standards (BIS) and BEE must tighten energy efficiency standards and test procedures to reduce margin of deterioration in the real world  

  • This is urgent as ACs contribute the most to peak electricity demand in cities and to electricity budgets of households. With extreme weather events, heat waves and heat island effects becoming common, local temperatures are expected to be much higher than the overall city levels – and this will trigger more use of ACs

New Delhi, July 27, 2016: “We wanted to find out how AC units perform under different outdoor temperature conditions and how that affects the energy savings from the star labeling programme of the Bureau of Energy Efficiency (BEE),” says Anumita Roychowdhury, executive director-research and advocacy, Centre for Science and Environment (CSE), while releasing the Centre’s latest study on air conditioners here today.

CSE released the results of its lab tests of energy performance of popular 5-star rated split room air conditioners (RACs) under normal and maximum temperature conditions. The tests were carried out in a National Accreditation Board for Testing and Calibration Laboratory (NABL)-accredited laboratory based in Delhi.

The tests indicate that when the outdoor temperature increases to 40oC, a 5-star rated RAC starts performing like a 2-star rated RAC; at above 45oC, it is worse than a 1-star RAC. In peak summers, when temperatures are in the 40-50oC range, a 5-star RAC can start consuming 10-28 per cent more power than its declared capacity -- thus adding to the peak load demand on the electricity grid.

Says Roychowdhury: “These tests have been carried out in view of the fact that air conditioners are responsible for peak energy consumption across cities. Their use increases when outside temperature is high.” In Delhi, air conditioning accounts for about 28 per cent of the total monthly electricity consumption during the hottest months. According to the BEE, ACs are responsible for almost 60 per cent of the Delhi’s peak electricity demand.

CSE researchers point out that while it is not unusual for RACs to consume more power to cool and suffer energy efficiency losses under climatic stress, the BIS and the BEE will have to address this with more stringent standards and test procedures to minimise deterioration in the real world. This, especially when extreme weather events and heat waves are expected to get more intense in future in many parts of India.  

About the CSE study
CSE commissioned an independent NABL-accredited laboratory to test RAC units. Three popular 5-star split RAC models – from Voltas, LG and Godrej -- were bought from the market and tested for their energy efficiency and cooling performances using the balanced ambient calorimeter method. These three brands cover about 50 per cent of the Indian RAC market. The tests investigated the following – (1) the effect of high external temperature on real world energy performance; (2) effect of lower internal room temperature on energy performance; and (3) effect of higher external relative humidity conditions. 

Only split RACs were selected for the study – because as per the Indian Society of Heating, Refrigerating and Air Conditioning Engineers (ISHRAE), the split RAC segment has seen the maximum market growth in India. Currently, split ACs corner 61 per cent of the RAC market.

CSE researchers emphasise that the study is not a ranking of companies or their products. To get indicative results, it has selected some popular models that represent a sizeable market share.

What has CSE found? 

  • With rise in outdoor temperature, energy performance of RACs drops: Energy efficiency ratio, a measure of energy efficiency of an RAC, drops when the outdoor temperature increases substantially -- on an average, there is a 2.5 per cent dip for every degree rise in external ambient temperature above 35oC. This means a 5-star rated RAC performs worse than a 1-star rated RAC when the external temperature reaches 45oC. At an extreme 50oC, the average energy efficiency ratio was at a level which has been outlawed by the BEE way back in 2010. 

  • Power consumption increases as outdoor temperature goes up: On an average, power input/consumption increases by 1.9 per cent for every degree rise in external ambient temperature above 35oC. In peak summers with afternoon external temperatures in the 45-50oC range, an RAC unit consumes 10-28 per cent more power compared to its declared power consumption. The consumer thus incurs more cost to run these ACs during peak times. 

  • Cooling capacity drops under high outdoor temperature conditions: On an average, the cooling capacity drops by 1.4 per cent for every degree increase in the external ambient temperature above 35oC. Overall, an 8-21 per cent drop has been measured at 40-50oC from the declared cooling capacity of the models. 

  • When RAC users lower room temperature more than it is required, energy efficiency drops: According to India’s National Building Code, thermal comfort lies between temperature values of 25°C and 30°C, with the optimum condition at 27.5°C; this is influenced by age, metabolic rate and clothing and other climatic conditions. But as comfort expectations of people change, users often take recourse to lowering room temperatures to as low as 20oC. This leads to enormous energy penalty -- energy efficiency was measured at 15.31 per cent when the room temperature was lowered from 27 to 20oC. This works out to a 2.19 per cent drop in energy efficiency ratio for every degree of lowering of internal temperature below the standard 27oC. Thus, 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 to 20oC.

Implications of the findings
Says Roychowdhury: “While some deterioration in energy performance and cooling capacity is expected under climatic stress during hot summer months, such short duration spikes can undermine long term energy savings and monetary gains.” For example, in monetary terms, running a 5-star RAC for a couple of hours in 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 per cent less. 

With climate change, more extreme weather conditions and heat waves, this has serious implications. The observed temperature data for 60 cities in different climatic zones available from the BIS shows that 41 cities have at least 175 hours in a year when external ambient temperature is above 35oC. As many as 22 out of these 41 cities – including Delhi-NCR, Jaipur, Ahmedabad, Lucknow and Raipur – experience temperatures around 40oC or above. 

This is worsened by the heat island effects that increase local temperature conditions by almost another 8-10oC than the ambient air temperature. For instance, a study by the Indian Institute of Technology in Delhi shows that average ambient temperature in Delhi during April, May and June is about 38oC, but in the micro-climate of Connaught Place in the centre of the city, it can be 46-48oC. Also RACs themselves contribute to the heat island by warming up the immediate environment outside. 

Currently, for energy efficiency testing and labeling of RACs, India has adopted ISO test procedures for mild climate – which is 35oC outside and 27oC inside. Additionally, a system reliability test is done at a maximum temperature of 46oC. These ranges are lower than the ISO’s testing requirements for hot climate (46oC outside and 32oC inside and a maximum temperature at 52oC). Says Roychowdhury: “The BIS should review and adopt additional tests at a higher and multiple temperature range appropriate for India for testing of energy performance of ACs.” 

What do other governments do? 

  • Test RACs under multiple high temperature conditions: Countries with harsh summers have adopted multiple temperature ranges for testing RACs. Saudi Arabia has adopted both ISO mild and hot climate testing requirements. Bahrain adopted the Saudi model in 2016. Australia has made it more stringent by adopting star rating system that is based on an annual efficiency calculation. It considers a range of parameters including installation, usage patterns, air temperature, water temperature, frosting, humidity and cloud cover, standby power, and power consumption of crank case heaters etc for rating. This gives a more accurate idea of energy efficiency across the year. Australia is now moving to a zone-based energy efficiency labelling system. 

  • Define cooling needs: There is a misconception among RAC consumers that drastic lowering of the room temperature will provide the desired comfort. But every degree of reduction in internal room temperature leads to an increase of 3-10 per cent in energy consumption. But by setting the RAC a couple of degrees higher and using a fan to blow cool air, electricity use can be considerably reduced. Tests in Tokyo show that raising the AC’s thermostat from 26  to 28oC and using an electric fan can reduce electricity consumption by up to 22 per cent. After the Fukushima disaster, Japan faced a major power crisis – the Japanese government mandated all ACs in the country to run at a temperature setting not lower than 28oC. It also introduced the ‘bush-shirt rule’ to encourage comfortable clothing in workplaces. 

The way ahead
CSE recommends the following steps to meet targeted real world energy efficiency performance:

  • BIS should amend Rule (IS 1391 part 2) to incorporate an additional test for testing of energy efficiency ratio based on multiple higher temperature range relevant for different climatic zones for testing and rating of ACs. 

  • BEE should make it mandatory for manufacturers to declare the tests results carried out based on multiple higher temperature range and declare the results on their product labels. The star labelling system should be adapted to this system. 

  • Manufacturers should declare the annual energy consumption based on cooling capacity tests. 

  • Ratchet the existing star rating to get the best technology in the Indian market.

  • Actively promote passive architectural features to reduce thermal load of buildings.

Says Roychowdhury: “While this study is limited to split RACs, a similar assessment will have to be done for inverter ACs and window ACs. At the next level of review of the star labelling programme, it is important to make the labelling programme technology-neutral and develop more stringent test procedures and systems for monitoring of real world performance.” 


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