Not as Cool: Ensure real world energy savings from ACs

With extreme weather events, heat waves and heat island effects becoming common, testing of ACs must become stringent to ensure real world performance

By Anumita Roychowdhury, Avikal Somvanshi
Published: Wednesday 27 July 2016

Credit: Centre for Science and Environment

Responsible consumers are expected to buy air conditioners (ACs), star labelled by the Bureau of Energy Efficiency (BEE) based on their energy efficiency to save energy, costs and the climate. But new results from testing of split room air conditioners (RACs) released by the Centre for Science and Environment (CSE) shows that during high summers, when temperatures are in the 40-50 degrees Celsius range, a "5-star" rated split AC becomes worse than a 2- or 1-star rated unit. It starts consuming 10-28 per cent more power than its declared capacity; and cooling capacity drops by about 30 per cent which means a 1.5-tonne AC acts like a 1-tonne AC.  This gets worse when users lower room temperature artificially to levels much below the recommended level of 27 degrees Celsius of Bureau of Indian Standards (BIS). 

This investigation has become necessary as RACs are inherent energy guzzlers and climate rogues and strongly influence the energy budget not only of households but also the country. India is still not a big RAC consumer but the market is growing very rapidly. An RAC consumes five-times more electricity than an evaporative air cooler, which in turn, consumes twice the electricity of a fan. 

Air conditioners are responsible for peak energy consumption across cities. This is high in the afternoon when residential and commercial peak demand overlaps. 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 Delhi’s peak electricity demand. It is important to understand and know how RAC units perform under different outdoor temperature conditions and how that affects the energy savings from the star labeling programme.

What is this test all about?

CSE commissioned an independent National Accreditation Board for Testing and Calibration Laboratories (NABL)-accredited laboratory to test RAC units. Three popular 5-star split RAC models—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: (a) The effect of high external temperature on real world energy performance; (b) Effect of lower internal room temperature on energy performance; and (c) 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 and is 61 per cent of the market. They were tested using the balanced ambient calorimeter method.

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

Stunning results

The test results have shown that as the outside temperature increases, the cooling capacity and energy efficiency dips while power consumption of RACs increases compared to their stated claims.

Graph: With increased outdoor temperature, power consumption increases and energy efficiency reduces

Credit: Centre for Science and Environment

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 35 degrees Celsius. This means a 5-star rated RAC performs worse than a 1-star rated RAC when the external temperature reaches 45 degrees Celsius. At an extreme 50 degrees Celsius, the average energy efficiency ratio was at a level which has been outlawed by the BEE way back in 2010. For instance, the Godrej split RAC sample that was tested is a 5-star model that has declared its energy efficiency ratio as 3.55. But at 40 degrees Celsius, this has dropped to 2.96 which is equivalent to a 2-star. It further dropped to 2.13 at 50 degrees Celsius which is worse than 1-star.

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 35 degrees Celsius. In peak summers with afternoon external temperatures in the 45-50 degrees Celsius 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. For instance, the sample 5-star Voltas model that was tested has declared a power input of 14.24 watts. But this model consumed 1,555 watts at 40 degrees Celsius and 1,833 watts at 50 degrees Celsius. This shows an increase in power consumption by 9 per cent to 29 per cent.

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 35 degrees Celsius. An overall 8-21 per cent drop has been measured at the 40-50 degrees Celsius range from the declared cooling capacity of the models. For instance, the 5-star model of LG that was tested has declared a cooling capacity at 5,275 watts. But at 40 degrees Celsius, it reduced to about 5,000 watts and at 50 degrees Celsius to 4,400 watts. This is a drop of 6 to 17 per cent.

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 degrees Celsius and 30 degrees Celsius, with the optimum condition at 27.5 degrees Celsius; 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 20 degrees Celsius. This leads to enormous energy penalty—energy efficiency was measured at 15.31 per cent when the room temperature was lowered from 27 to 20 degrees Celsius. 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 27 degrees Celsius. 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 20 degrees Celsius.

What do these results mean?

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 during a peak summer afternoon under normal conditions should cost about Rs. 490 a month. But with worsening of 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 also cools 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 35 degrees Celsius. As many as 22 out of these 41 cities—including Delhi-NCR, Jaipur, Ahmedabad, Lucknow and Raipur—experience temperatures around 40 degrees Celsius or above. “This is a serious concern as all scientific studies assume that RACs are used on an average for 8 hours for 180 days a year. RACs are not used throughout the year. But during the summer season, they contribute hugely to peak demand—as much as 60 per cent in Delhi. To prevent grid-collapse during peak hours and also to ensure energy savings, it is important to have energy performance guarantee at such high temperature levels.

This is worsened by the heat island effects that increase local temperature conditions by almost another 8-10 degrees Celsius than the ambient air temperature. For instance, a study by the Indian Institute of Technology, Delhi shows that average ambient temperature in Delhi during April, May and June is about 38 degrees Celsius, but in the micro-climate of Connaught Place in the centre of the city, it can be 46-48 degrees Celsius. 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 International Organization for Standardization (ISO) test procedures for mild climate—which is 35 degrees Celsius outside and 27 degrees Celsius inside. Additionally, a system reliability test is done at a maximum temperature of 46 degrees Celsius. These ranges are lower than the ISO’s testing requirements for hot climate (46 degrees Celsius outside and 32 degrees Celsius inside and a maximum temperature at 52 degrees Celsius). 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 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 the 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 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 28 degrees Celsius 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 28 degrees Celsius. It also introduced the "bush-shirt rule" to encourage comfortable clothing in workplaces.

Raise the bar

Even though the full energy efficiency gains from technology improvement are realised from the overall usage over time, short duration spikes can undermine long-term gains and savings. It is therefore important that the current test procedures for energy performance for the rating of the RACs are reviewed and improved to meet targeted real world energy efficiency performance.

BIS should amend Rule (IS 1391 part 2) to incorporate an additional test for the 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 the manufacturers to declare the tests results carried out based on multiple higher temperature range and declare the results on their product label.  The star labelling system should be adapted to this system. Manufacturers should declare the annual energy consumption based on cooling capacity tests.

At the same time, BEE should ratchet the existing star rating to get the best technology in the Indian market. At the same time, it should actively promote passive architectural features to reduce thermal load of buildings.

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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