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| Fig. 1: Cooling degree days (CDD) and peak electricity demand for South Korea in August from 2014 to 2024. CDD data is collected from KEEI, and peak electricity data for these months is collected from annual reports containing data from recent years [1,2,7,8-10] (Image source: S. Jeong) |
The world is trying to reduce energy consumption. One simple strategy is to minimize unnecessary electricity use. For example, Korean government institutions are required to keep air conditioning temperatures at 28°C (82.4°F) or higher. Similarly, most Stanford graduate housing does not provide air conditioning, reflecting the university's commitment to sustainability. However, I question whether imposing strict limits on electricity usage is truly sustainable. These restrictions may drive people to buy affordable portable air conditioners, which are often less energy-efficient.
This chapter explores the link between hot summers and electricity demand. To minimize compounding factors, I analyzed publicly available data from South Korea, where temperature differences across the country are relatively small.
A key metric for estimation and prediction of energy use, Cooling Degree Days (CDD), calculates how much daily temperatures exceed a baseline over a month. [1] Higher CDD values typically correspond to increased air conditioning usage. The formula is: CDD = ∑max(daily average temperature 24, 0). According to the Korea Power Exchange, the average peak power demand hit a record high of 87.8 GW in August 2024, a 6.1% increase from 82.7 GW in 2023. [2]
Fig. 1 shows CDD and peak electricity demand in August over the past decade in South Korea. While electricity demand has generally increased, years with extreme heat, such as 2016 and 2018, had temporary peaks in electricity demand. The Pearson correlation quantifies the strength of linear relationship. A value closer to 1 indicates a strong positive correlation, while a value of 0 suggests no linear correlation. [3] The Pearson correlation between CDD and average peak electricity demand over the past decade is 0.6735, indicating a moderate correlation. Although this cannot explain any causality, it strongly suggests increased energy demand in hotter summers.
The energy efficiency of air conditioners varies depending on operating conditions. While the international standard ISO 16358 provides a framework for evaluation, countries often develop their own standards to account for specific environmental factors. For example, Korea Standard C9306 defines CSPF (Cooling Seasonal Performance Factor) and Chinese Standard GB 21455-2013 defines SEER (Seasonal Energy Efficiency Ratio) and APF (annual performance factor) based on local environmental conditions. These metrics help assess products and guide energy policies.
In addition to environmental factors like humidity and temperature fluctuations, several other factors influence air conditioner efficiency. For example, smaller-capacity units are generally more energy-efficient. The type of refrigerant also plays a key role, while there is a trade-off between efficiency and ozone-depletion or chemical stability. [4] These complexities make it difficult for consumers to fully understand efficiency metrics and make informed decisions.
Many countries implement Minimum Energy Performance Standards (MEPS) that commercial products are required to satisfy. In addition to MEPS, many countries have developed their own labeling systems for air conditioner efficiency. In South Korea, air conditioners are required to display an efficiency grade on a label based on its standardized metric. A Grade 1 product can save approximately 30-40% of electricity compared to a Grade 5 product. In 2020, electricity used for air conditioning in households was 7691 GWh, representing 11.3% of total household electricity consumption. [5] Upgrading all air conditioners by two efficiency grades could reduce energy consumption by approximately 15% per unit. This improvement would save an estimated 1154 GWh, equivalent to 1.7% of total household electricity consumption. Other countries have similar systems: China uses Grades 1 to 3, while the European Union uses a scale from A+++ to D. These metrics provide consumers with a clear guide to air conditioner efficiency beyond company advertisements. They allow consumers to easily compare products and choose the one that provides the same cooling effect with lower energy consumption. However, as of 2017, the most efficient air conditioners already exceed the Grade 1 requirements by over 200%. [4] This limits incentives of further innovation for manufacturers.
As extreme heat increases, air conditioning use becomes inevitable. South Korea experienced its hottest summer and highest electricity demand in 2024, where the average number of air conditioners per household reached 0.92, and its electricity consumption accounted for 11.3% of total in 2020. [2,5,6] Countries with similar climates and economic conditions are likely to have similar trends. However, the power grid cannot handle peak demand every summer. Governments should continuously monitor climate patterns and update grading systems to provide clear and accessible information to consumers. High-efficiency units not only reduce energy consumption but also lower electricity bills, making them more attractive to consumers. As demand rises, manufacturers will be motivated to further invest in improving efficiency.
© Sehui Jeong. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
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