The following section presents results and discussion for each of four stated research objectives. Taken together, our results represent the first comparative analysis of electrical heating and cooling demand at the city-scale, including both OECD and non-OECD member cities.
A significant cooling signal was detected (90% confidence level) for 35 of 37 cities analyzed. The only cities without a clear cooling signal were Mbabane, Swaziland (elev. 1243m, lat. -26°, long. 31.3°) and Nairobi, Kenya (elev. 1661m , lat -1.3°, long. 36.8°). Both cities are at high elevation, with temperate climates and cool nights, suggesting that electrical cooling is unnecessary much of the year, and thus adoption of capital-intensive A/C is commensurately low. By comparison, Abidjan, Cote d'Ivoire had no detectable cooling signal as recently as 2010, but now has a highly significant (99% CI) cooling demand of approximately 3 Watts/(capita x °C), suggesting very recent uptake of cooling appliances.
In Accra, Ghana, both the effect of temperature on electricity demand, and the significance of that effect are increasing year-on-year. Virtually across the board among non-OECD cities, this holds true: cooling demand, both city-wide and per-capita, are higher now (most recent year data is available) than even just a few years ago (first year data is available). The overall trend is positive, but not strictly monotonic, for Abidjan, Cote d'Ivoire; Accra, Ghana; Chandigarh, India; Dakar, Senegal; and Manila, Philippines; see Table 2 (city-wide) and Table 3 (per-capita).
This suggests significant, latent, unmet demand for indoor thermal comfort services in emerging market cities. As incomes continue to rise, so will penetration of vapor-compression refrigeration window-units (e.g. A/C) and resistive electrical heaters in the near term, and central heating/cooling and reversible heatpumps in the mid- to long-term. Energy demand for cooling, dehumidification and heating will rise accordingly. How high it will ultimately go, is a central question of this research.
As an upper-estimate, we can presuppose that demand for heating and cooling will reach eventual parity with OECD cities of similar climate on a Watt/(°C x capita) basis. That is, a similar level of indoor thermal comfort is expected once a certain level of affluence is attained. Integrating heating/cooling demand over expected HDH/CDH for a given city, yields a reasonable estimate of total annual energy consumption for indoor thermal comfort. This method can be used for historical, current-year or future projections by adjusting the per-capita heating/cooling demand (intensive margin) and heating/cooling-degree hours (extensive margin). Adjustments can be made to reflect change over time along the development spectrum (intensive margin) and the effects of climate change (extensive margin).
As a group, non-OECD cities (n=15) were found to have maxima per-capita cooling demands ranging from 0-12 W/(capita x °C) in all but three cities 1. By comparison, OECD cities (n=18) ranged from 10-140 W/(capita x °C). The median per-capita cooling demand was seven-times higher in OECD compared to non-OECD cities (40.8 versus 5.8 W/(°C x capita), respectively). The univariate distribution of per-capita cooling demands comparing OECD and non-OECD cities yields statistically distinct sets <.
The only OECD cities in our study with per-capita cooling demands similar to that of the non-OECD set, were Los Angeles, Sand Diego and Honolulu (at 11, 23 and 19 W/°C x capita, respectively). All three of these locals have very mild, coastal climates with annual average temperatures at a near-perfect 22°C. While climate clearly attenuates or accentuates the intensity of demand for thermal comfort, it cannot explain all the difference. While L.A., San Diego and Honolulu have near perfect climates, they still have per-capita cooling demands 2-4 times higher than emerging economy cities with much more extreme climates, such as Delhi. Based on climate alone, we would expect the opposite.
Within the OECD set, there is substantial variation. Mid-size, relatively sprawling, U.S. cities such as Detroit, MI; Chattanooga, TN; and Omaha, NE; appear to have the highest per-capita demand for cooling, at approximately 100 W/(capita x °C). Population dense Singapore, on the other hand, has a cooling demand of just 13 W/(°C x capita) despite having seven times as many standardized CDH as Detroit, five times as many as Omaha, and three times as many as Chattanooga. In fact, Singapore has the highest number of standardized CDH of any city in our study, with over 70,000 per annum. Result 6 provides a summary table of per-capita peak demand for electrical cooling (and heating) alongside standardized and optimized CDH (HDH) for all cities in our study.
Returning to the three non-OECD cities with substantially higher per-capita cooling demand than their peer-group, we have: Manila, Philippines at 19 W/(capita x °C); Amman, Jordan at 47 W/(capita x °C); and New Delhi (not NCT Delhi as a whole or any of the other districts; just the governmental district) at 40 W/(capita x °C). These three cities may be harbingers of what is to come among peer non-OECD cities analyzed in this study, as well as thousands of other emerging-market cities worldwide, as incomes rise and demand for indoor thermal comfort increases.
For example, New Delhi (NDMC; the seat of government), has a per-capita cooling demand roughly four times that of neighboring parts of the city. This reflects stark differences in the building stock: many large government buildings have been retrofitted for air-conditioning, a departure from traditional open-envelope building design. Cooling demand in neighboring districts of Delhi will likely catch up quickly, as A/C rapidly becomes commonplace in middle-income households and businesses in all quarters of the city.
Amman, Jordan has per-capita cooling demand nine times as high as Beirut, although the cities are less than a 150 miles apart and have similar climates (although Beirut is more temperate given its location on the Mediterranean). Cooling demand in Amman is more similar to that of El Paso, TX, USA at 56 W/(capita x °C), than nearby Beirut.
Altogether, 15 of 37 cities were found to have statistically significant growth (90% CI) in cooling demand over the period of record, including all non-OECD cities except Beirut and Delhi. 11 of 15 of these cities experienced the highest cooling demand on record in the most recent year. This suggests continued, increasing penetration of air conditioning and increasing square-footage of air-conditioned space. The former is likely the driving force in seven non-OECD cities (Abidjan, Cote d'ivoire; Accra, Ghana; Chandigarh, India; Dakar, Senegal; New Delhi, India; Delhi Military Contonement, India; and Manila, Philippines), whereas the latter is more likely in the four OECD cities (New York City, USA; Philadelphia, USA; Tacoma, USA; Indianapolis, USA.). That is to say, business and residences in non-OECD cities are rapidly adopting A/C, whereas non-OECD cities have already reached market saturation for A/C ownership, but continue to build and convert new square-feet into residential/commercial air-conditioned space. In both cases, demand for thermal comfort continues to rise, suggesting a long-tailed distribution. Even after emerging market cities reach asymptotic adoption rates for heating and cooling appliances, energy demand will continue to rise, following a development pattern of increasing residential/commercial air-conditioned real-estate.
From a system-operator perspective, total urban demand for electrical cooling ranges from less than 10 MW/°C in Abidjan, Accra, Antigua, Beirut, Chandigarh, Dakar, Kano and Tema, to over 2000 MW/°C in Tokyo, 300 MW/°C in NYC and Detroit, and ~200 MW/°C in Philadelphia and Manila. Of course, population and economy explain much of that difference, but large disparities remain even on a per-capita basis, as noted above and illustrated in Tables 3 and 4.
For heating, 23 of 47 cities had a significant relationship between cooler temperatures and increased demand associated with electrical heating. <>.
Footnotes
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Manila, Philippines at 19 W/(capita x °C); Amman, Jordan at 47 W/(capita x °C); and New Delhi (not to be confused with Old Delhi nor NCT Delhi as a whole; only the relatively new governmental district) at 40 W/(capita x °C). ↩