G LOBAL TRENDS IN COOLING ENERGY

As the urban population numbers grow larger, living conditions improve and the economy continues to expand, an increase in energy demand associated with a growing number of households and businesses is inevitable. Energy consumption from space cooling in buildings increasing by nearly 60% between 2000 and 2010 and accounted for roughly 4% of total global buildings energy use in 2010. The cooling energy as a fraction of total energy demand of buildings is usually higher in OECD-countries (Organization for Economic Cooperation and Development) than non-OECD. The amount of cooling energy also depends on climate: in warmer climates, cooling accounted for as much as 10% of total energy use, while the cooling energy use in colder areas is typically less than 3%.

According to Waite et al. (2017), in a review of ten international cities, roughly half of building energy-related GHG emissions is associated with electricity generation to serve urban areas. Cooling energy use is also dependent on regional climates: in warmer climates, cooling accounted for as much as 10%

of total buildings energy use, while in cooler regions with greater heating demand, cooling is typically less than 3% of buildings energy consumption (IEA, 2013).

At the city-scale, heating, ventilation and air-conditioning (HVAC) may be of even greater significance as building energy use tends to dominate in urban areas. Cities generally have more limited opportunities for power generation. This energy demand may be intensified due to the urban heat island effect and tendency towards service-economy (the service sector will become increasingly important to the future economy of industrialized countries), which increases the relative share of air-conditioned commercial buildings (Waite et al., 2017). For example, in the United States, it has been shown that increases in air temperature can explain 5 – 10% of urban peak electric demand, with a typical rise of 2 – 4% for every 1 ∘C rise in daily maximum temperature over 15–20∘C, and the use of air conditioning systems is expected to increase significantly in the near future (Antunes et al., 2015).

As the economy of developing countries and population incomes increase, urban households are predicted to consume more energy per capita, and trends point towards higher electricity usage (Waite et al., 2017). Regional climatology will also be a key driver in energy use, but subtle variations in consumption will be apparent depending on the availability of energy efficiency measures for passive cooling systems and building construction (Antunes et al., 2015).

Electricity demand in hot areas during summertime has shown to be more sensitive to temperature variations than the cooler urban areas. Leaky building envelopes, heat island effects and increasing urbanization will have large impacts on the peak electricity demands in emerging megacities. While the interrelated effects among these factors are complex, five structural variables that drive long-term building energy use have been identified: 1) population growth, 2) economic growth, 3) urbanization, 4) per-capita floor space, and 5) demand for building energy services. Furthermore, population, economy size and functions drive baseload electricity demand at annual to decadal timescales; climate drives seasonal variability; and human behavior, physiology and meteorology drive diurnal patterns (Waite et al., 2017).

A study performed by Waite et al. (2017) provided a baseline assessment of urban electricity demand for cooling and heating in 35 global cities in both OECD and non-OECD countries. Their results indicated a significant difference in cooling electricity requirements of OECD cities (35-90 W/°C/capita), as compared to non-OECD cities (2-9 W/°C/capita). However, the observed trends indicate the gradual (and in some cases rapid) adoption of air conditioning equipment in developing cities. Furthermore, non-OECD cities in cooling climates likely exhibit lower cooling electricity response than OECD cities because of low penetration of cooling equipment. Some non-OECD cities

are further along the development spectrum, and cities that experience very high temperatures already have high electricity demands for cooling (and heating). According to Waite et al. (2017), these cities are likely to experience significant increases in both annual electricity usage and peak electricity demands for thermal comfort in the future.

As stated by Antunes et al. (2015), the temperature associated shift of energy requirements from heating to cooling can bring about a series of challenges; oil and gas are traditionally used for heating, whereas electricity is used for cooling. As electricity has a tendency to be less efficient, and therefore more expensive, current estimates indicate that additional expenditure of energy on cooling in summer can outweigh winter energy savings. Furthermore, electricity also has higher CO₂ emissions per unit of consumption, meaning that the shift from heating to cooling could potentially further exacerbate climate change and global warming. However, if renewable energy continues to replace fossil fuels in the electricity mix, the CO2 emissions per unit of consumption will be significantly reduced.

ELECTRICITY COSTS

Globally, space cooling is typically produced using electricity, although some regions use natural gas cooling equipment.

Figure 2-8: Space cooling energy consumption in different global regions as a share of total building energy use in 2010 (IEA, 2013)

Electricity costs will vary from country to country and also from one location to another within the countries. Costs also vary throughout the day; when the demand is high, the associated fuel demand increases. Consequently, fuel prices go up, resulting in higher costs to generate electricity. The cost related to the supply of electricity can change by the minute and will also vary among the different consumer groups; residential electricity prices are usually higher than for commercial and industrial consumers. Prices are determined by a number of factors, like cost of power generation in power plants, government subsidies, transmission and distribution infrastructure and industry regulation. Weather conditions will also affect the prices; rain and snow provide water for low-cost hydropower generation,

sunny conditions will increase productivity of photovoltaics and wind can provide cheap power generation from wind turbines when wind speeds are favorable. The selection of fuels to generate electricity is a main driver for electricity prices globally, and a country’s electricity mix can consist of natural gas, renewable energy, petroleum products and coal. Additionally, CO2 prices have increased significantly in recent years, and are likely to continue to rise in the near future. Extreme temperatures can also increase the demand for electricity for space cooling, and high demand can drive prices up.

Moreover, electricity prices are usually highest during summer, when total demand is high because more expensive generation sources are added to meet the increased demand (EIA, 2018).