Effects of Climate Change on the Indoor Thermal Environment
Little research has addressed specifically the potential effects of climate change on the indoor thermal environment. The major issues surrounding this topic and some information addressing it are outlined below.
Indoor temperature is a function of outdoor temperature, the amount of solar radiation striking the structure, building insulation and ventilation characteristics, factors that influence the ability of the structure to dissipate stored heat, intentional sources of heat (heating, ventilating, and air-conditioning [HVAC] systems), and other indoor sources of heat (artificial lighting, cooking appliances, occupant metabolic heat, and the like). Scott and Huang (2007) found that the demand for cooling energy increases by 5–20% for every 1°C (1.8°F) increase in outdoor temperature, depending on the assumptions used.3 Greater use of air conditioning for cooling implies more electricity demand, which is likely (at least in the short term) to be met through heavier use of fossil fuels, including coal, which in turn may lead to higher emissions of air pollutants, including the greenhouse gases that have been implicated in increased outdoor temperatures (IPCC, 2007). The positive feedback loop that characterizes those relationships is depicted in Figure 7-1.
The US Climate Change Science Program’s literature review concluded that “temperature increases with global warming would increase peak demand for electricity in most regions of the country” but that research results varied and were influenced by such factors as “whether the study allows for changes in the building stock and increased market penetration of air conditioning in response to warmer conditions” (Scott and Huang, 2007). Indoor relative humidity, another component of the thermal environment, is a part of the issue. In areas of the country where hot and humid outdoor conditions become more common, air-conditioning units may run longer to restore or maintain comfortable indoor humidity.
Potential increases in the magnitude and frequency of peak electricity demand due to heat waves and in the occurrence of extreme weather events have also led to concerns over power outages that could leave building occupants without sources of conditioned air. The 1995 Chicago (Changnon et al., 1996) and 1999 New York City (USGCRP, 2009) heat waves were accompanied by extended and widespread power outages. Electric-grid infrastructure disruptions after Hurricanes Katrina and Rita left some areas of the southern United States without power for weeks during the late summer of 2005.
3 The same study found that demand for heating energy decreases by 3–15% for every 1°C (1.8°F) increase in outdoor temperature. Cooling uses electricity almost exclusively whereas heating uses various energy sources; this complicates the evaluation of the implications of these changes on overall power-generation demands.