How Can Exhaust from Air Conditioning be used More Effectively?

Image of Atlanta, Georgia, showing temperature distribution, with hot areas appearing white (Photo credit: Wikipedia)

 Anthropogenic Heating of the Urban Environment due to Air Conditioning (F. Salamanca, M. Georgescu, A. Mahalov, M. Moustaoui and M. Wang, Journal of Geophysical Research: Atmospheres, Mar. 6, 2014) 

Also discussed here: Use of Air Conditioners Increases Nighttime Temperatures, Escalates Demand for Air Conditioning - Experts advise turning 'wasted heat' into 'useful energy' (Newswise, May 16, 2014) 

Today we review research carried out in Phoenix, Arizona to assess the impact of air conditioning on the urban heat island. Results indicate that air conditioning increases the mean air temperature by 1 deg C and that air conditioning consumes more than 50% of electricity used during extreme heat events. Instead of simply exhausting this heat into the atmosphere, the report recommends that it could be used for useful activities inside the house such as water heaters which could result in savings of at least 1200 MWh per day for the city. Continued climate warming will make this an even bigger issue affecting not only the formation of smog from ozone and excessive heat. Redirecting the exhaust heat offers the possibility of reducing electrical usage which itself is produced by the burning of carbon fuels which accelerate climate warming.  

Key Quotes: 

“We found that waste heat from air conditioning systems was maximum during the day but the mean effect was negligible near the surface. However, during the night, heat emitted from air conditioning systems increased the mean air temperature by more than 1 degree Celsius (almost 2 degrees Fahrenheit) for some urban locations,” 

 “air conditioning (AC) systems can consume more than 50 percent of total electricity during extreme heat and put a strain on electrical grids.” 

“hot summer nights will lead to increased air conditioning demand, which in turn will output additional waste heat into the environment, leading to further increase in AC demand, resulting in a positive feedback loop.” 

“the effect of the AC systems was more important during the night due to the limited depth of the urban boundary layer. The effect is stronger from late afternoon to early morning. A smaller quantity of excess AC systems heat ejected during the night can increase the air temperature more compared to a greater quantity released during the daytime when the hot sun is beating down.”

“Our work demonstrates one Celsius degree (almost 2 F) local heating of urban atmospheres in hot and dry cities due to air conditioning use at nighttime. This increase in outside air temperature in turn results in additional demands for air conditioning," 

“optimization of electricity consumption in cities would require turning ‘wasted heat’ from AC into ‘useful energy’ which can be utilized inside houses for various purposes including, for example, water heaters” 

“for the Phoenix metropolitan area that successfully reducing the urban heat island temperature with this strategy would result in at least 1200-1300 MWh of direct energy savings per day alone.”

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