Green Roofs - Living Architecture Monitor - Winter 2009 - (Page 24) “Is it more costeffective to utilize potable water for cooling than electricity? This is a pressing issue, since much of energy consumption is utilized to regulate the temperature within buildings.” would cost usd $0.51/hr or $13.50/day. In comparison, it would take 104,275 grams or 27.5 gallons of water to remove the same number of calories through evapotranspiration. The average cost per gallon of water in New York City is about usd $0.07 (sewer charge included), which means it would cost usd $0.0108/hr or $0.26/day to remove the same quantity of heat through evaporation through a vegetated roof. In sum, the cost of cooling air using the local drinking water supply on green roofs is between 41 and 93 times lower than using electric powered air conditioning in the four cities compared, as shown in Figure 1 (page 25). This cost would be lower still, or could reverse sign (i.e. become a negative cost, or in other words, a plus on the balance sheet), were stormwater or graywater or other wastewaters figured into this equation. As presented in Table 2 (page 23), a significant cost of power is a substantial quantity of water required for the production of electricity used in cooling interior spaces. As indicated in Figure 2 (page 25), the quantity of water needed for electricity production can be more than twice that needed for the same amount of cooling from a green roof or vegetated landscape, to slightly less than the green roof water cost in the case of Seattle. CONCLUSION As energy costs and temperatures increase, locally and globally, cost-effective solutions for cooling cities may be found in creative use and reuse of the principal solvent and primary thermal regulator on the planet: water. Because of the huge quantity of heat removed by the phase change of water from the liquid to gaseous state, 580 calories per gram, the principle fluid of the biosphere suggests itself as a primary means for regulating temperature in urban centers and on and around human-built structures. To the extent that stormwater, greywater, or treated wastewater can be used to support green roof and other vegetation, overall material and energy costs can be minimized. And while hvac systems create a cooler atmosphere within buildings, they also generate a higher heat load on nearby urban landscapes in hot weather by discharging heat into the surrounding environment. This effect may be more http://www.dinoflex.com
For optimal viewing of this digital publication, please enable JavaScript and then refresh the page. If you would like to try to load the digital publication without using Flash Player detection, please click here.