Taking into account that in Athens the Public Power Corporation refers a mean yield of 30% per kWh between production and final consumption and that the production of each kWh causes CO2 emissions equal to 0.9 kg, (European Commission, 2001), the CO2 emissions, (in tn), caused by the total Athens’ heat island energy cost have been calculated. Finally, the ecological footprint of the Athens’ heat island, (in ha), is calculated by dividing the estimated CO2 emissions by the average world CO2 sequestration rate by the forests which is 5128.205 kg CO2/ha.

By considering that all buildings are air conditioned, we calculated, Table 5, the maximum potential ‘Athens heat island energy cost’ in kWh/m2, the maximum potential ‘total Athens heat island energy cost’ in GWh, the maximum potential CO2 emissions due to the total Athens heat island energy cost, in tn, and finally the maximum potential ecological footprint of the Athens heat island in ha.

As it can be observed, there is a remarkable potential energy cost of the urban heat island phenomenon in Athens ranging between 1300-1500 GWh/y, a very high potential increase of the CO2 emissions ranging from 4 to 4.6 Mtn. The calculated maximum potential ecological footprint because of the heat island effect varies between 780000 to 900000 ha.

Table 6 shows the actual Athens’ heat island energy cost, the actual total Athens’ heat island energy cost, the actual CO2 emissions due to the total Athens’ heat island energy cost in tn, and finally the actual ecological footprint of the Athens’ heat island.

References

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Mean Temperature, Mean Maximum Temperature and Cooling Degree Hours for the year 1997 and for the five experimental stations

Table 1 Station Number Mean Temperature for the cooling season, (June, July, and August) in 0C Mean Maximum Temperature for the cooling season, (June, July, and August) in 0C Cooling Degree Hours (Base 26°C) Reference 25.8 28.3 3615 7 32.6 38.5 9280 9 29.2 34.6 8200 12 31.9 39.2 9750 13 28.6 31.9 7700

Mean Temperature, Mean Maximum Temperature and Cooling Degree Hours for the year 1998 and for the five experimental stations

Table 2 Station Number Mean Temperature for the cooling season, (June, July, and August) in °C Mean Maximum Temperature for the cooling season, (June, July, and August) in °C Cooling Degree Hours (Base 26°C) Reference 27.4 30.1 4508 7 33.2 39.4 10004 9 30.8 36.0 8945 12 32.5 40.4 9912 13 29.3 34.2 8600

Table 3 Description of the reference building Floor Area 200 m2 Floors’ Materials Concrete, Marble Roof’s Materials Concrete, Insulation, Clay Coverage The 90% of the External Walls Double Brick with an Air Gap between the two brick layers, External Insulation The 10% of the External Walls Concrete, External Insulation Windows One-pane single glazing with shading coefficient equal to 0.1 Occupancy 3 persons in each floor Artificial Lighting 5W/m2 for each floor Electrical Equipment 5W/m2 for each floor Infiltration 0.5 ACH Natural Ventilation 0.5 ACH Set Point Temperature for the air­conditioning system 26°C Ground Temperature 17°C

Table 4 The mean cooling load in kWh/m2 for all stations and for the years 1997 and 1998. Station Number Mean Electrical Cooling load for 1997 (kWh/m2) Mean Electrical Cooling load for Cooling load for 1998 (kWh/m2) Reference Station 22.7 38.0 Urban Station No 7 70.4 77.9 Urban Station No 9 53.2 61.6 Urban Station No 13 55.9 71.4 Urban Station No 14 44.0 57.1 Mean Urban 55.9 67.0

Table 5

The maximum potential Athens’ heat island energy cost, the maximum potential total Athens’ heat island energy cost, the maximum potential CO2 emissions due to the total Athens’ heat island energy cost in tn, and finally the maximum potential ecological footprint of the Athens’ heat island.

Year	1997	1998
Maximum Potential Athens’ heat island energy cost (kWh/m2)	33.2	29.0
Maximum Potential Total Athens’ heat island energy cost (GWh)	1540.5	1345.6
Maximum Potential CO2 emissions (Mtn)	4,621	4,036
Maximum Potential Ecological footprint of the Athens’ heat island (ha)	901180	787176

Table 6

The actual Athens’ heat island energy cost, the actual total Athens’ heat island energy cost, the actual CO2 emissions due to the total Athens’ heat island energy cost in tn, and finally the actual ecological footprint of the Athens’ heat island.

Year	1997	1998
Actual Total Athens’ heat island energy cost (GWh)	120.7	105.5
Actual Potential CO2 emissions (Mtn)	0,362	0,316
Actual Ecological footprint of the Athens’ heat island (ha)	70562	61714