ORIGINAL PAPER Energy consumption based on heating/cooling degree days within the urban environment of Athens, Greece K. P. Moustris & P. T. Nastos & A. Bartzokas & I. K. Larissi & P. T. Zacharia & A. G. Paliatsos Received: 22 June 2013 /Accepted: 29 October 2014 # Springer-Verlag Wien 2014 Abstract The degree-day method is considered to be a fun- damental and a rather simple method to estimate heating and cooling energy demand. This study aims in a detailed and accurate assessment of cooling and heating degree days in different locations within the Greater Athens area (GAA), Greece. To achieve this goal, hourly values of air temperature from eight different locations within the GAA, covering the period 2001–2005, were used. Thus, the monthly and the annual number of cooling and heating degree days for each one of the examined locations could be estimated separately. Furthermore, an effort is made to evaluate the energy con- sumption for a specific building, based on the degree-day method, to indicate the impact of the canopy layer urban heat island on neighboring regions within the GAA. Results reveal that there is great spatial variability of energy demand and energy consumption along with significant differences in ex- penses for heating and cooling among neighboring regions within the GAA. Finally, regarding the energy demands of buildings, it is important to take into account intra-urban variability of canopy layer climates against an ensemble mean throughout the city, because the latter can result in inaccurate estimations and conclusions. 1 Introduction The rational utilization of energy, along with better management of environmental issues associated with energy consumption, results in cost reduction and max- imized benefits for society. A simple and well- established tool for estimation of energy requirements is the heating/cooling degree-day method, which is based on outdoor air temperature measurements (ASHRAE 2001 ; Matzarakis and Balafoutis 2004 ; Christenson et al. 2006). Τhe influence of ambient air temperature fluctuations on energy consumption is di- rectly related to degree days and has been examined by various researchers (Sailor 2001; Valor et al. 2001; Pardo et al. 2002). Heating degree days (HDDs) are calculated by simple subtractions of the outdoor temperature from the base temper- ature, taking into account only positive values. The base temperature is considered as the outdoor temperature above which there is no need for a building to be heated. Likewise, cooling degree days (CDDs) are calculated from temperatures above the base temperature. In this case, a base temperature is considered as the outdoor temperature below which a building needs no cooling. The calculation of degree days can be carried out by a number of ways and timescales (CIBSE 2006) as it appears below: K. P. Moustris : P. T. Zacharia Department of Mechanical Engineering, Technological Educational Institute of Piraeus, 250 Thivon and P. Ralli Str., 122 44 Aigaleo, Greece K. P. Moustris e-mail: kmoustris@teipir.gr P. T. Nastos (*) Laboratory of Climatology and Atmospheric Environment, Faculty of Geology and Geoenvironment, University of Athens, Panepistimioupolis, 15784 Athens, Greece e-mail: nastos@geol.uoa.gr A. Bartzokas Laboratory of Meteorology, Department of Physics, University of Ioannina, 451 10 Ioannina, Greece e-mail: abartzok@uoi.gr I. K. Larissi : A. G. Paliatsos Laboratory of Environmental Technology, Department of Electronic-Computer Systems Engineering, Technological Educational Institute of Piraeus, 250 Thivon and P. Ralli Str., 122 44 Aigaleo, Greece I. K. Larissi e-mail: jklar@teipir.gr Theor Appl Climatol DOI 10.1007/s00704-014-1308-7