I. Livada

On the impact of urban climate on the energy consumption of buildings

Climatic measurements from almost 30 urban and suburban stations as well as specific measurements performed in 10 urban canyons in Athens, Greece, have been used to assess the impact of the urban climate on the energy consumption of buildings. It is found that for the city of Athens, where the mean heat island intensity exceeds 10°C, the cooling load of urban buildings may be doubled, the peak electricity load for cooling purposes may be tripled especially for higher set point temperatures, while the minimum COP value of air conditioners may be decreased up to 25% because of the higher ambient temperatures. During the winter period, the heating load of centrally located urban buildings is found to be reduced up to 30%. Regarding the potential of natural ventilation techniques when applied to buildings located in urban canyons, it is found that, mainly during the day, this is seriously reduced because of the important decrease of the wind speed inside the canyon. Air flow reduction may be up to 10 times the flow that corresponds to undisturbed ambient wind conditions.

Thermal and air flow characteristics in a deep pedestrian canyon under hot weather conditions

The present paper reports the results of a specific experiment carried out in a deep pedestrian canyon in Athens, Greece. The air flow inside and outside the canyon as well as the air and surface temperatures inside the canyon are measured for a period of seven continuous days during the whole day and night period. The air flow characteristics inside the canyon are analyzed. For perpendicular wind speeds, the air flow inside the canyon is characterized by either a circulatory vortex driven by the ambient air flow or a double vortex flow where the upper one is driven by the ambient air flow and the lower one is driven in the opposite direction by the circulation above. When the ambient air blows parallel to the canyon, the measured wind data inside the canyon indicate a flow in the same direction. When the air flows at a certain angle to the canyon axis, the measured data indicate that a spiral vortex is induced along the canyon length. The spatial and temporal variation of the surface and air temperature distribution inside the canyon is analyzed. The heat island intensity in the canyon is estimated based on measurements from a reference station.

High ambient air temperature frequency distribution at Hellenic islands

Abstract Energy consumption of buildings for cooling purposes partially depends on outdoor ambient air temperatures. Measured data from eight Hellenic islands in the Ionian and the Aegean sea is used to estimate the frequency of high temperature exceedance in these islands, useful for estimates of building cooling demand and comfort conditions in the area. The analysis is based on the calculation of the daily T E value which is the sum of the daily minimum outdoor temperature and half of the daily temperature amplitude. This parameter corresponds to a daily average value of 9–10 h, during the period of May through September, when the hourly ambient temperature exceeds 26 and/or 28 °C in the regions of interest. The analysis carried out shows that a two-parameter exponential law, is in excellent agreement with the large values distribution for the parameter T E .

Time series analysis of ambient air-temperature during the period 1970–2016 over Sydney, Australia

Providing evidence of potential changes in the climate has become increasingly important as it is the first step towards adopting mitigation and adaptation measures and planning for urban resilience. In this study a statistical analysis of the ambient air temperature time series over Sydney, Australia during 1970-2016 has been carried out with the aim to investigate potential changes towards higher temperatures. The dataset has been statistically analyzed using different techniques, concluding that the investigation should be performed on a monthly basis. A persistence analysis was conducted using different statistical approaches to investigate the dependence between consecutive monthly and daily ambient air temperature values. A trend analysis of the ambient air temperature and degree days time series has been conducted using linear regression to estimate the linear trend (slope) and its statistical significance (using a Student-t-test) and the Kendall-Mann test to identify the time at which the tendency starts to occur as well as the time after which it becomes statistically significant.