Konstantinos Papakostas

Residential hot water use patterns in Greece

Abstract This paper presents the results from the monitoring of hot water consumption in four apartment buildings that are located in Solar Village 3, in Greece. The buildings were monitored centrally for hot water consumption using a Data Acquisition System (DAS). The hot water is prepared in one building by an air-to-water heat pump and in the other three buildings by central solar plants. The main objective of the paper is the development of average residential hot water use patterns based on data from actual measurements conducted over the period September 1990 to August 1991. Average hourly, daily, and yearly profiles, which refer to central DHW systems, are presented and discussed. The average hot water consumption “per person” is also concluded. In addition, the effect of “family size” in hot water use is examined. It was found that the majority of the families consume between 25 and 35 liters per person per day, and the mean annual energy consumption is 0.83 kWh per person per day.

Technical note Bin weather data of Athens, Greece

The necessary analysis of the ambient dry bulb temperature and of the relative humidity for elaboration of bin weather data is discussed. Using weather data from Athens, Greece, the annual total bin data as well as monthly bin data in four-hour periods are calculated and presented in tabular form. The presented data serve for the estimation of the energy requirements and fuel consumption of heating and air conditioning systems for either short or long time periods of operation.

Bin weather data of Thessaloniki, Greece

The necessary analysis of the ambient dry bulb temperature and of the relative humidity for elaboration of bin weather data is discussed. Using weather data from Thessaloniki, Greece, the annual total bin data as well as monthly bin data in 4-h periods are calculated and presented in tabular form. The presented data serve for the estimation of the energy requirements, and fuel consumption of heating and air conditioning systems for either short or long time periods of operation.

Energy consumption of a residential building: comparison of conventional and RES-based systems

The energy needs of a typical one-family house in the Thessaloniki area for heating, cooling and domestic hot water production are calculated. The calculations are based on the typical average daily consumption of hot water and on the degree-day method for heating and cooling. The results are finally translated into thermal energy consumption, assuming the typical Greek situation (heating with diesel oil boilers and conventional radiators, cooling with local air-to-air split-type heat pumps and hot water production with electric heaters). The same energy needs are assumed to be covered by a vertical closed loop ground heat exchanger combined with a water-to-water heat pump system with fan-coils for heating and cooling and a thermosyphonic solar system for domestic hot water production. The ground heat exchanger/heat pump system efficiency is determined using data from an existing and continuously monitored similar system installed in the broader area of Thessaloniki. The solar system load coverage is calculated using the f-chart method. The energy consumption of the renewable energy systems is calculated and compared to that of the conventional system. The results prove that significant energy savings can be achieved.

Energy Requirements for the Treatment of Fresh Air in HVAC Systems: A Case Study for Athens and Thessaloniki, Greece.

Abstract The aim of this paper is to discuss the impact of the relation between varying indoor and outdoor conditions on the ventilation loads of buildings and to provide HVAC designers with the respective information needed for the optimum dimensioning of the system. The total load generated by one litre per second of fresh air brought from the outside environment to the indoor space conditions, called “ventilation load index”, is calculated for the cities of Athens and Thessaloniki, Greece. The same principles can be applied to other locations. Results are given in tabular form and ventilation loads for both heating and cooling periods are presented. The results separate the sensible and latent components of the load in order to provide the latent to sensible ratio. Operation periods of 8, 16 and 24 hours are considered for the air-conditioning system, in order to distinguish between different types of buildings. Various combinations of indoor conditions are also examined, in order to ascertain the influence of the temperature and relative humidity on ventilation loads. The resulting energy requirements due to the ventilation of the building are synoptically presented in tables.

30 Years Air Temperature Data Analysis in Athens and Thessaloniki, Greece

Climate change has a major influence on urban environment, and it will continue to pose challenges in the future. The recorded observations on climate change is in line with the projected increase of the average annual temperature in Europe between 2 and 4 °C until the end of the century, as well as with the change of rainfall patterns and the prevalence of drier conditions in the summer months in the Mediterranean area and wetter winters in the Nordic countries. The frequency and intensity of extreme weather events such as heat waves and floods are expected to increase in the coming years. The socioeconomic impacts of climate change in urban areas are also very important. Demographic changes, such as the increase of the average life expectancy and the intense urbanization will increase the percentage of people who are vulnerable to conditions of high temperature and heat waves, with negative effects on health, productivity, social life and use of open public spaces. Furthermore, high temperatures can cause problems in fields such as transport, energy and water supply, along with an indirect effect on agriculture, tourism, urban microclimate and air quality. The current paper attempts to analyze the ambient air temperature in Athens and Thessaloniki for 30 years, namely the period 1983–2012, in order to explore trends in the two largest Greek cities. Descriptive statistics such as average minimum, average maximum and average monthly values of dry-bulb temperature, minimum, average and maximum daily temperature values of the three decades (80s, 90s and 00s) and the cumulative frequency of hourly temperatures per decade, were calculated, analyzed and presented. The number of days with maximum temperature above 25 °C (summer day) and equal or greater than 35 °C, in accordance with internationally agreed criteria and indicators, were also calculated. Likewise, long periods with daily maximum temperature above 35 °C were recorded and presented. The analysis was based on hourly measurements of two meteorological stations, of the National Observatory of Athens and the Aristotle University of Thessaloniki, for the relevant period. The results prove a statistically significant raising trend in temperature values in the studied areas from decade to decade, in addition to the statistically significant increase in the number of days with average above 25 °C and with a maximum equal or greater than 35 °C. The conclusions drawn are particularly useful for planning and implementing policies of adaptation to climate change in different sectors in favour of environment protection and human well-being.

Heat recovery in an air-conditioning system with air-to-air heat exchanger

In comfort applications, air-to-air heat exchangers (HEs) lower the enthalpy of the building supply air during warm weather and raise it during cold, by transferring energy between the outdoor ventilation and exhaust airstreams. In this paper, a 250 person capacity auditorium located in Thessaloniki, Greece, is used as a model to calculate (i) the heating and cooling energy that can be recovered, (ii) the reduction in heating, ventilation, and air conditioning equipment, and (iii) the expected payback period from the installation of a fixed-plate, cross-flow HE in the air-handling unit of the system. An energy analysis with the modified bin method energy calculation was used to compare the energy consumption with and without HE, and with full or half occupancy. It is proved that, at the climatic conditions of Thessaloniki much more heating than cooling energy can be recovered and that the payback period of the HE is between 1 and 2 years.

Simulation of the Thermal Performance of a Hybrid Solar Assisted Ground Source Heat Pump System in a School Building

ABSTRACT A hybrid solar-assisted ground-source heat pump (SAGSHP) system was designed, in the frame of an energy upgrade study, to serve as a heating system in a school building in Greece. The main scope of this study was to examine techniques to reduce the capacity of the heating equipment and to keep the primary energy consumption low. Simulations of the thermal performance of both the building and of five different heating system configurations were performed by using the TRNSYS software. The results are presented in this work and show that the hybrid SAGSHP system displays the lower primary energy consumption among the systems examined. A conventional ground-source heat pump system has the same primary energy consumption, while the heat pump’s capacity is double and the ground heat exchanger 2.5 times longer. This work also highlights the contribution of simulation tools to the design of complex heating systems with renewable energy sources.

Air Conditioning: A Renewable Energy Perspective

Global challenges related to fossil fuels depletion, climate changes and growth of population with a higher comfort demand require a significant change of heating and cooling perspective in the building sector, from currently mainly fossil combustion to renewable energy sources. Solar heating and cooling may have an important role in providing an economically feasible and environmentally sustainable long-term solution to these essential requirements. This paper presents a brief overview on the available solar cooling technologies focus on thermally driven methods. A market study is also carried out and the potential of solar cooling is emphasized.

Estimating Heating and Cooling Degree Days through an Urban Environment Using Publicly Available Sensors

In this paper, data from 12 meteorological stations located throughout the greater metropolitan area of Thessaloniki - Greece are used for the calculation of location specific monthly Heating (HDD) and Cooling (CDD) Degree Days utilizing hourly records of the last three years. The HDD are calculated for base temperatures of 15 and 18°C and the CDD for base temperatures of 22 and 24°C by compacting average hourly data. The results show that the HDD average value of the various locations examined in Thessaloniki during the examined period (2010-2013), as compared to the corresponding value for the city center, is increased from 19% up to 48% (depending on the base temperature). The difference in the average value of CDD for the specified time period is more pronounced, as differences range from -10% to -40% compared to the corresponding value for the city center.