Haydar Aras

Forecasting Residential Natural Gas Demand

In Turkey, the major purpose of natural gas demand in residences is heating, where the residential gas usage is approximately 18% of total gas consumption. The studies on forecasting gas demand for future periods have a great importance because natural gas is an imported energy source. This article describes an approach to obtain appropriate models for forecasting residential monthly natural gas consumption. The method relies on dividing a year into two seasons as heating and non-heating periods and estimating individual autoregressive time series models for each period instead of attempting to capture the seasonal patterns in a single model. In the models, the dynamic relationships between natural gas consumption with time and degree-days measured by weather temperature variations are investigated. This method is applied to one of the five cities supplied by natural gas for residential use in Turkey. A comparison of the forecast accuracy of proposed procedure with that of a single model approach applied to the full set of observations is provided. The results reveal that to use separate models for each period reduces the forecast errors significantly when the major purpose of natural gas demand is space heating.

Exergetic and exergoeconomic analysis of an Aircraft Jet Engine (AJE)

This study deals with energy, exergy and exergoeconomic analysis of an Aircraft Jet Engine (AJE) as named J69-T25A used on T-37B/C model training aircrafts. In the analyses, the engine data measured in the engine test cell at First Air Supply and Maintenance Center of Turkish Air Forces are used. Quantitative exergy and exergoeconomic cost balance equations are derived for each components of the engine and the overall J69-T25A engine. Exergy destructions within the engine components are investigated to determine thermodynamic inefficiencies. Cost balances and auxiliary equations are also applied to each components of the engine for observing cost formation. Additionally, exergy cost rate and unit exergy cost rate of each products of the engine are accounted.

Global Solar Radiation Potential, Part 1: Model Development

Solar engineers, architects, agriculturists, and hydrologists dealing with many applications of solar energy require a reasonably accurate knowledge about the availability of solar resources at any place. For this purpose, in the past, several empirical correlations have been developed in order to predict the solar radiation around the world. The present study, consisting of two parts, analyzes global solar radiation over the Central Anatolia Region (CAR) of Turkey along with its twelve provinces. Part 1 of this study includes the solar radiation models developed, while their statistical analysis is presented in Part 2. In the analysis, the data of the monthly average daily global solar radiation and sunshine duration measured by the Turkish State Meteorological Service in the period from January 1990 to December 1996 are used. Empirical models to estimate the monthly global solar radiation on a horizontal surface for each province are developed. The results obtained have indicated that the models developed here predict solar radiation reasonably well for future projections.

Exergoeconomic analysis of a combined heat and power system with the micro gas turbine (MGTCHP)

This paper presents the results of exergy and exergoeconomic analyses applied to a combined heat and power system with micro-gas turbine (MGTCHP). Quantative balances of the exergy and exergy cost for each component and for the whole system are carefully considered, while exergy consumption and cost generation within the system are determined. The exergy analysis indicates that the exergetic efficiency of the MGTCHP system is 35.80% with 123 kW (as 99.15 kW-electrical power and 24.46 kW-hot water@363.15 K). On the other hand, the exergoeconomic analysis results show that the unit exergy cost of electrical power and hot water produced by the MGTCHP system are accounted as 26.808 €(GW)−1 and 7.737 €(GW)−1, respectively.

Energetic Analyses of the Combined Heat and Power (CHP) System

This study deals with the energetic analysis of a combined heat and power (CHP) system installed in Eskisehir City of Turkey. The mass and energy balance relations are derived and applied to the components of CHP system and overall CHP system. The performance characteristics of this CHP system are evaluated in terms of energetic aspects. Considering total output energy, the total energy efficiencies (electrical and thermal) of gas turbine cycle, heat recovery steam generator(HRSG), steam cycle and CHP system are 95.3 %, 83.56 %, 76.7 % and 79.3 %, respectively. Based on total useful energy output (excepting the stack gas, waste boiler loss, condenser line, medium pressure steam collector energies), the total useful energy efficiencies of gas turbine cycle, HRSG, steam cycle and CHP system are 82.3 %, 65.2 %, 18.5 % and 40.02 %, respectively.

Energy and Exergy Analysis of a Trigeneration Facility with Natural Gas Engine

Natural gas engine (Wartsila 18VSG) having meanly 5,993 kW electrical power output and used in a Trigeneration system located in Ankara was analyzed in terms of energy and exergy. Analysis, which is used actual data, was made to natural gas engine, heat recovery boiler and absorption chiller, while trigeneration system on full load operation conditions. Energy loss, energy efficiency, exergy destruction and exergy efficiencies of the trigeneration system was calculated. The energy and exergy efficiencies of system were determined as 64 and 39 % respectively. FESR (fuel energy saving ratio) and FESxR (fuel exergy saving ratio) were calculated as 27, 28 % respectively for Trigeneration facility.

Estimating and Statistically Analyzing the Global Solar Radiation Potential over Big Cities in Turkey

This study develops empirical models in order to estimate the monthly average daily global solar radiation on a horizontal surface (H). The seven big cities considered in the model have 33.4% of Turkeys population and are as follows: Izmir in the Aegean Sea, Samsun in the Black Sea, Ankara in the Central Anatolia, Van in the East Anatolia, Istanbul in the Marmara, Antalya in the Mediterranen Sea, and Urfa in the Southeast Anatolia Region of Turkey. The developed models were analyzed using the seven statistical analyzing methods such as the mean percentage error (MPE), mean absulate percentage error (MAPE), sum of squares of relative error (SSRE), relative standard error (RSE), mean bias error (MBE), root mean square error (RMSE) and correlation coefficient (R). It may be concluded that the present models estimate the values of H, reasonably well for the cities studied and possibly elsewhere with similar climatic conditions.