Orhan Ekren

Exergy analysis and environmental impact assessment of a photovoltaic-hydrogen production system

In this study, exergy analysis and environmental impact assessment of a Photovoltaic (PV)-hydrogen production system and its components are carried out. Actual data measured in the system are employed for analysis purposes. Daily hydrogen production amount from solar energy through water electrolysis is 4.43 kg. The average system exergy efficiency is determined to be 3.18%. It is found that the highest exergy destruction occurs in the PVs. In the PVs, 93.3% of the total exergy input (incoming solar exergy) is destroyed. The second highest exergy destruction is from the electrolyser as 4.76% of the total exergy destruction. The average percent exergy destructions are 1.29% and 1.94% for charge controllers-inverter and batteries, respectively.

Assessment and improvement of indoor environmental quality in a primary school

This study reports levels of indoor environmental quality variables before and after installation of heat recovery ventilation in a primary school located in an urban area in Izmir, Turkey. A CO2-based modeling was performed to determine the required flow rates that would comply with an international ventilation standard, followed by computational fluid dynamics modeling for best airflow distribution in a classroom. Temperature, CO2, PM2.5, and total volatile organic compounds were found at undesired levels, among which relative humidity, CO2, and PM2.5 were improved after the intervention. Reductions in the mean and maximum concentrations were 29% and 68% for CO2 and 29% and 46% for PM2.5. This intervention study was a part of the city-wide main project that aimed to increase awareness of the students and their families, teachers, and staff regarding importance of indoor environmental quality in both at school and home due to its possible effects on childrens health and academic performance, one of the major challenges of todays societies all around the globe.

Operation of Compressor and Electronic Expansion Valve via Different Controllers

The most critical problem in the world is to meet the energy demand, because of steadily increasing energy consumption. Refrigeration systems` electricity consumption has big portion in overall consumption. Therefore, considerable attention has been given to refrigeration capacity modulation system in order to decrease electricity consumption of these systems. Capacity modulation is used to meet exact amount of load at partial load and lowered electricity consumption by avoiding over capacity using. Variable speed refrigeration systems are the most common capacity modulation method for commercially and household purposes. Although the vapor compression refrigeration designed to satisfy the maximum load, they work at partial load conditions most of their life cycle and they are generally regulated as on/off controlled. The experimental chiller system contains four main components: compressor, condenser, expansion device, and evaporator in Fig.1 where this study deals with effects of different control methods on variable speed compressor (VSC) and electronic expansion valve (EEV). This chiller system has a scroll type VSC and a stepper motor controlled EEV.

Size Optimization of a Solar-wind Hybrid Energy System Using Two Simulation Based Optimization Techniques

Energy is an important fact for a country for both its socio-economic development and economic growth. Main energy source on earth is the fossil fuels. However, the usage of fossil fuels causes global warming whose negative effects have recently been felt by all over the world. Also, because it is limited on earth, increased energy demand and high energy prices increase concerns on fossil fuels. For instance, petroleum reservoirs are present only in few countries therefore the other countries mostly purchase petroleum from these countries more than their production amount. Hence, decrease of fossil fuel reservoirs may create a new ‘energy crisis’ and/or “energy wars” as in 1970s in near future. For a sustainable world the usage of fossil fuels must be decreased, in fact ended. Instead, the usage of renewable energy sources must be increased. As it is known, the interest in renewable energy sources has increased because it does not cause greenhouse effect in contrary to the fossil fuels. These energy sources are indigenous, environmental friendly and, they help to reduce the usage of fossil fuels. Solar, wind, wave, biomass and geothermal energies are renewable energy sources. Sun is the source of all energies. Solar energy is usually used in two aims: for thermal applications and for electricity production. Wind is the indirect form of solar energy and is always replenished. The past and the predicted amount of global renewable energy source status by 2040 are presented in Table 1. As seen in this table the renewable energy consumption is predicted to increase in the future. There are several studies on renewable energy sources and hybrid combination of these sources for electricity production. Electricity has high cost mostly due to centralized energy systems which operate mostly on fossil fuels and require large investments for establishing transmission and distribution of grids that can penetrate remote regions (Deepak, 2009). Unlike the centralized energy systems, decentralized energy systems are mostly based on renewable energy sources. They operate at lower scales (a few kWh scale) both in the presence and absence of grid, and easily accessible to remote locations due to generation of

Energetic and Exergetic Performance Evaluation of an AC and a Solar Powered DC Compressor

This study represents experimental performance analyses of an alternative current (AC) and a direct current (DC) refrigeration compressors implemented in a 79 liter refrigerator. Experiments were carried out at continuously running (ON) and periodically running (ON/OFF) operation modes. Data was analyzed and a comparison in terms of cooling capacity, power input, coefficient of performance (COP), Carnot COP, and exergy efficiency was conducted. The comparison showed that DC compressors can be much more efficient than AC compressors in refrigeration units.

Development and evaluation of transfer functions for a variable speed compressor

In this study, transfer functions of electronic expansion valve and variable speed scroll compressor in a chiller system are developed based on an experimental analysis. Dynamic behaviours of water temperature at chiller output and refrigerant superheat at evaporator outlet have either the first- or the second-order linear models, respectively. Different from the existing modelling studies in literature novel models are presented for variable speed refrigeration system with scroll compressor and liquid type evaporator. The scroll compressor used in the current study is not produced for variable speed operation however it is operated with some limitations in the range of 30 to 50 Hz through an inverter. Similar restrictions are presented for the electronic expansion valve as 10 per cent to 35 per cent opening range because of operational limitations. To validate transfer functions of the variable speed scroll compressor and electronic expansion valve, mean square error values for all transfer functions are calculated. The mean square error values vary between 0.0126 and 0.3116. In addition, all transfer functions are designed and tested using corresponding proportional–integral–derivative controllers in order to see their applicability. The results indicate that energy savings are a consequence of operating the chiller at smaller frequencies than the basic 50 Hz while partial load occurred.

Thermal and exergetic analysis of a rotary-type magnetic cooling system

Despite the high theoretical performance limits of magnetic refrigeration systems, coefficient of performance (COP) of these systems can be lower due to abortive magnet and magnetocaloric material (MCM) assembly orientation and space limitation. To address both of these problems, a rotary-type magnetic cooling system with varied geometric properties was modelled and simulated. Heat transfer from the MCM, which was selected to be gadolinium (Gd), to the working fluid, was considered as volumetric energy generation. Three different geometries of disc-MCM assembly were studied where the inner and outer radii were selected as 5, 10, 15 mm, and 10, 15, 20 mm, respectively. It was observed that the gradient between steady-state temperature and the room temperature decreases with decreasing gadolinium-to-disc area ratio. Conductive heat transfer through the thickness of the disc was found to be inconsiderable compared with the convective heat transfer through the top surface.

SÜT SOĞUTMA TANKININ BUHAR SIKIŞTIRMALI VE GÜNEŞ ENERJİLİ ABSORPSİYONLU (LiCl-H2O) SOĞUTMA SİSTEMLERİYLE SOĞUTMA PERFORMANSININ DENEYSEL İNCELENMESİ

Bu calismada ciftlik tipi bir sut sogutma tankinin, klasik buhar sikistirmali sogutma sistemiyle sogutulmasina alternatif olarak, gunes enerjili bir absorpsiyonlu sogutma sistemiyle sogutulmasi deneysel olarak incelenmistir. Calismada 1000 litre kapasiteli 2BII sinifi ciftlik tipi bir sut sogutma tanki kullanilmistir. Tank tabani klasik buhar sikistirmali sogutma yapabilecek ozellikte olup, tank cevresi ise absorpsiyonlu sogutma sistemine uygun ozel isi degistirici (rollbond) sistemiyle donatilmis olarak imal edilmistir. Deneysel calismalarda, klasik buhar sikistirmali sogutma sistemi ve hibrit yontem (icsel enerji depolamali LiCl-H 2 O ciftiyle calisan absorpsiyonlu sogutma ile ardindan klasik buhar sikistirmali sogutma sistemi) kullanilarak, sut sogutma tankinin ilk ve son sagim sogutma performanslari Uluslararasi ve Turk standartlarina gore ortaya konulmustur. Her iki sistemle yapilan sogutmada, ilk sagim sogutmasi sinir kabul edilen sure icinde tamamlanmistir. Son sagim sogutmasi ise, buhar sikistirmali sogutma sistemi ile zamaninda tamamlanirken, hibrit yontemle sinir kabul edilen sureden daha fazla zaman almistir. Genel olarak, ayni sogutma kapasitesi icin klasik buhar sikistirmali sogutma sisteminin ozgul enerji ihtiyaci 21,06 Wh/L olurken absorpsiyonlu sogutma sistemi ilaveli hibrit yontemin ozgul enerji ihtiyaci 18,01Wh/L olarak bulunmustur. Ulkemizin avantajli konumda oldugu gunes enerjisi, jeotermal enerji gibi yenilenebilir enerji kaynaklarinin kullanildigi absorpsiyonlu sogutma sistemlerinin farkli sogutma uygulamalarinda daha fazla yer almasiyla onemli duzeyde enerji tasarruflari saglamak mumkun olabilecektir.