scholarly journals Recommendations for Running a Tandem of Adsorption Chillers Connected in Series and Powered by Low-Temperature Heat from District Heating Network

Energies ◽  
2021 ◽  
Vol 14 (16) ◽  
pp. 4791
Author(s):  
Bartlomiej Nalepa ◽  
Tomasz Halon
Keyword(s):  
Cooling System ◽  
District Heating ◽  
Negative Influence ◽  
Asynchronous Operation ◽  
Heating Water ◽  
In Series ◽  
Water Mass Flow Rate ◽  
Operating Cycles ◽  
Secondary Device ◽  
Selection Of

In this paper, we investigate implications of running a cooling system of two silicagel/water adsorption chillers powered by a district heating network. The devices are connected in series, i.e., the heating water output from the primary chiller is directed to the secondary one. In consequence, the secondary device must deal with an even lower driving temperature and with temperature fluctuations caused by the primary device. We have evaluated three factors that influence the operation of those coupled devices: synchronization of their operating cycles, selection of their cycle time allocations (CTAs), and changing the heating water mass flow rate. Numerical analyses indicate that the performance of the secondary chiller drops significantly if the coupled devices that use the same CTA run asynchronously. The decrease is largest if the shift between the operating cycles is x=0.375 and x=0.875. We found that it is possible to reduce the negative influence of the asynchronous operation by implementing different CTA in each chiller. The best performance is achieved if the primary chiller uses an adsorption time to desorption time ratio f=1.0 and the secondary chiller uses f = 0.6–0.7.

scholarly journals Exploitation of Excess Low-Temperature Heat Sources from Cogeneration Gas Engines

2021 ◽  
Author(s):  
Darko Goričanec ◽  
Danijela Urbancl
Keyword(s):  
Low Temperature ◽  
Cooling System ◽  
District Heating ◽  
Exhaust Pipe ◽  
Gas Engine ◽  
Excess Heat ◽  
Temperature Excess ◽  
Heating Water ◽  
Temperature Heat ◽  
In Series

The chapter presents an innovative technical solution for the use of low-temperature excess heat from the combined heat and power (CHP) of gas engines using gas or liquid fuel for district heating, building heating or industry. The primary fuel efficiency of CHP gas engines for heat production can be significantly increased by using the low-temperature excess heat of the exhaust gasses and the cooling system of the CHP gas engine, which are released into the environment thereby also reducing CO2 emissions. District heating hot water systems generally work with higher temperatures of the heating water, which is transported to the heat consumer via the supply line, and the cooled heating water is returned to the CHP gas engine via the return line. In order to make use of the excess low-temperature heat of the exhaust gasses and the cooling system of the CHP gas engine, a condenser must be installed in the exhaust pipe in which the water vapor contained in the exhaust gasses condenses and a mixture of water and glycol is heated, which later leads to the evaporator of the high-temperature heat pump (HTHP). The cooled heating water is returned from the heat consumer via the district heating return pipe to a condenser of one or more HTHPs connected in series, where it is reheated and then sent to a CHP gas engine, where it is reheated to the final temperature. The Aspen plus software package is used to run a computer simulation of one or more HTHPs connected in series and parallel to the district heating system and to demonstrate the economics of using the excess heat from the exhaust gasses and the cooling system of the CHP gas engine.

scholarly journals An IoT-Based Participatory Antitheft System for Public Safety Enhancement in Smart Cities

Smart Cities ◽  
2021 ◽  
Vol 4 (2) ◽  
pp. 919-937
Author(s):  
Nikos Papadakis ◽  
Nikos Koukoulas ◽  
Ioannis Christakis ◽  
Ilias Stavrakas ◽  
Dionisis Kandris
Keyword(s):  
Smart Cities ◽  
Low Cost ◽  
Negative Influence ◽  
Asset Tracking ◽  
Tracking Tasks ◽  
Tracking Process ◽  
The Impact ◽  
Operation Center ◽  
Safety Enhancement ◽  
Selection Of

The risk of theft of goods is certainly an important source of negative influence in human psychology. This article focuses on the development of a scheme that, despite its low cost, acts as a smart antitheft system that achieves small property detection. Specifically, an Internet of Things (IoT)-based participatory platform was developed in order to allow asset-tracking tasks to be crowd-sourced to a community. Stolen objects are traced by using a prototype Bluetooth Low Energy (BLE)-based system, which sends signals, thus becoming a beacon. Once such an item (e.g., a bicycle) is stolen, the owner informs the authorities, which, in turn, broadcast an alert signal to activate the BLE sensor. To trace the asset with the antitheft tag, participants use their GPS-enabled smart phones to scan BLE tags through a specific smartphone client application and report the location of the asset to an operation center so that owners can locate their assets. A stolen item tracking simulator was created to support and optimize the aforementioned tracking process and to produce the best possible outcome, evaluating the impact of different parameters and strategies regarding the selection of how many and which users to activate when searching for a stolen item within a given area.

THE CONCEPT, TYPES, TASKS AND THE NEED FOR THE USE OF URGENT INVESTMENT TOOLS OF CRISIS MANAGEMENT AT ENTERPRISES

2017 ◽  
Author(s):  
Oksana Yurynets ◽  
Keyword(s):  
Crisis Management ◽  
Economic Condition ◽  
Negative Impact ◽  
Negative Influence ◽  
Management Program ◽  
Management Tools ◽  
The Subject ◽  
Effective Development ◽  
Selection Of

Currently, many Ukrainian enterprises are in crisis. Getting out of this situation requires the use of various types of urgent crisis management tools, among which investment instruments play an important role. The purpose of this article is to form the theoretical basis for the use of urgent investment tools of crisis management at enterprises. It was found that the urgent investment tools of crisis management in the enterprise should be understood as ways of immediate (urgent) investment actions which are aimed at eliminating or reducing the negative impact of the crisis on the economic condition of the enterprise and ensuring its further effective development. These instruments are grouped according to the following characteristics: the environment in which the relevant instruments are formed and operate, the relation to the current owners of the enterprise, the effectiveness of implementation, the duration of the effect of implementing instruments, the urgency of their implementation, the areas of investment, the objectives of application, the duration of application, the types of financial and economic crises at the enterprise, the elimination (reduction) of the negative influence of which the corresponding tools are directed at, the subject of investment. It is established that the main tasks of using investment urgent tools of anti-crisis management at the enterprises are: selection of the best types of investment urgent tools of anti-crisis management; selection of the best variant of each type of urgent investment tools of crisis management; setting deadlines for the implementation of selected types and options for urgent tools of crisis management at the enterprise; determination of the optimal amount of total investments that should be invested in the implementation of the crisis management program at the enterprise, and the corresponding to this volume of the general list of investment urgent tools of such management; identifying the best sources of investment and establishing the best structure of investment in terms of these sources.

scholarly journals Analysis and Suppression of Unwanted Turn-On and Parasitic Oscillation in SiC JFET-Based Bi-Directional Switches

Electronics ◽  
2018 ◽  
Vol 7 (8) ◽  
pp. 126 ◽  
Author(s):  
Lina Wang ◽  
Junyi Yang ◽  
Haobo Ma ◽  
Zeyuan Wang ◽  
Kabir Olanrewaju ◽  
...  
Keyword(s):  
Integrated Circuit ◽  
Matrix Converters ◽  
Turn On ◽  
High Efficient ◽  
Power Electronic Circuits ◽  
In Series ◽  
Ferrite Ring ◽  
Effect Transistor ◽  
Parasitic Oscillation ◽  
Selection Of

Silicon Carbide (SiC)-based Bi-Directional Switches (BDS) have great potential in the construction of several power electronic circuits including multi-level converters, solid-state breakers, matrix converters, HERIC (high efficient and reliable inverter concept) photovoltaic grid-connected inverters and so on. In this paper, two issues with the application of SiC-based BDSs, namely, unwanted turn-on and parasitic oscillation, are deeply investigated. To eliminate unwanted turn-on, it is proposed to add a capacitor (CX) paralleled at the signal input port of the driver IC (integrated circuit) and the capacitance range of CX is also analytically derived to guide the selection of CX. To mitigate parasitic oscillation, a combinational method, which combines a snubber capacitor (CJ) paralleled with the JFET (Junction Field Effect Transistor) and a ferrite ring connected in series with the power line, is proposed. It is verified that the use of CJ mainly improves the turn-off transient and the use of a ferrite ring damps the current oscillation during the turn-on transient significantly. The effects of the proposed methods have been demonstrated by theoretical analysis and verified by experimental results.

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