Energy-Pile Model Verification

Equipping the foundation piles with a liquid circuit pipeline makes it possible to use the advantageous ther-mal capacity of the soil for heating and cooling buildings at low cost. The energy performance of the energy-pile in a soil is a transient phenomenon dependent on many parameters, which could be investigate by a computational model. The contribution deals with the description and verification of a new numerical computational software based on a simplified 2D and 2D rotational symmetrical heat conduction model being developed for energy-piles modeling.

Numerical Analysis of the Influence of Basic Operating Parameters on the Performance Characteristics of Solar-Driven Ejector Cooling

Researchers are becoming growingly interested in the development of solar-driven ejector cooling systems, primarily due to their potential to be used as renewable energy sources. Absorption and adsorption refrigeration systems not only involve considerable investment but are also much less reliable than the ejector refrigeration sys-tems, which do not contain any movable parts. In adition, ejector refrigeration has the advantage of low capital cost, simple design, reliable operation, long lifespan and almost no maintance. The only weakness of this system is the low efficiency and its intolerance to deviations from design operation condition.The paper develops a mathematical mod-el with an algorithm which is based on the laws of thermodynamics and the principles of mass and momentum conser-vation. Based on the obtained model, the influence of temperature on the basic system parameters for two working fluids, R134a and R290, is presented. The working fluid temperature ranges are 80-100°C in the generator, 5-15°C in the evaporator and 33-40°C in the condenser. The important performace indicators are the characteristic ejector area ratio Ar (as a geometrical ejector parameter), ejector entrainment ratio, ejector efficiency and the COP. The results indicate that ejector geometry and working fluid type have a major impact on the ejector cooling system’s performance.

Application of Thermal Engineering in Building Stock, Sophisticated Thermotechnical Systems Integrated in Buildings, and Pathogenic Microorganisms

Planned and/or unplanned developments in the setting, which are directly or indirectly in connection to a certain profession or are of multidisciplinary character, have impact on initiation and steering of the course and direction of research campaigns of “vigilant” professional analysts and/or researchers of a profession, i.e. professions. It was the occurrence of the “vicious infection - SARS CoV 2” at the territory of Planet Earth which also initiated the subject professional research in the area of applied thermal engineering within two partial units which may be in interaction with the infection, i.e. which may also be in causal connection: “applied thermal engineering in building stock (only business and residential buildings)”- “sophisticated thermotechnical system integrated in a business or residential building”- “pathogenic microorganisms”. When general, professional and/or scientific public was faced with occurrence of plentitude of information, misinformation, interpretations, misconceptions, and/or ambiguities in the “black box of SARS CoV 2 pandemic”, the subject research was initiated in an analytical and principled manner with application of methods of analysis based on the “logic of rational action” in the given area. The aspects of the approach are adapted to the subject of the research, imperatively and consecutively imposed by the need for analysis and evaluation of causality between the given partial units and pathogenic microorganisms. In relation to the accepted partial units in the stage of utilization of the existing business or residential building for the dedicated purpose, the findings point that, inter alia, if such buildings were constructed as a result of conscientious, competent, responsible, and highly professional work of multidisciplinary builders and if they comprise adequate integrated sophisticated thermotechnical systems which have systematic, functional, and operating capability and which achieve satisfactory target function of the system, they do not “generate” pathogenic microorganisms, do not participate in their transfer, do not intensify their pathogenic properties and activity, do not contribute to occurrence of pandemics, do not jeopardize human health, and do not cause their mortality, etc. but are basically also not intended to “destroy” pathogenic microorganisms reaching the system from the outside and/or treated limited closed spaced within the building frequented by people off their working activities and/or pursuing their working activities, individually or in groups. Depending on the type of the current sophisticated thermotechnical system in the building, if necessary, it is possible to perform interventions aimed at reconstruction so as to “immunize” the system in a manner which may be recognized and designed by professional, competent, experienced, and dedicated thermal engineers. It needs to be noted that the subject exploration is conducted for deontological reasons, with the aim to promote theory and practice in the given.

Instability of Rayleigh-Bernard Convection Affected by Upper Wall Temperature Variation

This paper represents the analysis of Rayleigh-Bernard convection between two parallel plates. Lower wall is being cooled while upper is heated according to periodic spatial distribution. This process has been modeled using Navier-Stokes equations, equation of continuity and energy equation. Solution of the differential equations has been obtained using pseudo spectral numeric method. For discretization in homogeneous direction, Fourier-Galerkin model has been used, while for discretization in inhomogeneous direction Chebyshev collocation method is applied. Time discretization has been performed using Adams-Bashworth two step method of second order. The results of numeric simulation have been presented by figures where vorticity fields, stream-function and velocity are shown for six different time steps.

Air-to-Water Heat Pump Operation Analysis

The aim of this paper is a theoretical analysis of the operation of an air-to-water heat pump located in the Labo-ratory for Thermal Science at the Faculty of Mechanical Engineering in Belgrade. This results provide the basis for further experimental analyzes of this installation.The paper gives a comparative overview of the performance of a scroll and reciprocating compressor when pro-pane (R290) is used as a refrigerant. Also, the analysis of the influence of internal subcooling on the thermodynamic cycle is presented. Finally, according to the developed model of the heat pump performances investigation, the change in the average values of Coefficient of Performance (COP) during the average heating season, forthe period 2014 –2018, is shown.

Numerical Simulation of Fluid Flows in Rotary Discs

The object of this paper is to model the complex fluid motion that is caused by the rotational motion of rotary disks. In doing so, the rotary disk occupied a normal or parallel position with respect to the fluid flow axis. Various designs of rotary bodies were also applied, with the introduction of fluid through the central opening inside the impeller of the rotating bodies and with the introduction of fluid on the outer surfaces of these impellers (surfaces limited by the largest diameters of the rotary discs). During the modeling, different initial conditions for different structures and positions of rotating bodies were adopted. For each individual stream, flow diagrams are given through a cylindrical fluid stream whose translational motion is complicated by the rotational motion of the friction disks in its flow. The results obtained give a clear picture of the disturbances and changes in the front of the fluid motion wave which can be used as a necessary experience in the design of circulating technological systems.

Exergy Analysis of Building Heating with a Groundwater Source Heat Pump

The paper presents an exergy analysis of the groundwater heat pump operation for theneeds of building heat-ing. The analysis was conducted on a monthly basis, given the dependence of exergy on the changing state of the envi-ronment. Changes inheating coefficient and exergy efficiencyof thegeothermal heat pumpheating systemdepending onthe influentialparameters wereanalyzed: groundwater temperature fromthe pumping well, changes in the ground-water temperature on the heat pump evaporatorand water temperature inthe heating system.The obtained results provide insight into thermodynamic indicators of heat pump operation depending on the groundwater temperature and the operation mode of the building heating system. The conducted analysis provides guidelines for the design and opti-mization of heat pumps that work with groundwater as a heat source.

Characteristics of R718 Thermal Systems and Possibilities for Implementation in Refrigeration / Heat Pump Systems in Buildings

Regulations for CFCs and HCFCs refrigerants phase out and HFCs and HFEs reduction and renewed interest in natural refrigerants (water R718, CO2 R744, ammonia R717, air, hydrocarbons etc.) are discussed. Thermodynamic properties of water (R718) are analyzed and benefits of applicationas well as challenges in the implementation of R718 systems are explained. Deep vacuum operating conditions and low specific volumetric cooling capacity of R718 are peculiarities that cause large and extremely large volumetric flow rates for the temperature range of refrigeration / heat pump air –conditioning applications. The required pressure ratio for a given temperature lift is high. The high value of the water isentropic exponent causes high temperature at the compressor discharge. The specifics in the R718 turbo compressors caused by that reasons are analyzed and the range of optimum application of R718 refrigeration / heat pump systems are estimated

Application of Neolepenism in Climatic Conditions with Frequent Fog

Neolepenism is a new type of energy efficient architecture that could respond to the challenges of sustainable development, primarily as a passive means of protection in the fight against the effects of global warming and climate change. The author improved and optimized the positive experiences of the architecture of Lepenski Vir (Serbia) and made a model of a small family house of neolepenism with a flat roof, which he presented at the 50th International Congress and Exhibition on HVAC in Belgrade in 2019. During the presentation of the model, in the discussion at the exhibition, the question was asked: "Can this architecture be applied in climatic conditions with frequent occurrence of morning fog?" Using the meteorological databases of the Meteonorm program and the typical meteorological years for Ljubljana (Slovenia), as well as the previously developed program in Excel that was used in calculations for this architecture of neolepenism, the author presents the results for Ljubljana, a city located in the valley and where morning fogs are common. In meteorological data, the appearance of frequent morning fog is manifested through a reduced intensity of direct solar radiation in the morning. The paper presents conclusions concerning the optimal orientation of neolepenism buildings for this type of climate depending on the energy class of the building.The obtained results at the level of the whole year indicate that for the needs of heating, the eastern orientation is slightly better than the southern one for the buildings of energy class B, while for the less isolated buildings, the southern orientation has a slight advantage. For the area of ​​Ljubljana, the orientation of the neolepenism building does not play a significant role for heating needs, but still the author believes that the originally assumed eastern orientation should be kept as optimal, due to the need for cooling during the summer season. However, in addition to good thermal insulation, the compactness of the form of neolepenism architecture also plays a crucial role in saving energy and achieving thermal comfort.

Thermodynamic Optimization of Cascade Heat Pump

In today’s modern world, development of industry and technology has led to the increase in energy demand. Hence, more fossil fuels are burnt in order to cover this demand. Due to the multiple disadvantages, as well as the negative impact that burning of fossil fuels has on the environment, heat pumps are gaining more importance when providing energy for heating. This paper is aimed at conducting thermodynamic optimization of cascade heat pump in terms of different working fluid combinations and calculating maximum COP. In order to perform thermodynamic analysis, a software program that uses database of working fluids, was developed. The intermediate temperature within cascade heat exchanger represents a crucial parameter when analyzing and designing cascade heat pumps. Thus, when performing thermodynamic analysis, the intermediate temperature was varied in the range from 0°С to 25°С and the optimal temperature that provides maximum COP was defined. The analysis was performed on an air–to–water heat pump, that could be used for heating different types of buildings in places in Serbia where the outdoor design temperature is –20°С. The cascade heat pump would be used alongside radiator heating system operating at temperatures 70°С/50°С. Due to the high temperature difference between heat source and heat sink, cascade heat pumps have advantages over single stage or multi stage heat pumps. The optimization was performed on an air–to–water cascade heat pump where the evaporation and condensation temperatures were –25°С and 75°С, respectively. Following the conducted optimization, the analysis of the impact that isentropic efficiency of compressor has on COP was examined.