Design and Parametric Investigation of an Efficient Heating System, an Effort to Obtain a Higher Seasonal Performance Factor

The present work introduces an innovative yet feasible heating system consisting of a ground source heat pump, borehole thermal energy storage, an auxiliary heater, radiators, and ventilation coils. The concept is developed by designing a new piping configuration monitored by a smart control system to reduce the return flow temperature and increase the temperature differential between the supply and return flows. The radiators and ventilation heating circuits are connected in series to provide the heat loads with the same demand. The investigation of the proposed model is performed through developed Python code considering a case study hospital located in Norway. The article presents, after validation of the primary heating system installed in the hospital, a parametric investigation to evaluate the effect of main operational parameters on the performance metrics of both the heat pump and the total system. According to the results, the evaporator temperature is a significant parameter that considerably impacts the system performance. The parametric study findings show that the heat pumps with a thermal capacity of 400 kW and 600 kW lead to the highest heat pump and total seasonal performance factors, respectively. It is also observed that increasing the heat pump capacity does not affect the performance indicators when the condensation temperature is 40 °C and the heat recovery is 50%. Moreover, choosing a heat pump with a smaller capacity at the heat recovery of 75% (or higher) would be an appropriate option because the seasonal performance values are not varied by changing the heat pump capacity. The results reveal that reducing return temperature under a proper parameters selection results in substantially higher seasonal performance factors of the heat pump and total system. These outcomes are in-line with the United Nations sustainable development goals including Sustainable Cities and Communities.

Analysis of the influence of condensation temperature and compressor efficiency on heat pump system efficiency

In heat pump cycles, heat is supplied to the working fluid from a certain group of low-temperature bodies and transferred to a group of high-temperature bodies, i.e. the heat source is at a lower temperature and the heat sink at a higher temperature. Using the method of circular processes, in synergy with the possibility of mutual conversion of thermal and mechanical interactions, the process of heat transfer from a lower temperature level to a higher temperature level is enabled. Mechanical work, which, as compensation, should be given by the environment to the system (working substance), is a difference between heat removed and heat supplied. The efficiency of the heat pump mostly depends on the temperature interval at which the process takes place, however, the efficiency of the heat pump is also affected by the thermodynamic parameters of its parts: compressor, condenser, throttle valve, and evaporator. In this paper, the influence of condensing temperature and compressor efficiency on the efficiency of the system as a whole is examined. The calculation was performed for two working substances, R123 and R134a, using the EES software package (Engineering Equation Solver) which is used for numerical modeling of thermodynamic systems, process optimization, and making process diagrams.

Methodology for determining of the main characteristics of a refrigeration system with condensation heat removal by radiative cooling

To reduce the condensation pressure of the refrigerant in the summer, refrigeration system has been developed, in which, during periods of high air temperature, the heat of condensation is removed to the coolant, which was pre-cooled at night due to radiative cooling. A methodology has been developed for determining the main characteristics of the elements of the proposed system and calculating its daily energy consumption. The calculation shows that the proposed system with a nominal refrigerating capacity of 10 kW, using the R404a refrigerant, allows in the climate of the city of Shymkent to reduce the condensation temperature to +32.9°C, and daily energy consumption by 6.5% compared to an ordinary vapor compression refrigeration machine.

Reduction of tar from biomass gasification using a dielectric barrier discharge reactor

A non-thermal plasma reactor was used to investigate its effectiveness in reducing the by-products from biomass gasification. Biomass is used for generating heat and power through gasification, which is a process of converting solid fuel to gaseous fuel at temperatures of 700 to 900 °C by operating a reactor in sub-stoichiometric conditions. This gas mixture can be utilized for liquid fuel synthesis or for fuel cells. However, the by-product of gasification consists of tar, which consists of oxygenates, ringed-aromatics, phenolic compounds, and polyaromatic hydrocarbons (PAH). Depending on the composition, the condensation temperature can be as high as 450 °C, fouling downstream equipment. In this study, a dielectric barrier discharge (DBD) reactor with a coil as the inner electrode was used to reduce toluene, a model tar compound. Toluene was injected into a mixing chamber that was heated to 900 °C, evaporating the toluene, and is entrained by nitrogen into the DBD reactor. High voltage is injected into the DBD reactor to initiate ionization, decomposing the toluene into lighter hydrocarbons. A sampling bottle submerged in an ice bath collects the residual toluene, and the resulting decomposition rate is as high as 70%.

Dynamic Modelling and Experimental Validation of a Domestic Refrigeration Cycle

Performance analysis and design optimization of refrigerators are primarily carried out by time-consuming experiments. The current study presents an alternative method of analysing refrigerators through modelling of the cooling cycle using a software called Dymola, based on an object-oriented programming language, called Modelica. The main components of a domestic refrigerator (compressor, condenser, evaporator, cabinet and capillary tube-suction-line heat exchanger) are first modelled and validated individually. The full dynamic refrigeration cycle model is created afterwards. Both the simulations and the experiments have been conducted using R600a as the refrigerant with on-and off-modes of the reciprocating, single speed compressor. To represent the dynamic cyclic behaviour of the refrigerator, an algorithm block is also included. The algorithm controls the operation using two set-point temperatures of the cabinet. Experiments have been carried out on a single door refrigerator having an interior volume of 343 litres for the validation of the one-dimensional dynamic model. Results show that the cabinet air, evaporation temperature, condensation temperature, power and energy values deviate from experimental values by less than 2°C and 2% respectively. The dynamic modelling is found to be in good agreement with the experiments in the on mode of the compressor and a promising and rapid tool to represent the transient behaviour of the refrigerator.

Detailed elemental abundances of binary stars: Searching for signatures of planet formation and atomic diffusion

Binary star systems are assumed to be co-natal and coeval, thus to have identical chemical composition. In this work we aim to test the hypothesis that there is a connection between observed element abundance patterns and the formation of planets using binary stars. Moreover, we also want to test how atomic diffusion might influence the observed abundance patterns. We conduct a strictly line-by-line differential chemical abundance analysis of 7 binary systems. Stellar atmospheric parameters and elemental abundances are obtained with extremely high precision (< 3.5%) using the high quality spectra from VLT/UVES and Keck/HIRES. We find that 4 of 7 binary systems show subtle abundance differences (0.01 - 0.03 dex) without clear correlations with the condensation temperature, including two planet-hosting pairs. The other 3 binary systems exhibit similar degree of abundance differences correlating with the condensation temperature. We do not find any clear relation between the abundance differences and the occurrence of known planets in our systems. Instead, the overall abundance offsets observed in the binary systems (4 of 7) could be due to the effects of atomic diffusion. Although giant planet formation does not necessarily imprint chemical signatures onto the host star, the differences in the observed abundance trends with condensation temperature, on the other hand, are likely associated with diverse histories of planet formation (e.g., formation location). Furthermore, we find a weak correlation between abundance differences and binary separation, which may provide a new constraint on the formation of binary systems.

Building and using temperature chart to determine thermodynamic efficiency of ship steam-compression heat transformers

The article highlights the method of constructing a temperature chart, which allows evaluating the thermodynamic efficiency of ship combined thermal transformers. Refrigerants R134a, R717 were selected as the analyzed refrigerants in the construction of the temperature chart. The results of calculating the degree of thermodynamic perfection of single-stage combined thermal transformers without a regenerative heat exchanger are presented. The dependence of changing thermodynamic perfection on the melting and condensation temperature is given. The separation and classification of the areas of this dependence is proposed. The process of determining and constructing the characteristics that set the limit of application of the considered thermal transformers is described. The values influencing the position of the selected regions on the temperature chart are revealed. For the selected refrigerants there have been presented the dependences for correcting position of the areas depending on the amount of overheating, degree of supercooling and temperature difference between the boiling point and the temperature of low-potential heat source. The application of the temperature chart is analyzed under the following initial data: refrigerant R134a; condensation temperature 40°C; boiling point –20°C; ambient temperature 20°C; steam overheating 20 K; supercooling of the liquid 8 K; temperature difference between the low-grade heat source and the boiling point 8 K. The graph illustrates an example of using a temperature chart to determine the possibility of using combined heat transformers with specified parameters on the refrigerant R134a. Equations are derived for correcting the position of the lines of temperature charts for refrigerants permitted for the ship power plants.

Аналіз ефективності ежекторних холодильних машин на різних холодоагентах

Modern heat-using ejector refrigeration machines used in heat recovery systems for power plants based on gas turbine engines and internal combustion engines have many advantages over absorption refrigeration machines: smaller dimensions and weight; the ability to obtain lower temperatures. However, they are inferior in energy efficiency, and the thermal coefficient is much lower and can be 0.2…0.4. The efficiency of such refrigeration machines largely depends on the choice of the working fluid (refrigerant). Hence the need to choose a refrigerant that would provide the maximum heat factor, and hence the maximum efficiency of heat recovery. Given the relatively low efficiency of the ejector refrigeration machine, the search for a working fluid that will provide, on the one hand, higher thermal coefficients, and on the other hand high environmental friendliness, is one of the promising areas of development of heat recovery technologies in power plants. The study used the software complex developed by the authors to calculate the refrigeration cycles of heat-using refrigeration machines, taking into account the properties of many modern refrigerants, ejector characteristics, as well as basic heat exchangers (condenser, evaporator, generator). The efficiency of ejector refrigeration machines when working on the following working bodies was analyzed: R142b, R134a, R600, R600a, R1234ze(E), R1233zd(E), R1234yf, R227ea, R236fa, R245fa. R142b, R600, R600a, R245fa have the largest values of thermal coefficients. It is established that the most profitable in terms of environmental friendliness (ODP, GWP) and energy efficiency is the use of refrigerant R245fa, which has a condensation temperature range is 25…35 oC and boiling in the evaporator is 0…15 oC thermal coefficient is 0.40…1.03.

Continued Roots, Power Transform and Critical Properties

We consider the problem of calculation of the critical amplitudes at infinity by means of the self-similar continued root approximants. Region of applicability of the continued root approximants is extended from the determinate (convergent) problem with well-defined conditions studied before by Gluzman and Yukalov (Phys. Lett. A 377 2012, 124), to the indeterminate (divergent) problem my means of power transformation. Most challenging indeterminate for the continued roots problems of calculating critical amplitudes, can be successfully attacked by performing proper power transformation to be found from the optimization imposed on the parameters of power transform. The self-similar continued roots were derived by systematically applying the algebraic self-similar renormalization to each and every level of interactions with their strength increasing, while the algebraic renormalization follows from the fundamental symmetry principle of functional self-similarity, realized constructively in the space of approximations. Our approach to the solution of the indeterminate problem is to replace it with the determinate problem, but with some unknown control parameter b in place of the known critical index β. From optimization conditions b is found in the way making the problem determinate and convergent. The index β is hidden under the carpet and replaced by b. The idea is applied to various, mostly quantum-mechanical problems. In particular, the method allows us to solve the problem of Bose-Einstein condensation temperature with good accuracy.

KAJI PERFORMANSI REFRIGERAN R-290, R-32, DAN R-410A SEBAGAI ALTERNATIF PENGGANTI R-22

Refrigerant R-22 is a substance that destroys the ozone layer, so that in the field of air conditioning it has begun to be replaced, among others with refrigerants R-32 and R-410a, and also R-290. Through this research, we want to know how much Coefficient of Performance (COP) and Refrigeration Capacity (Qe) can be produced for the four types of refrigerants. The study was carried out theoretically for the working conditions of the vapor compression cycle with an evaporation temperature (Tevap) of 0, -5, and -10oC, a further heated refrigerant temperature (ΔTSH) of 5 oC, a condensation temperature (Tkond) of 45 oC and a low-cold refrigerant temperature. (ΔTSC) 10 oC and compression power of 1 PK . The results of the study show that the Coefficient of Performance (COP) in the use of R-22 and R-290 is higher than the use of R-32 and R-410a, which are 4,920 respectively; 4,891; 4.690 and 4.409 when working at an evaporation temperature of 0 oC; 4.260; 4,234; 4.060 and 3.812 when working at an evaporation temperature of -5 oC; and amounted to 3,730; 3,685; 3,550 and 3,324 if working at an evaporation temperature of -10 oC. Based on the size of the COP, if this installation works with a compression power of 1 PK, then the cooling capacity of the R-22 and R-290 is higher than the R-32 and R-410a, which are 3,617 respectively. kW; 3,597 kW; 3,449 kW and 3,243 kW. If working at an evaporation temperature of 0 oC; 3.133 kW; 3.114 kW; 2,986 kW and 2,804 kW if working at an evaporation temperature of -5 oC; and 2,741 kW; 2,710 kW; 2,611 kW and 2,445 kW if working at an evaporation temperature of -10oC.