A hybrid photovoltaic-thermal collector (PV-T) with the capability to produce thermal energy and electrical energy simultaneously has attracted the attention of researchers, especially in terms of improving PV-T performance. This study analyses the work of four model installations with PV-T and other devices built in the transient systems simulation program. The novelty of this article lies in a long-term approach to the operation of PV-T panels under selected climatic conditions. Influence of the installation’s configuration on the obtained temperatures of solar cells, and, in consequence, on electric power generated by PV-T and the amount of heat produced during one year in a selected location is presented. Among others, the impact of the temperature coefficient of photovoltaic cells for long-term PV-T operation was analyzed in the paper. The results showed that the type of cell used may decrease the yearly electric energy production from PV-T even by 7%. On the other hand, intensification of the process of heat reception from PV-T using a heat pump increased this production by 6% in relation to the base model. The obtained research results indicate possible methods for improving the effectiveness of PV-T operation in a long-term aspect.
EFEKTYWNOŚĆ ENERGETYCZNA KOLEKTORÓW SŁONECZNYCH WYKORZYSTUJĄCYCH WODĘ, JAKO PŁYN SOLARNYW Polsce najczęściej stosowanym płynem solarnym w instalacjach grzewczych z kolektorami słonecznymi są 35-50% wodne roztwory glikolu propylenowego lub etylowego. Takie mieszaniny wraz z dodatkami uszlachetniającymi skutecznie zabezpieczają instalację solarną przed skutkami zamarznięcia czynnika roboczego przy niskich temperaturach zewnętrznych panujących w okresie zimowym. Roztwory te, w porównaniu do wody, charakteryzują się wyższą lepkością i niższą wartością ciepła właściwego w zakresie typowych temperatur pracy cieczy roboczej w obiegu solarnym, mają wyższą cenę w przeliczeniu na jednostkową obję-tość oraz mogą powodować zatrucia w wyniku przypadkowego spożycia. W instalacjach solarnych pracujących również w okresie zimowym możliwe jest wykorzystanie samej wody, bez dodatku glikoli, ale konieczne jest wtedy wyposażenie układu regulacji automatycznej sterującego instalacją w funkcję ochrony przeciwzamrożeniowej. Celem niniejszej pracy jest omówienie funkcji przeciwzamrożeniowej w instalacji solarnej z kolektorami próżniowo-rurowymi, w której wykorzystano wodę, jako płyn solarny. Poddano szczegółowej analizie okres czasu, w którym ta funkcja była stosowana. Kolektory słoneczne pracujące w warunkach rzeczywistych dla przygotowania ciepłej wody użytkowej i wspomagania centralnego ogrzewania w obiekcie mieszkalno-usługowym, są częścią multiwalentnej instalacji hybrydowej, gdzie do wytwarzania ciepła dodatkowo zastosowano trzy różne urządzenia grzewcze. Określono również efektywność energetyczną kolektorów słonecznych.
Abstract:In order to predict long-term changes in the temperature of the ground in which a horizontal ground heat exchanger has been installed, it is beneficial to implement simplified mathematical models of heat transfer. The possibility of using a one-dimensional equation of heat conduction while modelling heat transfer in a ground heat exchanger with horizontal pipes has been demonstrated in the work. A theoretical analysis based on the linear heat source model as well as experimental research works have been carried out. It has been concluded that the temperature profiles of the ground in which parallel pipes of the heat exchanger are placed do not significantly differ from the profiles for the heat exchanger in the form of a plate; in particular, this refers to large distances from the level in which the pipes are positioned, small distances between pipes axes and the long duration of the process. Discrepancies between the calculated temperature increases for pipe and plate exchangers varied significantly in the individual time intervals, and were approx. 20-30%. The conducted experiments have demonstrated that the temperature field around parallel pipes of the heat exchanger may be described by the linear heat source model. The compatibility of temperature maps that were determined theoretically and experimentally was satisfactory with a good degree of accuracy.
Currently, the use of air-source heat pumps (ASHP) in combination with a photovoltaic (PV) installation is a very promising option for a necessary and urgent energy transformation in European countries. It is extremely important to develop solutions that will help maximize the use of energy generated from renewable energy sources. Such issues include the problem of insufficient use of generated electricity in PV on-grid microinstallations in residential buildings. This paper’s aim is to analyse the results of a one-year-round operation of a PV array grid-connected hybrid installation with ASHP for domestic hot water preparation in a residential building in Cracow, Poland, in the context of increasing self-consumption of PV energy. Models of systems are built and simulated in the Transient System Simulation software in release 18.05.0001. Simulations were carried out for different scenarios involving different building electricity consumption profiles, PV system capacity and specified runtime management of ASHP. The novelty of this study lies in the evaluation of the impact of a certain range of conditions on the energy performance of the system and in particular on increasing self-consumption. The results showed that the use of ASHP, with specified runtime management, results in an increase in monthly self-consumption values from 7% to 18%, and annual values up to 13%. Moreover, determining the appropriate size of the used PV system depending on whether it is present ASHP in the installation is crucial to increasing the value of this parameter. Overall, this study provides valuable insights into the potential benefits of PV panels and ASHP operating together, particularly on self-consumption values.
Solar energy systems and heat pumps are two promising means of reducing the consumption of fossil energy resources and the cost of delivered energy for residential heating. The integration of these two installations presents a novel combined heating system, so-called bivalent system, operating more economically. The major objective of this paper was to analyze the possibility of construction and benefits of a bivalent system composed of a heat pump and solar collectors for heating and cooling residential buildings.
The main task of mathematical modelling of thermal and flow processes in vertical ground heat exchanger (BHE-Borehole Heat Exchanger) is to determine the unit of borehole depth heat flux obtainable or transferred during the operation of the installation. This assignment is indirectly associated with finding the circulating fluid temperature flowing out from the U-tube at a given inlet temperature of fluid in respect to other operational parameters of the installation.The paper presents a model of thermal and flow processes in BHE consisting of two analytical models separately-handling processes occurring inside and outside of borehole. A quasi-threedimensional model formulated by Zeng was used for modelling processes taking place inside the borehole and allowing to determine the temperature of the fluid in the U-tube along the axis of BHE. For modelling processes occurring outside the borehole a model that uses the theory of linear heat source was selected. The coupling parameters for the models are the temperature of the sealing material on the outer wall of the borehole and the average heat flow rate in BHE. Experimental verification of the proposed model was shown in relation to BHE cooperating with a heat pump in real conditions.
Real and theoretical energy efficiency of vapour compression heat pumps Rzeczywista i teoretyczna wydajność energetyczna parowych sprężarkowych pomp ciepła Abstract This paper presents several ways of calculating real and theoretical energy efficiency coefficients of vapour compression heat pumps in short and long time. Differences in the calculation are associated with taking into account, among others, various components of the heat pump responsible for the consumption of electricity, steady state or transient conditions, part or the nominal load ratio of heat pump. The calculation results are compared with the values of coefficients, which have been obtained theoretically.Keywords: heat pump, seasonal performance factor, seasonal coefficient of performance Streszczenie W artykule przedstawiono kilka sposobów obliczania teoretycznych i rzeczywistych wartości współczynników wydajności parowych sprężarkowych pompy ciepła w krótkim i długim okresie. Różnice w obliczeniach związane są między innymi z uwzględnianiem różnych składowych odpowiedzialnych za konsumpcję energii elektrycznej w pompie ciepła, czy rozpatrywany jest stan ustalony czy nieustalony oraz czy pompa ciepła pracuje z nominalnym czy częściowym obciążeniem. Wyniki obliczeń porównano z wartościami współczynników, które zostały określone na drodze teoretycznej.Słowa kluczowe: pompa ciepła, sezonowy współczynnik wydajności, sezonowy współczynnik efektywności
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