experimental and numerical study of a parabolic trough linear cpvt system

Abstract The electric and thermal performance of a parabolic trough linear concentrating photovoltaic-thermal (CPVT) system operating in Padova (northern Italy) is experimentally investigated. The system moves about two axes and exhibits a geometrical concentration ratio around 130. The receiving module placed on the focus line displays a secondary optics made of two flat mirrors to gather some reflected radiation and to contribute to the concentrated flux on two lines of triple junction photovoltaic cells soldered on a ceramic substrate. The substrate is in thermal contact with a aluminium heat exchanger with water flow channels to cool the PV cells. During the test runs, the inlet water temperature ranges from 20 °C to 80 °C and the heat yield is obtained from mass flow rate and temperature measurements while a rheostat and a power analyzer are connected to the electric terminals of the module to assess the electrical production. The direct normal irradiation (DNI) is measured by a pyrherliometer mounted on a solar tracker. Experimental results are used to assess a numerical model of the solar receiver and the whole concentrator

A comparison of numerical simulation methods analyzing the performance of a ground-coupled heat pump system

Ground-coupled heat pumps are increasingly being utilized to heat and cool buildings. Although it is difficult to size and to predict their behavior and performance, their design can be optimized via simulations. EnergyPlus is a popular energy simulation program for modeling building heating and other energy flows and, since it is organized to consider borehole heat exchangers via the well-known g-functions approach, it can be used advantageously for that purpose. The Capacity Resistance Model is another recent numerical simulation tool devoted to ground and borehole heat exchangers. In this work, two methods to calculate the g-fucntions were analyzed, using as case-study a real office building, whose imbalance between the heat extracted and injected into the ground was found to be appreciable. The energy imbalance involves a ground temperature drift affecting the system efficiency. The results of the EnergyPlus g-functions and the Capacity Resistance Model model approaches were compared. The capacity of the two methodologies to accurately simulate this phenomenon were analysed also with reference to the available building's long-term monitoring data. The analysis showed the importance of using g-functions suitable to reflect the layout of the borehole field, in order to correctly evaluate the energy performance of the entire ground source heat pump system

A comparison between numerical methods for evaluating ground coupled heat pump systems performance

Ground coupled heat pumps are increasingly used for HVAC systems. The difficulty in sizing and predicting their behaviour and performance is well known. A suitable simulation is often advisable to help in the design choices. The code EnergyPlus is widely used in the field of building simulation and, since it includes a routine dealing with borehole heat exchangers, based on the wellknown concept of g-functions, it can be profitably used for the considered purpose. On the other hand a numerical tool, namely CaRM, based on a detailed finite difference model of both the ground and borehole heat exchangers has been developed. A comparison between the use and the results of the EnergyPlus g-functions approach and CaRM in ground subsystem modelling was carried out with particular reference to an office building with quite a critical unbalance between heat extracted from and heat injected into the ground