Abstract
The purpose of this work is to present a simple methodology which enables to size a thermosyphon system without always having to resort to a computational simulation. As a result of many system simulations using the TRNSYS software, whereby several project and equipment parameters were varied, a group of expressions were obtained which allow the determination of the system thermal daily efficiency (monthly average). The developed correlation includes geometric and thermal aspects related to the collector, the storage tank and the connecting pipes, as well as operational data such as thermal load, solar radiation and room temperature. This model is able to optimize several variables that comprise thermosyphon solar water-heating systems for the requirements of particular applications. The resulting correlation shows that the efficiency is a linear function of meteorological conditions, collector quality and parameters related to storage tank volume, volume load (consumption profile) and collector area. The correlation is very useful since it is a simple, fast alternative for the calculation of system efficiency without depending on experimental determination or numerical simulation results. The determination and sizing of the collector area and the volume storage tank that satisfy the required thermal load can be appropriately performed in a simple and fast way by using the proposed correlation.
Highlights
The resulting correlation shows that the efficiency is a linear function of meteorological conditions, collector quality and parameters related to storage tank volume, volume load and collector area
Solar domestic hot water (SDHW) systems can be divided in active systems and passive systems
The results show that the thermal efficiency: I. is directly proportional to values estimated by the correlation with (Vt/Ac)
Summary
Solar domestic hot water (SDHW) systems can be divided in active systems (fluid impelled by a pump) and passive systems (fluid flowing by natural convection in the circuit). It is common to use thermosyphon solar water-heating systems, a term that applies to some passive systems. Typical design and sizing methods generally contemplate active systems only, and are largely used in countries with colder weather. Due to the lack of specific methods, designers estimate the area required for a given application based on criteria established for the case of forced-flow operations, often employing the FChart methodology (Duffie & Beckman, 1991), for a fixed operating flow rate.
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