Abstract
Using TRNSYS software, a comparison of the energy performances of flat-plate collectors (FPCs) and evacuated-tube collectors (ETCs) in domestic solar water heating systems located in different climate areas was carried out in order to ascertain solar energy utilization. Investigations were carried out on single FPCs and ETCs and also for strings of four panels connected in series. Tests were conducted using simulations for water as heat transfer fluid with a fixed fluid flow rate and varying the temperature of the collector’s returning fluid. The maximum power peak decreases with the increase in the inlet temperature of the fluid to the collector in the FPC. The maximum outlet temperature of the FPC is higher than the ETC, most of the time. The evacuated-tube collector performs better only in cold climate areas. Simulations suggest that the use of the FPC is strongly discouraged in cold climatic areas due to thermal losses, whereas the ETC works well with reduced dispersion of heat. In warm seasons, on the contrary, the FPC takes advantage of the high environmental temperature which heats the fluid. The maximum yearly outlet temperature and useful power peak predicted in different climatic areas were investigated by varying the temperature of the fluid inlet fed to the two strings of four FPCs and ETCs. In all cases, the outlet temperature is higher in the ETC technology.
Highlights
Scientists who assess the health of our planet see indisputable evidence that the Earth has been getting warmer, in some cases rapidly
Annual peak temperature reached in Naples by the series of four flat-plate collectors (FPCs) is about 107 C, whereas a maximum yearly temperature reached by the series of four evacuated-tube collectors (ETCs) is equal to 120◦°C
To make make a monthly balance, January, one of the worst months for the use of solar energy, was chosen, a monthly balance, January, one of the worst months for the use of solar energy, was chosen, and we noticed that while the first column of the graph referring to the flat-plate collectors reached just 60 ◦ C, the first column of the graph referring to the evacuated-tube collectors reached 70 ◦ C
Summary
Scientists who assess the health of our planet see indisputable evidence that the Earth has been getting warmer, in some cases rapidly. Most believe that human activities, in particular the burning of fossil fuels and the resulting build-up of greenhouse gases in the atmosphere, due to vapor compression refrigeration and air-conditioning, have influenced this warming trend [1,2,3,4,5]. Scientists have documented record-high average annual surface temperatures and have been observing other signs of changes all over the planet—in the distribution of ice, and in the salinity, levels, and temperatures of the oceans [6,7]. The growing interest in finding alternatives to refrigeration and heating, ventilation, and air conditioning (HVAC) systems based on vapor compression has oriented the scientific community. Solar energy is largely employed for heating and cooling water for domestic and industrial uses, respectively, namely solar heating/cooling systems [21,22,23]
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