Abstract
Thermal solar systems are interesting solutions to reduce CO 2 emissions and gradually promote the use of renewable sources. However, sizing such systems and analysing their behavior are still challenging issues, especially for the trade-off between useful solar energy maximization and stagnation risk minimization. The new EPB (Energy Performance of Buildings) standard EN 15316-4-3:2017 offers several methods to evaluate the performance of a forced circulation solar system. One of them is a dynamic hourly method that must be used together with EN 15316-5:2017 for the simulation of the stratified storage tank connected with the solar loop. In this work, such dynamic hourly method is extended to provide more realistic predictions. In particular, modeling of the pump operation due to solar fluid temperature exceeding a set threshold, or due to low temperature differential between solar field and storage tank, is introduced as an on–off control. The implemented code is applied to a case study of solar system for the preparation of domestic hot water and the impact of different design parameters is evaluated. The model predicts a higher risk of overtemperature lock-out or stagnation when the solar field surface is increased, the storage volume is reduced and water consumption is set to zero to simulate summer vacation periods. Finally, a simple modulating control with a time step of a few seconds to a few minutes is introduced, quantitatively showing the resulting benefits in terms of useful solar energy increase, back-up operation savings and reduced auxiliary energy use.
Highlights
Thermal solar systems are of interest to reduce CO2 emissions and gradually introduce renewable sources as a replacement for fossil fuels
Thermal solar systems coupled with a storage are among the most economically viable renewable energy storage systems to produce domestic hot water enabling, inter alia, the reduction of peak loads associated with water heating
The available solar energy progressively reduces due to thermal solar system losses; on the demand side, the energy must be carried from the storage to the points of use, such as the taps or the heating terminals, the energy to be supplied is far more than the needs due to distribution losses
Summary
Thermal solar systems are of interest to reduce CO2 emissions and gradually introduce renewable sources as a replacement for fossil fuels. According to Ivancic et al [1], this large potential is not fully deployed yet, with a share in heating and cooling applications still below 1%. This may be partly due to the 2008 economic crisis, which hit hard on the works entailing a large initial investment, and to the existence of several alternatives to increase the energy performance of buildings and fulfill legal obligations [2], to the growth of competing sources, such as photovoltaic, and to the discontinuous availability of solar energy that requires storage capacity. Pezzutto et al [3] analyze data collected from various sources about the potential in space heating and domestic hot water applications
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