engleski

Roof integrated solar concrete collectors for domestic hot water heating in protected buildings

Solar collectors and, in general, renewable energy systems may not be installed on protected buildings which would have their historical and cultural character altered. Solar concrete collectors (SCC) with buried pipes in the roof slab are a possible alternative to roof-mounted solar collectors. In this paper, the performance of a domestic hot water heating system with solar concrete collector (DHW-SCC system) is studied. The main elements in the DHW-SCC system are a serpentine pipe buried in the concrete roof, a heat storage tank for DHW preheating and a gas burner for additional DHW heating. The finite volume method (FVM) has been used to solve heat conduction in the concrete roof, mixed convection-radiation heat transfer at the roof surface and heat transfer to the flow of water through the serpentine pipe. The results of the numerical simulations are: water temperature at serpentine pipe exit, heat storage temperature and overall efficiency of the DHW-SCC system. During sunny summer days, the water flowing through the serpentine pipe can be heated up to temperatures of 40 to 50 °C. The temperature of the heat storage tank is mostly between 30 and 40 °C, depending on atmospheric conditions. The average seasonal (May to September) efficiency of the DHW-SCC system is 65-70% (with 40 °C as reference DHW temperature), meaning that the DHW-SCC system saves 65-70% (550-600 kWh) of the energy needed in a reference gas or electric DHW heating system. Various parameters influencing the efficiency of the DHW-SCC system are studied: water flow rate, pipe spacing, total pipe length, pipe depth, roof solar absorptance, roof tilt angle and heat storage size. For example, the spacing between pipe bends should be at least 20 cm while serpentine pipes placed on roofs with tilt angles of 15-30° perform better than the ones placed on horizontal surfaces or roofs with 45° tilt. Pipe depth and roof solar absorptance have strong influence on the efficiency of the DHW-SCC system, while the size of the heat storage tank has only minor influence.

domestic water heating; solar concrete collector; finite volume method; energy saving

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