Control of a domestic hot water solar heater with weather forecast

Mihai Radulescu1* and Aude Lepeltier2

1 EDF R&D Site des Renardieres, Dept EnerBat, Avenue des Renardieres – Ecuelles, 77818 Moret sur Loing
2 Ecole des Mines de Douai, 941 rue Charles Bourseul, BP 10838, 59508 Douai Cedex
* Corresponding author, mihai. radulescu@edf. fr

Abstract

This paper presents the efficiency improvement and electricity economy obtained by introducing an advanced control of a hot water solar heater (HWSH) using a weather forecast. In order to quantify the energy gain of the advanced control a numerical model was built for the storage tank. This model takes into account all inlet and outlet energy fluxes and it’s able to determine the temperature inside the tank at any moment and height. The advance control is acting on the set-up temperature of the auxiliary electric heater in order to prepare a reduced quantity of hot water during night and to allow to the solar loop to recover as much as solar energy possible. The comparison between a standard system and a HWSH with weather forecast shows that a 7% annual electrical economy is found and a 3% efficiency improvement.

Keywords: solar thermal, hot water, control system, weather forecast.

1. Introduction

Electricity production in France is mostly nuclear with 88% completed by small parts of natural gas 4% and hydraulic 8%. The most important electricity producer is by far Electricite de France (EDF) with a total annual capacity of about 650 TWh, and just 490 TWh in France.

Face to global warming and approaching oil peak, research efforts turned toward renewable energy sources. Theses technologies can produce “clean” energy without or with low carbon dioxide emissions but remain still expensive and less widespread. One technology, with unlimited resources and a good potential to overcome the actual setbacks, is the solar thermal. Probably the main disadvantages leading to low solar energy use are the intermittent availability and the low reliability of the energy source. Transforming the solar energy in heat seams so simple, but to recover this heat and to use it efficiently becomes more complicated. Heat has to be carried by a fluid (air or water) to be used immediately or to be stored.

This paper focuses on domestic hot water solar heaters (HWSH) with a storage tank and forced circulation of the heat carrier fluid. Such a system is coupled with a meteorological device (not described) to provide the weather forecast. The energy economy and comfort gain are established with respect to a classical HWSH. The description of the system will be followed by a short explanation of the model. The results are divided in two parts: with and without the weather forecast.

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