Developing a Method for the Operational Control of an Ecovat System

Abstract

To decrease the emission of greenhouse gases, as well as to reduce our dependency on fossil fuels for satisfying our energy needs, we see a trend towards the use of more sustainable energy sources. However, one of the challenges of these renewable energy sources is the mismatch between energy demand and energy production that often occurs. One of the solutions to deal with this mismatch is energy storage. With storage, energy generated during times of excess production may be stored for use during times of energy shortage. The Ecovat system is an example of an energy storage technology, which aims to store excess thermal energy during times of the year with high thermal and/or electrical energy production, generally during the summer, for use during times of the year with high thermal energy demand, generally during winter. The Ecovat system is designed to be able to satisfy the heat demand of a neighbourhood of houses throughout the year. The Ecovat system consists of a large well insulated underground buffer (i.e. a large water tank), combined with a number of devices, namely photovoltaic-thermal panels, heat pumps, and a resistance heater, to charge the buffer. The buffer of the system consist of a number of segments, which although not physically separated, may be charged or discharged individually through heat exchangers integrated inside the buffer walls. The energy to charge the buffer can be obtained from locally available energy or can be bought on the energy market, preferably when the energy price is low. In this thesis we focus on the operational control of such an Ecovat system. We develop a model to determine which of the available devices in the system should charge which buffer segment at which point in time. Furthermore, the model also determines which buffer segment should be used to satisfy the heat demand from the neighbourhood. As the developed model should serve as the base for handling the operational control of a real Ecovat system, we develop a model that computes such charging strategies in at most a few seconds.