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Nowadays, heating power for buildings is often produced by on-site renewable energy sources. However, such sources typically cover only part of the energy demand of the building. Thus, electricity supply from the grid is necessary although it is usually the only necessary external energy source. Cost-effective utilization of electricity requires not only reduction in the share of electricity from the grid but also comprehensive control of all on-site energy systems. In this paper, such a control method is presented. The control procedure takes into consideration fluctuations in the price of electricity, environmental conditions, the thermal mass of the building, and energy storage. The study aims to reduce energy costs by flattening the electricity load's profile and switching the energy systems on and off at predetermined times according to a qualitative control procedure. Thermal and electricity loads are either forwarded or delayed in response to variations in the electricity price but maintain a comfortable indoor temperature. The control method is verified in a simulated residential building using weather data from Helsinki, Finland. The building includes a geothermal heat pump, a solar collector, and an electric heater as energy sources and a hot water tank for thermal storage. The main thermal loads consist of space heating and domestic hot water. The results of a full-year simulation are compared with those of a conventional method with no price-responsive features. The results indicate that load shifting is successful, especially during the cold season. The control method adapts correctly to large and abrupt scheduled loads. Although this method reduces electricity consumption by only 2%, the yearly cost of electricity is decreased by 11.6%.

Nowadays, many buildings are equipped with various energy sources. The challenge is how to efficiently utilize their energy production. This includes decreasing the share and costs of external energy—usually electrical energy delivered from the grid. The following study presents a qualitative approach with a combined control to solve the problem. The approach is demonstrated using a simulated residential building equipped with a hybrid energy system: a thermal energy storage combined with an electrical heater, a geothermal heat pump and a solar thermal collector. Consequently, the share of renewable energy was increased and, conversely, costs of the external energy from grid decreased by 12.2%. The results were based on a qualitative approach and the algorithm which predicts the need of energy of the building over the next 6 h with the aid of weather forecasting. This approach included a storage tank of 300 L. The energy costs can be further decreased 7.7% by increasing thermal storage capacity and modifying the control algorithm. In all cases, the indoor conditions were kept at a comfortable level. However, if the room temperature is temporarily allowed to slightly drop a few degrees during the heating season, the energy costs were further reduced.

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