Investigation of the potential for a smart thermostat to reduce energy consumption of a domestic hybrid heating system

Today almost 705 of the energy consumption can be attributed to spatial heating. Therefore domestic heating systems have a lot of potential for integration of sustainable energy technologies such as air source heat pumps creating a so-called hybrid heating system, decreasing the environmental impact for households.

Early work on the effectiveness of a programmable thermostats, used to control the room temperature, concluded that these devices have significant potential to reduce energy consumption. However, in practice these programmable thermostats are complicated devices to handle, resulting in incorrect and inefficient use of the thermostat. An alternative solution for the programmable thermostat is a self-learning thermostat able to program itself without the need for the user to program the thermostat.

The goal of this graduation project is to investigate the potential energy savings for using a self-learning algorithm which could be incorporated in a smart thermostat. Simulation are executed to investigate the performance of a hybrid heating system compared to a condensing boiler based on different (night) setback schedules using an existing Matlab/Simulink toolbox developed within Bosch Thermotechnology. Boundary conditions like the control strategy, house type and country (weather conditions and energy prices) are taken into account. The results are evaluated focussing on the annual energy costs, primary energy consumption and CO2 emissions of the heating systems investigated.

For the condensing boiler model the old house with the highest heat demand has most potential for energy savings using a night setback with savings between 7-11.5% (€140-200) per year depending on the control strategy. Both the new house with radiator and under floor heating showed energy savings between 3-7% (€30-80) using a night setback. Looking to the environmental impact of the system, the primary energy consumption and CO2 emission reductions are in line with the energy savings, showing the same percentages.

Comparing the energy costs for the hybrid heating system with the condensing boiler model taking into account energy prices and weather influences the potential energy savings for the hybrid heating system are most promising for France and the Netherlands with annual energy savings between €100-200 for the three house types based on the current energy. However, taking into account the additional investment costs for the hybrid heating system the payback time is at least 17 years.

Based on the EU trends for energy to 2030 the potential for the hybrid heating system is expected to improve compared to condensing boiler systems because of gas prices increasing faster than the electricity prices decreasing the energy price ratio’s resulting in higher energy savings.