Abstract

In the cold northern climate of Canada, building energy consumption for space heating during the winter have caused huge stress on electrical grids, especially during the peak hours. Shifting or shaving the peak demand can avoid additional capital investment required to meet extra peak demand for the electrical suppliers. Consequently, in the recent years, several utility companies adopted time-based rates to encourage the customers to shift their consumption from high demand hours to those with lower demand. In this regard, the two most commonly used time-based rates are time-of-use tariffs and critical peak pricing. Achieving peak shifting can reduce the heating cost under time-based rates for consumers. Overall, peak shaving is benefit not only for the electrical suppliers but also for the consumers.
Most Canadian residential houses are equipped with a concrete slab in their basement primarily for structural integrity. Such high thermal mass concrete slab can be exploited for heat storage to shift the peak power consumption. To take benefit of the concrete slabs in the basement, in previous research works, the self-learning control system and the heat extraction system were proposed to achieve peak shifting in the basement and in the other floors of the buildings, respectively. Despite several advantages, the major limitation of these studies is that the developed self-learning control system focused only on peak shifting in the basement, while the heat extraction system concept was investigated separately from the self-learning control system.
Accordingly, this study focused on developing an advanced controller, which can efficiently operate both electrically heated floor and heat extraction system with the objective of achieving the peak shifting, heating cost savings and guaranteeing the thermal comfort in the whole building. As a preliminary work of this study, the peak shifting ability and heating cost savings potential of the self-learning control system operated electrically heated floor under two electrical tariffs (i.e. time-of-use tariffs and critical peak pricing) was analyzed using a validated TRNSYS-MATLAB model. Later, the advanced controller was developed for extending the peak shifting from the floor with high thermal mass to that without high thermal mass by the electrically heated floors integrated with the heat extraction system. In this regard, the developed TRNSYS-MATLAB model was integrated with the heat extraction system. Consequently, the peak shifting ability, heating cost savings of the advanced controller was compared with the other commonly used peak shifting control strategies (i.e. constant set point control and rule-based control) and the respective results are presented. At last, a parametric study using Taguchi method was performed to explore the effective parameters that significantly influence the performance of electrically heated floor, heat extraction system in terms of peak shifting ability, thermal comfort and capital cost. For this purpose, three levels were considered for five factors (A) concrete slab thickness, (B) insulation thickness, (C) fan flow rate, (D) indoor air temperature upper limit and (E) floor surface temperature upper limit. Based on the results of the parametric study, overall recommendation to design the optimal electrically heated floors and heat extraction system was provided.
Regarding the results, the peak shifting, thermal comfort and heating cost saving are presented for two tariffs (time-of-use tariffs and critical peak pricing) considering the floor with concrete. The simulation results showed that the peak shifting can be achieved at 99.7% in critical peak pricing and 97.6% in time-of-use tariffs, respectively. On the other hand, to extend the peak shifting in the whole building, self-learning control integrated with a fan (heat extraction system) can improve the peak shifting in basement (up to 97%) and second floor (up to 88%). The cost saving can also increase around 35%, which can be proven financially attractive to both supplier and owner. At last, through parametric study, the optimal condition for efficient design and operation of electrically heated floor system and heat extraction system was found to be concrete slab thickness of 152.4 mm, an insulation thickness of 101.6 mm, a fan flow rate of 400 CFM, air indoor upper limit of 24.5 °C and floor surface temperature upper limit of 28 °C