# Thermal Energy Storage for Building Load Management: Application to Electrically Heated Floor
###### Abstract  
In cold climates, electrical power demand for space conditioning becomes a critical issue for utility companies during certain periods of the day. Shifting a portion or all of it to off-peak periods can help reduce peak demand and reduce stress on the electrical grid. Sensible thermal energy storage (TES) systems, and particularly electrically heated floors (EHF), can store thermal energy in buildings during the off-peak periods and release it during the peak periods while maintaining occupants' thermal comfort. However, choosing the type of storage system and/or its configuration may be difficult. In this paper, the performance of an EHF for load management is studied. First, a methodology is developed to integrate EHF in TRNSYS program in order to investigate the impact of floor assembly on the EHF performance. Then, the thermal comfort (TC) of the night-running EHF is studied. Finally, indicators are defined, allowing the comparison of different EHF. Results show that an EHF is able to shift 84% of building loads to the night while maintaining acceptable TC in cold climate. Moreover, this system is able to provide savings for the customer and supplier if there is a significant difference between off-peak and peak period electricity prices. e +
Footnote †: journal: Applied Sciences  
_Applied_  
floor (EHF). Benefits of floor heating systems are numerous; heating elements are installed within the floor assembly and therefore are invisible to the occupants in the building. Moreover, thermal radiation could provide a better thermal comfort (TC) for the occupants if the floor surface temperature stays below 29 \({}^{\circ}\)C [11]. In fact, using a radiative heating system in comparison to a convective heating system allows diminishing the forced air-circulating loop in the room and the heat sensation will be higher for people with the same indoor temperature. Thus, the possibility to have a lower indoor temperature with the same thermal comfort to reduce the energy consumption of the building (18% in the study of [PERSON] [12]). Moreover, in comparison to hydronic system, the addition of a hot water tank is not necessary and maintenance is almost non-existent for electrically heated floor. Floor heating systems have been used in previous studies to reduce the peak energy consumption. [PERSON] et al. [13] reported that a hydronic floor heating system could reduce the load by 26% during the peak periods and the total energy consumption by 30% in comparison to a conventional convective system. [PERSON] et al. [14] investigated a number of control strategies for shifting the peak demand while the heating system was allowed to operate between 8:00 p.m. and 6:00 a.m., unless the TC was jeopardized. Their results showed that there is an 80% load reduction during the peak period. However, the simulation was carried out during office hours, thus the TC was only studied between 8:00 a.m. and 6:00 p.m. Moreover, the study did not report the floor surface temperature (FST). [PERSON] et al. [15] carried out an experiment with an EHF integrated with PCM in an environment with an average outdoor temperature of 13.6 \({}^{\circ}\)C. The system did not operate from 8:00 a.m. to 11:00 p.m. During the night, their control strategy was based on the heating element temperature (heaters stopped working when the heater temperature was over 70 \({}^{\circ}\)C and worked again when it was below 55 \({}^{\circ}\)C). It was found that the system did not have a good control over the room and floor surface temperatures, which resulted in high average indoor temperature (31 \({}^{\circ}\)C) and FST (40 \({}^{\circ}\)C). [PERSON] et al. [16] conducted simulations and experiments with an EHF with a shape-stabilized PCM. The heating time lasted 10 hours and the intermittent time lasted 14 hours, with outdoor temperature between 0 \({}^{\circ}\)C and 6 \({}^{\circ}\)C. In comparison with other heating strategies (i.e., operating all day), the EHF with PCMs was able to completely shift the load from peak periods to off-peak periods.