Civil Engineering Reference
In-Depth Information
3.1.5 Sensible Heat Storage Using Electric Heating
The electric heating of building fabric component (mainly hollow-core bricks)
during off-peak hours with good electricity tariff plan is a feasible method to store
the thermal energy significantly. The hollow-core bricks made up of either mag-
netite or magnesite material suitably encased by a metal container when subjected
to electrical resistance heating would capture and store the desired heat energy
during part-load conditions. The stored heat energy is then dissipated to the
individual or centralized zones during on-peak load conditions in building using
passive or active air movement across the brick components.
Typically, the room air circulating over the heated bricks during daytime picks
up and transmits the heat energy to the indoor spaces. For passive system oper-
ation, the room air by natural convection transfers the required heat energy into the
room, whereas active systems utilize air circulation by fan or blower to meet out
the heating load demand.
The temperature of brick components can be increased up to 760 C during
part-load conditions. Besides, the outer surface of the brick heater can still remain
at temperatures below 80 C. The TES capacity of the brick components can vary
from 49 to 216 MJ (ASHRAE Handbook
2012
). The charging (heat storage)
period of these bricks approximately varies between 6 and 7 h, and the rate of
discharging (heat release) into indoor spaces can vary on an average from 4 to 5 h.
Also, the thermal energy discharging efficiency of bricks depends on the room
size, space heating load demand during the entire day's operation and the heat loss
effects in addition to climatic variations. Brick heaters can also cater the inter-
mediate or fluctuating heating load conditions that might occur in buildings with
variation in the outdoor air temperature. The heat energy that is transferred by the
electrically heated hollow-core bricks to the room air can possibly supplement the
heating load demand without losing the thermal comfort to occupants in indoor
environment.
The heat storage capacities for residential equipment and large commercial/
industrial systems vary from 310 to 864 MJ and 3,460 MJ, respectively. Likewise,
the electric power input to the above systems varies from 14 to 46 kW and 53 to
160 kW, respectively. On the other hand, the radiant hydronic heating storage
system utilizes a separate air-to-water heat exchanger, wherein the heat energy
stored in the brick components is transferred to the heat transfer fluid through the
heat exchanger module.
This module can be integrated to an air-handling system or room-heating
systems (underfloor or ceiling unit) for effectively discharging the thermal energy
into the conditioned space. The electric power input to radiant hydronic heating
system varies from 20 to 46 kW, and their heat storage capacity range from 430 to
865 MJ.
