## 2 Thermochemical Energy Storage Design
### Experimental Prototype Design  
The experimental prototype developed for this study slightly differs from the concept in Figure 2 as the solar collectors E2 and the heat exchanger HX3 were replaced by an electric heater. The prototype was implemented using the commercially available modular equipment for the ductwork, custom made heat exchangers, and custom design parts (see Figure 3). The ductwork was realized with stainless steel air ducts of a nominal diameter of 200 mm and was jacketed by fiber glass insulation of 5 cm in thickness. The air-to-air heat exchanger HX2 is the cross flow custom assembled unit, whose nominal effectiveness was measured as high as 0.95 for the air volume flow rate of 150 m\({}^{3}\)/h. The circulation of air across the aeraulic circuit was realized with a centrifugal in-line commercial fan from SIG Air Handling International (commercial office at Zaventem, Belgium), series BCS-EC200. The air-to-water heat exchanger HX1 has a custom design and is composed of a network of horizontal finned tubes mounted in a wooden insulated box. The water storage tank is a vacuum insulated vertical cylinder of 49 L of capacity, containing the stratification device. The water is pumped by the hydraulic rotary vane pump from GOTEC SA (Sion, Switzerland), series TS60. The hydraulic connections were made from insulated polyamide tubing with internal diameter of 10 mm.  
The reactor module was conceived as a vertical moving bed with controlled solid flow rate. The schematics of the reactor module is shown in Figure 3. The reactor consists of two 72.5 L symmetric stainless steel hollow compartments with tightly fixed metallic sieve on each. The compartments are stacked in such a way they form the 3 L free room between both metallic sieves, which is used for a micro-granular solid material to be flown through the vertical plane. The cross section area for the air flow through the metallic sieves and the solid in between is 0.31 m\({}^{2}\). The feeding of reactor by the solid material is realized by the 10l upper plexiglass hopper as shown in Figure 3. The control over material flow through the reactor is realized with a mechanically driven rotary valve anchored to the bottom part of the reactor. The speed of the valve rotation is adjusted by the stepper motor (denoted as \"M\" in Figure 3).  
The distribution of the air temperature at the inlet and outlet of the reactor is measured by two grids of K-type thermocouples, which are mounted inside the reactor enclosure at the proximity of the metallic sieve on the distance of 3 mm from both sides. The temperature measuring grids at the reactor inlet and outlet are shown in Figure 3 (elements 4 and 5). Moreover, the inlet and outlet air ducts are equipped with additional K-type thermocouples to measure the average inlet and outlet air temperature. The air humidity at the inlet and outlet reactor boundaries is measured by the humidity sensors from VAISALA Corporation (Helsinki, Finland), series HMP5 connected to the analog transmitters Indigo(tm) 201. The air flow rate is measured by the vane wheel flow sensor from Hontzch, series FA, which is mounted on the reactor inlet airduct. The flow rate of the hot water is measured by the turbine type flow meter FT2 from NATEC Sensors GmbH (Garching, Germany) mounted on the water tank inlet. Furthermore, the air-to-air (HX2) and air-to-water (HX1) heat exchangers are also equipped with one K-type thermocouples at each inlet and outlet. The data acquisition system is assembled from the modular National Instruments(tm) CompactDAQ C-series hardware. The characteristics of the measurement equipment are presented in Table 1.