Components description

The paragraph offers a detailed overview of components and sensors within the hardware of the prototype. The system is characterized by three loops, one works with ambient air while the others respectively manage harvested water and water for regeneration. These two are:

 The condenser circuit: closed loop that collects water by condensing vapour extracted from silica bed and delivers heat to external environment.

 The solar circuit : closed loop acting as heat source of the system, indeed it delivers the heat needed during regeneration using thermal solar collectors and water as working fluid.

Instead, air loop has the duty of taking in and out the system ambient air, whose pathway is regulated by a 4-way valves able to alternatively address air to regeneration and adsorption loops. A brief description of components will be given following.

Figure 20. 3-D representation of Breath

Solar collectors. A pair of flat plate solar collectors is installed on the top of the machine with a tilt angle of 30°and 2 [m²] of gross area each. In addition, the design allows both parallel and series connections according to project specifications.

Batteries. The two batteries within the system are conventional heat exchanger filled with silica gel spheres of 3 [mm] of diameter. The geometry of each battery is 630x485x190 [mm] and these are installed symmetrically on left and right sides of Breath considering the frontal view.

The total mass of silica embedded in a single battery is 18.77 kg.

Figure 21. Adsorption battery

Condenser. The condenser is in charge of cooling air stream below the dew point and pre-heating the air exiting the system directed toward the adsorption battery. The entire process is realized separately in the upper and lower sections of the condenser. In particular, the upper part is equipped with a heat exchanger used to cool down the stream before reaching the bottom of the condenser. The heat extracted goes to the battery involved in regeneration, in this way an internal heat recovery is performed. In the lower part condensation takes place using a radiator interconnected with the condenser circuit, that customs water as working fluid. After air cooling, freshwater is collected at the bottom and water flow of condenser circuit is regenerated. This process is performed by two radiators that treats half of the total mass flow involved and exchange heat with ambient air, used as cold shaft.

Double four-way valve. The double four-way valve is the component responsible to switch working function of heat exchangers, from adsorption to regeneration and vice versa. It makes use of an actuator placed on top to change the position of the inner shaft, that alternately closes 2 out of 4 ways available.

Figure 22. Four-ways valve

Fans. The system presents a total number of four fans, two used to move air in the regeneration/adsorption circuits (F2 and F1 respectively) and the others (F3 and F4) embedded in the condenser circuit to cool down water flow. The firsts are centrifugal blowers with nominal rated power of 65W, where only F2 can be regulated to test the system at different flow rates.

Fans in the condenser are axial type characterized by maximum rated power of 170W with the possibility of being regulated.

Figure 23. Centrigugal (Sx) and axial (Dx) blowers

Sensors. The system is equipped with several sensors that constantly control temperature and relative humidity of the process.

In particular, temperature sensors are LM35 type thar supplies an output voltage linear function of the temperature measured in input. The accuracy of the instruments varies according to ambient temperature from a minimum of +-1/4°C at Tamb=25°C to a maximum of +-3/4°C over the full range [-55,150]°C.

Instead relative humidity is constantly controlled by the HIH-4000 Series Humidity Sensors, which realizes the analogical-analogical conversion suppling linear voltage in output.

Moreover, the accuracy of the sensor is +-3.5%.

In both cases sensors provides analogical outputs, then converted by controllers which acts as the brain of the entire process. The next table summarises all sensors involved, location and fluid checked.

NAME FLUID TYPE LOCATION

TBD1 Air Temperature Inlet Bed Dx

TBD2 Air Temperature Outlet Bed Dx

TBS1 Air Temperature Inlet Bed Sx

TBS2 Air Temperature Outlet Bed Sx

TBD3 Water Temperature Inlet Bed Dx

TBD4 Water Temperature Outlet Bed Dx

TBS3 Water Temperature Inlet Bed Sx

TBS4 Water Temperature Outlet Bed Sx

TC1 Air Temperature Inlet Condenser

TC2 Air Temperature Outlet Condenser

TPD Water Temperature Outlet Solar Collector Dx

TPS Water Temperature Outlet Solar Collector Sx

RHBD1 Air Relative Humidity Inlet Bed Dx

RHBD2 Air Relative Humidity Outlet Bed Dx

TAMB Air Temperature Ambient

Table 1. Sensors inventory

Arduino. Arduino is a Programming Logic Controller “PLC” used to collect and read signals coming out from sensors. It is used as intermediate component between sensors and Controllino, whose function is explained below.

Controllino. Controllino is a PLC usually involved in industrial application, suitable for receiving analogical signals and converting these in analogical or digital output to components of the system. In practise, this device implements a control logic program in order to enhance the performance of the system.

Loadcell. The loadcell acts as scale to measure the weight variations of the battery. Indeed, the heat exchanger varies its mass according to adsorption and desorption phase performed, therefore the total amount of water collected from air can be easily evaluated having knowledge of mass of empty battery.