**2. System description**

The present section describes the system configuration of the energy harvester (or scavenger) used to supply a thermostatic motorized valve of a heating system for residential applications.

The Scavenger of Fig. 1 is composed by three main subsystems:


**Figure 1.** Hydraulic Energy Harvester system scheme

A cross flow turbine transforms the hydraulic power of the water flow into mechanical power used to drive a small electric generator. The device includes an energy storage unit to match the relatively constant power production profile of the generator unit with the more discontinuous one that characterizes the load. Additionally, since the generator and the valve are in series, the energy storage ensures the possibility to open the valve from the closed state (no flow). The energy is then stored during the peaks of production and then reuse it in a second time when prompted by the operational unit, the valve in our case. To this end the power management system is made to operate at its Maximum Power Point (MPPT) through closed loop control of recovered current from the scavenger unit.

## **2.1. Specifications and design choices**

468 Smart Actuation and Sensing Systems – Recent Advances and Future Challenges

et al., 2010) and an Helmholtz resonator based generator (Kim et al. 2009).

The Scavenger of Fig. 1 is composed by three main subsystems:

**Figure 1.** Hydraulic Energy Harvester system scheme

systems.

applications.

**2. System description** 

• hydraulic machine • electric generator • energy storage unit

environmental monitoring. The basic concept is to convert a fraction of the energy that would be normally dissipated by the process into electrical energy. These "secondary" energy sources are then used as primary sources in micro generators whose electrical current will be used to power the devices distributed along the process. The physical phenomena involved in this energy conversion can be essentially: the piezoelectric, photovoltaic and thermoelectric effects and phenomena related to fluid dynamics. Significant examples of energy harvesting are evident in particular in the following scientific fields: the construction of electric generators coupled to microturbines (Chunyan et al., 2010), (Bansal et al, 2009), (Yan et al., 2011), (Zainuddin, H et al., 2009); the Stirling thermodynamic cycle (Valdes, 2004), the Seebeck effect in thermoelectric generators (Lineykin et al., 2007), (Lu

Within this context the objective of this work is to present a trade-off analysis between different types of hydraulic machines, electric generators and energy storage units to reach a good compromise in the design of harvesting devices to be integrated in fluid distribution

The present section describes the system configuration of the energy harvester (or scavenger) used to supply a thermostatic motorized valve of a heating system for residential The collection of specifications starts from the hydraulic data available for the system from which we want to extract the energy. The typical flow rate of household heating system pipelines is between 1.3 and 4 l/min. The geometrical size of the device must be compliant with the available space at the interface between the heating element of conditioning systems and the pipeline. Other specifications are related to electrical power and voltage that must be generated. A campaign of experimental tests performed on motorized thermostatic valves shows that the average power is about 100mW with peaks that can reach 1 W for a short time during valve actuation. The minimum nominal voltage must be compatible to the voltage generated by a couple of AA-type batteries currently used to power the electronic thermostatic valves actuation units. Table 1 lists the above-mentioned specifications.


**Table 1.** System specification

In addition to specification some key choices are taken to proceed with the design, they are summarised in Tab. 2. One aspect which strongly influences the design of the system is the size of the inlet nozzle of the hydraulic machine. This choice is driven by the need to avoid chocking of the nozzle because of the large amount of dirt particles that characterize the fluid of heating systems. The design choice is to have a nozzle diameter *d* larger than 4 mm, as shown in the cross-section view of Fig. 17. Moreover a relatively large inlet nozzle diameter reduces the hydraulic losses due to the introduction of the scavenger into the heating system. The advantage is of reducing the need of increasing the size of the main pump that produces the hydraulic flow in the system. Another design choice about the realization of the turbine concerns the speed rotation of the runner. Here, a rated nominal speed of 1000 rpm has been chosen for the device. This rotation speed should be compatible

with the precision that can be reached with standard production process of some details of the generator unit as impeller and bushings. A limited angular speed also ensures an adequate degree of durability and strength. This speed value is precautionary as regards the possibility of creating vibrations, that may occur at higher speeds and lead to the failure of the rotating parts.


**Table 2.** Design choices
