The Stirling engine as cogeneration unit is capable of supplying part of the heat with the hydraulic circuit CH7. The heat transfer from the Stirling engine is achieved through the recirculation of the thermal agent with a recirculation pump located inside the Stirling engine. When selecting care should be taken from the outset to ensure the lowest possible flow temperature (CHP outlet), because the electrical efficiency depends on the cooling water temperature. This should not exceed 65 °C. For this reason the system must automatically vent to the outside the heat. The CH8 circuit has the role of rejecting the heat taken up from the CH7 and
Fig. 22 Stirling heat recuperation and protection hydraulic circuit
of thus maintaining the efficiency of the Stirling engine. Circuit CH7 is placed inside of the residence. Circuit CH8 has heat exchanger (HE1) located inside of the residence while the re-cooler is located outside. The thermal load is represented by a heat sink, fitted outside the system, which has the role of reducing the temperature of the thermal agent to 45 °C. The heat sink is cooled through forced convection with a ventilator, so as to dissipate the heat flux. Figure 22 presents the position of the CH7 and CH8 circuits in the functional scheme of the system.
Circuits of hot water from ST panel to heat storage (CH9.1 and CH9.2)
Hydraulic circuit for obtaining heat from solar energy and storing it in the hot water tank (CH9) has six solar panels of the direct flow type (Fig. 23).
Placing the solar panels on the roof of the building was done according to the available space; that is why two groups were formed, one of four panels and one of two panels. Each group has its own pumping group. The CH9.1 and CH9.2 circuits are united into a single circuit which goes to the inferior coil of the hot water tank. The hydraulic circuit is characterized by the use of a soft water solution and monoethylene glycol as thermal agent, so that the normal liquid water use limits increase in the range of negative temperatures (during winter), but also in the range of temperatures exceeding 100 °C (during summer).