The DHW circuit is fuelled with energy from the DHW tank. The amount of water is sufficient for the daily consumption of the residence.
This water is heated through conduction from the water of the hot water tank. The continuous refreshing of the water in the DHW tank presupposes resolving the
Fig. 23 Solar thermal panels connecting scheme
problem of calcareous residues with negative effects on the heat transfer. In the case of this tank, the method of the soluble magnesium anode is used.
The thermal load of the circuit is represented by DHW consumption in the adequate spaces (kitchen, baths). The consumption is variable and requires an adequate replacement of the consumed water volume with fresh tap water. The CH10 circuit (Fig. 24) is made up of two parts. One part is included in the residence and complies with the construction and exploitation rules of the domestic hot and cold water distribution systems. Another part is included in the boiler appliance, located in the basement.
The recirculation pump has the role of maintaining constant temperature in the pipes, so that the time interval between opening a consumption valve and reaching the DHW optimal temperature is the lowest possible. The circuit is equipped with separation valves in order to allow easy interventions, and elements belonging to the pumping and safety groups: filter, indicating manometer, indicating thermometer, one – way valve, ventilation valve, safety valve.
The following variables represent the operating parameters of each hydraulic circuit when it is intended to carry thermal energy:
Q—Heat flow (kW);
V—Volume flow (m3/h);
Fig. 24 DHW hydraulic circuit scheme (CH10)
D#—Temperature difference (°C); p—Density of thermal fluid (kg/m3);
Ho—Pressure of the thermal fluid (mbar); c—Specific heat capacity of the thermal fluid (kWh/kg °C); v—fluid velocity (m/s).
The connection of all circuits in a hydraulic scheme is shown in Fig. 25.
Table 23 Hydraulic circuits features
The thermal requirement of the system fluctuates depending on the following factors: user behaviors and comfort, extraneous heat influence, influence of hydraulic control devices (three-way valve of the ventilo-convectors).
Any reduction of volume flow in convectors or convector closed leads to higher return temperature. The volume flow conveyed through a circulating pump is depending on the thermal output/cooling output requirement of the system being supplied. For this reason was necessary the control of the volume flow conveyed through circulating pumps. The controls consist in to adapt the pump performance (and thus the power consumption) continuously to the actual requirement/demand. The control mode adopted was Дp – T, where the power electronics circuitry varies the set point differential pressure value, to be maintained by the pump as a function of the measured fluid temperature.