Hitachi YUTAKI M RASM-3WF2E Installation And Operation Manual page 27

5.3.4 Requirements and recommendations for the hydraulic circuit
• The maximum piping length depends on the maximum pressure availability in the water outlet
pipe. Please check the pump curves
• The units are equipped with a manual air purger (factory supplied) at the highest location of
the unit. If this location is not the highest of the water installation, air might be trapped inside
the water pipes, which could cause system malfunction. In that case additional air purgers (field
supplied) should be installed to ensure no air enters the water circuit.
• For heating floor system, the air should be purged by means of an external pump and an open
circuit to avoid air bags.
• When the unit is stopped during shut-off periods and the ambient temperature is very low,
the water inside the pipes and the circulating pump may freeze, thus damaging the pipes and
the water pump. In these cases, the installer shall ensure that the water temperature inside
the pipes does not fall below the freezing point. In order to prevent this, the unit has a self-
protection mechanism which should be activated (refer to the Service manual,
functions" chapter).
• Check that the water pump of the space heating circuit works within the pump operating range
and that the water flow is over the pump's minimum. If the water flow is under 3.17 GPM (12 lt/
min) (with flow switch tolerance), alarm will be displayed on the unit.
• When selecting a tank for DHW operation, take into consideration the following points:
✓ The storage capacity of the tank has to meet with the daily consumption in order to avoid
stagnation of water.
✓ Fresh water must circulate inside the DHW tank water circuit at least one time per day during
the first days after the installation has been performed. Additionally, flush the system with
fresh water when there is no consumption of DHW during long periods of time.
✓ Try to avoid long runs of water piping between the tank and the DHW installation in order to
decrease possible temperature losses.
✓ lf the domestic cold water entry pressure is higher than the equipment's design pressure 145
psi (10 bar), a pressure reducer must be fitted with a nominal value of 101.5 psi (7 bar).
• Ensure that the installation complies with applicable legislation in terms of piping connection
and materials, hygienic measures, testing and the possible required use of some specific
components like thermostatic mixing valves, Differential pressure overflow valve, etc.
• The maximum water pressure is 43.5 psi (3 bar) (nominal opening pressure of the safety valve).
Provide adequate reduction pressure device in the water circuit to ensure that the maximum
pressure is NOT exceeded.
• Ensure that the drain pipes connected to the safety valve and to the air purger are properly
driven or oriented to avoid water being in contact with unit components.
• Make sure that all field supplied components installed in the piping circuit can withstand the
water pressure and the water temperature range in which the unit can operate.
• YUTAKI units are conceived for exclusive use in a closed water circuit.
• The internal air pressure of the expansion vessel tank will be adapted to the water volume of
the final installation (factory supplied with 14.5 psi (0.1 MPa) of internal air pressure).
• Drain taps must be provided at all low points of the installation to permit complete drainage of
the circuit during servicing.
PMEN0657 rev.0 - 02/2024
"4.3.2 Pump performance curves".
"Optional
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