Hitachi YUTAKI S Series Technical Catalogue page 111

8 Refrigerant and water piping
Space heating and DHW
8.3.5 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 indoor unit is equipped with an air purger (factory supplied) at the highest location of the Indoor 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, "Optional 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 below 6 litres/minute for 2.0/2.5/3.0HP unit, alarm is displayed on the
unit.
• An additional special water filter is highly recommended to be installed on the space heating (field installation), in
order to remove possible particles remaining from brazing which cannot be removed by the indoor unit water strainer.
• When selecting a DHW tank, take into consideration that 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 (6 bar), a pressure reducer
must be fitted with a nominal value of 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 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 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 0.1 MPa of internal air pressure).
• Do not add any type of glycol to the water circuit in YUTAKI S / S COMBI units. The use of glycol is only allowed for
YUTAKI M units in order to prevent water pipes from freezing. If using glycol for the water circuit of YUTAKI M units,
refer to the specific information throughout the document.
• Drain taps must be provided at all low points of the installation to permit complete drainage of the circuit during
servicing.
103 TCGB0123 rev.2 - 10/2019
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