Hitachi YUTAKI M RASM-2VRE Instruction Manual page 25

DRAIN PIPING
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N O T E
• The unit is equipped with a manual air purger (factory supplied) at
the highest location of the unit. Anyway, if there are higher points in
the water installation, air might be trapped inside water pipes, which
could cause system malfunction. In that case, additional air purgers
(field supplied) should be installed to ensure no air enters into the
water circuit. The air vents should be located at points which are
easily accessible for servicing.
• The water pressure indicated on the manometer may vary depending
on the water temperature (the higher temperature, the higher
pressure). Nevertheless, it must remain above 1 bar in order to
prevent air from entering the circuit.
• Fill in the circuit with tap water. The water in the heating installation
must comply with EN directive 98/83 EC. Non-sanitary controlled
water is not recommended (for example, water from wells, rivers,
lakes, etc.) (See "Water quality"
• 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.
• For heating floor system, air should be purged by means of an external
pump and an open circuit to prevent the formation of air pockets.
• Check carefully for leaks in the water circuit, connections and circuit
elements.
9.3 MINIMUM WATER VOLUME
DESCRIPTION
The following part shows how to calculate the minimum water
volume in the system for product protection (anti-hunting) and
temperature drop at defrosting.
1 Protective water volume for product
Ensure that the water volume is equal or greater than
those shown below, in order to lower ON/OFF frequency of
YUTAKI M unit at no load or extreme light load. When water
volume is less than the volume indicated (minimum water
volume), compressor operation frequently stops at light load,
which should result in shorter life or failure.
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N O T E
The factory default ON/OFF temperature differential is "4 °C". Note that
the minimum water volume varies for different setting for each purpose
as shown in the next table:
ON/OFF Temperature differential RASM-2VRE RASM-3VRE
4ºC
3ºC
2ºC
1ºC
2 Minimum required water volume during defrosting
• The following formula is used to make the calculation:
360 x Q
Where:
V =
ΔT x 4168.8
V = Required water volume (m
The minimum volume of water needed in the installation
to cover the heat loss caused by a reduction in the
delivery water temperature during defrosting.
13 PMML0506 rev.1 - 09/2019
section at the CD-ROM).
(Units: ltrs.)
Model
28 28
36 36
50 50
80 80
DEF
; Q =Q + Q
DEF I Y
)
3
ΔT = Permissible water temperature drop (ºC)
Drop in the delivery water temperature that the client is
willing to allow in the installation.
Q = Heat loss during defrosting (kW)
DEF
Heat loss caused in the system by reducing the delivery
water temperature, which may affect the user's comfort
level of warmth. This value is the sum of the two following
items:
Q = Heat demand from the installation (kW)
I
While defrosting is taking place, the unit is not providing the
heat required to cover the heat demand from the installation.
This value can be obtained in 2 ways:
1. By using the value of the energy demand from the
installation, if known.
2. If this value is not known, it can be estimated by using
the heating capacity of the unit at an air temperature
of 0ºC WB and a delivery water temperature at, for
example, 45ºC.
Q = Cooling load on the YUTAKI M unit (kW)
Y
In addition to not providing the heat required to cover
the heat demanded by the installation during defrosting,
the unit is also producing cold. It can be estimated that
this value is approximately 85% of the heating capacity
on the unit under standard conditions (air temperature:
6/7ºC (WB/DB) and input/output temperature of the
water: 40 / 45ºC)
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N O T E
The maximum time for defrosting considered is 6 minutes per hour.
The following table shows the minimum water volume needed in
each YUTAKI M unit in case of a permitted drop in temperature
of 10ºC.
Water temperature drop
5ºC
10ºC
15ºC
20ºC
25ºC
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N O T E
• The values shown on the table are based on theoretical installation
conditions. In addition, YUTAKI M unit admits several hydraulic
circuits configurations, and the value can be different depending on
each specific installation.
• Therefore, it rests with the client to recalculate these values depending
on the real conditions of the installation.
(Unit: ltrs.)
Model
RASM-2VRE RASM-3VRE
212 212
106 106
71 71
53 53
42 42