Hitachi YUTAKI M Serie Manuel D'utilisation page 25

DRAIN PIPING
8.3 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.
?
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
RASM-
Temperature
3VNE
differential
4ºC 28
3ºC 36
2ºC 50
1ºC 80
2 Minimum required water volume during defrosting
• The following formula is used to make the calculation:
360 x Q
Where:
DEF
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.
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
15 PMML0342B rev.1 - 03/2016
(Unit: ltrs.)
Model
RASM- RASM- RASM-
4(V)NE 5(V)NE 6(V)NE
38 46 56
48 58 70
65 80 96
107 130 156
; Q =Q + Q
DEF I Y
)
3
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 / 45 ºC)
?
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 RASM-3VNE
drop
5ºC 212
10ºC 106
15ºC 71
20ºC 53
25ºC 42
?
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 (as shown in the Manual of the system controller), 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- RASM- RASM-
4(V)NE 5(V)NE 6(V)NE
276 342 410
138 171 205
92 114 137
69 86 103
55 68 82