Hitachi YUTAKI M RASM-3WF2E Installation And Operation Manual page 35

1 Minimum required water volume during defrosting
The following formula is used to make the calculation:
Where:
360 x Q
DEF
V =
ΔT x 4168.8
V =
ΔT x 14.957
1.8
• V = Required water volume ft
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 °F (°C)
Drop in the delivery water temperature that the client is willing to allow in the installation.
• Q = Heat loss during defrosting BTU/hr (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 BTU/hr (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 32°F (0°C)WB and a delivery water temperature at, for example, 113
°F (45 °C).
Q = Cooling load on the YUTAKI M BTU/hr (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: 42.8/44.6°F (6/7°C) (WB/DB) and input/output temperature of the water:
104/113 °F (40 / 45 °C)).

NOTE
The maximum time for defrosting considered is 6 minutes per hour.
PMEN0657 rev.0 - 02/2024
V = Required water volume (m
; Q =Q + Q
ΔT = Permissible water temperature drop (°C)
DEF I Y
Q
Q
Q
V = Required water volume(ft
0.1 x Q
ΔT = Permissible water temperature drop (°F)
DEF
Q
Q
Q
(m
3 3)
= Heat loss during defrosting (kW)
DEF
= Heat demand from the installation (kW)
I
= Cooling load on the YUTAKI M (kW)
Y
= Heat loss during defrosting (BTU/hr)
DEF
= Heat demand from the installation (BTU/hr)
I
= Cooling load on the YUTAKI M (BTU/hr)
Y
)
3
)
3
5
34