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Design of Mini VRF SYSTEM
1. Model Selecting and Capacity Calculator
Minimum indoor volume & floor area as against
the amount of refrigerant is roughly as given in the
following table.
the amount of refrigerant is roughly as given in the
following table.
CAUTION
Pay special attention to any location, such as a basement, etc., where
leaking refrigerant can accumulate, since refrigerant gas is heavier than air.
leaking refrigerant can accumulate, since refrigerant gas is heavier than air.
Table 1-10 Ranges that Apply to Refrigerant Tubing Lengths and to Differences in Installation Heights
L = Length, H = Height
Always check the gas density limit for the room in which the
unit is installed.
unit is installed.
WARNING
1-12. Check of Limit Density
When installing an air conditioner in a room, it is
necessary to ensure that even if the refrigerant gas
accidentally leaks out, its density does not exceed the
limit level for that room.
If the density could exceed the limit level, it is
necessary to provide an opening between the unit
and the adjacent room, or to install mechanical
ventilation which is interlocked with the leak detector.
(Total refrigerant charged amount: k
g)
(Min. indoor volume where the indoor unit is installed: m
3
)
< Limit density 0.3 (k
g/m
3
)
The limit density of refrigerant which is used in this
unit is 0.3 k
unit is 0.3 k
g/m
3
(ISO 5149).
The shipped outdoor unit comes charged with the
amount of refrigerant fixed for each type, so add it
to the amount that is charged in the field. (For the
refrigerant charge amount at shipment, refer to the
unit’s nameplate.)
40.5
54.0
27.0
13.5
13.5
0.0
20
10
0
30
40
60
70
80
90 100
50
67.5
81.0
94.5
108.0
121.5
135.0
148.5
162.0
175.5
189.0
202.5
216.0
229.5
243.0
256.0
270.0
m
2
m
3
15
10
10
5
0
0
20
25
30
35
40
45
50
55
60
65
70
75
80
85
90
95
100
105
110
115
120
125
283.5
297.0
310.5
324.0
337.5
k
g
Range below the
density limit of
0.3 k
density limit of
0.3 k
g/m³
(Countermeasures
not needed)
not needed)
Range above the
density limit of 0.3
k
density limit of 0.3
k
g/m³
(Countermeasures
needed)
needed)
Total amount of refrigerant
Min. indoor volume
Min. indoor floor area
(when the ceiling is 2.7 m high)
Items
Marks
Contents
Length (m)
Allowable tubing
length
length
L1
Max. tubing
length
length
Actual length
≤ 120
Equivalent length
≤ 140
ΔL (L2 – L3)
Difference between max. length and min.
length from the No.1 distribution joint
length from the No.1 distribution joint
≤ 40
1
,
2
...
n
Max. length of each distribution tube
≤ 30
1
,
2
...
n-1
+L1
Total max. tubing length including length of each
distribution tube (only narrow tubing)
distribution tube (only narrow tubing)
≤ 150
Allowable elevation
difference
difference
H1
When outdoor unit is installed higher than indoor unit
≤ 50
When outdoor unit is installed lower than indoor unit
≤ 40
H2
Max. difference between indoor units
≤ 15
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Design of Mini VRF SYSTEM
1. Model Selecting and Capacity Calculator
1-13. Calculation of Actual Capacity of Indoor Unit
Calculating the actual capacity of each indoor unit
Because the capacity of a multi air-conditioner changes according to the temperature conditions, tubing length,
elevation difference and other factors, select the correct model after taking into account the various correction values.
When selecting the model, calculate the corrected capacities of the outdoor unit and each indoor unit.
Use the corrected outdoor unit capacity and the total corrected capacity of all the indoor units to calculate the actual final
capacity of each indoor unit.
(A) Capacity correction for the outdoor unit temperature conditions (%)
Read the capacity correction for outdoor unit temperature, indoor unit temperature and indoor/ outdoor ratio as shown
in the section “9. CAPACITY TABLE”.
(B) Capacity correction coefficient for outdoor unit tubing length (%)
From the graph of capacity change characteristics resulting from tubing length and elevation difference on page “ 2-11 ”,
read the capacity correction coefficient.
* Indoor unit temperature is indoor unit rated capacity - weighted average temperature.
Rated capacity-weighted average temperature =
((a)×(b))
(a)
= 17.1WB
* The indoor/ outdoor ratio should be selected according to the real rated capacity.
* Use the lowest capacity changing ratio. Usually, the furthest and highest or the lowest indoor unit is used.
(C) Surplus capacity correction coefficient for outdoor unit temperature conditions (%)
From the graph of surplus capacity characteristics resulting from outdoor temperature on page “ 2-10 ”, read the capacity
correction coefficient.
(D) Capacity correction coefficient for outdoor unit frosting and defrosting during heating operation (%)
From the outdoor unit heating capacity correction coefficient during frosting / defrosting on page “ 2-10 ”, read the capacity
correction coefficient.
Example
Cooling operation
Example
There are 4 indoor units for class 22, 28, 45, 56 and the outdoor unit HP is 6 (15.5kW in the cooling-mode, 18.0kW in the
heating-mode).
(a) Rated capacity
(b) Intake temperature
(a) × (b)
2.2 kW
19 WB
41.8
2.8 kW
50.4
18 WB
4.5 kW
17 WB
76.5
5.6 kW
16 WB
89.6
1. Outdoor unit capacity correction
Outdoor unit capacity correction (kW) = Rated capacity × (A) × (B) × (C) × (D)
Rated cooling capacity
Rated heating capacity
2.2 kW
2.5 kW
2.8 kW
3.2 kW
4.5 kW
5.0 kW
5.6 kW
6.3 kW
No.
1
2
3
4
No.
1
2
3
4
15.1 kW
17.0 kW
97.4%
94.4 %
Total
I/O ratio
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Design of Mini VRF SYSTEM
1. Model Selecting and Capacity Calculator
(E) Capacity correction for the indoor unit temperature conditions (kW)
From the graph of indoor capacity characteristics on page “ 2-11 ”, read the capacity correction coefficient for indoor unit
temperature conditions.
(H) Capacity correction coefficient for tubing length and elevation difference (%)
From the graph of capacity change characteristics resulting from tubing length and elevation difference on page “ 2-11 ”,
read the capacity correction coefficient.
(E) = Capacity correction coefficient for indoor unit temperature conditions × Rated capacity
(F) Calculate the Capacity distribution ratio (%)
(F) =
(E)
(E)
(G) Distribute the outdoor unit capacity among each indoor unit (kW)
(G) = (A) × (F) × rated capacity of outdoor unit (kW)
2. Indoor unit capacity correction coefficient
Indoor unit capacity correction (kW) = (G) × (H) × (C) × (D)
*
Indoor unit capacity correction
≦ (G)
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Design of Mini VRF SYSTEM
1. Model Selecting and Capacity Calculator
Surplus capacity correction coefficient (%)
Note :
This capacity graph is used for the calculation of the tubing length correction.
Therefore, this is different from the outdoor unit’s capacity graph.
Therefore, this is different from the outdoor unit’s capacity graph.
Outdoor air intake temp.( °C WB)
Outdoor air intake temp.( °C DB)
Surplus capacity correction coefficient (%)
Surplus capacity correction coefficient (%)
5. Graph of capacity correction coefficients
Outdoor unit heating capacity correction coefficient during frosting/defrosting (1 – (4))
To calculate the heating capacity with consideration for frosting/defrosting operation, multiply the heating capacity
found from the capacity graph by the correction coefficient from the table above.
*
Outdoor intake
air temp.
air temp.
Correction
coefficient
coefficient
–1
0
1
2
3
4
5
6
0.89 0.87 0.87 0.87 0.88 0.89 0.91 0.92 0.95
1.0
0.91
0.94
0.96
0.97 0.97 0.97
(°CWB, RH85%)
–20
–15
–10
–8
–6
–2
–4
–5
-20 -15 -10
-5
0
5
10
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90
95
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110
105
120
115
125
90
95
100
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110
115
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g
n
i
t
a
e
h
g
n
il
o
o
c
-5
0
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18
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