Mitsubishi Electric MXZ-SM36NAM2 Technical & Service Manual page 18

2. Heating Calculation
(1) Temporary Selection of Indoor Units
Room1
PEFY-P15
Room2
PEFY-P18
(2) Total Indoor Units Capacity
P15 + P18 = P33
(3) Selection of Outdoor Unit
The P36 outdoor unit is selected as total indoor units capacity is P33
MXZ-SM36NAM2
(4) Total Indoor Units Capacity Correction Calculation
Room1
Indoor Design Dry Bulb Temperature Correction (69.8ºF)
Room2
Indoor Design Dry Bulb Temperature Correction (73.4ºF)
Total Indoor Units Capacity (CTi)
CTi = Σ (Indoor Unit Rating × Indoor Design Temperature Correction)
= 17.0 × 1.00 + 20.0 × 0.92
= 35.4 kBtu/h
(5) Outdoor Unit Correction Calculation
Outdoor Design Wet Bulb Temperature Correction (35.6ºF)
Piping Length Correction (328 ft)
Defrost Correction
Total Outdoor Unit Capacity (CTo)
CTo = Outdoor Unit Rating × G(CTi)
× Piping Length Correction × Defrost Correction
= 41.0 × 1.0 × 0.94 × 0.89
= 34.3 kBtu/h
*1 G(CTi) is used only when greater than 100% indoor model size are connected in total,
refer to STANDARD CAPACITY DIAGRAM.
Table 1 Table of correction factor at frost and defrost
Outdoor Intake temperature <W.B.°F (°C)>
Correction factor
(6) Determination of Maximum System Capacity
Comparison of Capacity between Total Indoor Units Capacity (CTi) and Total Outdoor Unit Capacity (CTo)
CTi = 35.4 > CTo = 34.3, thus, select CTo.
CTx = CTo = 34.3 kBtu/h
(7) Comparison with Essential Load
Against the essential load 34.0 kBtu/h, the maximum system capacity is 34.3 kBtu/h: Proper outdoor units have been selected.
(8) Calculation of Maximum Indoor Unit Capacity of Each Room
CTx = CTo, thus, calculate by the calculation below
Room1
Maximum Capacity × Room1 Capacity after the Temperature Correction/(Room1,2 Total Capacity after the Temperature Correction
= 34.3 × (17.0 × 1.00) / (17.0 × 1.00 + 20.0 × 0.92)
= 16.5 kBtu/h
Room2
Maximum Capacity × Room1 Capacity after the Temperature Correction/(Room1,2 Total Capacity after the Temperature Correction
= 34.3 × (20.0 × 0.92) / (17.0 × 1.00 + 20.0 × 0.92)
= 17.8 kBtu/h
Completed selecting units since the selected units fulfill the heating loads of Room 1, 2.
OCH810A
17.0 kBtu/h (Rated)
20.0 kBtu/h (Rated)
41.0 kBtu/h
*1
× Outdoor Design Temperature Correction
43(6) 37(4) 36(2) 32(0) 28(−2)
1.00 0.98 0.89 0.88 0.89
OK: fulfills the load 16.3 kBtu/h
OK: fulfills the load 17.7 kBtu/h
1.3
1.2
1.1
1.0
0.9
0.8
0.7
0.6
59 60.8 62.6 64.4 66.2
15 16
Figure 4 Indoor unit temperature correction
1.4
1.3
1.2
1.1
1.00 (Refer to Figure 4)
1.0
0.9
0.8
0.7
0.92 (Refer to Figure 4) 0.6
0.5
0.4
-13
-25
Figure 5 Outdoor unit temperature correction
1.00
1.0 (Refer to Figure 5)
0.94 (Refer to Figure 6)
0.95
0.89 (Refer to Table 1)
0.90
0.85
0.80
0.75
0.70
0 50
Figure 6 Correction of refrigerant piping length
25(−4) 21(−6) 18(−8) 14(−10)
0.90 0.95 0.95 0.95
18
68 69.8 71.6 73.4 75.2 77 78.8 80.6
17 18 19 20 21 22 23 24 25 26 27
Indoor Temperature
To be used to correct indoor unit only
21.1°C (70.0°F) D.B.
-4 5 14 23 32 41 50
-20 -15 -10 -5 0 5 10
Outdoor Temperature
To be used to correct outdoor unit only
Total capacity of indoor unit
100 150 200 250 300 350 400 450 500 550
Piping equivalent length (ft)
5(−15) −4(−20) −13(−25)
0.95 0.95 0.95
[°F D.B.]
[°C D.B.]
Indoor
Temperature
59
[°F W.B.]
15 [°C W.B.]
600