41
CHAPTER
9
Model selection and capacity calculation
(2) Air condition difference factor
(3) Corrected refrigerant pipe length factor
(4) Adjusted Dx-coil unit capacity
Characteristics written in the specification sheet are based on air conditions of outdoor air: 35˚CDB, 24˚CWB and return air:
27˚CDB, 19˚CWB.
Read out the air volume factor C
2-2
by outdoor air dry-bulb temperature and Dx-coil inlet air wet-bulb temperature using the
performance curves on the page 62.
Specification condition
Designing condition
For the quick reference of air condition difference factor C
2
, see the page 63.
Enthalpy of supply air from Dx-coil: h
o
= h
i
– C
a
/ (
ρ
x Q
f
/ 3600) [kJ/kg(DA)]
Enthalpy of supply air from Dx-coil:
Read out the refrigerant pipe length factor C
3
using the capacity correction ratio curve on the page 63.
Specification condition
Outdoor air
Return air
Dx-coil inlet air
(Lossnay outlet air)
Dry-bulb temperature [˚C] (A) 35
27
29.3
Wet-bulb temperature [˚C] 24
19
(B) 20.6
Absolute humidity [kg/kg(DA)]
0.0142
0.0104
0.0116
Relative humidity [%] 40
47
45
Enthalpy [kJ/kg(DA)] 71.7
53.8
59.0
(A) Outdoor air dry-bulb temperature
(B) Dx-coil inlet air wet-bulb temperature
(C) Air condition difference factor C
2-1
All of cooling specification for each Dx-coil unit are designed under above condition.
Therefore C
2-1
( = 1.08) is fixed value for all unit.
(D) Outdoor air dry-bulb temperature
(E) Dx-coil inlet air wet-bulb temperature
(F) Air condition difference factor C
2-2
(Find C
2-2
from the graph on the page 62. )
(G) Total air condition difference factor C
2
= C
2-2
/C
2-1
= (F) / (C) = 1.12 / 1.08
(A) Refrigerant pipe length
(B) Refrigerant pipe length factor C
3
(A) Dx-coil unit cooling capacity on the specification
(B) Adjusted Dx-coil unit cooling capacity
= (A) x C
1
x C
2
x C
3
= 7.1 x 1.0 x 1.04 x 1.0
35 ˚CDB
33 ˚CDB
7.5 m
7.4 kW
62.0 kJ/kg(DA)
20.6 ˚CWB
21.4 ˚CWB
1.0
1000 m
3
/h
39.8 kJ/kg(DA)
1.08
1.2 kg/m
3
1.12
7.1 kW
1.04
7.4 kW
IV: Calculate the supply air conditions from Dx-coil unit
h
i
: Enthalpy of Dx-coil inlet air
(equal to Lossnay outlet air) [kJ/kg(DA)]
C
a
:
Adjusted capacity of Dx-coil unit [kW]
ρ
:
Density of air [kg/m
3
]
Q
f
:
Ventilation air volume [m
3
/h]
h
o
= h
i
– C
a
/ (
ρ
x Q
f
/ 3600) [kJ/kg(DA)]
= 62.0 – 7.4 / ( 1.2 x 1000 / 3600 )
Summary of Contents for GUG-01SL-E
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