43
CHAPTER
9
Model selection and capacity calculation
STEP4. Comparison of L Dx-coil unit capacity with required capacity
STEP1. Calculation of required heating capacity
By calculations from STEP 1 to 3, the capacity of L Dx-coil unit is summate as shown below.
As a result, (D) is smaller than (A). Therefore, consider to add other cooling equipment.
(In this example, air-conditioning equipment whose capacity is 16.5 kW ( 31.4 - 14.9 ) is necessary.)
See page 37 for the way to calculate required ventilation air volume.
In this Example 1-2, the floor is assumed the same room as Example 1-1.
Therefore, required air volume is also same as Example 1-1.
Ventilation load can be calculated by same formula as Example 1-1.
Ventilation load per unit area under above condition can be calculated as following.
Ventilation load per unit area
In this example, other heating loads are regarded as a general value in Tokyo shown in the table below.
Calculate them in an appropriate way in the actual designing.
During heating, the heat generated by persons and electrical equipment in the room can be subtracted from the heating load.
If the warming-up time at the start of heating is short, however, the generated heat may be ignored in some cases.
Capacity calculation result
(A) Required cooling capacity
(B) Lossnay energy recovery
(C) Dx-coil cooling capacity
(D) L DX-coil unit system cooling capacity
= (B) + (C)
7.5 kW
7.4 kW
31.4 kW
14.9 kW
Example 1-2 : Heating for an office floor by RA temperature control
I: Calculation of required ventilation air volume and selection of Lossnay unit
II: Calculation of heating load to determine the required capacity
Classification of Heating Load
In this example, the outdoor and return air conditions are assumed as shown in table below.
Class
Heat Load
(a)
Indoor heat loss
Heat escaping from walls (qws)
Heat escaping from glass (q
GS
)
Heat loss from conduction and convection (q
GS
)
Accumulated heat load in walls (qss)
(b)
Ventilation load
Sensible heat (q
FS
)
Latent heat (q
FL
)
Dry Bulb Temp. Relative Humidity Wet Bulb Temp.
Enthalpy
Enthalpy Difference
Heating
Outdoor Air
0 °C
50%
–3 °C
4.7kJ/kg(DA)
33.6kJ/kg(DA)
Return Air
20 °C
50%
13.7 °C
38.3kJ/kg(DA)
=
ρ
[kg/m
3
]
x n [person/m
2
] x V
f
[m
3
/h·person] x (h
R
- h
O
) [kJ/kg(DA)]
= 1.2 [kg/m
3
] x 0.2 [person/m
2
] x 25 [m
3
/h·person] x 33.6 [kJ/kg(DA)]
= 201.6 [kJ/h·m
2
]
= 56.0 [W/m
2
]
Percentage of load
Conditions: Middle south-facing floor of a typical office building.
Ventilation
air load 41.9%
56.0 W/m
2
Indoor heat
loss 58.1%
77.7 W/m
2
133.7 W/m
2
Type of load
Load
Ventilation Air Load
56.0 W/m
2
Internal Heat
77.7 W/m
2
Total
133.7 W/m
2
Required heating capacity to make up for above heating loads
= 133.7 [W/m
2
] × 200 [m
2
] =
26.7 [kW]
Summary of Contents for GUG-01SL-E
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