How to Calculate Cooling / Heating Capacity Si30-408
198 Appendix
3. How to Calculate Cooling / Heating Capacity
Measure the temperatures of suction air and discharge air of indoor unit. Then, calculate the
capacity by using the psychrometric chart.
How to calculate the cooling capacity
How to calculate the heating capacity
Example for cooling capacity calculation
Suction air. . . . . . Dry-bulb temperature: 30°C Wet-bulb temperature: 24°C
Discharge air. . . . Dry-bulb temperature: 20°C Wet-bulb temperature: 18.5°C
Air flow rate. . . . . 800 m
3
/h
According to the psychrometric chart, following values are obtained.
Enthalpy of suction air: 72.7 kJ/kg
Enthalpy of discharge air: 52.9 kJ/kg
Specific volume of discharge air: 0.85 m
3
/kg
Cooling capacity is obtained by substituting those values to the above calculation formula.
Specific volume of discharge air
3600
Cooling capacity = (Enthalpy of suction air – Enthalpy of discharge air) ×× Air flow rate ×
11
(kW) (kJ/kg) (kJ/kg) (kg/m
3
)
(m
3
/h)
Cooling capacity = (72.7 – 52.9) ×
0.85 3600
× 800 ×
11
=
5.18kW
·
·
Example for heating capacity calculation
Suction air temperature . . . . . 15°C
Discharge air temperature . . . 45°C
Air flow rate. . . . . . . . . . . . . . . 800 m
3
/h
According to the psychrometric chart, following value is obtained.
Specific volume … 0.91 m
3
/kg
Heating capacity is obtained by substituting those values to the above calculation formula.
Specific volume
3600
Heating capacity = 1.00 × Discharge air temperature – Suction air temperature × Air flow rate × ×
11
(kW) (kJ/kg · k) (˚C) (˚C) (kg/m
3
)
(m
3
/h)
0.91
3600
Heating capacity = 1.00 × (45 –15) × 800 × ×
11
= 7.33kW
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