AIRAH
Common Equations
1 kWh = 3.6 MJ
WATER
kW = 4.187 x (L/s) x ∆T(K)
kWh = 4.187 x L x ∆T(K) / 3600
where:
4.187 = Specific heat capacity of water (k J/kg K @ 14°C)
HEAT CONTENT OF AIR
Latent
Watt =
Watt =
where:
2450 =
0.845 =
Sensible
Watt =
Watt =
where:
1.025 =
Total
Watt =
where:
1.184 =
(2450 k J/kg / 0.845 m³ /kg) x (L/s / 1000) x g/kg
2.900 x L/s x g/kg
Latent heat of water (kJ/kg @ 21°C)
Specific volume of moist air (m³/kg)
(1.025 k J/kg K / 0.845 m³/kg) x L/s x ∆T(K)
1.213 x L/s x ∆T(K)
Specific heat of moist air k J/kg.K
1.184 x L/s x (kJ/kg)
Density of moist air @ 20°C and 50% RH (kg/m³)
POWER – GENERAL EQUATION
kW
where:
ρ
h
ç
Q
= 9.81 x h x ρ x Q / 1000 x ç
=
=
=
=
Density (kg/m3)
liquid column height (m) Note: h = kPa / 9.81 (m)
efficiency (where 0 ≤ ç ≤ 1)
Flow rate (L/s)
Note: P = 9.81 x h x ρ = Pressure (Pa)
POWER – FAN AND PUMP
kW = kPa x Q
1000 x η
W
= ( 9.81 x h x r x Q ) / 1000 x η
POWER SHAFT
kW
= {2 π x r.p.s. x torque (Nm)} / 1000
187