How to calculate theoritical size of electric heater (KW) for air heating?

Question

I want to calculate the size of electrical heater for 1000 cubic meter air flow from 30 C to 120 C temperature. Can anyone tell me the formula for it... I hv surf all websites and all search engines but didn't find this details.

Answer 1

specific heat capacity of dry air is 1.006 kJ/kgC

Density of air at 30C is 1.165 kg/m³

1000m³ x 1.165 kg/m³ = 1165kg, weight of the air

energy to heat the air in Joules:

E = 1.006 kJ/kgC x 1165kg x 90C = 105,480 J <---- error, see below

Now you need the flow rate, which you omitted.

if the air flow changes the air every minute, a fast flow, then the

power (energy per second) is

P = 105,480 J / 60 sec = 1758 J/s = 1758 watts

which is the size of the heater.

edit, correct arithmetic mistake. missed the kJ in energy equation.

Corrected versions:

energy to heat the air in Joules:

E = 1.006 kJ/kgC x 1165kg x 90C = 105,480 kJ

Now you need the flow rate, which you omitted.

if the air flow changes the air every minute, a fast flow, then the

power (energy per second) is

P = 105,480 kJ / 60 sec = 1758 kJ/s = 1758 kW

which is the size of the heater.

Answer 2

I can tell you what it is in imperial units, you would have to convert it from Celsius to Fahrenheit and from cubic meter/minute (you do not have a time rate on your air flow, which it must have or it is a volume) to cubic feet/minute, and then convert your answer from Btuh to KW.

The formula is Q = Btuh/(1.08*(t2-T1))

Q = air flow in Cubic Feet per Minute

Btuh = heating capacity

t2 = 120C converted to F

t1 = 30C converted to F

rearrange and get CFM*1.08*(t2-t1) = heating capacity required in Btuh, then convert it to KW.