Diesel generator room ventilation calculation

In this article generator room ventilation calculation will be briefly explained along with the example. Sit tight and follow the design calculations step by step. Let's start

First of all you have understand some important notes regarding generator room ventilation calculation. Those general notes are stated below:

1. Clean , cool and dry air circulates around the switchgear, flows through the rear of the generator, across the engine, and discharges through the radiator 
2. Cool air should always be available for the engine air cleaner (air filter)
3. For best ventilation results, air should flow first across the generator then to both sides of the engine
4. Inlets located at the end of the room will provide adequate ventilation only to the engine nearest the inlet
5. Air flow restriction should be 0.5 inch W.G

Objectives:

Here we have 2 objectives first to calculate the ventilation air quantity and 2nd to calculate the intake air louver area

So basic formula which is used for diesel generator ventilation calculation is:

Ventilating air (cu.m/min.) =  H / (D x SH x Dt) + Engine combustion air

Where:-

H =  Heat Rejection to atmosphere in (KW) (for engine + generator)

H = 124.9KW  (Refer To manufacturer data Sheet)

V = Ventilating air (cu.m/min)

D = Density of air = 1.09 kg/m3 @50 °C (Refer to air density table)

SH = Specific heat of air ( kw.min/Kg.°C)

SH = 0.017 kw.min/Kg.°C

Dt = (T2-T1) Temp. Rise inside generator room (°C)

T1 = Design temperature = 40 °C

T2 = Max allowable room temperature = 50 °C

Dt = (T2-T1) = 50-40 = 10 °C

ECA = Engine  Combustion Air (Exhaust gas flow)

ECA = 130 cu.m/min (Refer To manufacturer data Sheet)

ECA = 7182 cu.m/hr

Air density at different temperatures listed below in table

Specific heat of air is given below in table

Now we know all the values we can put them in ventilation calculation formula

V = 124.9 / (1.093 x 0.017 x 10) +130

V = 802 cu.m/min

If we multiply above ventilation value with 35.28 then we get ventilation in cu.ft/min, So

V = 802 x 35.28

V = 28,295 cu.ft/min

So based on design conditions ventilation air required is 28,295 cu.ft/min. Now let's calculate the Intake louver size as well by using equation

Q = V x A

A = Q/V

Consider velocity of 1000 ft/min

A = 28295 / 1000

A = 28.3 Sq.ft = 2.6 Sq.m

Please see my tutorial for more detailed explanation. Let me know if you have any questions I would love to answer. Thank you