Question

The minimum fresh air requirement of a residential building is specified to be 0.35 air changes per hour (ASHRAE, Standard 62, 1989). That is, 35 percent of the entire air contained in a residence should be replaced by fresh outdoor air every hour. If the ventilation requirement of a 2.7-m-high, 200-m2 residence is to be met entirely by a fan, determine the flow capacity in L/min of the fan that needs to be installed. Also determine the minimum diameter of the duct if the average air velocity is not to exceed 5.5 m/s.

Answer 1

We know that

$A=200m^2\\h=2.7m\\\upsilon= 5.5m/s\\\%_{air} = 35%$

So, the volume of the entire building is

$V=2.7*200 = 540m^3$

The flow capacity of the fan

$\dot{V} = \frac{0.35*540}{60}$

$\dot{V} = 3.15m^3/min$

As $1L=10^{-3}m^3,$

$\dot{V}=3150L/min$

For the other part we know

$\dot{V}=\frac{\pi d^2}{4}V$

The diameter is,

$d=\sqrt{\frac{4\dot{V}}{\pi V}}$

$d=\sqrt{\frac{4*3.15}{\pi* 5.5* 60}}$

**Note 60 is for the minutes

$d= 0.1101m$