Building types, mechanical ventilation, air flow

Residential building

A building used for living and sleeping: houses, flats, apartments, hostels, hotels.

Institutional building

A building used for medical treatment, care or custody of people, where they stay or attend: hospitals, clinics, sanatoriums, homes for the aged, orphanages, jails. (Some textbooks also include schools and colleges, but the building code treats educational buildings as a separate class.)

Types of mechanical ventilation

1. Extract (exhaust) system: Fans remove air from the room, and fresh air comes in through openings. Used in kitchens, toilets and factories. It creates negative pressure.
2. Plenum (supply or positive-pressure) system: A fan forces filtered air in, and stale air leaves through openings. Used in hospital operating theatres and clean rooms.
3. Balanced (combined supply and extract) system: Both supply and exhaust fans are used, so the pressure is balanced. Used in theatres, halls and basements.
4. Ducted system with air-handling unit: A central fan, filters and ducts distribute the air; it can be combined with air conditioning.

 Extract:  out <-[fan]  room  <- air leaks in
 Plenum:   in ->[fan]   room  -> air leaks out
 Balanced: in ->[fan] room [fan]-> out

Given

• Inlet and outlet openings: 0.32 m × 0.32 m and 0.42 m × 0.42 m, so $A_1 = 0.1024\ \text{m}^2$ and $A_2 = 0.1764\ \text{m}^2$
• Wind speed $v = 5$ km/h $= 5/3.6 = 1.3889$ m/s, at 45° to the opening
• Coefficient of effectiveness $E = 0.33$ (already accounts for the wind direction; the room size does not enter the formula)

Formula

For wind-driven ventilation through two openings in series, the effective area is

$$A = \frac{A_1 A_2}{\sqrt{A_1^2 + A_2^2}}, \qquad Q = E\, A\, V$$

Calculation

$$\begin{aligned} A &= \frac{0.1024 \times 0.1764}{\sqrt{0.1024^2 + 0.1764^2}} = 0.08856\ \text{m}^2 \\ Q &= 0.33 \times 0.08856 \times 1.3889 = 0.04059\ \text{m}^3/\text{s} \end{aligned}$$

Answer: $Q = 0.0406$ m³/s $= 146.1$ m³/h.