Garage Ventilation

In a garage or workshop where exhaust gases like Carbon Monoxide (CO) and NOx from vehicles are very dangerous, proper ventilation of the area is very important.

Garages or workshops with floor areas more than 500 ft2 (50m2) should always have mechanical ventilation with fans. Smaller garages can have natural ventilation with evacuation of air through ducts with larger area than 0.2% of the floor area.

Required Air Changes per Hour As a general rule of thumb the minimum

air changes per hour in a storage garage should be least 4 to 6 air changes per hour in a repair garage or workshop should be at least 20 to 30

The fresh air supply to the garage can be calculated as

Q = n V (1)

where

Q = total fresh air supply (m3/h)

n = required air changes per hour (h-1)

V = volume of the garage (m3)

CO Emission The fresh air requirement in a garage can also be calculated using the CO emission from the vehicles in the garage.

qCO = (20 + 0.1 l1) c1 + 0.1 c2 l2 (2)

where

qCO = CO emission (m3/h)

c1 = capacity of parked cars in the garage

l1 = mean driving distance for cars in the parking garage

c2 = numbers of cars driving through the garage

l2 = mean driving distance for cars driving through the garage

The required fresh air supply can be estimated with

Q = k qCO (3)

where

Q = required fresh air supply (m3/h)

k = application coefficient

The application coefficients used are

k = 2 where people are in the garage temporarily k = 4 where people are in the garage permanently - service shops or similar

Example - Fresh air supply to a garage A Storage Garage

The fresh air supply to a storage garage with 10 cars, floor area 150 m2, volume 300 m3 and a mean driving distance for the cars of 20 m, can be calculated as:

Required air changes per hour

Fresh air supply due to air change requirement of 4 per hour can be calculated as

Q = (4 1/h) (300 m3)

= 1200 m3/h

CO emission

CO emission can be calculated as

qCO = (20 + 0.1 (20 m)) (10 cars)

= 220 m3/h CO

Required air flow due to CO emission can be calculated as

Q = 2 (220 m3/h)

= 440 m3/h air

Comparing the two calculations - the fresh air supply should be 1200 m3/h.

A Repair Garage

The fresh air supply to a repair garage with 10 cars, floor area 150 m2, volume 300 m3 and a mean driving distance for the cars of 20 m, can be calculated as:

Required air changes per hour

Fresh air supply due to air change requirement of 4 per hour can be calculated as

Q = 20 (300 m3/h)

= 6000 m3/h

CO emission

CO emission can be calculated as

qCO = (20 + 0.1 (20 m)) (10 cars)

= 220 m3/h CO

Required air flow due to CO emission can be calculated as

Q = 4 (220 m3/h)

= 880 m3/h air

Comparing the two calculations the fresh air supply should be 6000 m3/h.

Local Codes Local regulations and codes must always be adapted. Is important not to underestimate the traffic in the garage and the required air flow.

NOTE! CO is very dangerous!

Alternative Systems A typical solution for smaller garages is shown below.

The fresh air is supplied through openings in the outside wall. Polluted air is evacuated through openings close to the floor and the roof.

In larger buildings and garages it is common to use air from the ventilation systems in the surrounding buildings as fresh air supply to the garages.

Air with room temperature (or the temperature after the heat recovery unit) is supplied to the garage. Polluted air is evacuated through openings close to the floor and the roof.