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Garage Ventilation

Exhaust ventilation from garages and workshops.

In a garage or workshop where exhaust gases like Carbon Monoxide (CO) and NOx from vehicles are very dangerous - proper ventilation 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

Fresh air supply to a garage can be based on the CO emission from vehicles parked and driving through as

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

where

qCO = CO emission from cars (m3/h)

c1 = capacity (numbers) of parked cars in the garage

l1 = mean driving distance for cars in the parking garage (m)

c2 = numbers of cars driving through the garage

l2 = mean driving distance for cars driving through the garage (m)

Required fresh air supply can be estimated with

Q = k qCO                                      (3)

where

Q = required fresh air supply (m3/h)

 k = application coefficient

Typical application coefficients:

  • 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

Storage Garage - Fresh Air Supply

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 required 4 air changes 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 at least 1200 m3/h.

Repair Garage - Fresh Air Supply

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 required 20 air changes 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 at least 6000 m3/h.

Local Codes

Local regulations and codes must always be adapted. It is important not to underestimate the influence of traffic in the garage on the required air flow.

Alternative Systems

A typical ventilation system for a smaller garage

ventilation of garage

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

For larger buildings and garages it is common to use outlet air from the ventilation systems in the surrounding buildings as fresh make-up air to the garages.

ventialtion garage from larger house

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

Related Topics

  • Ventilation Systems

    Design of systems for ventilation and air handling - air change rates, ducts and pressure drops, charts and diagrams and more.

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