Air Change Cfm Calculator

The rate at which air is exchanged (in the premises) represents another method of measuring ventilation capacity & effectiveness. Air exchange rate is typically expressed in Air Changes per Hour – “ACH”. Air changes per hour can be estimated by determining the total air supplied to, and removed from, the premises “total air exchange” or the outdoor (fresh) air supplied to, and removed from, the premises “outdoor air exchange”.

This table provides suggested air changes per hour (ACH) under normal conditions based on good experince.

Assembly rooms	4 – 8	Hairdressing salons	10 – 15
Bakeries	20 – 30	Hospitals – sterilizing	15 – 25
Banks/Building Societies	4 – 8	Hospitals – wards	6 – 8
Bathrooms	6 – 10	Kitchens – domestic	15 – 20
Bedrooms	2 – 4	Kitchens # – commercial	30 minimum
Billiard Rooms *	6 – 8	Laboratories	6 – 15
Boiler Rooms	15 – 30	Launderettes/Laundromats	10 – 15
Cafes and coffee bars	10 – 12	Laundries	10 – 30
Canteens	8 – 12	Lavatories	6 – 15
Cellars	3 – 10	Lecture theaters	5 – 8
Changing Rooms Main area	6 – 10	Libraries	3 – 5
Changing Rooms Shower area	15 – 20	Living rooms	3 – 6
Churches	1 – 3	Mushroom houses	6 – 10
Cinemas & theatres *	10 – 15	Offices	6 – 10
Club rooms	12 minimum	Paint shops (not cellulose)	10 – 20
Compressor rooms	10 – 20	Photo & X-ray darkrooms	10 – 15
Conference rooms	8 – 12	Public house bars	12 minimum
Dairies	8 – 10	Recording control rooms	15 – 25
Dance halls	12 minimum	Recording studios	10 – 12
Dental surgeries	12 – 15	Restaurants	8 – 12
Dye works	20 – 30	Schoolrooms	5 – 7
Electroplating shops	10 – 12	Shops and supermarkets	8 – 15
Engine rooms	15 – 30	Shower baths	15 – 20
Entrance halls & corridors	3 – 5	Stores & warehouses	3 – 6
Factories and workshops	8 – 10	Squash courts	4 minimum
Foundries	15 – 30	Swimming baths	10 – 15
Garages	6 – 8	Toilets	6 – 10
Glasshouses	25 – 60	Utility rooms	15 – 20
Gymnasiums	6 minimum	Welding shops	15 – 30

*Increase by 50% where heavy smoking occurs or if the room is underground.

#Some commercial kitchens may require higher ventilation rates, based on cooking equipment in use.

FREQUENTLY ASKED QUESTIONS

What is the significance of air changes per hour (ACH) in ventilation systems?

Air changes per hour (ACH) is a crucial parameter in ventilation systems as it directly affects indoor air quality, occupant comfort, and energy consumption. ACH measures the rate at which air is exchanged in a premises, influencing the removal of pollutants, moisture, and heat. Adequate ACH ensures a healthy and comfortable indoor environment, while insufficient ACH can lead to poor air quality, discomfort, and even health issues.

How do I calculate the total air exchange rate in a premises?

To calculate the total air exchange rate, you need to determine the total air supplied to and removed from the premises. This can be done by summing up the airflow rates of all supply and exhaust fans, as well as any natural ventilation sources. The total air exchange rate is then divided by the volume of the premises to obtain the air changes per hour (ACH). For example, if the total air supplied is 10,000 CFM and the premises has a volume of 50,000 cubic feet, the total air exchange rate would be 10,000 CFM / 50,000 cu.ft = 0.2 air changes per hour.

What is the difference between total air exchange and outdoor air exchange?

Total air exchange refers to the total amount of air supplied to and removed from a premises, including recirculated air. Outdoor air exchange, on the other hand, only considers the fresh air brought in from outside and exhausted to the outdoors. While total air exchange provides a broader picture of ventilation, outdoor air exchange is a more direct indicator of the premises’ ability to remove pollutants and provide fresh air to occupants.

How do I determine the required air changes per hour for a specific space?

The required air changes per hour (ACH) for a specific space depends on various factors, including occupancy, activity level, and desired indoor air quality. The table provided in the blog post offers suggested ACH values for different spaces under normal conditions. However, it’s essential to consult relevant standards, such as ASHRAE 62.1, and consider specific requirements for your project. Additionally, you may need to perform calculations based on the space’s volume, occupancy, and ventilation system design.

Can I use air changes per hour to estimate ventilation system sizing?

Air changes per hour (ACH) can be used as a rough estimate for ventilation system sizing, but it’s not a direct correlation. ACH provides a general indication of the required ventilation rate, but it doesn’t account for factors like duct losses, fan efficiency, and heat gain/loss. To accurately size a ventilation system, you should perform detailed calculations considering these factors, as well as the specific requirements of your project.

How does air changes per hour impact energy consumption in HVAC systems?

Air changes per hour (ACH) has a significant impact on energy consumption in HVAC systems. Higher ACH values require more energy to operate fans, heat, and cool the air. Conversely, lower ACH values can lead to reduced energy consumption. However, it’s essential to strike a balance between ACH and energy efficiency, as inadequate ventilation can lead to poor indoor air quality and occupant discomfort. Optimizing ACH based on the specific needs of your project can help minimize energy consumption while maintaining a healthy and comfortable indoor environment.