This article will explain what is meant by the term ACH and why it is important in the context of air purifiers.
What is ACH and How it is Calculated?
ACH stands for Air Changes per Hour. The ACH rating is a measure that tells how many times per hour an air purifier device can exchange the air within a room. More fresh air exchange means better air quality in general.
ACH ratings provides information about the number of times an air purifier can filter the air in a room each hour.
For instance, an air purifier with an ACH rating of 3 means that it will purify the air throughout the entire room up to 3 times every hour.
Ideal ACH values for different spaces are calculated and specified by scientists. So different ACH valued are recommended for different spaces like bedrooms, kitchens etc.
The formula for calculating ACH for a space is given by the formula, ACH=CFM*60/Area*Height.
Thus ACH depends on the volume of the room/space and the CFM (CFM stands for cubic feet per minute, it’s a unit used to measure how quickly air flows through a purifier)value of air purifiers.
Why is ACH Important for Air Purifiers
The ACH value is important for air purifiers as it helps us to determine whether an air purifier with a specific CFM value is suitable for a specific type of room/space.
Experts and scientists recommend ACH values for different types of spaces and we can calculate the ACH for an air purifier if we know its CFM value and the volume of the space we plan to use the purifier in.
For example, it is generally accepted that an ACH between 5-6 is adequate for bedrooms.
With this information we can decide a particular air purifier with a specific CFM value is suitable for a bedroom of certain dimensions.
Assume that the area of the room is 200 square feet and height is 10 feet. Then the volume of the room is 2000 cubic feet. Let us assume that the air purifier in consideration have a CFM of 300
Now applying the formula ACH=CFM*60/Area*Height, we get: ACH=300*60/200*10=9
Since the ACH is greater than the recommended value the purifier in question is suitable for the room.
Further, it is clear that for this particular room purifiers with a CFM between 167 and 200 is the minimum requirement.
What are Ideal ACH guidelines for various spaces?
As mentioned before ideal ACH values vary across different types of spaces.
These values are recommended by scientists and experts after considering various factors.
The table below gives information about recommended ACH values for a variety of settings/spaces.
Table: ACH for various Buildings / Rooms
|Assembly halls||4 to 6|
|Attic spaces for cooling||12 to 15|
|Auditoriums||8 to 15|
|Bakeries||20 to 30|
|Banks||4 to 10|
|Barber Shops||6 to 10|
|Bars||20 to 30|
|Beauty Shops||6 to 10|
|Bed Rooms||2 to 4|
|Boiler rooms||15 to 20|
|Bowling Alleys||10 to 15|
|Cafeterias||12 to 15|
|Churches||8 to 15|
|Classrooms||6 to 20|
|Clubhouses||20 to 30|
|Cocktail Lounges||20 to 30|
|Computer Rooms||15 to 20|
|Court Houses||4 to 10|
|Dance halls||6 to 9|
|Dental Centers||8 to 12|
|Department Stores||6 to 10|
|Dining Halls||12 to 15|
|Dining rooms (restaurants)||12|
|Dress Shops||6 to 10|
|Drug Shops||6 to 10|
|Engine rooms||4 to 6|
|Factory buildings, ordinary||2 to 4|
|Factory buildings, with fumes or moisture||10 to 15|
|Fire Stations||4 to 10|
|Foundries||15 to 20|
|Galvanizing plants||20 to 30|
|Garages repair||20 to 30|
|Garages storage||4 to 6|
|Homes, night cooling||10 to 18|
|Hospital rooms||4 to 6|
|Jewelry shops||6 to 10|
|Kitchens||15 to 60|
|Laundries||10 to 15|
|Living rooms||3 to 6|
|Lunch Rooms||12 to 15|
|Luncheonettes||12 to 15|
|Nightclubs||20 to 30|
|Machine shops||6 to 12|
|Malls||6 to 10|
|Medical Centers||8 to 12|
|Medical Clinics||8 to 12|
|Medical Offices||8 to 12|
|Mills, paper||15 to 20|
|Mills, textile general buildings||4|
|Mills, textile dye houses||15 to 20|
|Municipal Buildings||4 to 10|
|Museums||12 to 15|
|Paint shops||10 to 15|
|Paper mills||15 to 20|
|Photo dark rooms||10 to 15|
|Pig houses||6 to 10|
|Police Stations||4 to 10|
|Post Offices||4 to 10|
|Poultry houses||6 to 10|
|Precision Manufacturing||10 to 50|
|Residences||1 to 2|
|Restaurants||8 to 12|
|Retail||6 to 10|
|School Classrooms||4 to 12|
|Shoe Shops||6 to 10|
|Shopping Centers||6 to 10|
|Shops, paint||15 to 20|
|Substation, electric||5 to 10|
|Supermarkets||4 to 10|
|Swimming pools||20 to 30|
|Textile mills dye houses||15 to 20|
|Toilets||6 to 10|
|Town Halls||4 to 10|
|Taverns||20 to 30|
|Theaters||8 to 15|
|Transformer rooms||10 to 30|
|Turbine rooms, electric||5 to 10|
|Waiting rooms, public||4|
|Warehouses||6 to 30|
|Wood to working shops||8|
Should You Choose Air Purifiers with High CADR?
CADR stands for Clean Air Delivery Rate. CADR rating indicates how fast the air purifier can clean the air within a particular size room. A purifier with a higher CADR means that it can purify air faster.
While high CADR is good measure generally, it should not be the only consideration.
Higher CADR value can improve ACH also and so generally while choosing an air purifier it should be ensured that the CADR of the device will satisfy the minimum recommended ACH value for the space in which it will be used.
To calculate Air Changes Per Hour (ACH), find the CFM of your device and multiply that by 60 then divide that total by the total cubic feet of the room to get your total ACH.
Recommended Air Changes Per Hour value changes across different kinds of spaces. Bedrooms,offices, kitchens, auditoriums, etc all have a recommended range of ACH values which are determined by scientists and experts.
ACH stands for Air Changes per Hour. The ACH rating is a measure which tells how many times per hour an air purifier device can exchange the air within a room. Thus an ACH of 10 means that the air in the room/space will be changed/purified ten times an hour.
We hope that this article has helped you in creating a clear picture of ACH, its meaning, importance, and uses. If you have further queries or doubts regarding ACH, please mention them in the comments section.
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