What is ACH and Why It is Important?

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In Brief: What is ACH and Why It is Important

ACH stands for Air Changes per Hour. The ACH rating is a measure that tells how many times per hour an air purifying device can exchange the air within a room. Ideal ACH values for different spaces are calculated and specified by scientists. The formula for calculating ACH for space is given by the formula, ACH=CFM*60/Area*Height.

Are you planning to buy an air purifier and is not quite clear about some of the technical parameters associated with air purifiers like ACH, CFM, CADR etc? If so, you have come to the right place.

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

TypeACH value
Assembly halls4 to 6
Attic spaces for cooling12 to 15
Auditoriums8 to 15
Bakeries20 to 30
Banks4 to 10
Barber Shops6 to 10
Bars20 to 30
Beauty Shops6 to 10
Bed Rooms2 to 4
Boiler rooms15 to 20
Bowling Alleys10 to 15
Cafeterias12 to 15
Churches8 to 15
Classrooms6 to 20
Club rooms12
Clubhouses20 to 30
Cocktail Lounges20 to 30
Computer Rooms15 to 20
Court Houses4 to 10
Dance halls6 to 9
Dental Centers8 to 12
Department Stores6 to 10
Dining Halls12 to 15
Dining rooms (restaurants)12
Dress Shops6 to 10
Drug Shops6 to 10
Engine rooms4 to 6
Factory buildings, ordinary2 to 4
Factory buildings, with fumes or moisture10 to 15
Fire Stations4 to 10
Foundries15 to 20
Galvanizing plants20 to 30
Garages repair20 to 30
Garages storage4 to 6
Homes, night cooling10 to 18
Hospital rooms4 to 6
Jewelry shops6 to 10
Kitchens15 to 60
Laundries10 to 15
Libraries, public4
Living rooms3 to 6
Lunch Rooms12 to 15
Luncheonettes12 to 15
Nightclubs20 to 30
Machine shops6 to 12
Malls6 to 10
Medical Centers8 to 12
Medical Clinics8 to 12
Medical Offices8 to 12
Mills, paper15 to 20
Mills, textile general buildings4
Mills, textile dye houses15 to 20
Municipal Buildings4 to 10
Museums12 to 15
Offices, public3
Offices, private4
Paint shops10 to 15
Paper mills15 to 20
Photo dark rooms10 to 15
Pig houses6 to 10
Police Stations4 to 10
Post Offices4 to 10
Poultry houses6 to 10
Precision Manufacturing10 to 50
Pump rooms5
Railroad shops4
Residences1 to 2
Restaurants8 to 12
Retail6 to 10
School Classrooms4 to 12
Shoe Shops6 to 10
Shopping Centers6 to 10
Shops, machine5
Shops, paint15 to 20
Shops, woodworking5
Substation, electric5 to 10
Supermarkets4 to 10
Swimming pools20 to 30
Textile mills4
Textile mills dye houses15 to 20
Toilets6 to 10
Town Halls4 to 10
Taverns20 to 30
Theaters8 to 15
Transformer rooms10 to 30
Turbine rooms, electric5 to 10
Warehouses2
Waiting rooms, public4
Warehouses6 to 30
Wood to working shops8

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.

FAQs

How do I calculate air changes per hour?

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.

What is the standard air changes per hour?

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.

What is 10 air changes hourly?

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.

Summary

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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