What is ACPH in HVAC?

What is ACPH in HVAC? ACPH Stands for “air changes per hour,” which is an important measure of indoor air quality.

Have you ever wondered why some spaces feel stuffy and uncomfortable while others feel fresh and invigorating? It has a lot to do with the air quality, which is influenced by several factors, including ventilation. One important measure of ventilation is air changes per hour (ACPH). 

Today, we’ll take a comprehensive look at ACPH in HVAC. So, whether you’re a homeowner, business owner, or HVAC professional, this blog post is for you.

Why is ACPH important? 

ACPH is important because it helps to remove indoor air pollutants and maintain a comfortable temperature and humidity level. 

Good ventilation is essential for maintaining good indoor air quality, which can have a significant impact on human health and well-being.

Here are some specific reasons why ACPH is important–

Removes indoor air pollutants

Your Indoor air can be polluted with various contaminants, such as dust, pollen, smoke, chemicals, and VOCs (volatile organic compounds).

These pollutants can come from various sources, including cooking, cleaning, burning wood, and building materials. ACPH helps to remove these pollutants from the air, creating a healthier environment for occupants.

Maintain a comfortable temperature and humidity level

ACPH can help to maintain a comfortable temperature and humidity level in a space. This is important for human comfort and productivity. For example, if a space is too hot or too humid, occupants may experience discomfort, fatigue, and difficulty concentrating.

Prevents mold growth

Mold can grow in humid environments. ACPH can help to prevent mold growth by removing moisture from the air. Mold growth can lead to various health problems, including respiratory problems, allergies, and asthma.

In a study of schools in California, researchers found that classrooms with higher ACPH had lower rates of respiratory infections, allergies, and asthma among students.

Reduce the spread of germs

Odors can come from various sources, including cooking, pets, and smoking. ACPH helps to reduce odors by diluting them with fresh air.

Overall, ACPH is an important metric for ensuring good indoor air quality and protecting human health and well-being. 

What is the difference between ACH and ACPH?

ACH and ACPH are both abbreviations for air changes per hour, but there is a subtle difference between the two.

ACH stands for actual air changes per hour. It is the actual number of times the volume of air in a space is completely removed and replaced in an hour. ACH can be measured using various methods, such as tracer gas testing or airflow measurement devices.

ACPH stands for nominal air changes per hour. It is the theoretical number of times the volume of air in a space is completely removed and replaced in an hour, based on the design of the HVAC system. ACPH is calculated using the CFM (cubic feet per minute) of airflow and the volume of the space.

In other words, ACH is the actual number of air changes that occur in a space, while ACPH is the theoretical number of air changes that should occur in a space based on the design of the HVAC system.

In most cases, ACH will be lower than ACPH due to factors such as air leaks and obstructions to airflow. However, if the HVAC system is properly designed and maintained, ACH should be close to ACPH.

Characteristic	ACH	ACPH
Definition	Actual air changes per hour	Nominal air changes per hour
Calculation	CFM / Volume	Design airflow / Volume
Factors that can affect	Air leaks, obstructions, HVAC system performance	HVAC system design

Now, the question may arise– which one is more important? Well, both actual ACH and nominal ACH are important metrics for evaluating the air quality and ventilation of a space. 

However, actual ACH is a more accurate measure of the actual air quality in a space.

How to calculate air changes per hour (ACPH)

To calculate air changes per hour (ACPH), you need to know the cubic feet per minute (CFM) of airflow and the volume of the space in cubic feet.

Step 1: Calculate the CFM of airflow.

The CFM of airflow can be measured using various methods, such as anemometers or flow hoods. If you do not have access to a CFM meter, you can estimate the CFM of airflow by using the following formula:

CFM = (Area of the air vent) * (Velocity of the air).

The area of the air vent can be calculated by multiplying the length and width of the vent. The velocity of the air can be measured using an anemometer.

Step 2: Calculate the volume of the space.

The volume of the space can be calculated by multiplying the length, width, and height of the space.

Step 3: Calculate ACPH

Once you have calculated the CFM of airflow and the volume of the space, you can calculate ACPH using the following formula:

ACPH = CFM / Volume

For example, let’s say you have a room that is 10 feet long, 10 feet wide, and 8 feet high. The room has a single air vent that is 1 foot wide and 1 foot high. You measure the velocity of the air at the vent to be 200 feet per minute.

To calculate the CFM of airflow, you would use the following formula–

CFM = (1 foot * 1 foot) * (200 feet per minute) = 200 CFM

To calculate the volume of the room, you would use the following formula–

Volume = 10 feet * 10 feet * 8 feet = 800 cubic feet

To calculate ACPH, you would use the following formula–

ACPH = 200 CFM / 800 cubic feet = 0.25 ACPH

This means that the air in the room is completely removed and replaced once every four hours.

Recommended ACPH for different types of spaces

The  air changes per hour requirements for different types of spaces vary depending on the occupancy type and the activities that take place in the space. 

For example, spaces with high occupancy levels or that generate many pollutants require higher ACPH rates.

Here are some recommended ACPH rates for common types of spaces–

Residential Space	Recommended ACPH
Bedrooms	4-6
Living rooms	4-6
Kitchens	6-8
Bathrooms	10-12
Commercial Space	Recommended ACPH
Open offices	6-8
Conference rooms	8-10
Server rooms	10-12
Computer rooms	10-14
Break rooms	12-15
Hallways	6-8
Retail stores	6-10
Hospitals	Recommended ACPH
Patient rooms	15-20
Operating rooms	20-25
Isolation rooms	30-40
Other types of spaces	Recommended ACPH
Classrooms	6-10
Warehouses	2-4
Gyms	8-10
Swimming pools	10-12
Parking garages	4-6

Factors that affect ACPH

So, now that you know what ACPH is and the different types of ACPH, it’s time to talk about the factors that can affect it.

There are many factors that can affect ACPH, including–

HVAC system design and performance

A properly designed and maintained HVAC system will be able to deliver the required amount of air to the space, resulting in higher ACPH. Conversely, a poorly designed or maintained HVAC system may not be able to deliver enough air, resulting in lower ACPH.

Air leaks and obstructions

Air leaks and obstructions can prevent air from circulating properly in a space, leading to lower ACPH. Air leaks can occur around doors, windows, and other openings in the building envelope.

Obstructions can include furniture, plants, and other objects that block the flow of air.

Building construction

The construction of a building can also affect ACPH. Buildings with poor ventilation, such as those with few windows or no central HVAC system, are more likely to have lower ACPH.

Occupancy type and activities

The occupancy type and activities that take place in a space can also affect ACPH. Spaces with high occupancy levels or that generate a lot of pollutants, such as kitchens and smoking lounges, require higher ACPH rates to ensure that the air is clean and fresh.

Climate

The climate can also affect ACPH. Spaces in hot and humid climates require higher ACPH rates to maintain a comfortable temperature and humidity level.

How to improve ACPH

Air changes per hour (ACPH) measures how often the air in a space is completely replaced. It is an important metric for evaluating the air quality and ventilation of a space. 

There are a number of things you can do to improve ACPH in your home or workplace, including–

Make sure your HVAC system is properly sized and maintained

An HVAC system that is too small or not properly maintained will not be able to deliver enough air to the space, which will reduce ACPH. Have your HVAC system inspected and maintained regularly by a qualified professional.

Seal any air leaks in your home or business

Air leaks can occur in a variety of places, such as around doors and windows, through cracks in the foundation, and through ductwork. Air leaks can significantly reduce ACPH. Seal any air leaks you find with caulk or weatherstripping.

Remove any obstructions to airflow

Obstructions to airflow, such as furniture, plants, and curtains, can also reduce ACPH. Make sure that your HVAC system vents are not blocked and that there is adequate space around them for air to circulate.

Install exhaust fans in kitchens and bathrooms

Exhaust fans can help to remove cooking fumes, smoke, and other pollutants from the air, which can improve ACPH. Install exhaust fans in your kitchen and bathrooms and use them whenever you are cooking or showering.

Open windows and doors regularly to let in fresh air

Opening windows and doors is a simple way to increase ACPH. If possible, open windows and doors on opposite sides of the space to create cross-ventilation.

Avoid smoking and cooking indoors

Smoking and cooking can release pollutants into the air, which can reduce ACPH. Avoid smoking and cooking indoors whenever possible. If you must smoke or cook indoors, use an exhaust fan to remove pollutants from the air.

Consider using air purifiers

Air purifiers can help to remove pollutants from the air, which can improve ACPH. Air purifiers can be especially helpful in spaces with high levels of pollutants, such as kitchens and smoking lounges.

Conclusion 

So that was all about – What is ACPH in HVAC? You can use this knowledge to ensure you’re breathing the best air possible in your home or workplace.

If you’re concerned about the air quality in your home or workplace, there are a few things you can do to test it. You can buy a home air quality tester or hire a professional to test the air for you.

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