Sirrrrrrr, I was so lost in this topic taking my classes for the Commercial Drying Specialist, I asked 100 times to my instructor and I couldn't understand, so I decided to look here and I came here : NOW I GOT IT !!! Your calm and clear way to talk gets into my brain, THANKS A TON !!!
Thank you sooo much for this. I've been searching online to understand this formula. Because I am a visual learner I have not understood it until I saw you demonstrate it. 😊😊
I was trying to figure out how to determine the number of air changes you need for a specific room. Is it based all on code? Maybe Square footage? Where can you find that information?
That's great but I have a question, that 108 CFM that you got from your results, is the CFM that supplied for the room or that to be exahuasted outside the room as an return?
The 108 CFM is the amount of air that needs to be Exhausted from the space or Recirculated (Return Air) through filters in situations like cleanrooms. Hospitals have many rooms that require a certain amount of ventilation air indicated in Air Changes, and also a minimum amount of air to be recirculated indicated in ACH. The air change calculation is just an indication of how much air is to be replaced within the space, which can either be exhausted or recirculated out of the space and back again through filters or some other process, depending on the application.
As per one of your video "how to calculate CFM" in which you show a formula "total sensible btuh / 1.08(EAT-LAT)" As per this calculation CFM is not matching with this equation. And now I am confusion which one right to consider.
Hello Sir, you explained back calculations only. First you declared 4 Air changes per hour and calculated CFM. Again same CFM value used for Air changes per hour calculations. Can you explain, how to calculate CFM without knowing the Air Changes per hour value?
Ventilation requirements can be found in ASHRAE 62.1 for Commercial Buildings and 62.2 for Residential Buildings. The use of residential bathroom and kitchen exhaust fans assist with any pollutants generated in those spaces, so it's important to make sure that those fans are operating when those spaces are being used.
Does this calculation mean that based on this example, a fan rated for 108 CFM would have to run continuously for 24 hours in order to fulfill the 4 air changes per hour?
No. At 108 CFM (Cubic Feet per Minute) this would achieve 4 ACH (Air Changes per Hour) in just 1 Hour for this size of a room. ACH calculations, or Air Changes per Hour determines the amount of CFM required to accomplish changing the air volume of a space in just 1 hour, hence Air Changes per HOUR. So to achieve 4 Air Changes in just one (1) hour for this size room would require a fan that can do 108 CFM.
Depends on your local code. There are standards, like ASHRAE 62.1 which has several variables to calculating ventilation, but basically its based on the area (Ft2). For instance a Kitchen would require 7.5 CFM/Person + 0.12 CFM/Ft2. Bathrooms would require 50 CFM of Exhaust for every Toilet or Urinal. See ASHRAE 62.1-2019 Table 6-1 Minimum Ventilation Rates in Breathing Zone
Hello sir, I have a 36×12×20 ft volume of a room but i dont know how much air changes per hour of that room So pleasw tell me how to calculate cfm of my room
Please watch our video on how to calculate CFM for your room. ruclips.net/video/x59AS0SQtCg/видео.html There are many factors that go into answering your question. You need to know if it's an exterior or interior space. Is this Exterior glass, if so, how many square feet of glass, and what is the solar exposure and "U" factor of the glass? Where in the world is the building located, each location has different weather conditions. How many people will be in the room? How many watts from lighting and plug loads? What is the design Outdoor and Indoor Temperatures?
Air Changes refers to the volume of the room. This can be done with a mix of ventilation air (OSA) and room air. High air change rates using room air is to provide a clean environment usually through HEPA filters.
You want to use the minimum ACH approved by code because that would allow you to save energy. The choice of CFM is based on your local code and the standards which they have adopted. What country do you live in, and which standards have been adopted by your local code? Sometimes thermal heat gains will dictate CFM as opposed to ACH.
Air Recirculating within the room can count as part of the Air Changes, but make sure that whatever room you're designing also has Ventilation Air Changes or CFM as dictated by your local code or ASHRAE Standard 62.1.
Hey Please Do you have any idea?? The air outlet area of the indoor unit of the air conditioner is 0.1 square meters, the flow rate is 2m/s, the density is 1.2 kg/m3, and the flow direction is upward 45 degrees. How much is the air exchange rate in cubic meters per hour? How many kilograms?
The air change rate is based on the volume of the room. What is the width, length and height of the room? This will give you Ft3 or M3. The calculation is based on the volume of the room.
It depends on what the room is designed for. If it’s negative space you would go off the return. If it’s a positive space (operating room) you would go off the supply. I’m a air balancer and asked the same question recently
Some Energy Codes look at it differently. They don't use Air Changes but state that Whole House Ventilation must equal 1 CFM for every 100 Ft2 plus another 7.5 CFM per occupant + 1, so if you have a 1,800 FT2, 3-bedroom home you would be required to provide 48 CFM of ventilation. (1,800 Ft2 x 1 cfm/100 FT2)+(3 occupants +1 = 4 * 7.5 CFM/Occupant) Codes very, so its important to always check your local code for this requirement.
With natural ventilation it's not ACH you need to consider as much as code requirements. There are so many factors that play into how much natural ventilation enters a building. Consideration must be made for wind speed, wind direction, pressure differential, shape of the building, temperature/buoyancy effect, building opening locations and the size of the openings, etc . You should use ASHRAE 62.1 to determine the required ventilation for the space, then review your local code for the requirements when using natural ventilation, such as in California, USA, Title-24 of the Energy Code Section 120.1, which allows natural ventilation under strict guidelines, such as Naturally Ventilated spaces shall be within 20 feet of wall or roof openings to the outdoors, the operable area of which is not less than 5% of the conditioned floor area or ventilated space, etc.. Hope this helps.
I used 4 air changes just an example. The amount of air changes required will be dictated by your local code or by good engineering practices for the type of space being ventilated.
Design recommendations for air change rates for various applications are primarily contained within the 2015 ASHRAE Handbook- HVAC Applications. www.ashrae.org Requirements for outside air ventilation rates are contained in ASHRAE Standard 62.1-2016, "Ventilation for Acceptable Indoor Air Quality" Air change rate - imperial Units n = 60 q / V n = air changes per hour (1/h) q = fresh air (make up air) flow through the room (Cubic Feet per Minute, cfm)V = volume of the room (Cubic Feet) Air Change Rate - SI Units n = 3600 q / V n = air changes per hourq = fresh air (make up air) flow through the room (m3/s)V = volume of the room (m3) Rush, I hope this is enough information to get you started in the right direction.
Why not Ft^3 / 60 to get CFM at 1 ACH and then *4 for 4ACH or /3 for .3ACH, so on and so forth? With the given example of 12*15*9=1620 it'd be just 1620/60=27 CFM(1ACH) 27*4=108 CFM (4ACH)
@@VRFWizard Oh, yeah it's not wrong- I meant for simplicity, it seems (to me at least, and I may be odd!) that it would be easier to explain. Great video by the by :)
You can use an anemometer to measure the CFM coming out of your supply grille, then multiply by 60 (60 minutes in an hour) and then divide by the Total Cubic Feet of the Room.
Depending on the use of the room the code may dictate the required Air Changes per Hour. The first thing you need to determine is what is the designed use of the room, and then what does the code require for that type of room, such as an Operating Room in a Hospital or Bathroom. Check your local code for any requirements based on the use of the room. After you have the code required ACH then you figure out the volume of the space and do the simple math to figure out the CFM required.
Ok, I tried something about an air change per hour by, for example: if the room is using 8 hours per day, so I used 8 x volume of a room and divided by 60 and the answer is total CFM... correct?
You should be looking only at how many air changes are required in a 1-Hour period, as that will be used to size the equipment or be taken in to consideration. Looking at it over an 8-hour period is not how it's figured. Looking at most codes, especially those involving hospital rooms, they will have a requirement based on how many Air Changes in a 1-Hour period are set as a minimum. Your 8 x the volume would give you 8 Air Changes in an Hour. Everything is figured for a 1-Hour period. How many air changes do you want in a 1-hour period?
@@hvacrefrigeration5204 That was just an example for simplicity. Depending on the type of room the Air Changes per hour can be 6, 12, 20 ,30, 50 or more. Cleanrooms, operating rooms and other type rooms need large volumes of air re-circulated. Now with COVID everyone is looking at increasing the Air Change Rate and using better filtration to mitigate the virus from spreading or infecting occupants.
I like to know more about measuring CFM by using pitot tube tested at the return side close to filter placement. Most of time I have seen by CARRIER approach method. Can I use the location at discharge side where at about foot or two above evaporator coil, do you think it’s better that way to get a better result of actual air flow through both of secondary heat exchanger and evaporator coil? Please send me a RUclips video if you have it. Thank you,
Ive looked at a dozen references for the proper air changes per hour for different areas and every single one is different lol. Either super low or super high.
This is a simple example of how to determine the amount of air changes in a room. The amount of return air that gets removed from the room is determined by the room type and the amount of exhaust from that room and its pressure relationship with the surrounding spaces. For a room with no exhaust and equal pressure relationship to the surrounding space, then your return air will be the same as your supply. For an operating room in a hospital you may have 100% exhaust and no return air. Its important to first determine the room type and its requirements.
It depends on your local code or ASHRAE standards for the type of room. Depending on the room type the requirements will vary, such as a Hospital Operating Room, Laboratory or Cleanroom. Look at ASHRAE 62.1 for some examples of the requirements per space type.
@@VRFWizard To be clear, I don't have a commercial building so forget codes. It's just a workshop, 30X30X12, or 10,800 cu. ft. I work alone. No air conditioning. Few obstacles What ceiling fan CFM rating would I need to move enough air to feel a breeze on the back of my sweaty neck? Thx.
@@rustyicepick8462 To be safe, make sure to capture any emissions from welding, grinding, painting or other hazardous processes with a local exhaust. For what you want to accomplish, all you need is to go to your local hardware store and grab one or more oscillating fans, and direct them wherever you are working. You just need to have air blow over your sweat for the process of evaporative cooling to take effect.
The quantity of air changes is often dictated by code for the different types of spaces, such as for bathrooms, or hospital operating rooms. Once you know the code required Air Changes per Hour (ACH) required, you can determine how many CFM would be required.
Outside Air is determined by many factors, including the type of space and the quantity of occupants. In hospital and healthcare facilities, the driving factor can be Air Changes per Hour, as some hospital rooms require 100% Outside Air. So, it's important to start with the space requirements as dictated by the code authority. Look at ASHRAE Table 6.1 Minimum Ventilation Rates (CFM/FT2) ashrae.iwrapper.com/ViewOnline/Standard_62.1-2019
Wow! So real-world application wise, what if a city's Housing Code for rental apartment (especially buildings built from the 1920s to 1970s) mandates 2 ACPs for a kitchen room. But most manufacturer's advocate a minimum 350 CFM stove hood fan if one's stove/oven is 30" or higher wide? Challenge the Housing Code is outdated when cross-referenced to Housing Safety Codes -- that the exiting rental apartment appliances (stove hood) must be replaced? Or claim the lower CFM overn hood is "grandfathered" -- exempt from higher manufacture CFM specs (even if the property owner updates the stove but not the hood) per the current (even if outdated) Housing Code? Yep! This is a real world issue, aggravated by Housing Code Inspectors that have no mechanical/match skills on how to calculate CFMs or ACP of the applicance vis-a-vis the Kitchen Volume! Their inspection test (if you can call it that) is to 1) turn on the oven hood, 2) flick a cigarrette lighter, 3) see whether the fan moves the flame, and 4) whether the fan sounds loud to their ears. 1) if the fan moves the flame and 2) the fan produces a loud sound, then 3) the Housing Code Inspector claims the oven hood meets the 2 ACPs mandated by the Housing Code for Kitchens.
If it's an existing system you can take measurements at the fan for the CFM at the system level or in the room that you are trying to determine the actual CFM for.
This was really disappointing - it is just a lesson in basic arithmetic and conversion of units that common sense and high school should have provided for. I was hoping for a discussion of the likely air changes in real life buildings and how to arrive at the best assumptions when making heat-loss calculations.
Your right that this is a basic overview of how air changes are determined. Heat-loss calculations are based determined using one of the many cooling load software programs and there shouldn't be any assumptions about ACH. For Hospitals Air Changes can be the driving force for various rooms, but that is beyond the scope of this video.
And why would you expect all of that in a video that is literally titled "how to calculate air changes per hour" The video provided exactly what it was titled
Hi. I have a question. I am completing a ventilation air schedule for floor plans. I have figured out the required OA CFM but it also requires that I calculate the actual OA CFM. Is there a formula to help do that? Thanks.
It depends on which code is required in your area. ASHRAE 62.1 defines the standard for calculating the ventilation (OSA) requirements for various building space types. Depending on the type of room, there will be a requirement for so many CFM per person, and older standards include a certain amount of CFM based on the floor area. The calculation is based on Quantity of People (CFM/Person) and some codes require additional CFM for the off gassing of furniture and interior finishes (CFM/Ft2) Hope that helps.
Sirrrrrrr, I was so lost in this topic taking my classes for the Commercial Drying Specialist, I asked 100 times to my instructor and I couldn't understand, so I decided to look here and I came here : NOW I GOT IT !!!
Your calm and clear way to talk gets into my brain, THANKS A TON !!!
Your Welcome. Good luck in your classes.
Great teaching!! Keep it up... no extras no blah blah blah.. thanks !!!
Glad it was helpful!
Loud and Hear. We all heard it!! Good instructor. This is how I also teach.
Thank you sooo much for this. I've been searching online to understand this formula. Because I am a visual learner I have not understood it until I saw you demonstrate it. 😊😊
You're Welcome
Thank you for very informative article, it's help me a lot in my work as a hospital maintenance technician!more power to your channel!
Hi Yuan
excellent job Sir. Thanks!
How to determine ACH for a windcatcher
Which velocity we should take inlet or outlet
I was trying to figure out how to determine the number of air changes you need for a specific room. Is it based all on code? Maybe Square footage? Where can you find that information?
That's great but I have a question, that 108 CFM that you got from your results, is the CFM that supplied for the room or that to be exahuasted outside the room as an return?
The 108 CFM is the amount of air that needs to be Exhausted from the space or Recirculated (Return Air) through filters in situations like cleanrooms. Hospitals have many rooms that require a certain amount of ventilation air indicated in Air Changes, and also a minimum amount of air to be recirculated indicated in ACH. The air change calculation is just an indication of how much air is to be replaced within the space, which can either be exhausted or recirculated out of the space and back again through filters or some other process, depending on the application.
As per one of your video "how to calculate CFM" in which you show a formula "total sensible btuh / 1.08(EAT-LAT)" As per this calculation CFM is not matching with this equation. And now I am confusion which one right to consider.
Hello Sir, you explained back calculations only. First you declared 4 Air changes per hour and calculated CFM. Again same CFM value used for Air changes per hour calculations. Can you explain, how to calculate CFM without knowing the Air Changes per hour value?
It's very neat 👍 anyway, will that the same with metrics?
What is the recommended ACH kitchen and living room ?
Ventilation requirements can be found in ASHRAE 62.1 for Commercial Buildings and 62.2 for Residential Buildings. The use of residential bathroom and kitchen exhaust fans assist with any pollutants generated in those spaces, so it's important to make sure that those fans are operating when those spaces are being used.
Im korean your video is good!
Thank you
Does this calculation mean that based on this example, a fan rated for 108 CFM would have to run continuously for 24 hours in order to fulfill the 4 air changes per hour?
No. At 108 CFM (Cubic Feet per Minute) this would achieve 4 ACH (Air Changes per Hour) in just 1 Hour for this size of a room. ACH calculations, or Air Changes per Hour determines the amount of CFM required to accomplish changing the air volume of a space in just 1 hour, hence Air Changes per HOUR. So to achieve 4 Air Changes in just one (1) hour for this size room would require a fan that can do 108 CFM.
Sssoo simple to understand 🤙🏻
Thanks, very well explained and calculated
You are welcome!
How many times per hour is the change of ventilation in bathrooms, toilets and kitchens?
Depends on your local code. There are standards, like ASHRAE 62.1 which has several variables to calculating ventilation, but basically its based on the area (Ft2). For instance a Kitchen would require 7.5 CFM/Person + 0.12 CFM/Ft2. Bathrooms would require 50 CFM of Exhaust for every Toilet or Urinal. See ASHRAE 62.1-2019 Table 6-1 Minimum Ventilation Rates in Breathing Zone
Hello sir,
I have a 36×12×20 ft volume of a room but i dont know how much air changes per hour of that room
So pleasw tell me how to calculate cfm of my room
Please watch our video on how to calculate CFM for your room. ruclips.net/video/x59AS0SQtCg/видео.html
There are many factors that go into answering your question. You need to know if it's an exterior or interior space. Is this Exterior glass, if so, how many square feet of glass, and what is the solar exposure and "U" factor of the glass? Where in the world is the building located, each location has different weather conditions. How many people will be in the room? How many watts from lighting and plug loads? What is the design Outdoor and Indoor Temperatures?
Sorry what is different between minimum outdoir air change and minimum total air change
Good information ji sir
Thank you
Please inform..is ACH.means change with outside air? Or just resirculate throught AHU?
Air Changes refers to the volume of the room. This can be done with a mix of ventilation air (OSA) and room air. High air change rates using room air is to provide a clean environment usually through HEPA filters.
Which CFM reading should be used and when? Exhaust for negative pressure rooms, supply for positive pressure
Or just use highest number CFM?
Thanks
You want to use the minimum ACH approved by code because that would allow you to save energy. The choice of CFM is based on your local code and the standards which they have adopted.
What country do you live in, and which standards have been adopted by your local code? Sometimes thermal heat gains will dictate CFM as opposed to ACH.
Hi, i'm asking if the room has circulation fan just like AHU (supply fan & return fan with the same air flow) is this formula still works..?
Air Recirculating within the room can count as part of the Air Changes, but make sure that whatever room you're designing also has Ventilation Air Changes or CFM as dictated by your local code or ASHRAE Standard 62.1.
Hey Please Do you have any idea??
The air outlet area of the indoor unit of the air conditioner is 0.1 square meters, the flow rate is 2m/s,
the density is 1.2 kg/m3, and the flow direction is upward 45 degrees. How much is the air exchange
rate in cubic meters per hour? How many kilograms?
The air change rate is based on the volume of the room. What is the width, length and height of the room? This will give you Ft3 or M3. The calculation is based on the volume of the room.
Superb guide and explanation , thank you
Please describe more about, how did you come up with 4 air change in an hour?
4 ACH is just an example. See ASHRAE 62.1 for Ventilation rate requirements.
Very good presentation!! Thank you.
How come 4 ACH
To determine CFM, do you combine both supply and return CFM or take the greater CFM of the two?
It depends on what the room is designed for. If it’s negative space you would go off the return. If it’s a positive space (operating room) you would go off the supply.
I’m a air balancer and asked the same question recently
is 1 exchange per hour adequate for house? I read something like 2-4 for bedrooms and 4-8 for living rooms which is crazy!!
Some Energy Codes look at it differently. They don't use Air Changes but state that Whole House Ventilation must equal 1 CFM for every 100 Ft2 plus another 7.5 CFM per occupant + 1, so if you have a 1,800 FT2, 3-bedroom home you would be required to provide 48 CFM of ventilation. (1,800 Ft2 x 1 cfm/100 FT2)+(3 occupants +1 = 4 * 7.5 CFM/Occupant)
Codes very, so its important to always check your local code for this requirement.
Very informative lecture
can you achieve 4 ach with natural ventilation?
With natural ventilation it's not ACH you need to consider as much as code requirements. There are so many factors that play into how much natural ventilation enters a building. Consideration must be made for wind speed, wind direction, pressure differential, shape of the building, temperature/buoyancy effect, building opening locations and the size of the openings, etc . You should use ASHRAE 62.1 to determine the required ventilation for the space, then review your local code for the requirements when using natural ventilation, such as in California, USA, Title-24 of the Energy Code Section 120.1, which allows natural ventilation under strict guidelines, such as Naturally Ventilated spaces shall be within 20 feet of wall or roof openings to the outdoors, the operable area of which is not less than 5% of the conditioned floor area or ventilated space, etc.. Hope this helps.
Thank you. Very well explained.
Thank you for very informative article
Thanks
Thank you for your sharing ❤️❤️
احسنت شرح مميز فعلا ،جزاكم اللة خيرا
Thanks, very clear and concise!!
Really Informative Thanks
Dear sir, how we assume it 4 times??? 🤔
I used 4 air changes just an example. The amount of air changes required will be dictated by your local code or by good engineering practices for the type of space being ventilated.
@@VRFWizard still confusion, any technique?
Design recommendations for air change rates for various applications are primarily contained within the 2015 ASHRAE Handbook- HVAC Applications. www.ashrae.org
Requirements for outside air ventilation rates are contained in ASHRAE Standard 62.1-2016, "Ventilation for Acceptable Indoor Air Quality"
Air change rate - imperial Units
n = 60 q / V
n = air changes per hour (1/h)
q = fresh air (make up air) flow through the room (Cubic Feet per Minute, cfm)V = volume of the room (Cubic Feet)
Air Change Rate - SI Units
n = 3600 q / V
n = air changes per hourq = fresh air (make up air) flow through the room (m3/s)V = volume of the room (m3)
Rush, I hope this is enough information to get you started in the right direction.
i have a question. what is used to supply those cfmsto replace the air ?
you refer web www.tombling.com/cooling/ventilation-fan.htm..
Great video thanks
Why not Ft^3 / 60 to get CFM at 1 ACH and then *4 for 4ACH or /3 for .3ACH, so on and so forth?
With the given example of 12*15*9=1620 it'd be just
1620/60=27 CFM(1ACH) 27*4=108 CFM (4ACH)
Yes, you're correct that both ways of using the same values come up with the same answer. Either method of calculation works.
@@VRFWizard Oh, yeah it's not wrong- I meant for simplicity, it seems (to me at least, and I may be odd!) that it would be easier to explain. Great video by the by :)
very clear thanks
How to find the air change rate,does it have any instrument?
You can use an anemometer to measure the CFM coming out of your supply grille, then multiply by 60 (60 minutes in an hour) and then divide by the Total Cubic Feet of the Room.
Thank q sir mq q ention has review at previos reply👍
if i dont know the cfm & ach of the room, how can i calculate the ach?
Depending on the use of the room the code may dictate the required Air Changes per Hour. The first thing you need to determine is what is the designed use of the room, and then what does the code require for that type of room, such as an Operating Room in a Hospital or Bathroom. Check your local code for any requirements based on the use of the room. After you have the code required ACH then you figure out the volume of the space and do the simple math to figure out the CFM required.
Ok, I tried something about an air change per hour by, for example: if the room is using 8 hours per day, so I used 8 x volume of a room and divided by 60 and the answer is total CFM... correct?
You should be looking only at how many air changes are required in a 1-Hour period, as that will be used to size the equipment or be taken in to consideration. Looking at it over an 8-hour period is not how it's figured. Looking at most codes, especially those involving hospital rooms, they will have a requirement based on how many Air Changes in a 1-Hour period are set as a minimum. Your 8 x the volume would give you 8 Air Changes in an Hour. Everything is figured for a 1-Hour period. How many air changes do you want in a 1-hour period?
@@VRFWizard so, I see the way you used 4 air change per hour;..is that a minimum or an average figured?
@@hvacrefrigeration5204 That was just an example for simplicity. Depending on the type of room the Air Changes per hour can be 6, 12, 20 ,30, 50 or more. Cleanrooms, operating rooms and other type rooms need large volumes of air re-circulated. Now with COVID everyone is looking at increasing the Air Change Rate and using better filtration to mitigate the virus from spreading or infecting occupants.
@@VRFWizard thank you so much, I understand now.
I like to know more about measuring CFM by using pitot tube tested at the return side close to filter placement.
Most of time I have seen by CARRIER approach method.
Can I use the location at discharge side where at about foot or two above evaporator coil, do you think it’s better that way to get a better result of actual air flow through both of secondary heat exchanger and evaporator coil?
Please send me a RUclips video if you have it.
Thank you,
Exactly>>
Ive looked at a dozen references for the proper air changes per hour for different areas and every single one is different lol. Either super low or super high.
what about return air quantity?
This is a simple example of how to determine the amount of air changes in a room. The amount of return air that gets removed from the room is determined by the room type and the amount of exhaust from that room and its pressure relationship with the surrounding spaces.
For a room with no exhaust and equal pressure relationship to the surrounding space, then your return air will be the same as your supply. For an operating room in a hospital you may have 100% exhaust and no return air. Its important to first determine the room type and its requirements.
I have already subscribed your channel. Your videos are good about basics. I have channel about HVAC / MEP and suggested to review my channel too.
Your channel name please
Great
How do we know how many air changes we need?
For example, will I feel a breeze at 4 air changes per hour? At 50 air changes per hour?
It depends on your local code or ASHRAE standards for the type of room. Depending on the room type the requirements will vary, such as a Hospital Operating Room, Laboratory or Cleanroom. Look at ASHRAE 62.1 for some examples of the requirements per space type.
@@VRFWizard To be clear, I don't have a commercial building so forget codes. It's just a workshop, 30X30X12, or 10,800 cu. ft. I work alone. No air conditioning. Few obstacles What ceiling fan CFM rating would I need to move enough air to feel a breeze on the back of my sweaty neck? Thx.
@@rustyicepick8462 To be safe, make sure to capture any emissions from welding, grinding, painting or other hazardous processes with a local exhaust. For what you want to accomplish, all you need is to go to your local hardware store and grab one or more oscillating fans, and direct them wherever you are working. You just need to have air blow over your sweat for the process of evaporative cooling to take effect.
I dont know cfm, then how i will find number of ach?? It is assumption??
The quantity of air changes is often dictated by code for the different types of spaces, such as for bathrooms, or hospital operating rooms. Once you know the code required Air Changes per Hour (ACH) required, you can determine how many CFM would be required.
How does OA% play a role in this equation?
Outside Air is determined by many factors, including the type of space and the quantity of occupants. In hospital and healthcare facilities, the driving factor can be Air Changes per Hour, as some hospital rooms require 100% Outside Air. So, it's important to start with the space requirements as dictated by the code authority. Look at ASHRAE Table 6.1 Minimum Ventilation Rates (CFM/FT2) ashrae.iwrapper.com/ViewOnline/Standard_62.1-2019
Here is another link for Healthcare Facilities showing minimum Air Changes per Hour ashrae.iwrapper.com/ViewOnline/Standard_170-2017_(86529)
Wow! So real-world application wise, what if a city's Housing Code for rental apartment (especially buildings built from the 1920s to 1970s) mandates 2 ACPs for a kitchen room. But most manufacturer's advocate a minimum 350 CFM stove hood fan if one's stove/oven is 30" or higher wide?
Challenge the Housing Code is outdated when cross-referenced to Housing Safety Codes -- that the exiting rental apartment appliances (stove hood) must be replaced? Or claim the lower CFM overn hood is "grandfathered" -- exempt from higher manufacture CFM specs (even if the property owner updates the stove but not the hood) per the current (even if outdated) Housing Code?
Yep! This is a real world issue, aggravated by Housing Code Inspectors that have no mechanical/match skills on how to calculate CFMs or ACP of the applicance vis-a-vis the Kitchen Volume! Their inspection test (if you can call it that) is to 1) turn on the oven hood, 2) flick a cigarrette lighter, 3) see whether the fan moves the flame, and 4) whether the fan sounds loud to their ears.
1) if the fan moves the flame and 2) the fan produces a loud sound, then 3) the Housing Code Inspector claims the oven hood meets the 2 ACPs mandated by the Housing Code for Kitchens.
That does sound like some old school inspection criteria. Good luck.
Need to calculate air changes but you just assumed.hahah
😂
Why did you assume 4
I is an assumption based on the requirements that the owners of the room might have requested
Now all I need to know is how do I know how much CFM I actually have
If it's an existing system you can take measurements at the fan for the CFM at the system level or in the room that you are trying to determine the actual CFM for.
How come 4 ACH ??
We used 4 ACH to make the example easier to follow.
@@VRFWizard can you tell me page no and any reference by ashrae
@@fmepengineering3435 You can find the information in ASHRAE's Fundamentals Handbook Chapter 16 Ventilation and Infiltration. www.ashrae.org
This was really disappointing - it is just a lesson in basic arithmetic and conversion of units that common sense and high school should have provided for. I was hoping for a discussion of the likely air changes in real life buildings and how to arrive at the best assumptions when making heat-loss calculations.
Your right that this is a basic overview of how air changes are determined. Heat-loss calculations are based determined using one of the many cooling load software programs and there shouldn't be any assumptions about ACH. For Hospitals Air Changes can be the driving force for various rooms, but that is beyond the scope of this video.
And why would you expect all of that in a video that is literally titled "how to calculate air changes per hour"
The video provided exactly what it was titled
Hi. I have a question. I am completing a ventilation air schedule for floor plans. I have figured out the required OA CFM but it also requires that I calculate the actual OA CFM. Is there a formula to help do that? Thanks.
It depends on which code is required in your area. ASHRAE 62.1 defines the standard for calculating the ventilation (OSA) requirements for various building space types. Depending on the type of room, there will be a requirement for so many CFM per person, and older standards include a certain amount of CFM based on the floor area. The calculation is based on Quantity of People (CFM/Person) and some codes require additional CFM for the off gassing of furniture and interior finishes (CFM/Ft2) Hope that helps.
This calculation is applicable for the confined space such as vessel, tanks ?
Its good for any enclosure as long as you can calculate the volume.