Calculating Cooling Loads and Room CFM
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- Опубликовано: 11 ноя 2017
- How to Calculate Cooling Loads and Figure Room CFM for commercial buildings.
What are the basic components that make up a Cooling Load?
How do you calculate the CFM for a room?
How many tons of cooling are required?
Visit the www.VRFWizard.com for additional information related to commercial & Residential HVAC & VRF/VRV Systems.
#coolingloads #engineering #hvac
Thank you for sharing the right heat loads calculations
excellent tutorial! is helping me understand better how to calculate heat loads! thanks
thanks for this wonderful lecture.. hope to have more sample calculations like this....
Thank u so much really helpfull for me I like it good work thank u once again please give more information about HVAC.
thanks .. very simple & useful
Thanks for this video and its really helpful to our family business which is related to technical (aircon services) we are an authorized dealer installer and supplier of any acu brand here in the Philippines..
THIS IS ADDITIONAL KNOWLEDGE.. thanks for sharing
Robert, where are you located in the Philippines? We were there in January 2019 in Manila and Coron. Next time we visit the Philippines, we would love to stop by and see your facility.
Thanks sir for the very needed information about.
Its a great pleasure to understand excellent experience most relevant to HVAC people.
You can also visit our other company which provides free training for the HVAC, Electrical & Plumbing Trades at www.mepacademy.com
That is the info I needed! THANKS
That was really cool explanation. Made it very understandable.
Glad you liked it. Please see our other channel for more great HVAC, Electrical and Plumbing Training Videos at MEPAcademy
You are doing a great job, keep it up
Very helpful info thank you. This is helpful for basic sizing of cooling coils.
You're Welcome. Thanks for watching.
Thank you very much greet job
Very good for teaching & learning purpose. Tqvm
Excellent.informative for fresh graduates.
Much needed fundamentals
Thanks very much for wonderful & simplified explanation. i would like to have complete design for VRF system.
Excellent and vrry useful video. Those others saying just multiple room dimensions and multiply by a "factor", should clearly qualify that as only a very rough estimation for sizing a room window AC!
Thanks.
Good job! thank you for the video
Thank you for the Amazing information. A whole career in just 16 Min. Could you please attach the SCL Chart from ASHRAE and an example of how to use it?
Very helpful. Thank you.
You're Welcome
Good information
Hello, I've been finding your video on calculating cooling loads extremely informative. I have some specific queries about the Solar Cooling Load (SCL) component of the calculation.
I understand that SCL is influenced by factors such as the orientation of the glass, the month, and the time of day, and it's a dimensionless ratio typically ranging from 0 to 1. However, in your equation, you've utilized a value of 250 for the SCL.
Could you please explain how this number was derived and why it's used instead of a value between 0 and 1? Is this value a constant, or does it change based on certain variables? If it does vary, how would I go about calculating or finding the appropriate value for my own home's specific conditions?
Your clarification on these matters would be greatly appreciated. Thank you for your time and assistance in advance!
Thanks very much for your simplified explanation!
So do I care about ventilation and to neglect the #latent heat as its done by other factors in the system and does this run for most regions if they are "modern designed buildings" as you have said ? "knowing that iam in the middle east"
also please tell me how to contact you for more information later
Sincerely thanks back to you =)
The latent heat from your ventilation will be handled by your cooling coil at the equipment. Your cooling coil will be sized to handle the outside air brought into the building for ventilation/fresh air requirements and any infiltration that is considered. This is where the moisture in the air that reaches the dew point temperature of the cooling coil will condense into liquid and become part of the condensation. I hope I have answered your question. Please feel free to contact us through our website at www.vrfwizard.com
Very thorough and clear explanation. Thank you for your effort.
Hello, thanks for the video, great explanation. Could you explain how to size the coil in order to deal with latent heat and to keep the desired tempetature??
Check out ou other video where we cover this topic. If you still have a question, please let us know. ruclips.net/video/0G0RkWHY1Jg/видео.html
Hi, thank you vey much for this simple explanation :) . May you please explain more about the room area isn't that become a contributor too? and how to include that in the calculation?
The area of the room becomes a factor only because it increases the lighting and plug loads and it may increase the occupant load (More People). The larger the Interior rooms are the greater is the load from internal sources of heat (People, Lights, Plug Loads). If the larger space includes more exterior wall area, then you have an increase in solar and transmission load through the walls and windows. Hope this helps
Thank you for your video
I have one quetion.
Can we use these formula in metric system or we have to convert it
Sorry, but you will have to convert these formulas to metric
Very interesting discussion. Does this also work for heating? The numbers seem like they would be considerably higher if you use a delta-T in the winter time for instance NYC winter design temp is around 17 degrees F. If we want to make the inside temp 70 degrees F are we supposed to use 53 as the temp difference in the calculations?
Yes, the temperature difference is also used in the heating load calculations for conductance through exterior walls, windows and the roof, and the 1st floor if you have an occupied space over an unheated garage or similar space. That's why insulation is really important along with a properly sealed building envelope.
Thank you
thank you!
Welcome!
How are loads calculated if the room is centrally located in the building with no windows? Do you still do the solar load for the building envelope?
Thanks
Saidur Rahman
Great .thanks 👍
You are welcome!
Good teaching
Thank you
helpful
Please subscribe my RUclips Channel
thanks
Good job bro
Informative
thank u so much so so much
Your Welcome
Nice
excellent
Thank you
So would the CL be equivalent to thermal inertia?...
Nice..
Usefull information , can you tell me how we calculate the 0F water raise temperature 215 F , how many BTu required
Are you asking how many BTU's it takes to raise water from 0 degrees to 215 F? For water, which at atmospheric conditions starts from 32 degrees until 212 degrees F, it depends on the pounds of water you have, so that for each pound of water it takes 1 BTU to raise the 1 Pound 1 degree F. After the water reaches 212 degrees it then enters the Latent Heat of Vaporization stage where any additional heat causes the water to change into vapor. Water from 32 degrees to 212 degrees is all sensible heat as it involves only a change in temperature, after that it is all latent heat which involves a change in state from water to vapor at atmospheric conditions.
Can we use this practically during designing cfu and ahu or this is only basics
These are the basic steps for calculating the room load and room CFM. When sizing the Air Handler, you will need to consider the additional load from Ventilation Air (Fresh Air brought into the building per code), including infiltration (Thermal load that leaks into the building). Here is a link to a 61 page document on "Heating & Cooling Loads" that might help.
www.cedengineering.com/userfiles/Cooling%20Load%20Calculations%20and%20Principles.pdf
thank you sir for sharing that knowledgeble page with us
Dear Sir,
Is this calculation including the cooling load that required to cool the space? Please kindlly advise. Thank you!
Yes, Calculating the CFM for the space provides for cooling the space. Latent heat (Moisture) will be taken care of at the cooling coil.
Noted with thanks!
I always thought that calculation the cooling demand for a space is considered as the total cooling require to cool the space in sqt +sensible heat +radiation heat
+latent heat. Learn a lot from your kindly sharing tutorial. Thank you!
Good
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What are the book recommendations that you often use to learn VRF
ASHRAE is the industry leader and they have a chapter in their handbook on VRF that provides a good explanation.
Does AREA OF wall include the ceiling/roof if it’s an outside wall?
Yes, there would also be a heat gain calculation for the roof of a single story building and for the top floor in a multi-story building. The example given was just to show the main factors contributing to the calculation of room CFM.
Fools 4 Christ can I get ur contact or mail
admin@vrfwizard.com You can visit our website at www.vrfwizard.com for more information
How would you find the Rvalue of the insulation in an exterior wall if you dont have a set of plans for an existing home?
One option would be to make an exploratory hole in the wall to discover what type if any insulation was used. Make a hole that is hidden from view.
@@VRFWizard o okay that makes sense. Thank you
So by using the cfm formula for 12,000 btu/h i get 555 cfm. I was always told you need 400 cfm per ton. So if you needed a 1 ton system hypothetically speaking would you be able to put out 555 cfm by providing large enough duct work?
400 CFM per ton is just a rule of thumb. Actual CFM should be calculated based on actual conditions.
With the formula CFM = Q / 1.08 x Delta-T, if you keep Q constant at 1-Ton (12,000 btu/hr) then CFM and Delta-T work inversely, meaning when one goes up the other goes down.
By keeping 12,000 Btu/hr (1-Ton) as a constant value while using different Delta-T’s, higher Delta-T’s will require less CFM/Ton because the system has to do less work per CFM.
CFM = 12,000 (Q) / 1.08 x 20 = 555 CFM
CFM = 12,000 (Q) / 1.08 x 25 = 444 CFM
CFM = 12,000 (Q) / 1.08 x 30 = 370 CFM
CFM = 12,000 (Q) / 1.08 x 35 = 317 CFM
Hopefully this was helpful.
@@VRFWizard yes that does make sense. Thank you
VRF Wizard thanks . I recall this many years ago . But this is more for someone as an engineer is it not ? Not all people as installers and techs are processing this in to a work order .Their job is as noted , installation and technical repair .Though your material presentation is important more for sales and management ?
Kevin, we believe anyone in the HVAC business from dispatchers to technicians should understand the basics of their business, which includes how loads are calculated. It helps in the discussions with customers as many issues in commercial construction can be related to improper zoning, which is related to the heating and cooling loads, such as block loads and zone loads. An informed technician can be more effective at his/her job by understanding the basics of cooling loads. Thanks.
What about second floors? How does that factor in? Would I just measure temperature gain through the floor?
If the floor above or below is air conditioned then there is no load. If you have a floor above or below that is not conditioned, like a garage, then you would do the same calculation with the heat gain and loss through the floor.
Thanx
Welcome
Is it the standard value that consumed by 1 watt equal to 3.14 Btu/watt
3.412 BTU/Watt
Do we need to consider the roof as well?
Yes of course. Anything that effects the heat gain or heat loss to the space, including interior spaces that are unconditioned and share a wall with the conditioned space.
why wall outside temperature and inside temperature different is (100-75) =25? how
The design outside air temperature for the example is 100 degrees, while the inside temperature is designed to maintain 75 degrees. Depending on where your building is located geographically there will be historical weather data that indicates the expected outside air temperature for that region of the world. Obviously the coastal areas will have a lower outdoor design temperature than the desert.
The inside temperature is based on local energy codes, ASHRAE standards or standard practice. For this example we choose 75 Degrees. The difference in the temperature between the outside and inside is what drives the heat transfer.
How do you get or where do you get the supply air design temp? Thank you,
The Supply Air Temperature is based on the type of Equipment your using, for instance a Packaged DX Unit might deliver 55 (F) Degrees Supply Air, while a Chilled Water System might deliver 42 (F) Degree chilled water to an Air Handler Coil where the Supply Air Temperature would be the results of how much Outside Air was mixed with Return Air, resulting in a Mixed air temperature passing over the cooling coil. The supply air temperature is always going to be a function of the mixed air temperature and the temperature of the heat transfer medium (Refrigerant, CHW, HHW, etc) The room temperature set point is determined by the OPR (Owners Project Requirements) if there are any, or industry standards such as ASHRAE. Hope I answered your question.
@@VRFWizard thank you for answering, i have a follow up question, what if you are designing the room, and you really dont know the supply air temperature delivered from the coil? How will you get that value? Or is there a table of it from ASHRAE? Or you can assume for the value? Lets just say we need to maintain the design temperature to 75°F at 50%RH. Thank you for accomodating my quiries.
@@keithwo1 Maybe if you think of the process in order. The first thing you would do is run a Heating and Cooling Load. This would tell you how many BTU/Hr the room needs to maintain your conditions of 75 F at 50%RH. Then you would search AC manufacturers Performance Submittals for a unit that would give you the values you need. At that point you really don't need to think about supply air temperatures as long as the AC unit meets your BTU/Hr requirements. Hope that helps.
@@VRFWizard thank you for this info's i really appreciate it,
Why don't you include latent loads in airflow calculations in a room? Is it because the air is exhausted or returned?
Latent loads are taken care of at the cooling coil.
@@VRFWizard
The video is great.
So the airflow you're calculating is that recirculated by a VRF unit... and the cooling coil you refer to, presumably in an AHU supplying the imaginary office, would be sized only for latent cooling load (the AHU coil won't provide any sensible cooling)? Is that right?
I've had a look at your site, good range of tutorials. Thanks
@@vixenviolet Yes, Latent heat is taken care of by the cooling coil, while the calculation for the room CFM includes the sensible load. The example used was for a typical central station air handler. Either way the moisture is taken care of by the cooling coil and not with the CFM delivered to the room. Moisture comes mostly from the ventilation requirement for outside air, but can also come from infiltration or process loads.
How about the size of the room? Is it can affect the design?
Yes, the size of the room will definitely affect the quantity of CFM required; If you just increase the interior portion of the room you will increase the cooling load due to more lighting and plug load wattage, and more people. If you increase the size of the exterior wall then you would also have an increase due to the solar load and conductance.
For example of 300 cubic feet room, how many btu?
Thanks a lot for your reply.
@@wendellblanco3250 to determine the Total BTU of an exterior room you would need to know all about the location of that room in the building and its orientation and location in the world, including the quantity and U-Values of the construction components of the wall and windows. Then you need to know how many people, how much lighting and plug loads are in the room. A 300 Cubic Foot room is a small space and if it's an interior space the calculation is much easier as their is no exterior elements to influence the cooling load.
@@VRFWizard Thank you so much for your clear answer.
God bless 🙏.
Sir how to get Delta temperature please explain me
The temperature difference is between your design indoor temperature and the Outdoor Design Temperature as indicated by ASHRAE or some other weather data source.
Wouldn't it be better to propose a lower supply air temperature (50F), so in this way, with the same cooling load and larger delta T, airflow CFM would be lower therefore smaller MUA or AHU footprint?
Great question. The answer is not as simple. It’s best to use Energy Modeling software to explore the options. There are many factors that go into that decisions including the local climate where the building will be installed and the utility rate structure. Lower temperature Supply Air can reduce economizer usage in some milder climates, such as California. The thought to reduce fan energy is a good one but at what cost to drive the supply air temperature down? Now, if you couple the lower supply air temperature with some form of Thermal Storage system then the energy profile looks much better and might make more sense. This will also allow you to shift peak electrical demand to a better utility rate structure. It is best to model your options as there is no straight answer that covers all situations and all geographical locations.
I live in the land of leaky houses where air leakage is a MAJOR source of heat loss in winter. Do you have any actual evidence that the air infiltration is a small sum of the load in cooling mode?
We mostly handle large commercial properties. For an older home, infiltration or exfiltartion could be much greater, depending on the quality of construction, window and door types, etc.
Like
Btw what is the unit of temp.?
F for Fahrenheit
niec
Clear content,Grate Job. Shalom.✍🏻🇮🇱
Thank you
HI this SOHAIL ALI I M HVAC TECH pleaser share more information about HVAC how to the calculation to unit tons to area thank u so much for help.
What is BTU?
BTU stands for British Thermal Unit. It is a measure of heat. It is defined as the amount of heat it takes to raise the temperature of 1 pound of water 1 degree Fahrenheit
14/2/2020
What about the ceiling load 🤔 sensible heat is a lot from the roof.
Yes of course the roof is included. Anywhere there is an exposure to the outside conditions would need to be considered. This would include floors above an unconditioned space. Thanks
You're correct. Any area including the roof which is exposed to the outside conditions will be included in the calculations. The example was of a floor in a high-rise between other conditioned floors. You would also include the heat gain from any unconditioned space adjacent to your conditioned space.
I thought that the heat been produced by people is considered a latent heat, not a sensible heat.
I am confused now
People produce both Latent (Moisture) and Sensible Heat. When calculating room CFM we take into consideration the Sensible Heat. The latent heat will be taken care of at the Cooling Coil.
What is EAT - LAT?
EAT = Entering Air Temperature, LAT = Leaving Air Temperature
Roof ? 🤔
Of course the load from the roof would be added if you are on the top floor.
You are putting 2 tons of a/c into a room that only needs 1/2 ton. The purpose of going through these calculations is to prevent oversizing. I rate this an epic fail.
The purpose of the exercise is to show what goes into a cooling load calculation. With the current focus of jurisdictions on building envelop energy performance, the cooling load calculation will be dictated by the "U" values of the building assemblies and the code required maximum allowable "U" values.
There are many rooms in the commercial and industrial industry that require much more CFM per Ft2 than the example in this video. So it is not unheard of to have this many tons in this small of a space. Most cooling load calculations are done with software, so this video is just to show the basics of what is considered in a cooling load.
Exactly. My house is 1200 square feet, and I have a 2.5 ton Goodman with efficient ductwork. Here in sticky hot SC, it works great.
This guy's calculations conclude I'm undersized by 4 tons!
Baloney.
is this based on the wall that has the biggest square footage
When they showed the outlet 1:24 , did anybody get bothered about the screw not being straight?
OCD is rough lol
How the hell do you calculate SCL though, that was a very poor explanation of it.
You are confusing energy with power. BTU is energy (heat). Watt is power (heat/time). So, at minute 3.00, 1 watt should equal 3.41 BTU PER HOUR.
I thought the playback speed was on 0.5
Everyone listens at different speeds. The good thing is that the user can always adjust the speed to fit their own preference.
@@VRFWizard thanks for the video mate I am just being silly
get rid of the windows!
No windows, I think they call those prisons. I'm sure you're joking, but your right windows are a main factor in heat gain, but the window manufactures have gotten better at creating high visibility, low "U" factor windows.