HVAC-Talk: Heating, Air & Refrigeration Discussion banner
Cancel
Create thread New Forums

Digital Manometer

Jump to Latest
41 - 60 of 62 Posts
#41 ·
thanks!

I love that video, especially the part about the hook!!!!!!!!!!!!!!!!!

I just got done with a six million dollar job down in ft leonard wood mo.

we put in 5 180 ton Intellipaks a few dozen small splits . five boilers and 450 vav's and a couple hundred fan powered boxes.

I did start up on all of them, did the TAB and the commissioning.

On the dx stuff this is what I did.

First started at the supply fan on the Ipak, used a shortridge/pitot tube to determine that the IPAK was delivering the CFM as per the TAB specs from the engineer. so we are straight, it is exactly 400 cfm per ton.

then I went to every single fan powered box and vav and set their minimum and maximum flows on the BAS. I set the outside air and heat recovery wheel to design specs also using a shortridge/pitot tube.

When that is all done I plotted it all on a psych chart to determine sensible btu and latent btu.

It is for the US ARMY corp of engineering so it all had to be within ten percent.

The only time I really needed the fan curve was on the small 5 ton Trane AHU would not develope 2ooo cfm???

I went on line and downloaded the fancurve, It told me the AHU should develope 2040 cfm and it was not.
I noticed the static on the return was too high and found the outside air damper actuator was broken and not bringing in the 10% outside air or additional 240 cfm?
I fixed the damper and it was good!

So I only needed the fan curve to validate that I had the correct fan motor, voltage etc.

That is why I was curious why you needed the fan curve?

On the hydronics I had to have all the pump curves, but that is completely different.:playing:





nchvac said:
Ok, first of all, the digi cool video is hilarious. Love the part about hanging the gauges and the simple subtraction on the subcooling.

You can take the static pressure with the manometer and the 303's and use it to find your cfm on the fan curve chart. To get out the ductolator you have to figure the Friction Rate (FR) per the manual D calculation. Personally, I like the BTU method, but find no way to know the true efficency of the equipment when dealing with oil and gas.
Are you using a pitot tube and a Testo 510? I hear this is the better way, but there is still a calculation involved to my understanding.

As far as what do I do with the numbers? Hope like heck they come in because my customers are too cheap to modify the duct work.
Click to expand...
 
Save
Like Like
#42 ·
sensible heat 400 cfm x 1.08 x delta 20
400 x 1.08= 432 x 20 = 8640 btus

The latent heat (3360 btu/hr) is absorbed at the coil by condensing moisture from the air.


8640 + 3360 = 12000 btu's one ton


You should use the equation Q = 4.5 x cfm x Delta h to get total heat




400 x 4.5 x 1.867 = 3360
 
Save
Like Like
Discussion starter · #43 ·
What I am really needing is the simplest way to verify cfm. I was thinking it would be the pitot tube and a 510, but it sounds like some folks here prefer to use the static and the fan curve. My problem with the fan curve is what you pointed out, they are hard to locate.
So lets say I buy a Testo 510 and a Pitot Tube that is something like 18 or 24 inches long.
What is the process for using this? I think you set it on FPM. How many holes do you have to drill to take the measurments, how far in the duct do you have to insert the tube, and what are the calcs? Seems like there is an area calc. The text books don't talk a whole lot about this process.
to me, the pitot tube sounds like the most accurate for verifing actual airflow without taking into account so many variables that are somewhat theoretical.
 
Save
Like Like
#44 ·
nchvac said:
What is the process for using this? I think you set it on FPM. How many holes do you have to drill to take the measurments, how far in the duct do you have to insert the tube, and what are the calcs? Seems like there is an area calc.
Click to expand...
Go back and look at the attachment in my post #29. It states that for a 2% accuracy you need to take readings in all the locations shown for the round and rectangular ducts.

For a 5% accuracy, take one reading in the center of the duct and multiply by a factor of .9.


CFM = FPM x Area of Duct.

FPM = √velocity pressure x 4004.5 (√ = square root)
 
Save
Like Like
#45 ·
cheater!1

LOL!!!!!!!!!!



rundawg said:
Go back and look at the attachment in my post #29. It states that for a 2% accuracy you need to take readings in all the locations shown for the round and rectangular ducts.

For a 5% accuracy, take one reading in the center of the duct and multiply by a factor of .9.


CFM = FPM x Area of Duct.

FPM = √velocity pressure x 4004.5 (√ = square root)
Click to expand...
 
Save
Like Like
#46 ·
I gotcha!!!!!!!!!!!!!!!!!!!

you do not need an expensive tool like that!!

A simple magnahelic or any manometer will do!!


I for one just use a magnahelic or an inclined manometer

anyhow??

have you ever seen a small book by carrier called properties of air???????

I think this little 30 or 40 page pamphlet would help you a lot!

try to find it on ebay or on the carrier web site, it will help you alot!

Frank










nchvac said:
What I am really needing is the simplest way to verify cfm. I was thinking it would be the pitot tube and a 510, but it sounds like some folks here prefer to use the static and the fan curve. My problem with the fan curve is what you pointed out, they are hard to locate.
So lets say I buy a Testo 510 and a Pitot Tube that is something like 18 or 24 inches long.
What is the process for using this? I think you set it on FPM. How many holes do you have to drill to take the measurments, how far in the duct do you have to insert the tube, and what are the calcs? Seems like there is an area calc. The text books don't talk a whole lot about this process.
to me, the pitot tube sounds like the most accurate for verifing actual airflow without taking into account so many variables that are somewhat theoretical.
Click to expand...
 
Save
Like Like
Discussion starter · #49 ·
Save
Like Like
Discussion starter · #50 ·
rundawg said:
Go back and look at the attachment in my post #29. It states that for a 2% accuracy you need to take readings in all the locations shown for the round and rectangular ducts.

For a 5% accuracy, take one reading in the center of the duct and multiply by a factor of .9.


CFM = FPM x Area of Duct.

FPM = √velocity pressure x 4004.5 (√ = square root)
Click to expand...
What is the accuracy of the static pressure and fan curve method?
 
Save
Like Like
Discussion starter · #51 ·
What the heck happened to Air Mechanical. I just saw your protest sign, went to my dear friends home page and he is banned. Why do they ban the guys that know what the heck they are talking about. There won't be any need to come here just to talk to a bunch of Rookies. Are no opinions allowed?
 
Save
Like Like
#52 ·
I know!

they ban all the smart guys and just leave us dumb guys here to figure it all out ourselves!:playing:









nchvac said:
What the heck happened to Air Mechanical. I just saw your protest sign, went to my dear friends home page and he is banned. Why do they ban the guys that know what the heck they are talking about. There won't be any need to come here just to talk to a bunch of Rookies. Are no opinions allowed?
Click to expand...
 
Save
Like Like
Discussion starter · #53 ·
Maybe a little extreme on the comment, but he isn't the first old timer to be banned.
Anyone know what happened?
He is a pretty good refrigeration cycle guy.
 
Save
Like Like
Discussion starter · #54 ·
Save
Like Like
#55 ·
nchvac said:
What is the accuracy of the static pressure and fan curve method?
Click to expand...
Excellent question. But that answer is above my pay grade.

I have never seen any notes on the bottom of the blower performance tables stating the accuracy of the charts.

I'm not even sure the manufacturers could answer that question, but it might be worth a call to one or two of them.

Post the results if you find out something.
 
Save
Like Like
#56 ·
yes!
it is Carrier air properties and measurements!

I guess I should have already asked you if you had the book already???





nchvac said:
Air Properties and Measurement

They want you to have a minimum of $25 order. They are listing it as
Air Properties and Measurement. What does the cover say? Is it something like Carrier- Air Properties and Measurement. In other words, what do I look for it on ebay as?
Click to expand...
 
Save
Like Like
#57 ·
rundawg said:
Excellent question. But that answer is above my pay grade.

I have never seen any notes on the bottom of the blower performance tables stating the accuracy of the charts.

I'm not even sure the manufacturers could answer that question, but it might be worth a call to one or two of them.

Post the results if you find out something.
Click to expand...
I'm sure the charts are very accurate, it's the field measurements you need to watch. You need to be careful with existing equipment. Things like a dirty blower wheel or secondary heat exchanger will really mess with your accuracy.
 
#58 ·
hey Des!

Is it snowing up there??????




DesMech said:
I'm sure the charts are very accurate, it's the field measurements you need to watch. You need to be careful with existing equipment. Things like a dirty blower wheel or secondary heat exchanger will really mess with your accuracy.
Click to expand...
 
Save
Like Like
Discussion starter · #60 ·
supertek65 said:
yes!
it is Carrier air properties and measurements!

I guess I should have already asked you if you had the book already???
Click to expand...
Are you saying yes, they have it at Totaline?
 
Save
Like Like
41 - 60 of 62 Posts
You have insufficient privileges to reply here.
About this Discussion
61 Replies
15 Participants
Last post:
supertek65
HVAC-Talk: Heating, Air & Refrigeration Discussion
posts
5M
members
275K
Since
2000
The #1 HVACR Community
Full Forum Listing
Explore Our Forums
AOP Residential HVAC/Refrigeration(Beenthere Zone) General Discussion Tech to Tech Chat - Residential Controls Refrigeration & Ice Making