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Static Pressure befor filter or after

7K views 33 replies 5 participants last post by  beenthere 
#1 ·
I have a Trane XV95 100k btu furnace and a XL15i 4 ton AC condenser.

My question is about static pressure. I've heard that External static pressure should be obtained by taking readings before the blower and after the furnace but before the coil. What I am uncertain about is if the reading is taken before or after the filter?
Anyone know?
Key1
 
#5 ·
if thats a vari speed motor than it adjusts for static by itself but id take readings before and after removeing the filter cause if your using electrostatic or pleated there very restrictional
The system came with an electrostatic filter but I have replaced it with a 5 inch media filter.

Key1
 
#9 ·
That's fine for the filter. Take reading after filter and before the a/c coil....altkey
Thats what I thought but I recently noticed a footnote in my service and facts document that came with my furnace and it indicates the static presure and airflow data is "With filter"
I also saw another right up (not sure if I can post links on this forum as this is my first day). The other write-up indicates
esp is taken before the filter and before the coil if a filter is shipped with the unit.
Key1
 
#11 ·
Key.

Look for another foot note, that will tell you what the PD of the factory air filter is.
Also, keep in mind that this is what is to be done during installation, and the air filter is presumed to be brand new and clean.

If they list the factory filter as a .05"PD, and tell you to read upstream of the factory filter.
Then you measure before your media filter, and subtract .05" from that reading.

You have/are getting a better education on ESP and air filters then many in the trade.


Did you figure out the .2" for heat only, and .5" for cooling, yet.
 
#12 ·
Been,
You just gave this site a whole lot of credibility in my mind (as I just joined yesterday and did not know what to expect).
Good to be able to chat without the restriction that is on that other site.

To answer what I think your question is.... my nameplate value indicates "0.5 max external static pressure for heating". ....no indication for cooling. although when I wrote to Trane I was told "0.8 is fine".
Key1
 
#14 ·
I'm still at the other site.

I was sorry to see that your post there got closed.
Guess someone reported it as too technical. :(

Keep in mind. Trane can only give you certain answers.
Contractors are their "customers". And they aren't inclined to give out info that may reflect bad for 90% of their customers.

.8" is ok for all VS blowers that I know of.
But, at .8", your using close to the same amout of electric as a PSC motor.
Exceed 1", and your using more. And also reducing the life span of the motor/module.
 
#15 ·
I'm still at the other site.

I was sorry to see that your post there got closed.
Guess someone reported it as too technical. :(
.
That's why I'm here....Actually the moderator indicated he was moving it to the "Pro" section :) which is good...... but I don't have access:( which is bad...
 
#17 ·
Take a look at this link on static pressure, specifically the sentence under the static pressure tip. Since my unit was shipped with the filter , it suggests to include it in the measurement similarly to my service and facts document that indicates static pressure numbers are with filter.

I checked the footnotes and there is no other mention of the filter other than the title phrase that states "Airflow and watts versus external static pressure with filter"

http://www.bacharach-training.com/Tips/esp.htm

Key1
 
#19 ·
Different brands have foot notes weather to include the air filter or not.
Not all brands include the filter.
Some just give you a PD to allow for the air filter, so you know what to allow if you want to use a media filter.

If in your service facts, it says to include the factory filter when measuring.
You should pull your media filter.
Then measure your static with the factory filter. And also measure its PD.
From there you can put your media back in, and calc your CFM from that info.

I don't think I have any service facts in PDF. So I can't read how Trane is wording it.
 
#20 ·
I ran the factory and the media and a bunch of other filters to compare pressure drops across different filters. (I can post all of the data if anyone is interested)....

At my current air flow setting both the factory and the media have a PD of 0.1.......at the 100% air flow setting both had a PD 0f 0.14.

I had been measuring my static as -0.28 for neg before the blower but after the filter and 0.44 for positive after the furnace right before the coil for a total of 0.72 (in the "fan only" seting of 80% airflow). Are you suggesting that at 80% airflow I get to subtract the 0.1 out of the .28 so my total is 0.62? Since my Service facts data states "airflow and watts versus external static pressure with filter" :thumbup:

Key1
 
#21 ·
No, you don't get to subtract it.

If you were using a filter that had a .4 PD. Then you would subtract the .1". When you designed the duct work.

I think your SF sheets are trying to show the cost increase of higher static.
Not what is and isn't accounted for in there blower CFM at static pressures.

Not sure I'm saying it right.
 
#27 ·
wow, thanks for the handy PDF version of the service facts sheet! Very useful!
Your welcome....however it is not that useful. Each furnace model from each manufacturer has it's own set of data. This data is only applicable to that one model number listed at the top. It is essentially worthless for all other manufacturers as well as all other model numbers within this manufacturer. Each time a new 90% or higher condensing furnace is sold, the installer is suppose to leave the service facts data (which is in the installation manual) with the owner. So all owners should have the correct data for their furnace....in case a tech needs to work on it he will have a handy and accurate reference.

Key1
 
#33 ·
For completeness I decided to run and post the corresponding 2nd stage data.

Recall I have a Trane XV95 2-stage variable speed 100k btu natural gas furnace. All the data was generated in the heat mode on the medium setting.

The data from 1st stage:

External static pressure: 0.69
Wattage draw: 365 watts
Temperature Rise: 46F
Corresponding airflow from table: ~1180 CFM.

The data from 2nd stage:

ESP: 1.04
Wattage draw: 660 watts
Temperature Rise: 55F
Airflow?? (Table does not go above 0.9 ESP.)

Key1
 
#34 ·
Fans laws would say at 1.04" you should be at about 1450 CFM.

There is some inaccuracy, due to some fittings become more turbulant at higher CFM.
 
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