Comments welcome

[honglo]

Ok guys, this is my last attempt at getting you to speak up about the realities of static pressures. I've read all 25 (wow!) posts on the subject. There a lot of smart cookies out there who can explain every aspect of static pressure and how to measure it but I have yet to see a post on how to use this knowledge and data in reality!!!!!!

Below is a mock system design. It attempts to properly load the blower motor for 1: proper CFM at the register and
2: proper static pressurers for maximum unit life. Every attempt was made at keeping the suggested mfg recommendations at proper static pressurers. Example: mfg suggest filter static pressure at .2 and coil mfg suggest .3 static pressure across the coil and it is suggested by the mfg to not exceed the maxim blower TSP of .7

(NOTE: I am guessing at these manufacturer specs. Don't expect to find these readings in ANY unit. My goal is to establish a proper design METHOD.)

http://groups.msn.com/_Secure/0ZwAAAEYdPvDHFKv3I75CTLOjEn4MVk1kbmvJufv1YqQNR*7gm yWQzWbfx1Q4LCMA5FRw2ofzg4d9tfDESwCCdsqeXERod98mbdW 25g7!NwJzK5fsNWNNVr6ZmjyZDRKBUwpteP0ilGWk497eQqZbu A/design1.JPG?dc=4675489644481626847

After re-designing the system I come up with this:

http://groups.msn.com/_Secure/0ZwARA0cdnfDHFKv3I75CTERyba3iyJSSY8TNjg3O0K9MZK0it vDpbIVQKk2jF4NPlve9wYJABwqf7J!7oMlnpo0RYCDKRqeZPB8 ziJl6YCQ3xvgxUzNcr*fXbcSdASxzrUG8k1yLBEtsQ7U*Xu97l w/design2.JPG?dc=4675489644484760582

Well, HOW DID I DO????????????

Can I now move on to hVac102? I'm too old to go back to school so how else should I learn? I've only been doing this since 1973 and only now question things I've always taken under faith. Go ahead and try to make an A$@ of me if you can.


P.S.
Please excuse my rather rough attitude here. I do not mean to embarrass or scold anyone. It is just that I have had quite some difficulty picking your brains on this subject. If you have no knowledge on it, I appreciate your silence. If you have much experience with it and have a good track record of success, by all means (CUT ME TO SHREDS!)
Fact is, (I believe) most of us realize we should know this static pressure stuff like the back of our hands and we tend to get defensive when someone mentions it to us in a question and haven't the foggiest how to respond. Hey, what's wrong with a little math now and then? Don't worry about the (HO) watching. It freezone is Greek to them anyway.

[Green Mountain]

[QUOTE][i]Originally posted by honglo
I'm too old to go back to school so how else should I learn? I've only been doing this since 1973 and only now question things I've always taken under faith. Go ahead and try to make an A$@ of me if you can.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~

I've only been doing this since 1964. I'm not too old to go back to school. Sheeedit I just got my first college degree in 2001.

[hvac45]

I have been in this since 1972 and still learn everyday, in this field if you quit learning you slowly fade away.

[dash]

Originally posted by honglo
Ok guys, this is my last attempt at getting you to speak up about the realities of static pressures. I've read all 25 (wow!) posts on the subject. There a lot of smart cookies out there who can explain every aspect of static pressure and how to measure it but I have yet to see a post on how to use this knowledge and data in reality!!!!!!

Below is a mock system design. It attempts to properly load the blower motor for 1: proper CFM at the register and
2: proper static pressurers for maximum unit life. Every attempt was made at keeping the suggested mfg recommendations at proper static pressurers. Example: mfg suggest filter static pressure at .2 and coil mfg suggest .3 static pressure across the coil and it is suggested by the mfg to not exceed the maxim blower TSP of .7

(NOTE: I am guessing at these manufacturer specs. Don't expect to find these readings in ANY unit. My goal is to establish a proper design METHOD.)

http://groups.msn.com/_Secure/0ZwAAAEYdPvDHFKv3I75CTLOjEn4MVk1kbmvJufv1YqQNR*7gm yWQzWbfx1Q4LCMA5FRw2ofzg4d9tfDESwCCdsqeXERod98mbdW 25g7!NwJzK5fsNWNNVr6ZmjyZDRKBUwpteP0ilGWk497eQqZbu A/design1.JPG?dc=4675489644481626847

After re-designing the system I come up with this:

http://groups.msn.com/_Secure/0ZwARA0cdnfDHFKv3I75CTERyba3iyJSSY8TNjg3O0K9MZK0it vDpbIVQKk2jF4NPlve9wYJABwqf7J!7oMlnpo0RYCDKRqeZPB8 ziJl6YCQ3xvgxUzNcr*fXbcSdASxzrUG8k1yLBEtsQ7U*Xu97l w/design2.JPG?dc=4675489644484760582

Well, HOW DID I DO????????????

Can I now move on to hVac102? I'm too old to go back to school so how else should I learn? I've only been doing this since 1973 and only now question things I've always taken under faith. Go ahead and try to make an A$@ of me if you can.


P.S.
Please excuse my rather rough attitude here. I do not mean to embarrass or scold anyone. It is just that I have had quite some difficulty picking your brains on this subject. If you have no knowledge on it, I appreciate your silence. If you have much experience with it and have a good track record of success, by all means (CUT ME TO SHREDS!)
Fact is, (I believe) most of us realize we should know this static pressure stuff like the back of our hands and we tend to get defensive when someone mentions it to us in a question and haven't the foggiest how to respond. Hey, what's wrong with a little math now and then? Don't worry about the (HO) watching. It freezone is Greek to them anyway.



Not sure what your method is.

Looks like the design change was to select a coil with a lower pressure drop,which I doubt you would find.Plus some change in the plenum.


Why not get a copy of Man. D,instead ??

[honglo]

Your right about the manual D, dash, Only wouldn't it be nice to know how this information is calculated? The pictures show how a possible diagnosis might be made using static pressure as a diagnostic tool. Of course, a (coil cleaning) remedied the high stat pressure situation; (not replacing the coil with one of lower sp.)

I did notice a mistake in my first picture. The FSP=B-F not B+F. In previous posts I read on this forum it is said to ignore the -+ and always add but this is not so. Sometimes you add and somtimes you subtract. Take another look and see what I mean. It is this (confusion)of adding or subtracting (I think) that turns people off from using static pressure readings.

Note the reading designations: P,C,B,F, well, I made them up but they designate the position of the sp probe to take the readings. Also note the order of readings on an AIR HANDLER (not shown) the order is P,B,C,F and the -+ readings will be (somewhat) reversed. Having the position of (where) to take the readings are less confusing than simply calling for External static pressure and Total static pressures. (I think this is what confuses most people.)

I now have completed an Excel spreadsheet that uses these readings to (suggest) corrective actions when (off) readings are seen... ie, dirty filter, dirty coil, low supply duct and that the blower is turning too fast. It takes the confusion of when to add and when to subtract out of the equation because it does it automaticly. Only, I don't know how useful it will be in the field because a laptop is not (that) convienent to carry around. :)

Because of the mild summer we have experienced, I was hoping for a (tool) in which to diagnose air conditioning problems this WINTER! Trying to extend the summer a bit!
Isn't it pretty well understood that a sure fire condition of a dirty coil (for example) in the summer is low superheat, hi subcooling and low gauge pressures? How do you determine that on a Heat PM (preventative maintenance) call? With a temp rise test of course. But is the excessive temp rise due to a dirty coil or overfiring or poor duct work? Hummmmmmm. Sounds like a job for a System Static Pressure Analyzer. (that's what I named the spreadsheet :) )

I'm not sure but there might be enough diagnostic possibility using static pressure that it might warrant a new category on this forum. We have one called INDOOR AIR QUALITY. How about one called AIR FLOW?

I know for one, I'd like to know things like equivalent lengths of all the duct fittings,(and does the static pressure drop across that fitting act the same as it would through a single stretch of duct?), proper ratios of unit components like how much by percentage will each component be expected to utilize, ie, the coil should be expected to consume 20% of the fans energy, the filter should consume 10%, how much of the fans energy should be devoted to the actual ductwork and so on.

[honglo]

dash, Here is a photo of the spreadsheet (for gas/electric upflow units). It shows what components are suspect with (off) readings.

http://groups.msn.com/_Secure/0ZQDfAmMca5Qy5t4Ds!jScPK34p9BkyVncl6R40c4WKi8hFTje bkE3hINNAbnOzIiAjCIO95lnyc0KI6fREP3I518!1W4FQ8c**A R1icBrIU3uu2viX3!rbByNTw04sjFEE*TF8rcaYqrfBCiD5weN A/SSPA1.jpg?dc=4675489771084918679

Since the spreadsheet automatically calculates FSP,TSP,CSP and ESP, It should make diagnosing a problem a little easier. (theoretically :) )

[dash]

honglo,

Is the diagram a furnace ,with a coil on it?

[honglo]

Yes it is. It can also be an electric furnace with elements instead of a heat exchanger.
Of course the more (modern) air handlers have the coil at the intake of the unit and the readings will be reversed in some readings. The System Static Pressure Analyzer has a second page (not posted) in which to enter readings for those types of units.

[dash]

Originally posted by honglo
dash, Here is a photo of the spreadsheet (for gas/electric upflow units). It shows what components are suspect with (off) readings.

http://groups.msn.com/_Secure/0ZQDfAmMca5Qy5t4Ds!jScPK34p9BkyVncl6R40c4WKi8hFTje bkE3hINNAbnOzIiAjCIO95lnyc0KI6fREP3I518!1W4FQ8c**A R1icBrIU3uu2viX3!rbByNTw04sjFEE*TF8rcaYqrfBCiD5weN A/SSPA1.jpg?dc=4675489771084918679

Since the spreadsheet automatically calculates FSP,TSP,CSP and ESP, It should make diagnosing a problem a little easier. (theoretically :) )


ESP,for a furnace would be inlet and outlet of the funace,it appears you are using inlet of furnace,and above the oil,instead of below the coil.

[dash]

In your before and after example,why and how ,does the static at the supply plenum get reduced in the after version,or are these numbers you just made up?

[honglo]

dash, True! You see, I have (standardized) the readings of ESP to fit real life conditions. If you look on an electric furnace (non-heatpump) you will find in most cases 2 ESP readings. Without a coil the ESP is around .2, with a coil, it might give you a .3. What good are these readings if there is no (standard)? How units are (specked) in the lab usually has no bearing in reality once the unit is installed in a house!
I don't (demand) that I am right but that's what this post is for...... To (find out) how we can use these readings for diagnostic purposes.

[honglo]

dash, The numbers used in the picture examples are (calculated) results. Given a desired output from a register, we calculate the static pressure drops all the way back to the intake of the filter. In order to maintain (factory specs) of the filter, blower, and evaporator, we MUST see the static pressures shown.
Not explained was the fact that the original supply duct was a 19" duct. It was converted to a 21"(I think) in order to achieve a lower (.05)sp and still deliver 2000 cfm.

[dash]

Originally posted by honglo
dash, True! You see, I have (standardized) the readings of ESP to fit real life conditions. If you look on an electric furnace (non-heatpump) you will find in most cases 2 ESP readings. Without a coil the ESP is around .2, with a coil, it might give you a .3. What good are these readings if there is no (standard)? How units are (specked) in the lab usually has no bearing in reality once the unit is installed in a house!
I don't (demand) that I am right but that's what this post is for...... To (find out) how we can use these readings for diagnostic purposes.


There are standards:
The factory provides the ESP for the product,and where the test points are,if you don't follow the correct test points,you have no data to determine cfms.

The lab specs are ,very close to reality,there are minor differences ,but not enough to worry about ,and not a reason to reinvent the standards.

[dash]

Originally posted by honglo
dash, The numbers used in the picture examples are (calculated) results. Given a desired output from a register, we calculate the static pressure drops all the way back to the intake of the filter. In order to maintain (factory specs) of the filter, blower, and evaporator, we MUST see the static pressures shown.
Not explained was the fact that the original supply duct was a 19" duct. It was converted to a 21"(I think) in order to achieve a lower (.05)sp and still deliver 2000 cfm.



The change in supply duct size,accounts for the drop in plenum static,that would have otherwise increased.

Care to tell ,what other changes were made?

[honglo]

Good point dash, Only, are those specs available to us on every call? Probably not. This is why exact readings are not my goal here, rather, a ratio that (should be) somewhat consistant for any unit. (if there is one)

[honglo]

Originally posted by dash

Originally posted by honglo
dash, The numbers used in the picture examples are (calculated) results. Given a desired output from a register, we calculate the static pressure drops all the way back to the intake of the filter. In order to maintain (factory specs) of the filter, blower, and evaporator, we MUST see the static pressures shown.
Not explained was the fact that the original supply duct was a 19" duct. It was converted to a 21"(I think) in order to achieve a lower (.05)sp and still deliver 2000 cfm.



The change in supply duct size,accounts for the drop in plenum static,that would have otherwise increased.

Care to tell ,what other changes were made?


The only other change was made to the static pressure of the coil itself. Either cleaning or replacing was necessary to maintain the factory specs on the blower static pressure.

[dash]

Originally posted by honglo

Originally posted by dash

Originally posted by honglo
dash, The numbers used in the picture examples are (calculated) results. Given a desired output from a register, we calculate the static pressure drops all the way back to the intake of the filter. In order to maintain (factory specs) of the filter, blower, and evaporator, we MUST see the static pressures shown.
Not explained was the fact that the original supply duct was a 19" duct. It was converted to a 21"(I think) in order to achieve a lower (.05)sp and still deliver 2000 cfm.



The change in supply duct size,accounts for the drop in plenum static,that would have otherwise increased.

Care to tell ,what other changes were made?


The only other change was made to the static pressure of the coil itself. Either cleaning or replacing was necessary to maintain the factory specs on the blower static pressure.


Cleaning or replacing?You mean you don't know whick was done??

[dash]

Originally posted by honglo
Good point dash, Only, are those specs available to us on every call? Probably not. This is why exact readings are not my goal here, rather, a ratio that (should be) somewhat consistant for any unit. (if there is one)


They are not consistant,for unit to unit.A lot of data is available on the net,we have printed a lot for our techs to carry on the truck.

[honglo]

dash, Does it matter? As long as we change the static pressure of the coil, we have achieved our goal of keeping our components within factory specs. Remember, this is only a (mock) unit. My purpose here is not to teach you how it is done, rather, the other way around! :)

I find that when a customer (for example) asks me a question on how something works, I give an explanation of it and it seems that only when I do that, can I fully understand it myself. The customer won't know the truth, but as it comes out of my mouth, it will have a certain ring of truth or NOT to ME. That lets me know if my explanation was accurate or not. (not an infallable method of learning, I agree but it seems like I have to answer my own questions most of the time because there doesn't seem to be enough "know-it-alls" to help me. :) )

[honglo]

Originally posted by dash

Originally posted by honglo
Good point dash, Only, are those specs available to us on every call? Probably not. This is why exact readings are not my goal here, rather, a ratio that (should be) somewhat consistant for any unit. (if there is one)


They are not consistant,for unit to unit.A lot of data is available on the net,we have printed a lot for our techs to carry on the truck.

True the actual static pressures are NOT consistant. They seem to always be different. But I don't carry around all the wiring diagrams for units either. When I come across a wiring problem that some "hack" has "tampered" with, I don't try to figure out the mess he made, I simply rip it all out and start from scratch. I re-wire it according to my understanding of what should happen and when. The more technical the wiring (ie,.. boards) the less "hack tampering" I see, but I should still know the sequence of operation and how to identify a component out of sequence even without a wiring diagram. Don't you think?

Why should static pressures and how they (relate) to one another be any different?

[dash]

Originally posted by honglo
dash, Does it matter? As long as we change the static pressure of the coil, we have achieved our goal of keeping our components within factory specs. Remember, this is only a (mock) unit. My purpose here is not to teach you how it is done, rather, the other way around! :)

I find that when a customer (for example) asks me a question on how something works, I give an explanation of it and it seems that only when I do that, can I fully understand it myself. The customer won't know the truth, but as it comes out of my mouth, it will have a certain ring of truth or NOT to ME. That lets me know if my explanation was accurate or not. (not an infallable method of learning, I agree but it seems like I have to answer my own questions most of the time because there doesn't seem to be enough "know-it-alls" to help me. :) )


Does what matter??Not ure what you are refering to?

How can you say you have achieved the goal of factory specs.,if you say you don't have them?


I don't the ,"my purpose here...........",statement?

[honglo]

Originally posted by dash

Originally posted by honglo
dash, Does it matter? As long as we change the static pressure of the coil, we have achieved our goal of keeping our components within factory specs. Remember, this is only a (mock) unit. My purpose here is not to teach you how it is done, rather, the other way around! :)

I find that when a customer (for example) asks me a question on how something works, I give an explanation of it and it seems that only when I do that, can I fully understand it myself. The customer won't know the truth, but as it comes out of my mouth, it will have a certain ring of truth or NOT to ME. That lets me know if my explanation was accurate or not. (not an infallable method of learning, I agree but it seems like I have to answer my own questions most of the time because there doesn't seem to be enough "know-it-alls" to help me. :) )


Does what matter??Not ure what you are refering to?

How can you say you have achieved the goal of factory specs.,if you say you don't have them?


I don't the ,"my purpose here...........",statement?

dash, I apologize for any error on my thought processes here. (I got poor marks in englis lit for the same reasons :) )
Let me try this again. "Does what matter??Not ure what you are refering to?" . Well, the drawings are of a (mock) system. Not a real one. But if it were (real) could we go about analyzing it like the diagram shows?

Next you say, "How can you say you have achieved the goal of factory specs.,if you say you don't have them?"

Well, once again, this is a (mock) system and I gave the (mfg/specs) a value so as to conduct this model.

I hope that explains it better.

[dash]

Originally posted by honglo

Originally posted by dash

Originally posted by honglo
Good point dash, Only, are those specs available to us on every call? Probably not. This is why exact readings are not my goal here, rather, a ratio that (should be) somewhat consistant for any unit. (if there is one)


They are not consistant,for unit to unit.A lot of data is available on the net,we have printed a lot for our techs to carry on the truck.

True the actual static pressures are NOT consistant. They seem to always be different. But I don't carry around all the wiring diagrams for units either. When I come across a wiring problem that some "hack" has "tampered" with, I don't try to figure out the mess he made, I simply rip it all out and start from scratch. I re-wire it according to my understanding of what should happen and when. The more technical the wiring (ie,.. boards) the less "hack tampering" I see, but I should still know the sequence of operation and how to identify a component out of sequence even without a wiring diagram. Don't you think?

Why should static pressures and how they (relate) to one another be any different?


They are different in that,you need the specs.

If you test a coil,for static pressure rop,whta does it tell you,without knowing what it should be.

Coil PD is:

.25,.30,.35,.40,or.45

At what point do you say clean the coil??

True ESP is .55,what's the cfm,what should it be,what speed should the fan be set on?


With th specs,you'll know what to do.

[honglo]

dash, The reason my "honglo logo" Air conditioning is not so much an invention but an observation, means so much to me is because of the way I explain the Air Conditioning Theory. Someone (observed) a boiling pot of water and questioned everything that was going on. They then imagined all the processes that went on from the flame heating up the water, to it's final condensation back into rain. While refrigerant performs these change of states at different temperatures and pressures than water, never the less, the process or (method) and RESULT is the same.

In this little (air flow study) I am hoping for a better understanding of all the processes that need to be considered in the movement of air and it's ultimate goal of cooling/heating the conditioned space.

I really do appreciate your insight.

[honglo]

Originally posted by dash

Originally posted by honglo

Originally posted by dash

Originally posted by honglo
Good point dash, Only, are those specs available to us on every call? Probably not. This is why exact readings are not my goal here, rather, a ratio that (should be) somewhat consistant for any unit. (if there is one)


They are not consistant,for unit to unit.A lot of data is available on the net,we have printed a lot for our techs to carry on the truck.

True the actual static pressures are NOT consistant. They seem to always be different. But I don't carry around all the wiring diagrams for units either. When I come across a wiring problem that some "hack" has "tampered" with, I don't try to figure out the mess he made, I simply rip it all out and start from scratch. I re-wire it according to my understanding of what should happen and when. The more technical the wiring (ie,.. boards) the less "hack tampering" I see, but I should still know the sequence of operation and how to identify a component out of sequence even without a wiring diagram. Don't you think?

Why should static pressures and how they (relate) to one another be any different?


They are different in that,you need the specs.

If you test a coil,for static pressure rop,whta does it tell you,without knowing what it should be.

Coil PD is:

.25,.30,.35,.40,or.45

At what point do you say clean the coil??

True ESP is .55,what's the cfm,what should it be,what speed should the fan be set on?


With th specs,you'll know what to do.





Well, dash, I would say that the point in which cleaning the coil would be evident would be similar to asking the question "At which point do you consider suction pressure too low". To that, I'd say, "When the suction pressure allows the formation of ice on the coil and starts spread like a cancer clogging up all air flow through the coil". If you notice, I gave no refrence to the actual pressure at which this would occur rather a point in which it would happen!
Likewise, I would think minimum and maximum static pressure (standards) would point to not just a dirty coil but all other components that influence static pressure drops in the system. My point,,,,,, There must be a consistant ratio of events that must be kept in balance. This balance would not pertain to one, rather ALL systems.

There doesn't seem to be much advice on this. (at least, I haven't found it).

[honglo]

I read that last post and decided it didn't really explain your question as to when the coil is decidedly dirty. Well, neither will you find on the manufacturers spcs of a coil of say .3 that a reading of .35 indicates a dirty coil...... Or did I miss that info the last time I read the equipment specs? Again, it is not the actual specific static pressures that need to be taken into account but rather how those sp's relate to each other in the system. That still says to me, "There must be a constant relationship in ALL systems".

Anyway, are there any other mis-understood static pressure relationships shown in my diagrams that I have understood incorrectly? I have read in this forum (I couldn't give you the specific thread) Someone asked, "Isn't TSP AND BSP (blower static pressure) the same thing?" Well, I think it is..... Right?? Do you think it is possible to determine a problem with say an insufficient quantity of duct installed in the system using this data? Do you think a spreadsheet-like diagnostic tool could be used to come to these conclusions? If so, are there any variables I may have missed? Regardless how you come to a conclusion of a problem whether or not manufacturer specs were used, or, is manufacturer specs the only way to make a determination of system performance?

Remember, I don't know (with any certainty) what I'm talking about here. I have seen some of your posts on static pressure and know you have a good knowledge about it and I value your opinion and suggestions.

[dash]

You can have one brand,that can deliver the required cfm,at .6 and another that can only deliver the required cfm at point .4,the difference is to great,to use a "one size fits all" ,approach.

Don't know what more I can say.

[honglo]

Originally posted by dash
You can have one brand,that can deliver the required cfm,at .6 and another that can only deliver the required cfm at point .4,the difference is to great,to use a "one size fits all" ,approach.

Don't know what more I can say.

I totally agree with you on that dash. If you notice on my spreadsheet, there are entry blanks for entering the mfg info for coil, filter and blower. (That one will be hard to get even if you have the data sheets. They rarely show blower static pressures.) The blank for ESP is difficult to enter due to the type of installation but it also must be entered in order to do all the math and assumptions. In fact, the spreadsheet won't work without them. I never said you shouldn't use mfg/specs.

I have to admit though, I have NEVER considered a models static pressure capability for a bid proposal. Then again, I've never installed a unit in a mobile home either. Residential units are pretty much the same from house to house. There have been some that has been a problem and this little (study) hopefully has shed some light on them.

Thanks for your input,

[dash]

honglo,

I see by your profile ,that you are in Texas.

This site has had many posters that had ,really bad dcut system,I tought Texas ,was close to Florida,in undersized ducts.


Checking static before the install,a good idea:

If you had a brand X air handler,with .55 static capability,to replace,that the duct system was at .55,an delivering required cfms,and you replace it with a brand Y that can only produce .35 ESP,you'll be in trouble.


Customer will say,not my problem,the old one worked with that duct system,it's your problem to make the one you sold me work.

[dash]

Originally posted by honglo
Good point dash, Only, are those specs available to us on every call? Probably not. This is why exact readings are not my goal here, rather, a ratio that (should be) somewhat consistant for any unit. (if there is one)



Posts like the above,gave me the impression,you wanted a method that,would not need mfrs. specs.

Sorry, my bad.

[honglo]

dash, Now you're begining to see what my true purpose of this little (study) is. Yes, Texas is really bad about having (competitors if you call them that) install improperly sized duct systems. Like I said, until now, I have not really understood the importance of giving an existing duct system much thought (except when intentionally up-sizing the system) when I install a new (Unit). However, as you said, "replacing a .5 system with a .3 system", is a very big problem that can easily become
MY problem when I accept the job. I am somewhat careful though, in that I explain that in most cases, duct work WILL or (MAY) be necessary. The customer (seems) to understand that and it really hasn't been a liability to me (YET). Thus, this study in AIR FLOW!!!!

You never commented on it but do you think I'm on the right track with the "System Static Pressure Analyzer" spreadsheet? Do you see any corrections or additions to the data gathered that should be made in order to make and informed decision?

Is the (method) of comparisons between differing observed pressures sound? Should not the total equivalent length and its respective static pressure be ADDED to the DESIRED output static pressure to (calculate) an expected plenum pressure? It seems to me that this would almost (dictate) what type of equipment would be needed.

You seem to be the only one in this forum willing to share info on this. (seems a bit odd) I don't mean to burden you with ALL the answers but we do seem to be having a somewhat personal conversation about this whole topic.

Do you suppose you and I are the ONLY ones conserned about this problem? (Hummmmmmmm..... kind of sounds like it.)

Thanks again for your help!

[dash]

Originally posted by honglo
dash, Now you're begining to see what my true purpose of this little (study) is. Yes, Texas is really bad about having (competitors if you call them that) install improperly sized duct systems. Like I said, until now, I have not really understood the importance of giving an existing duct system much thought (except when intentionally up-sizing the system) when I install a new (Unit). However, as you said, "replacing a .5 system with a .3 system", is a very big problem that can easily become
MY problem when I accept the job. I am somewhat careful though, in that I explain that in most cases, duct work WILL or (MAY) be necessary. The customer (seems) to understand that and it really hasn't been a liability to me (YET). Thus, this study in AIR FLOW!!!!

Test the static of the existing system,with clean blower.Check the PD of the coil,to guestimate how dirty it is,and include that.

You never commented on it but do you think I'm on the right track with the "System Static Pressure Analyzer" spreadsheet? Do you see any corrections or additions to the data gathered that should be made in order to make and informed decision?

your are on the right track,but mfrs specs are needed.I don't think it will be helpful without them.

Is the (method) of comparisons between differing observed pressures sound? Should not the total equivalent length and its respective static pressure be ADDED to the DESIRED output static pressure to (calculate) an expected plenum pressure? It seems to me that this would almost (dictate) what type of equipment would be needed.

The TEL,is being "read" when testing the statc,just in In of WC,not EL

You seem to be the only one in this forum willing to share info on this. (seems a bit odd) I don't mean to burden you with ALL the answers but we do seem to be having a somewhat personal conversation about this whole topic.

Do you suppose you and I are the ONLY ones conserned about this problem? (Hummmmmmmm..... kind of sounds like it.)

That's becoming apparent.Hate to speculate on why.


Thanks again for your help!

[honglo]

dash, If upgrading or replacing an existing system, I do follow that the TEL reading can be taken for granted at the registers according to the sp found there. But, what about designing a new system (no existing duct) would you add the equivalent length (calculated) static pressure to the desired output? It does sound reasonable to me.... ?

This means I MUST have equivalent length values of the duct fittings I use. There seems not to be a standard EL for them and the manufacturer I normaly use (M&M) tells me that they don't have that info. (#$&$#@@.what to do???)

(dash, Scratch that last question,,, I see you answered it already on another thread.. Thanks..)

In fact it seems I've been going about system design all wrong. I have been calculating the load then setting a unit (what ever brand the customer chooses) then calculate with a ductulator (apparently incorrectly so) which duct to install into the room. It seems I need to first discover what the total equivalent static pressures will be THEN decide on a model/brand that will deliver THAT quantity of pressure to the plenum. Shame on me!!!!

I guess the only reason I haven't gotten into trouble is because of my (unwritten) personal law of never splitting a duct more than once. And NEVER have single duct runs longer than 25ft. (I sometimes see what looks like a family tree configuration with 8 to 10 generations installed by some of my competitors) It of course has been good that I use a .08 static pressure with a .06 return design. (ignorant luck you might say)

I also use huge amounts of common sense when replacing a system but that is NO EXCUSE for lack of proper installation methodology.

One thing very confusing is the ESP rating on a furnace/air handler.... Lets say the nameplate rating is .5 for a particular gas furnace. Now of course this rating is WITHOUT FILTER OR COIL IN PLACE! In the installation manual you will then find various cfm outputs ranging from 0.0 ESP all the way to 1.0 The .5 is in there right in the middle. Is that a (suggested) esp? NOOOOOoooooo! In fact, that is a TSP!!!!! Without a filter or evaporator, aren't we reading the Blower only static pressure??? Now, since there are other available (ESP) values from which to choose, does this mean that the blower will operate (safely) anywhere from 0.0 to 1.0??? I think not!!!! What happens to a blower if you remove it from the cabinet and put power to it sitting there on the floor?????? it pulls VERY HIGH current. So high I'll bet it wouldn't last very long. That is 0.0"wc!

Now look at the other extreme of 1.0 Are they saying that the blower will only produce a maximum of 1.0"wc or that it should not be subjected to pressurers higher than 1.0?
If I capped off the output of a blower what would it read??? I have a feeling it will ALSO NOT RUN LONG!!!

So,,.... Could you explain the meaning of those different static pressures (besides the obvious of different CFM's) ????

Thanks again, and as for the apparent (silence) from the rest of the guys,,,,,, I DID ask them not to comment if they had no knowledge on this subject. In fact, if this is true, they are indeed SMARTER than I am. After all, it's "honglo" that is showing his ignorance here. :)






[Edited by honglo on 09-20-2004 at 08:08 PM]

[midhvac]

Originally posted by honglo

One thing very confusing is the ESP rating on a furnace/air handler.... Lets say the nameplate rating is .5 for a particular gas furnace. Now of course this rating is WITHOUT FILTER OR COIL IN PLACE! In the installation manual you will then find various cfm outputs ranging from 0.0 ESP all the way to 1.0 The .5 is in there right in the middle. Is that a (suggested) esp? NOOOOOoooooo! In fact, that is a TSP!!!!! Without a filter or evaporator, aren't we reading the Blower only static pressure??? Now, since there are other available (ESP) values from which to choose, does this mean that the blower will operate (safely) anywhere from 0.0 to 1.0??? I think not!!!! What happens to a blower if you remove it from the cabinet and put power to it sitting there on the floor?????? it pulls VERY HIGH current. So high I'll bet it wouldn't last very long. That is 0.0"wc!

Now look at the other extreme of 1.0 Are they saying that the blower will only produce a maximum of 1.0"wc or that it should not be subjected to pressurers higher than 1.0?
If I capped off the output of a blower what would it read??? I have a feeling it will ALSO NOT RUN LONG!!!

So,,.... Could you explain the meaning of those different static pressures (besides the obvious of different CFM's) ????

Thanks again, and as for the apparent (silence) from the rest of the guys,,,,,, I DID ask them not to comment if they had no knowledge on this subject. In fact, if this is true, they are indeed SMARTER than I am. After all, it's "honglo" that is showing his ignorance here. :)


Yes.... I've been lurking in the shadows watching you squirm :D

Although I'm not totally sure what your question is about ESP and TSP, it's my understanding that the static rating you see in most furnaces is prefaced by the word "maximum". Most are .5. This means that it's undesirable for the blower system to be seeing higher external static pressures than .5. This is measured at the blower inlet and outlet (before the coil) because this is the actual static pressure the blower system is working against. This is also the figure used by the manufacturers in their blower performance charts.

The more you exceed this pressure the more the cfm output drops and typically, the less amps the motor will draw. When the motor underamps by more than 25% of its rated amperage it begins to overheat.

Conversely if you drop this pressure too low, the motor moves more air but begins to overamp and slow down. If it overamps by 10% over the rated amperage bad things happen.

I think maybe you're confused about the terminology of external static pressure vs total static pressure. This is understood. Some of the manufacturers literature makes this more confusing. But almost invariably the .5 static pressure rating on a furnace is the maximum static pressure desirable across the blower.

Air handlers and package units are a different story.


[Edited by midhvac on 09-20-2004 at 10:24 PM]

[honglo]

midhvac, Hi! You say that either 25% over or 10% under (amps) indicates danger points of the blower. Does the manual information with regards to the 0.0 to 1.0 reflect these limits as well?
I seem to recall that I DID do a test on a blower assy I have in the garage (to cool down the garage a bit every now and then), to a maximum possible static pressure test. I believe it was measured at 2.0"wc.
Does this mean that the info in the manual is in essence, giving the maximum (safe) upper limit of the blower being 1.0 or (the 10% underamped) condition? I did NOT amp the motor while doing this. Perhaps I should run that (test) tomorrow if I have a slow day.
I HAVE run the blower for days on end in a 0.0" sp condition (sitting on the garage floor) with no apparent damage to it. (that would be of course the 25% overamped condition). It might have continued running only because of the cool air keeping the motor from tripping out. Again, perhaps I should re-test this with an amp meter.

Anyway, isn't this foolhardy of the manufacturers calling this reading ESP? When in fact it is TSP!!!! Why don't they call a snake a snake? Or is it they just want to baffle us with their engineering brilliance? How tacky is THAT??????

Maybe I am confused about TSP and ESP. Perhaps you could explain it to me? Pictures might help :)

Isn't the blower motor an internal part? Maybe they should have called it ISP :o







[Edited by honglo on 09-21-2004 at 02:27 AM]

[honglo]

midhavac,
At what point would you say an evaporator is dirty if it is rated a say .2 static pressure? 10% over .2 or 30% over .2?
I often wonder how when reading an invoice from a previous competitor says, "The coil is 75% covered with dirt!" Exactly how do you think they come up with that figure?
I doubt they actually read static pressures... Especially when I see no (test) holes anywhere in the area.... Hummmm.
Perhaps they are using ESP (extra sensory perception)

With actual readings, I would say in the neighborhood of (just guessing of course) 30-35% increase in static pressure. What would you say?

[midhvac]

Originally posted by honglo
midhvac, Hi! You say that either 25% over or 10% under (amps) indicates danger points of the blower. Does the manual information with regards to the 0.0 to 1.0 reflect these limits as well?

You've got the numbers backwards. Standard blower motors are designed to be overamped by 10% max or underamped by 25% max. I think these numbers are for high blower speed on a multi-speed motor. Still don't have a good answer on how it works with the lower speeds, but that's a whole nuther thread.

Some of the manufacturers blower curves list cfm at 0.0 and 1.0. These shouldn't even be published as the motors can't really deliver those for very long without serious overamping. (A dog who sh*ts quick won't sh*t long.) Go look in a Graingers catalog at the blower motor assy's. You'll see a much more realistic blower curve chart showing which static pressures are too low to be used.

I seem to recall that I DID do a test on a blower assy I have in the garage (to cool down the garage a bit every now and then), to a maximum possible static pressure test. I believe it was measured at 2.0"wc.
Does this mean that the info in the manual is in essence, giving the maximum (safe) upper limit of the blower being 1.0 or (the 10% underamped) condition? I did NOT amp the motor while doing this. Perhaps I should run that (test) tomorrow if I have a slow day.
I HAVE run the blower for days on end in a 0.0" sp condition (sitting on the garage floor) with no apparent damage to it. (that would be of course the 25% overamped condition). It might have continued running only because of the cool air keeping the motor from tripping out. Again, perhaps I should re-test this with an amp meter.

Once again, you've got the numbers backwards. Yes, you'll see what I'm talking about with the ampmeter. As far as the blower chart giving you the maximum (safe) upper limit of the blower being 1.0, it just depends on what the person who made the chart is trying to illustrate. It could be either that the cfm output renders it useless, or that the motor's getting too far underamped (under 25%), so it's in the danger zone.

Anyway, isn't this foolhardy of the manufacturers calling this reading ESP? When in fact it is TSP!!!! Why don't they call a snake a snake? Or is it they just want to baffle us with their engineering brilliance? How tacky is THAT??????

Maybe I am confused about TSP and ESP. Perhaps you could explain it to me? Pictures might help :)

Isn't the blower motor an internal part? Maybe they should have called it ISP :o


You and I are both confused about the terminology. This makes it tough to get past that point and delve further into the mysteries of static pressures. All of the correct phrases aren't consistently used by manufacturers and textbooks.

You first must find a valid definition of the terms:

total static pressure
fan static pressure
external static pressure
maximum static pressure

On an air handler or package unit this could be even more confusing if you aren't sure whether the coil's included or not.

At this point about the only thing I'm sure of is that .5 is the maximum static pressure most *furnaces* are designed for. High-static designated furnaces allowing .7 and .8 maximum static have the same blower housing and wheel with the next size up in hp motor (same rpm) and additional cabinet insulation to keep the furnace from whistling and sucking air in due to the increased negative static pressure at the blower door and seals.

Use of the higher hp motor allows the motor to overcome some of the static pressure force so that more air is moved. This is at the expense of digging into the 25% underamp margin, so the blower will run hotter, but will still be within safe limits.

[dash]

1.Design or redesign the duct to be within the ESP limits of the equipment being installed.Not the other way around.

2.Yes,.08 and .06 ,will keep you out of trouble ,most of the time.However check the ESP,after install,it could be too low,causing higher cfms than desired.

3.If you want to do the install Right,Man.J ,then S,then D.

4.Fan data:Read the fine print,some will include,some will exclude,filter,electric heaters,wet coils,etc..You must adjust for this,as per Man. D.

5.TSP versus ESP,ESP is the static of the duct system ,external to the furnace(including the coil),air handler,or package unit.
TSP,can mean velocity plus duct pressure.In this discussion,and others it would mean the Total ,ESP on the blower assembly,and always be higher than ESP.

Mfrs. are correct in there usage of ESP,in rating the equip..

6.Extremes:Blowers can produce ESP ,off the the fan data chart,just don't run the system there.

7.Maximum static:I see "certified static",much lower value the the highest on the fan data chart,on the Carrier information.Mid-range (on the chart)ESP is better,but if it's on the chart,you can use it,read all the fine print ,water blow off,etc ,etc..

8.Air handler package,versus furnace,the rules stay the same.The coil being in a different location,often causes confusion,but the rules are the same.

9.Dirty coil static(PD),if you know the PD for the coil when it's clean,clean when or before, it becomes plus .1 PD.

honglo,

Do a search on "fefarms" ,his posts on duct design are the best I've seen on this board.

[midhvac]

Originally posted by honglo
midhavac,
At what point would you say an evaporator is dirty if it is rated a say .2 static pressure? 10% over .2 or 30% over .2?
I often wonder how when reading an invoice from a previous competitor says, "The coil is 75% covered with dirt!" Exactly how do you think they come up with that figure?
I doubt they actually read static pressures... Especially when I see no (test) holes anywhere in the area.... Hummmm.
Perhaps they are using ESP (extra sensory perception)

With actual readings, I would say in the neighborhood of (just guessing of course) 30-35% increase in static pressure. What would you say?


I think it would be very difficult, if not impossible to accurately determine that much of the time for many reasons.

I've seen new residential evaporators with factory sp drop ratings ranging from .18 to .40 and obviously you have to know what the factory specs are to go any further.

Even if you know what the specs are, you often won't have the same test conditions, because you also have to consider duct leakage and how much air is bypassing the coil, and don't forget that this increases when the coil becomes dirty. This is more of a variable than you think, if it's an uncased coil. Then you have those cases I see all of the time where the plenum and coil are bigger than the top of the furnace, and there's no transition, so part of the coil is getting no airflow. Then you have the ones where they used a coil which was much narrower than the plenum, and they mounted the coil all the way over to one side.

It would also depend on what type of debris was in the coil. I've read that some of the debris tends to be more porous than others and allows air to be forced through.

[midhvac]

Originally posted by dash

Do a search on "fefarms" ,his posts on duct design are the best I've seen on this board.

He doesn't come around too often and yes, he's brilliant. Is he like a design engineer or something?

[dash]

Dirty coil detection;

Record coil PD on first start,your invoice and a sticker on the blower.Later holes for testing and original PD are already there.

[johnl45]

[QUOTE]Originally posted by honglo

I also use huge amounts of common sense when replacing a system but that is NO EXCUSE for lack of proper installation methodology.


Thanks again, and as for the apparent (silence) from the rest of the guys,,,,,, I DID ask them not to comment if they had no knowledge on this subject. In fact, if this is true, they are indeed SMARTER than I am. After all, it's "honglo" that is showing his ignorance here. :)[/i]

With no disrespect I think your making this way too complicated. Take Dash's suggestion and study Manuals J, S and D. It may take a while but the common sense you speak of will kick in like a light going on. Best of Luck

[honglo]

midhvac,
Thanks for clarifying that it is 25%under and 10%over.

dash,
(apprecieate the number breakdown.) Wouldn't it be safe to say that the printed ESP on the furnace/air handler is in fact the reading in which the blower motor is at its rated amperage as well? Taking an amp reading of the blower after install, should it also reflect the (posted) amps for the blower motor? I would think the manufacturer would post a recommended esp for the particular piece of equipment based on the (desired) amps of the motor itself. The CFM would just be what it is at that point of optimum motor safety.
This would explain why it is RARE for me to find ANY motor or blower for that matter actually running at it's rated amps. Because the CFM'S ARE ALWAYS WRONG. Interesting!

midhvac,
I see what you mean about some furnaces with wider coils than the output of the furnace itself could have problems with the coils not getting enough or proper air distribution but in many cases, the manufacturer expects you to use this mis-match combo to achieve the rated SEER. Do they expect us to build some sort of transition from the furnace to the coil? I'll check with Goodman today but I don't think upflow furnace/coil transitions are sold.

johnl45,
I am purposely making this subject complicated in order to understand the thought processes involved. I agree the manual d, the manual s, and the manual d should be used. I am simply trying to understand all the principals involved.
Kind of like the two guys boiling water.
The first guy boils the water to cook his food.
The second guy observes boiling water and discovers air conditioning!

[midhvac]

Originally posted by honglo

midhvac,
I see what you mean about some furnaces with wider coils than the output of the furnace itself could have problems with the coils not getting enough or proper air distribution but in many cases, the manufacturer expects you to use this mis-match combo to achieve the rated SEER. Do they expect us to build some sort of transition from the furnace to the coil? I'll check with Goodman today but I don't think upflow furnace/coil transitions are sold.


Actually what I was referring to was not a new matched coil and furnace, but a hacked retrofit where no air is going through the outside part of the evaporator. I wouldn't think you would encounter that situation on a matched furnace and coil.

[johnl45]

Originally posted by honglo
johnl45,
I am purposely making this subject complicated in order to understand the thought processes involved. I agree the manual d, the manual s, and the manual d should be used. I am simply trying to understand all the principals involved.
Kind of like the two guys boiling water.
The first guy boils the water to cook his food.
The second guy observes boiling water and discovers air conditioning!
You can't boil water until you learn how to light the stove.