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Post subject:Taking Air Flow Readings Across A New Air Handler?
 Posted: Dec 20, 2005 - 03:36 AM #4110
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Tinner
Joined: May 11, 2003
Posts: 40
Location: Philadelphia, PA.
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Hello All 
Have a question and would appreciate some feedback on this particular subject.
We manufacture equipment, including custom air handlers, as you well know. On this particular job we have 12 custom RTU's with mixing box station, filter station, hot and chilled water coils, face and bypass dampers and then the supply fan box. On this particular job, as can be with many other jobs, the spec. calls for the equipment to be "totally balanced".
We have conducted many total equipment balance reports for customers, but we usually take our readings after the balancer has completed thier work. In this case we could not find any holes in any of the panels in any of the units?!? We were wondering how the balancer concured with the readings that they supplied to the engineer. In the report, our units are not meeting spec. according to the balancers readings. When we questioed how the readings were found, we were informed that the access panels of each section of the unit were held open slightly and the readings were taken with a pito tube!?! Does this sound like standard practice?
We are going to return to the site and take readings ourself, with the panels slightly open and then we are going to make access holes in each panel and take readings to compare, but this time with the panels completely closed. We will take these readings with 6' long refernece tubes that stretch completely across the width of the unit interior. After we are finished we will plug up the holes with our little plugs. Sound right?
My real question for you is this: Where in any book may it state "How to properly measure total static pressure of an Air Handler"? I have the SMACNA book on balancing air and water, but I could not find any place where it states how to measure the actual air handler (air source). All we found was related to the actual ductwork. And in every chapter we refered to, the SMACNA book does always state to traverse your readings. Shouldn't that be done on the air source as well?
Oh well, so much for just one questions! Would appreciate your thoughts or opinions on this subject.
Thank you for your time and a very Merry Christmas to ALL!!!!
John |
_________________
Learn...Do...Teach...
Pay attention, be proud of your accomplishments, pass on your knowledge and you will grow!
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Post subject:RE: Taking Air Flow Readings Across A New Air Handler?
Posted: Dec 20, 2005 - 06:09 PM #4111
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Pro Tinner
Joined: Feb 01, 2004
Posts: 826
Location: Mobile, Alabama
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John,
Testing the AHU with the panels slightly open does not seem right to me. I think if you install the test ports into the panels, you will find a more accurate reading. Traverse readings in the duct are what we always did. I have also found in the past that you can read the same air moving device two different times with the same testing equipment and get a different reading. I have seen the results vary by 10%.
Surely by the balance people testing the AHU while leaving the door slightly open, they are not getting an accurate reading? I had a book once that gave a demonstration of balancing a large AHU like the one you are talking about. I will have to remember who I loaned that one to.
Wouldn't you just measure the pressure drop across all of the sections of the air handler? It would seem to me that the ultimate end result readings would be gotten at each end of the AHU. I would check the positive end at a location of 10 diameters down the duct line from the end of the AHU given that you have that set up.
Using a "pito" tube, I would traverse the ducts cross section and find the readings that way. I have also found that the more readings you take, the more accurate the average will be. I would think you are on the right track to finding the facts by installing the test ports.
Hope this helps, Have a Merry Christmas! |
_________________
Pricer
Many Minds, Many Hands, Many Solutions
Air Specialty
www.air-specialty.com
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Post subject:RE: Taking Air Flow Readings Across A New Air Handler?
Posted: Dec 21, 2005 - 12:05 AM #4112
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Tinner
Joined: May 11, 2003
Posts: 40
Location: Philadelphia, PA.
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Thanks Pricer.
With regards to your question about taking pressure drops across all of the sections of air handlers? You are correct that we really only need total in (negative presure) and total out (positive pressure), but some specs (more often than not in todays specs, expecially in schools) can require "total air flow" of each air handler. Then we (the manufacturer) need to provide our desgn specs for pressure loss across each component in the air handler (dampers, filters, coils, fans, etc.) along with our estimated total static.
Thanks for that interesting note about have various readings from the same unit, we have seen that when we take velocity readings across our water coils. We've already experienced up to 6 different readings on the same unit in the same day with the fan doing the same speed every time. go figure, we're not alone?!?
We will return to the site in the beginning of January and do our test and see what the difference is between taking readings with panels loose or with them totally closed up.
If any one finds anything in writing that may state the correct way to measure an air handler, please let us know.
Thank You,
John |
_________________
Learn...Do...Teach...
Pay attention, be proud of your accomplishments, pass on your knowledge and you will grow!
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Post subject:RE: Taking Air Flow Readings Across A New Air Handler?
Posted: Dec 22, 2005 - 03:18 AM #4115
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Joined: Oct 18, 2005
Posts: 4
Location: slidell,la
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| of course there should be drill holes for the static probe. there should be drill holes for a velocity traverse. i have seen equipment as you described,no holes for the pitot tube.maybe your company should install test probes at the appropriate points on the equipment. if possible do a velocity traverse of the appropriate duct sections,after all the correct airflow is the objective.as we all know pressures vary depending many conditions. theoreticaly static pressure should be measured at the duct wall and should be the same anywhere ,at that point, in the system. |
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Post subject:RE: Taking Air Flow Readings Across A New Air Handler?
Posted: Dec 23, 2005 - 04:32 PM #4139
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Tinner
Joined: Apr 02, 2005
Posts: 19
Location: New England
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We have been doing air balance as part of our company for the past 10 years. We do installation work as well as service and have found that there are a lot of companies who go thru the motions. The one thing about Connecticut it is a regulated and licensed state in regards to HVAC. The new mechanical code requires air balancing.
We have heard and seen a lot of shortcuts. If there are no test holes and panels were slightly opened for testing then their practices are incorrect and faulted. There are several standards for test and balance companies to follow, If they did not comply then I would pick apart the report. Start with certification of calibration on all instruments used, right down to the RPM gauge and electrical meters. Documentation is important.
Look at the type of instruments being used (the $2500.00 hot wire TSI data logging capable or the $50.00 gauge "take the technicians word for it")Then ask to see the certification or training records of the technicians performing the test. Then look at the balance report and have them field verify some of their tests with you or the Engineer of record on site for verification. I don't suggest these things as a way of beating the system just that you need to know if sloppy test and balance is being done or is there an issue with your equipment or is the problem with the duct distribution system.
The air handler is measured in several ways, all which is done on the bigger built up systems.
1. obtain the fan curves for the blower from the manufacture. Ideal information should contain RPM, Static pressure and Air flow
remember none of the information takes into account system effect.
2. obtain the pressure drops of the coils. They should have the relationship of static pressure and airflow, some manufactures will include wet coils and dry.
3. obtain pressure drop of the dampers. Again airflow and static pressure ratings
4. Filter media pressure drops If available, usually a tough one if it is just throwaways
5. If you purchased any completed section of the air handlers then the manufactures static pressure to air flow information
6. If VFD make sure to test on full speed and measure across the blower section
This information will allow you to measure static pressure in the equipment and help determine if the airflow is being met again this does not take into account the system effect of the ductwork, vertical or horizontal discharge. The reason for measuring across each is to help verify the readings and approximate the performance
That is how we start, we also measure before and after the equipment to see how close the system is to the design pressure of the duct system. External static pressure is usually speced by the engineer, because that is how we size the motor by the total required static pressure.
With these tests we have done nothing to truly determine our CFM flow. We have only approximated the static pressure relationship to the manufacture's published information on what they are telling us is the CFM they tested in a lab. Means nothing in the field. System effect is the loophole. That is why we try to test each component as well as having future reference to determine dirty coils plugged filters ect. The more tests the more accurate you can be.
Then from there you must do Traversing of the supply, return, exhaust, and fresh air ductwork in a good spot for accurate readings. The number of readings is determined by several standards and is based on the size of the ductwork. Here is where the benefit of something like the TSI hot wire pays off big. Quick and direct CFM readings and full data logging. The better the meter the closer the retest will be but remember the temperature and humidity during testing also needs to be recorded because this will effect all readings.(colder air is heavier more energy to move) We usually run the a/c during testing this provides us with a wet coil for testing as well as a more consistent test when and if the Engineer wants to field verify our report. We like it when this is done, a matter of pride to prove what we do and how we do it.
I seem to be rambling, your question was written procedures from a book, yes I have some. Send me your fax and I will photo copy and send you the sections. |
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Post subject:RE: Taking Air Flow Readings Across A New Air Handler?
Posted: Dec 29, 2005 - 01:47 AM #4174
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Tinner
Joined: May 11, 2003
Posts: 40
Location: Philadelphia, PA.
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Tanner,
I greatly appreciate your response and did find it useful. If you could send me something from a book or simply give me the title, we can certainly purchase the book.
We thought we were doing our job correct, but we were questioned recently on a project that has several of our custom "build up" model air handlers. I work for the manufacturer and am a service engineer. We usually have issues with chillers and the such, but this is a case of air flow and we are being blamed for the "lack of" proper air flow. We own the tools to measure air flow, we have had units that were ordered or even built wrong. We get involved, figure out the problem and make the corrections, but only on the units. We do not install the equipment or make the duct, etc. We simply manufacture the units based on a design.
In the case of this particular job, our sales engineer did submit the equipment build with design criteriera for dirty filters and wet coils. I have a copy of the air handler builder order and reviewed the build of the units on site to see if there was an order problem or a build problem. I found no problem with either, but did find the balancer did not make any holes in any of our sections of the unit, but yet we have a final balance report that claims each unit is not producing the designed amount of air.
When we questioned how the balancer concluded the results, they became quite offended. We have even been told that it does not matter if you take air flow readings with doors slightly open or completely closed?
I would certainly appreciate any information you could send me. We are going to return next week and make our own holes and take readings ourselves. We'll let you know how we make out. Again, thank you for the information.
John Williams
Fax: 6108340880
Office: 6105675038 |
_________________
Learn...Do...Teach...
Pay attention, be proud of your accomplishments, pass on your knowledge and you will grow!
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