View Full Version : Please help.
I am very new to the field and hope that you guys can give me some expert opinion on the Air Handler performance. We have a 20 tons air handler here at our shop. I am suspecting that it doesn't work properly or may be it is but is not enough for the heat load. The problem is that when the outside temp. is cold the AH works great and within specs. But, when it gets hot outside (above 80 degF) then it's hot inside and the AH is out of specs. Anyhow, I am trying to characterize the performance of this air handler before I am pushing my opinion to next level of management. So, my question is: How am I going about characterize the performance of an air handler? I am thinking of installing a sensor for the wind velocity to determine if the air handler put out the maximum capacity or not. Is this a correct method? Is there anything else that I need to do? Do I need to measure temperature rise?
Thanks very much
02-19-2007, 06:24 PM
Is this a split system your talking about or a package roof top unit?
This A/H system is tie-in to another A/H system which used as a booster of some sort.
02-19-2007, 06:34 PM
Im not even sure what you have there. Any models #s??
It's a trane brand climate changer draw thru
Serial number U83B32665
Unit type CCDB14CE00 model number 12000 k00000000000-00000PR
Max rated pressure 200 psi 1st.. Coil max rated 2nd. Coil N/A
Basic unit HSA1RO2RO2ROAL Primary Coils 100J0A2H00000000
Design test static pressure N/A
Fan motor 7.5 hp. 480 VA. 3 phase 20 tons. Size
2 ½ ‘’ pipe supply and return steel iron size of the ah is 48’’ width x 105’’ length x70’’ high
02-19-2007, 06:55 PM
Man, Im not a choochoo guy. Hopefully one of the other guys will throw some info your way.
02-20-2007, 01:33 AM
now we need numbers...air temps in/out, it appears that this is water cooled? if so, we need water temps in/out. give up any technical numbers you can measure...this is a good start though
02-20-2007, 09:06 AM
It sounds like you're dealing with an air handler on a two pipe system...same pipes bring hot water for heating in winter and chilled water for cooling in summer. Correct?
This is a single pipe chiller. Only for the cooling no heating.
Also, do you guys have any recomendation on what brands or types of sensors for velocity and pressure measurements? I want to mount them inside the duct.
thanks very much
02-21-2007, 05:49 AM
no reccommendations for sensors yet, but how about the airflow issue?
what if you could find out if any air balancing has been done on the bldg in that area (of the AH). If no one objected from that standpoint, I'd close the motor pulley to get more than 90% of RLA, or more depending on SF. I could never figure out why more pulleys weren't closed more than 60-80% of RLA, but then again...I was dealing with data centers and usually air is already moving like crazy.
02-21-2007, 06:58 AM
The problem is? You only have problems in the summer at over 80 degrees. Unless you have the history of your coil temperatures in and out, it will be hard to do any thing. We don’t have your loop temperature. If your coil is clean and nothing has changed with your unit then flow across the coils probably is not your issue. I would look more at your loop temperature how are you cooling and does some one have a history on your cooling temps. It maybe that there not running or are unable to run the chiller at the design temperatures needed for your coil to deliver on above 80 degree days.
One more question though, I measure the amperage on the fan motor today and it's running at 70% of it's maximum capacity. This may be the problem why it's hot in the summer? You think I could replace a new motor or just try to replace the smaller wheel to pump the amperage up?
02-21-2007, 05:27 PM
First and foremost, welcome to this forum. Second……..STOP! No one here on this thread, or even in this forum, can tell you exactly what your problem, if any, is. An accurate diagnoses is based on an accurate assessment of the operating conditions of the system, you have not provided that to us.
As my colleague Propmanage has already pointed out in his above post, guessing at the problem, again if there really is a problem, is not something we do here friend. If you want us to help you out on this problem, then this is the minimum of what we will need to start the diagnostic process on your system:
Entering dry bulb temperature of the air handler
Entering wet bulb temperature of the air handler
Leaving dry bulb temperature of the air handler
Leaving wet bulb temperature of the air handler
CFM through the air handler
Entering chilled water temperature at the air handler
Leaving chilled water temperature at the air handler
RLA , FLA, and/or SF of the air handler motor
What the motor of the air handler is pulling
With the above operating conditions we will be able to supply you the following information:
BTU/Hr of total cooling capacity
BTU/Hr of latent cooling capacity
BTU/Hr. of sensible cooling capacity
Compare the above cooling capacity to a typical 20 ton air handler to determine if the air handler is operating correctly.
If the air handler is not operating to rated capacity, then we will be able to point you in the right direction to continue the diagnostic process.
Anything less than the above, is nothing more than a guess, maybe an educated guess, but after all is said and done, it’s just a guess, and as I’ve posted above, we don’t do that here.
Now if you have any problem obtaining the above information, then maybe we can help, or maybe it’s time to bring in a professional with the right diagnostic tools and skill sets to complete this diagnostic process for you.
Hope this helps……..
John J. Dalton CM
02-22-2007, 06:04 AM
do what you want. it won't hurt to close the fan sheave (sp?) to increase blower output, as long as you are within rated whatnots. or you can try to answer all the questions about everything you ever wanted to know about your system. don't get me wrong. those things matter. and the original data at the design and install phase of that shop area may have changed and be different from your actual current conditions there, so the mgmt may afford you some time to try blower speed. the thing is, that is not usually the solution. the change in air volume from 70% to 95 or whereever you lock it in is generally not as we say statistically significant. it may be worth a shot if the room is not too far off when it's over 80 outside. how many days a year does it get over 80? keep us posted..
02-22-2007, 07:27 AM
Look and see if you have fresh air or an economizer on the system?
see if your damper is open?
02-22-2007, 07:53 AM
Check RPM and rated RPM.:D
02-22-2007, 08:12 AM
:cool: If the voltage decreases, the current will increase in roughly the same proportion that the voltage decreases. For example, a 10% voltage decrease would cause a 10% amperage increase. This would not damage the motor, if the current stays below the nameplate value.
02-23-2007, 03:33 PM
lejm, john dalton is correct if you want to take this on as an enginerring project , a lot of info needed for answers here. and he knows his stuff.
if you want to take this on from a service techs point of view ie give 'em 20 tons of cooling , heres what you need to look at.
if their is economizer is it leaking with damper closed, measure return air temp in duct between last return and econo, then at filter face temp, any significant rise (on hot day) you got leakage, repair seals or replace damper.
is chilled water piped corect, entering water on downstream side of coil ie coolest water at coolest air.( get in there and look at it, stickers pointing in don't mean much)
is chilled water temp and flow correct, temp from specs, flow from specs or circuit setter if installed.
air flow!!!!!! buy a pitot tube and manometer that has FPM feet per minute.
get FPM multiply by square feet of duct and bingo CFM. you need 400- 600 CFM per ton depending on what you are cooling. if it is typical office space you would be on the 400/ ton end of engineering, if it has a lot of data rooms, kitchens, big fancy glass wall buildings or any other high heat loads you might push it up towards 600/ ton.
wet bulbs will give you the most accurate performance of it but this will get you going if you need to bring a bigger "case" upstairs.
keep us posted
Thank you everyone for all the advises. They are very helpful. This gives me a good start on this project. Again, thank you.
BTW, does anyone know the formular on how to calculate the CFM using water temperature and flowrate?
02-28-2007, 04:16 PM
the formula for heat transfer in/out of water (not glycol) is:
water temp difference * gpm / 24 = tons
you can reconfigure it for btuh
to backward calculate the cfm with this is possible, but only for sensible heat. it will not work if any latent heat is added or subratcted.
Thanks very much, Jayguy.
Also, if you guys don't mind help me answer this. What is the normal range for the pressure drop across the cooling coils inside the air handling unit? I measured my at 0.45 inch of water with damper open 100%.
03-02-2007, 03:13 PM
Call a professional.....
For the dollars you will spend the information you gain will save you even more on what could be just a service call.
Does the unit have outside air capabilities?
What is the design gpm vs. actual rating and Delta T at full flow with the chilled water being supplied at the proper design (10 or 15 degree rated coil)
If this air handler is part of a system with two air-handlers is it being used on process, or just comfort.
Air flow is only one small part of the overall equation.
Spend the money on a Tech. instead of air flow sensors.
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