Professional Member
Instead of a practical exam if an engineer wants to be certified he should be required to balance jobs and submit a balance report on the jobs. They could lie and submit a report someone else did but if ask a few questions it wouldn't be too hard to figure out if they knew what they were doing.
I would have told the engineer to go get a can of soda so we could try his idea and while he was gone would have sped the fan up.
No man can be both ignorant and free.
Thomas Jefferson
Professional Member
Without fan test data, here's a guess of the engineers intent...Originally Posted by bradluke0
Opening the fan access door is a quick way to find out two possibilities...
1) if the upstream (to the fan) ahu dampers, ra fans, ductwork, inlets are restrictive
2) And if restrictive can the present configuration downstream (from fan) provide design cfm.
And opening the fan access door is a quick, low labor cost way to determine if speeding up the fan will help.
Professional Member
If you know the airflow and fan RPM you can easily calculate the new fan speed needed to obtain the desired airflow. All you find out by opening the door is if the fan will move more air with less total static pressure. Of course it will but the total static pressure will go up as fan speed is increased not down. The engineer didn't know what he was talking about.
No man can be both ignorant and free.
Thomas Jefferson
Professional Member
As I said, not knowing fan data, I gave possibilities.
If the airflow to the fan is restricted, the open door would/may provide design cfm due to reduced TSP.
Perfect world is to know design TSP as calculated.
Again, we are talking about a very quick test.
Also, what if the door is opened and no change is noted? Possible restriction in SA somewhere...fire damper partially closed, system effect due to creative duct transitions that are an abortion.
If these are present, changing fan speed will not solve the problem.
Jogas
Four wheel therapy, my 1968 Camaro is gone and will be missed
Professional Member
Static pressure profiles will tell you if you have a restriction and where if you know how to do them. Part of air balance is obtaining fan date. If you open the door fan airflow will increase but that doesn't tell you if or where you have a restriction. If you have a fan curve that dips and recovers and you open the door you don't know which side of the dip in the curve you were on before you opened the door and which side you are on after you opened the door. Opening the door could also put the fan in it's unstable region or in some cases take a fan out of that region.
Opening the door is a cheap way to screw up.
No man can be both ignorant and free.
Thomas Jefferson
Professional Member
Agree to disagree.
Jogas
Four wheel therapy, my 1968 Camaro is gone and will be missed
Regular Guest
The problem with the unit was that the coil had a little higher than design pressure drop at 20-25% low of design . We first thought the coil wasn't protected properly during construction and was impacted but that wasn't the case . The coil had more fins per inch than was specified . We told the engineer the coil was the problem but he didn't buy it , hence the crazy field visit by him and the soda can debacle . I am always totally against testing things in a way that is not consistent with the intended conditions . This includes holding the fan door open , testing with dirty filters , testing with slipping belts , etc . I am also not a fan ( no pun intended ) of just traversing a unit or testing the flow on a pump and not obtaining all data on that piece of equipment . I had a guy tell me all he wanted me to do was traverse the unit as he believes he is low and he just wanted to know how much low . If he already believes he is low why wouldn't he want to know what to do next ? Without all the data you cant . Cheers .
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