HVAC airflow design issues and measurement

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Rfsmith48

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Folks,

Not sure if this is the best venue for these questions, and I am looking for website references as well.

I have an older furnace with a new AC grafted on top.

I need to understand what the ideal air flow speeds are across the Coil, and the upstream/downstream flow restriction guidelines.

Is there a grassroots method for measuring flow speeds across the coil? Simulation software?

I suspect that I am looking for a reference to an HVAC forum, and all help is appreciated.

Rog
 

DonL

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A difference of return air temp to vent outlet temp is a good indicator.

15-20 is good, If it working about right, and removing moisture.

My method is old school, But can tell you a lot about the condition of your system. You can even detect a dirty filter or coil.

If it is not icing up, then you are moving enough air. If the coil is dry, you could be moving to much air, or your air is dry.

The fan speed for heating is another story.


Good Luck.
 
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Sino King

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Folks,

Not sure if this is the best venue for these questions, and I am looking for website references as well.

I have an older furnace with a new AC grafted on top.

I need to understand what the ideal air flow speeds are across the Coil, and the upstream/downstream flow restriction guidelines.

Is there a grassroots method for measuring flow speeds across the coil? Simulation software?

I suspect that I am looking for a reference to an HVAC forum, and all help is appreciated.

Rog
The air flow speed across the cooling coil should be lower than 2.5 m/s.
 

Rfsmith48

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A difference of return air temp to vent outlet temp is a good indicator.

15-20 is good, If it working about right, and removing moisture.

My method is old school, But can tell you a lot about the condition of your system. You can even detect a dirty filter or coil.

If it is not icing up, then you are moving enough air. If the coil is dry, you could be moving to much air, or your air is dry.

The fan speed for heating is another story.


Good Luck.
 

Rfsmith48

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Thanks DonL,

The temp range from inlet to outlet vents is in the 15 to 20 degree range.
Does this temp range indicate that the coil is not icing?
The coil drain does not flow much water, but this is CO, and the humidity is usually low.

Thanks for the input, I have a lot more data to collect before AC season is over.

Rog
 

Rfsmith48

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Hi Sino King,

What is an effective way to measure the airflow across the coil? Pressure drop? (mm of H2o?)

Thanks,

Rog Smith
 
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