Rows of coil selection 1

[Manu68]

Hi Experts,

What should be parameters for a no of coils decision for a AHU.
As the coil no increases from 4 to 6 or 8, the gap becomes less and can cause a high bypass factor.
What implications should be taken care while the no of rows is decided.

Thanks in advance.

Manu

 

[willard3]

Sensible heat capacity becomes less as the number of coil rows increase.

 

[Manu68]

Given the area/space larger no of coils will increase the capacity, as I believe.
How does that connect to the sensible heat capacity that too inversely.

Manu

 

[willard3]

More coil rows increase air contact time and remove more moisture.

 

[dbill74]

More coils also means more air pressure drop and more work for the fan(s). Keep an eye on the coil face velocity, rule-of-thumb is <= 500 FPM, but check with coil manufacturer. (You don't want to blow condensed water back into the air stream.)
Bill

 

[Manu68]

So would it be correct to understand that In a coil where more rows are available will be for the Latent heat removal or dehumidification. Will the both section be available in the same frame of the coil or the coils for sensible and dehumidification are different set of coils with their respective rows and spacing accordingly.

 

[dbill74]

Yes more rows will mean more moisture removal, it also means more sensible cooling and a lower discharge air temperature. And as I mentioned earlier more pressure drop for the fan(s) to overcome resulting in a less efficient system.

The number of rows you have is not the only variable in selecting a coil. You need to also consider number of fins per inch, fin material and whether or not protective coatings are needed. All these will impact a coil's capacity to one degree or another (increasing or decreasing the capacity). For example you may be able to reduce the number of rows by increasing the number of fins per inch or using a different fin material.

The best advice I can give you is to take your load calculations, air flow rate, and any special requirements (i.e. coatings or size limitations) to a manufacturer's representative and work with him/her to select a coil to match your needs.
There is to my knowledge no magical equation to determine the best coil design, number of rows, fins per inch, etc. Each coil manufacturer can vary these to provide the amount of cooling you need.

 

[ChasBean1]

More rows and fins per inch is more air pressure drop but more efficient sensible heat transfer. For the best dehumidification, you want a low apparatus dew point and a higher coil bypass factor. This means less rows and fins per inch; colder chilled water.

 

[RossABQ]

The amount of moisture removed also depends on how the coil is circuited. There are too many variables to make a definitive statement on how many rows to use. There are plenty of coil design programs available on the internet, where you can evaluate the performance of several different configurations.

 

[ChasBean1]

To clarify, you select a high efficiency coil with 14 fins per inch (fpi) that gives saturated outlet conditions. If you can find a coil that gives the same outlet temperature at 8 fpi, you have better dehumidification...