Sensible heat ratio and number of rows 1

[Bobfd7dbf]

Hi all,
I have recognized in AHU cooling coil selection that as the sensible heat ratio value increases the number of rows in a cooling coil increase.
It does not make any sense for me , as i see higher sensible heat ratio means less latent heat value.
So why the coil have more rows when SHR value increase ??

Thanks in advance.

 

[EnergyProfessional]

The selection software (based on thermodynamics and heat transfer fundaments) takes into account velocity, fluid temperatures, flowrates, tube and fin material, air psychometrics, piping configuration, fin shape and spacing....... so just looking at one property doesn't tell much. If in doubt, talk to the manufacturer of the coil to verify you entered all values correctly t select the correct coil.

 

[Bobfd7dbf]

All parameters you have mentioned are taken in consideration. I kept everything constant and i just changed the return air temperature's humidity to a lower value in the comparison.

I have found that as relative humidity of the on coil air decreases , sensible heat ratio increases and number of rows increase.

Can you please clarify what happens here.

 

[MintJulep]

The efficacy of the latent heat transfer is better than that of sensible heat transfer from the airstream to the coil per unit surface area of coil contact.

So as the SHR increases the coil surface needs to increase.

In your example that was done by adding rows, but it could also be done by closer fin spacing or going to wavy fins.

 

[Bobfd7dbf]

So as i know, higher SHR (closer to 1.0) = More change in temperature and less humidity removed and Lower SHR = less change in temperature and more humidity removed.

I thought before that there is a relation between the number of rows and it's effectiveness for removing moisture ( as air have more contact time with coils ) , so how that relates with the above equations !!
As i can see when there is a higher amount of latent heat we use lower number of rows.

Does that means there is no relation between latent heat removal and high number of rows?

 

[SAK9]

OP I would suggest a recheck here.I have usually found that the number of rows required in a coil increases as the SHF goes down.If you have high latent load such as in a restaurant or cinema yo would typically require a 6R coil

 

[GT-EGR]

Are you sure everything is staying fixed and you are just adding sensible and removal latent load and keeping the same total load?

In the end the coil selections don’t lie, but make sure you are comparing the same things. Sensible heat ratio can go up but load can come down if you don’t keep all the other coil inputs correct.

Conventional wisdom I thought was higher latent means deeper coil, but all those higher latent were mostly 100% OA systems in my experience so they were really higher total loads.

 

[Compositepro]

For a given set of conditions, the only way to keep the SHR high is to avoid condensing water. This means that the coil temperature has to stay above dewpoint. This limits the delta T available, which requires more surface area in the coil to achieve the sensible heat load.