What is the best location for the fan on the evaporator side?

[jasno999]

Here is a question I have been askign myself and I am not sure what the best answer is.

You have a system where the condenser section and the evaporator sections are located in different areas and have different fans and motors.

When you configure your evaporator layout is it better to place yoru supply air fan prior to the evaporator (so you push air thru the evaporator) or is better to place the fan after the evaporator (so you pull air thru the evaporator)?

I would think that there are benifits to each location but I wanted to see if there was a standard used in the industry or if you guys had soem suggestions on which setupt to use and why.

 

[atlas06]

Residential or commercial?
Residential units are typically Blow-thru type with the coil on top of the fan section.
Commercial units are typically Draw-thru units with fan after the coil, although there are applications out there for blow-thru in commercial.

For blow-thru, the condensate drain removal is not so critical, the trap is on the positive pressure side of the fan, so no risk of legionaire's disease.
The coil is sized for load plus fan heat.

For draw-thru, the coil and the cooling coil trap are before the fan, so sizng and installing the condensate trap peoperly is critical. You also need to account for fan heat for supply temperature to your space.

Summary:
Residential = Blow-thru.
Commercial = Draw-thru.

 

[MintJulep]

There is no "best" answer. Like most things, each has some good and bad points. These include:

Blow-thru:
Coil attenuates some fan noise from the discharge.
Higher fan noise at the inlet.
Coil face velocity may be very non-uniform.
Coil will be positive pressure wrt ambient. Help condensate drain.
Air moving thru fans and over motor will be at room conditions.

Draw-thru:
Coil attenuates som fan noise from the inlet.
Higher fan noise at the outlet.
Unit discharge velocity may be very non-uniform.
Coil will be negative pressure wrt ambient. Condensate drain actually requires thought. Air leak will draw in unfiltered air.
Air moving thru fans and over motor will be cold and near saturation.

 

[AbbyNormal]

if the load is highly sensible sometimes it is better to blow the air through the coil, especially on a bigger system with significant fan heat.

Take the "V" out of HVAC and you are left with a HAC(k) job.

 

[AbbyNormal]

if the load is highly latent, needing reheat, a draw through fan gives you some reheat

Take the "V" out of HVAC and you are left with a HAC(k) job.