Condenser Intake and Discharge Duct Separation

[montoy]

We have a project that use an indoor condenser. The intake and discharge are ducted to a Building Louver. They share the same louver. The intake and discharge duct are 1 foot apart, edge to edge. Do you need to separate the ducts? If so, how many feet?

 

[marcoh]

Are they horizontally or vertically separated? Subject to the louvre design, but weather proof louvres will generally discharge the air down so you would prefer the have intake/discharge side by side.

 

[MintJulep]

You really want to avoid recirculation of the discharge into the intake.

If there is a prevailing breeze the discharge should be downwind.

If you can't count on a breeze then the discharge should have a sufficiently high velocity to achieve dilution quickly, and should be directed away from the intake.

 

[MechEngNCPE]

I think no less than about 3000fpm on the discharge would prevent short circuiting.

 

[berkshire]

If you can, put the discharge above the intake so that the more bouyant hot air can rise above the intake.
The louvres will deflect it down, but it will turn and rise again taking it away from the intake.
B.E.

 

[Drazen]

I doubt it can work as those few condensers who are constructed for indoor use mostly have high-flow/low pressure fans. Pressure is just slightly higher than with "ordinary" condensers, as they would be very noisy.

If you ever can, you should make additional louver to supply make-up air for room, and duct exhaust only.

 

[montoy]

@marcoh - they are horizontally separated, 12" apart. The Louver is 70"W x 25"H and our discharge and intake ducts are both 24"H.

@mechengncpe - "I think no less than about 3000fpm on the discharge would prevent short circuiting."
Do you suggest making the discharge duct a little bit smaller to achieve 3000fpm? Would that increase the noise?

 

[montoy]

@mechengcpe - discharge duct is 20x24. condenser air is 6000 cfm. velocity probably - 1800 fpm
intake duct is 30x24. velocity is 1200 fpm.

 

[AnotherEllis]

This can be made to work. Look at the equations governing air flow in suction.

An application engineer at Titus once told me when I was going through a similar issue that you can visualize it with a match. "It's easy to blow a match out... but you ever try to 'suck' one out?" <insert inappropriate but well deserved comments now>

Just get your discharge velocity up enough to satisfy the equation and you should be fine.

http://www.ellisconsultingengineers.com

 

[montoy]

@anotherellis - "equations governing air flow in suction", this is not the volumetric flowrate equation, right? can you please tell me what is that equation?

 

[imok2]

Intake and discharge louver can be in separate frames or, for a VertiCool ... same blade design and angle). The discharge louver blades should be ..... ASHRAE HVAC Applications Handbook - Building Air Intake and Exhaust. Design, Chapter 44 ... “System Effects, How Do They Impact The Performance Of A Fan?”
Found this:
The combination intake/discharge
louver design offers an advantage
over separate louvers because
it requires only one wall opening
which decreases installation costs.
However, the blades cannot be
of uniform configuration (i.e. the
same blade design and angle). The
discharge louver blades should be
angled to direct the airflow straight
out horizontally from the unit and
the intake blades should be angled
down at approximately 45°.

 

[Drazen]

I am not sure that high velocity by itself can solve the problem.

High velocities undoubtedly create effective dilution which is useful in many exhaust application, and even necessary in some.

In this particular case, however, one other aspect could be relevant - high velocity creates ejection effect.

Whatever jet pattern exhaust flow develops, there will be lateral streams and the one on side of intake lover could significantly reduce effective area of intake opening.

I am not sure whether HVAC Applications manual mentions it, but combined louvers were mostly related to limited flow applications