[Nuno Santos]

AHu whit mixing section and recovery wheel.

Hello I have a problem that I cant resolve.

I need to select a unit whit mixing section and a recovery wheel. Were do I put the mixing section ( before or after the recovery wheel)?

From the efficiency point of view were is more effective?

I can give temperatures and airflow if need.

If same one can help!!! Please try!


See attched files!

 

[Carnak]

Typically you would be transferring heat between an exhaust air stream and a freesh air stream. So what would you want to mix?

You want to take the outside air leaving the unit and mix it with return air in another system?

Surely you do not want to mix the outside and exhaust air on purpose.

 

[heatingman]

There would not be a mixing section, other than the recovery wheel section if you are using 100% fresh air, if you will not allways be pulling 100% fresh, then the supply blower section would be the mixing section.

 

[ChilledBeam]

You need to tell us what that application is before a configuration is recommended.

If you are recirculating 80% of the air and bringing in 20% outside air then you don't need a full CFM wheel, you only need to size a wheel for the 20% air you are bringing in and exhausting.

20% outside air is a pretty typical number for office buildings, etc.

Is the unit indoors or outdoors?

 

[Nuno Santos]

Hello

This is for a shopping center that only need’s cooling ( it’s in Portugal).

The units are going to work whit 75% of fresh air ( 34ºc) , the other 25% recirculation air (24ºc). By putting the mixing section and the recovery wheel we try to optimize the efficiency.

This is a unit whit 36000m3/h on the supply and 3200m3/h on the exhaust ( recirculation 9000m3/h)

The units are for outdoor, and they are around 50 units.

 

[atmosphere]

Following your return air from the grilles to the return duct , to the recirc. damper, then the wheel, then the exhaust blower drive then outside.

Following your outdoor air. Through the OD grille, then the filters,then the heat wheel, into the mixing chamber with the recirc damper above horizontally,then to the supply fan, next the evap. coil, hot gas reheat coil (if used) then elec.strip heat, or steam or HW coil, to the supply plenum, and into the space you go.

 

[atmosphere]

CO2 sensor in space drives the OD damper and the recirc. damper at the same time and percentage inversely.

 

[ChilledBeam]

How can your unit have 36,000 m3/h supply and be exhausting 3,200 m3/h and recirculating 9,000 m3/h???

If you bring in 75% fresh air you have to exhaust roughly the same amount, you will exhaust slightly less to maintain a positive pressure within the building to keep humidity out.

I'm assuming the units are rooftops?

 

[Nuno Santos]

How can your unit have 36,000 m3/h supply and be exhausting 3,200 m3/h and recirculating 9,000 m3/h???

If you bring in 75% fresh air you have to exhaust roughly the same amount, you will exhaust slightly less to maintain a positive pressure within the building to keep humidity out.

I'm assuming the units are rooftops?

Hi its 32000 m3/h ( not 3200 m3/h) its missing one zero!


Its a normal air handling unit whit only cooling. ( not rooftop)

 

[Nuno Santos]

Following your return air from the grilles to the return duct , to the recirc. damper, then the wheel, then the exhaust blower drive then outside.


Why do you say that configuration?

Think that for same estrange situation you need only to make recirculation, and you are not throwing air to the outside, (100 % recirculation) then the exhaust fan is out of the circuit, and the supply fan has to support all the pressure from the system ( need bigger motor). Or not?

 

[atmosphere]

So do you really want to know how you do away with that 75% requirement to save money on the power bill?

That is not so "estrange" of a situtation, just not a good idea.

If you keep the requirements, the customers will prefer shopping there.

 

[atmosphere]

Just looked at your drawing.
If you want to know where to put the recirc damper, it goes in the horizontal mullion cutout just to the right of the heat wheel.

 

[Nuno Santos]

Just looked at your drawing.
If you want to know where to put the recirc damper, it goes in the horizontal mullion cutout just to the right of the heat wheel.

Why not on the left side of the recovery wheel?

 

[atmosphere]

Wherever you like.

 

[Nuno Santos]

Are you shore that the efficiency is the same!?

 

[atmosphere]

I have new batteries (from China!) in my calculator( from Malaysia) and have calculated in my Brain (from Starkwether Avenue in Tremont, Cleveland, Ohio,USA 44101) that you are going to be getting a monthly check from Portugal Power and Light if you have accepted my design comments.