Balanced external static pressure question

[KYOnscuffle]

I have a 3 ton package heat pump system and have a question about External Static Pressure. The system list a max ESP 0.5 iwc. My measured ESP is .42 iwc, which includes 0.25 of the return filter. The thing I'm finding strange is the entire ESP is in the return duct, with the supply duct barely registering and back pressure unless I start closing down registers. Is this unbalanced situation an issue and why?

 

[Drazen]

When talking about duct pressure, you need to note specific location, it is different at each position on each duct. The closer you are to the atmosphere, the less pressure difference compared to atmosphere - and the final difference equals terminal unit pressure drop.

That by itself has nothing to do with balancing.

 

[willard3]

All you have to do to reach rating is have the correct air volume.

If your pressure is at or below rated pressure, the machine should work as cataloged......it doesn't care if the pressure drop is in the supply or return.

 

[KYOnscuffle]

Thanks for the responses. With this unit being a package system, the recommended location for testing ESP is in the ducts just as they leave or enter the the system.
At the pressures that I am measuring and referring to the blower performance data charts, the system should be delivering right at 1200 CFM with a clean filter, so it sounds like I can relax and not worry about the differences.
I just wasn't sure if the load on the blower would be less or more with all of the work being pulling and none pushing air through the system.

 

[willard3]

Consider the physics......how can it take more hp to pull than push the sqame load?

A brush-up in basic physics may be in order.