Altitude and Coil Sizing in Trane Trace

[John_187]

Hello, this is a trivial, age old question, but I just want to confirm that HVAC COOLING equipment should be oversized due to altitude? Trane TRACE does not seem to oversize cooling coils due to altitude. Obviously it requires a higher CFM of airflow to deliver the same amount of heating/cooling. I may have to manually mark up a Trane Trace report because Trace does not automatically upsize the cooling coil.

This seems like an obvious answer, but I recently stumbled on this below article, and have heard varying answers. Maybe the logic behind not needing oversized cooling at altitude is that the cooling LOADS
(sensible and latent) are also derated and thus it offsets the cooling supplied. However, that wouldn't make sense because the same logic would apply to heating.

http://www.gearypacific.com/docs/04 - How Does Altitude Affect HVAC Units.pdf

For heating with gas, there should be (2) derates correct? The gas heat output and the heat exchanger less dense air.

Thanks for any feedback

 

[lukaiENG]

most manufacturers typically have a threshold below which they don't de-rate. Typically around 3000 ft. anything above this and they should most definitely de-rate.

 

[GT-EGR]

There should be a global input in trace somewhere for altitude and the really important number in all this which is air density.

The load calc should be done the same, but it takes more volumetric airflow to deliver the cooling because cooling capacity is actually based on the mass of air that you move (along with the temperate difference). So your mass of airflow would be the same anywhere, but then at high altitudes air is less dense, so you need more of it.

Not sure about the gas derate question, but you do run into the same issue with heating and cooling. That other derate I think you just mean combustion efficiency, which you always have to consider.

 

[DMaxwell]

Nortek will build your unit custom to location/elevation. All of these parameters are taken into account there.