Zeus 46 wrote: "19W total possible error"
I think it is much less.
the variation of Cp with humidity is very small (less than or equal to 4%) at 20C and 35 C
Cp: the variation in Cp is shown in the attached graph
for 20 C from 1.006 to ~1.01,( for 0%RH to 100%RH)
for 35 C from 1.008 to ~1.04 (Tsilingiris).
In addition the variation in density OPPOSES the Cp effect ( the fan is blowing volume rather than kg??).
Density: the variation in density is shown in the attached graph.
for 20 C from 1, to ~ 0.98
for 35 C from 0.96 to ~0.93 (engineeringtoolbox.com)
I calculate that relative to dry air at 20 C , 100%RH at 35 C has a combined 'effective' change in specific heat to ~ 96%.
How does this relate to the Joules calculation (e.g Pg 17, 152 Mj) ?
4% of 152MJ is 6MJ potential error due to the change in humidity from 0% to 100%.
I doubt whether the ambient humidity was so great as 100%. so the potential error is likely to be less than 4%
In addition the inlet and outlet temperatures were not 35 deg.,but 25 and 33 max, so the potential error is likely to be less than 4%.
Summary: Potential variations in air density/specific heat due to humidity are insignificant compared to the magnitude of the calculated MJ values.