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Re: [EnergyPlus_Support] Purchased Air vs. PTAC

If the zone temperature is held at the same temperature in both cases, 
compare the zone humidity levels. You will probably find that the DX 
Coil maintains a lower zone humidity level which would probably account 
for the difference in cooling energy..You could also compare the 
humidity ratio of the supply air for each system. Does the DX Coil 
provide a lower humidity ratio? You could also report the supply air 
mass flow rate and enthalpy and calculate the delivered cooling energy 
as a check.

anarui.oliveira wrote:
>
> Hello all.
>
> If (for cooling only), maintaining all other parameters in a model:
>
> - a PTAC is fully set to autosize, and a simulation is run,
> - and then it is substituted by a simple Purchased Air configuration,
> for the exact same zone and thermostat,
>
> why is the "DX Coil Total Cooling Energy" between 1.5 to 4 times higher
> than the "Purchased Air Total Cooling Energy"?
>
> I know "Purchased Air" is a simplification, but since we're looking
> directly at the thermal loads, and not any efficiency-dependent
> consumption variable, where does this difference come from?
>
> Regards,
> Ana Rui.
>
>  

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