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# Why do IT Equipment Air Inlet Temperatures deviate from Supply Air Node Temperatures ?

My EnergyPlus model contains IT Equipment with Supply Air Node name =ZoneIN.

When outputting ITE Air Inlet DryBulb Temperature (HVAC System Type Step) and corresponding System Node Temperature ZoneIN (HVAC System Type Step) , these values however deviate in a way which is difficult to interpret, although the two output time series logically should be identical.

Can anyone explain why these two output variables differ, and why ITE Air Inlet DryBulb Temperature (HVAC System Type Step) has only a fraction of valid values as a time series with System Time Step. ? What is the underlying algorithm by which the output values are derived (mere averageing for skipped time steps is apparently not the case).

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From the Input Output Reference:

Air Inlet Connection Type Specifies the type of connection between the zone and the ITE air inlet node. The choices are: AdjustedSupply = This option is used to apply a recirculation adjustment to the ITE inlet conditions. If this option is specified, then the Supply Air Node Name is required and the air inlet temperature to the ITE will be the current supply air node temperature adjusted by the current recirculation fraction.

ITE Air Inlet Dry-Bulb Temperature is the temperature entering the equipment after adjusting for recirculation, so this will not be the same as the supply inlet node temperature unless the recirculation fraction is set to zero.

IT equipment is simulated at the zone time step (same as other internal gains such lights, people, etc)he, so the ITE output variables are all reported at the zone time step.

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