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return air node enthalpy not matching plenum enthalpy

asked 2019-08-22 19:50:13 -0600

xchen's avatar

updated 2019-09-29 10:18:14 -0600

Hi I'm modeling a VAV air handling unit with zonal hot water reheat coil with 4 zones and plenum return.

I noticed the return air of the AHU has very low enthalpy (78F drybulb, 21.7 enthalpy and 13% RH). When I track it to the zone level, all room and plenum conditions looks normal (78F drybulb, 45-55% RH).

image description

78F dbt and 47.4% RH is about 29.1 for enthalpy. I don't understand why the condition can change so drastically between the plenum and the return air node (21.7 vs 29.1, 13.4% RH vs 47.4% RH). And it's typical for all room under the system.

Any inputs appreciated. I'm using openstudio v2.4.1.

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answered 2019-08-26 19:56:50 -0600

xchen's avatar

looks like the enthalpy output in the hourly eso does not include dry air @ 0°C. here's a post related,

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Asked: 2019-08-22 19:50:13 -0600

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Last updated: Aug 26 '19