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drop in absolute humidity when using HVAC:Template:Zone:PTAC

asked 2017-11-15 10:22:33 -0500

hullaballoo's avatar

updated 2017-11-15 13:39:36 -0500

Hi everyone! I am simulating an existing building with a cooling split unit, using HVAC:Template:Zone:PTAC with a SingleSpeedDX with no dehumidification unit added. However, when I look at the results, there is a huge drop in absolute humidity indoors compared to outdoors (about 10g/m3). Can anyone explain me why or how can I avoid that?

Thank you in advance!!

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answered 2017-11-15 10:29:18 -0500

A DX cooling coil removes both sensible (temperature) and latent (moisture) energy from the air stream. Water cooling coils also have this same property. When using a cooling coil in your simulation roughly 25% of the energy transfer will be moisture. So the result will be that the indoors are dryer than outdoors.

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Thank you for your answer! Do you know if there is any way to simulate a cooling unit which removes only the sensible energy and not the latent?

hullaballoo's avatar hullaballoo  ( 2017-11-18 12:02:51 -0500 )edit

Well, I've never tried this but you could make the SHR = 1. You must ensure that the total capacity and air flow inputs result in a supply air condition that is on the psychrometric chart (i.e., outlet air RH < 100%).

  1.0,                !- Gross Rated Sensible Heat Ratio
rraustad's avatar rraustad  ( 2017-11-20 07:46:09 -0500 )edit

Thank you now it works just fine!!

hullaballoo's avatar hullaballoo  ( 2017-11-24 12:10:09 -0500 )edit

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Asked: 2017-11-15 10:22:33 -0500

Seen: 124 times

Last updated: Nov 15 '17