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

asked 7 years ago

hullaballoo
63 ●2

updated 7 years ago

__AmirRoth__

4446 ●5 ●17 http://bleedinggreenna...

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!!

answered 7 years ago

rraustad

13924 ●82 ●13 http://www.fsec.ucf.edu/

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 ( 7 years ago )

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%).

Coil:Cooling:DX:SingleSpeed,
  1.0,                !- Gross Rated Sensible Heat Ratio

rraustad ( 7 years ago )

Thank you now it works just fine!!

hullaballoo ( 7 years ago )

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