Why is RH(relative humidity) so small?

asked 2016-12-19 05:02:31 -0500

poppo92
875 ●2 ●12

updated 2016-12-19 09:09:16 -0500

Hi everyone, I'm running energy simulation in OpenStudio, and these are the results of mean temperature and RH (%). The mean temp of the thermal zones is quite good, the most of the hours is between 68-76 F (without HVAC, only with internal gains and natural ventilation). But RH basically is very low (several hours between 30-35%). Does anyone have any suggestion? How can I encrease it and making it more reliable? PS. no hvac in the building

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answered 2016-12-20 06:27:24 -0500

Jim Dirkes
3424 ●25 ●15

You did not mention the climate or the time of year during which you see the low RH, however it is common for RH to be low in many climates during the heating season. As well, many climates (SW USA, for example) have low humidity year 'round.

Regardless, with no HVAC, there is no way to control it. (Unless you consider some sort of evaporative humidifier as "not HVAC")

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The cimate is the climate of Austria (cold). I can see from the RH chart that in winter the RH is between 60-100 %, and in summer time between 40-60 %. Is there an object in OpenStudio that can simulate a evaporative humidifier?

poppo92 ( 2016-12-21 09:42:34 -0500 )edit

Keep in mind that it is the outdoor RH which is 40-100%. Once you warm the winter air to 20C (indoors), RH goes down a lot. Summer RH will also change with the air temperature change from outdoor to indoor.

Jim Dirkes ( 2016-12-21 12:54:08 -0500 )edit

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answered 2016-12-22 13:21:36 -0500

Mike06
175 ●6

You could look at the "absolute" humidity and compare outdoors to indoors (it does not change with the temperature rise from outdoor to indoor). Use as an output humidity ratio of zone and of environment. Look at your internal humidity load: how many persons are there to provide moisture to the air?