Humidity Issue 1

[KoolTemp]

I have a 7000 sg ft office building with a 20 ton cooling, 360 MBH heating RTU. RTU has an economizer and it is bringing in 1,635 cfm for O/A. Air distribution is to a VVT system. After a week of data logging recordings average a temp of 72F and an RH of 24%. Location is southern ohio and the system is maybe 5 years old.
Can anyone help or point me in the right direction to solving this issue, at a loss right now.
Thanks

 

[cdxx139]

Whats the issue? Low humidity? Its the winter, thats normal. Office building usually dont have humidifier's.

knowledge is power

 

[MintJulep]

And the outside conditions were?

The occupancy was?

Averages are nice, but is the average representative?

 

[KoolTemp]

Yes you are correct with the low humidity for winter but complaints from the office personnel: dry eyes, dry hands, static, etc...

outside conditions were mid 20's F during data collection time. the high temp in the building was 75 and low was 68. Occupied time was set on 72 F. RH high was 25% and low 23%. it was pretty consistent.

 

[MintJulep]

Install humidifiers or pass out eye drops and hand lotion.

 

[willard3]

Wet bulb/RH is waaaayyyyy too low. Get a psychrometric chart and some humidifiers.

 

[meloair1]

Is this a new problem? I can't imagine people going 5 years with 24% RH without complaining.

http://www.meloairinc.com

 

[DRWeig]

I can imagine it, meloair1.

I worked for a company that designed and sold humidity sensors, in Memphis TN. Winter humidity in the building on cold days <25°F averaged 15% RH. It would dip down to 12°F or so if the outdoor temperature got below 5°F.

Same in most of the buildings -- schools, churches, office buildings, retail stores, almost everything except hospitals. You just don't find humdifiers south of the 37th parallel. People don't usually complain, because they have experienced it in the winter all their lives. The designers hide behind the "usual standard of care in the community" principle. Of course, I guess you could consider the people who bring giant-size bottles of skin lotion to work are complaining silently.

Best to you,

Goober Dave

Haven't see the forum policies? Do so now: Forum Policies

 

[tys90]

Careful about over-humidifying a space during cold outdoor air temps. Anything above 30% is likely to bring condensation to windows and exterior doors, which is a worse problem than a little dry air. There's a reason that hospital guidelines have reduced the minimum allowed humidity ratio. 25% is completely normal when outdoor air temps are below freezing.

 

[KoolTemp]

We are sitting around the 23% mark and your saying be hesitant to go above 30% and stay closer to 25%? what else could be the issue? are the people complaining just complaining? There were a few complaint of static electricity but not compared to health complaints. Should i just handle this as a test trial and increase the humidity in 2% incriments?

 

[ElSid1]

Lower the temperature! This will bring the humidity ratio up. You mentioned some areas @ 68 while others were at 75 and a aet point of 72! Check the calibration on the T-Stats or lock them out. People will complain, but the placebo effect (people thinking they are controlling the T-Stat) works very well. In the desert southwest, I recommend 70F in the winter (that is also where I set my home thermostat). Most people who complain with it being dry are willing to put a sweater on to increase the RH (and it fits within the ASHRAE recommendations). Added benefit of reduced heating costs. I had this happen at ... of ALL places, a DOE administration building Insert sarcasm here <---

 

[tys90]

If it's a new building with perfect construction, great windows and doors you may be able to handle a higher humidity ratio before seeing condensation/frost on the windows. If you have the ability to humidify, then yes, increase in small increments and keep an eye on it. It's going to be related to the current outdoor air temperature though, so a "safe" humidity ratio at one indoor/outdoor temperature combination might not be safe at other temperatures.

The University of Minnesota developed a chart for corresponding indoor humidity ratio to outdoor temperature, assuming an indoor temperature of 70F and residential style construction. I will try to paste it here. They don't guarantee no condensation, this is just a guideline.

Based on a 70ºF interior room temperature, engineering studies established the following guidelines:

Outside Temperature Inside Humidity
20º to 40ºF Not over 40%
10º to 20ºF Not over 35%
0º to 10ºF Not over 30%
-10º to 0ºF Not over 25%
-20º to –10ºF Not over 20%
-20ºF or below Not over 15%

 

[EnergyProfessional]

an ERV may help to recover some of the humidity. It also reduces energy cost.

Humidifiers are maintenance nightmares and some stupid people occupants may just set them high and the you have mold all over.