Winter Humidity, commercial 1

[MechGuy22]

Going to evaluate a newly renovated commercial building. The building has two sides. One half is fine, the other is experiencing elevated humidity somewhere around 60%. I haven't visited the site yet but my gut feeling is that the building is leaky and they probably dont have the thermostat low enough. Any opinions or input? Any opinions on how to fix the problem?

 

[KiwiMace]

There doesn't appear to be a problem, what is wrong with 60%?

 

[MechGuy22]

I don't think its a problem, especially during the winter time when the AC isn't running at all.

 

[imok2]

The recommended level of indoor humidity is in the range of 30-60%.

 

[tys90]

Depends on the outdoor temperature. Say the indoor temp is 70F and 60% RH. If the outdoor air temp is low enough that an inside surface of a window drops to just 55F you will see condensation, which is never good.

It's a common problem with hospitals in cold climates because when humidity drops below 30% there is a strong correlation to increased health problems. So they add moisture to the air. However, even at 70F and 35%, northwest facing window's temperature can drop low enough to cause condensation/frost on the inside of the window if the window does not have direct heat (air or radiation).

 

[mauricestoker]

I would recommend looking at humidistats and humidifiers, if your HVAC is provding humidification. If you have 60% RH inside, and typcially low outside RH for heating season(typically the reason to humidify) then I would not think that outside RH is causing your problem. Raising the temperature shouldn't be noticeably impacting the indoor RH, unless you have condensate running down the walls onto perimeter heaters. Recommended indoor RH is 30-60%, which I usually take to mean heating season humdify to minimum 30%, cooling season dehumidify to 60%.

 

[MechEngNCPE]

To solve this problem, reset the supply air temperature after the cooling coil to 52 degrees, it is probably set at 55 or 57. This will de-humidify the air going into the space. Review your phsychrometric chart for what the unit is doing.

 

[KiwiMace]

tys90 - OK, I agree, but that is a problem with the windows, not with the humidity.

 

[ChrisConley]

I can't see a leaking building being the problem. In the winter leakiness would reduce your indoor RH (unless your winter conditions are above 70F, at that point I'm going to consider moving there).

If it is real winter, and the space is 60% RH it sounds like there is a shortage of ventilation air. Lowering t'stat temperature will increase the _relative_ humidity in the space.

Without active humidification, the only latent load in the winter should be people (or a fountain I'm sure you would have mentioned). At a dewpoint of anything below 55F code required ventilation should have no problems keeping the indoor humidity below 50%.