Determining Humidity...

copper kip

We are installing a hydronic system in a large custom home with a variety of floor coverings. A couple of the hardwood floor coverings have a required humidity of between 40-60% to keep the wood from buckling. How do you determine the relative humidity inside a building? We also live in a dry climate, what is the best way to monitor and regulate the humidity?

Steve K

Measuring Humidity

Well measuring is the easy part, pick up a psychrometer. That is a wet bulb and a dry bulb thermometer that is on a sling, once you swing it around you take the readings on each bulb and use the slide rule that it is contained within to arive at the % of relitive 'H'. Or pick up a digital type meter and take the reading without all the
hubbub. Adding humidity is done in the airstream of the A.C. system. Do a search in Grainger for both items.

Good Luck, Steve Kritzberg (TBS Controls)

Mark Hunt

Kip


Remember this.

Whether the building is dry or moist is COMPLETELY the result of how tight the structure is built. The HVAC system has 0, none, nanda, zero, zip, zilch, effect on it.

Stack effect 100%.

Mark H

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hr

An air system

may be needed to pump some humidity into the space, however, if you live in a dry climate.

Do you have cooling loads also?

hot rod

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Weezbo

Truck over to the Archives Room at the local University...

i'm gonna say sight unseen there is abouteverything you ever wanted to know about humidity control ,controlling That Space. to quote some body here Peace and tap it light.

Boilerpro_3

I disagree, Mark

If you have a forced air system with out of balance supplies and returns, you cause some areas to pressurize and others to depressurize. This will increase air leakage in those spaces, decreasing humdiity in the winter.

Also, at least around here, the typical practice is using joist spaces and stud spaces as returns. I can almost guarantee that outdoor air is being sucked into the system from air leaks at the sill from outdoors. I bet a huge amount of outdoor air is sucked in at the top plates on the walls where the drywall is attached. Air is just sucked out of the attic through the insulation. Until air tight duct systems are the norm and the supplies and returns are kept in constant perfect balance, Forced air is always going to have humdity problems because of the excessive air leakage it causes.

Also, the hot air stratification that tends to take place with steam radiators and convectors and nonmodulating hot water systems, especially with convectors or high temp radiation, increases air leadage. This stratification increases pressure at the highest point in a space (like you said, stack effect) and increases air leakage. Air exiting on top sucks in cold dry outdoor air from low in the space, reducing humidity levels.

One last interesting observation/ theory. When replacing a chimney vent boiler in a typical older house basement with a sealed combustion unit or one with a stack damper, I bet we are increasing the air leakage into the living space. The sealed unit or stack damper prevents the chimney from creating a low pressure point in the basement. This low pressure helped to counteract the stack effect through the home, so without it more cold air is drawn through the heated upper main level living spaces.

Just something to chew on, IMHO.

Boilerpro

copper kip

no ac system max temp. up here in the summer is around 90 deg. for two maybe 3 weeks.