[Shophound]

To the OP, do your children spend considerable time outside your own home, such as at school or outdoors? The air at school may be much drier than what you maintain in your home. And the outdoor air is obviously dry...it is what dries out our buildings in winter.

Your hardwood floors...I would want to take humidity readings right where the floor material is installed. Additionally, I'd want to know if any of these floors are over spaces that are not humidified, such as a basement or crawl space. Wood will always dry to the side of lower moisture content, and if it's through the subfloor, even with your home maintained at +40%RH, you could see movement in your hardwood.

I would also not depend solely on the Infinity thermostat for your humidity readings. Obtain some inexpensive humidity indicators from an electronic store or hardware store and place them in various rooms throughout the house. Monitor them over several weeks and log the results. You may be surprised by what your data indicates.

 

[Shophound]

Good stuff TB. If you have links or PDF's that list how much moisture various stuff in an average house puts out in an hour, and how to calculate those numbers against the square ft of a home, I would greatly appreciate it. I would like to quit speaking with my usual broard statements.

Tips, check out my data logging thread in the building science forum. TB posted a nifty little formula that can give you a general estimate of infiltration via monitoring indoor and outdoor air dew points, and understanding psychrometrics.

 

[Shophound]

Tips, I think you would benefit from a copy of the ASHRAE Handbook of Fundamentals. It has what you're looking for concerning typical sources of humidity inside a building. Also good is "Humidity Control Design Guide", published by ASHRAE.

Most moisture generation sources in a house, apart from infiltration where outdoor dew points exceed desired indoor dew points, are incidental. A 15 minute shower generates about 1.4 pounds of moisture. Cooking dinner can produce up to .68 lbs. of moisture. TB stated around .5 lbs. of moisture per person, combining persiration and respiration. One of the things I will be looking at in my long term data logging efforts is a running comparison between indoor and outdoor air dew points, and using TB's formula as part of the evaluation process. With the holidays I haven't yet redeployed the data loggers but will do so soon. What I've found so far is my house is now sufficiently tight enough that interior moisture generation stays sufficiently ahead of infiltration to where the house air does not become overly dry, as it once did. TB's formula can be used to derive a rough estimate of infiltration in CFM based on the delta between interior and exterior grains of moisture. I'm hoping to refine my knowledge of this, and to see if it can be a handy tool for tracking CFM leakage during cold weather.

 

[Shophound]

Good advice, tipsrfine.

I just figured the infiltration cfm rate of my limited 800sf heated area.

Outdoors; 33-F; dew point 21-F; RH 61; 20.19 gr/lb air.

Indoors 64-F; 47% RH; 13.58 cu.ft./lb air.; 21.96 btu/lb air; 43.4 dew point; 42.41 gr/lb air.

Wind 5.8-mph from the South.

Got a very low 35.65 CFM of infiltration; & a very low 0.334 (ACH) air changes per hour.

That is below the 0.35 minimum ACH without mechanical ventilation.

You expert math guys can figure this, as I believe I screwed-up.
I don't like figuring stuff; where did I mess-up?

Formula: one occupant at 3500 grains moisture.
/(indoor air grains of moisture - outdoor air grains of moisture) *(figured at 13.58 cu.ft per lb air /60 min.per hour) = resultant cfm 2139 cu.ft. infiltration air / 6400 cu.ft. air.

Is the formula correct? Teddy Bear formula...

Can't believe infiltration would be that low; I must have made some errors?

I ran your numbers through the formula (which TB has separately confirmed I am using it correctly) and arrived at the same answer. What I might offer in response to your wonderment about that number is that you're looking at a snapshot of data. Provided you measured the indoor dew point, outdoor dewpoint, etc. at one fixed interval of time and then crunched the numbers. So your CFM may seem low...but at that moment of time, going by what you wrote above, it wasn't all that windy out. Here in TX in winter we can get 20-30 MPH winds with higher gusts from an arctic cold front of very dry, cold air, which I imagine might skew the CFM rates higher.

 

[Shophound]

The system is new last week!

Via your old ways of doing things (prior to this system's installation) were the humidity levels you kept in the house more effective for your children's skin conditions?

We replaced all the returns with hard piping. I watched them seal it tight. We opened all of the connections on the supply lines and used mastic to seal. House might be too tight now.

I doubt your house is too tight. If it was, you would not need a humidifier at all. Tight homes in winter can build up moisture inside if they are not ventilated adequately.

Slab is under the whole house. wood floor is finish in place installed to 3/4 inch plywood shot to floor, oak.

Is there a vapor barrier between the slab top and the plywood subfloor?

We have run humidifiers with integral gadges for past two years and they do read about 5% different from the Infinity controller.

I would not trust any gauge that is right next to where the humidity is being created. The Infinity controller is likely not adjacent to your new humidifier, so it reading lower is to be expected.

Should I ask my installer to take back the Infinity controller if i am going to use a separate humistat? What good is it? :\

No, you paid for the Infinity controller, and you'll want it come summertime to control humidity as well. You may be just now finding out (if what my hunch stated above proves correct) that your interior humidity levels weren't as high as you thought during your old way of doing things. The Infinity system is helping you to realize that, it seems.

Also, spouse is complaining about the low burner/fan combo says can't feel they house warm up when it is kicked on.

Are you using a setback on the thermostat? Also, your house, apart from your new ductwork, may have leakage and insulation issues that are effecting your comfort levels. The old way of doing things with heating systems was for the furnace to kick on and shoot out a lot of heat until it warmed things up enough to make the thermostat happy. In fact, these old systems actually would go past your thermostat setting (called "overshoot") and THEN shut down. Even after that the blower kept running to cool down the furnace, so you got even more heat until the blower shut down.

Your new system likely fires at lower rates until it just can't keep up anymore, and then ramps up. But it could also underserve certain rooms if these rooms have a higher heat loss than others. Was there any air balancing done of the supply ducts to each room?

 

[Shophound]

Shophound, thanks for running those numbers.

The psychrometric numbers should be on target.

I don't have a humidifier that works, needs parts I'd have to order, (I may get one), so when I enter the bathroom I run the shower, quite often, using cold water just to wet the tub area. Also, have a three speed Wind Machine 3300 fan I can use to speed up evaporation.

You, teddy bear, tipsrfine & many more are real interesting important experts in this important HVAC community.

Teddy bear is really into all the humidity factors & formulas, I had never thought of using that kind of formula to estimate infiltration ACH - air changes per hour.

Going back over your numbers above, I see how you arrived at .334 ACH. Using the same formula for info from TB's data loggers I ran last week, I arrived at .25 ACH for my 1,800 square foot/14,400 cubic foot dwelling for the snapshot data grab from the loggers. Meaning for that given set of conditions recorded and used for plugging into the formula, the .25 ACH is what was obtained. What I intend to do is hand pick a variety of indoor/outdoor conditions and run each through the formula to note any variance in the ACH. That will happen after I redeploy the loggers and let them run for some time.

I expect to see the ACH number vary as indoor/outdoor temps and wind conditions vary, but my snapshot results seem to indicate I've made noteworthy progress for tightening up a 52 year old house. I also do not run a humidifier, and data from the loggers I've obtained so far indicate the indoor dew point, even during unoccupied times, does not go below 40 degrees, even with outdoor dew points in the 20's.

With the results I've obtained so far, it is causing me to think, as I've stated above, that I now have a pretty good handle on infiltration. So the next challenge is looking at the envelope itself to see where thermal bridging/thermal bypass issues might be, in order to improve the mean radiant temperature of the surfaces in any given room that compose of walls, windows, ceilings, and floors.

 

[Shophound]

Wow, your Air Changes per Hour look extremely good.

Well, when I subtract the estimated added shower moisture I get 42.84-CFM * 60-mins is 2570.5776 -cu.ft./hr infiltration / by 6400-cu.ft of heated air in home = 0.40-ACH. That seems a little more like it. You can't figure the indoor outdoor difference if you have extra moisture being added...

Example:
A .25 lbs per occupant (if active double it), for 2 occupants X .5 lbs X 7,000 grains) 3500 grs / (42.41 gr. inside air grains subtract – 20.19 gr. outside air grains) = 18.49 difference | 3500 / 18.49 difference = 189.2915 * (13.58 FT^3 * 60 min. per hour) = 0.2263333-FT^3 * 189.2915 = 42.84-cfm of air infiltration per minute * 60 = 2570.5781 cu.ft. air infiltration per hour / 6400 cu.ft. my heated air area = 0.40% ACH.

Since this is one of the easiest ways to estimate air infiltration rates per hour; here is the complete formula for anyone who wants to get the data & work it.

I might be able to provide some of you out with getting the psychrometic numbers to get your ACH results; furnish as much indoor/outdoor information as possible.

I've tried streamlining the formula in algebraic form like this (using my numbers as an example):

2([.5*7000]/[42-16]) * (13.5/60) = CFM infiltration

Remember PEMDAS...parenthesis, exponents, multiply/divide left to right, add or subtract left to right. The "2" in front of the left parenthesis is assuming TB's .5 lbs per occupant times two occupants.

The result gives you the number you need to crunch for ACH in reference to total enclosed cubic feet. At least that's how I'm seeing it. In my case, 60 CFM = 3600 CFH. Divide that into 14,400 cubic feet volume of enclosed space for my house (1,800 square feet * 8 foot consistent ceiling height) = 0.25 ACH. Houses that have variable ceiling heights will require more figuring to obtain a value for calculating cubic feet.

I have a feeling my ACH above is just a snapshot example, not a consistent standard my house enjoys. The data loggers will help me determine results under different conditions. I would expect higher ACH numbers when outdoor wind speeds are higher.