New Thoughts on basement mildew

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Hi,
Various mags have some new products to use on floor and between wall and insulation to help basement not trap moisture. I suppose by nature, some moisture is there because the basement wall is under ground.
Are these new products hype, or do they provide some serious improvement?
Anyone have experience with these new products or ideas of their own on some of the not seen prep work which must go on before you re-finish the basement?
Thanks.
J
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j wrote:

Nothing new there. It is an attempt to keep moisture from coming into the basement AFTER it already has come through the wall or floor.
In some cases it may work, but it is going to trap that moisture on the other side of the barrier and in many cases it will not help at all. It all depends on your problem.
Sorry but most of the time the only fix is to keep the water away from your foundation in the first place and second to provide additional ventilation or dehumidifiers.
--
Joseph Meehan

Dia duit
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The problem may be too much uncontrolled ventilation, esp in an older home with lots of air leaks or a slab with no vapor barrier.
Basement exhaust with a differential humidistat (a Smart Vent?) can use 100X less electrical energy than a dehumidifier, climate permitting. My hunch is that most do. A Key West house with no AC might be one exception.
Smart Vent's 12/19/2000 US patent no. 6,161,763 "Module-controlled building drying system and process" at http://www.freepatentsonline.com describes a controller connected to indoor and outdoor absolute humidity sensors. If outdoor air has a lower absolute humidity than indoor air, the controller turns on a ventilation fan. If outdoor air has higher absolute humidity than indoor air, it turns the fan off.
Oddly enough, this patent measures "absolute humidity" in grams/m^3 vs a humidity ratio in g/g, so it looks like the controller would turn on the fan with outdoor air at 95 F and 17.4 g/m^3 and indoor air at 80 F and 17.5 g/m^3, even though cooling 1 m^3 of the 95 F air would lower its volume to (460+80)/(460+95) = 0.973 m^3 and raise the absolute humidity to 17.4/0.973 = 17.9 g/m^3, so this would add moisture to a house.
As an alternative to "absolute humidity sensors" or calculations, we might mount an RH sensor on each side of a single pane window or a steel plate and insulate the plate indoors, except near the sensor, and turn on the fan when outdoor RH is less than indoor RH.
Nick
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snipped-for-privacy@ece.villanova.edu wrote:

True, while less likely in my experience it is certainly possible and should be considered.
--
Joseph Meehan

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This came from a Humidex installer who said they help more with older houses.
Nick
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Nick, you scare me.
Move to South Carolina and try your idea here. Then after your house rots down, you can move back up north.
It does not matter what the RH differaece is unless the temperature is the same when you ventilate. If the humidity ratio(in grains of water per pound of dry air) is higher outside than it is inside, you DO NOT want to ventillate! If the humidity ratio is lower outside than inside, then ventilating MAY do the trick. Either way, you MUST be sure that the surface temperatures in the basement are ABOVE the dew point of the air present. If the air outside is dryer than the air inside, but the wall temperatures in the basement is still below the outside air dew point, ventillation WILL NOT HELP!!!!!!!!!
A dehumidifier will use more electricity, but is not likely to damage anything. Using fans with an improper control system can rot the walls out!!! The cost of repairing the walls will be MUCH HIGHER than the cost of the electricity saved!
In order to determine the proper fix for the OP problem, I would want to check the weathe data for his area, measure the wall temperatures over time with data loggers and measure the humidity inside and outside over time with data loggers. He will be safe, if a littel poorer with a dehumidifier, assuming he drains it outside or into a proper drain. Using your RH sensor scheme may destroy his house!!!
I can't see how you can recommend such an option without measuring the conditions inside and outside his house with data loggers and his wood moisture in the basement walls using a wood moisture meter.
You have lots of nifty formulas Nick, but seem to have no idea on proper practical application. Here in the "land of the midnight fungus", recommending ventillation to solve such a problem is downright irresponsible!
Please remember Nick, most people with mosture problems do not live in dry climates! Therefore dehumidifiers are usually a better solution to high humidity than exhaust fans.
By the way, if he installs a $250.00 dehumidifier instead of a $1,000.00 Humidex exhaust fan, the money he saves on equipment will be enough to pay for dehumidifier electricity for many, many years!! And his walls will be safe!
Please start recommending practical solutions that are climate specific, instead of your pie in the sky (unless it is cherry pie) control schemes requiring computers and more psychrometric knowledge than the homeowner is likely to ever possess.
Stretch
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No thanks. Altho houses in western NC seem cheap. BTW, this scheme might work in a reasonably airtight house that can store some dryth in Charleston, with w = 0.0166 on an average July day and w < 0.0100 from October through April. I could determine that with a little TMY2 simulation. You probably couldn't.

I'm not sure what you are saying or why you are saying it, but it seems to me that you are wrong. For instance, if a basement is 50 F at 70% RH and outdoor air is 40 F at 50%, it's time to ventilate. Perhaps you would like to clarify your claim. I also suggested a way to make a bit of indoor and outdoor the same temp so we could simply compare RHs as a measure of the humidity ratios. Sounds like you didn't understand that. You may be over your head and mired in old cut-and-dried HVAC techniques in this case.

That's what I said (with one L :-)

It will. The question is how often that happens and for how long, compared to how fast the house collects moisture and how much it can store. Looks like it works fine in Phila, with a max 75 wet hours in a row in a typical year.

Now think hard: if we ventilate when the weight of water in a pound of basement air is more than the weight of water in a pound of outdoor air, we are removing water from the basement. If you think we are adding water, where do you think it comes from?

I disagree (with one L and an "are" vs "is" :-)

I suggest using fans with a proper control system.

That might see you into retirement.

Nope. The patent described a technique for drying out flood-damaged houses.

I know... Pity.

Recommending dehumidifiers to solve such a problem is downright irresponsible!

I disagree (about moIsture :-)

Unlike you, I've been doing so all along, with detailed weather data.
Nick
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Nick, The weather data is nice, but only available for selected cities. The weather data says 78 degrees wet bulb here in Myrtle Beach, but I commonly MEASURE over 80 degrees wet bulb.. Yesterday it was 83 degrees wet bulb in Murrells Inlet for 3 hours. Murrells Inlet is just 15 miles south of Myrtle Beach, SC.
BTW, I am glad you are a good speller.

I disagree (with one L and an "are" vs "is" :-)
You can disagree all you want, the walls will still sweat!
Stretch
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A time to stop basement ventilation, but unimportant in the long run.
Nick
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Nick,
Based on long term data logger use here, the times when ventilation will work is from the middle of Otober to the middle of March. Basically late fall, all winter and early spring. During that time, you may need to worry about freezing pipes.
The further south you go, especially in coastal areas, the more extreme conditions are.
Stretch
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We've been through this before. NREL says Wilmington NC has a 63.4 F deep ground temp, with these long-term averages...
Apr May Jun Jul Aug Sep Oct
Avg daily max 74.0 80.8 85.4 88.5 87.6 85.2 76.9 F humidity ratio 0.0080 0.0114 0.0147 0.0168 0.0167 0.0142 0.0099 vapor pressure 0.380 0.539 0.691 0.787 0.782 0.668 0.469 "Hg dew point 56.7 60.6 67.7 71.5 71.3 66.7 56.7 F

No. During that time, we'd move air near the basement floor upstairs vs outdoors to store dryness in the basement.
Nick
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Nick,
My MEASURED data does not agree with your book data. Myrtle Beach is only about 50 miles south of Wilmington, NC; so the data should be close. Who is NREL anyway? Spell out and don't use abbreviations so much.
Here in the summer the normal dew point is 75 to 82 degrees. If you used real data nstead of old book data, you would get different results. Any one trying to dry out a basement or crawl space should MEASURE their local conditions any way.
Stretch
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Too bad. Perhaps you should measure and average for 30 years, like NREL.

Google is your friend.

I disagree. Short term measurements can mislead, and nearby long-term averages are sufficient, and less trouble.
Nick
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Nick, Here s data logger data from one day in June 2000.
Stretch
Date     Time    Temp     DP    RH (%)
06/17/00 00:22:17.0    78.88    74.58    87.2 06/17/00 01:22:17.0    78.53    74.72    87.6 06/17/00 02:22:17.0    77.7    74.46    88.9 06/17/00 03:22:17.0    77.27    73.78    88.9 06/17/00 04:22:17.0    77.09    73.34    87.6 06/17/00 05:22:17.0    76.83    73.1    88.9 06/17/00 06:22:17.0    76.48    73.22    89.3 06/17/00 07:22:17.0    77.83    74.02    87.6 06/17/00 08:22:17.0    77.75    73.9    87.2 06/17/00 09:22:17.0    81.53    75.6    82.3 06/17/00 10:22:17.0    82.28    75.96    81.4 06/17/00 11:22:17.0    84.47    77.34    79.5 06/17/00 12:22:17.0    85.6    76.84    74.7 06/17/00 13:22:17.0    86.73    77.54    74.7 06/17/00 14:22:17.0    87.59    77.42    72.7 06/17/00 15:22:17.0    84.02    75.92    77.6 06/17/00 16:22:17.0    87.27    76.58    70.7 06/17/00 17:22:17.0    93.54    80    65.7 06/17/00 18:22:17.0    85.46    76.72    76.1 06/17/00 19:22:17.0    81.04    74.74    81.8 06/17/00 20:22:17.0    79.46    74.96    86.3 06/17/00 21:22:17.0    78.58    74.86    88 06/17/00 22:22:17.0    78.62    75.3    89.3 06/17/00 23:22:17.0    78.8    75.16    88.9
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A single day is unimportant.
Nick
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This is Turtle.
Nick , Two question here. Nick would you stay in a house at 17C and 88% RH ?
If you could lower one of them and live there . Which one would you lower?
If you say you know the hvac business you will know exactly which one you want lower to get by.
TURTLE
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Hiya Turtle.

No. Too cold and moldy.

Neither.
Nick
20 CLO = 1'clothing insulation (clo) 30 MET=1.1'metabolic rate (met) 40 WME=0'external work (met) 50 VEL=.1'air velocity 60 PA=0'water vapor pressure 70 DEF FNPS(T)=EXP(16.6536-4030.183/(TA+235))'sat vapor pressure, kPa 80 DATA 62.6,88 90 DATA 71.689,88 100 FOR CASE = 1 TO 2 110 READ TA,RH 120 TA=(TA-32)/1.8 130 TR=TA 140 IF PA=0 THEN PA=RH*10*FNPS(TA)'water vapor pressure, Pa 150 ICL=.155*CLO'clothing resistance (m^2K/W) 160 M=MET*58.15'metabolic rate (W/m^2) 170 W=WME*58.15'external work in (W/m^2) 180 MW=M-W'internal heat production 190 IF ICL<.078 THEN FCL=1+1.29*ICL ELSE FCL=1.05+.645*ICL'clothing factor 200 HCF.1*SQR(VEL)'forced convection conductance 210 TAA=TA+273'air temp (K) 220 TRA=TR+273'mean radiant temp (K) 230 TCLA=TAA+(35.5-TA)/(3.5*(6.45*ICL+.1))'est clothing temp 240 P1=ICL*FCL:P2=P1*3.96:P3=P1*100:P4=P1*TAA'intermediate values 250 P508.7-.028*MW+P2*(TRA/100)^4 260 XN=TCLA/100 270 XF=XN 280 N=0'number of iterations 290 EPS=.00015'stop iteration when met 300 XF=(XF+XN)/2'natural convection conductance 310 HCN=2.38*ABS(100*XF-TAA)^.25 320 IF HCF>HCN THEN HC=HCF ELSE HC=HCN 330 XN=(P5+P4*HC-P2*XF^4)/(100+P3*HC) 340 N=N+1 350 IF N>150 GOTO 480 360 IF ABS(XN-XF)>EPS GOTO 300 370 TCL0*XN-273'clothing surface temp (C) 380 HL1=.00305*(5733-6.99*MW-PA)'heat loss diff through skin 390 IF MW>58.15 THEN HL2=.42*(MW-58.15) ELSE HL2=0'heat loss by sweating 400 HL3=.000017*M*(5867-PA)'latent respiration heat loss 410 HL4=.0014*M*(34-TA)'dry respiration heat loss 420 HL5=3.96*FCL*(XN^4-(TRA/100)^4)'heat loss by radiation 430 HL6L*HC*(TCL-TA)'heat loss by convection 440 TS=.303*EXP(-.036*M)+.028'thermal sensation transfer coefficient 450 PMV=TS*(MW-HL1-HL2-HL3-HL4-HL5-HL6)'predicted mean vote 460 PPD0-95*EXP(-.03353*PMV^4-.2179*PMV^2)'predicted % dissatisfied 470 GOTO 490 480 PMV999!:PPD0 490 PRINT TA,RH,PMV,PPD 500 NEXT CASE Temp RH PMV score % people dissatisfied
17 C 88 -1.119888 31.42974 22.04945 88 7.560884E-06 5.00000
Innova AirTech Instruments has an excellent comfort web site... http://www.impind.de.unifi.it/Impind/didattica/materiale /'microclima/innova/thermal.htm
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This is Turtle.
NO Nick , you had to stay in this house but which would you lower or raise if you could change just one of them. You can only raise or lower just one of them and not the other. Which one would you raise or lower ?
TURTLE
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Stretch, All Nick knows is books and numbers..... He knows nothing of real life. Remember the old Far Side cartoon whith the scientists looking at the chalkboard that is filled with figures and calculations on both ends and in the middle has some words "Then a miracle happens" ?? Thats Nick

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Noon wrote: Stretch, All Nick knows is books and numbers..... He knows nothing of real life.
Remember the old Far Side cartoon whith the scientists looking at the chalkboard that is filled with figures and calculations on both ends and in the middle has some words "Then a miracle happens" ?? Thats Nick
Noon, guess your right. Arguing with Nick is like mud wrestling with pigs. The pigs love it and you get all dirty :-)
Stretch
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