DIY Dehumidifier

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I realize that I am not actually talking about a dehumidifier.
My house suffers from too much humidity. The wood floors my DH installed (his trade) are beginning to buckle. So the situation has now become somewhat critical.
As I understand it I should build able to build basically an exhaust fan that is controlled by humidity.
But I have no clue exactly how to go about it. I intend initially to fit it into a window (similar to the way a window air conditioner is installed in a window). I don't know where to obtain the fan (get a bathroom exhaust fan and rip the guts out?) and I definitely don't know where to get the humidity control.
Any help?
Take care, Melody
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Melody,
The controller you want is called a humidistat. You can buy it at most Heat and AC stores but these stores may not sell retail. I'm not sure that your plan will work however. First, why do you think that humidity is causing problems? Have you measured the humidity? A cheap hygometer can be bought at Radio Shack for about $30. I would think that an average humidity above 70% would be needed to cause problems and you should be seeing mold and mildew as well. Second, Your plan is the replace the air in your house with air from outside so measure the humidity outside. Third, figure out where the source of the humidity is and try and fix the problem. Finally, if all else fails go with your fan, though AC or a dehumidifier would be much better. You'll need a whole house fan such as a large attic fan wired to the humidistat rather than a bathroom vent fan. All in all I think that one fan would be fairly expensive and also noisy.
Good luck, Dave M.
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DH is a hardwood flooring guy... been in the business for over 26 years. He says the problem is the humidity. That's why we have a hygrometer on every floor. :) This morning it was 51% on the top floor and 64% in the basement. It's never been that high. DH says that for hardwood floors it's best to keep the humidity around 35-40%, even lower if possible.
At one point DH was wanting a Humidex - which is just a big exhaust fan hooked up to a humidistat but for the wonderful price of like over $1K.
We have someone coming out tomorrow to see about a whole house dehumidifier hooked up to the central HVAC. I suspect it will be mega bucks and I'd be happier with something less expensive that would do the job.
The AC in the house is geothermal and doesn't seem to pull as much moisture out of the air as a regular system.
Take care, Melody
David Martel wrote:

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Thank you for explaining who DH is. I was wandering ... Dear Husband or Deceised Husband but did not want to ask. :<)) MG

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Sure, if it's less humid outdoors, in the absolute sense, ie if wo < wi, ie ln(Ro/Ri) < 9621(1/(460+To)-1/(460+Ti)). For example, if it's 70 F with 80% RH indoors and 80 F outdoors, ventilate when Ro < 0.8e^-0.336 = 0.57, ie the outdoor RH is less than 57%. This could use 100X less energy than a dehumidifier with a compressor. For efficient house heating and cooling, you'd want to ventilate at night in summertime and during the day in wintertime, every few days, when outdoor air happens to be dry.

You might put Lasko's 2155A reversible window fan (2470 cfm, 90 W, $53 from Ace hardware stores) in a partition wall that divides the house into two "airtight" spaces and run it whenever the house RH exceeds 50%, along with the calc above, and reverse from time to time to turn all the exterior house wall cracks and crevices into efficient bidirectional heat exchangers. You can do this automatically with a repeat cycle timer like Grainger's $83.90 2A179 (with its $4.26 5X582 socket), with adjustable off and cycle times from 1.2 seconds to 300 hours.
Herbach and Rademan (800) 848-8001 http://www.herbach.com sell a nice $4.95 Navy surplus humidistat, their item number TM89HVC5203, with a 20-80% range, a 3-6% differential, and a 7.5A 125V switch that can be wired to open or close on humidity rise.
We may see a wireless home automation controller that can do all this and more automatically at the U Mass DOE Decathlon contest house on the Washington DC Mall in October :-)
Nick
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Melody,
It depends on where you are. If the air outside has a higher absolute humidity than the air inside, the fan will make it worse. To determine that you need a sling psychrometer and a psychrometric chart. In the humid south, what you are suggesting would be a very bad idea, because the air you blow out creates a vacuum inside the house. Then humid outside air is sucked in to the house to replace the missing air and the humidity goes up!
Stretch
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Or a calculator, or a home automation computer.
Nick
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Nick. a calculator or computer will not measure wet bulb or relative humidity, but once the data is collected could convert it with the proper software. Paul Milligan has software to do that. But most people need someone with a strong HVAC background to determine what they need. Even most a/c contractors don't use psychrometrics enough to figure it out.
Stretch
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songofruth wrote:

I think you are doing this backwards. Don't think getting the humidity out, think keep it out. Where is the moisture coming from? If it is the humid air outside, you won't fix it with a fan.
--
Joseph Meehan

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I think I've seen line voltage dehumidistats from Graingers, or Johnstone.
If you find a dehum on the curb, you might be able to scavenge the dehumidistat off of it. I used to have a couple I'd pulled off old equipment.
Bathroom fan is good, or perhaps a window fan from Walmart.
--

Christopher A. Young
Learn more about Jesus
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Melody,
Are you certain you want to build and install this? Stating that you don't know what a humidistat is, how to obtain one or how to obtain a basic exhaust fan gives me the impression that you might be better off purchasing what you need and/or considering a different approach.
The exhaust fan approach works well only when the outdoor humidity is acceptable. Even then, you are exhausting indoor air which you may have paid to heat or cool. Whenever your exhaust system is running, you need to keep a window cracked open somewhere to relieve negative pressure in your house. Otherwise, you can greatly increase the radon levels in your home since the negative pressure will draw radon from the basement floor (this is especially bad if you have a sump pump or you have cracks in the basement floor or the basement walls.)
If your windows are open, then your device will give you the same inside humidity as the ambient (outdoor) air, which may not be desirable. If you are running AC, then you are getting the air dehumidified automatically by the AC and you probably don't need your device. If you are running the furnace, then you can also run a $100-$150 dehumidifier, which has automatic controls. If needed, you can also use a dehumidifier in a problem room while running the AC, if needed. (Usually, low humidity levels are the problem in furnace season.)
You seem intent upon reinventing the wheel but you don't sound like an experienced inventor. Buy what you need and avoid a lot of hassle. I know how to acquire the materials and build what you want, but I'd never consider wasting my time when the $100 dehumidifier would work better and be a much easier solution. If the initial cost was a concern, then I'd look for a dehumidifer in a garage sale, or better yet I'd grab one of the many that sit on the curb on trash day. One half hour cleaning the coils will usually restore one to excellent operating condition.
A dehumidifer uses more electricity per hour than an exhaust fan, but the dehumidifer is going to run a lot less than a fan set to run automatically by a humidistat which isn't aware of the ambient humidity. When you consider the heated or air conditioned air which is wasted by the exhaust fan, then the dehumidifer is going to be much less expensive to operate.
FYI - my next door neighbors have a humistatically controlled basement exhaust system that was installed by a basement waterproofing company. It is extremely rare to walk by the house and not hear it running. They paid a small fortune to have it installed (about $1000 !) and they are continuing to pay dearly as it runs even when the furnace or the AC is running. That's like leaving a front and back window open when running the furnace or the AC.
Good luck, Gideon
====== songofruth wrote in message
I realize that I am not actually talking about a dehumidifier.
My house suffers from too much humidity. The wood floors my DH installed (his trade) are beginning to buckle. So the situation has now become somewhat critical.
As I understand it I should build able to build basically an exhaust fan that is controlled by humidity.
But I have no clue exactly how to go about it. I intend initially to fit it into a window (similar to the way a window air conditioner is installed in a window). I don't know where to obtain the fan (get a bathroom exhaust fan and rip the guts out?) and I definitely don't know where to get the humidity control.
Any help?
Take care, Melody
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Gideon wrote:

hear, hear
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Thank you very much, Gideon. My gut feeling was that such a system would be practical only a certain amount of time during the year. The humidity is due to the general tightness of the house and (imo) the geothermal HVAC system not pulling as much moisture out of the air as a standard system would have.
We would have to manually disable the system I'm talking about during times of high humidity outside. The radon is of course a concern as well. Although I suspect that air would be drawn in thru the bathroom exhaust fans... but then could add the whole new problem of drawing in septic air since I suspect that our bathroom exhaust fans are tied into the waste system vents.
My gut feeling is that dehumidifiers are the only practical way to go and we just live with the expense of running them (they can add around $10-$20 a month around here to the electricity bill). We have a small 40pint portable unit in the basement that keeps freezing up. I wish I knew what size we would really need to do the job properly.
Take care, Melody
Gideon wrote:

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A properly controlled exhaust fan can dehumidify with 100X less energy than a dehumidifier.
Nick
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Do you have any links to information about these units being 100X more efficient? That would be interesting reading for me! Thanks, Rich
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I measured a new efficient dehumidifier, which produced 1.6 kWh of heat for every kWh consumed, ie 1 kWh from motors plus 0.6 kWh to condense about 2 pints of water, ie it consumed 0.5 kWh per pound of water, ie 5 cents/pint at 10 cents/kWh. A 70 F basement with 60% RH has humidity ratio w = 0.00947 pounds of water per pound of dry air. NREL says w = 0.008 for outdoor air on an average May day in Phila with a 62.9 F 24-hour average temp and 52.7 and 73.1 daily min and max. On an _average_ (vs dry) May day, we might run Lasko's 16" 2470 cfm 90 watt 2155A window fan ($53 from Ace Hardware) for an hour and remove 60x2470x0.075(0.00947-0.008) = 16.34 pounds of water at 90/16.34 = 5.5 Wh/pint, ie $0.1x90/1000/16.33 = 0.055 cents/pint, 91X less than the dehumidifier.
But some days are drier than average. Running the fan longer on dry days vs running it every day would be more efficient. We might invent a nice adaptive algorithm with the help of a simulation using TMY2 weather data.
And the outdoor humidity ratio (vs the RH) doesn't change much over a day, so we might as well run the fan when it's warmer outdoors if the house needs heat or when it's cooler outdoors if the house needs cooling.
Nick
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Stretch wrote:

A computer with sensors can. Check out the U Mass team house at the 2005 DOE DC Decathlon contest in October.

Radio Shack sells "data collectors." Here's some "proper software" for an $8 Casio FX-260 calculator: ventilate when Ro < Rie^(9621(1/(460+To)-1/(460+Ti)), ie Ro < Rie^(9621(1/(460+To)-1/530) if it's 70 F indoors. For example, if it's 70 F with 80% RH indoors and 80 F outdoors, ventilate when Ro < 0.8e^-0.336 = 0.57, ie the outdoor RH on the $20 Radio Shack display is less than 57%.

I've noticed that few a/c contractors have strong HVAC backgrounds.

Raleigh looks fairly humid, but a properly controlled exhaust fan might help from October (w = 0.0081) through May (w = 0.0099). July is dampest, with w = 0.0149 on a 78.1 F average day with 68.1 and 88.0 daily min and max. An "airtight" house with 15 cfm of natural air leakage (vs. 2.5 cfm in Canada) and w = 0.0120 indoors would need about 24hx60x15x0.075(0.0149-0.0120) = 4.7 lb/day of dehumidification from air leakage plus about 2 gallons per day from human activities (Andersen's estimate for a family of 4), about 21 lb/day.
On an average July day, 1920 Btu/ft^2 falls on the ground and 750 falls on a south wall in Raleigh. We might have an EPDM rubber liner with a passive greenhouse-type solar still with shallow LiCl lakes separated by dry EPDM beds to act as water collectors and parasitic air heaters, like this, viewed in a fixed font like Courier:
| 2' | carbo poly s nate flat p clear clear a flat c poly nate... e carbo epdm LiCl r lake epdm heater dry bed epdm epdm 2x4 epdmepdmepdm 2x4 epdmepdmepdmepdmepdmepdmepdm 2x4 epdm --------------------------------------------- top of SIP ------
(What's a good lake to heater area ratio?)
How many square feet of 80 F LiCl solution (precooked to 160 F) are needed to remove 20 pounds of water from 80 F house air with w = 0.012 in 12 hours? Here's a 9-pound calc for Miami, based on some crude assumptions:
1) The LiCl still operates at a constant temp for 12 hours per day. 2) The solar energy that enters the R1 glazing with 90% transmission equals the sensible and latent heat energy needed for concentration. 3) The solution cools to 25 C at night. 4) The solution gains heat like an ASHRAE pool loses heat.
The next step might be a simple TMY2 simulation.
10 A1.7409'LiCl vapor pressure constants from the 1993 Hawlader paper 20 A2=-.065536 30 A3=-8.2416E-04 40 B1=-4675.4 50 B2=+29.31 60 B3=+.66911 70 C172690! 80 C2=-1689.8 90 C3=-187.1 100 TA.8'average ambient August temperature in Miami (F) 110 SG70'average August sun on ground in Miami (Btu/ft^2-day) 120 H'distillation day length (hours) 130 W=.0176'average ambient August humidity ratio in Miami 140 PV%.4*29.921/(1+.62198/W)'ambient vapor pressure (mmHg) 150 P=9'dehumidification load (lb H2O/day) 160 FOR TC` TO 90 STEP 10'solution temp (C) 170 TK'3.1+TC'solution temp (K) 180 C+B1/TK+C1/TK^2-LOG(PV)/LOG(10) 190 B+B2/TK+C2/TK^2 200 A+B3/TK+C3/TK^2 210 CONC=(-B-SQR(B^2-4*A*C)/(2*A))'equilibrium soln conc (wt%) 220 TF=1.8*TC+32'solution temp (F) 230 CONCSURF00*P/(.9*SG-H*(TF-TA))'LiCl surf needed for conc (ft^2) 240 TK)8.1'solution temp (25 C) 250 AP+A2*CONC+A3*CONC^2 260 BP+B2*CONC+B3*CONC^2 270 CP+C2*CONC+C3*CONC^2 280 PVC^(AP+BP/TK+CP/(TK^2))'vapor pressure at 25 C (mmHg) 290 PVI).921/(1+.62198/.012)'indoor vapor pressure ("Hg) 300 PVL=PVC/25.4'LiCl vapor pressure ("Hg) 310 DRYRATE=.1*(PVI-PVL)'lb/h/ft^2 H2O (like an ASHRAE pool) 320 DRYSURF=P/(12*DRYRATE)'LiCl surface needed to dry P lb H2O in 12 h (ft^2) 330 PRINT TC,CONC,PVC,DRYSURF,CONCSURF 340 NEXT
still solution LiCl Pv drying concentrating temp (C) conc (wt%) (mmHg) surf (ft^2) surf (ft^2)
60 39.15389 5.493444 21.42437 9.927201 70 45.89019 2.75522 16.3801 13.03215 80 52.33653 1.244954 14.49746 18.96333 90 58.57794 .5091767 13.72873 34.80277
If the still temp is too low, it looks like we need lots of drying surface. If it's too high, we need lots of concentrating surface. A 70 or 80 C still temp seems good...
Nick
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Just curious, are you a high school student that happen to be doing a science project on this subject?
snipped-for-privacy@ece.villanova.edu wrote:

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Possibly. Are you a nubile senior with similar interests? :-)

That's a Clausius-Clapeyron approximation.
Nick
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Have you been voted most boring nerd on campus yet?
====================== snipped-for-privacy@ece.villanova.edu wrote in message ... Stretch wrote:

A computer with sensors can. Check out the U Mass team house at the 2005 DOE DC Decathlon contest in October.

Radio Shack sells "data collectors." Here's some "proper software" for an $8 Casio FX-260 calculator: ventilate when Ro < Rie^(9621(1/(460+To)-1/(460+Ti)), ie Ro < Rie^(9621(1/(460+To)-1/530) if it's 70 F indoors. For example, if it's 70 F with 80% RH indoors and 80 F outdoors, ventilate when Ro < 0.8e^-0.336 = 0.57, ie the outdoor RH on the $20 Radio Shack display is less than 57%.

I've noticed that few a/c contractors have strong HVAC backgrounds.

Raleigh looks fairly humid, but a properly controlled exhaust fan might help from October (w = 0.0081) through May (w = 0.0099). July is dampest, with w = 0.0149 on a 78.1 F average day with 68.1 and 88.0 daily min and max. An "airtight" house with 15 cfm of natural air leakage (vs. 2.5 cfm in Canada) and w = 0.0120 indoors would need about 24hx60x15x0.075(0.0149-0.0120) = 4.7 lb/day of dehumidification from air leakage plus about 2 gallons per day from human activities (Andersen's estimate for a family of 4), about 21 lb/day.
On an average July day, 1920 Btu/ft^2 falls on the ground and 750 falls on a south wall in Raleigh. We might have an EPDM rubber liner with a passive greenhouse-type solar still with shallow LiCl lakes separated by dry EPDM beds to act as water collectors and parasitic air heaters, like this, viewed in a fixed font like Courier:
| 2' | carbo poly s nate flat p clear clear a flat c poly nate... e carbo epdm LiCl r lake epdm heater dry bed epdm epdm 2x4 epdmepdmepdm 2x4 epdmepdmepdmepdmepdmepdmepdm 2x4 epdm --------------------------------------------- top of SIP ------
(What's a good lake to heater area ratio?)
How many square feet of 80 F LiCl solution (precooked to 160 F) are needed to remove 20 pounds of water from 80 F house air with w = 0.012 in 12 hours? Here's a 9-pound calc for Miami, based on some crude assumptions:
1) The LiCl still operates at a constant temp for 12 hours per day. 2) The solar energy that enters the R1 glazing with 90% transmission equals the sensible and latent heat energy needed for concentration. 3) The solution cools to 25 C at night. 4) The solution gains heat like an ASHRAE pool loses heat.
The next step might be a simple TMY2 simulation.
10 A1.7409'LiCl vapor pressure constants from the 1993 Hawlader paper 20 A2=-.065536 30 A3=-8.2416E-04 40 B1=-4675.4 50 B2=+29.31 60 B3=+.66911 70 C172690! 80 C2=-1689.8 90 C3=-187.1 100 TA.8'average ambient August temperature in Miami (F) 110 SG70'average August sun on ground in Miami (Btu/ft^2-day) 120 H'distillation day length (hours) 130 W=.0176'average ambient August humidity ratio in Miami 140 PV%.4*29.921/(1+.62198/W)'ambient vapor pressure (mmHg) 150 P=9'dehumidification load (lb H2O/day) 160 FOR TC` TO 90 STEP 10'solution temp (C) 170 TK'3.1+TC'solution temp (K) 180 C+B1/TK+C1/TK^2-LOG(PV)/LOG(10) 190 B+B2/TK+C2/TK^2 200 A+B3/TK+C3/TK^2 210 CONC=(-B-SQR(B^2-4*A*C)/(2*A))'equilibrium soln conc (wt%) 220 TF=1.8*TC+32'solution temp (F) 230 CONCSURF00*P/(.9*SG-H*(TF-TA))'LiCl surf needed for conc (ft^2) 240 TK)8.1'solution temp (25 C) 250 AP+A2*CONC+A3*CONC^2 260 BP+B2*CONC+B3*CONC^2 270 CP+C2*CONC+C3*CONC^2 280 PVC^(AP+BP/TK+CP/(TK^2))'vapor pressure at 25 C (mmHg) 290 PVI).921/(1+.62198/.012)'indoor vapor pressure ("Hg) 300 PVL=PVC/25.4'LiCl vapor pressure ("Hg) 310 DRYRATE=.1*(PVI-PVL)'lb/h/ft^2 H2O (like an ASHRAE pool) 320 DRYSURF=P/(12*DRYRATE)'LiCl surface needed to dry P lb H2O in 12 h (ft^2) 330 PRINT TC,CONC,PVC,DRYSURF,CONCSURF 340 NEXT
still solution LiCl Pv drying concentrating temp (C) conc (wt%) (mmHg) surf (ft^2) surf (ft^2)
60 39.15389 5.493444 21.42437 9.927201 70 45.89019 2.75522 16.3801 13.03215 80 52.33653 1.244954 14.49746 18.96333 90 58.57794 .5091767 13.72873 34.80277
If the still temp is too low, it looks like we need lots of drying surface. If it's too high, we need lots of concentrating surface. A 70 or 80 C still temp seems good...
Nick
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