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  #1   Report Post  
jay
 
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Default basement humidity (do I need dehumidifier and, if so, would this setup work well)

I live in Northern NJ. I'm beginning to monitor humidity levels in my
basement to determine whether or not I need a dehumidifier. Today, I put a
hygrometer and the relative humidity of my basement was around 66%. Today
was not warm enough to use AC, but I decided to turn the blower motor of my
furnace/AC system on, and since there are return ducts in the basement, the
added circulation caused the basement humidity to drop to around 59% after
leaving the fan on for an hour or more. If I shut the fan off for an hour
the humidity would rise into the mid 60s again. The humidity at the rest of
the house was still at the low 40% range.

If I can keep the basement humidity below 60% by simply leaving the fan on,
do I really need a dehumidifier?

Does leaving the blower fan on all the time use up too much electricity or
cause blower motor to wear out very quickly?

By the way, my basement is finished, and I don't want mold problems. If
you think I should get a dehumidifier to further reduce humidity, then I
think the only convenient logical place to drain the condensation would be
to install a T fitting into the existing narrow PVC A/C condensation drain
pipe. (and presumably some dehumidifiers have the ability to pump the
condensation upward through a tube which I would connect to the T fitting.
If I want to avoid having to empty out tanks, then is the setup I just
described a good setup?

(If so, then hopefully basement humidity would not be a problem during the
heating season, because the only practical location is within the furnace
room, and since the furnace room gets hot/dry when the gas furnace is
running, the dehumidifier would not function correctly during the winter
months. Presumably I would only need to use the dehumidifier in the warmer
months)

Thanks,

J.


  #2   Report Post  
Hopkins
 
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Uh, I wouldn't run the blower all the time.

Yeah, dehumidifiers are typically necessary during only the warm
months.

Where does the "AC condensation drain" go? I'm guessing there's no
floor drain.

The typical dehumidifier often has a small hose to allow water to drain
without emptying the tank, but there's no pump to pump the water out.
From what you've written, a T fitting shouldn't be a problem but it

needs to be close to the floor. Of course, you'll have to figure a way
to seal the hose-to-T connection.

  #3   Report Post  
Harry Everhart
 
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By the way, my basement is finished, and I don't want mold problems. If
you think I should get a dehumidifier to further reduce humidity, then I
think the only convenient logical place to drain the condensation would be
to install a T fitting into the existing narrow PVC A/C condensation drain
pipe. (and presumably some dehumidifiers have the ability to pump the
condensation upward through a tube which I would connect to the T fitting.
If I want to avoid having to empty out tanks, then is the setup I just
described a good setup?


I have a dehumidifier running in my Pennsylvania home basement in the
summer. If you have a clothes washer down there - you can run the drain
tube into the washer drain tube. That way you will not to empty the
tank. You will have to mount the dehumidifier high enough to drain by
gravity.
  #4   Report Post  
twfsa
 
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I run a dehumidifier in the summer as it seem to take the musty smell out of
the basement and mine is finished, and there is nothing wrong with running
the fan on the furnace constantly, mine runs 24-7 365.

Tom


"jay" wrote in message
news:TxHse.13367$Nx1.5087@trndny05...
I live in Northern NJ. I'm beginning to monitor humidity levels in my
basement to determine whether or not I need a dehumidifier. Today, I put a
hygrometer and the relative humidity of my basement was around 66%. Today
was not warm enough to use AC, but I decided to turn the blower motor of my
furnace/AC system on, and since there are return ducts in the basement, the
added circulation caused the basement humidity to drop to around 59% after
leaving the fan on for an hour or more. If I shut the fan off for an hour
the humidity would rise into the mid 60s again. The humidity at the rest
of the house was still at the low 40% range.

If I can keep the basement humidity below 60% by simply leaving the fan
on, do I really need a dehumidifier?

Does leaving the blower fan on all the time use up too much electricity or
cause blower motor to wear out very quickly?

By the way, my basement is finished, and I don't want mold problems. If
you think I should get a dehumidifier to further reduce humidity, then I
think the only convenient logical place to drain the condensation would be
to install a T fitting into the existing narrow PVC A/C condensation drain
pipe. (and presumably some dehumidifiers have the ability to pump the
condensation upward through a tube which I would connect to the T fitting.
If I want to avoid having to empty out tanks, then is the setup I just
described a good setup?

(If so, then hopefully basement humidity would not be a problem during the
heating season, because the only practical location is within the furnace
room, and since the furnace room gets hot/dry when the gas furnace is
running, the dehumidifier would not function correctly during the winter
months. Presumably I would only need to use the dehumidifier in the
warmer months)

Thanks,

J.



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jay wrote:

I live in Northern NJ. I'm beginning to monitor humidity levels in my
basement to determine whether or not I need a dehumidifier. Today, I put a
hygrometer and the relative humidity of my basement was around 66%. Today
was not warm enough to use AC, but I decided to turn the blower motor of my
furnace/AC system on, and since there are return ducts in the basement, the
added circulation caused the basement humidity to drop to around 59% after
leaving the fan on for an hour or more.


Not a big change. Did you warm the basement?
Removing moisture from materials can take a long time.

...The humidity at the rest of the house was still at the low 40% range.

If I can keep the basement humidity below 60% by simply leaving the fan on,
do I really need a dehumidifier?


Maybe not.

Does leaving the blower fan on all the time use up too much electricity or
cause blower motor to wear out very quickly?


I'd say so... maybe 400 watts, $400/year.

Then again, you might store dryth in the basement on dry days.
Kurt Kielsgard Hanson's 142 page catalog of sorption isotherms
as LBM technical report 162/86 under
http://www.byg.dtu.dk/publications/reports.htm
says concrete stores about 1% moisture by weight as the RH of the
surrounding air increases from 40 to 60%, and it weighs about 150 lb/ft^3,
so a 4"x1000ft^2 50K pound floorslab might store 500 pints of water as
the basement RH increases from 40 to 60%. Mold forms in about 2 weeks,
above 60% RH.

The catalog also says the equilibrium moisture content of some woods
is about 30% by weight of the RH of the surrounding air, so a 25 lb
cubic foot of dry hem-fir might weigh 28 pounds in 40% air and 30 at 60%,
after storing 2 pints of water. Paper and clothing also store water.

The calc below says outdoor air is dry enough to keep a house below 60%
at 70 F for all but 360 hours in NREL's TMY2 Typical Meteorological Year
in Phila, with at most 75 "wet hours" in a row near the end of July.

20 PH=.6*EXP(17.863-9621/(70+460))'house vapor pressure ("Hg)
30 WH=.62198/(29.921/PH-1)'house humidity ratio
40 DAYSTART=150'display start time (days)
50 DS=DAYSTART*24'display start time (hours)
60 RANGE=3000'dISPLAY RANGE (HOURS)
70 LINE (0,0)-(639,349),,B:XDF=640/RANGE:YDF=3.88
80 FOR TR=60 TO 80 STEP 10'temp ref lines
90 LINE (0,349-YDF*(TR-10))-(639,349-YDF*(TR-10)):NEXT
100 CFM=2470'whole house window fan cfm (Lasko 2155A)
110 OPEN "ecayear" FOR INPUT AS #1:LINE INPUT#1,H$
120 FOR H=1 TO 8760'hours of typical (TMY2) year
130 INPUT#1,MONTH,DAY,HOUR,TDB,WIND,TDP,IGLOH,SS,WS,NS ,ES
140 PA=.6*EXP(17.863-9621/(TDP+460))'ambient vapor pressure ("Hg)
150 WA=.62198/(29.921/PA-1)'ambient humidity ratio
160 PSET(XDF*(H-DS),349-YDF*(TDB-10))
170 'PSET(XDF*(H-DS),349-YDF*(TDP-10))
180 IF WAWH THEN WETSTRING=0:GOTO 230'dry hour
190 WETHOURS=WETHOURS+1'accumulate wet hours
200 WETSTRING=WETSTRING+1'accumulate wet string length
210 IF WETSTRINGWETMAX THEN WETMAX=WETSTRING'measure max wet string length
220 LINE (XDF*(H-DS),290)-(XDF*(H-DS),300)'mark wet hours
230 IF DAY=1 AND HOUR=.5 THEN LINE (XDF*(H-DS),349)-(XDF*(H-DS),345)
240 NEXT H
250 PRINT WETHOURS,WETMAX

wet hours per year: 360
longest wet string: 75

Nick



  #6   Report Post  
Mikepier
 
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Do you have windows in the basement? Opening the windows will allow air
to circulate and reomove some of the dampness and humidity.

  #7   Report Post  
 
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Mikepier wrote:

Do you have windows in the basement? Opening the windows will allow air
to circulate and reomove some of the dampness and humidity.


Or maybe add it.

Nick

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jay
 
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Do you have windows in the basement? Opening the windows will allow air
to circulate and remove some of the dampness and humidity.

Yes, there are windows, but opening them is not very convenient, and leaving
them open could worsen the problem if it is a humid day.

By the way, simply by keeping the blower motor of the heating/ac system
running continuously, the circulation of the air throughout the house, so
far, seems to be keeping the basement's relative humidity within the mid to
upper 50s (as opposed to sometimes creeping up into the mid 60s if the
blower motor is turned off). The humidity in the rest of the house is still
well below 50%.

Is a basement relative humidity level in the upper 50s too high if the goal
is to prevent potential mold/mildew in my finished basement?

Thanks,

J.


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Okoidogo@@hotmail.com
 
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What should be a resonable humidity level in the summer ?

On 18 Jun 2005 18:43:10 -0400, wrote:

Mikepier wrote:

Do you have windows in the basement? Opening the windows will allow air
to circulate and reomove some of the dampness and humidity.


Or maybe add it.

Nick


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Okoidogo wrote:

What should be a resonable humidity level in the summer ?


I'd say 60% max in the basement, to avoid mold.

Nick



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jay
 
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I'd say 60% max in the basement, to avoid mold.

Nick

So far I can keep the Basement's humdiity level below 60% as long as I leave
the blower motor on the Furnace/AC system turned on all the time. This
causes some of the basement air to circulate throughout the rest of the
house (with the rest of the house still having humidity below 50%).

Would I be better off with a dehumidifier rather than leaving the blower
motor on all summer?

Thanks,

J.


  #12   Report Post  
Stretch
 
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Normally running the furnace fan constantly to reduce humidity during
the summer is a bad idea. I did it in my house as a test, using data
loggers to measure and record relative humidity. When I ran the blower
constantly one summer, it raised the relative humidity 10% to 15% over
letting it run just when the compressor run. TThe extra relative
humidity is from water re-evaporating from the cooling coil and drain
pan.

But I live in Myrtle Beach, SC and humidity is a big problem here.
Since you are measuring the humidity in the rest of the house and it is
staying at an acceptable level. I would say that it is OK to continue
to do so. Just continue to monitor the humidity in the basement and
house. Do whatever works in your climate and your house. The furnace
blower should use less electricity than a dehumidifier.

Stretch

  #13   Report Post  
 
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I am running my dehuminifer at 45% humidity level in my basement, and I
am also in Northern New Jersey.

I have two things that I need to mention about the use of a
dehuminifer:

1. Seem like its air moving capability is not that great even at high
fan speed. I have a feeling that it is only dehuminifing the adjacent
area. This "may" be a problem if the basement is partitioned in
multiple rooms or closets. Honestly, I am not sure about this. After
using it for two years, I don't have any mildew problem in my basement
(I had mildew problem in my basement before I started using the
dehuminifer). I guess it is doing something good in my basement despite
my concern about its coverage and despite the fact that my basement is
partitioned into two large rooms (with opening between rooms) and with
two closets.

2. Running dehuminifer can generate enough heat that we can feel
uncomfortably warm in the summer even with reduced humidity level. This
is especially bad if we have an exercise room in the basement. You
"may" need to add air-conditioning in addition to using the
dehuminifer. Still, using the dehuminifer should be the first choice
over the use of air conditoning to reduce humidity level because I am
under the impression that the air conditioner will stop as soon as the
room temperatur has dropped down to the pre-set level regardless if the
humidity level is reduced enough or not (and basement tends to be
cooler than the rest of the house to begin with; hence the air
conditioner will only run for a short while and probably will not
dehuminify enough).

Jay Chan


jay wrote:
Do you have windows in the basement? Opening the windows will allow air
to circulate and remove some of the dampness and humidity.

Yes, there are windows, but opening them is not very convenient, and leaving
them open could worsen the problem if it is a humid day.

By the way, simply by keeping the blower motor of the heating/ac system
running continuously, the circulation of the air throughout the house, so
far, seems to be keeping the basement's relative humidity within the mid to
upper 50s (as opposed to sometimes creeping up into the mid 60s if the
blower motor is turned off). The humidity in the rest of the house is still
well below 50%.

Is a basement relative humidity level in the upper 50s too high if the goal
is to prevent potential mold/mildew in my finished basement?

Thanks,

J.


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jay wrote:

So far I can keep the Basement's humdiity level below 60% as long as I leave
the blower motor on the Furnace/AC system turned on all the time. This
causes some of the basement air to circulate throughout the rest of the
house (with the rest of the house still having humidity below 50%). Would
I be better off with a dehumidifier rather than leaving the blower motor
on all summer?


A dehumidifier would add significant heat to the house in summertime...

Here's a calc for the minimum basement slab temp needed to keep a basement
less than 60% RH for a typical year in Baltimore, using long-term monthly
weather data, assuming a fairly airtight house. It looks like the basement
has no problem staying below 60% in wintertime (months 1-4 and 11-12 below),
when outdoor air is dry and the 55.3 F ground supplies enough heat to make
the natural slab temp more than the min slab temp required for 60% RH, given
the moisture in outdoor air.

Psat = e^(17.8653-9621/(460+53.2)) = 0.413 "Hg at 53.2 F and 100% RH in
January, and the vapor pressure of outdoor air with a w = 0.0025 humidity
ratio is Pa = 29.921/(0.62198/w+1) = 0.120 "Hg, so RH = 100Pa/Psat = 29%,
approximately, for a slab that doesn't store moisture.

20 ASLAB=1000'slab area (ft^2)
30 RGRND=10'R-value of deep ground (h-F-ft^2/Btu)
40 TGRND=55.3'deep ground temp (F)
50 CLEAK=10'air leakage rate (cfm)
60 RHMAX=60'max basement relative humidity (%)
70 TAC=80'AC temp (F)
80 RAC=50'AC RH (%)
90 DATA 31.8,.0025,34.8,.0027,44.1,.0037,53.4,.0052,63.4,. 0083,72.5,.0115
100 DATA 77.0,.0134,75.6,.0131,68.5,.0106,56.6,.0070,46.8,. 0048,36.7,.0032
110 DIM T(12),W(12)
120 FOR M=1 TO 12'month
130 READ T(M),W(M)'average outdoor temp and humidity ratio
140 PA=29.921/(.62198/W(M)+1)'vapor pressure of outdoor air ("Hg)
150 TSMIN=9621/(17.863-LOG(100*PA/RHMAX))-460'min winter slab temp (F)
155 TSNAT=TGRND+(T(M)-TGRND)/(1/CLEAK+RGRND/ASLAB)*RGRND/ASLAB'nat slab temp
160 PRINT M,T(M),TSMIN,TSNAT
170 NEXT

month outdoor min slab natural slab
air (F) temp (F) temp (F)

1 31.8 34.03717 53.16364
2 34.8 35.98914 53.43637
3 44.1 44.13639 54.28182
4 53.4 53.22431 55.12728

The average daily max in May (month 5 below) is 74.2 F. A 66.2 F slab might
lose 24h(66.2-55.3)1000ft^2/R10 = 26K Btu/day to the ground, which might
come from a minimal 230 kWh/mo of indoor electrical use or a 90 W 2470 cfm
intake window fan running 26K/(2470(74.2-70)) = 2.5 hours per day, or less,
on a dry that's warmer and drier than an average May day.

5 63.4 66.21149 56.03636

It looks like AC will help for the next 3 months, with basement-house air
circulation, which would reduce the AC load. At 80 F and 50% RH, a 400 cfm
basement return would make the slab about 55.3+(80-55.3)(1/400+0.01)0.01
= 75.1. With Pa = 0.5e^(17.863-9621/(460+80)) = 0.524 "Hg indoors and Psat
= e^(17.863-9621/(460+75.1)) = 0.890 "Hg near the slab, RH = 100Pa/Psat = 59%
in the basement, approximately. The slab might give (75.1-55.3)1000ft^2/R10
= 1980 Btu/h of sensible cooling.

6 72.5 75.61597 56.86364
7 77 80.12378 57.27273
8 75.6 79.4524 57.14546

The average daily max in September (month 9) is 78.5. This might be another
ventilation month, or an air conditioning month, if it's warmer than average,
or a dehumidification month, if it's cooler.

9 68.5 73.23895 56.5

The average daily max in October is 67.3, so it's a dehumidification month,
with possible help from ventilation.

10 56.6 61.41242 55.41818

And we might do nothing again in months 11 and 12.

11 46.8 51.05957 54.52727
12 36.7 40.35092 53.60909

A TMY2 hourly simulation would show less energy use, since some days are drier
and/or warmer than average in winter and drier and/or cooler in summer. And
concrete can store lots of water, about RH/2K % by weight, in RH% air, and
it takes little additional house heat to reduce the basement RH and dry out
the concrete and desirably increase the house RH in wintertime. A 4"x1000ft^2
50K pound slab can slowly store and evaporate (0.03-0.01)50K = 1000 pints of
water as the RH of the basement air rises from 30 to 60% and falls back again.

Hour-by-hour smart ventilation controls that manage heat and moisture storage
in a basement might reduce the AC and heating load and eliminate the need for
a dehumidifier.

Nick

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The average daily max in September (month 9) is 78.5. This might be another
ventilation month, or an air conditioning month, if it's warmer than average,
or a dehumidification month, if it's cooler.


month outdoor min slab nat slab
temp (F) temp (F) temp (F)

9 68.5 73.23895 56.5

We might automatically change a $69 window AC from AC to dehumidification and
back by adding a box around the outside with a $50 2 W (Honeywell 6161B1000)
motorized damper with a hinge h at the top that opens for AC and closes for
dehumidification, with horizontal partitions p and one-way passive plastic
film dampers Di and Do on each side of the AC in the window mount flanges.
It might look like this in the AC damper position, viewed in a fixed font:

--------
ceiling |
|
| window
|
|
---|---------------------h---damper--- (AC)
| |. | .
| |.Do f c| .
| |. a o| = .
| | n n| .
| | d| .
| |--------p------|--p--.
| .| condenser | .
| Di.| inlet air | = .
| .| | .
------------------------- (dehum)
|
|
|
floor |
--------------

The exterior damper would close and the passive interior dampers would open
in the dehum (heat pump) position, as the condenser fan makes in-house air
pressure and flow above and out-house suction and flow below:

--------
ceiling |
|
| window
|
|
---|---------------------h............ (AC)
| |. | |
| / .Do f c| |
|/ . a o| = d
| | n n| a
| | d| m
| |--------p------|--p--p
| .| condenser | e
| Di. \ inlet air | = r
| . \ | |
------------------------- (dehum)
|
|
|
floor |
--------------

It might look like this from the inside:

| |
| window |
|-------------------------------------------------|
| ----- | | |
| | | | | |
| | | | | |
| | Do | | | |
| | | | | |
| | | | | |
| --p-- | AC | --p-- |
| | | | | |
| | | | | |
| | | | Di | |
| | | | | |
| | | | | |
| | | ----- |
| | | |
-------------------------------------------------

It might look like this from above:


--------------------damper-----------------------
| |
| |
| p |
| |
| |
| ----------------------------- |
| | | |
| | | |
| | | |
| | | |
| p | | p |
| | | |
| | | |
| | | |
| | AC | |
| | | |
| | | |
| | | |
| | | |
| | | |
| | | |
-------------Do-------------------------------------Di---------
| |
| |
-----------------------------

Nick



  #16   Report Post  
blueman
 
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writes:
jay wrote:

So far I can keep the Basement's humdiity level below 60% as long as I leave
the blower motor on the Furnace/AC system turned on all the time. This
causes some of the basement air to circulate throughout the rest of the
house (with the rest of the house still having humidity below 50%). Would
I be better off with a dehumidifier rather than leaving the blower motor
on all summer?


A dehumidifier would add significant heat to the house in summertime...

Here's a calc for the minimum basement slab temp needed to keep a basement
less than 60% RH for a typical year in Baltimore, using long-term monthly
weather data, assuming a fairly airtight house. It looks like the basement
has no problem staying below 60% in wintertime (months 1-4 and 11-12 below),
when outdoor air is dry and the 55.3 F ground supplies enough heat to make
the natural slab temp more than the min slab temp required for 60% RH, given
the moisture in outdoor air.

Psat = e^(17.8653-9621/(460+53.2)) = 0.413 "Hg at 53.2 F and 100% RH in
January, and the vapor pressure of outdoor air with a w = 0.0025 humidity
ratio is Pa = 29.921/(0.62198/w+1) = 0.120 "Hg, so RH = 100Pa/Psat = 29%,
approximately, for a slab that doesn't store moisture.

20 ASLAB=1000'slab area (ft^2)
30 RGRND=10'R-value of deep ground (h-F-ft^2/Btu)
40 TGRND=55.3'deep ground temp (F)
50 CLEAK=10'air leakage rate (cfm)
60 RHMAX=60'max basement relative humidity (%)
70 TAC=80'AC temp (F)
80 RAC=50'AC RH (%)
90 DATA 31.8,.0025,34.8,.0027,44.1,.0037,53.4,.0052,63.4,. 0083,72.5,.0115
100 DATA 77.0,.0134,75.6,.0131,68.5,.0106,56.6,.0070,46.8,. 0048,36.7,.0032
110 DIM T(12),W(12)
120 FOR M=1 TO 12'month
130 READ T(M),W(M)'average outdoor temp and humidity ratio
140 PA=29.921/(.62198/W(M)+1)'vapor pressure of outdoor air ("Hg)
150 TSMIN=9621/(17.863-LOG(100*PA/RHMAX))-460'min winter slab temp (F)
155 TSNAT=TGRND+(T(M)-TGRND)/(1/CLEAK+RGRND/ASLAB)*RGRND/ASLAB'nat slab temp
160 PRINT M,T(M),TSMIN,TSNAT
170 NEXT

month outdoor min slab natural slab
air (F) temp (F) temp (F)

1 31.8 34.03717 53.16364
2 34.8 35.98914 53.43637
3 44.1 44.13639 54.28182
4 53.4 53.22431 55.12728

The average daily max in May (month 5 below) is 74.2 F. A 66.2 F slab might
lose 24h(66.2-55.3)1000ft^2/R10 = 26K Btu/day to the ground, which might
come from a minimal 230 kWh/mo of indoor electrical use or a 90 W 2470 cfm
intake window fan running 26K/(2470(74.2-70)) = 2.5 hours per day, or less,
on a dry that's warmer and drier than an average May day.

5 63.4 66.21149 56.03636

It looks like AC will help for the next 3 months, with basement-house air
circulation, which would reduce the AC load. At 80 F and 50% RH, a 400 cfm
basement return would make the slab about 55.3+(80-55.3)(1/400+0.01)0.01
= 75.1. With Pa = 0.5e^(17.863-9621/(460+80)) = 0.524 "Hg indoors and Psat
= e^(17.863-9621/(460+75.1)) = 0.890 "Hg near the slab, RH = 100Pa/Psat = 59%
in the basement, approximately. The slab might give (75.1-55.3)1000ft^2/R10
= 1980 Btu/h of sensible cooling.

6 72.5 75.61597 56.86364
7 77 80.12378 57.27273
8 75.6 79.4524 57.14546

The average daily max in September (month 9) is 78.5. This might be another
ventilation month, or an air conditioning month, if it's warmer than average,
or a dehumidification month, if it's cooler.

9 68.5 73.23895 56.5

The average daily max in October is 67.3, so it's a dehumidification month,
with possible help from ventilation.

10 56.6 61.41242 55.41818

And we might do nothing again in months 11 and 12.

11 46.8 51.05957 54.52727
12 36.7 40.35092 53.60909

A TMY2 hourly simulation would show less energy use, since some days are drier
and/or warmer than average in winter and drier and/or cooler in summer. And
concrete can store lots of water, about RH/2K % by weight, in RH% air, and
it takes little additional house heat to reduce the basement RH and dry out
the concrete and desirably increase the house RH in wintertime. A 4"x1000ft^2
50K pound slab can slowly store and evaporate (0.03-0.01)50K = 1000 pints of
water as the RH of the basement air rises from 30 to 60% and falls back again.

Hour-by-hour smart ventilation controls that manage heat and moisture storage
in a basement might reduce the AC and heating load and eliminate the need for
a dehumidifier.

Nick


Not sure I understand this, but am I right in interpreting that you
are basically saying that a dehumidifier is going to be relatively
helpless against a cold slab with warm, humid outside air?
(Plus we have the added comlication of dampness (not puddles) seeping
in during rainstorms?

So if a large cold slab stores so much moisture, what is the best
thing to do?
- Heat the slab?
- Circulate *in* hot air from outside (even if it is humid) to
attempt to heat up the slab?
- ????
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m Ransley
 
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What nick is saying nobody will ever know as he advocates flooding your
basement floor in winter for humidity and shrink wrapping your house to
stop air exchanges. I use a basement dehumidifier it only ads a few
degrees of heat which I welcome as my basement is always cool. My
dehumidifier costs 3-4$ a month to run, a furnce fan running 24x7 would
cost me 35 $ a month.

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blueman wrote:

writes:


jay wrote:


...I can keep the Basement's humdiity level below 60% as long as I leave
the blower motor on the Furnace/AC system turned on all the time. This
causes some of the basement air to circulate throughout the rest of the
house (with the rest of the house still having humidity below 50%). Would
I be better off with a dehumidifier rather than leaving the blower motor
on all summer?


A dehumidifier would add significant heat to the house in summertime...


...am I right in interpreting that you are basically saying that
a dehumidifier is going to be relatively helpless against a cold slab
with warm, humid outside air?


It would work, if the air leakage is not too large. For instance, if C cfm
of outdoor air with wo = 0.0134 pounds of water per pound of dry air leaks
into a 55F 60% RH wb = 0.0051 Baltimore basement on an average July day,
a 40 pint per day dehum could keep up as long as 24hx60C0.075(wo-wb) 40,
ie C 45 cfm, or more, if the dehumidifier and the incoming air warm the
basement, BUT that uses lots of electricity and makes lots of heat, about
1.6x40x1000 = 64K Btu/day. You might run a 5K Btu/h window AC 13 hours per
day to remove all that heat :-)

It can be a lot more energy-efficient to use a fan to circulate air between
the basement and the house when the basement is humid, warming the basement
and cooling the house.

(Plus we have the added comlication of dampness (not puddles) seeping
in during rainstorms?


Maybe we can adjust the gutters and downspouts and
slope the soil away from the house to improve that.

So if a large cold slab stores so much moisture...


The long term moisture content of concrete might be 5% of the RH
of the air surrounding it. Concrete weighs about 150 lb/ft^3.

...what is the best thing to do?
- Heat the slab?


Maybe a little, in wintertime, by moving air from the basement floor up
into the house. A Baltimore basement with 10 cfm of outdoor air leakage
might be 53 F in January, with Pa = 29.921/(0.62198/0.0025+1) = 0.120 "Hg
vs Ps = e^(17.863-9621/(460+53) = 0.440 "Hg at 100%, and 100Pa/Ps = 29%.
Circulating some air between the house and the basement could lower that
and add desirable humidity to the house, with a little more heating fuel.
(Unless the home is 100% solar-heated :-) Outdoor air warmed to 70 F would
have 100Pa/0.748 = 16% RH. A 4"x1000ft^2 50K pound slab can slowly store
(0.03-0.01)50K = 1000 pints of water as the RH of the basement air rises
from 20 to 60%.

- Circulate *in* hot air from outside (even if it is humid) to
attempt to heat up the slab?


I don't think so, if it's more humid outside, in the absolute sense.

Nick

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m Ransley wrote:

What nick is saying nobody will ever know as he advocates flooding your
basement floor in winter for humidity and shrink wrapping your house to
stop air exchanges...


I'm afraid you have erred, my good man.

Nick

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pat smith
 
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Why not subfeed the Heat/AC blower with a circuit, " HumidistateRelayFan
SwitchMotor". Set Humidistate to close circuit at about 55%fan runs52%
circuit opensfan stops....

wrote in message
oups.com...
I am running my dehuminifer at 45% humidity level in my basement, and I
am also in Northern New Jersey.

I have two things that I need to mention about the use of a
dehuminifer:

1. Seem like its air moving capability is not that great even at high
fan speed. I have a feeling that it is only dehuminifing the adjacent
area. This "may" be a problem if the basement is partitioned in
multiple rooms or closets. Honestly, I am not sure about this. After
using it for two years, I don't have any mildew problem in my basement
(I had mildew problem in my basement before I started using the
dehuminifer). I guess it is doing something good in my basement despite
my concern about its coverage and despite the fact that my basement is
partitioned into two large rooms (with opening between rooms) and with
two closets.

2. Running dehuminifer can generate enough heat that we can feel
uncomfortably warm in the summer even with reduced humidity level. This
is especially bad if we have an exercise room in the basement. You
"may" need to add air-conditioning in addition to using the
dehuminifer. Still, using the dehuminifer should be the first choice
over the use of air conditoning to reduce humidity level because I am
under the impression that the air conditioner will stop as soon as the
room temperatur has dropped down to the pre-set level regardless if the
humidity level is reduced enough or not (and basement tends to be
cooler than the rest of the house to begin with; hence the air
conditioner will only run for a short while and probably will not
dehuminify enough).

Jay Chan


jay wrote:
Do you have windows in the basement? Opening the windows will allow air
to circulate and remove some of the dampness and humidity.

Yes, there are windows, but opening them is not very convenient, and
leaving
them open could worsen the problem if it is a humid day.

By the way, simply by keeping the blower motor of the heating/ac system
running continuously, the circulation of the air throughout the house, so
far, seems to be keeping the basement's relative humidity within the mid
to
upper 50s (as opposed to sometimes creeping up into the mid 60s if the
blower motor is turned off). The humidity in the rest of the house is
still
well below 50%.

Is a basement relative humidity level in the upper 50s too high if the
goal
is to prevent potential mold/mildew in my finished basement?

Thanks,

J.




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