OT-basement venting help please

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   I know, no electronics repair  really but there is a lot of varied
experience here.  
   I need to vent a basement room. It's about 20'; x 12'. What happens
now is moisture laden air goes down the stairs and then drops the
moisture in the basement room. I want to keep the room cool so heating
to get rid of the moisture is out. So I have been looking at vent fans
and pretty much all I see are fans for venting crawl spaces and
attics.
  So what kind of fan should I use? Thewre must be some sort of
shutter and a screen but I think those can be added to the outside.
And do I need two fans? One at each end of the room? So that fresh air
comes in and old air goes out. Or just an exhaust fan?
   The room is aligned lenghtways sort of north to south. The southern
fan would be the exhaust fan and would vent under the front porch. The
northern fan, if there is one, would draw air in from the north facing
end of the house.
   I live about 30 miles north of Seattle so I guess weather should be
taken into account too.
Thanks,
Eric

Re: OT-basement venting help please
First, given your location, all fans will do is relocate outside moisture t
o the inside, and push inside moisture to the outside. What you need is an  
effective dehumidifier - which is heat/cool neutral, but does remove moistu
re - albeit at a cost (electricity).  

Second, based on venting to the south, drawing in from the north, you are d
oing exactly the opposite of what you should do for your purpose, at least  
in the northern hemisphere. You want to draw air from the warm(est) side of
 the house, which will be the sunward side, even in Seattle. And you want t
o vent to the cool(est) side, which will be to the north (no direct sunligh
t).  

Short of deliquescent materials, there is no passive means to remove humidi
ty. Any anyone that suggests otherwise is telling porkies. Some other point
s:

a) Concrete and stone (typical foundation materials) are, emphatically, not
 vapor barriers, so unless an effective vapor barrier was installed on the  
*outside* face of the foundation walls, and beneath the concrete slab, you  
will have a constant source of moisture at all times, weather notwithstandi
ng.  

b) I really hope that you are not intending to do any sort of work involvin
g electronics or you handling electrified equipment in that space. Working  
over a concrete floor over dirt is, essentially, equivalent  to standing in
 an inch of water. To prove the point, with a decent VOM on AC volts, one p
robe to the hot side of a receptacle, the other to the floor. As your body,
 assuming you are otherwise healthy, is not much more than a 10,000 ohm, 1/
4 watt resistor, be careful!

c) Cellars (more than 50% below grade) or basements (50% or less below grad
e) unless designed as such from the git-go are simply not meant to be used  
as finished, habitable space. And in your climate, even more so. And, if yo
u happen to be in an older house where local stone was used in the foundati
on walls, drying them out is absolutely not a good idea unless you want you
r house to start settling, big time. There is a long explanation for this,  
but typically old foundations were built with a mud/lime mortar with very l
ittle Portland Cement involved. The stuff is solid when damp, but when drie
d out, it shrinks, crumbles and fails. Here in the Philadelphia region, the
 likes of Dr. Desert Dry and their ilk won't touch older houses for that re
ason. Again, be careful!  

Best of luck - fans are a waste of money if dehumdification is the specific
 goal. Deliquescent materials have a high first cost, and will have you ups
etting your significant other as you will be baking them dry in the oven co
nstantly. But, they do work. Leaving you with machines as quick, relatively
 efficient means to that end. Invest in the additional condensate pump so y
ou are not constantly emptying the bucket.  

Best of luck!

Peter Wieck  
Melrose Park, PA

Re: OT-basement venting help please
On 11/14/2019 11:10 AM, snipped-for-privacy@whidbey.com wrote:
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  Can you add enough positive pressure to the basement to reduce the  
flow down the stairs? I know that would be drawing cold air into the  

  Get a dehumidifier, you get heat and dry air.

                                  Mikek

Re: OT-basement venting help please
On Thursday, November 14, 2019 at 1:20:58 PM UTC-5, amdx wrote:

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That would involve bringing outside humidity inside. Keep in mind that the  
average relative humidity in that region is 79%, and the average number of  
sunlight hours per day (not cloudy) is two (2). It IS humid. All. The. Time
.  

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Dehumidifiers are heat/cool neutral. They use refrigeration to pull the moi
sture out of the air, but dump the residual heat at the same time. The air  
feels less clammy, so the perception is that it is warmer. It really is not
.  

Peter Wieck
Melrose Park, PA

Re: OT-basement venting help please
On 11/14/2019 12:35 PM, snipped-for-privacy@aol.com wrote:
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  I disagree about heat/cool neutral as it concerns the room temperature.

  I tried running a dehumidifier to assist my air conditioning. I found  
if I reduced the humidity to 40% I could raise the temperature 3* F and  
even 4* F higher and still have the same comfort. The only convenient  
place for the dehumidifier was in a foyer, and that foyer got very warm.

While I understand it would be an adiabatic process except for motor  
inefficiencies, some of the removed heat is stored in the waste water  
and is put back into the room.


The air feels less clammy, so the perception is that it is warmer. It  
really is not.

That is just opposite of my experience, give me low humidity Please! I  
feel much more comfortable and even want a warmer temp if the humidity  
is low. I run my auto air conditioning in the winter just to lower the  
humidity. I live in North Florida.

                                       Mikek

Re: OT-basement venting help please
You need to brush up on your Sensible Heat and Latent Heat definitions, and
 how they affect temperature vs. humidity vs. comfort. Dryer air is general
ly perceived as warmer than wetter air, except at the extremes (sauna vs. s
team bath), and why it is that Dubai is insufferable, whereas Phoenix is mo
re tolerable at the same actual temperature. That is Part A.

Now, a standard dehumidifier cools by refrigerating a coil, then drawing ai
r across it, thereby cooling it and dehumidifying it, then using the waste  
heat from the cooling process to reheat the air so that it comes out at mor
e-or-less the same temperature it started at, only dryer. Sure, there will  
be some heat-gain from the motor(s) and condensate pump, if used, but that  
gain will be relatively tiny, with much of it being absorbed into the conde
nsate if the unit is well designed. That is Part B.  

Being as you are in Florida, and let's make a leap that you are on/near the
 coast or other wetlands, you are in a climate much closer to Dubai than Ph
oenix. You are running your AC to dehumidify not to cool - which is perfect
ly valid, and why it is that large commercial and institutional systems use
 reheat coils, or local VAV boxes or Phoenix valves. They maintain a consta
nt discharge temperature, typically running about 55F discharge air from th
e central AHU, reheating at the VAV to a set temperature. A VAV gives const
ant temperature, at a variable volume. A Phoenix Valve gives constant tempe
rature and flow - useful in classrooms and labs where air-changes must meet
 some standard.  

Hope that clarifies.  

Peter Wieck
Melrose Park, PA

Re: OT-basement venting help please
Oh, and why it is that I advised the OP to invest in a condensate pump - to pull the warmed water out of the room. This eliminates re-evaporation as well as the heat it absorbs. It is all part of the process.  

Peter Wieck
Melrose Park, PA  

Re: OT-basement venting help please
On 11/15/2019 2:02 PM, snipped-for-privacy@aol.com wrote:
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  So you agree with me, dry air is more comfortable, with your  
qualification that I must be at an extreme.

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You forgot the heat that was removed from in the condensate container,  
or pumped down the drain. That also gets put into the room.

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Clearly it's both, but as I said, if I can get the humidity 40 or below,  
I can raise the temp about 4*F and still be just as comfortable.

  You are missing the human body in all your equations. To cool you need  
to remove perspiration by evaporation, low humidity aids that and makes  
for comfort. We keep the thermostat at 78*f in summer, there are low  
humidity days when the air conditioning runs to keep temp down to 78*F,
but the humidity gets low and I get cold, to where I need to put more  
clothes on.



and why it is that large commercial and institutional systems use reheat  
coils, or local VAV boxes or Phoenix valves. They maintain a constant  
discharge temperature, typically running about 55F discharge air from  
the central AHU, reheating at the VAV to a set temperature. A VAV gives  
constant temperature, at a variable volume. A Phoenix Valve gives  
constant temperature and flow - useful in classrooms and labs where  
air-changes must meet some standard.
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Re: OT-basement venting help please
A dehumidifier should be heat neutral as you say.

I?m not so sure about the process.  A phase change is involved, whe
n water goes from gas to liquid it has to dump all that phase change energy
.

I use a dehumidifier in the basement.  If you figure out how to make one la
st more than 2 years let me know.

Re: OT-basement venting help please
snipped-for-privacy@aol.com says...
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The dehumidifiers in homes do produce some heat from the motors.  Not  
much, but some.  Then if you have to empty the water by hand, you are  
not loosing heat by the water to ammount to anyting.

Many people do not get very many years out of their dehumidifires.  
Looks like they should as they are nothing much more than a refrigerator  
with an open door or even an airconditioner.

I have not thought about it , but I wonder if you put a window AC in a  
room and a drain bucket under it if it would not be just as good as the  
dehumidifier and last longer.

I think the newer ones do use the splash from the condenced water to  
help cool the coils.


Re: OT-basement venting help please
On 11/16/2019 10:16 AM, Ralph Mowery wrote:
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  I have found several sites that either complain about the extra heat  
produced by a dehumidifier or explain why they produce heat.

Dehumidifiers are over unity heat producers with a 1.5 COP.

My dehumidifier was recalled as a fire hazard, had to send in the cutoff  
power cord. I'm tempted to reinstall a cord, run and then measure the  
temperature of the condensate to see if heat is removed and how much.
  It may not be much as I have seen that as part of the calculation.
I thought it was applicable and still not sure it isn't.
                                      Mikek




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Re: OT-basement venting help please
On 11/16/2019 12:08 PM, amdx wrote:
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   Must have gotten rid of the recalled Dehumidiier, if anyone has a  
running dehumidifier could you check the temperature of the condensate
and see how it compares to the air temp. I suppose it has to be cold if  
it is dripping off the condenser coil, the question is how long does it  
have to re-absorb heat from the room, or is it dumped down the drain or  
run outside.

Re: OT-basement venting help please
I haven't measured.  This is what seems logical to me:

When a dehumidifier cools air in the evaporator section and warms the same  
air up in the condenser section, there should be no net loss or gain to the
 room.  Air comes in, gets cooled, gets heated back the same amount less wh
atever inefficiencies exist.

However the water in the air condenses.  The "heat of condensation" is a lo
t of energy, given by one source as 590 calories per gram where 1 calorie i
s the energy to raise one gram of water 1 degree.  The water comes off the  
coil at the coil temperature, while the heat is transferred into the coil.  
 The refrigerant then moves the heat over to the condenser coil, where it i
s transferred to the air.  So, net gain greater than the simple dry air cas
e.

That's what my thought experiment suggests anyway.  

Re: OT-basement venting help please
On 11/17/2019 6:03 PM, Tim R wrote:
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  That's my argument also, so at least you and I think that happens.
This link has some calculations on heat removed from the condensing of  
the water and delivered to the room, assuming the condensed water goes  
out of the room.
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And a quote from this page.
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"*Update: A typical home dehumidifier removes roughly 2L of water per  
kWh of energy used. That soaks up a bit  over 1 kWH of latent heat. So  
the room warming is about 2kWh per kWh input energy. The efficiency is  
over 200%, not bad if you want to dry your house air also."

                            Mikek

Re: OT-basement venting help please
On Monday, November 18, 2019 at 10:32:23 AM UTC-5, amdx wrote:
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I don't think it's really 200% though.  It won't run when it's not condensi
ng.  I think a small amount of heat is generated by the motor and fan, mayb
e friction of the refrigerant in the pipes, but the majority of the heat pr
oduced is the latent heat.  It should be 100% efficient but it may not be m
uch more, maybe 110%.  

Where would that other kWh of heat come from, or go?  Not into the air, bec
ause we've already agreed the air is cooled and reheated to effectively no  
loss or gain.  The refrigerant is compressed, expanded, evaporated, and con
densed, but again I don't think there is a net loss or gain.  


Re: OT-basement venting help please
snipped-for-privacy@aol.com says...
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I have not had time to really research it,but seems to me if the  
condensed water stays in the room long enough  to equal the room  
temperature,

Then the total heat gain would be what ever the electrical power drawn  
from the AC outlet would make. That heat would be mostly the power it  
takes to run the compressor and fan motors.  

There is no way for the power drawn from the AC outlet to escape from  
the room except what may go through the walls.

Re: OT-basement venting help please
On Monday, November 18, 2019 at 1:16:47 PM UTC-8, Ralph Mowery wrote:
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Typically, it DOES reach room temperature (empty the tank every couple of days),
but the 'latent heat' also has to include the heat that evaporated that water in the first place;
you get  heat out of the vapor that originally evaporated the recovered liquid-water,
and that shows up in the 'hot' side of the coils, it's not in the water-vapor any more.

Pumping heat of evaporation OUT of the airstream causes the condensation, putting heat into
the hot-side coils and raises the outflowing air temperature accordingly.

Re: OT-basement venting help please
to the OPs question...

concrete and cinder block are porous to moisture.

Paint the walls with Drylock and the floors with a suitable low permeability paint.    That will help a lot right off the bat.

In the winter, if your furnace is in the basement, that is usually enough to keep it warm and dry.

 In the summer, do not promote outside air exchange when it is humid outside.

I have my electronic gear down there, I try to turn it all on once a week for n hour and I do run a dehumidifier near the gear.  If you have AC, make sure the condensate is dumped outside, not into the basement.

Do promote outside air exchange when it is sunny and dry and a nice breezy day, open the window.

Its a process.  :-)


m



Re: OT-basement venting help please
On 14/11/2019 17:10, snipped-for-privacy@whidbey.com wrote:
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Seems you need to block the air coming down the stairs. Is there a door  
at the top? Can you install another a few feet in like an air lock, and  
vent out the air in-between with a timer/humidity operated fan?

--  
Adrian C

Re: OT-basement venting help please
On Thursday, November 14, 2019 at 9:10:26 AM UTC-8, snipped-for-privacy@whidbey.com wrote:

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A bathroom or kitchen vent fan would be appropriate, but for control, you'd want to
run it only when the absolute (not relative) humidity in the basement is higher
than the absolute humidity in the make-up air (presumably the outside air), that
will filter into the basement.

As an approximate control, you might consider that before dawn, when there's dew on
the grass, the outside air humidity will be low; a time switch that runs a fan for
a couple of hours in the early  morning might work.

A more complex system could be imagined, circulating basement air
to an air/air heat exchanger with outside air, to make the 'dew' effect produce
droplets into a drain, from the basement air.   Drain into a jar, and you can
get a measure of the effectiveness.   If the basement windows fog up in the
mornings now, that's an encouraging indication.

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