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

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

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?

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Adrian C

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 .

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

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.

Some basic facts about the Pacific Northwest:

a) Average relative humidity, all four seasons such as they are is 79%. By comparison, in Philadelphia, PA it is 54.6%.

b) Most of the time, interior humidity (inside an occupied house) will be m uch less than outside. Why? Because the hottest months (July & August) aver age 73 by day, and 55 by night.

c) 152 average rainy days per year.

Put another way, it is a damp climate with a lot of rain.

The air in the house, for 12 out of 12 months, by night, and 10 out of 12 m onths by day will be *warmer* than the outside, and therefore LESS HUMID, b ut based only on temperature. What is happening is that the warm air is hit ting the cool cellar, and moisture is condensing - as with a glass of ice-w ater.

Isolating the cellar from the upstairs will not lower the humidity in the c ellar, but it will avoid the shock from the warmer air from above. Circulating outside air will, in fact, increase humidity in the cellar. Why ? Odds are that the cellar will be marginally warmer than outside, so the l atent heat (humidity) will be lower. Cool that down, and the sensible heat will drop like a stone as the relative humidity will jump.

Remember, you are starting from an average of 79% RH.

This is not an easy fix. And a mechanical solution to address the specific issue of humidity is the single practical answer. HOWEVER - if the goal is only to avoid the heavy condensation issue, and dropping overall humidity i s not the goal, then isolation of the conditioned areas of the house from t he cellar is the single practical solution. Either by installing a function al vapor-barrier and sealed doors, or some other solution. Beware the vapor barrier, however as it will collect condensate which most be managed.

Peter Wieck Melrose Park, PA

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

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

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

So you agree with me, dry air is more comfortable, with your qualification that I must be at an extreme.

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

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.

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.

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.

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

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.

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.

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.

And a quote from this page.

"*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

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.

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.

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.