water in the air

[Frank Foder]

OK, here's a question with some science to back me up.

I have a leak in my a/c drain line. It happens to be right under the a/ c unit. Took a while to find the leak, and it turned out just to be a cracked hose under the unit. Pretty strange. But that's not the question.

Now, before I located the leak, I was sopping up the mess with beach towels. LOTS of water. When I found the leak, I put a pan under it, and started emptying the pan every few hours. The amount of drain water amazed me. It's pretty hot and humid outside in the daytime, and my a/c runs ever two hours or so. When it does, I end up with about

**6 cups** of drain water each time it runs. Holy toledo! That's coming out of the air in my house every two hours???

So I did a calculation, and found that in my house, with about 2000 square feet of HVAC space (with 8 foot ceilings), 50% humidity at 75F means that there are about 19 cups of water total in the air in my house. Again, holy toledo! So my a/c is pulling about a third of that out every few hours. Now, I might expect my a/c to do that.

But wait a minute. That means that about 6 cups of water is entering my house every few hours! Now, my house is very well sealed. Where are those 6 cups of water coming from? If I don't open the exterior door, how are those 6 cups getting in? I can't believe it's evaporation from toilets, sink, etc., and I can't believe that I'm exhaling that amount. So where is it coming from?

I'm on a slab. Is the slab permeable enough that water is soaking up from underneath? I'm well above the water table, BTW. Is drywall permeable to water, such that the humid exterior air that makes it past my (substantial) blown-in insulation gets through into the house? Now, I understand that when the temp/RH is 90F/60% outside, that air holds twice as much water as my 75F/50% air inside. So it doesn't take a lot of outside air getting in to bring lots of water in, but still ...

I always think about a/c in terms of heat management, and thermal insulation. But it's pretty interesting to think about water management, and to what extent the inside of the home is insulated from water.

[Molly Brown]

You=92re exhaling it along with CO2 if you=92re not perspiring it, you=92re refrigerator is putting it out from the food in it and if you take a shower well, Holy toledo.

[Frank Foder]

To be fair, there are no showers being taken here in the daytime, nor laundry being done. I don't recall opening the fridge since this morning. And, give me a break, I'm exhaling/perspiring 6 cups of water (actually, often 7-8) in two hours? Um, no. I'm sure not drinking anywhere near that much, so if I were exhaling/perspiring that amount, I'd be drying up.

[gfretwell]

You get a whole lot of water out of an A/C unit. I had a bucket out of one of my mini-splits in an area with no kitchen or bath and it still filled the bucket every day. (construction had caused us to disconnect the pipe going outside)

[NGDirect]

Compare it to what you see drip from the A/C on your car. A relatively small area cubic feet-wise compared to your house, and yet it will leave a pretty good sized puddle on the road while you sit idling. Multiply the size of the car by 100 or 150 for the comparable size of a house and a lot of water will be taken out of the air.

When I first installed my new A/C I didn't have the drain line run yet and put a 5 gallon pail under the drain. When I first turned it on it filled the bucket in a few hours.

My neighbor has a pump that pumps the water out thru a small hose through the side of their house. There is a small garden near the discharge that never needs watered!

[Ed Pawlowski]

Not the same situation. Unless you run the car in recirc mode, it is constantly changing air, thus lots of humidity to remove. In a house, you get far fewer air changes

[ransley]

Thats nothing when we had a new space pack 3 ton installed in 3500 sq ft I measured every day over several day 225 Gallon per Day the space pack removed,

[trader4]

And even on recirculate, all the cars I've been involved with just REDUCE the amount of outside air taken in, not cut it off all together.

Exactly how all the new moisture enters a house is a good question. I would suspect most of it is due to air leakage. If houses were really well sealed, without some kind of air exchange, I suspect you'd detect stale air before very long, which you don't. The amount of water Frank is seeing isn't unusual, that's for sure.

[HeyBub]

2000 sq ft with 8 ft ceilings = 16,000 cu ft of air. The maximum water vapor in air is 4%. If at the maximum, you could have 640 cu ft of water vapor. Six hundred and forty cubic feet of water is a bit over 76,000 cups of water.

If your A/C extracts 6 cups of water every 4 hours, it would take, let me see, mumble-mumble, carry the 3, ah, yes, 50,733 hours (almost six years) to get all the moisture out.

'Course it wouldn't REALLY take that long - some of the 16,000 cu ft of space is taken up by furniture, rugs, bowling trophies, the cat, and so forth. And you're probably not at the maximum water vapor density anyway. Say three years. Give or take, depending on the breaks.

[xx dfl]

Nope. Try again. "Water vapor" isn't the same thing as "water", volume- wise.

75F 50% RH air has 0.01 kg/m3 of water. See the nice tool at 2000 sq foot house with 8' ceilings has a volume of 465 m3, so that makes 4.65 kg of water in the air in my house. 1 cup = 0.240 kg of water, BTW.

So get out the calculator and try it again! I like the guy (see above) who claims to have gotten 225 gallons/day out of his house. Either his measuring cup was a bit off, he's decimally challenged, or left the door open to his BIG steam room.

But again, the question is, what is an optimal air exchange rate for a house in a climate where you DON'T want to leave the windows open? I suppose there are variables, such as the BO-rating of the residents. In principle, the effort to seal a house could be done too well.

[gfretwell]

That is a tad over a gallon. Now lets talk about a place that has humidity, line most of the Atlantic seaboard so your delta will be at least a gallon, just to get down to 50% RH

[Frank Foder]

Well, if I were air conditioning the outside air, I'd get lots more water. But I'm not. In fact, I'm in Houston. Think I don't have much humidity outside? Whew!

The point is that in order to get about a gallon o fwater out of the air in my house every two hours, I need to have a gallon coming in every two hours. With outside air right now at 90F

60%RH, I need about a hundred cubic meters of air coming into my house every two hours to bring in a gallon of water every two hours. About a quarter of the volume of the house.

[Nate Nagel]

That actually sounds about right. a typical house, even a well built, tight one, has something around 0.3-0.4 ACH (air changes per hour.)

nate

[Tony]

I always run it in recirculate mode. I love the dry air. After turning the fan to the lowest speed and it's still too cold in the car, I turn up the temperature knob so I'm getting heat from the engine coolant and A/C at the same time. Talk about dry air, that works great!

[ransley]

Im glad you like my calculations but its fact, I liked them so much I did them for 3 days testing, I could not believe it at first, First, Space Pack removes more moisture than regular AC, Second it was tested when we got the worst heat humidity wave in recent history, the system was new and the house loaded with humidity to near 80+%, it was maybe

1993 when over 1000 died in chicago, Temps reached 112 in the shade and humidities were around 90+% for over a week. Space Pack first removes humidity before lowering the temp, it might takes hours to lower the temp 1f, but humididty will have been lowered 20% by then. Read up about space pack, then you will understand its the design that makes 225 GPD possible. The way Space Pack cools is totaly different from regular ductwork, it also has to run near continously in hot times as its usualy sized small due to the extreme cost of running tubes through old walls. Yes it was 225 GPD 4 floors of a large house where tools would rust in the basement, but no more with Space Pack.

[terry]

t

de quoted text -

Well humans need air to breathe! Not living with 100% stale air one hopes? Here where a/c is rare we use air exchangers. These recover some of the heat from the exhausted air and return it to the fresh incoming air.

[Frank Foder]

250 gallons per day from a 3500 square foot house is extraordinary. But he extraordinary conditions you describe (112F at 90% RH???? Geez!) are certainly extraordinary. That's 0.06 kg of water per cubic meter of air, or 16 gallons of water in your 1000 cubic meters. So if your house leaks like a sieve (windows wide open?) and exchanges 60% of the air every hour, *and* your a/c pulled all the water out of the air (which even the best a/cs cannot), I guess you might be able to get a 250 GPD in your drainpipe.

The question wasn't whether you could get an a/c to pump out that much water. With a big enough a/c, I have no doubt that you could. The question is where you got all the water! I guess you got it by leaving the doors and windows open. I would think that a house that was outfitted with a top of line a/c would be sealed a whole lot better than that!