Frugal dehumidification

[nicksanspam]

Ventilate when the outdoor vapor pressure P(Ta,RHa) is less than the indoor vapor pressure P(Ti,RHi) in the table below, and try to do this with warmer outdoor air when the house needs heat and cooler outdoor air when it needs coolth.

20 FOR R=0 TO 5 30 PRINT TAB(6+10*R);50+5*R; 40 NEXT 50 PRINT TAB(66);80 60 PRINT 70 FOR TA=50 TO 80 STEP 2'temperature (F) 80 PRINT TA; 90 FOR R=0 TO 5 100 RHA=50+5*R'RH (%) 110 PA=RHA/100*EXP(17.863-9621/(460+TA))'vapor pressure ("Hg) 120 PRINT TAB(5+10*R);PA; 130 NEXT 140 RHA=85 150 PA=RHA/100*EXP(17.863-9621/(460+TA)) 160 PRINT TAB(5+10*6);PA 170 NEXT 50% 55 60 65 70 75 80%

50F .1836264 .201989 .2203516 .2387143 .2570769 .2754395 .3121648

52 .1976689 .2174358 .2372027 .2569696 .2767365 .2965033 .3360371 54 .2126632 .2339295 .2551959 .2764622 .2977285 .3189948 .3615275 56 .2286653 .2515319 .2743984 .2972649 .3201315 .342998 .3887311 58 .2457342 .2703076 .2948811 .3194544 .3440279 .3686013 .4177481 60 .2639307 .2903237 .3167168 .3431098 .3695029 .395896 .4486822 62 .2833194 .3116514 .3399833 .3683152 .3966472 .4249791 ..481643 64 .3039678 .3343646 .3647614 .3951581 .4255549 .4559517 .5167452 66 .3259469 .3585417 .3911363 .423731 .4563257 .4889204 .5541098 68 .3493307 .3842637 .4191968 .4541299 .4890629 .523996 .5938621 70 .3741957 .4116153 .4490348 .4864544 .523874 .5612935 .6361327 72 .4006234 .4406858 .4807481 .5208105 .5608728 .6009351 .6810598 74 .4286993 .4715692 .5144391 .5573091 .600179 .6430489 .7287888 76 .45851 .504361 .550212 .596063 .641914 .687765 .779467 78 .4901487 .5391635 .5881784 .6371932 .6862081 .735223 .8332528 80F .5237118 .576083 .6284541 .6808253 .7331965 .7855676 .89031 "Hg

We need a little computer to do this automatically, eg a Smart Vent!

Nick

[Robert Gammon]

Doesn't do a thing for life on the Gulf Coast.

The number of hours where we are off the end of this table (i.e. greater than 80F AND greater than 80% RH) is over 6000 hours a year. Travel away from here in almost any direction and lips will chap and crack.

[Robert Gammon]

Right now at 8:36am, the temp outside is 75 degrees and the RH is 83%. High temp today will be in the mid-90s with RH staying in the 80 to 90% range.

[nicksanspam]

You might enjoy an extended table (above the ASHRAE comfort zone):

70 75 80 85 90 95 100% 80F .7331965 .7855676 .8379388 .89031 .9426811 .9950522 1.047424 "Hg 82 .7830198 .8389498 .8948798 .9508098 1.00674 1.06267 1.1186 84 .8358255 .8955274 .9552292 1.014931 1.074633 1.134335 1.194037 86 .8917653 .9554628 1.01916 1.082858 1.146555 1.210253 1.273951 88 .9509972 1.018926 1.086854 1.154782 1.222711 1.290639 1.358568 90 1.013691 1.086098 1.158505 1.230911 1.303318 1.375724 1.448131 92 1.080018 1.157162 1.234307 1.311451 1.388595 1.465739 1.542883 94 1.150158 1.232312 1.314466 1.396621 1.478775 1.560929 1.643083 96 1.2243 1.31175 1.3992 1.48665 1.574099 1.661549 1.748999 98 1.302636 1.395682 1.488727 1.581773 1.674818 1.767864 1.860909 100 1.385372 1.484328 1.583283 1.682238 1.781193 1.880148 1.979103

Hard to believe, with only 8760 hours per year. Then again, YOU are often hard to believe. Perhaps your town has lots of 10 day wintertime months :-)

NREL says the average daily MAX temp is less than 80 F from October through April in New Orleans and Port Arthur, less than 80 from November through March in Corpus Christi, and so on.

Nick

[Robert Gammon]

as one local guy put it, we have 11 months of summer, and then there's August.

NREL does not accurately depict what Houston weather is like. RH is almost always above 50% and in the summertime, the air has WEIGHT when stepping outside on a sunshiny day with temps in the 90s and RH nearly 90.

Year round apparel is short, tshirts and sandals. The number of days where the temperature at any time of the day drops into the 30s can be counted on your fingers and still have fingers left over. In the nearly

30 years we have been here, it has snowed twice and we've had one or two ice storms.

[nicksanspam]

Robert Gammon errs again:

Well, They've only been measuring it every hour for the last 30 years in Houston... They say the average daily max in Houston is less than

80 F from November through April. That's 6 months, ie 50% of the year, ie 4380 hours. The 24-hour average temps in May through October are 74.5, 80.4, 82.6, 82.3, 78.2, and 69.6, which eliminates 6 months of nights, another 2190 hours. There are only 2190 hours left in a year, on this planet. How many hours per year on your planet? :-)

Oh. That's different. The air has WEIGHT :-)

That statement has little to do with your claim:

How can you combine such a huge ignorance with such a huge arrogance? :-)

Nick

[Robert Gammon]

Looking at weather.com, average high temps are above 80 from April thru October Average low temps are above 60 for the same time period.

Average precipitation per month ranges from just about 3 inches to almost 6 inches.

Record Highs are All above 80 for the ENTIRE year.

Record lows are all above the freezing point from April thru September.

wikipedia.com says average annual precip is 48 inches here with prevailing winds from the south and southeast for most of the year bringing heat from Mexico deserts and moisture from Gulf Of Mexico. "The air tends to feel still and the humidity (often 90 to 100 percent relative humidity, while average afternoon relative humidity is between

57 and 60 percent in the summer) results in a heat index higher than actual temperature. To cope with the heat, people use air conditioning in nearly every car and building in the city."

My thermostat is set to 80F, we have two ceiling fans and a box fan to keep the air moving in here and we still feel quite warm

The number of weeks in the year where the outside air temp is in an acceptable range and the RH is also in an accceptable range to allow one to open the windows and doors and let the outside air in, is a very very small number of weeks, my estimate is less than 3 weeks of the year.

We visited Palm Springs in the heart of the summer several years ago. Outside air temps were well above 100, approaching 110. It was a VERY pleasant environment for us as the temps were only a little above what we were used to, but the humidity was so much lower (course we paid with severely chapped lips as a result)

[nicksanspam]

Would you have any evidence for this article of faith?

That means the outdoor air temp was above 80 once every 30 years or so.

How can you combine such huge ignorance with such huge arrogance? :-)

Nick

[Robert Gammon]

Nick, You deliberately misinterpret what I said. The data shows that the high temp for ANY given month in the history of record keeping for Houston TX, even in January and February, there have been days where the high temp was above 80F. The AVERAGE high temp is above 80F from April thru October.

Arrogance, hardly. The shoe clearly is on your foot not mine.

I invite you to spend a year on the southeast Texas Gulf Coast and then tell me that I am full of it.

OK, 6000 hours was way too high. I got interested after you made your posting.

BTW way do you continue to use BASIC for these simulations???? C or C++ will do the job as well and most anyone with a technical background can understand

I stand my my claim after living here since 1982, there are only about 3 weeks of the year when the temperature is in the right range and the humidity is in the right range that we want to throw open the windows and doors to let the nice outside air in.

Right now, we are in a low humidity state. Outside air temp is in the low 90s (TV says 90, my local in the shade thermometer is 92). RH is 43%, lower than average for afternoon temps. NO WAY DOES ANYONE WANT THIS AIR INSIDE!! Forecast temps for the rest of the week are highs of 94 to 97 and lows of 71 to 72.

$75 for heating for the ENTIRE winter is NO joke. Thats all I spend TOTAL for the ENTIRE YEAR!!

[nicksanspam]

Well?

No.

So?

So?

As in "I was wrong." That's progress :-) Congratulations!

Nick

[Ether Jones]

Humid air is LIGHTER than dry air at the same temperature and pressure, NOT heavier.

[Robert Gammon]

On what basis is this argument???

Seems to me that the more water vapor per cubic meter, the heavier the volume of enclosed air is.

Hot air will rise over the top of cold air, yes, but hot is not necessarily humid.

[digitalmaster]

That may work very well for your area..but is impractical for the deep south(middle Georgia).

[JohnR66]

Well, things are not always what they seem. Mercury, at room temp, is a liquid, yet is nearly twice as dense as solid iron. It is true that moisture laden air is LESS dense than dry air at the same temperature. John

[Ether Jones]

Physics.

Your intuition is wrong in this case.

I did not say that hot air is necessarily humid... I said that humid air is lighter than dry air at the same temperature and pressure.

So for example one cubic foot of dry air at 90 degrees Fahrenheit and one atmosphere pressure is HEAVIER than one cubic foot of humid air at the same temperature and pressure.

The reason is simple: air is mostly nitrogen. Nitrogen occurs naturally as a diatomic molecule, N2. Water is H2O. Use a periodic table to figure the molecular weights of the nitrogen molecule and the water molecule. You will see that the water molecule is much lighter than the nitrogen molecule.

[Logan Shaw]

It might also help in explaining to point out that, at a given temperature and pressure, a given volume of gas contains the same number of molecules no matter what those molecules are. This isn't exactly the most intuitive thing: after all, it's not how solids behave.

- Logan

[nicksanspam]

It turns out there are now two Smart Vents, a floating flood gate and a ventilation fan controlled by a vapor pressure difference...

NREL says w

[digitalmaster]

NREL doesn't live here.And obviously you don't either or you would know better .

[nicksanspam]

Their instruments do.

Nick

[Robert Gammon]

OK, OK, Its not weight we feel.

Still air with high humidity prevents our skin from effectively dissipating heat thru evaporation of sweat. The brain interprets this as weight, somewhat akin to the feeling of suffocation, but very very mild.