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

wrote:
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


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 wrote:
wrote:
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


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.


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.

Robert Gammon wrote:

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

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

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

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.

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

wrote:
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


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.

Robert Gammon errs again:

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.

wrote:
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.

NREL does not accurately depict what Houston weather is like.

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? :-)

RH is almost always above 50% and in the summertime, the air has WEIGHT...

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

... The number of days where the temperature at any time of the day drops
into the 30s can be counted on your fingers.

That statement has little to do with your claim:

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.

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

Nick

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

Nick

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)

Robert Gammon wrote:

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.

Would you have any evidence for this article of faith?

... Record Highs are All above 80 for the ENTIRE year.

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

wrote:
Robert Gammon wrote:


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.


Would you have any evidence for this article of faith?


... Record Highs are All above 80 for the ENTIRE year.


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


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!!

Robert Gammon wrote:

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.

Would you have any evidence for this article of faith?

Well?

... Record Highs are All above 80 for the ENTIRE year.

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? :-)

You deliberately misinterpret what I said.

No.

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.

So?

The AVERAGE high temp is above 80F from April thru October.

So?

OK, 6000 hours was way too high.

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

Nick

Robert Gammon wrote:
the air has WEIGHT when
stepping outside on a sunshiny day with temps in the 90s and RH nearly 90.

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

Ether Jones wrote:
Robert Gammon wrote:

the air has WEIGHT when
stepping outside on a sunshiny day with temps in the 90s and RH nearly 90.


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


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.

wrote in message
...
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

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

"Robert Gammon" wrote in message
om...
Ether Jones wrote:
Robert Gammon wrote:

the air has WEIGHT when
stepping outside on a sunshiny day with temps in the 90s and RH nearly
90.


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


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.

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

Robert Gammon wrote:
Ether Jones wrote:
Robert Gammon wrote:

the air has WEIGHT when
stepping outside on a sunshiny day with temps in the 90s and RH nearly 90.


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


On what basis is this argument???

Physics.



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

Your intuition is wrong in this case.




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

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.

Ether Jones wrote:
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.

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

digitalmaster wrote:

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.

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!

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

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

NREL says w0.0112 from October through May in Macon, on average...

Nick

wrote in message
...
digitalmaster wrote:

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.

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!

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

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

NREL says w0.0112 from October through May in Macon, on average...

Nick

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

digitalmaster wrote:

NREL doesn't live here...

Their instruments do.

Nick

Logan Shaw wrote:
Ether Jones wrote:
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.

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
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.

Logan Shaw wrote:
Ether Jones wrote:
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.

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.

Yes. This is known as the "ideal gas law". It is only an
approximation, but for air at atmospheric temperatures and pressures,
it is a good approximation.

So, as humidity is added to dry air, it displaces an equal amount
(number of molecules) of air. The resulting mixture is lighter than
the original dry air (at the same temperature and pressure).

wrote:
digitalmaster wrote:


NREL doesn't live here...


Their instruments do.

Nick


Macon Georgia, Houston Texas, Mobile Alabama.......

All across the region that NREL classifies as Humid-Semitropical, the
number of weeks varies with each location, but the number of weeks where
outdoor humidity is LOWER than indoor humidity is small, maybe 3 maybe 6
maybe 12.

We live in these areas and we know when it is OK to open the doors and
windows to let large quantities of outside air in.


Ventilation dampers work well in some climates, less well in others.
Heat pumps work well in some climates, less so in others. geothermal
heat pumps work well in areas that have winters, not so good here in
Houston TX After talking to a well driller who has assisted with
installation of geothermal heat pumps and has made repairs to wells
drilled for geothermal heat pumps, he has come to the conclusion that
here, we need a river, large lake, or a simple leaky evaporation pond to
displose of the hot water out of the geothermal heat pump.

One size does not fit all, not even close. So Nick solution will work
OUTSIDE the Deep South and the Desert Southwest.

Robert Gammon wrote:

RH is almost always above 50% and in the summertime, the air has WEIGHT...

Most air has weight, about 0.075 lb/ft^3, on this planet.

OK, OK, Its not weight we feel.

This is progress :-) But your claim had nothing to do with feelings...

Now why not check your "facts" before posting them? :-)

Nick

Robert Gammon wrote:

Macon Georgia, Houston Texas, Mobile Alabama.......

All across the region that NREL classifies as Humid-Semitropical, the
number of weeks varies with each location, but the number of weeks where
outdoor humidity is LOWER than indoor humidity is small, maybe 3 maybe 6
maybe 12.

Would you have any evidence for this your present vague article of faith?

The average humidity ratio is less than 0.0092 pounds of water per pound
of dry air from October through April in Macon. How many weeks is that
in your little ol' Texas town? :-)

Nick

"Ether Jones" wrote:


Robert Gammon wrote:
the air has WEIGHT when
stepping outside on a sunshiny day with temps in the 90s and RH nearly 90.

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

Kinda has to be if you want clouds, isn't it?
If you watch how clouds boil up, it is obvious.

Moist air, however, feels "thicker," leading to terms like "pea-soup
fog." As a totally wild guess, I wonder if the effect is a subjective
one, partly from the humdity displacing part of the air and thus
reducing the oxygen content, and partly from the water being more
reactive than nitrogen, and therefore wanting to bond together in
larger structures, which in turn create more drag on objects moving
through the vapor?

wrote:
Robert Gammon wrote:


RH is almost always above 50% and in the summertime, the air has WEIGHT...


Most air has weight, about 0.075 lb/ft^3, on this planet.


OK, OK, Its not weight we feel.


This is progress :-) But your claim had nothing to do with feelings...

Now why not check your "facts" before posting them? :-)

Nick


This will be the LAST time I EVER respond to ANYTHING that Nick at
Villanova posts to the alt.home.repair newsgroup.

For those of us who live in the region that NREL classifies as
Humid-SemiTropical, lots of things that work elsewhere do not work
here. For Instance.

Vapor barriers go on the OUTSIDE of the house, insulation is ALWAYS
unfaced, and vinyl wallpapers should NEVER be applied.

Vegetation should never be closer than 3 feet from the house, and an
appropriate ground cover should be maintained over than area. Ground
should slope away from the foundation at least 2 inches per linear foot.

Windows on Southern exposure sides of the house should be eliminated, or
scaled back in size dramatically if elimination is not possible.

geothermal heat pumps will either require open loop cooling, or will
require multiple large diameter wells, 400 feet or more, likely two of
these per ton of installed capacity to make a closed loop system.

RH levels outdoors much of the year make outdoor activities uncomfortable.

Construction workers all wear long sleeves, hats and scarves to keep the
sun off their skins. Even the very low paid yard care crews do this.

Natural fiber clothing is preferred in most regions as polyester and
rayon are poor at wicking perspiration off of the skin.

I wear sunglasses ALL the time when out of doors.

Relative Humidity levels and temperatures for most of the year are such
that the struggle is almost always to keep moisture out, as we are NEVER
too dry inside.


In the new house I will build, I MAY decide to include a ventilation
damper to allow the ventilation system to inject some fresh air from
time to time AprilAire makes one that is reasonably priced, it wont
open the vent trigger the fan unless outside air temp is under 100F and
over 0F, or if allowing the ventilation would cause indoor RH to rise
above 55% However these requirements mean that the damper will not
operate for most of the summer. The plus side of this is that it runs
the fan in the hvac while fresh air is introduced.

Nick, your system should closely model what the AprilAire Ventilaion
Control System Model 8126 does. The more deluxe ERV as documented at
www.ourcoolhouse.com works ALL the time, exchanging heat and moisture
with outside air. This one works better in climates that have 4
seasons, and ourcoolhouse is located in Colorado.

In article ,
says...
"Ether Jones" wrote:


Robert Gammon wrote:
the air has WEIGHT when
stepping outside on a sunshiny day with temps in the 90s and RH nearly 90.

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

Kinda has to be if you want clouds, isn't it?
If you watch how clouds boil up, it is obvious.

Moist air, however, feels "thicker," leading to terms like "pea-soup
fog." As a totally wild guess, I wonder if the effect is a subjective
one, partly from the humdity displacing part of the air and thus
reducing the oxygen content, and partly from the water being more
reactive than nitrogen, and therefore wanting to bond together in
larger structures, which in turn create more drag on objects moving
through the vapor?

Moist air is "lighter" than dry air (air pressure tends to be
lower when it storms and higher in fair weather), however the body
is heavier since lighter air is less buoyant. ...kinda like liquid
water is denser than air but people float. ;-)

--
Keith

Robert Gammon wrote:

This will be the LAST time I EVER respond to ANYTHING that Nick at
Villanova posts to the alt.home.repair newsgroup.

Nickie is a math and theory lover. That can be great if you want to
know how much heat a standard ASHRE mouse puts out, but Nick sometimes
gets confused when confronted with the fact that not all mice are
ASHRE compliant.

Weather station instruments are commonly placed at airports or other
open areas. That may not be representative for an area that otherwise
has dense vegetation and/or standing water. Airports have to be level
and dry enough to land planes, and they also usually have a lot of
paved or concrete areas and low cut grass. That means more wind can
sweep the ground, less groundwater can be transferred by vegetation
into the immediate air, and temperatures and humidity can differ from
areas nearby.

If Nick builds his constructions on or near a runway, he may be right.
If he builds on a typical wooded or swampy southern lot, he may find
the real world intruding.

In other areas, the representative weather stats can be off because
the weather instruments are NOT at an airport. I used to take
measurements at a radio station where my father worked. That station
was (logically) on a hill, and the town below might be lost in fog
while I was recording clear skies, low humidity, and a mild wind for
the town. Fast foreword a few years. Now, another weather reporting
site in that community is located about 50 feet above a river, at a
spot where it enters a small canyon. It also has different
measurements than if you set up a station in the middle of the small
town. On a practical basis, weather is an extremely local phenomenon.

Here in south Florida, I have become accustomed to seeing rain-soaked
streets that are totally dry 500 feet up the road. I've had my pool
fill with four inches of water, while the airport reported no rain at
all. The heavy rainstorms here can be that localized. Depending on
the winds and the season, the coast may get strong breezes and a cool
temperature, while five to fifteen miles inland, clouds billow up and
create a line of storms that never touch the coast. You can't always
go by reported weather from a selected set of sources

Having been through southern Georgia many times, I know there are
large differences in temperature and humidity around the peanut and
cotton farms compared to the pine forests and towns. That is common
sense and experiential knowledge.

However, Nick takes it as an article of faith that discrete samples
from professionals always represent a greater norm. :-)


FWIW, I've used economizer dampers on theatre HVAC units in Vermont
and in Alabama. The greatest use was over Christmas vacation, when
crowds would overheat the theatre and the outside air was less than 40
degrees F. Much of the rest of the time in Vermont they had to be
sealed with plastic and duct tape to prevent drafts and heat loss.
The integrated ones also had more electro-mechanical problems than
other systems. That may have been design related - unsupported lever
arms, corrosion, ice, etc. but they were only marginally cost
effective overall. In Alabama, the vents were straightforward exhaust
vents, and were used only if the AC was overwhelmed or there were
smokers (which were still allowed in certain sections of some
theatres).

Whole house fans were common in the south before AC, and venting is
just a variation on this. The success of those whole house fans often
depended on measures such as opening certain windows after 10 PM and
closing the house up tight before 8 AM, drawing all the curtains, and
sweating out the early evening on a porch. Once AC became affordable,
life changed for the better. Getting people to go back is nearly
impossible, and Nick should know this, but his stubbornness lack of
experiential knowledge prevents it.

Robert Gammon wrote:

RH is almost always above 50% and in the summertime, the air has WEIGHT...

Most air has weight, about 0.075 lb/ft^3, on this planet.

OK, OK, Its not weight we feel.

This is progress :-) But your claim had nothing to do with feelings...

Now why not check your "facts" before posting them? :-)

This will be the LAST time I EVER respond to ANYTHING that Nick at
Villanova posts to the alt.home.repair newsgroup.

That's progress. Now we need your vow to stop posting falsehoods :-)

For those of us who live in the region that NREL classifies as
Humid-SemiTropical, lots of things that work elsewhere do not work
here. For Instance.

Vapor barriers go on the OUTSIDE of the house, insulation is ALWAYS
unfaced, and vinyl wallpapers should NEVER be applied.

Vegetation should never be closer than 3 feet from the house, and an
appropriate ground cover should be maintained over than area. Ground
should slope away from the foundation at least 2 inches per linear foot.

Windows on Southern exposure sides of the house should be eliminated, or
scaled back in size dramatically if elimination is not possible.

geothermal heat pumps will either require open loop cooling, or will
require multiple large diameter wells, 400 feet or more, likely two of
these per ton of installed capacity to make a closed loop system.

RH levels outdoors much of the year make outdoor activities uncomfortable.

Construction workers all wear long sleeves, hats and scarves to keep the
sun off their skins. Even the very low paid yard care crews do this.

Natural fiber clothing is preferred in most regions as polyester and
rayon are poor at wicking perspiration off of the skin.

I wear sunglasses ALL the time when out of doors.

Relative Humidity levels and temperatures for most of the year are such
that the struggle is almost always to keep moisture out, as we are NEVER
too dry inside.

Irrelevant, unless all this makes your air heavier :-)

In the new house I will build, I MAY decide to include a ventilation
damper to allow the ventilation system to inject some fresh air from
time to time AprilAire makes one that is reasonably priced, it wont
open the vent trigger the fan unless outside air temp is under 100F and
over 0F, or if allowing the ventilation would cause indoor RH to rise
above 55% However these requirements mean that the damper will not
operate for most of the summer. The plus side of this is that it runs
the fan in the hvac while fresh air is introduced.

Nick, your system should closely model what the AprilAire Ventilaion
Control System Model 8126 does...

You are probably wrong again. Would you have any evidence for this article
of faith? :-) Recall AprilAire's claim that winter humidification saves
energy? What does their 8126 Ventilaion system do, exactly?

How can you keep combining such monumental ignorance and arrogance? :-)

Oh wait. You are from Texas, like George II.

Nick

wrote:

Weather station instruments are commonly placed at airports or other
open areas. That may not be representative for an area that otherwise
has dense vegetation and/or standing water. Airports have to be level
and dry enough to land planes, and they also usually have a lot of
paved or concrete areas and low cut grass. That means more wind can
sweep the ground, less groundwater can be transferred by vegetation
into the immediate air, and temperatures and humidity can differ from
areas nearby.

Houston has two measuring stations, the airport, with a 96' elevation
and a 96 F 1% summer design temp, and "Houston County," with a 108'
elevation and a 97 F 1% summer design temp. Not vastly different :-)

Whole house fans were common in the south before AC, and venting is
just a variation on this. The success of those whole house fans often
depended on measures such as opening certain windows after 10 PM and
closing the house up tight before 8 AM, drawing all the curtains, and
sweating out the early evening on a porch. Once AC became affordable,
life changed for the better. Getting people to go back is nearly
impossible, and Nick should know this, but his stubbornness lack of
experiential knowledge prevents it.

Automatic controls can turn on a fan when outdoor air is cooler and drier
than indoor air, in the absolute sense. This is quite recent, with existing
unexpired patents for drying out houses after floods and so on. See
http://smartvent.net.

Nick

wrote:
wrote:


Weather station instruments are commonly placed at airports or other
open areas. That may not be representative for an area that otherwise
has dense vegetation and/or standing water. Airports have to be level
and dry enough to land planes, and they also usually have a lot of
paved or concrete areas and low cut grass. That means more wind can
sweep the ground, less groundwater can be transferred by vegetation
into the immediate air, and temperatures and humidity can differ from
areas nearby.


Houston has two measuring stations, the airport, with a 96' elevation
and a 96 F 1% summer design temp, and "Houston County," with a 108'
elevation and a 97 F 1% summer design temp. Not vastly different :-)


Whole house fans were common in the south before AC, and venting is
just a variation on this. The success of those whole house fans often
depended on measures such as opening certain windows after 10 PM and
closing the house up tight before 8 AM, drawing all the curtains, and
sweating out the early evening on a porch. Once AC became affordable,
life changed for the better. Getting people to go back is nearly
impossible, and Nick should know this, but his stubbornness lack of
experiential knowledge prevents it.


Automatic controls can turn on a fan when outdoor air is cooler and drier
than indoor air, in the absolute sense. This is quite recent, with existing
unexpired patents for drying out houses after floods and so on. See
http://smartvent.net.

Nick


I am about 40 feet lower than either of those two measuring stations.
The NWS station at Alvin is closer to me and to my elevation than either
of those two.

The airport is, by comparison, somewhat odd

1. It sits surrounded on all sides by trees
2. Commercial development near the airport is limited as is residential
development

Southwest Houston where I live is INTENSELY developed with lots of
concrete everywhere and the only trees around are young, 10-20 years
This area was Rice Farms 20 years ago.

From May thru October, there will be very very few hours DAY or NIGHT
when RH OUTSIDE be lower than RH inside. Temps outside may be cooler
than the 80F that I keep this thermostat set on, but not drier than inside.

48 inches or rainfall, very very flat land with heavy clay soils means
lots of moisture around to evaporate into the air. Its why we stay so
near saturation here.

wrote in message
...
Robert Gammon wrote:

Macon Georgia, Houston Texas, Mobile Alabama.......

All across the region that NREL classifies as Humid-Semitropical, the
number of weeks varies with each location, but the number of weeks where
outdoor humidity is LOWER than indoor humidity is small, maybe 3 maybe 6
maybe 12.

Would you have any evidence for this your present vague article of faith?

The average humidity ratio is less than 0.0092 pounds of water per pound
of dry air from October through April in Macon. How many weeks is that
in your little ol' Texas town? :-)

Nick

come spend a summer down here...maybe then you will know what you are
talking about.

Robert ("I'll never respond to Nick again") Gammon responds again:

Houston has two measuring stations, the airport, with a 96' elevation
and a 96 F 1% summer design temp, and "Houston County," with a 108'
elevation and a 97 F 1% summer design temp. Not vastly different :-)

The airport is, by comparison, somewhat odd

1. It sits surrounded on all sides by trees
2. Commercial development near the airport is limited as is residential
development

But both measurements are similar...

From May thru October, there will be very very few hours DAY or NIGHT
when RH OUTSIDE be lower than RH inside.

What does that mean, and is it true, and why is it relevant?

We've been discussing ABSOLUTE vs relative humidity.

Nick

digitalmaster wrote:
wrote in message
...

Robert Gammon wrote:


Macon Georgia, Houston Texas, Mobile Alabama.......

All across the region that NREL classifies as Humid-Semitropical, the
number of weeks varies with each location, but the number of weeks where
outdoor humidity is LOWER than indoor humidity is small, maybe 3 maybe 6
maybe 12.

Would you have any evidence for this your present vague article of faith?

The average humidity ratio is less than 0.0092 pounds of water per pound
of dry air from October through April in Macon. How many weeks is that
in your little ol' Texas town? :-)

Nick


come spend a summer down here...maybe then you will know what you are
talking about.



AMEN TO THIS BROTHER.

Nick is sitting at a balmy 72F while I am at 93F, Macon is 90F, Mobile
is 88F, Atlanta is 89F

Nick and Mobile are tied for highest humidity at about 55% currently,
the rest of us are in the 30% to 45% range.

Nick is like many in a university setting, they are isolated from the
rest of the world and have little idea what problems are being faced
elsewhere. And like many in an ivory tower setting, it is difficult for
them to believe that anyone knows more than they do. Nick has shown
this to us with nearly EVERY comment he makes. No one is infallible,
everyone makes some mistakes from time to time, yet Nick appears to want
to SMASH your face in with nearly every comment.

The message to Nick is that the world is NOT a copy of what he sees in
Pennsylvania, things that will work well in Villanova may not work even
in upstate NY (i.e Buffalo)


And for Nick's benefit, ALL the cities mentioned here have very high
humidities at night in particular. Residents will avoid bringing in
night time air if at all possible as that time is when the RH climbs
towards saturation (80-100%)

My parent's house in North Carolina was far enough into the hills that
after 10PM, the air temp and humidity dropped off enough that a whole
house fan could dump alot of excess heat outside

Robert Gammon wrote:

... ALL the cities mentioned here have very high humidities at night
in particular.

Exactly what does that mean, and is it true, and how is it relevant?

We're discussing ABSOLUTE vs relative humidity.

Nick

wrote in message
...
Robert ("I'll never respond to Nick again") Gammon responds again:

Houston has two measuring stations, the airport, with a 96' elevation
and a 96 F 1% summer design temp, and "Houston County," with a 108'
elevation and a 97 F 1% summer design temp. Not vastly different :-)

The airport is, by comparison, somewhat odd

1. It sits surrounded on all sides by trees
2. Commercial development near the airport is limited as is residential
development

But both measurements are similar...

From May thru October, there will be very very few hours DAY or NIGHT
when RH OUTSIDE be lower than RH inside.

What does that mean, and is it true, and why is it relevant?

We've been discussing ABSOLUTE vs relative humidity.

Nick

go put your nose back in your calculator.My family has lived here in Georgia
for over 150 years.We know exactly how to deal with our local climate.When
to go on the porch,when to open a window,when to pull the blinds,and when we
need to ventilate or not.We know how to dress for working the fields,or
fishing ,or any other activity.If I tell you your idea is impractical for my
area....take it to the bank.

wrote:
Robert Gammon wrote:


... ALL the cities mentioned here have very high humidities at night
in particular.


Exactly what does that mean, and is it true, and how is it relevant?

We're discussing ABSOLUTE vs relative humidity.

Nick


All we can really calibrate to is RELATIVE as it is what WE feel, not
what the intruments are telling us. All reporting on TV, Radio,
Internet, its ALL RH

Robert Gammon wrote:

... ALL the cities mentioned here have very high humidities at night
in particular.

Exactly what does that mean, and is it true, and how is it relevant?

We're discussing ABSOLUTE vs relative humidity.

You might enjoy learning the difference.

All we can really calibrate to is RELATIVE as it is what WE feel, not
what the intruments are telling us.

Whaddya mean "WE," Kemosabe?

Nick

wrote:
Robert Gammon wrote:


... ALL the cities mentioned here have very high humidities at night
in particular.

Exactly what does that mean, and is it true, and how is it relevant?

We're discussing ABSOLUTE vs relative humidity.


You might enjoy learning the difference.


All we can really calibrate to is RELATIVE as it is what WE feel, not
what the intruments are telling us.


Whaddya mean "WE," Kemosabe?

Nick


The rest of us, everyone except Nick

see
http://apollo.lsc.vsc.edu/classes/me...nd_parcel.html

This says that absolute humidity is NOT a good moisture variable even
though the amount of moisture is constant as a given volume of air
rises This is a useful tool only to calculate how much water is in the
air at any given time and as that water rises towards the stratosphere,
how likely are clouds to form and rain to fall.

http://members.tripod.com/running4fun/run/humidity.html

This page is written by a Meteorologist. He gives a good explanation of
the problem and points out that RH without Dew Point temp is half a loaf.

For instance, right now in Houston
Temp 73F
RH is 87%
Dew Point is 69F

Right now in Villanova
Temp 59F
RH 88%
Dew Point is 56F

I do not imagine that you want to introduce this moisture laden air into
your apartment/home if you can help it. Doesn't matter whether we talk
Deep South or Pennsylvania. And in no case, do you want 90+F air in any
significant quantity coming inside to increase your A/C bill.


The Meteorologist points out that the highest dew point ever recorded in
his location was 88F right after a thunderstorm. Other than that, on
very humid days, the dew point only gets to the low 80s there
(Cincinatti) although Gulf War vets do know 90/90 days as the Red Sea
heats to above 90 F and with air temps in Kuwait rising to 110 or higher
lots of water is in the air. 90% RH with air temps above 90F is a very
very real situation for that location.

Robert Gammon wrote:

http://apollo.lsc.vsc.edu/classes/me...nd_parcel.html

... says that absolute humidity is NOT a good moisture variable even
though the amount of moisture is constant as a given volume of air rises

But it's quite useful for house ventilation control. So's the dew point,
but that's harder to measure with electronic sensors.

Nick