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
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.
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.
That's progress. Now we need your vow to stop posting falsehoods :-)
Irrelevant, unless all this makes your air heavier :-)
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.
This is true.
Another thing about hot, humid air is the difference in human breathing.
High humidity can actually reduce the partial pressure of oxygen in the air,
so one has to breath more for the same O2. The water vapor also changes the
viscosity slightly, making it 'feel' different to people that are breathing
heavily (such as while exerting themselves). Not to mention the
physiological response of the mucus membranes to the higher humidity.
For example, the vapor pressure at 70F and 50% is about 0.181 psia and pp of
O2 is 3.048 psia. But at 110F and 90% humidity, the vapor pressure rises to
1.14 psia and the pp of O2 is reduced to about 2.85 psia (~93%). Compare
this to the drop in partial pressure with altitude, and this is about the
equivalent change in pp of O2 as going from sea-level to 1600 feet up. But
the overall density of the mixture moving in/out the lungs is more than what
one would experience from just rising in elevation.
A layman in casual conversation might use words like 'heavy' or 'weighty' to
describe breathing in these conditions.
Nick needs to spend a summer in either Macon Georgia, Mobile Alabama,
New Orleans Louisiana, Houston Texas or Atlanta Georgia staying in a
home that does not have Air Conditioning BEFORE
says a another word about how wrong we all are, those of us who actually
live in these cities, and KNOW how hot and MISERABLE the summers are.
He simply has NO idea what we endure.
Did he actually ever build his homebrew sewage waste heat recovery
unit? He talked about it, but never showed us the end result or showed
the actual heat recovered.
Someone's ego is way over inflated.
I see no sign of arrogance.I don't try to tell Inuit people how to keep
their home warm.In order to do so with any semblance of intelligent ideas I
would need to spend some time in that locale.Some situations cannot be fully
appreciated until experienced.
Then again, there is no claim, because he's already said that he
was wrong about the 6000 hours/year thing.
By the way, the "smart vent" idea is a workable idea in some climates,
but not in the part of Texas where I live. The low last night was
73F, and it was only that low for about an hour. Considering that I
leave my thermostat set at 74F, the air inside the house has to be at
a lower humidity than the air outside since the A/C has been running
all night leading up to that point in the very early morning when
it's almost a comfortable temperature outside for an hour or two,
and during that whole time, it's been working to decrease the humidity
of the indoor air.
And, it's only June. The nights will continue to get hotter for a
few months. So, the smart vent might help at some time of the year
in the part of Texas that I live in, but it wouldn't be for the
part of the year when A/C is the most expensive, so when you consider
the smart vent's benefit in terms of saving energy, you've got to
consider that: if this device cuts (say) 20% off my electric bill
during the few months of the year when the bill is smallest, what
is the total savings over the course of a year? Not that large.
Then again, that was just one of many false claims :-) I was referring
to his more recent claim than humid air is denser than dry air.
Is anything denser than Mr. Gammon? :-)
We might say it's "workable" if it can significantly reduce an AC bill.
It can't replace AC or dehum in places like Galveston or Key West. It IS
a good way to dry out flood-damaged houses in New Orleans.
I'm unable to follow this logic, but we need to look at more than
one night. The idea is to dehumidify a house by ventilating it with
outdoor air if and when the absolute moisture content of the outdoor air
happens to be less than the absolute moisture content of the indoor air.
Or if the outdoor dew point is less than the indoor dew point, which
amounts to the same thing. That may not happen every night, but most
house materials can store moisture, or in this case, dryness.
For instance, Kurt Kielsgard Hanson's sorption isotherm catalog (as LBM
tech report 162/86 under http://www.byg.dtu.dk/publications/reports.htm )
says concrete stores about 1% moisture by weight as the RH of the air
around it increases from 40 to 60%, and it weighs about 150 lb/ft^3, so
a 4"x1000ft^2 50K pound floorslab could store 500 pints of water as
a basement RH increases from 40 to 60%. Mold forms in about 2 weeks,
above 60% RH. We might fire up the dehum or AC after 2 weeks...
And given the random nature of weather, we'd like to ventilate with
cooler air in summertime and warmer air in wintertime, other things being
equal, harvesting coolth and warmth when possible, avoiding condensation
inside the house. We might say "Never ventilate if the indoor dry bulb
is less than the outdoor dew point," or "Only when Tdbi-Tdpo > 5 F," or
"Only when Tdbi > Tdbo."
For instance, if your house were 80 F (460+80 = 540 R) with 60% RH indoors,
Tdpi = 540/(1-540ln(0.6)/9621) = 525 R (65 F). Outdoor air at 73 F and 50%
RH has Tdpo = 53 F, so ventilation will dehumidify and cool the house. If
Tdpo = 65, ie RH = 100e^(9621(525-533)/(525x533)) = 76%, ventilation will
not dehumidify, but it will cool the house. If RH > 76%, ventilation won't
help at all.
A 65 F house with 60% RH and Tdpi = 50.8 F and 80 F outdoor air might vent
whenever Tdpo < Tdbi-5 = 60 F, ie RH < 100e^9621(60-80)/(520x540)) = 50%
for warmth. This adds moisture to the house, but that's OK if there's no
condensation and the indoor temp rises to keep the RH < 60% to avoid mold.
Additional humidity makes it feel warmer and more comfortable.
Where do you live? This could work well in Abilene, with a w = 0.0130
yearly humidity ratio and 71.7 F daily min temp in August, or Amarillo
(0.0119) or El Paso (0.0112) or Lubbock (0.0127) or San Angelo (0.0132.)
Not every day, of course. How many hours per month are below average?
We might quantify this with a TMY2 simulation.
We use last night as an EXAMPLE OF A TYPICAL NIGHT. If you are unable
to see the logic of that, you need some more education. In the
Humid-SemiTropical region, which includes New Orleans as well as
Houston, there will be very very few nights when outdoor absolute
moisture content is LESS than the indoor condition.
Again, in the Humid-SemiTropical region, such a condition will not
happen on a daily or even weekly basis during the summertime. You
extrapolate too much from the conditions in your Pennsylvania location.
During the summertime, in most of the region within the
Humid-SemiTropical region, such a condition will exist so rarely that
the ventilator might as well not be there. At this moment, 6:00am in
mid-June, we have a fairly typical summertime condition for Houston
TX. Temp is 72F, RH is 89%, Dew Point is 69F. My interior is
currently sitting at just under 80F and RH feels like it is about 50%
and that suggests Dew Point is about 45F. From this point we will
climb to about 94F and RH will drop to about 50%. We will have mornings
where Dew Point is within one degree of outside air temp and RH will
decline only to about 80% with Dew Point tracking to within a few
degrees of actual air temp.
In the Humid SemiTropical region, for most of the year, certainly May
thru October, Outdoor RH will be HIGHER than indoor RH. Absolute
moisture content of outside air will remain higher than indoor moisture
for greater than 80% of the time. The ventilator will remain shut
almost all of the time. AprilAir's 8126 ventilator is an example, it
will never ventilate if indoor RH rises above 60%
Abilene is in a very different climate than Humid SemiTropical. It is
on the border with Desert Southwest. It gets half the rainfall of
Houston Tx. It gets much cooler there in the fall/winter than we do,
average low temps are in the low 40s there.
Our point is that ONE SIZE DOES NOT FIT ALL. Building standards for
Pennsylvania SHOULD be different from Humid SemiTropical areas like
Houston, as you are concerning about keeping moisture inside the house
for much of the year. Houston, New Orleans (never mind the flood
damage).... we worry about keeping moisture OUT for much of the year.
Would you have any evidence for this rather vague article of faith? :-)
No. I use real weather data measured every hour for the last 30 years in
Abilene, with w = 0.0130 and 71.7 F daily min in August, Amarillo (0.0119),
El Paso (0.0112), Lubbock (0.0127), San Angelo (0.0132), and Houston...
NREL says Houston has average daily min temps and humidity ratios of 64.4
and 0.0138, 70.6 and 0.0163, 72.4 and 0.0172, 72.0 and 0.0171, and 67.9
and 0.0154 in May through September. We can cool by ventilation then, but
dehum is less likely, so we probably need some AC dehumidification by day.
Condensation can be avoided. It seems to me that house materials that absorb
water will warm at night and lose that warmth to ventilation air and then
cool by evaporation during the day as the AC removes water, for a net energy
savings. You needn't reply if you have no idea what I'm talking about :-)
Would you have any evidence for this rather vague article of faith? :-)
How vague. That would depend on how you ventilate or use AC, no?
And we are discussing absolute vs RH.
They are. This would work better in Amarillo than Phila or Houston. So?
The weather data is from WeatherSource.
A typical, average summer day in this region shows nighttime temps in
the low to mid 70s with RH in the upper 80s to 90s. The indoor air temp
will be dependent on the homeowners setting of the thermostat, but will
range from the mid 70s to the low 80s. There is NO opportunity for
cooling from outside air as indoor moisture levels will increase to very
Right now, 8:15am June 10, 2006, outside air temp is 76F, winds are
calm, and RH is 82%, dew point is 70F Indoor conditions are just under
80F and RH is about 50%
The figures will change from location to location in the Humid
subTropical belt (or Humid SemiTropical belt as it is sometimes known),
but outdoor RH will rarely be lower than indoor RH, and outdoor air will
be lower in temp than indoor temps for only a very short intervals (a
few hours in the depths of the night) and only when RH is 80% or higher
(dew point within a few degrees of air temp)
There is NO help from the climate, in the summer months. We fight to
keep moisture OUT, almost all the time. 48 inches a year of rainfall
(yes Virginia, I said FOURTY EIGHT INCHES OF RAINFALL A YEAR, very flat
land, high clay content in soils, so water pools, it does not drain away
NREL data doe not correlate the time periods when low temp and humidity
ratios occur. They do not occur at the same time of day. Low temps
are the times when the humidity is the highest of the day, we are very
close to saturation in the hours when the low temp is recorded. The
low point for humidity will be late in the day when temperature is the
25 years of experience living in this environment is NOT a rather vague
article of faith.
Other when there is a thunderstorm in Villanova, what time of day do YOU
have the lowest relative humidity????
YOU are discussing absolute, YOU are the only person using that term.
25 years of experience in THIS climate is REAL world application of
information. This is not an urban myth. We invite you to to fly to
Houston, or New Orleans for a few days to observe FRIST hand what we
experience. As was mentioned by another poster, we do not attempt to
tell the Native Canadians/Americans that live in the northern reaches of
Canada and Alaska how to heat their homes in winter, not until we have
been there and get some experience with local conditions, and see how
people are dealing with the problems now, BEFORE we make recommendations.
SouthWest Airlines will get you here in a fully refundable RT ticket for
about $600, less than half of that if you plan ahead.
We are agreed then FINALLY. This is not appropriate technology for all
regions. Yes dry climates like Amarillo, or anywhere in the desert
southwest could benefit from this technology, however, the INTENSE heat
requires either refrigeration, or evaporative cooling to make the days
Outside of summertime, this technology will work well in any region that
has a relatively mild climate, and is relatively average to dry in
One other data point comes from this web site
I am in region 5. It says that I have 2803 cooling hours per year
Region 5 includes Houston, New Orleans, Mobile, and most of Florida
Region 4 has 1986 cooling hours per year and includes Macon Georgia,
Nick lives in Region 2 with only 935 cooling hours per year
So I have TRIPLE the cooling time requirement of Nick
Sounds like these opportunities will happen on non-average days, about
which we know little, given this data, except that half the days will be
cooler and half will be drier... 50% isn't bad odds. Nor is 25%, if cool
and damp are well-correlated.
A single instant has little meaning.
Would you have any evidence for this rather vague article of faith? :-)
I disagree. You also seem to have missed this subtlety:
Wrong again. Their monthly averages don't, but their hourly measurements do,
in the form of TMY2 data files. Then again, humidity ratios don't change
much over a day, since they are independent of temperature. Newer ASHRAE
HOFs give mean coincident summer design temps and humidity ratios.
It is, given real numerical data ("It shore feels hot when my bunion hurts!")
Wrong again. Lots of people use that term.
Great. Send me an airplane or train ticket, s'il te plait.
Given only that data, you can make those assumptions about percentages,
and those are pretty valid assumptions. But the reality, at least in
Austin, TX, is different. In practice, the typical day is very hot
during the daytime hours with mild temperatures (75F to 80F) and high
humidity during the night.
However, if it's not a typical day, there's a 99.999% chance it's because
we've had a summer afternoon thunderstorm where the heat of the day
drives massive convection and we get drenched with water. On such a
day, the temperatures will drop below normal during the evening and
night, but the humidity is through the roof. So, in practice, the
probabilities of cold and of dry are NOT independent. They are VERY
 Not totally valid though: if you have a group of 10 people
with an average income of $145,000, it is not safe to assume
that half the people make more than $145,000 and half the
people make less. It's quite possible you have one person
with an income of $1,000,000 and nine people with an income
of $50,000. So in that case, 90% of the people have a
Yes, Nick is arguing that he does not believe the average day is what we
say it is.
Ok, these ARE averages, and we DO get a cool front to move thru and yes
we have a thunderstorm. Temps drop from high 80s to mid 90s to low 80s,
but then RH is close to 100% after the storm, uncomfy at best. Storms
dissipate in the wake of the cool front. Daytime temps are now hitting
the mid 80s vs low 90s, AH relief. But then the next High pressure
system moves in and we BAKE for two to three weeks with no rain and
cloudless skies. Daytime highs climb to mid to upper 90s, and with all
the surface water surrounding us (Austin and Houston aren't that much
different in the amount of surface water surrounding us, execpt for our
proximity to Galveston Bay and Gulf of Mexico) evaporation rates climb
and so does humidity. Well contractor talked to me about pumping ground
water thru a geothermal heat pump and into a pond. Said pond will lose
1/2 inch to 1 inch of water level a day of more water is not supplied.
Logan is making EXCELLENT comments. However, in Nick's defense, he has
backed off on saying that the system will work for US, and is now saying
that it works better in dryer climates, cooler climates than what we
The weatherbase.com web site points out some interesting facts about
where I live.
COOLING DEGREE DAYS EXIST HERE EVEN IN JANUARY AND FEBRUARY!!
Yes, I have run my AC at times all thru the year, in every month. It
gets cool for a short while then we have a spike that puts daytime highs
in the upper 70s to low 80s, and with interior heat sources(TV, cooking,
showers, people), house temps go above that so the AC runs for a few hours.
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