"Robert Gammon" wrote in message
. com...
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.


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.

daestrom

daestrom wrote:

"Robert Gammon" wrote in message
. com...
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.


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.

daestrom

EXACTLY how I feel here on the numerous summer day where the air temp is
in the mid-upper 90s and afternoon RH is well above 75% Its harder to
do EVERYTHING. and the car I drive now has its AC broken.

Robert Gammon wrote:

A layman in casual conversation might use words like 'heavy' or
'weighty' to describe breathing in these conditions.

EXACTLY how I feel here on the numerous summer day...

Then again, that has nothing to do with your claim.

Nick

wrote:
Robert Gammon wrote:


A layman in casual conversation might use words like 'heavy' or
'weighty' to describe breathing in these conditions.


EXACTLY how I feel here on the numerous summer day...


Then again, that has nothing to do with your claim.

Nick


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.

Robert Gammon wrote:

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...

How extraordinarily arrogant :-)

Nick

wrote in message
...
Robert Gammon wrote:

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...

How extraordinarily arrogant :-)

Nick

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.

wrote:
Robert Gammon wrote:

A layman in casual conversation might use words like 'heavy' or
'weighty' to describe breathing in these conditions.

EXACTLY how I feel here on the numerous summer day...

Then again, that has nothing to do with your claim.

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.

- Logan

Logan Shaw wrote:
wrote:
Robert Gammon wrote:
Daestrom wrote:
A layman in casual conversation might use words like 'heavy' or
'weighty' to describe breathing in these conditions.

EXACTLY how I feel here on the numerous summer day...

Which numerous summer day? :-)

Then again, that has nothing to do with your claim.

Then again, there is no claim, because he's already said that he
was wrong about the 6000 hours/year thing.

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? :-)

... the "smart vent" idea is a workable idea in some climates,
but not in the part of Texas where I live.

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.

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.

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.

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.

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.

Nick

wrote:
Logan Shaw wrote:

wrote:

Robert Gammon wrote:

Daestrom wrote:

A layman in casual conversation might use words like 'heavy' or
'weighty' to describe breathing in these conditions.


EXACTLY how I feel here on the numerous summer day...


Which numerous summer day? :-)


Then again, that has nothing to do with your claim.

Then again, there is no claim, because he's already said that he
was wrong about the 6000 hours/year thing.


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? :-)


... the "smart vent" idea is a workable idea in some climates,
but not in the part of Texas where I live.


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.


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.


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.


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.
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."

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.
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.


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.



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.


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%

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.


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.



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.

Robert Gammon wrote:

... 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."

... in the Humid-SemiTropical region, such a condition will not
happen on a daily or even weekly basis during the summertime.

Would you have any evidence for this rather vague article of faith? :-)

You extrapolate too much from the conditions in your Pennsylvania location.

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 :-)

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.

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.

Would you have any evidence for this rather vague article of faith? :-)

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.

In the Humid SemiTropical region, for most of the year, certainly May
thru October, Outdoor RH will be HIGHER than indoor RH.

How vague. That would depend on how you ventilate or use AC, no?
And we are discussing absolute vs RH.

... ONE SIZE DOES NOT FIT ALL.

Agreed.

Building standards for Pennsylvania SHOULD be different from Humid
SemiTropical areas like Houston...

They are. This would work better in Amarillo than Phila or Houston. So?

Nick

wrote:
Robert Gammon wrote:


... 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."


... in the Humid-SemiTropical region, such a condition will not
happen on a daily or even weekly basis during the summertime.


Would you have any evidence for this rather vague article of faith? :-)

http://en.wikipedia.org/wiki/Houston%2C_Texas#Climate

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
uncomfortable levels.

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
efficiently.


You extrapolate too much from the conditions in your Pennsylvania location.


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 :-)


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
highest.

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.


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.


Would you have any evidence for this rather vague article of faith? :-)


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????

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.


In the Humid SemiTropical region, for most of the year, certainly May
thru October, Outdoor RH will be HIGHER than indoor RH.


How vague. That would depend on how you ventilate or use AC, no?
And we are discussing absolute vs RH.


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.


... ONE SIZE DOES NOT FIT ALL.


Agreed.


Building standards for Pennsylvania SHOULD be different from Humid
SemiTropical areas like Houston...


They are. This would work better in Amarillo than Phila or Houston. So?


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
bearable.

Outside of summertime, this technology will work well in any region that
has a relatively mild climate, and is relatively average to dry in
humidity levels.

One other data point comes from this web site

http://www.hvacopcost.com/


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,
Midland TX

Nick lives in Region 2 with only 935 cooling hours per year

So I have TRIPLE the cooling time requirement of Nick

Robert Gammon wrote:

... 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."

... in the Humid-SemiTropical region, such a condition will not
happen on a daily or even weekly basis during the summertime.

Would you have any evidence for this rather vague article of faith? :-)

http://en.wikipedia.org/wiki/Houston%2C_Texas#Climate

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...

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.

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%

A single instant has little meaning.

... 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)...

Would you have any evidence for this rather vague article of faith? :-)

There is NO help from the climate, in the summer months...

I disagree. You also seem to have missed this subtlety:

ACHTUNG: SUBTLETY!

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 :-)

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.

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.

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.

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.

Would you have any evidence for this rather vague article of faith? :-)

25 years of experience living in this environment is NOT a rather vague
article of faith.

It is, given real numerical data ("It shore feels hot when my bunion hurts!")

Other when there is a thunderstorm in Villanova, what time of day do YOU
have the lowest relative humidity????

In the Humid SemiTropical region, for most of the year, certainly May
thru October, Outdoor RH will be HIGHER than indoor RH.

How vague. That would depend on how you ventilate or use AC, no?
And we are discussing absolute vs RH.

YOU are discussing absolute, YOU are the only person using that term.

Wrong again. Lots of people use that term.

... We invite you to to fly to Houston, or New Orleans for a few days
to observe FRIST hand what we experience.

Great. Send me an airplane or train ticket, s'il te plait.

Nick

"Robert Gammon" wrote in message
. com...
wrote:
Robert Gammon wrote:
snip
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 :-)


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 highest.


This is why Nick is trying to keep to absolute humidity ratios. When you
take a quantity of air with some moisture in it (say, 70F @90% RH) and heat
it up (to say 95F), the RH will drop from 90% to 41%, but the absolute
humidity ratio of the moisture does *not* change (nor does the dew point).
As we all 'know', warm air can hold more moisture than cool air, so the
amount of moisture *relative* to how much it could hold goes down. That's
one reason why warm air dries things out better than cool air.

So, *IF* the dew point of the outside air is low at night, then the absolute
humidity is also low and one could get some benefits from ventilation. But
if the dew point is upwards of 70F (as it often is in the summer along the
Gulf Coast), then ventilation hurts, not helps. I don't think this idea
would work well along the Gulf Coast (spent several years in MS), but it can
work in other areas. I think the key is to track the dew point (a direct
measure of absolute humidity).

My brother lives in Spring Tx (near Houston) and he mentions that they often
report the RH as 100% in summer in late afternoon. At first this seems
impossible (how can air be holding more moisture than the total amount of
moisture air can hold??). But the answer lies in haze/ hot-fog. Moisture
levels are so high during the day that as the air cools it actually becomes
'super-saturated' and as moisture condenses it doesn't 'fall' out of the air
and remains suspended as haze.

It may be interesting to note that the 'overnight low' predicted by
meteorologists is often tied closely with dew point. If the dew point is
78F on a sweltering evening in MS, you could bet the overnight low would not
drop more than a degree or two below 78F. Not unless a cooler/dryer air
mass was predicted to move into the area. Once the air cools to the dew
point, the latent heat that must be rejected to condense moisture out of the
air in cooling below the dew point pretty well stops any further cooling.

daestrom

wrote:
Logan Shaw wrote:

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.

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.

Yes, what I'm trying to say is this: in the climate where I live,
unless you like it being 85F or even 90F indoors, you *will* run the
air conditioning in a typical house for many hours a day. So, you
have to take that fact into account when you try to understand whether,
in actual practice, the outdoor air will have less moisture than the
indoor air.

To put it another way, if you left the A/C and heat turned off
indefinitely, eventually the indoor air and outdoor air would reach a
point something like an equilibrium where the indoor and outdoor air
have the same moisture content. That's because there is leakage and
the two bodies of air are actually mixing all the time. So, with
no climate control intervention taking place, they have the same
average moisture content. Now, add in the assumption that you are
running the A/C at probably a 50% duty cycle during the day and
that the nights are hot enough that it continues to run all night.
This tends to make the indoor air less humid, right? That is,
after all, what air conditioners do.

So, to summarize, if you start with the assumption that the A/C runs
several hours every day, the likelihood that outdoor air has less
moisture in it than indoor air does is very low, because the indoor
air is having its moisture level artificially lowered on a continuous
basis.

To illustrate the difference, here's an analogy. Imagine that you
were crazy enough to build a 5-story parking garage below ground
right by the beach just a hundred feet away from the ocean. You
encase the whole thing in concrete and anchor it into bedrock so
it doesn't float due to buoyancy, but you find that there is a
leak and the seawater is seeping in somewhere.

The water fills up 4 of the 5 levels of the garage. Because of tides,
the water table changes; sometimes it's high enough that if it stayed
at that level, it would fill up all 5 levels, and sometimes it's low
enough that it would only fill up 3 levels if it stayed. But because
it varies and sometimes water is flowing in and sometimes flowing out,
the garage stays full up to about the 4th level.

What do you do? You put in a bilge pump. The seawater seeps in at
a good rate during high tide, but you discover if you run the bilge
pump at the right duty cycle, you can keep the water out of the top
4 floors even then. So you run the bilge pump, with nearly a 100%
duty cycle during high tide and with a much lower duty cycle during
low tide, and you manage to keep the top 4 floors free of water,
which makes the garage useful, and you can charge people to park in
it and make money.

Now you start looking at ways to save money. You suddenly hit upon an
idea: instead of a pump, you can put in a valve that is controlled by
a water level sensor. When the water table is lower than the level
in your parking garage, the valve will open and water will flow out
by gravity. When it's higher, the valve will close. Sounds good.
But then you do the math and you realize that the lowest level that
water table is ever at is 3 floors up in your garage, and since you
are running the bilge pump to keep the water down to only the first
floor of the garage, the water level in your garage is never actually
going to BE higher than the water table. So you realize that the valve
will never open and you will never save any money by installing it.

And given the random nature of weather, we'd like to ventilate with
cooler air in summertime

What I'm saying is that, in my climate, there IS no cooler air in the
summertime. The indoor air is always cooler and has less moisture
than the outdoor air, for months in a row. The only time when outdoor
air is relatively cool is when we have a thunderstorm. Then the
temperature drops, but the humidity goes way up.

If you go to http://www.weatherbase.com/ and look at the average low
temperature for Austin, TX, you'll see that during the months of
June, July, and August, the average lows are 72, 74, and 74,
respectively. Also, go to

http://weather.noaa.gov/weather/current/KATT.html

and look at the 24-hour weather history for Austin to see what time
that lower-70's weather occurs. It's usually only for 1-3 hours,
right between 5:00am and 7:00am. Now go back to weatherbase.com
and look at "All Data" instead of "Summary", and look at the
"Average Morning Relative Humidity" data. You can see that in the
mornings in June, July, and August, it's nearly 90% relative
humidity. Meanwhile, with the thermostat set at 75F and with the
air conditioning having run a moderate amount all night since it
was probably still 90F at 10:00pm, would I want to ventilate the
house and get some of that outside air? The indoor air is about
the same temperature but the indoor moisture is low since the A/C
has been taking moisture out of the air all night.

Now go back and look at the average high temperature for June,
July, and August in Austin. It's 90-95F average for all three
months. So, when do you think people in Austin spend the most
on electricity for A/C? It's June, July, and August. If you want
to make a dent in the cost of A/C and be frugal, you've got to
attack the part where most of the money is going. A smart vent
might be able to lower the bills for the months when the weather
is relatively mild, but that isn't going to help much since
those months are a small part of the total expenditures.

- Logan

wrote:
Robert Gammon wrote:

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...

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.

Given only that data, you can make those assumptions about percentages,
and those are pretty valid assumptions[1]. 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
strongly correlated.

- Logan

[1] 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
below-average income.

Logan Shaw wrote:
wrote:
Robert Gammon wrote:

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...

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.

Given only that data, you can make those assumptions about percentages,
and those are pretty valid assumptions[1]. 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.

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.

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
strongly correlated.

- Logan

[1] 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
below-average income.


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
enjoy/suffer with.

Logan Shaw wrote:
wrote:
Logan Shaw wrote:

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.

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.

And given the random nature of weather, we'd like to ventilate with
cooler air in summertime

What I'm saying is that, in my climate, there IS no cooler air in the
summertime. The indoor air is always cooler and has less moisture
than the outdoor air, for months in a row. The only time when outdoor
air is relatively cool is when we have a thunderstorm. Then the
temperature drops, but the humidity goes way up.

If you go to http://www.weatherbase.com/ and look at the average low
temperature for Austin, TX, you'll see that during the months of
June, July, and August, the average lows are 72, 74, and 74,
respectively. Also, go to
And from that weatherbase web site, I look at Alvin TX as it is 42 feet
above sea level and I am about 50 ft above, Alvin is about the same
distance from me as the 100ft measuring point for Houston, and MUCH
closer than the airport measuring point.

COOLING DEGREE DAYS EXIST IN EVERY MONTH OF THE YEAR!! Nick may not
believe, but yes A/C runs some days even in January and February if for
no other reason than to remove humidity and the heat buildup from
cooking, TVs, ironing, people showers, etc.

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.

Robert Gammon wrote

The weatherbase.com web site points out some interesting facts about where I live.

COOLING DEGREE DAYS EXIST HERE EVEN IN JANUARY AND FEBRUARY!!

Not necessarily best handled with AC tho in Jan and Feb.

Yes, I have run my AC at times all thru the year, in every month.

Not a very frugal approach.

It gets cool for a short while then we have a spike that puts daytime highs in the upper
70s to low 80s,

Doesnt really require the use of the AC.

and with interior heat sources(TV, cooking, showers, people), house temps go above that

Unlikely since most of that doesnt happen when the outside temps peak.

so the AC runs for a few hours.

Mad.

Rod Speed wrote:
Robert Gammon wrote


The weatherbase.com web site points out some interesting facts about where I live.



COOLING DEGREE DAYS EXIST HERE EVEN IN JANUARY AND FEBRUARY!!


Not necessarily best handled with AC tho in Jan and Feb.


Yes, I have run my AC at times all thru the year, in every month.


Not a very frugal approach.


It gets cool for a short while then we have a spike that puts daytime highs in the upper
70s to low 80s,


Doesnt really require the use of the AC.


and with interior heat sources(TV, cooking, showers, people), house temps go above that


Unlikely since most of that doesnt happen when the outside temps peak.


so the AC runs for a few hours.


Mad.



Ok, you do not believe. That's up to you. With inside temps in the
mid 80s in January here and indoor RH above 75%, YOU COME SWEAT IT OUT HERE.

wrote in message
...
Logan Shaw wrote:
wrote:
Robert Gammon wrote:
Daestrom wrote:
A layman in casual conversation might use words like 'heavy' or
'weighty' to describe breathing in these conditions.

EXACTLY how I feel here on the numerous summer day...

Which numerous summer day? :-)

Then again, that has nothing to do with your claim.

Then again, there is no claim, because he's already said that he
was wrong about the 6000 hours/year thing.

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? :-)

... the "smart vent" idea is a workable idea in some climates,
but not in the part of Texas where I live.

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.

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.

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.

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.

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.

Nick

I can see you have not learned yet.The people who live in a certain are KNOW
if the air outside the home is drier than inside.Your number crunching is
foolish.

wrote in message
...
Robert Gammon wrote:

... 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."

... in the Humid-SemiTropical region, such a condition will not
happen on a daily or even weekly basis during the summertime.

Would you have any evidence for this rather vague article of faith? :-)

You extrapolate too much from the conditions in your Pennsylvania
location.

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 :-)

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.

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.

Would you have any evidence for this rather vague article of faith? :-)

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.

In the Humid SemiTropical region, for most of the year, certainly May
thru October, Outdoor RH will be HIGHER than indoor RH.

How vague. That would depend on how you ventilate or use AC, no?
And we are discussing absolute vs RH.

... ONE SIZE DOES NOT FIT ALL.

Agreed.

Building standards for Pennsylvania SHOULD be different from Humid
SemiTropical areas like Houston...

They are. This would work better in Amarillo than Phila or Houston. So?

Nick
speaking of faith...you have much too much faith in your interpritation of
the numbers.You do not have a clue about actual local conditions.You try to
dazzle with numbers ..then ask "where is your proof?"well....where is your
proof...what house in middle georgia..or new orleans...or lower texas...have
you used this frugal dehumid on????
there is a house for sale right down the road...I will get the realtors
number and you can come try your idea.

wrote in message
...
Robert Gammon wrote:

... 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."

... in the Humid-SemiTropical region, such a condition will not
happen on a daily or even weekly basis during the summertime.

Would you have any evidence for this rather vague article of faith? :-)

http://en.wikipedia.org/wiki/Houston%2C_Texas#Climate

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...

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.

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%

A single instant has little meaning.

... 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)...

Would you have any evidence for this rather vague article of faith? :-)

There is NO help from the climate, in the summer months...

I disagree. You also seem to have missed this subtlety:

ACHTUNG: SUBTLETY!

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
:-)

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.

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.

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.

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.

Would you have any evidence for this rather vague article of faith? :-)

25 years of experience living in this environment is NOT a rather vague
article of faith.

It is, given real numerical data ("It shore feels hot when my bunion
hurts!")

Other when there is a thunderstorm in Villanova, what time of day do YOU
have the lowest relative humidity????

In the Humid SemiTropical region, for most of the year, certainly May
thru October, Outdoor RH will be HIGHER than indoor RH.

How vague. That would depend on how you ventilate or use AC, no?
And we are discussing absolute vs RH.

YOU are discussing absolute, YOU are the only person using that term.

Wrong again. Lots of people use that term.

... We invite you to to fly to Houston, or New Orleans for a few days
to observe FRIST hand what we experience.

Great. Send me an airplane or train ticket, s'il te plait.

Nick

you are a vague article of faith...put your money where your mouth is and
show us...come down here and use your idea.

"Logan Shaw" wrote in message
...
wrote:
Logan Shaw wrote:

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.

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.

Yes, what I'm trying to say is this: in the climate where I live,
unless you like it being 85F or even 90F indoors, you *will* run the
air conditioning in a typical house for many hours a day. So, you
have to take that fact into account when you try to understand whether,
in actual practice, the outdoor air will have less moisture than the
indoor air.

To put it another way, if you left the A/C and heat turned off
indefinitely, eventually the indoor air and outdoor air would reach a
point something like an equilibrium where the indoor and outdoor air
have the same moisture content. That's because there is leakage and
the two bodies of air are actually mixing all the time. So, with
no climate control intervention taking place, they have the same
average moisture content. Now, add in the assumption that you are
running the A/C at probably a 50% duty cycle during the day and
that the nights are hot enough that it continues to run all night.
This tends to make the indoor air less humid, right? That is,
after all, what air conditioners do.

So, to summarize, if you start with the assumption that the A/C runs
several hours every day, the likelihood that outdoor air has less
moisture in it than indoor air does is very low, because the indoor
air is having its moisture level artificially lowered on a continuous
basis.

To illustrate the difference, here's an analogy. Imagine that you
were crazy enough to build a 5-story parking garage below ground
right by the beach just a hundred feet away from the ocean. You
encase the whole thing in concrete and anchor it into bedrock so
it doesn't float due to buoyancy, but you find that there is a
leak and the seawater is seeping in somewhere.

The water fills up 4 of the 5 levels of the garage. Because of tides,
the water table changes; sometimes it's high enough that if it stayed
at that level, it would fill up all 5 levels, and sometimes it's low
enough that it would only fill up 3 levels if it stayed. But because
it varies and sometimes water is flowing in and sometimes flowing out,
the garage stays full up to about the 4th level.

What do you do? You put in a bilge pump. The seawater seeps in at
a good rate during high tide, but you discover if you run the bilge
pump at the right duty cycle, you can keep the water out of the top
4 floors even then. So you run the bilge pump, with nearly a 100%
duty cycle during high tide and with a much lower duty cycle during
low tide, and you manage to keep the top 4 floors free of water,
which makes the garage useful, and you can charge people to park in
it and make money.

Now you start looking at ways to save money. You suddenly hit upon an
idea: instead of a pump, you can put in a valve that is controlled by
a water level sensor. When the water table is lower than the level
in your parking garage, the valve will open and water will flow out
by gravity. When it's higher, the valve will close. Sounds good.
But then you do the math and you realize that the lowest level that
water table is ever at is 3 floors up in your garage, and since you
are running the bilge pump to keep the water down to only the first
floor of the garage, the water level in your garage is never actually
going to BE higher than the water table. So you realize that the valve
will never open and you will never save any money by installing it.

And given the random nature of weather, we'd like to ventilate with
cooler air in summertime

What I'm saying is that, in my climate, there IS no cooler air in the
summertime. The indoor air is always cooler and has less moisture
than the outdoor air, for months in a row. The only time when outdoor
air is relatively cool is when we have a thunderstorm. Then the
temperature drops, but the humidity goes way up.

If you go to http://www.weatherbase.com/ and look at the average low
temperature for Austin, TX, you'll see that during the months of
June, July, and August, the average lows are 72, 74, and 74,
respectively. Also, go to

http://weather.noaa.gov/weather/current/KATT.html

and look at the 24-hour weather history for Austin to see what time
that lower-70's weather occurs. It's usually only for 1-3 hours,
right between 5:00am and 7:00am. Now go back to weatherbase.com
and look at "All Data" instead of "Summary", and look at the
"Average Morning Relative Humidity" data. You can see that in the
mornings in June, July, and August, it's nearly 90% relative
humidity. Meanwhile, with the thermostat set at 75F and with the
air conditioning having run a moderate amount all night since it
was probably still 90F at 10:00pm, would I want to ventilate the
house and get some of that outside air? The indoor air is about
the same temperature but the indoor moisture is low since the A/C
has been taking moisture out of the air all night.

Now go back and look at the average high temperature for June,
July, and August in Austin. It's 90-95F average for all three
months. So, when do you think people in Austin spend the most
on electricity for A/C? It's June, July, and August. If you want
to make a dent in the cost of A/C and be frugal, you've got to
attack the part where most of the money is going. A smart vent
might be able to lower the bills for the months when the weather
is relatively mild, but that isn't going to help much since
those months are a small part of the total expenditures.

- Logan

You explained that very well..I wish I could have made the point as simply
and straightforward as you.

Robert Gammon wrote
Rod Speed wrote
Robert Gammon wrote

The weatherbase.com web site points out some interesting facts about where I live.

COOLING DEGREE DAYS EXIST HERE EVEN IN JANUARY AND FEBRUARY!!

Not necessarily best handled with AC tho in Jan and Feb.

Yes, I have run my AC at times all thru the year, in every month.

Not a very frugal approach.

It gets cool for a short while then we have a spike that puts daytime highs in the
upper 70s to low 80s,

Doesnt really require the use of the AC.

and with interior heat sources(TV, cooking, showers, people), house temps go above
that

Unlikely since most of that doesnt happen when the outside temps peak.

so the AC runs for a few hours.

Mad.

Ok, you do not believe.

I didnt say I didnt believe that YOU choose to use an AC like that.

I JUST said that its not a very frugal approach and it isnt the only possibility.

With inside temps in the mid 80s in January here

Bet thats rare there. And is mostly the result of having the AC set point too high.

and indoor RH above 75%,

And AC aint the only way to deal with that. Most obviously with the showers.

YOU COME SWEAT IT OUT HERE.

Thats not sweating it out and running the AC for hours aint
the only way to deal with that in those months anyway.

Logan Shaw wrote:

Scheme I: we need to look at more than one night... 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.

Scheme II: Ventilate a house with some internal thermal mass at night
when outdoor air is cooler and dry enough to avoid condensation inside
the house, and AC the house during the day, for a net sensible cooling
gain, compared to AC alone.

... in the climate where I live, unless you like it being 85F or even
90F indoors, you *will* run the air conditioning in a typical house
for many hours a day.

OK.

... you have to take that fact into account when you try to understand
whether, in actual practice, the outdoor air will have less moisture
than the indoor air.

Then again, we have scheme II...

... if you left the A/C and heat turned off indefinitely, eventually
the indoor air and outdoor air would reach a point something like
an equilibrium where the indoor and outdoor air have the same moisture
content. That's because there is leakage and the two bodies of air
are actually mixing all the time.

Airsealing houses with blower door testing can help a lot in these
regions, but I suppose that's rarely done. They need dehumidification,
but they don't need lots of cooling compared to Southwest houses, so
airsealing can save a lot more energy than insulation.

... if you start with the assumption that the A/C runs several hours
every day, the likelihood that outdoor air has less moisture in it
than indoor air does is very low, because the indoor air is having
its moisture level artificially lowered on a continuous basis.

Agreed...

And given the random nature of weather, we'd like to ventilate with
cooler air in summertime

... in my climate, there IS no cooler air in the summertime.

The numbers below belie the statement above.

... The only time when outdoor air is relatively cool is when we have
a thunderstorm. Then the temperature drops, but the humidity goes way up.

Hmmm.

If you go to http://www.weatherbase.com/ and look at the average low
temperature for Austin, TX, you'll see that during the months of
June, July, and August, the average lows are 72, 74, and 74...

NREL's long-term average Austin lows are 71.5, 73.9, and 73.9, but
these are averages, so half the nights are cooler. The 30-year record
hourly lows are 53, 64, and 61. These might be 4 or 5 sigma tails of
a Gaussian distribution. We could do a simple TMY2 simulation.

... Also, go to http://weather.noaa.gov/weather/current/KATT.html
and look at the 24-hour weather history for Austin to see what time
that lower-70's weather occurs. It's usually only for 1-3 hours,
right between 5:00am and 7:00am.

We can do a lot with 1-3 hours of ventilation. If it's 80 F indoors
and 70 outdoors, 2 hours at 5000 cfm (eg 2 90 watt Lasko window fans)
can remove about 2(80-70)5000 = 100,000 Btu, like a 5,000 Btu/h 500W
window AC running for 20 hours. At 65, we can move 150K Btu, like
a 3-ton AC running 4 hours.

Now go back to weatherbase.com and look at "All Data" instead of
"Summary", and look at the "Average Morning Relative Humidity" data.
You can see that in the mornings in June, July, and August, it's
nearly 90% relative humidity.

Sounds like scheme II...

... with the thermostat set at 75F and with the air conditioning
having run a moderate amount all night since it was probably still
90F at 10:00pm, would I want to ventilate the house and get some
of that outside air?

Perhaps, if you want to save energy and money.

Now go back and look at the average high temperature for June,
July, and August in Austin. It's 90-95F average for all three
months. So, when do you think people in Austin spend the most
on electricity for A/C? It's June, July, and August. If you want
to make a dent in the cost of A/C and be frugal, you've got to
attack the part where most of the money is going. A smart vent
might be able to lower the bills for the months when the weather
is relatively mild, but that isn't going to help much since
those months are a small part of the total expenditures.

We might ask "How much does it save?" and "How much does it cost?"

Nick

wrote in message
...
Logan Shaw wrote:

Scheme I: we need to look at more than one night... 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.

Scheme II: Ventilate a house with some internal thermal mass at night
when outdoor air is cooler and dry enough to avoid condensation inside
the house, and AC the house during the day, for a net sensible cooling
gain, compared to AC alone.

... in the climate where I live, unless you like it being 85F or even
90F indoors, you *will* run the air conditioning in a typical house
for many hours a day.

OK.

... you have to take that fact into account when you try to understand
whether, in actual practice, the outdoor air will have less moisture
than the indoor air.

Then again, we have scheme II...

... if you left the A/C and heat turned off indefinitely, eventually
the indoor air and outdoor air would reach a point something like
an equilibrium where the indoor and outdoor air have the same moisture
content. That's because there is leakage and the two bodies of air
are actually mixing all the time.

Airsealing houses with blower door testing can help a lot in these
regions, but I suppose that's rarely done. They need dehumidification,
but they don't need lots of cooling compared to Southwest houses, so
airsealing can save a lot more energy than insulation.

... if you start with the assumption that the A/C runs several hours
every day, the likelihood that outdoor air has less moisture in it
than indoor air does is very low, because the indoor air is having
its moisture level artificially lowered on a continuous basis.

Agreed...

And given the random nature of weather, we'd like to ventilate with
cooler air in summertime

... in my climate, there IS no cooler air in the summertime.

The numbers below belie the statement above.

... The only time when outdoor air is relatively cool is when we have
a thunderstorm. Then the temperature drops, but the humidity goes way up.

Hmmm.

If you go to http://www.weatherbase.com/ and look at the average low
temperature for Austin, TX, you'll see that during the months of
June, July, and August, the average lows are 72, 74, and 74...

NREL's long-term average Austin lows are 71.5, 73.9, and 73.9, but
these are averages, so half the nights are cooler. The 30-year record
hourly lows are 53, 64, and 61. These might be 4 or 5 sigma tails of
a Gaussian distribution. We could do a simple TMY2 simulation.

... Also, go to http://weather.noaa.gov/weather/current/KATT.html
and look at the 24-hour weather history for Austin to see what time
that lower-70's weather occurs. It's usually only for 1-3 hours,
right between 5:00am and 7:00am.

We can do a lot with 1-3 hours of ventilation. If it's 80 F indoors
and 70 outdoors, 2 hours at 5000 cfm (eg 2 90 watt Lasko window fans)
can remove about 2(80-70)5000 = 100,000 Btu, like a 5,000 Btu/h 500W
window AC running for 20 hours. At 65, we can move 150K Btu, like
a 3-ton AC running 4 hours.

Now go back to weatherbase.com and look at "All Data" instead of
"Summary", and look at the "Average Morning Relative Humidity" data.
You can see that in the mornings in June, July, and August, it's
nearly 90% relative humidity.

Sounds like scheme II...

... with the thermostat set at 75F and with the air conditioning
having run a moderate amount all night since it was probably still
90F at 10:00pm, would I want to ventilate the house and get some
of that outside air?

Perhaps, if you want to save energy and money.

Now go back and look at the average high temperature for June,
July, and August in Austin. It's 90-95F average for all three
months. So, when do you think people in Austin spend the most
on electricity for A/C? It's June, July, and August. If you want
to make a dent in the cost of A/C and be frugal, you've got to
attack the part where most of the money is going. A smart vent
might be able to lower the bills for the months when the weather
is relatively mild, but that isn't going to help much since
those months are a small part of the total expenditures.

We might ask "How much does it save?" and "How much does it cost?"

Nick

now you are making sense

http://www.synapse9.com/airnets.htm
http://www.motherearthnews.com/libra...s_House_Part_V

look for rockbed

wrote:
Logan Shaw wrote:


Scheme I: we need to look at more than one night... 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.


Scheme II: Ventilate a house with some internal thermal mass at night
when outdoor air is cooler and dry enough to avoid condensation inside
the house, and AC the house during the day, for a net sensible cooling
gain, compared to AC alone.


... in the climate where I live, unless you like it being 85F or even
90F indoors, you *will* run the air conditioning in a typical house
for many hours a day.


OK.


... you have to take that fact into account when you try to understand
whether, in actual practice, the outdoor air will have less moisture
than the indoor air.


Then again, we have scheme II...


... if you left the A/C and heat turned off indefinitely, eventually
the indoor air and outdoor air would reach a point something like
an equilibrium where the indoor and outdoor air have the same moisture
content. That's because there is leakage and the two bodies of air
are actually mixing all the time.


Airsealing houses with blower door testing can help a lot in these
regions, but I suppose that's rarely done. They need dehumidification,
but they don't need lots of cooling compared to Southwest houses, so
airsealing can save a lot more energy than insulation.


... if you start with the assumption that the A/C runs several hours
every day, the likelihood that outdoor air has less moisture in it
than indoor air does is very low, because the indoor air is having
its moisture level artificially lowered on a continuous basis.


Agreed...


And given the random nature of weather, we'd like to ventilate with
cooler air in summertime

... in my climate, there IS no cooler air in the summertime.


The numbers below belie the statement above.


... The only time when outdoor air is relatively cool is when we have
a thunderstorm. Then the temperature drops, but the humidity goes way up.


Hmmm.


If you go to http://www.weatherbase.com/ and look at the average low
temperature for Austin, TX, you'll see that during the months of
June, July, and August, the average lows are 72, 74, and 74...


NREL's long-term average Austin lows are 71.5, 73.9, and 73.9, but
these are averages, so half the nights are cooler. The 30-year record
hourly lows are 53, 64, and 61. These might be 4 or 5 sigma tails of
a Gaussian distribution. We could do a simple TMY2 simulation.


... Also, go to http://weather.noaa.gov/weather/current/KATT.html
and look at the 24-hour weather history for Austin to see what time
that lower-70's weather occurs. It's usually only for 1-3 hours,
right between 5:00am and 7:00am.


We can do a lot with 1-3 hours of ventilation. If it's 80 F indoors
and 70 outdoors, 2 hours at 5000 cfm (eg 2 90 watt Lasko window fans)
can remove about 2(80-70)5000 = 100,000 Btu, like a 5,000 Btu/h 500W
window AC running for 20 hours. At 65, we can move 150K Btu, like
a 3-ton AC running 4 hours.


In the hours when Austin, Houston, Macon, New Orleans hit their low
temps, the moisture content of the outside air is FAR higher than inside
air. Ventilate a house that has 78F air in it at RH of 50% with 72F
air at RH of 88% is a recipe for EXTREME discomfort. For instance,
tight now in Houston at 7:15am, it is a morning that is close to the
averages, 71F outside, 93% RH, 69F dewpoint. Introducing this air to my
79F will cool it down, BUT will introduce LOTS of added MOISTURE. And
cause me to trigger the AC JUST to get rid of the added moisture. OK,
get the temp of the house down to 74F with dewpoint of 70F is progress
of a sort, but we had house temp of 78F with dewpoint in the upper 50s.
Driving the dewpoint inside the house UP is the WRONG direction.

Now in more arid climes, YES this is a good idea, take 75F outside air
at 40%RH (current conditions in Midland TX), and pump that into a 78F
house, and we have a CLEAR solution. Midland is actually a VERY good
example of this as it has average low temps that NEVER get up into the
70s, and the air is generally quite dry there. So ventilation of these
houses is a GOOD idea.

OTOH, Midland has another problem, severe dust. Attics can get 1-3
inches of airborne dust deposited on top of the insulation over a 10-20
year period.
Now go back to weatherbase.com and look at "All Data" instead of
"Summary", and look at the "Average Morning Relative Humidity" data.
You can see that in the mornings in June, July, and August, it's
nearly 90% relative humidity.


Sounds like scheme II...


It will be a 3 or 4 sigma case for Austin, Houston, south Georgia, etc.
to have cool air in the morning at a low enough absolute humidity that
we will want to introduce that moisture laden air to our homes.
... with the thermostat set at 75F and with the air conditioning
having run a moderate amount all night since it was probably still
90F at 10:00pm, would I want to ventilate the house and get some
of that outside air?


Perhaps, if you want to save energy and money.


Save energy and money at the expense of EXTREME discomfort. Frugality
can be carried to EXTREMES. It is possible to pinch a penny TOO hard.
Now go back and look at the average high temperature for June,
July, and August in Austin. It's 90-95F average for all three
months. So, when do you think people in Austin spend the most
on electricity for A/C? It's June, July, and August. If you want
to make a dent in the cost of A/C and be frugal, you've got to
attack the part where most of the money is going. A smart vent
might be able to lower the bills for the months when the weather
is relatively mild, but that isn't going to help much since
those months are a small part of the total expenditures.


We might ask "How much does it save?" and "How much does it cost?"


OK, save us ALOT of money, reverting back to the houses of our
grandfathers, big wide porches to screen the sun off of the windows and
exterior awnings over the windows that can't be under a porch (built 4-6
ft wide porches ALL the way around the house). I have seen a house near
here that got built in the last 2 years with EXACTLY those features.
We'll sweat alot more, smell bad to others who come in contact with us,
BUT WE WILL SAVE A TON OF MONEY BY NOT USING AC.


For Austin, Houston, and the other cities we have been discussing, it
seems foolish to ventilate a house with lower temp outside air at the
expense of RAISING interior absolute humidity to uncomfortable levels.
Lowering temp is not the ultimate goal for us, dehumidification is.

It is ALOT more comfortable to be in Palm Springs, Palm Desert CA in the
summertime, be out of doors in the sun, than to do the same thing in any
of the other cities mentioned. Temps there often exceed 100F even over
110F, but RH is under 30%, dew points stay VERY low there. Mist cooling
is a feature that WORKS there!!

Scheme II: Ventilate a house with some internal thermal mass at night
when outdoor air is cooler and dry enough to avoid condensation inside
the house, and AC the house during the day, for a net sensible cooling
gain, compared to AC alone.

This may be like Honeywell's differential enthalpy economizer, which
measures the RH and temp of outdoor and duct return air and calculates
which contains more heat and uses the air with less heat for cooling.

Air has a specific heat of 0.24 Btu/F per pound, and 1000 Btu evaporates
a pound of water, so a pound of air at temp T (F) containing w pounds of
water vapor has about 0.24xT+1000w Btu, where w = 0.62198/(29.921/P-1)
is the humidity ratio and P = e^(17.863-9621/(460+T)) is the saturated
vapor pressure in mercury column inches at temp T.

We might use the air with more heat for warming a house, within a comfort
zone, with an additional dew point calc to avoid condensation, unless it
can harmlessly drain away.

It's 65.1 F with 63% RH in my house now, and it's 53.6 at 86% outdoors,
so Pi = 0.63e^(17.863-9621/(460+65.1)) = 0.398 "Hg and wi = 0.00839 and
hi = 0.24x65.1+1000x0.00839 = 24.0 Btu/lb. Po = 0.360 and wo = 0.00758,
ho = 20.4, so outdoor air would work for cooling, if that were needed.

Nick