Yes. This is known as the "ideal gas law". It is only an approximation, but for air at atmospheric temperatures and pressures, it is a good approximation.
So, as humidity is added to dry air, it displaces an equal amount (number of molecules) of air. The resulting mixture is lighter than the original dry air (at the same temperature and pressure).
Macon Georgia, Houston Texas, Mobile Alabama.......
All across the region that NREL classifies as Humid-Semitropical, the number of weeks varies with each location, but the number of weeks where outdoor humidity is LOWER than indoor humidity is small, maybe 3 maybe 6 maybe 12.
We live in these areas and we know when it is OK to open the doors and windows to let large quantities of outside air in.
Ventilation dampers work well in some climates, less well in others. Heat pumps work well in some climates, less so in others. geothermal heat pumps work well in areas that have winters, not so good here in Houston TX After talking to a well driller who has assisted with installation of geothermal heat pumps and has made repairs to wells drilled for geothermal heat pumps, he has come to the conclusion that here, we need a river, large lake, or a simple leaky evaporation pond to displose of the hot water out of the geothermal heat pump.
One size does not fit all, not even close. So Nick solution will work OUTSIDE the Deep South and the Desert Southwest.
Most air has weight, about 0.075 lb/ft^3, on this planet.
This is progress :-) But your claim had nothing to do with feelings...
Now why not check your "facts" before posting them? :-)
Nick
Would you have any evidence for this your present vague article of faith?
The average humidity ratio is less than 0.0092 pounds of water per pound of dry air from October through April in Macon. How many weeks is that in your little ol' Texas town? :-)
Nick
Kinda has to be if you want clouds, isn't it? If you watch how clouds boil up, it is obvious.
Moist air, however, feels "thicker," leading to terms like "pea-soup fog." As a totally wild guess, I wonder if the effect is a subjective one, partly from the humdity displacing part of the air and thus reducing the oxygen content, and partly from the water being more reactive than nitrogen, and therefore wanting to bond together in larger structures, which in turn create more drag on objects moving through the vapor?
This will be the LAST time I EVER respond to ANYTHING that Nick at Villanova posts to the alt.home.repair newsgroup.
For those of us who live in the region that NREL classifies as Humid-SemiTropical, lots of things that work elsewhere do not work here. For Instance.
Vapor barriers go on the OUTSIDE of the house, insulation is ALWAYS unfaced, and vinyl wallpapers should NEVER be applied.
Vegetation should never be closer than 3 feet from the house, and an appropriate ground cover should be maintained over than area. Ground should slope away from the foundation at least 2 inches per linear foot.
Windows on Southern exposure sides of the house should be eliminated, or scaled back in size dramatically if elimination is not possible.
geothermal heat pumps will either require open loop cooling, or will require multiple large diameter wells, 400 feet or more, likely two of these per ton of installed capacity to make a closed loop system.
RH levels outdoors much of the year make outdoor activities uncomfortable.
Construction workers all wear long sleeves, hats and scarves to keep the sun off their skins. Even the very low paid yard care crews do this.
Natural fiber clothing is preferred in most regions as polyester and rayon are poor at wicking perspiration off of the skin.
I wear sunglasses ALL the time when out of doors.
Relative Humidity levels and temperatures for most of the year are such that the struggle is almost always to keep moisture out, as we are NEVER too dry inside.
In the new house I will build, I MAY decide to include a ventilation damper to allow the ventilation system to inject some fresh air from time to time AprilAire makes one that is reasonably priced, it wont open the vent trigger the fan unless outside air temp is under 100F and over 0F, or if allowing the ventilation would cause indoor RH to rise above 55% However these requirements mean that the damper will not operate for most of the summer. The plus side of this is that it runs the fan in the hvac while fresh air is introduced.
Nick, your system should closely model what the AprilAire Ventilaion Control System Model 8126 does. The more deluxe ERV as documented at
Moist air is "lighter" than dry air (air pressure tends to be lower when it storms and higher in fair weather), however the body is heavier since lighter air is less buoyant. ...kinda like liquid water is denser than air but people float. ;-)
Nickie is a math and theory lover. That can be great if you want to know how much heat a standard ASHRE mouse puts out, but Nick sometimes gets confused when confronted with the fact that not all mice are ASHRE compliant.
Weather station instruments are commonly placed at airports or other open areas. That may not be representative for an area that otherwise has dense vegetation and/or standing water. Airports have to be level and dry enough to land planes, and they also usually have a lot of paved or concrete areas and low cut grass. That means more wind can sweep the ground, less groundwater can be transferred by vegetation into the immediate air, and temperatures and humidity can differ from areas nearby.
If Nick builds his constructions on or near a runway, he may be right. If he builds on a typical wooded or swampy southern lot, he may find the real world intruding.
In other areas, the representative weather stats can be off because the weather instruments are NOT at an airport. I used to take measurements at a radio station where my father worked. That station was (logically) on a hill, and the town below might be lost in fog while I was recording clear skies, low humidity, and a mild wind for the town. Fast foreword a few years. Now, another weather reporting site in that community is located about 50 feet above a river, at a spot where it enters a small canyon. It also has different measurements than if you set up a station in the middle of the small town. On a practical basis, weather is an extremely local phenomenon.
Here in south Florida, I have become accustomed to seeing rain-soaked streets that are totally dry 500 feet up the road. I've had my pool fill with four inches of water, while the airport reported no rain at all. The heavy rainstorms here can be that localized. Depending on the winds and the season, the coast may get strong breezes and a cool temperature, while five to fifteen miles inland, clouds billow up and create a line of storms that never touch the coast. You can't always go by reported weather from a selected set of sources
Having been through southern Georgia many times, I know there are large differences in temperature and humidity around the peanut and cotton farms compared to the pine forests and towns. That is common sense and experiential knowledge.
However, Nick takes it as an article of faith that discrete samples from professionals always represent a greater norm. :-)
FWIW, I've used economizer dampers on theatre HVAC units in Vermont and in Alabama. The greatest use was over Christmas vacation, when crowds would overheat the theatre and the outside air was less than 40 degrees F. Much of the rest of the time in Vermont they had to be sealed with plastic and duct tape to prevent drafts and heat loss. The integrated ones also had more electro-mechanical problems than other systems. That may have been design related - unsupported lever arms, corrosion, ice, etc. but they were only marginally cost effective overall. In Alabama, the vents were straightforward exhaust vents, and were used only if the AC was overwhelmed or there were smokers (which were still allowed in certain sections of some theatres).
Whole house fans were common in the south before AC, and venting is just a variation on this. The success of those whole house fans often depended on measures such as opening certain windows after 10 PM and closing the house up tight before 8 AM, drawing all the curtains, and sweating out the early evening on a porch. Once AC became affordable, life changed for the better. Getting people to go back is nearly impossible, and Nick should know this, but his stubbornness lack of experiential knowledge prevents it.
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.
Nick
Houston has two measuring stations, the airport, with a 96' elevation and a 96 F 1% summer design temp, and "Houston County," with a 108' elevation and a 97 F 1% summer design temp. Not vastly different :-)
Automatic controls can turn on a fan when outdoor air is cooler and drier than indoor air, in the absolute sense. This is quite recent, with existing unexpired patents for drying out houses after floods and so on. See
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
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.
come spend a summer down here...maybe then you will know what you are talking about.
Robert ("I'll never respond to Nick again") Gammon responds again:
But both measurements are similar...
What does that mean, and is it true, and why is it relevant?
We've been discussing ABSOLUTE vs relative humidity.
Nick
AMEN TO THIS BROTHER.
Nick is sitting at a balmy 72F while I am at 93F, Macon is 90F, Mobile is 88F, Atlanta is 89F
Nick and Mobile are tied for highest humidity at about 55% currently, the rest of us are in the 30% to 45% range.
Nick is like many in a university setting, they are isolated from the rest of the world and have little idea what problems are being faced elsewhere. And like many in an ivory tower setting, it is difficult for them to believe that anyone knows more than they do. Nick has shown this to us with nearly EVERY comment he makes. No one is infallible, everyone makes some mistakes from time to time, yet Nick appears to want to SMASH your face in with nearly every comment.
The message to Nick is that the world is NOT a copy of what he sees in Pennsylvania, things that will work well in Villanova may not work even in upstate NY (i.e Buffalo)
And for Nick's benefit, ALL the cities mentioned here have very high humidities at night in particular. Residents will avoid bringing in night time air if at all possible as that time is when the RH climbs towards saturation (80-100%)
My parent's house in North Carolina was far enough into the hills that after 10PM, the air temp and humidity dropped off enough that a whole house fan could dump alot of excess heat outside
Exactly what does that mean, and is it true, and how is it relevant?
We're discussing ABSOLUTE vs relative humidity.
Nick
go put your nose back in your calculator.My family has lived here in Georgia for over 150 years.We know exactly how to deal with our local climate.When to go on the porch,when to open a window,when to pull the blinds,and when we need to ventilate or not.We know how to dress for working the fields,or fishing ,or any other activity.If I tell you your idea is impractical for my area....take it to the bank.
All we can really calibrate to is RELATIVE as it is what WE feel, not what the intruments are telling us. All reporting on TV, Radio, Internet, its ALL RH
You might enjoy learning the difference.
Whaddya mean "WE," Kemosabe?
Nick
The rest of us, everyone except Nick
see
For instance, right now in Houston Temp 73F RH is 87% Dew Point is 69F
Right now in Villanova Temp 59F RH 88% Dew Point is 56F
I do not imagine that you want to introduce this moisture laden air into your apartment/home if you can help it. Doesn't matter whether we talk Deep South or Pennsylvania. And in no case, do you want 90+F air in any significant quantity coming inside to increase your A/C bill.
The Meteorologist points out that the highest dew point ever recorded in his location was 88F right after a thunderstorm. Other than that, on very humid days, the dew point only gets to the low 80s there (Cincinatti) although Gulf War vets do know 90/90 days as the Red Sea heats to above 90 F and with air temps in Kuwait rising to 110 or higher lots of water is in the air. 90% RH with air temps above 90F is a very very real situation for that location.
But it's quite useful for house ventilation control. So's the dew point, but that's harder to measure with electronic sensors.
Nick
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