High Humidity with Heat Pump

[Joe Buemi]

What would cause high humidity(~ 65%) while cooling a house to 70 degrees with a heat pump?

[Vern Heiler]

The first question all HVAC contractors are going to ask is; was the system sized correctly. If the unit is over sized it does not run long enough to remove the humidity. Short cycles of on.

The other question, and in my opinion the more common problem, is do you have a moisture barrier under the house? If you are punching in more humidity than the a/c can remove you have a problem.

I don't know that I would call 65% all that high anyway.

[Scott Patterson]

I agree with Vern.

Does the house have 65% humidity or is that in the air stream at a register?

How did you measure the humidity and with what?

What is the SF of the home and what is the tonnage or BTU of the unit?

[Jim Luttrall]

What would cause high humidity(~ 65%) while cooling a house to 70 degrees with a heat pump?

Some of the possibilities are:
improperly sized unit which keeps the unit from running long enough to drop the humidity,
uncontrolled moisture source (showers, cooking, wet exterior weather),
clogged drain or lack of trap on a draw through system,
improper system charge, valve function, or defective compressor which raises the evaporator temperature near or above dew point.

I'm sure there are other things possible, but you really need more information to even begin looking.

[Jerry Peck]

but you really need more information to even begin looking.

That is key, and you do not have enough information, and did not give us enough information, to form viable answers.

Sizing would be my first guess to, then common sense would kick in and say "What else is going on?", and THAT is the likely problem, unless your system is so vastly oversized your home feels like a meat cooler.

[Bruce King]

All good advice but the most likely problem is "coil blow back".

A problem with the condensate drainage or a dry trap is causing the condensation to blow back all over the coil. The airhandler then sends all of this moisture right back into the house.

[Vern Heiler]

All good advice but the most likely problem is "coil blow back".

A problem with the condensate drainage or a dry trap is causing the condensation to blow back all over the coil. The airhandler then sends all of this moisture right back into the house.

The air leaving the coil is at 100% humidity, how does it pick up more?

[Bruce King]

Actually it leaves the coil at around 95 percent humidity and goes to 100 percent when condensation is incorrectly blowing all over it. It also stays at 100 percent for the time period when the fan is blowing and condensor is off such as the end of the cycle because water is blowing all over the inside.

If blow back is not the problem, the speed of the air across the coil can be lowered to help lower the humidity (by getting the coil temperature lower).

[Vern Heiler]

Actually it leaves the coil at around 95 percent humidity and goes to 100 percent when condensation is incorrectly blowing all over it. It also stays at 100 percent for the time period when the fan is blowing and condensor is off such as the end of the cycle because water is blowing all over the inside.

If blow back is not the problem, the speed of the air across the coil can be lowered to help lower the humidity (by getting the coil temperature lower).

I disagree. When the air leaves the coil surface it is at dew point and can hold no more moisture until it warms.

[Bruce King]

95 or 100 no big deal, the 95 actually came out of a textbook.

The main thing is experience, the guy who told me that coil blow back will put humidity back into the house owns a large hvac company and has been in the business for decades and does a lot of commercial work too.

Some Trane gas packs are bad about doing this, since they suck air when the p-trap is dry at the start of the season.


More on tweaking airflow:

Humidity control can be achieved in different parts of the country with the same equipment by simply changing the speed of the air across the coil. This eliminates having to sell specific equipment based on the varying climates.

[DavidR]

If the reference is to interior humidity levels of 65% they are way too high.

At 70º indoor dry bulb with the outdoor relative humidity levels we have been experiencing here in KY it won't be long before moisture is condensing inside the exterior wall cavities.

Could be a number of things contributing to this problem Joe.

Infiltration and duct leakage come to mind off the top of my head.

[Vern Heiler]

If the reference is to interior humidity levels of 65% they are way too high.

At 70º indoor dry bulb with the outdoor relative humidity levels we have been experiencing here in KY it won't be long before moisture is condensing inside the exterior wall cavities.

Could be a number of things contributing to this problem Joe.

Infiltration and duct leakage come to mind off the top of my head.

As Scott said, a lot depends on where the measurement was taken and how accurate the measurement was.

All of the psychrometric comfort zone charts I have seen put the 65% humidity at 70 degrees inside the zone. I don't think it should be considered bad.

[DavidR]

As Scott said, a lot depends on where the measurement was taken and how accurate the measurement was.

All of the psychrometric comfort zone charts I have seen put the 65% humidity at 70 degrees inside the zone. I don't think it should be considered bad.

Scrapping the bottom of the chart with those numbers Vern, to tell a customer that's acceptable isn't going to be in their best interest.
Would you like the interior of your home at those conditions?

70º outdoor dewpoint like we've had here and 70º interior dry bulb temperature with 65% interior humidity is a recipe for disaster.
The walls are at dewpoint in those conditions.

If you tweak those conditions a little more you can start to grow fungus on and in the walls.
Pushing the interior humidity above 55% regardless of whatever any ASHRAE chart says is a bad idea.

Maybe Joe will reply back and give us some specifics on the job.
If he took his measurements in the airstream I will be really surprised.

[Vern Heiler]

Scrapping the bottom of the chart with those numbers Vern, to tell a customer that's acceptable isn't going to be in their best interest.
Would you like the interior of your home at those conditions?

70º outdoor dewpoint like we've had here and 70º interior dry bulb temperature with 65% interior humidity is a recipe for disaster.
The walls are at dewpoint in those conditions.

If you tweak those conditions a little more you can start to grow fungus on and in the walls.
Pushing the interior humidity above 55% regardless of whatever any ASHRAE chart says is a bad idea.

Maybe Joe will reply back and give us some specifics on the job.
If he took his measurements in the airstream I will be really surprised.



David, if we told Joe to raise the temperature to 78 degrees and the humidity went to 50%, would that be ok?

Because if he were to take the air in his house now, 70 deg. and 65%, and heat it to 78 deg., it would be at 50% relative humidity.

At 70% and 70deg. the dew point is 60 deg. so the walls would have to be cooled to 60 or lower for condensation.

[DavidR]

David, if we told Joe to raise the temperature to 78 degrees and the humidity went to 50%, would that be ok?

Because if he were to take the air in his house now, 70 deg. and 65%, and heat it to 78 deg., it would be at 50% relative humidity.

At 70% and 70deg. the dew point is 60 deg. so the walls would have to be cooled to 60 or lower for condensation.

Yes it would change conditions if the home was warmed up, would reduce the wetting potential in those walls.
In your example if it reached 60º it would be raining from his ceiling. :)

Those surface temperatures are only concerned with what the humidity is relative to them.
If the outdoor dewpoint is 70º and the interior dry bulb is 70º that is at saturation.
The high indoor humidity is the whole purpose they are driving the indoor temps down to begin with.

Good discussion.

[Vern Heiler]

Yes it would change conditions if the home was warmed up, would reduce the wetting potential in those walls.
In your example if it reached 60º it would be raining from his ceiling. :)

Those surface temperatures are only concerned with what the humidity is relative to them.
If the outdoor dewpoint is 70º and the interior dry bulb is 70º that is at saturation.
The high indoor humidity is the whole purpose they are driving the indoor temps down to begin with.

Good discussion.

In my example the walls only must be droped to 60 deg. for dew point to be reached, the air temp would have to remain at 70.

How does mixing outdoor dew point have anything to do with indoor?

[DavidR]

How does mixing outdoor dew point have anything to do with indoor?

Moisture drive through the wall assemblies.

That outdoor air is constantly trying to get indoors many times with the help of various building and mechanical defects.
When air that is already saturated hits a surface that is at the same dewpoint temperature you get condensation. Just like taking a glass of ice tea outside on a humid day or the suction line sweating back on a properly charged condenser.
It's the whole reason why walls start to grow mold inside the wall cavities versus on the interior of the building shell.

[Jerry Peck]

It's the whole reason why walls start to grow mold inside the wall cavities versus on the interior of the building shell.

Because the dew point has moved to someplace within that wall cavity, possibly the backside of the interior drywall, possibly the inside of the exterior sheathing, possibly even in the center of the insulation.

Years ago I did some consulting on a hotel on the beach, the wall cavity RH was at 99.9%, and, yes, it was "raining" in the walls - the insulation was saturated with water and when the interior drywall was removed, you could pull the insulation out and water would drain out of the insulation.

[Vern Heiler]

The numbers I used, 78 deg. and 50% humidity, was not a number I pulled out of my a$$. That is the bulls-eye that is painted on psychrometric charts. A cubic foot of air contains the same amount of water vapor at 70 deg. and 65% humidity as air at 78 deg and 50%.



Years ago I did some consulting on a hotel on the beach, the wall cavity RH was at 99.9%, and, yes, it was "raining" in the walls


Relative humidity is just that, relative to the temperature of the air.


Because the dew point has moved to someplace within that wall cavity, possibly the backside of the interior drywall, possibly the inside of the exterior sheathing, possibly even in the center of the insulation.


I believe that is a good reason to have "insulation" don't you?

[Jerry Peck]

I believe that is a good reason to have "insulation" don't you?

Vern,

You are missing an important fact I included: there WAS insulation in that wall.

The dew point had moved to somewhere near the center of the wall cavity ... within the insulation ... thus it was condensing within the insulation.

[Vern Heiler]

You are missing an important fact I included: there WAS insulation in that wall.

The dew point had moved to somewhere near the center of the wall cavity ... within the insulation ... thus it was condensing within the insulation.


You did not give us the RH of the interior air? Was it at 100%?


Jerry, if the insulation was functioning the warm humid exterior air would not have reached the cold interior surface, wherever it was.

The OP situation is 70 deg. and 65%. That is considered the optimum amount of moisture contained in the volume of air.

The exterior RH and the interior RH are not relative to each other. The only surface that RH is relative to is the surface it can come in contact with.

[Jerry Peck]

The exterior RH and the interior RH are not relative to each other.

I know that.


The only surface that RH is relative to is the surface it can come in contact with.

With my point being ... THAT surface COULD BE LOCATED ANYWAY ... yes, even IN the wall.

[Vern Heiler]

With my point being ... THAT surface COULD BE LOCATED ANYWAY ... yes, even IN the wall.

Your problem was with insulation, not the RH.

[Jerry Peck]

Your problem was with insulation, not the RH.


No, the problem was the location of the dew point, which caused a problem with the insulation, which made the location of the dew point worse, which caused an even worse problem with the insulation, which ... and it all goes downhill from there, but "the insulation" was not the original "cause" of the problem, "the insulation" was the first casualty of the problem.

[Vern Heiler]

If it was not an insulation problem how did the dew point move to the wrong side of it?

[Jerry Peck]

Vinyl wallpaper and hurricanes as a vapor and moisture driving force, among other contributing factors.

[Vern Heiler]

hurricanes

Hmmmmm, kinda forgot to mention that:rolleyes: .

But the only way condensation formed was for warm moist air to come in contact with a cold surface. "Insulation" seperation of one thing from another.

[Jerry Peck]

Hmmmmm, kinda forgot to mention that:rolleyes: .

You mean you kinda forgot to CONSIDER that. :rolleyes: :p


But the only way condensation formed was for warm moist air to come in contact with a cold surface. "Insulation" seperation of one thing from another.

"But the only way condensation formed was for warm moist air to come in contact with a cold surface."

And there WAS insulation in those walls. THE INSULATION ... WAS NOT ... THE PROBLEM. Which is what you were saying it was. :p

[Vern Heiler]

If hurricanes are an important factor, and the air was condensing inside the wall, then the insulation was not doing its job due to getting wet from hurricanes, not that the indoor air was above 50% humidity.

The moisture condensed from the outdoor air not the indoor. To be from the indoor air, the indoor surface of the wall would have to be warmer than the exterior wall or center of the insulation. You would have to blow cold air into the wall cavity for this to happen. Still sounds like insulation failure to me.

[Jerry Peck]

If hurricanes are an important factor, and the air was condensing inside the wall, then the insulation was not doing its job due to getting wet from hurricanes, not that the indoor air was above 50% humidity.

And NOT a fault of the insulation.

Which you kept trying to say was the problem.


The moisture condensed from the outdoor air not the indoor.

No kidding.

And that condensation was caused by DEW POINT LOCATION ... which is what I have been telling you.

The dew point moved as the vapor changes affected the temperature and RH inside the wall cavity, and the dew point IS WHAT CAUSES the condensation.

[Vern Heiler]

The dew point moved as the vapor changes affected the temperature and RH inside the wall cavity, and the dew point IS WHAT CAUSES the condensation.


No the dew point is the temperature that air, with a given amount of moisture content, will begin to condense. The dew point never moved! The cold surface is what moved. It moved to a location beyond the interior surface of the wall which is what insulation is supposed to prevent.

[Steve Zabarylo]

Since the interior of the wall cavity is normally/usually "connected" to the outside it is affected by the water vapor pressure of the exterior air. The vapor pressure is related to the dew point directly whereas RH varies in relation to the exterior dry bulb temperature. If some point within the wall cavity is cooler than the outside dew point then the air in contact with that point will be cooled below the dew point and condensation will occur. Cooling the interior of a structure below the dew point of the exterior air will always cause this problem. The forgoing assumes a reasonable barier to vapour travel on the inside of the building envelope.

[Vern Heiler]

Cooling the interior of a structure below the dew point of the exterior air will always cause this problem.

Really! I guess we better tell everyone south of Minnesota to turn there thermostats up to somewhere above 80. Give me a break!

[Jim Luttrall]

Really! I guess we better tell everyone south of Minnesota to turn there thermostats up to somewhere above 80. Give me a break!
Just need to move the vapor barrier to the outside wall instead of the inside.
See the BSC article and there is one which Dr. Joe lists as one of the top ten dumb things to do when building in the south... something about Yankees not being allowed:p
BSI-015: Top Ten Dumb Things To Do In the South — (http://www.buildingscience.com/documents/insights/bsi-015-top-ten-dumb-things-to-do-in-the-south/)

[Steve Zabarylo]

Thanks Jim. I think Vern missed the point. Climate is the determining factor in where a vapor barrier is placed or even if there should be one. North Dakota buildings don't work well in Florida and visa versa but Boyles laws are inviolate.

[Jerry Peck]

No the dew point is the temperature that air, with a given amount of moisture content, will begin to condense. The dew point never moved! The cold surface is what moved. It moved to a location beyond the interior surface of the wall which is what insulation is supposed to prevent.

Vern,

Not sure you you've been drinking today, but ... the wall has not moved.

The DEW POINT has moved.

Not referring to moving in degrees, which it also has moved, but referring to its location in the wall.

[Vern Heiler]

[quote]
I think Vern missed the point. Climate is the determining factor in where a vapor barrier is placed or even if there should be one./QUOTE]

Can you explain the code requirement of having the vapor barrier on the conditioned side of the insulation? North, South, East or West.

And Boyle's law deals with temperature/pressure relationship in a closed container. It has no relationship to this discussion.

[Vern Heiler]

Vern,

Not sure you you've been drinking today, but ... the wall has not moved.

The DEW POINT has moved.

Not referring to moving in degrees, which it also has moved, but referring to its location in the wall.

Jerry,

The normal location of the coldest surface of the exterior wall is the paint on the interior side of the wall. If the insulation becomes wet the location of the coldest surface, relative to the exterior wall, moves toward the exterior surface of the wall. The dew point does not move unless you remove or add moisture to the air.

[Jerry Peck]

The dew point does not move unless you remove or add moisture to the air.

Vern, Vern, Vern,

What have you been sipping on?

THAT'S WHAT I SAID HAPPENED ... the dew point moved ... and you've been arguing against the dew moving, insisting that it does not move.

The dew point moves all during the day, and night, and changes by the day, and the week, and the month ... the dew point is not fixed as nothing else is fixed either.

[Vern Heiler]

Vern, Vern, Vern,

What have you been sipping on?

THAT'S WHAT I SAID HAPPENED ... the dew point moved ... and you've been arguing against the dew moving, insisting that it does not move.

The dew point moves all during the day, and night, and changes by the day, and the week, and the month ... the dew point is not fixed as nothing else is fixed either.

Jerry, If you are going to be an authority on the subject you need to look up some definitions. Here's one to start with:

Dew Point Temperature
The temperature of moist air saturated at the same pressure and humidity ratio. Or more simply the temperature at which water vapor will begin to condense from a sample of air.


The sample of air could be a milk jug with a cap on it. The moisture content is constant, therefore the dew point is constant for that sample.

[Jerry Peck]

Jerry, If you are going to be an authority on the subject you need to look up some definitions. Here's one to start with:

Dew Point Temperature
The temperature of moist air saturated at the same pressure and humidity ratio. Or more simply the temperature at which water vapor will begin to condense from a sample of air.


The sample of air could be a milk jug with a cap on it. The moisture content is constant, therefore the dew point is constant for that sample.

Vern,

Still not admitting you were wrong so you are trying to confuse and misdirect the discussion. :rolleyes:

Not absolutely sure here, but to my knowledge we HAVE NOT been talking about a sample in a capped MILK JUG, but we have been talking about a structure's wall. :rolleyes:

Please DO correct me if I am wrong and we have been talking about a capped milk jug. :rolleyes:

[Vern Heiler]

If we have 78 deg. air that contains 50% RH it has 10,299 ppm water. If we take a closed container of that air, its dew point is 57.979 degrees at the same pressure. The only way to change that dew point temperature is to add or remove moisture from that sample of air.

In your example where moist air condenses on anything other than the paint on the interior wall surface, where it should if that surface is at or below DP, moisture was not added or removed from the air. The first cold surface the air reached did move.

[Jerry Peck]

If we have 78 deg. air that contains 50% RH it has 10,299 ppm water. If we take a closed container of that air, its dew point is 57.979 degrees at the same pressure. The only way to change that dew point temperature is to add or remove moisture from that sample of air.

In your example where moist air condenses on anything other than the paint on the interior wall surface, where it should if that surface is at or below DP, moisture was not added or removed from the air. The first cold surface the air reached did move.

Vern,

You need to quick sucking out that sample of moisture laden air from that jug and put the cap back on it: 1) you are changing the air in the jug; 2) you need to clear your head and go back and read, and understand, what has been posted.

I thought you might have been sipping something, but now I suspect you are just sucking air ... stale, moist air at that..

[Steve Zabarylo]

Vern

When looking at a cross section of the building envelop there is a change of temperature from the paint on the inside that is at the interior temperature of the building to the exterior finish of the wall that is at the outside air temperature (or higher if the sun is beating down on it). The air encapsulated within the wall that for this argument sake, we can consider as being exposed to the outside air and isolated from the inside air by a vapour (air) barrier, will have the same partial pressure conditions as the outside air. The important partial pressure is that of the water vapour in the outside air which will be in equilibrium with the air encapsulated within the wall structure. As we move through the wall from outside to inside, and the inside surface is colder than the point of condensation (dew point), we will eventually come to a point where the air is cooled below the point at which it can hold all the water disolved in it. I never said this is the way a wall should be built south of the 49th parallel. Indeed, many in the south seem to have the idea that the walls north of 49 are made of water in another state (sic).

[Vern Heiler]

Vern,

You need to quick sucking out that sample of moisture laden air from that jug and put the cap back on it: 1) you are changing the air in the jug; 2) you need to clear your head and go back and read, and understand, what has been posted.

I thought you might have been sipping something, but now I suspect you are just sucking air ... stale, moist air at that..

Wow Jerry, you gave up easy! Reverting to diatribe when facts get in the way.

[Jerry Peck]

Wow Jerry, you gave up easy! Reverting to diatribe when facts get in the way.


Vern,

(sigh)

So far, you have not presented ANY FACTS which say other than I have been saying.

Then you tried to misdirect to your sample in a capped milk jug, which has no relevance to what we are discussing.

Now you are trying to redirect from you to me and saying that *I* have changed and you have not.

Please, stick to the facts and to the discussion ... don't bother trying to misdirect or redirect ... simply follow the discussion as it progresses along.

THE STRUCTURE (and its wall) NEVER MOVED.

THE DEW POINT ... MOVED.

BOTH in relation to its location in the wall and to the temperature and RH in the environment around the dew point. The dew point is neither stationary in time or in physical location, it it totally dependent on what is going on around it.

Your first mistake, I shall point out AGAIN, was in NOT CONSIDERING the environmental effects, such as hurricanes.

Here is an example:
- outside temperature is 95 degree and the inside temperature is 70 degrees (I don't know what the RH was for either)
- along comes a hurricane
- along comes NO POWER ... did I just hear another drop of your jaw ... along with a 'Oh, I did NOT CONSIDER that either.'

Do you really think the indoor temperature is now lower than the exterior temperature?

Where is the dew point now? Is it still where it was before?

Are you waking up yet? :rolleyes:

I'm not into diatribe mode, I just cannot understand a smart person like you insisting on what you are insisting on without actually thinking about what may be going on, instead of trying to prop up your original position with some "capped milk jug" thing.

[Vern Heiler]

Vern,

(sigh)

So far, you have not presented ANY FACTS which say other than I have been saying.

Then you tried to misdirect to your sample in a capped milk jug, which has no relevance to what we are discussing.

Now you are trying to redirect from you to me and saying that *I* have changed and you have not.

Please, stick to the facts and to the discussion ... don't bother trying to misdirect or redirect ... simply follow the discussion as it progresses along.

THE STRUCTURE (and its wall) NEVER MOVED.

THE DEW POINT ... MOVED.

BOTH in relation to its location in the wall and to the temperature and RH in the environment around the dew point. The dew point is neither stationary in time or in physical location, it it totally dependent on what is going on around it.

Your first mistake, I shall point out AGAIN, was in NOT CONSIDERING the environmental effects, such as hurricanes.

Here is an example:
- outside temperature is 95 degree and the inside temperature is 70 degrees (I don't know what the RH was for either)
- along comes a hurricane
- along comes NO POWER ... did I just hear another drop of your jaw ... along with a 'Oh, I did NOT CONSIDER that either.'

Do you really think the indoor temperature is now lower than the exterior temperature?

Where is the dew point now? Is it still where it was before?

Are you waking up yet? :rolleyes:

I'm not into diatribe mode, I just cannot understand a smart person like you insisting on what you are insisting on without actually thinking about what may be going on, instead of trying to prop up your original position with some "capped milk jug" thing.

You really don't have a clue do you!

You enter the thread backing up a claim that RH above 50% will travel through the wall and condense in the insulation. You have a story to verify your position, but forget to mention the moisture in the wall might be due to a hurricane. Hurricanes are not normally in a load calculation or any other calculation I know of. Then you incest that dew points change without changing the vapor content of the air. You will not concede that wet insulation may be colder than dry and its surface may be at DP. Then you grab hold of an explanation using a known container (milk bottle) to try to discredit.

Looking a little republican here Jerry:D

[Jerry Peck]

but forget to mention the moisture in the wall might be due to a hurricane. Hurricanes are not normally in a load calculation or any other calculation I know of.

Vern,

The only one without a clue here is you.

You have your mind preset NOT TO INCLUDE ANY FACTORS OTHER THAN those in your head.

*I* should not be the one needing to tell you (if you are aware of what is going on) about outside conditions affecting what is going on in and with the walls.

*YOU* should have been opened minded and thinking about the conditions which COULD cause things other than what was in your little chart.

*MY* entire point was that you were too focused on your chart to really think about what was going on.

*YOU* proved that out all by yourself.

[Vern Heiler]

*MY* entire point was that you were too focused on your chart to really think about what was going on.

Lets talk about what was going on.

(1) The original post questioned why he had 65% at 70 deg.

I responded with a possible way to reduce the RH (vapor barrier) and stated that the RH was not that bad. This flew in the face of the chicken littles of the board.

(2) You jump in with story of moisture condensing in the wall and the insulation was not the problem but that a moving dew point was. I tried to explain that a dew point is a temperature not a place and only changes with the addition or removal of moisture. (that escapes you still)

(3) You divulge a minor detail, HURRICANE! My god man when was that normal! I deduce that if the hurricane wet the insulation the insulation would conduct the cold from the inside wall to a position somewhere in the wall ( the position of the condensing surface moved toward the exterior wall) That escapes you also.

(4) With a chart I found that the 70 deg. 65% air has the exact same vapor content as the widely accepted 78 deg, 50% target temp and humidity. 65% is not a high humidity at 70% temp! Also flew in the face of the chicken littles.

[Cobra Cook]

The first item you have to do is to put a set of gauges on the system to determine if it is charged properly, that the superheat and subcooling are at the right size. An overly large sized unit could be the culprit as well as a low charge which is allowing the coils to ice up. Simply lowering the fan speed is not the correct way to go due to the fact that it will allow the coil to maybe start to freeze or be too saturated with condensation thus blowing out wet or fully saturated air in the 100% rh range. Unless you have an airflow meter to determine how many CFM of air the unit is moving in comparsion to the square feet the building is, how many windows,how much insulation,what exposure to the sun and so on. This is why you have a trained HVAC mechanic with an EPA certification to service the equipment to determine the problem.

[Jerry Peck]

Lets talk about what was going on.

(4) With a chart I found ...

And that is what is still going on ... you have not gotten your head out of that chart to consider the real world and its real effects on what has been stated.

[Vern Heiler]

And that is what is still going on ... you have not gotten your head out of that chart to consider the real world and its real effects on what has been stated.

I know Jerry, the facts be damned.

[Jerry Peck]

I know Jerry, the facts be damned.

Vern,

No, the facts are the facts, and those FACTS ... INCLUDE ... the fact that the environment around a building affects the building ... AND THE DEW POINT's location.

Which is something you do not seem to either understand or be willing to acknowledge or admit.

Your table and chart works fine with your capped milk jug, but as soon as real world occurrences happen you are not allowing yourself to adapt to the changes, which affect your table and chart as the temperature and humidity you are reading from change, meaning your chart is not static, but dynamic with those changes. THAT is what you are not getting or not following.

[Vern Heiler]

AND THE DEW POINT's location.

Do you have the same problem with light years being a measure of distance not time?

[Jerry Peck]

Do you have the same problem with light years being a measure of distance not time?

Huh?

First you don't understand what is being discussed, or at least it appears that way, and now you are trying to say we need to measure in light-years?

What do you not understand about "changing" temperatures and humidities?

[Vern Heiler]

Huh?

First you don't understand what is being discussed, or at least it appears that way, and now you are trying to say we need to measure in light-years?

What do you not understand about "changing" temperatures and humidities?

And why do you avoid items 1,2, and 3 of post #49? Or for that matter the rest of 4?

It is good to know that you have accepted that you do have a diatribe mode. Thats a step in the right direction to your cure :D .

[Jerry Peck]

It is good to know that you have accepted that you do have a diatribe mode. Thats a step in the right direction to your cure :D .

And once you accept the error of your posts above you will be in the right direction to your cure. :D

Do you, or do you not, agree that the psychometric chart is a static graphical representation of dynamic readings taken as representing one point in time?

And that, because it is representing dynamic readings the static graphical representation will change when recalculated for each no dynamically changing set of readings?

[Vern Heiler]

Let’s summarize.

POST #

13. DavidR States that if the outdoor DP is 70° and the indoor DB temp is 70°, the outdoor air is at saturation. Well that would be true if the outdoor air was indoors, but its not. That’s why we use something called “INSULATION”. David goes on to say that if the indoor RH goes above 55% then DISASTER AWAITS US ALL! (Ya gotta love the chicken littles of the board!)

14. I explain that 70° air with a RH of 65% is the same RH as 78° and 50%. I mistakenly assume David knows the indoor air is separate from the outdoor air and state that the DP is 60° for the OP’s condition, 10° below the DB temp.

15. ??? Still doesn’t know indoor is separate from outdoor! David says if the temp gets to 60° it will rain from the ceilings. ??? What I had stated was that if a surface was at 60° in that 70° 65% air there would be condensation. (How do you get the ceilings to 60° without lowering the air temp?)

16. David does a little left turn here and does not address the question asked. “How does ID DP relate to OD DP?” States that it is the outdoor air that might get to the interior wall due to faulty insulation. OK, I’ll buy that.

18. Jerry enters the fray. States that the DP has physically moved, even though a DP is not a physical thing or place (but I understand the confusion). Then backs the idea that high RH will cause walls to sop with moisture. Uses story of motel wall that was saturated with water. (We latter learn the water may have come from a HURRICANE!)

19. I question the motel story regarding insulation.

20. Jerry swears there was insulation but somehow the DP had moved (physically) in the wall, and all the moisture was due to condensation. (we still don’t know about the HURRICANE)

20. Still don’t acknowledge the HURRICANE. Just a little bully tatics.

21 – 24 Getting a little closer to the HURRICANE. (still thinks DP is a physical location)

25. I play along with DP being physical. Question, “how did it move?”

26. Ahh, the HURRICANE. What relevance does a wall damaged by a HURRICANE, have with this discussion?

27. I state that good insulation (not damaged by a HURRICANE) would prevent warm moist air from contacting the cold surface. (seems like it works pretty well for millions of structures)

28. I should have known there was a HURRICANE from the beginning? Jerry says the wet insulation was not the problem.

29. (Hmmm I thought wet insulation was always a problem?) Back to OP question I try dig from Jerry what is the relation of the ID RH?

30. Nope, insulation was fine (forget the HURRICANE) the DP moved and wet the insulation. Huh?

31. I try to explain what dew point is. (what a waste of good ink!) Make another point for good insulation.

32. Steve Z. says if you cool your house to below the OD DP, you will have big problems.

33. Gonna have a lot of problems in the humid south!

34 - 35. JL tries to help but doesn’t really want to get in the line of fire.

36. Jerry gets flustered and starts into diatribe.

37. Boyle’s Law, come on!

38. Try again in vain to get Jerry to understand DP and RH.

39 - 43. In vain verified! Jerry going deep into diatribe mode.

44. Steve Z. Tries to make Boyle’s Law work. (air pressures are in equilibrium so I don’t see the point he is trying to make) Minimal at best.

45. Jerry’s diatribe sets in and his shell game starts.

46 – 48 We turn into kids fighting in the playground. Shame on us!

49. Short summary.

50. Cobra, that ground has already been plowed and I’m tired. Been writing two townhouse reports in between post and I hope I haven’t given the wrong one a porcelain sink or something!

-56. Just more diatribe.

57. Of course DP’s change, but they change because of the addition or removal of moisture. The OP point was that 65% was too high and condensation will ruin whole cities at this RH. Well it is too high in 78° air, but not in 70° air.

[Jerry Peck]

Let's summarize:

A simple question.

A single simple question.

A simply 'yes' or 'no' question.


Do you, or do you not, agree that the psychometric chart is a static graphical representation of dynamic readings taken as representing one point in time?

And that, because it is representing dynamic readings the static graphical representation will change when recalculated for each no dynamically changing set of readings?

Vern,

What is it?

A simple 'yes'?

A simple 'no'?

You are going on tangents instead of answering a simple question.

[Vern Heiler]

Let's summarize:

A simple question.

A single simple question.

A simply 'yes' or 'no' question.



Vern,

What is it?

A simple 'yes'?

A simple 'no'?

You are going on tangents instead of answering a simple question.


I answered the best I could to a poorly written question at the end of the summary.

[Jerry Peck]

I answered the best I could to a poorly written question at the end of the summary.

If that was your lame attempt at an answer to a very simply written question, your answer is only partially correct, meaning that you are still not correct.

Go back and re-read your poorly written attempt at an answer and see if you can figure out why you are only partially correct.

[Vern Heiler]

If that was your lame attempt at an answer to a very simply written question, your answer is only partially correct, meaning that you are still not correct.

Go back and re-read your poorly written attempt at an answer and see if you can figure out why you are only partially correct.

And why would I do that? You have not answered any of my questions and I am not on the stand and you are not Perry Mason.

[Jerry Peck]

Vern,


You have not answered any of my questions and I am not on the stand and you are not Perry Mason.

I am addressing these in order: You whipped your little chart out at post #12, ... LONG BEFORE my post with the the dew point moving - post #18.

Post #12:

As Scott said, a lot depends on where the measurement was taken and how accurate the measurement was.

All of the psychrometric comfort zone charts I have seen put the 65% humidity at 70 degrees inside the zone. I don't think it should be considered bad.

And you have not answered any questions about your chart, dew point, etc.

You say that:

57. Of course DP’s change, but they change because of the addition or removal of moisture.

So I am presuming, because you have not explained yourself well at all or answer the other questions, that your statement that dew points change but ONLY because of the addition or removal of moisture ... THAT IS what YOU said.

I am giving you a chance to further state what causes dew points to move and change.

Name the thing(s) which affect dew point:
-
-
-
-
- (however many there are)

[Vern Heiler]

Vern,



I am addressing these in order: You whipped your little chart out at post #12, ... LONG BEFORE my post with the the dew point moving - post #18.

Post #12:


And you have not answered any questions about your chart, dew point, etc.

You say that:


So I am presuming, because you have not explained yourself well at all or answer the other questions, that your statement that dew points change but ONLY because of the addition or removal of moisture ... THAT IS what YOU said.

I am giving you a chance to further state what causes dew points to move and change.

Name the thing(s) which affect dew point:
-
- The amount of moisture contained in a volume of air.

also see:Observed Dew Point Temperature: indicates the amount of moisture in the air (http://ww2010.atmos.uiuc.edu/(Gh)/guides/maps/sfcobs/dwp.rxml)
-
- Read the first line of the second paragraph.
- (however many there are)


- The amount of moisture contained in a volume of air.

also see:
- The amount of moisture contained in a volume of air.

also see:Observed Dew Point Temperature: indicates the amount of moisture in the air (http://ww2010.atmos.uiuc.edu/(Gh)/guides/maps/sfcobs/dwp.rxml)
-
- Read the first line of the second paragraph.
- (however many there are)[/quote]
-
- Read the first line of the second paragraph.
- (however many there are)[/quote]

[Jerry Peck]

Vern, Vern, Vern,

When are you ever going to learn? :rolleyes: :p

Now that you have progressed from crayons to reading THE FIRST LINE ... let's see if I can help you progress EVEN FURTHER in your endeavor of learning to read, so, with that being the intent, ...

I am sure that you are good at drawing pictures and understanding them too, so, let us now READ ON TO THE FIRST LINE BELOW THE PICTURE.

In fact, let us address the first paragraph below the picture one line at a time.


Dew points indicate the amount moisture in the air. The higher the dew points, the higher the moisture content of the air at a given temperature. Dew point temperature is defined as the temperature to which the air would have to cool (at constant pressure and constant water vapor content) in order to reach saturation. A state of saturation exists when the air is holding the maximum amount of water vapor possible at the existing temperature and pressure (http://ww2010.atmos.uiuc.edu/(Gh)/wwhlpr/pressure_def.rxml?hret=/guides/maps/sfcobs/dwp.rxml).

"Dew points indicate the amount moisture in the air."

Okay, you have that down pretty good.

"The higher the dew points, the higher the moisture content of the air at a given temperature."

However, Vern, you did not read far enough " ... at a given temperature."

Oh, wait, there IS another factor in dew point, isn't there? Dang, well I'll be! There it is, there is that thing called "temperature".

"Dew point temperature is defined as the temperature to which the air would have to cool (at constant pressure and constant water vapor content) in order to reach saturation."

Holy crap! There is that "temperature" word again: " ... the temperature to which the air would have to cool ... ", in fact, a CHANGE in "temperature".

"A state of saturation exists when the air is holding the maximum amount of water vapor possible at the existing temperature and pressure (http://ww2010.atmos.uiuc.edu/(Gh)/wwhlpr/pressure_def.rxml?hret=/guides/maps/sfcobs/dwp.rxml)."

Dang! We just cannot get away from that "temperature" word, can we?: " ... at the existing temperature ... "

Oh, lookee, there is also ANOTHER FACTOR ... "pressure".

Now, Vern, keep reading and in the next paragraph down you will see "Therefore, if the air cools, ... "

Dang! So not only does the "amount of moisture in the air" affect dew point, but the "temperature" also affects due point, as does "pressure".

Now, Vern, please explain to me how ONLY "the amount of moisture in the air" affect the dew point?

[Vern Heiler]

I will concede pressure, (though normal atmospheric pressure changes have only a small effect) but the temperature does not dictate the dew point, the amount of moisture in the air dictates what the temperature will be.

[Jerry Peck]

Are you saying that temperature does not affect dew point in any way?

[Vern Heiler]

Are you saying that temperature does not affect dew point in any way?

Now ya got it!

[Jerry Peck]

Are you saying that temperature does not affect dew point in any way?


Now ya got it!

Okay, so explain this, from the link you posted:

Dew points indicate the amount moisture in the air. The higher the dew points, the higher the moisture content of the air at a given temperature. Dew point temperature is defined as the temperature to which the air would have to cool (at constant pressure and constant water vapor content) in order to reach saturation. A state of saturation exists when the air is holding the maximum amount of water vapor possible at the existing temperature and pressure (http://ww2010.atmos.uiuc.edu/(Gh)/wwhlpr/pressure_def.rxml?hret=/guides/maps/sfcobs/dwp.rxml).

Remember that part?

"at a given temperature"

So, if I am doing as you say, I take a given amount of air, at a given temperature, add a given amount of moisture which is sufficient to reach dew point "at that given temperature", and then ...

... and then the only thing I change is "temperature", you are trying to tell me that the dew point will be the same?

[Vern Heiler]

Okay, so explain this, from the link you posted:


Remember that part?

"at a given temperature"

So, if I am doing as you say, I take a given amount of air, at a given temperature, add a given amount of moisture which is sufficient to reach dew point "at that given temperature", and then ...

... and then the only thing I change is "temperature", you are trying to tell me that the dew point will be the same?

One last time (I gotta get this report done!).

If you have a cubic foot of air with 50% humidity and that air is at 78 degrees F. and the pressure is 29.921 inches Hg, the temperature that that air will condense at is 57.9 degrees F at 29.921. If you contain this air and don't let any moisture in or out, you can take the temperature from below zero to above boiling and the dew point is still 57.9. That is the temp at which that percentage of moisture in air will condense. (pressure at 29.921)

[Cobra Cook]

I think you are both wackey. where did all of this come from just some one asking why is the humidity 65% and the tempature 70. darn i have to agree with Jerry for once in that tempature is the determing factor as to what the dewpoint is followed by pressure. Vern what do you not understand about that 70% and 70 degree is satuated. Raise the tempature the humidity goes down. lower the temp and the humidity goes up. put it in a 29.9" vacuum and the moisture boils at around 70 degrees and the moisture boils off thus lowering the moisture thus you will have 70 degrees at o% moisture. what is the dewpoint now?

[Steve Zabarylo]

Vern and Jerry, Wayne and Shuster, Laurel and Hardy, Dean and Jerry, Desi and Lucy. Wow! Move over vaudville, this threads on a roll!

Here's another way of looking at dew point, a temperature where a water droplet suspended in the air has an equilibrium of the rate of evaporation with the rate of condensation. A drop of water in air at the dew point temperature will stay the same size but if we change the temperature we tip the ratio of the two rates. When the saturated air carrying the droplet is cooled by contact with a cooler surface that droplet will grow. The same thing happens in rising air that cools adiabatically and the droplets grow becoming collectively visible as clouds and eventually rain.

I'm hoping other poor sops that stumble onto this thread get some value from mine and other posts since you two only seem to have space in your attention for your own keyboard rants. You sound like some married couples I know that circle one another in that dance of redirection and plumage fluffing.

[Jerry Peck]

Vern,

Read the last two posts.

That have said it better than I have been saying it - same thing but better.

[Vern Heiler]

I think you are both wackey. where did all of this come from just some one asking why is the humidity 65% and the tempature 70. darn i have to agree with Jerry for once in that tempature is the determing factor as to what the dewpoint is followed by pressure. Vern what do you not understand about that 70% and 70 degree is satuated. Raise the tempature the humidity goes down. lower the temp and the humidity goes up. put it in a 29.9" vacuum and the moisture boils at around 70 degrees and the moisture boils off thus lowering the moisture thus you will have 70 degrees at o% moisture. what is the dewpoint now?

Really! Cobra you need to do a little more study. You don't have much of that right!

One more reference to the definition of DP.
From Wikipedia, the free encyclopedia


The dew point is the temperature (http://www.inspectionnews.net/wiki/Temperature) to which a given parcel of air (http://www.inspectionnews.net/wiki/Air) must be cooled, at constant barometric pressure (http://www.inspectionnews.net/wiki/Barometric_pressure), for water vapor (http://www.inspectionnews.net/wiki/Water_vapor) to condense (http://www.inspectionnews.net/wiki/Condensation) into water.

[Vern Heiler]

Vern,

Read the last two posts.

That have said it better than I have been saying it - same thing but better.

Jerry I am begining to believe you are an incorrigible.

[Vern Heiler]

I think you are both wackey. where did all of this come from just some one asking why is the humidity 65% and the tempature 70. darn i have to agree with Jerry for once in that tempature is the determing factor as to what the dewpoint is followed by pressure. Vern what do you not understand about that 70% and 70 degree is satuated. Raise the tempature the humidity goes down. lower the temp and the humidity goes up. put it in a 29.9" vacuum and the moisture boils at around 70 degrees and the moisture boils off thus lowering the moisture thus you will have 70 degrees at o% moisture. what is the dewpoint now?

Cobra I apologize for being short with you. You did bring up a very good point.

put it in a 29.9" vacuum and the moisture boils at around 70 degrees and the moisture boils off thus lowering the moisture thus you will have 70 degrees at o% moisture. what is the dewpoint now?

This is what we do when evacuating an a/c system. We remove the moisture to the point that there is no dew point. The moisture blows out the hole in the handle of the vacuum pump.

Taking this a little further, with an evacuated system (no moisture in it) can you make the dew point 50 deg. by heating it? Come on you and Jerry say that temp. is the main factor in changing the dew point! Just heat it or cool it what ever it takes. You do realize you will win the Nobel Prise and the deserts of the world will flourish green with plenty of water if you can do this.

[Jerry Peck]

Taking this a little further, with an evacuated system (no moisture in it) can you make the dew point 50 deg. by heating it? Come on you and Jerry say that temp. is the main factor in changing the dew point!

Vern,

You really do need to learn to read and understand what you read.

*I* said "temperature" is *a factor*, now *you* are trying to say I said it was 'the main' factor.

I realize it is easier to try to confuse things than it is to try to understand things, but if you would stop trying to confuse things you would ... should ... easily understand what we are saying.

Even your reference stated what we are saying: "The higher the dew points, the higher the moisture content of the air at a given temperature."

Even they state "at a given temperature", which means that if the "given temperature" is not as given, all other things being equal and unchanged, then the dew IS NOT THERE ANYMORE.

How much simpler does it need to be for you?

[Jerry Peck]

Vern,

Try this: Dew Point Calculator (http://www.decatur.de/javascript/dew/index.html)

Change the temperature 1 degree and see what happens to the dew point.

[Vern Heiler]

Vern,

Try this: Dew Point Calculator (http://www.decatur.de/javascript/dew/index.html)

Change the temperature 1 degree and see what happens to the dew point.

That calculator takes two knowns to find the third. It does not change the dew point of a cubic foot of air containing an ounce of water.

The importance of this consept is directly related to the OP who worried that 65% RH was too high. Why would one worry? Because of condensation. Is 65% too high? Well we don"t have two of the knowns to find the third yet. We find that the other known is 70 deg DB. Now we have enough to plug into the calculator. We find the DP is 57.71. Is that bad? I don't know, but I do know 50% at 78 deg is considered good. Let's plug that in. Oh look! It's the same!

That same air has the same DP no matter what we do with the temp.

[Jerry Peck]

That calculator takes two knowns to find the third. It does not change the dew point of a cubic foot of air containing an ounce of water.

The importance of this consept is directly related to the OP who worried that 65% RH was too high. Why would one worry? Because of condensation. Is 65% too high? Well we don"t have two of the knowns to find the third yet. We find that the other known is 70 deg DB. Now we have enough to plug into the calculator. We find the DP is 57.71. Is that bad? I don't know, but I do know 50% at 78 deg is considered good. Let's plug that in. Oh look! It's the same!

That same air has the same DP no matter what we do with the temp.

Vern,

What happens when the amount of moisture in the air is left constant (unchanged) and the temperature drops to, say, 70 degrees to 30 degrees? You get your condensation.

Temperature ... temperature is a factor.

Moisture content ... moisture content is a factor.

"It does not change the dew point of a cubic foot of air containing an ounce of water"

What happens to air when it is heated and cooled? You need to get your head and nose out of that book and read other material and think in real life.

You are trying to defend your original statement instead of just acknowledging that you were incorrect, and each additional defense position/statement you add only shows that instead of getting closer to understanding what is going on, you are getting further from understanding what is really going on.

I doubt there is anything else I can point out to you, you will need to discover your errors on your own. SEVERAL OF US have tried to help you understand this concept, but you refuse to be helped.

[Vern Heiler]

What happens to air when it is heated and cooled? You need to get your head and nose out of that book and read other material and think in real life.



OMG! Is this what has had you confused all of this time!

When you heat or cool the air the relative humidity changes not the dew point!

[Jerry Peck]

It does not change the dew point of a cubic foot of air containing an ounce of water.


What happens to air when it is heated and cooled?


When you heat or cool the air the relative humidity changes not the dew point!

Let's see ... "Why?" does the relative humidity change?

Oh, wait, because the volume of the AIR CHANGED, it is no longer your "cubic foot of air" which is "containing an ounce of water", it is a larger volume of air now (presuming a rise in temperature), containing the same ounce of water. Which means your dew point IS NOT WHERE IT WAS.

The AMOUNT OF MOISTURE has not changed, the volume of air changed, and that was because of TEMPERATURE CHANGE.

[Vern Heiler]

Let's see ... "Why?" does the relative humidity change?

Oh, wait, because the volume of the AIR CHANGED, it is no longer your "cubic foot of air" which is "containing an ounce of water", it is a larger volume of air now (presuming a rise in temperature), containing the same ounce of water. Which means your dew point IS NOT WHERE IT WAS.

The AMOUNT OF MOISTURE has not changed, the volume of air changed, and that was because of TEMPERATURE CHANGE.

I don't remenber seeing "air volume" in your calculator. Could you point it out please?

[Jerry Peck]

I don't remenber seeing "air volume" in your calculator. Could you point it out please?

It's taken into account for in the equation which ... changes the dew point.

Jeez, Vern, ...

Q. What happens when things are heated?
A. They expand.

Q. What happens when things are cooled?
A. They contract.

Q. What causes things to become heated or cooled?
A. The application of, or removal of, heat.

Q. What does the application of, or removal of, heat do to things?
A. Changes the temperature of it.

[Jerry Peck]

Vern,

I am having a very hard time understanding what you do not understand about what was stated in that reference you posted: "at a given temperature".

Which means, at ANY OTHER "given temperature" the dew point will be different.

I have tried and tried to help explain it to you ... but I have not been able to.

So I guess I will have to let you continue your diatribe about how right you think you are when the rest of the world understands you are not, and how wrong you think we are.

We have beat the horse to death and drowned it while trying to force it to drink from the waters of knowledge.

The thread is yours.

[Ted Menelly]

Dew point

From Wikipedia, the free encyclopedia


Jump to: navigation (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Dew_point#column-one), search (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Dew_point#searchInput)
The dew point is the temperature (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Temperature) to which a given parcel of air (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Air) must be cooled, at constant barometric pressure (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Barometric_pressure), for water vapor (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Water_vapor) to condense (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Condensation) into water. The condensed water is called dew (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Dew). The dew point is a saturation (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Saturation) point. When the dew point temperature falls below freezing it is often called the frost point, as the water vapor no longer creates dew but instead creates frost (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Frost) or hoarfrost (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Frost#Hoar_frost) by deposition (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Deposition_(meteorology)).
The dew point is associated with relative humidity (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Humidity). A high relative humidity (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Relative_humidity) indicates that the dew point is closer to the current air temperature. Relative humidity of 100% indicates the dew point is equal to the current temperature and the air is maximally saturated with water. When the dew point remains constant and temperature increases, relative humidity will decrease.[1] (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Dew_point#cite_note-Horstmeyer-0)
At a given barometric pressure (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Barometric_pressure), independent of temperature, the dew point indicates the mole fraction (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Mole_fraction) of water vapor in the air, and therefore determines the specific humidity (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Specific_humidity) of the air. The dew point is an important statistic for general aviation (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/General_aviation) pilots, as it is used to calculate the likelihood of carburetor icing (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Carburetor_icing) and fog (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Fog), and estimate the height of the cloud base (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Cloud_base).

Humidity

Humidity

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Humidity is the amount of water vapour in the air. In daily language the term "humidity" is normally taken to mean relative humidity (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Relative_humidity). Relative humidity is defined as the ratio of the partial pressure (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Partial_pressure) of water vapour (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Water_vapour) in a parcel (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Air_parcel) of air (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Air) to the saturated vapour pressure (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Vapour_pressure) of water vapour at a prescribed temperature (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Temperature). Humidity may also be expressed as absolute humidity and specific humidity. Relative humidity is an important metric (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Metric_(mathematics)) used in forecasting weather (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Weather_forecasting). Humidity indicates the likelihood of precipitation (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Precipitation_(meteorology)), dew (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Dew), or fog (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Fog). High humidity makes people feel hotter outside in the summer because it reduces the effectiveness of sweating (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Sweating) to cool the body by reducing the evaporation (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Evaporation) of perspiration from the skin. This effect is calculated in a heat index (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Heat_index) table.
Contents

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<LI class=toclevel-1>1 Types of humidity (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Humidity#Types_of_humidity)
<LI class=toclevel-2>1.1 Absolute humidity (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Humidity#Absolute_humidity) <LI class=toclevel-2>1.2 Mixing ratio or humidity ratio (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Humidity#Mixing_ratio_or_humidity_ratio) <LI class=toclevel-2>1.3 Relative humidity (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Humidity#Relative_humidity) <LI class=toclevel-2>1.4 Specific humidity (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Humidity#Specific_humidity) <LI class=toclevel-2>1.5 Humidity during rain (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Humidity#Humidity_during_rain)
1.6 Dew point and frost point (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Humidity#Dew_point_and_frost_point)<LI class=toclevel-1>2 Measuring and regulating humidity (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Humidity#Measuring_and_regulating_humidity) <LI class=toclevel-1>3 Humidity and air density (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Humidity#Humidity_and_air_density) <LI class=toclevel-1>4 Effects on human body (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Humidity#Effects_on_human_body)

4.1 Recommendations for comfort (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Humidity#Recommendations_for_comfort)<LI class=toclevel-1>5 Effects on electronics (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Humidity#Effects_on_electronics) <LI class=toclevel-1>6 Humidity in construction (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Humidity#Humidity_in_construction) <LI class=toclevel-1>7 Most humid places on Earth (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Humidity#Most_humid_places_on_Earth) <LI class=toclevel-1>8 See also (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Humidity#See_also) <LI class=toclevel-1>9 References (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Humidity#References)
10 External links (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Humidity#External_links)//
[edit (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/w/index.php?title=Humidity&action=edit&section=1)] Types of humidity


[edit (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/w/index.php?title=Humidity&action=edit&section=2)] Absolute humidity

Absolute humidity is the quantity of water in a particular volume of air. The most common units are grams per cubic meter, although any mass unit and any volume unit could be used. Pounds per cubic foot is common in the U.S., and occasionally even other units mixing the Imperial and metric systems are used.
If all the water in one cubic meter (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Cubic_meter) of air were condensed into a container, the container could be weighed to determine absolute humidity. The amount of vapor in that cube of air is the absolute humidity of that cubic meter of air. More technically: the mass of water vapor mw, per cubic meter of air, Va .
http://www.inspectionnews.net/home_inspection/mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://upload.wikimedia.org/math/0/0/0/000751b7018e3d5a5aadcd3616bdf614.png Absolute humidity ranges from 0 grams per cubic meter in dry air to 30 grams per cubic meter (0.03 ounce per cubic foot) when the vapour is saturated at 30 °C.[1] (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://www.britannica.com/eb/article-53259/climate#292984.hook) (See also Absolute Humidity table (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://www.tis-gdv.de/tis_e/misc/klima.htm))
The absolute humidity changes as air pressure (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Pressure) changes. This is very inconvenient for chemical engineering (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Chemical_engineering) calculations, e.g. for dryers (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Clothes_dryer), where temperature (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Temperature) can vary considerably. As a result, absolute humidity is generally defined in chemical engineering as mass of water vapor per unit mass of dry air, also known as the mass mixing ratio (see below), which is much more rigorous for heat and mass balance calculations. Mass of water per unit volume as in the equation above would then be defined as volumetric humidity. Because of the potential confusion, British Standard (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/British_Standard) BS 1339 (revised 2002) suggests avoiding the term "absolute humidity". Units should always be carefully checked. Most humidity charts are given in g/kg or kg/kg, but any mass units may be used.
The engineering of physical and thermodynamic properties of gas-vapor mixtures is named Psychrometrics (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Psychrometrics).

[edit (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/w/index.php?title=Humidity&action=edit&section=3)] Mixing ratio or humidity ratio

Mixing or humidity ratio is expressed as a ratio of water vapour mass, mw, per kilogram of dry air, md, at a given pressure. The colloquial term moisture content is also used instead of mixing/humidity ratio. Humidity ratio is a standard axis on psychrometric charts, and is a useful parameter in psychrometrics (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Psychrometrics) calculations because it does not change with temperature except when the air cools below dewpoint.
That ratio can be given as:
Mixing ratio can also be expressed with the partial pressure (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Partial_pressure) of water vapor[1] (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Humidity#cite_note-0) :
where
δ = 0.62197 is the ratio of specific gas constants, of water vapour to dry air pw = partial pressure of water vapor in moist air pa = atmospheric pressure of moist air Technically speaking, this is a dimensionless quantity (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Dimensionless_quantity) as it is the mass of water vapor to the mass of dry air. So it is expressed as Kg/Kg. However, the mass of water vapor is much less than the value of the mass of dry air and most commonly meteorologists use g (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Gram)/Kg which is 10 − 3 Kg/Kg.[2] (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Humidity#cite_note-1)

[edit (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/w/index.php?title=Humidity&action=edit&section=4)] Relative humidity

Main article: Relative humidity (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Relative_humidity)
Relative humidity is defined as the ratio of the partial pressure of water vapor (in a gaseous (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Gas) mixture of air and water vapor) to the saturated vapor pressure of water at a given temperature. Relative humidity is expressed as a percentage and is calculated in the following manner:

where
is the partial pressure (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Partial_pressure) of water vapor in the gas mixture; is the saturation vapor pressure (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Saturation_vapor_pressure) of water at the temperature of the gas mixture; and is the relative humidity of the gas mixture being considered. Relative humidity is often mentioned in weather forecasts (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Weather_forecasting) and reports, as it is an indicator of the likelihood of precipitation (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Precipitation_(meteorology)), dew, or fog. In hot summer weather (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Weather), it also increases the apparent temperature (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Heat_index) to humans (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Human) (and other animals (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Animal)) by hindering the evaporation (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Evaporation) of perspiration (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Perspiration) from the skin as the relative humidity rises.

[edit (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/w/index.php?title=Humidity&action=edit&section=5)] Specific humidity

Specific humidity is the ratio of water vapor to air (including water vapor and dry air) in a particular mass. Specific humidity ratio is expressed as a ratio of kilograms of water vapor, mw, per kilogram of air (including water vapor), mt .
That ratio can be shown as:
Specific humidity is related to mixing ratio (and vice versa) by:

[edit (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/w/index.php?title=Humidity&action=edit&section=6)] Humidity during rain

Humidity is a measure of the amount of water vapor dissolved in the air, not including any liquid water or ice falling through the air. For clouds (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Cloud) to form, and rain (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Rain) to start, the air doesn't have to reach 100% relative humidity at the Earth's surface, but only where the clouds and rain drops form. This normally occurs when the air rises and cools. Typically, rain falls into air with less than saturated humidity. Some water from the rain may evaporate into the air as it falls, increasing the humidity, but not necessarily enough to raise the humidity to 100%. It is even possible for rain falling through warm, humid air to be cold enough to lower the air temperature to the dew point (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Dew_point), thus condensing water vapor out of the air. Although that would indeed raise the relative humidity (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Relative_humidity) to 100%, the water lost from the air (as dew) would also lower the absolute humidity (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Absolute_humidity).

[edit (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/w/index.php?title=Humidity&action=edit&section=7)] Dew point and frost point

Associated with relative humidity is dew point (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Dew_point) (If the dew point is below freezing, it is referred to as the frost point). Dew point is the temperature (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Temperature) at which water vapor saturates from an air mass into liquid or solid usually forming rain (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Rain), snow (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Snow), frost (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Frost), or dew (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Dew). Dew point normally occurs when a mass of air has a relative humidity of 100%. This happens in the atmosphere (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Earth%27s_atmosphere) as a result of cooling through a number of different processes.


[edit (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/w/index.php?title=Humidity&action=edit&section=8)] Measuring and regulating humidity

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A [URL="mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Hygrometer"]hygrometer (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/File:Umidaderelativa.jpg) is a device used for measuring the humidity of the air


There are various devices used to measure and regulate humidity. A device used to measure humidity is called a psychrometer or hygrometer (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Hygrometer). A humidistat (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Humidistat) is used to regulate the humidity of a building with a de-humidifier. These can be analogous to a thermometer (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Thermometer) and thermostat (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Thermostat) for temperature control.
During coating applications Humidity and air temperature are measured in combination with surface temperature to determine the dewpoint (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Dewpoint). This is done by use of a dewcheck (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Dewcheck) dewpoint gauge.
Humidity is also measured on a global scale using remotely placed satellites (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Satellite). These satellites are able to detect the concentration of water in the troposphere (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Troposphere) at altitudes between 4 and 12 kilometers. Satellites that can measure water vapor have sensors that are sensitive to infrared radiation (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Infrared). Water vapor specifically absorbs and re-radiates radiation in this spectral band. Satellite water vapor imagery plays an important role in monitoring climate conditions (like the formation of thunderstorms) and in the development of future weather forecasts (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Weather_forecasts).

[edit (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/w/index.php?title=Humidity&action=edit&section=9)] Humidity and air density

Main article: Density of air (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Density_of_air)
Humid air is less dense than dry air because a molecule of water (m (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Molecular_mass) = 18) is less dense than a molecule of nitrogen (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Nitrogen)(m = 28) and a molecule of oxygen (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Oxygen) (m = 32). About 78% of the molecules in dry air are nitrogen (N2). Another 21% of the molecules in dry air are oxygen (O2). The final 1% of dry air is a mixture of other gases. For any gas, at a given temperature and pressure, the number of molecules present is constant for a particular volume - see ideal gas law (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Ideal_gas_law). So when water molecules (vapor) are introduced to the dry air, the number of air molecules must reduce by the same number in a given volume, without the pressure or temperature increasing. Hence the mass per unit volume of the gas (its density) decreases. Isaac Newton (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Isaac_Newton) discovered this phenomenon and wrote about it in his book Opticks (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Opticks).[3] (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Humidity#cite_note-optics-2)

[edit (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/w/index.php?title=Humidity&action=edit&section=10)] Effects on human body

The human body sheds heat by a combination of evaporation of perspiration, heat convection (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Heat_convection) in the surrounding air, and thermal radiation (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Thermal_radiation). Under conditions of high humidity, the evaporation of sweat from the skin is decreased and the body's efforts to maintain an acceptable body temperature may be significantly impaired. Also, if the atmosphere is as warm as or warmer than the skin during times of high humidity, blood (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Blood) brought to the body surface cannot shed heat by conduction to the air, and a condition called hyperpyrexia (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Hyperpyrexia) results. With so much blood going to the external surface of the body, relatively less goes to the active muscles (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Muscle), the brain (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Brain), and other internal organs (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Organ_(anatomy)). Physical strength (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Physical_strength) declines and fatigue (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Fatigue_(physical)) occurs sooner than it would otherwise. Alertness and mental capacity also may be affected. This resulting condition is called heat stroke or hyperthermia (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Hyperthermia).

[edit (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/w/index.php?title=Humidity&action=edit&section=11)] Recommendations for comfort

Humans control their body temperature mainly by sweating (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Sweating) and shivering (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Shivering). The United States Environmental Protection Agency (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/United_States_Environmental_Protection_Agency) cites the ASHRAE (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/ASHRAE) Standard 55-1992 Thermal Environmental Conditions for Human Occupancy, which recommends keeping relative humidity between 30% and 60%, with below 50% preferred to control dust mites (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Dust_mites). At high humidity sweating is less effective so we feel hotter; thus the desire to remove humidity from air with air conditioning (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Air_conditioning) in the summer. In the winter, heating cold outdoor air can decrease indoor relative humidity levels to below 30%, leading to discomfort such as dry skin and excessive thirst.

[edit (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/w/index.php?title=Humidity&action=edit&section=12)] Effects on electronics

Many electronic devices have humidity specifications, for example, 5 to 95%. At the top end of the range, moisture may increase the conductivity of permeable insulators leading to malfunction. Too low humidity may make materials brittle. A particular danger to electronic items, regardless of the stated operating humidity range, is condensation (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Condensation). When an electronic item is moved from a cold place (eg garage, car, shed, an air conditioned space in the tropics) to a warm humid place (house, outside tropics), condensation may coat circuit boards and other insulators, leading to short circuit (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Short_circuit) inside the equipment. Such short circuits may cause substantial permanent damage if the equipment is powered on before the condensation has evaporated (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Evaporated). A similar condensation effect can often be observed when a person wearing glasses comes in from the cold. It is advisable to allow electronic equipment to acclimatise for several hours, after being brought in from the cold, before powering on. The inverse is also true.
Low humidity also favors the buildup of static electricity (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Static_electricity), which may result in spontaneous shutdown of computers when discharges occur. Apart from spurious erratic function, electrostatic discharges can cause dielectric breakdown in solid state devices, resulting in irreversible damage. Data centers (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Data_center) often monitor relative humidity levels for these reasons.

[edit (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/w/index.php?title=Humidity&action=edit&section=13)] Humidity in construction

Traditional building designs typically had weak insulation (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Insulation), and this allowed air moisture to flow freely between the interior and exterior. The energy-efficient, heavily-sealed architecture introduced in the 20th century (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/20th_century) also sealed off the movement of moisture, and this has resulted in a secondary problem of condensation (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Condensation) forming in and around walls, which encourages the development of mold and mildew. Solutions for energy-efficient buildings that avoid condensation are a current topic of architecture.

[edit (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/w/index.php?title=Humidity&action=edit&section=14)] Most humid places on Earth

See also: Humid subtropical climate (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Humid_subtropical_climate) and Humid continental climate (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Humid_continental_climate)
The most humid cities on earth are generally located closer to the equator, near coastal regions. Cities in South and Southeast Asia are among the most humid, such as Kolkata (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Kolkata) and those in Kerala (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Kerala) in India (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/India), the cities of Manila (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Manila) in the Philippines (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Philippines) and Bangkok (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Bangkok) in Thailand (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Thailand): these places experience extreme humidity during their rainy seasons combined with warmth giving the feel of a lukewarm Sauna.[4] (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Humidity#cite_note-3) Darwin, Australia experiences an extremely humid wet season from December to April. Kuala Lumpur (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Kuala_Lumpur) and Singapore (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Singapore) have very high humidity all year round because of their proximity to water bodies and the Equator (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Equator) and overcast weather; despite sunshine, perfectly clear days are rare in these locations and it is often misty. In cooler places such as Northern Tasmania, Australia, high humidity is experienced all year due to the ocean between mainland Australia and Tasmania. In the summer the hot dry air is absorbed by this ocean and the temperature rarely climbs above 35 degrees Celsius.
In the United States the most humid cities, strictly in terms of relative humidity (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Relative_humidity), are Forks (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Forks,_Washington) and Olympia, Washington (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Olympia,_Washington).[5] (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Humidity#cite_note-4) This fact may come as a surprise to many, as the climate in this region rarely exhibits the discomfort usually associated with high humidity. Dew points are typically much lower on the West Coast than on the East. Because high dew points play a more significant role than relative humidity in the discomfort created during humid days, the air in these western cities usually does not feel "humid."
The highest dew points are found in coastal Florida (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Florida) and Texas (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Texas). When comparing Key West and Houston, two of the most humid cities from those states, coastal Florida seems to have the higher dew points on average. But, as noted by Jack Williams of USA Today,[6] (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Humidity#cite_note-5) Houston lacks the coastal breeze present in Key West, and, as a much larger city, it suffers from the urban heat island (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Urban_heat_island) effect.
The US city with the lowest annual humidity is Yuma (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Yuma,_Arizona), Arizona (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Arizona), averaging under 50% for a high and 22% as a low. The next-lowest humidity is Tucson, Arizona (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Tucson,_Arizona), average high humidity of 57% and a low of 26%. Lowest in the world is Antarctica (mhtml:{BD2BC3F8-FD89-4501-9EA2-78782864A32B}mid://00000224/!x-usc:http://en.wikipedia.org/wiki/Antarctica).

[Vern Heiler]

Ok, last time I promise;) .

Lets take a room and fill it with nitrogen, forcing all other gasses out of the room. No water vapor.

Now lets start the a/c and fill the room with air that has condensed on its coil at lets say 45 deg. Reasonable?

Now lets assume the RH at the coil is 100% ( It will be very close to that as that is saturation.) Also reasonable?

Now lets use Jerry's calculator to find the dew point of this air. Comes out to 45 degrees. (just proving Jerry's calculator)

Now after the a/c has run long enough to stabilize at some temp and has replaced all of the nitrogen with its air, lets take a temp reading...just pick one, it doesn't matter. Lets say the room temp is 74 deg. (a common temp for an indoor room)

Now lets find what the RH is. For this we need a little more sophisticated program than Jerry's. I have down loaded and installed Trane's HDPsyChart for this. (You can do the same or take my word)

I hope we can agree that even Jerry's program shows that there is a point that temp. RH and DP are a plot-able point, and that if we know two values we can find the third.

In our room we know that the only moisture in the room came from the a/c coil. We know that the DP is 45 deg. Plotting the DP and changing the temp to 74 deg. (we just raised the temp that's all) we get RH of 35 deg. (took two known points and plotted for the third) We could erase the numbers and re-enter 74 deg. and RH 35 in Jerry's calculator and obviously it would return a DP of 45. The point is that it is a plot-table point.

Another way of visualizing this is to suck that 74 deg air back into the a/c. Would it condense at a different temp than it did when it was filling the room? We are sure there was no moisture added or removed from this air, and we know it squeezed out all the moisture it could while filling the room. Is it not logical that that same air will have to be cooled to 45 deg. to begin to condense or be at saturation. The DP has remained the same though the temp has changed.

[Jim Luttrall]

I have stayed out of this as long as I can.
You and Jerry both have a basic understanding of RH, Dew Point, and temperature and are just debating for debating sake, straining at gnats.
Looks like Jerry has declared himself a winner and left the room. I suggest the same for everyone else involved.

[Cobra Cook]

I wasn't going to say any more but after the statement (In our room we know that the only moisture in the room came from the a/c coil.) I just have to say that no moisture comes from an ac coil, the coil is actually pulling the moisture from the air not the other way around. The fan is blowing the warm air through fan and as the freon passes through the coils it is lowering the dewpoint by removing the heat from the air so the moisture collects on the fins and falls down to the pan below and is called condensation which then goes out to a drain. All of this results in cooler drier air in the room. When i pull avacuum i use a wetbulb thermometer to pull down the system to -25 wetbulb, about as cold as you can get with normal vacuum pumps. I did not really lower the temperature I just lowered the pressure to almost 5 microns or below. No more:p

[DavidR]

Let’s summarize.

POST #

13. DavidR States that if the outdoor DP is 70&#176; and the indoor DB temp is 70&#176;, the outdoor air is at saturation. Well that would be true if the outdoor air was indoors, but its not. That’s why we use something called “INSULATION”. David goes on to say that if the indoor RH goes above 55&#37; then DISASTER AWAITS US ALL! (Ya gotta love the chicken littles of the board!)

14. I explain that 70&#176; air with a RH of 65% is the same RH as 78&#176; and 50%. I mistakenly assume David knows the indoor air is separate from the outdoor air and state that the DP is 60&#176; for the OP’s condition, 10&#176; below the DB temp.

15. ??? Still doesn’t know indoor is separate from outdoor! David says if the temp gets to 60&#176; it will rain from the ceilings. ??? What I had stated was that if a surface was at 60&#176; in that 70&#176; 65% air there would be condensation. (How do you get the ceilings to 60&#176; without lowering the air temp?)

16. David does a little left turn here and does not address the question asked. “How does ID DP relate to OD DP?” States that it is the outdoor air that might get to the interior wall due to faulty insulation. OK, I’ll buy that.



Man did this thread take off since I got back. :D

It's not an insulation failure causing this problem Vern, it's an air and vapor barrier failure that cause these problems combined with building depressurization or any other driving force such as wind.
Fiberglass insulation does not stop air and moisture flow in fact it makes a great air and moisture filter.
It's the surface temperature of the wall cavities that is concerned with the dewpoint temperature not the interior ambient air here.
You assume too much in thinking outdoor air is separated from indoor air.

Four people have already agreed with what I originally stated and provided documented proof from BSC.

Chicken little does this type of thing for a living, I diagnose and teach others how to correct this very thing. I'm apparently not doing a very good job of explaining it here.

[Mike Schulz]

What "I" believe Vern is trying to get across and everybody seems to just pass it by is that DP is the same at a "given" where Jerry claims it moved at a "given".

I give Vern a thumbs up on trying to get his point across and taken the banter.

[Jerry Peck]

What "I" believe Vern is trying to get across and everybody seems to just pass it by is that DP is the same at a "given" where Jerry claims it moved at a "given".

Mike,

Not sure where you came up with me saying that is has moved at a "given".

I have repeated, and I do mean repeatedly, stated that the TEMPERATURE MOVED ... and thus the DEW POINT MOVED ... which means that the dew point at the "given" no longer applies.


I give Vern a thumbs up on trying to get his point across and taken the banter.

I give Vern a thumbs up for his efforts too, but like you (if that is what Vern thought) I give Vern, and you, a thumbs down for not paying attention to what has been said repeatedly.

[Vern Heiler]

What "I" believe Vern is trying to get across and everybody seems to just pass it by is that DP is the same at a "given" where Jerry claims it moved at a "given".

I give Vern a thumbs up on trying to get his point across and taken the banter.

Thanks Mike, thought I was in the twilight zone:rolleyes: .

I have one poster who says if I take a shower and raise the RH inside I will cause the outside air to condense on my insulation.

I have another who measures a deep vacuum with a wet bulb thermometer:confused: .

And another who knows that if the temperature is raised the RH will decrease at a predictable rate that can and has been graphed. But doesn't believe that if the temperature is lowered the RH will follow the same graph line.

Credibility on this subject is questionable at best.

[DavidR]

I've attached a copy of the ASHRAE comfort chart.

Can someone please point out to me where 70º at 65% RH is acceptable in summer time conditions?

[Vern Heiler]

I've attached a copy of the ASHRAE comfort chart.

Can someone please point out to me where 70º at 65% RH is acceptable in summer time conditions?

By that chart anything below 72.5 deg. is unacceptable at any RH.

[DavidR]

It's based off of ASHRAE standard 55-2004 which addresses where conditions need to be for thermal comfort.

[Randy Mayo]

Joe

Start with the basic process of elimination:

Check the RH in the house and then outside.

If the RH is higher in the house than outside look for the problem in the house.
A heat pump can't add water vapor it can only recirculate the current water vapor if it is not working properly or it can remove water vapor. Look for another source is there a humidifier in the house or attached to the furnace? Is there a water leak? Is the dryer venting into the house?, etc.

If the RH is higher outside then inside this gets a little harder,it could have come form outside air, inside source or a combination of both.
First check the items listed above, leaks, dryer, etc. Check the condensation output to see if you are getting water out, a simple plugged line could be your problem. Last but not least check the size of your heat pump compared to the volume of the house and verify cycle times to see if the heat pump runs long enough to remove a sufficient amount of water.

Good Luck

[Cobra Cook]

It is obvious Vern that you have a limited intelligence on the principle of refrigeration and ac mechanics. Both systems are based on temperature and pressure. They are married in that they go in equal directions with each other. As the temperature goes up or down the pressure also goes up or down. Pressure is the determining factor at which water will boil and when it will turn to steam, when Freon will turn to vapor and when it will turn back to a liquid. The same is with humidity. Take an air temperature at a fixed set point of 50% rh and 72 degree temp, if you lower or raise the temperature the moisture content in the air is the same amount but the % of rh will change in % wise.
As far as taking a wet bulb temp while taking a deep or not so deep vacuum, that is the only way to determine the moisture content left in the system. It is a special tool used in conjunction with the vacuum pump with either water if above 32 degree or alcohol is below as it’s liquid medium. to make since of that you can have a 25 micron or say 29.92 inch vacuum and it is still possible to have a moisture content that will freeze components on a looooow temp refrigeration system or a low temp ac system lets say at 0 degrees. If the moisture in the air is not below -25 degree you are going to have problems with expansion or epr, evp and back pressure controls sticking when that little drop of moisture tries to get through. Take that same drop of moisture on a conventional ac system in the med temp
range with an evaporator temp of 50 degree then the moisture might not freeze the controls but since moisture causes the oil turn acidic it still can cause damage in another way.

[Vern Heiler]

It is obvious Vern that you have a limited intelligence on the principle of refrigeration and ac mechanics. Both systems are based on temperature and pressure. They are married in that they go in equal directions with each other. As the temperature goes up or down the pressure also goes up or down. Pressure is the determining factor at which water will boil and when it will turn to steam, when Freon will turn to vapor and when it will turn back to a liquid. The same is with humidity. Take an air temperature at a fixed set point of 50% rh and 72 degree temp, if you lower or raise the temperature the moisture content in the air is the same amount but the % of rh will change in % wise.
As far as taking a wet bulb temp while taking a deep or not so deep vacuum, that is the only way to determine the moisture content left in the system. It is a special tool used in conjunction with the vacuum pump with either water if above 32 degree or alcohol is below as it’s liquid medium. to make since of that you can have a 25 micron or say 29.92 inch vacuum and it is still possible to have a moisture content that will freeze components on a looooow temp refrigeration system or a low temp ac system lets say at 0 degrees. If the moisture in the air is not below -25 degree you are going to have problems with expansion or epr, evp and back pressure controls sticking when that little drop of moisture tries to get through. Take that same drop of moisture on a conventional ac system in the med temp
range with an evaporator temp of 50 degree then the moisture might not freeze the controls but since moisture causes the oil turn acidic it still can cause damage in another way.

Cobra, I have a very good understanding of the refrigeration cycle but admittedly I have been out of the business for quite some time. My apologies for not having stayed current. Tripple evacuations were the standard practice back in the day. I have never seen a tool that can measure the moisture content inside the system such as the wet bulb tool you have mentioned. Could you give me some more info on the tool? Name of, where to buy, mfg. etc.

[Vern Heiler]

I wasn't going to say any more but after the statement (In our room we know that the only moisture in the room came from the a/c coil.) I just have to say that no moisture comes from an ac coil, the coil is actually pulling the moisture from the air not the other way around. The fan is blowing the warm air through fan and as the freon passes through the coils it is lowering the dewpoint by removing the heat from the air so the moisture collects on the fins and falls down to the pan below and is called condensation which then goes out to a drain. All of this results in cooler drier air in the room. When i pull avacuum i use a wetbulb thermometer to pull down the system to -25 wetbulb, about as cold as you can get with normal vacuum pumps. I did not really lower the temperature I just lowered the pressure to almost 5 microns or below. No more:p

I would also be interested in how the teperature drops to the -25 without moisture in the system. The way I understand it there has to be liquid boiling off to see a temp drop?

[DavidR]

Cobra, I have a very good understanding of the refrigeration cycle but admittedly I have been out of the business for quite some time. My apologies for not having stayed current. Tripple evacuations were the standard practice back in the day. I have never seen a tool that can measure the moisture content inside the system such as the wet bulb tool you have mentioned. Could you give me some more info on the tool? Name of, where to buy, mfg. etc.

I would like to hear about this also, never seen one that does wet bulb on a sealed system either.

Purge with nitrogen while brazing, pressure test, and evacuate to a holding vacuum of less than 500 microns is how we've always done it.

[Cobra Cook]

Hi sorry i have been busy, i am looking for the paper work on the wet buld as soon as i find it i will share it with all. At 500 microns that is usually ok for an AC system but there is still moisture present.

[DavidR]

Hi sorry i have been busy, i am looking for the paper work on the wet buld as soon as i find it i will share it with all. At 500 microns that is usually ok for an AC system but there is still moisture present.

So how deep would you recommend pulling a vacuum?

It's not uncommon to pull less than 100 microns and holding on a newer system with the rigs we use.

[Vern Heiler]

So how deep would you recommend pulling a vacuum?

It's not uncommon to pull less than 100 microns and holding on a newer system with the rigs we use.

I'm beginning to suspect Cobra works on chillers.

[Gary Burnett]

Joe,
To answer your question I think having to use your "Heat Pump" to cool your home may be an issue. Most of us use the Air Conditioner. If you are using the heat pump your reversing valve is reversed. As far as the humidity, I always turn on the range vent to exhaust when I cook Spagett.....Spegett.......Speighet...........Noodl es!

Dew Point - What Obama's advisors tell him to do every time he walks out on stage............When you get out there "Dew Point" at someone in the crowd and act like you're glad to see them.

[Cobra Cook]

Hi guys and girls. Sorry took so long to get back. The wet bulb gauge is made by C E Ray Company Inc. Located in Carmel IN 46032. You can find them on the net or call @ 317-844-9600. I always try to get the wet bulb back to factory spec. when i have to open a system. -12 for mid range ac and coolers and -25 for refridgeration and low temp ac systems, even lower for sub zero temp systems. you simply attach this tool with a tee while pulling a vacuum and watch the thermometer temp go down. As the ambient temp stays the same at lets say 72 degree when the vacuum pump lowers the pressure to say 28 inch the wet bulb is now 40 degree, at 29.57 the wet bulb is zero and at 29.72 the wet bulb is -12. Microns do not tell us how much moisture is left in the system only the wet bulb gauge can. Of course both can tell if even the tinest leak exsits. If you add heat to the system results will be quicker to cause the moisture in a system to evaporate and be sucked out of the system. Yes I work on chillers, cooling tunnels, low and medium temp ac and refridge systems. Even lithium bromide systems.

[Cobra Cook]

I tried to send pictures but they will not upload?????:confused:

[Vern Heiler]

Googled every veriation I could come up with but did not find C E Ray Company Inc.

Still courious as to what temp does the wet bulb gauge read on a system that has no (zero) moisture in it?

[Cobra Cook]

www. c e ray. it gives real web sites. then look for equipment sales. I have had mine for around ten years is why i have no papers for it . The lowest WB reading temp is - 30 degree at 29.83 vacuum. at - 50 at 29.88 I assume you can not totally remove all of the moisture since you can not pull a perfect vacuum. you can convert to microns and grains of moisture with a phyc chart. I will do it later when i can find my charts.