Thread: High Humidity with Heat Pump

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.

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

Originally Posted by Jerry Peck

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

Now ya got it!

Originally Posted by Jerry Peck

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

Originally Posted by Vern Heiler

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.

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?

Originally Posted by Jerry Peck

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)

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?

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.

Vern,

Read the last two posts.

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

Originally Posted by 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?

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 to which a given parcel of air must be cooled, at constant barometric pressure, for water vapor to condense into water.

Originally Posted by Jerry Peck

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.

Originally Posted by 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?

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.

Originally Posted by Vern Heiler

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?

Vern,

Try this: Dew Point Calculator

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

Originally Posted by Jerry Peck

Vern,

Try this: Dew Point Calculator

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.

Originally Posted by Vern Heiler

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.

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!

Originally Posted by Vern Heiler

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

Originally Posted by Jerry Peck

What happens to air when it is heated and cooled?

Originally Posted by Vern Heiler

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.

Originally Posted by Jerry Peck

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?

Originally Posted by Vern Heiler

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.

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.

Dew point

From Wikipedia, the free encyclopedia


Jump to: navigation, search
The dew point is the temperature to which a given parcel of air must be cooled, at constant barometric pressure, for water vapor to condense into water. The condensed water is called dew. The dew point is a 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 or hoarfrost by deposition.
The dew point is associated with relative humidity. A high 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]
At a given barometric pressure, independent of temperature, the dew point indicates the mole fraction of water vapor in the air, and therefore determines the specific humidity of the air. The dew point is an important statistic for general aviation pilots, as it is used to calculate the likelihood of carburetor icing and fog, and estimate the height of the cloud base.

Humidity

Humidity

From Wikipedia, the free encyclopedia


Jump to: navigation, search
Humidity is the amount of water vapour in the air. In daily language the term "humidity" is normally taken to mean relative humidity. Relative humidity is defined as the ratio of the partial pressure of water vapour in a parcel of air to the saturated vapour pressure of water vapour at a prescribed temperature. Humidity may also be expressed as absolute humidity and specific humidity. Relative humidity is an important metric used in forecasting weather. Humidity indicates the likelihood of precipitation, dew, or fog. High humidity makes people feel hotter outside in the summer because it reduces the effectiveness of sweating to cool the body by reducing the evaporation of perspiration from the skin. This effect is calculated in a heat index table.
Contents

[hide]

• <LI class=toclevel-1>1 Types of humidity
  • <LI class=toclevel-2>1.1 Absolute humidity <LI class=toclevel-2>1.2 Mixing ratio or humidity ratio <LI class=toclevel-2>1.3 Relative humidity <LI class=toclevel-2>1.4 Specific humidity <LI class=toclevel-2>1.5 Humidity during rain
  • 1.6 Dew point and frost point
  <LI class=toclevel-1>2 Measuring and regulating humidity <LI class=toclevel-1>3 Humidity and air density <LI class=toclevel-1>4 Effects on human body
  
  • 4.1 Recommendations for comfort
  <LI class=toclevel-1>5 Effects on electronics <LI class=toclevel-1>6 Humidity in construction <LI class=toclevel-1>7 Most humid places on Earth <LI class=toclevel-1>8 See also <LI class=toclevel-1>9 References
• 10 External links

//
[edit] Types of humidity


[edit] 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 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 .
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] (See also Absolute Humidity table)
The absolute humidity changes as air pressure changes. This is very inconvenient for chemical engineering calculations, e.g. for dryers, where 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 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.

[edit] 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 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 of water vapor[1] :
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 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/Kg which is 10 − 3 Kg/Kg.[2]

[edit] Relative humidity

Main article: Relative humidity
Relative humidity is defined as the ratio of the partial pressure of water vapor (in a gaseous 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 of water vapor in the gas mixture; is the 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 and reports, as it is an indicator of the likelihood of precipitation, dew, or fog. In hot summer weather, it also increases the apparent temperature to humans (and other animals) by hindering the evaporation of perspiration from the skin as the relative humidity rises.

[edit] 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] 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 to form, and 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, thus condensing water vapor out of the air. Although that would indeed raise the relative humidity to 100%, the water lost from the air (as dew) would also lower the absolute humidity.

[edit] Dew point and frost point

Associated with relative humidity is dew point (If the dew point is below freezing, it is referred to as the frost point). Dew point is the temperature at which water vapor saturates from an air mass into liquid or solid usually forming rain, snow, frost, or dew. Dew point normally occurs when a mass of air has a relative humidity of 100%. This happens in the atmosphere as a result of cooling through a number of different processes.


[edit] Measuring and regulating humidity


A hygrometer 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. A humidistat is used to regulate the humidity of a building with a de-humidifier. These can be analogous to a thermometer and thermostat for temperature control.
During coating applications Humidity and air temperature are measured in combination with surface temperature to determine the dewpoint. This is done by use of a dewcheck dewpoint gauge.
Humidity is also measured on a global scale using remotely placed satellites. These satellites are able to detect the concentration of water in the troposphere at altitudes between 4 and 12 kilometers. Satellites that can measure water vapor have sensors that are sensitive to infrared radiation. 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.

[edit] Humidity and air density

Main article: Density of air
Humid air is less dense than dry air because a molecule of water (m = 18) is less dense than a molecule of nitrogen(m = 28) and a molecule of 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. 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 discovered this phenomenon and wrote about it in his book Opticks.[3]

[edit] Effects on human body

The human body sheds heat by a combination of evaporation of perspiration, heat convection in the surrounding air, and 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 brought to the body surface cannot shed heat by conduction to the air, and a condition called hyperpyrexia results. With so much blood going to the external surface of the body, relatively less goes to the active muscles, the brain, and other internal organs. Physical strength declines and fatigue occurs sooner than it would otherwise. Alertness and mental capacity also may be affected. This resulting condition is called heat stroke or hyperthermia.

[edit] Recommendations for comfort

Humans control their body temperature mainly by sweating and shivering. The United States Environmental Protection Agency cites the 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. At high humidity sweating is less effective so we feel hotter; thus the desire to remove humidity from air with 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] 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. 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 inside the equipment. Such short circuits may cause substantial permanent damage if the equipment is powered on before the condensation has 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, 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 often monitor relative humidity levels for these reasons.

[edit] Humidity in construction

Traditional building designs typically had weak 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 also sealed off the movement of moisture, and this has resulted in a secondary problem of 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] Most humid places on Earth

See also: Humid subtropical climate and 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 and those in Kerala in India, the cities of Manila in the Philippines and Bangkok in Thailand: these places experience extreme humidity during their rainy seasons combined with warmth giving the feel of a lukewarm Sauna.[4] Darwin, Australia experiences an extremely humid wet season from December to April. Kuala Lumpur and Singapore have very high humidity all year round because of their proximity to water bodies and the 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, are Forks and Olympia, Washington.[5] 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 and 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] Houston lacks the coastal breeze present in Key West, and, as a much larger city, it suffers from the urban heat island effect.
The US city with the lowest annual humidity is Yuma, Arizona, averaging under 50% for a high and 22% as a low. The next-lowest humidity is Tucson, Arizona, average high humidity of 57% and a low of 26%. Lowest in the world is Antarctica.

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.

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.

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

Originally Posted by Vern Heiler

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.

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.

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.

Originally Posted by 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".

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.

Originally Posted by 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.

Thanks Mike, thought I was in the twilight zone .

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 .

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.

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?

Originally Posted by 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?

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

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

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

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.

Originally Posted by 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.

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.

Originally Posted by 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

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?

Originally Posted by Vern Heiler

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.

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.

Originally Posted by 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.

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.

Originally Posted by DavidR

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.

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.

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.

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

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?

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.