superheat

[BigJon3475]

"My statement is correct for TEV or cap tubes. If TEV is used then the superheat can be adjusted but with cap tube the super heat depends on the load and refrigerant charge."

Right I agree....for TEV you charge by subcooling not superheat. Although you want all your readings to look for things like restrictions or clogged evaps....ect..ect..

"There is no absolute dry air. When the cooling system cools the air (if coil temp is lower than the air dew point) then you have de-humidification. When this happens, the air relative humidity increases.
ONLY evaporative cooling process depends directly on Wet Bulb (constant wet bulb process). And this is the outside air wet bulb not the indoor."

"Completely wrong . Study Psychrometric my friend. Relative humidity is different than the actual humidity or moisture content."

"Often the concept of air holding water vapor is used in the description of relative humidity. Relative humidity is wholly understood in terms of the physical properties of water alone and therefore is unrelated to this concept. Relative humidity is the ratio of the amount of water vapor in air to the maximum amount of water vapor that could be present if the vapor were at its saturation conditions."

Are you saying because the temp is going down the amount of moisture that the air can hold goes down also? Maybe I'm not following you. If the temp of the air decreases it holds less air...But if you decrease the temp of the air you have also removed more humidity to be able to decrease the temp. It will take longer to cool 80F air with 70% RH than it would take 80F with 50% RH

[lana]

Hi,

Relative Humidity is the ratio of the amount of water vapor in Air to the maximum amount of water vapor that could be present if the vapor were at its saturation conditions

What you explained is called "Percentage Saturation" NOT relative humidity.

Relative Humidity is the ratio of the partial pressure of water vapor in Air to the partial pressure of water vapor at saturation condition (at the same temperature).

You see : relative humidity is the ratio of two pressures.

There are three parameters defined for humidity.
1- Moisture content (kg/kg).
2- Percentage saturation (%).
3- Relative Humidity (%).

Moisture content is the actual humidity in the air. If physically moisture is added to the air this parameter will increase and vis versa.

Percentage Saturation is the ratio of the amount of water vapor in Air to the maximum amount of water vapor that could be present if the air were at its saturation conditions.

If air is cooled sensibly :
1- Moisture content stays constant.
2- Percentage Saturation increases.
3- Relative Humidity increases.

If air is cooled with de-humidification :
1- Moisture content decreases.
2- Percentage Saturation increases.
3- Relative Humidity increases.


Mathematically the value of relative humidity and percentage saturation are very close together. As temperature goes down this difference becomes less and if temperature goes up this difference increases.
@ 45°C RH=50% PS=47.48%
@ -15°C RH=50% PS=49.96%

Hope this helps
Cheers

[BigJon3475]

The amount of water vapor in the air at any given time is usually less than that required to saturate the air. The relative humidity is the percent of saturation humidity, generally calculated in relation to saturated vapor density.

RH=actual vapor density/sat. vapor density

The most common units for vapor density are gm/m3. For example, if the actual vapor density is 10 g/m3 at 20°C compared to the saturation vapor density at that temperature of 17.3 g/m3 , then the relative humidity is

RH=10g/m(cubed)/17.3g/(cubed)x100%=57.8%

Calculation


Careful! There are dangers and possible misconceptions in these common statements about relative humidity.Relative humidity is the amount of moisture in the air compared to what the air can "hold" at that temperature. When the air can't "hold" all the moisture, then it condenses as dew.








Straight out of the physics book.....



Maybe you call it something different over there....

[lana]

The explanation you gave is the definition of "Percentage Saturation" not the relative humidity.

Relative humidity is the ratio of two partial pressures.

Check the ASHRAE or CIBSE of other psychometric books.

I don't call it something different here, you call it incorrectly over there.

Check this http://en.wikipedia.org/wiki/Relative_humidity

Specially " A common misconception " section.

Also check http://www.taftan.com/thermodynamics/PERCESAT.HTM


Thaaaaaaaank yooooooooou

[BigJon3475]

The explanation you gave is the definition of "Percentage Saturation" not the relative humidity.

Relative humidity is the ratio of two partial pressures.

Check the ASHRAE or CIBSE of other psychometric books.

I don't call it something different here, you call it incorrectly over there.

Check this

Specially " A common misconception " section.

Also check


Thaaaaaaaank yooooooooou

That's where I got my information from the first time....

And you told me it was wrong.

"Relative humidity is the ratio of the amount of water vapor in air to the maximum amount of water vapor that could be present if the vapor were at its saturation conditions."

" Thaaaaaaaank yooooooooou"

No need to get arrogant how will that lead to anything being solved here or anyone learning? :;-)

"Relative humidity is the ratio of the amount of water vapor in air to the maximum amount of water vapor that could be present if the vapor were at its saturation conditions."

From wikipedia....

Since I can't post weblinks I am at a disadvantage here... sorry I will prove my point after 15 posts.

Here is a relative humidity calculator:

go to www johnsnhweather .com/rh.html

Add the l at the end of the link.....You can play around with different temps and different RH points...


So are you still saying the amount of moisture in the air inside the apartment does not affect superheat? Since that is what this thread is about...

[BigJon3475]

Why would you not allow someone to post links? That doesn't really lead to a very fair discussion?

[BigJon3475]

Specific humidity or moisture content of air is the ratio of the mass of water to the mass of dry air in a given volume of moist air.

Percentage saturation is defined as the ratio of the percentage saturation of air to the specific humidity of saturated air at the same temperature

Relative humidity is defined as the ratio of the partial pressure of water vapor in a gaseous mixture of air and water 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.

Again we are saying the same thing. You feel your words are right and I'm wrong because why? We are on two different parts of the world? You just choose links from the exact same places I gave you the first time.

[frank]

Hi BigJon

The restriction on posting links for newcomers to the forum is to stop single post advertising and spamming.

With your posting history I can't see it being too long before you are posting links.

If you wish to post a link to make your point in the meantime then just write it out using spaces instead of full stops and if it's a good link I'm sure one of the Mods will make it into a proper url.

[lana]

Hi there,

That's where I got my information from the first time....

And you told me it was wrong.

"Relative humidity is the ratio of the amount of water vapor in air to the maximum amount of water vapor that could be present if the vapor were at its saturation conditions."

Go to the link and read.

Relative humidity is defined as the ratio of the partial pressure of water vapor in a gaseous mixture of air and water 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 relative humidity of the gas mixture being considered; is the partial pressure of water vapor in the gas mixture; and is the saturation vapor pressure of water at the temperature of the gas mixture.

You see it is a ratio of two pressures.
Thanks.

No need to get arrogant how will that lead to anything being solved here or anyone learning? :;-)

This is a bad thing to say and I have nothing to say to you about this.

"Relative humidity is the ratio of the amount of water vapor in air to the maximum amount of water vapor that could be present if the vapor were at its saturation conditions."

From wikipedia....

This is the definition of "Percentage Saturation". The Wikipedia definition is given above.

Here is a relative humidity calculator:

go to www johnsnhweather .com/rh.html

Add the l at the end of the link.....You can play around with different temps and different RH points...

I don't need software, I already have one and also I developed one.

So are you still saying the amount of moisture in the air inside the apartment does not affect superheat? Since that is what this thread is about

As I said before (read my previouse post), moisture in the room adds to the load on the coil, so a lot of energy is used to condense this moisture. Definitely it effects the super heat (because it effects the load).

Good Luck with your study.

Cheers