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orland25
04-05-2005, 07:58 PM
Hi friend ;Which air is more heavy, return or supply air?

heatpumpjesus
04-05-2005, 08:28 PM
the one that weighs the most

HVAC/Stud
04-05-2005, 08:31 PM
well supply air has more letters. So i'd say supply air weighs more.

PS Is this on the NATE test?

STUD

brettln
04-09-2005, 10:05 AM
air is air

rubobornot
04-09-2005, 12:15 PM
It depends on the enthalphy, and the grains of moisture per pound of dry air. Dry air is lighter than wet air. If you have 70 db and an 70 wb at 110 grains and you cool the air down to 60 db and 60 wb at 80 grains you have removed 30 grains of moisture per pound od dry air.

amickracing
04-09-2005, 12:29 PM
heating or cooling?

Carrene #2
04-10-2005, 12:52 PM
a pound of air or a pound of feathers?

roc service
04-12-2005, 06:17 AM
When I got my first car back in 1970. I brought it to a service station and I asked the guy there what was the right inflation pressure for my tires. He asked me if I had summer air or winter air in my tires and I told him I think it's winter air. They all had a great laugh at my expense because it really doesn't matter. There are no dumb questions. Just dumb responses. Always ask questions that is how we learn.

brettln
04-12-2005, 07:22 AM
Originally posted by rubobornot
It depends on the enthalphy, and the grains of moisture per pound of dry air. Dry air is lighter than wet air. If you have 70 db and an 70 wb at 110 grains and you cool the air down to 60 db and 60 wb at 80 grains you have removed 30 grains of moisture per pound od dry air.

It was not specified that it was dry, nor wet air. Therefore air is air. Like another gentleman stated, what is heavier? A LB. of Return Air , or a LB. of Supply Air.
Hmmm.
The moisture would contain its own weight and values, and the air its own weight and values.

Why is it no one here can just answer a question based on the information given. It is always more info, I dont have this or that, or some just get rude and say,"you must be a home owner".
Being a Field technician means being an investigator. You must be able to answer those questions with the given information, till more evidence comes about.

Its not that I was giving a smart ass answer in my first answer, " Air is Air", I was just answering the question at hand. Maybe if the question was asked differently, I would of answered differently!

john dalton
04-13-2005, 11:08 AM
Dear Brettln,

First of all, here’s a straight forward answer to the original question posted by Orland25.

You have not given us enough information to accurately answer your question. In order to give you an accurate answer we need to know the temperature and humidity of both the supply and the return air.

“Why is it no one here can just answer a question based on the information given. It is always more info, I dont have this or that……”

Respectfully Submitted,
John J. Dalton

john dalton
04-13-2005, 11:33 AM
Dear Brettln,

“air is air”

First of all, sorry, but the above statement is completely incorrect and inaccurate. Air IS NOT air. I can see by the information you’ve posted in your bio that you are relatively new to the HVAC field. If you get someone to show you a psychometric chart and have them explain it to you, you will find that the temperature and moisture content of the air defines how heavy the air weights. The following site will give you a sample psychometric chart to check out on your own, but you will still need to invest some time in self study or better yet, have someone familiar with it to completely explain it to you since most service technicians find it extremely difficult to read and understand:

http://www.rfcafe.com/references/general/psychometric_chart.htm

Second of all, the reason that most of us here ask for additional information is because like the above answer, the original poster has neglected to provide us with the information or data required to accurately answer the question mainly because the original poster isn’t knowledgeable enough to provide it.

Cut the “old men or ladies” in this forum some slack kid, you might just learn something new……………….

Most Respectfully Submitted,
John J. Dalton (one of the old men…..)

PS: By continuing to read and post in this forum, you are gaining the valuable knowledge and experience of countless years in the HVAC field, and in the engineer’s office. Good luck in your chosen profession young man

[Edited by john dalton on 04-13-2005 at 11:36 AM]

ozone drone
04-13-2005, 11:34 AM
Originally posted by rubobornot
It depends on the enthalphy, and the grains of moisture per pound of dry air. Dry air is lighter than wet air. If you have 70 db and an 70 wb at 110 grains and you cool the air down to 60 db and 60 wb at 80 grains you have removed 30 grains of moisture per pound od dry air.

Wet air is lighter than dry air...water vapor is lighter than dry air ...that's why low pressure fronts in the weather have storms and high pressure areas are sunny.

Pilots need more runway to take off on humid days than dry days....

So if you have condensate running down the drain...your discharge air would be heavier than return.

[Edited by ozone drone on 04-13-2005 at 11:43 AM]

john dalton
04-13-2005, 11:55 AM
Dear Brettln,

Lastly, be careful and think it though, all questions are not as easy to answer as they may first appear to be, for example:

Which is heavier, a pound of gold or a pound of feathers?

Careful, the answer will probably surprise you, and defiantly applies to this particular example.

Respectfully Submitted,
John J. Dalton

Carnak
04-13-2005, 12:04 PM
Originally posted by brettln

Originally posted by rubobornot
It depends on the enthalphy, and the grains of moisture per pound of dry air. Dry air is lighter than wet air. If you have 70 db and an 70 wb at 110 grains and you cool the air down to 60 db and 60 wb at 80 grains you have removed 30 grains of moisture per pound od dry air.

It was not specified that it was dry, nor wet air. Therefore air is air. Like another gentleman stated, what is heavier? A LB. of Return Air , or a LB. of Supply Air.
Hmmm.
The moisture would contain its own weight and values, and the air its own weight and values.

Why is it no one here can just answer a question based on the information given. It is always more info, I dont have this or that, or some just get rude and say,"you must be a home owner".
Being a Field technician means being an investigator. You must be able to answer those questions with the given information, till more evidence comes about.

Its not that I was giving a smart ass answer in my first answer, " Air is Air", I was just answering the question at hand. Maybe if the question was asked differently, I would of answered differently!

There are many variables in the questions asked here. Without asking for more specific information in order to provide a correct answer, you could just answer. "It depends"

john dalton
04-13-2005, 12:35 PM
Dear Ozone drone,

“Wet air is lighter than dry air...water vapor is lighter than dry air ...that's why low pressure fronts in the weather have storms and high pressure areas are sunny.

Pilots need more runway to take off on humid days than dry days.... “

Your statement that wet air is lighter than dry air is inaccurate. Your additional statement that water vapor is lighter than air is also incorrect. Check any psychometric chart and you will plainly see that wet air is “heavier” than dry air….period. As far as your analogies regarding the weather and a pilot’s runway requirement, they are not applicable in this case based upon the information and data found on a simple psychometric chart.

”So if you have condensate running down the drain...your discharge air would be heavier than return..”

Although I would agree with your above statement most of the time, there are circumstances when it is not accurate, such as if a reheat coil was operating in a dehumidification mode in the system.

Respectfully Submitted,
John J. Dalton

ozone drone
04-13-2005, 01:40 PM
Mr Dalton,

I maintain my statements are correct and upon checking a psychometric chart, see that the chart supports my statements, rather than refutes them.

Using the chart found in Modern Refrigeration and Air Conditioning by Althouse, Turnquist and Bracciano 1979 edition.

The chart on page 650 shows that air at 55 degrees fahrenheit at 16% relative humidity has a density of 10.75 cubic feet/pound of air.

Maintaining 55 degrees fahrenheit, as the relative humidity rises to 100 % it will take 13.4 cubic feet of air to weigh the same 1 pound. If the humid air was more dense than dry air the opposite would hold true.

It's a common misconception that humid air is heavier.A barometer is used to measure the weight of the atmosphere.
Check any weather map on the web...anywhere it's raining the barometic pressure will be lower than anywhere it is dry and sunny.

john dalton
04-13-2005, 04:31 PM
Dear Ozone drone,

After reviewing your post I must confess the following:

I stand corrected sir. Wet air is “lighter: than dry air……I obviously was reading the psychometric chart incorrectly, I can see that now. Thank you for your gentle correction regarding this matter.

Respectfully Submitted,
John J. Dalton

PS: To answer you question of why you are here…..its to educate people like…..me….thank you again.

ozone drone
04-13-2005, 04:50 PM
You're welcome, and I have to admit that I've received much more helpful information on this site than I've been able give back.

hvacker
04-13-2005, 07:38 PM
Standard conditions for US air @ sea level are 59degF, an air density of 0.075 lb/sq ft at a barometric pressure of 29.921 in.HG or 14.7 lb/ sq in. Change any of that and the weight changes. Also altitude has a large affect.
ASHRAE

hvacker
04-13-2005, 07:57 PM
I guess I should finnish my thought. What is being done to the supply air? If nothing then all that needs to be concidered is the blower motor heat, converting all mechanical air movement to heat, and all frictional additions that resist air flow and the air would weigh less. The increase in pressure from the fan the air would be more dense and would gain weight per cubic foot. If the supply air was heated, cooled, humidified that's gets more involved.

tinner73
04-13-2005, 09:40 PM
who let Mr.Dalton out of the serverroom?;)

who forgot to lock the door?

respectfully submitted,
Tinner73

john dalton
04-16-2005, 10:43 AM
Dear Brettln,

You’ve neglected to answer my question to you outlined in the last post on page 1 of this thread so I guess I’ll answer it for you. The original question was as follows:

“Which is heavier, a pound of gold or a pound of feathers?”

The correct answer was “feathers” are heavier. The fact of the matter is that a pound of feathers are approximately 33% heavier than a pound of gold.

Respectfully Submitted,
John J. Dalton

PS: Tinner73, no one unlocked the server room door, I tried to pick the lock with my needle nose pliers but that didn’t work so I tried a fresh new approach to the problem. By the way, those text books are right……..refrigeration oil and oxygen doesn’t mix well……and I wouldn’t be surprise to find a return call when I get back to my office.

[Edited by john dalton on 04-16-2005 at 10:50 AM]