Short #10 - Air Has Weight and Takes up Space

HVAC School - For Techs, By Techs

Bryan Orr

Training, Careers, Airconditioning, Self-improvement, Hvac, Business, Education, Refrigeration, Heating, Ac, Apprenticeship

4.8 • 985 Ratings

🗓️ 15 June 2018

⏱️ 12 minutes

🔗️ Recording | iTunes | RSS

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Summary

In this episode, we talk about air as a form of matter. We cover air volume, density, weight, and mass and why it matters to you.

So, air has weight and takes up space. When we measure air, we typically measure it by volume (CFM or cubic feet per minute). When we say that air takes up space, we are referring to air volume. A cubic foot of air is equivalent to a 1'x1'x1' box of air. When we measure CFM, we measure how many boxes of air we move per minute. We usually want around 400 CFM per ton, though the exact number varies by system, function, and ambient conditions. Lower CFM per ton is better for moisture (latent heat) removal, while higher CFM per ton is better for sensible heat removal.

Air also has weight. When we are at higher altitudes, the air is thinner and less dense. Therefore, the air has less weight. Standard air weighs about 0.75 pounds per cubic foot (box of air). If you multiply the 400 CFM per ton standard by the standard air weight, you get 30 pounds of air per minute. That pounds-per-minute value is what we call the mass flow rate. The air density affects mass flow rate; temperature and relative humidity can change the density of air. So, the volume is the box, but density (which affects mass) is what's in the box.

Even though our goal is to move pounds of refrigerant (mass), we care about CFM (volume) because fans move air regardless of density. The blower affects the CFM, but the mass flow rate is more important to the coil. We have to adjust our volume flow rate to achieve a proper mass flow rate.

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Transcript

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0:00.0	Hey, this is the, hold on a second, that was a little over and
0:06.2	enthusiastic. You got to rein in the enthusiasm a little bit, even when you're
0:10.0	talking about something as exciting as the fact that air has weight and takes
0:14.8	up space which is a very exciting topic when you think about it. Oh by the way I'm
0:19.5	Brian and this is the HVAC school podcast this is a quick episode and the name of this
0:22.8	quick episode is what I just mentioned. That air has weight and it takes up
0:26.8	space and that has a lot of ramifications for us in the work that we do every
0:30.6	day whether you know it or not. But before we get into that I need to thank
0:33.7	our sponsors and our sponsors are Mitsubishi Electric heating and cooling carrier. The
0:38.7	UEEI Hubs Kit, Probes Kit, which is the Thermoigrometereter kit which is two of those two temperature
0:45.6	and humidity sensing thermal hygrometers that go induct with nice quarter inch
0:50.3	probes as well as the pressure probes and
0:54.2	temperature probes are called the hub four and when you put all six of those
0:57.4	probes together you got yourself the hub six you can find out more by going
1:01.2	to UEI test.com refrigeration technologies at
1:04.4	Refriger tech.com. We've been really enjoying the Viper spray cans.
1:09.5	Actually, have aerosol cans full of Viper Cleaner and I used it just yesterday to clean a
1:14.8	a Vapert coil in place. It has a really nice stream of cleaner that comes out and
1:19.7	does not have any nasty odors. It's neither acidic nor alkaline so it doesn't attack
1:25.4	the coil. It's not going to damage anything. It's a really nice product and
1:29.4	does a good job. You do have to let it sit for a little bit though so you got to let it sit and foam for five or ten minutes to make it work properly and that is Viper
1:36.8	HD cleaner from refrigeration technologies at refriggedec.com and then finally I have to mention my friend's over at Air Oasis, makers of the
	...

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