Short #11 - Superheat, The True Meaning

HVAC School - For Techs, By Techs

Bryan Orr

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

4.8 • 985 Ratings

🗓️ 25 June 2018

⏱️ 10 minutes

🔗️ Recording | iTunes | RSS

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Summary

In this podcast, we discuss the real significance of superheat and why it is much more than "a way to set the refrigerant charge on a fixed metering device."

Superheat is the temperature of a vapor above saturation. Many people use it to set the charge on a piston or fixed orifice, but that's not its only purpose. Superheat is a much more important reading than that, and you can take that measurement at a few different places. For example, most of us measure it outside. However, to determine how the system is feeding the evaporator coil, we would take superheat at the evaporator outlet (6-14 degrees is normal for a TXV). However, superheat matters regardless of the metering device type.

Zero superheat indicates that the refrigerant is still at saturation; it is in a mixed state, not entirely vapor. So, we know that we are "overfeeding" the evaporator coil. The boiling process does not finish in the evaporator; it continues into the suction line. Overfeeding is a problem because our evaporator might not boil off all the refrigerant, and we could send liquid to the compressor. The system may be overcharged, or the evaporator load may be too low.

Excessive superheat indicates that the refrigerant is boiling off too quickly in the evaporator coil. In those cases, we are starving or underfeeding the evaporator coil. The boiling process ends too early in the evaporator coil. The system may be undercharged or have too much load on the evaporator coil.

When our superheat is within the proper range, we are feeding the evaporator coil correctly. The majority of that evaporator coil is being fed with boiling refrigerant.

Learn more about Refrigeration Technologies at refrigtech.com.

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Transcript

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0:00.0	Hello there. This is the HVAC school podcast and today we're going to talk about
0:07.4	superheat, the often misunderstood story about superheat, not the silly
0:11.5	basics that we hear over and over again.
0:14.0	But the thing that I'm surprised that so many new technicians don't get at times,
0:18.0	I shouldn't be surprised.
0:19.0	I mean, we're all new at different points, but it's a very important thing that you need to get.
0:23.4	And so this is the podcast you want to send to all the newbies in your life,
0:26.5	because you may be shocked to find out that they really don't understand this.
0:29.6	But before we get into that, let's talk about our sponsors.
0:31.8	Our sponsors today are carrier, Mitsubishi
0:35.5	Comfort, the UEEI Hub Smart Kit, WRS scales from UEOI, refrigeration technologies at refriggedec.com, Air Oasis.com, makers of the
0:46.5	bipolar and the nano. Those are our sponsors. Those are people who make it possible.
0:50.1	If you're interested in any of their products, then by golly give them a try.
0:54.0	But I want to talk quickly about Superheat.
0:56.0	Most technicians, if you ask them, what is Superheat, they will tell you.
1:00.0	It's a reading that you take on a piston or fixed or fist system to set the charge.
1:04.4	You may not believe that, but go ahead and ask four or five new texts and see what they say.
1:10.2	And I think that's the answer that you'll get.
1:12.3	Or you might get a more detailed answer.
1:15.0	They might say, well, it's the temperature above saturation on the suction line.
1:19.0	If they're real fancy or they may say it's the difference in temperature between the suction line outside and the
1:25.8	saturated temperature inside the evaporator coil if they want to be real fancy but generally
	...

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