Best explanation on the net! You need a digial whiteboard software for your videos. I think many guys will just see your thumbnail or start watching but will stop shortly after since you are not suing a digital whiteboard that you can overlay on the video.
Hi Mukesh, Thanks for the compliment. As for superheat, it enters the evaporator as a saturated mixture of liquid and vapor. The refregerant can exit the evaporator as a vapor (superheated above saturation) Or it can leave as a saturated mixture of liquid and vapor. (0⁰ superheateed vapor) For us to have a negative superheat, it would be a Subcooled liquid. That means it would be below saturated. That would mean the refregerant would have to be cooled below it's saturation. Meaning the air would have to be lower than the saturated temperature. This is just not going to happen. What a negative superheat means is a measurement issue, inaccurate thermometer, thermometer placement, inaccurate pressures air improper temperature pressure conversion. I'm short negative superheat means something with the tech or the instruments.
Fantastic explanation Ty! Newby question: In your experience, is there any possibility for measuring temp of evaporator outlet instead of measuring suction pressure?
That is a great question! Its beat to get both but it's not always necessary or practical. When I'm setting TXV or diagnosing I look at the evap outlet superheat. This is a lot easier now with digital instruments. I like to have my students do both so they can see the gain in superheat to the outside especially on long lone sets. Generally tecks use superheat at outsides and just allow for more superheat for longer line sets. In either of case I still need my suction pressure to convert it to saturation temperature. There is a method of getting suction saturated without pressure. You would need to record the temperature (with the doors on) where a distribution tube attaches to the evaporator coil. That temperature will be the same as saturation. Then take the temperature of the suction line and you can get superheat.
So just yo make sure, when youre gauged up to the suction line, youre technically not reading the true saturation temp at the center of the coil, rather you are getting an average pressure reading which would include the portion of the coil that is superheating the vapor? Wouldnt it be more accurate to take a pressure reading from a center point of the evap coil and compare that to the line temp at the suction line?
We want to know how much superheat is at the end of the evaporator. Even considering the overall small pressure drop across the evaporator it still in saturation/boiling state. The TXV also gets the suction pressure in most cases after the evaporator coil. The suction pressure is almost the same on the whole suction side. Checking suction pressure in the middle of the coil would be
Hello sir, when the refrigerant gets superheated won't the pressure also get increased? So then the measured pressure when converted to temp, will get equal to the suction temp. And superheat will be 0.
Ask a question. In evaporator, refrigerant absorb heat, and change the mode from liquid to vapor without temp change. If sensible heat let vapor increase the temp, does the vapor pressure change? If the pressure change, is it accurate to use the suction line pressure to find out the saturation temp? thanks
The saturation is our base line. The sensible heat added to vapor above saturation is superheat. The heat your accounting for is already taken into consideration with the compressor metering device and external temperature. All of those work together to get the saturation point. For example oxygen boiles at -297 at 0 psig. That's it's saturation temperature. In my room it's actually 80F. The oxygen is superheated 377 degrees above it's saturation point. As the air temperature increases my saturation temperature stays the same because of the conditions.
0:21 - Ty, how can this pressure be converted to a saturated pressure when the point of your pressure reading is vapor only - no liquid (at least that’s what we want)?! Our typical desired superheat is close to ten degrees, so isn’t that a large error since the temperature conversion needs to be extremely close to the PT relationship for that refrigerant?
There are several videos before this one that focuses on that in detail. But the short answer is, it's not saturated where you take the reading, it's saturated in the coil. The pressure is the same in the coil and I'm the line. When you convert the pressure to a saturated temperature that temperature will be right after the metering device. You can put a thermometer there and they will be the same. After all the refrigerant boils to a vapor then the temperature will superheat Above saturation. The temperature at the service port will be superheated above the saturation point in the coil
Best explanation on the net! You need a digial whiteboard software for your videos. I think many guys will just see your thumbnail or start watching but will stop shortly after since you are not suing a digital whiteboard that you can overlay on the video.
your explaination is so geart.
Thank you
Awesome description. Great passion. Keep preaching we will eventually get it.
Apart from converting almost everything to metric units, everything is great!! Thank you.
I love your method of teaching. Each day you make it clear to me.
Thank you
This is a great explanation. All your videos are packed with good information and really simple to follow along with. Excellent teacher.
Great videos.
Gettin down with the physics.
Great teacher, thank you.
Love to hear lecture from you sir
Thanks from Bangladesh.
Great explanation sir thanks
Amazing explanation ❤
Hello Branaman love your videos . So if it’s a negative number would it not be the difference between .
Hi Mukesh,
Thanks for the compliment.
As for superheat, it enters the evaporator as a saturated mixture of liquid and vapor.
The refregerant can exit the evaporator as a vapor (superheated above saturation)
Or it can leave as a saturated mixture of liquid and vapor. (0⁰ superheateed vapor)
For us to have a negative superheat, it would be a Subcooled liquid. That means it would be below saturated. That would mean the refregerant would have to be cooled below it's saturation. Meaning the air would have to be lower than the saturated temperature. This is just not going to happen.
What a negative superheat means is a measurement issue, inaccurate thermometer, thermometer placement, inaccurate pressures air improper temperature pressure conversion.
I'm short negative superheat means something with the tech or the instruments.
Is superheated tolerance value of 5 degree applicable to automobile hvac too cos I deal vehicle hvac
Fantastic explanation Ty!
Newby question: In your experience, is there any possibility for measuring temp of evaporator outlet instead of measuring suction pressure?
That is a great question!
Its beat to get both but it's not always necessary or practical.
When I'm setting TXV or diagnosing I look at the evap outlet superheat. This is a lot easier now with digital instruments. I like to have my students do both so they can see the gain in superheat to the outside especially on long lone sets.
Generally tecks use superheat at outsides and just allow for more superheat for longer line sets.
In either of case I still need my suction pressure to convert it to saturation temperature.
There is a method of getting suction saturated without pressure.
You would need to record the temperature (with the doors on) where a distribution tube attaches to the evaporator coil. That temperature will be the same as saturation. Then take the temperature of the suction line and you can get superheat.
So just yo make sure, when youre gauged up to the suction line, youre technically not reading the true saturation temp at the center of the coil, rather you are getting an average pressure reading which would include the portion of the coil that is superheating the vapor? Wouldnt it be more accurate to take a pressure reading from a center point of the evap coil and compare that to the line temp at the suction line?
We want to know how much superheat is at the end of the evaporator. Even considering the overall small pressure drop across the evaporator it still in saturation/boiling state. The TXV also gets the suction pressure in most cases after the evaporator coil.
The suction pressure is almost the same on the whole suction side. Checking suction pressure in the middle of the coil would be
Hello sir, when the refrigerant gets superheated won't the pressure also get increased? So then the measured pressure when converted to temp, will get equal to the suction temp. And superheat will be 0.
So how do you make liquid o2, helium, nitrogen, do you increase thier pressures to thier respective saturation points?
Flow oxygen in a heat exchanger through liquid nitrogen, or cascade cryogenic refrigeration system.
Ask a question. In evaporator, refrigerant absorb heat, and change the mode from liquid to vapor without temp change. If sensible heat let vapor increase the temp, does the vapor pressure change? If the pressure change, is it accurate to use the suction line pressure to find out the saturation temp? thanks
The saturation is our base line. The sensible heat added to vapor above saturation is superheat.
The heat your accounting for is already taken into consideration with the compressor metering device and external temperature. All of those work together to get the saturation point.
For example oxygen boiles at -297 at 0 psig. That's it's saturation temperature.
In my room it's actually 80F. The oxygen is superheated 377 degrees above it's saturation point.
As the air temperature increases my saturation temperature stays the same because of the conditions.
@@love2hvac Thanks for your clarification.
Start the Learn HVAC playlist in sequential order here
ua-cam.com/play/PLc7QlzR-srBgknwzlXjoESxNbzHQJ-TIq.html
Already on my telegram channel 😉
0:21 - Ty, how can this pressure be converted to a saturated pressure when the point of your pressure reading is vapor only - no liquid (at least that’s what we want)?! Our typical desired superheat is close to ten degrees, so isn’t that a large error since the temperature conversion needs to be extremely close to the PT relationship for that refrigerant?
There are several videos before this one that focuses on that in detail.
But the short answer is, it's not saturated where you take the reading, it's saturated in the coil.
The pressure is the same in the coil and I'm the line.
When you convert the pressure to a saturated temperature that temperature will be right after the metering device. You can put a thermometer there and they will be the same. After all the refrigerant boils to a vapor then the temperature will superheat Above saturation. The temperature at the service port will be superheated above the saturation point in the coil
I'll swap helium for 290 🤔👀😂🥃🥃🍺🍺🍺🍇🏌
Stay safe.
Retired(werk'n) keyboard super tech.
Wear your safety glasses.
R290 is my favorite