Blends and Midpoint w/ Jim Bergmann
HVAC School - For Techs, By Techs
Bryan Orr
4.9 • 1K Ratings
🗓️ 27 June 2019
⏱️ 37 minutes
🧾️ Download transcript
Summary
Jim talks about dew point, bubble point, and midpoint in refrigerant blends. He also covers the purpose of each and why MeasureQuick displays midpoint on the gauges.
We've formerly used mostly pure refrigerants. However, as new refrigerant blends come on the scene, we have to deal with glide, which indicates that we have a range of boiling temperatures instead of a fixed boiling point. We have bubble point and dew point, which are when the refrigerant starts to boil and finishes boiling, respectively; you generally use dew point to determine the superheat and bubble point to determine the subcooling. Zeotropic refrigerants have larger glides than near-azeotropic refrigerant blends; azeotropes have no glide at all.
The midpoint is the halfway point between the bubble point and dew point in refrigerant blends. Coil temperature typically corresponds with the midpoint.
To find the midpoint of refrigerant in the condenser coil, add the dew and bubble points and divide the sum by two. The process is a bit trickier on evaporator coils. In the evaporator, you run refrigerant through the metering device and get some flash gas; when the refrigerant undergoes that change, the bubble and dew points change. As a result, the midpoint becomes a bit more weighted towards the dew point (60%).
In MeasureQuick, the temperature-pressure charts go a step above and beyond to give you the superheat, subcooling, and midpoint. The midpoint is the effective temperature of the evaporator coil, which is a critical piece of information in refrigeration systems where food products are at stake. You can also use the midpoint for coil DTD and TD.
Jim and Bryan also discuss:
- R-410A and near-azeotropic refrigerants
- Metering devices as reactive components
- Coil temperature misconceptions and uncertainty
- Pressure differentials and drops in the system
- Maintaining food quality in refrigeration
- MeasureQuick mathematical models and formulas
Learn more about Refrigeration Technologies HERE.
Transcript
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| 0:00.0 | and This episode of the HVAC School Podcast is made possible by our great sponsors and those |
| 0:20.7 | are Speed Clean and Speed Clean.com. Speed Clean is a newer sponsor but they are a company that I really enjoyed |
| 0:26.0 | visiting up in Connecticut. They make great products for cleaning HVAC equipment. |
| 0:31.1 | Specifically, coil jet, coil shot, the bib kit for |
| 0:36.1 | duckless systems known as the mini split bib kit, a lot of really great products. |
| 0:39.7 | If you haven't yet, I would ask that you take a look at their duckless cleaning guide that |
| 0:43.4 | we helped them right you can find it by going to HVACR school.com for slash mini |
| 0:48.8 | split that's there on their site they did a really nice shot putting that together and |
| 0:52.2 | it gives you kind of a soup to nuts look at how to do a really good maintenance on a duckless system. |
| 0:57.0 | Both the cleaning aspects and some of the technical aspects, I think you're going to enjoy it. |
| 1:01.0 | Speed Clean, like I said, makes a lot of really good products for cleaning, |
| 1:04.9 | unitary systems, ductless systems, rooftops, everything you want to clean. |
| 1:09.2 | Speed Clean has some great solutions for that. |
| 1:11.4 | Also, I want to thank refrigeration technologies. |
| 1:13.3 | Refrig detect.com and the Pastorellis have built a really great company. |
| 1:17.5 | I would encourage you to take a look at their leak detection guide that's on their website. |
| 1:22.4 | It's a really good soup to nuts look at leak detection |
| 1:24.8 | Refrigeration Technologies of makers a big blue which is one of the best soap bubbles or leak reactants out on the marketplace for finding everything for big leaks done in micro leaks. |
| 1:34.3 | They also make Nylog which is a great product for helping to seal threads and mating |
| 1:38.6 | surfaces when putting together refrigeration connections such as flares and chattlet fittings and air-equipped |
| 1:45.2 | fittings and all those sorts of things it just really helps to prevent galling and |
| 1:48.0 | just make sure everything goes together nice and smooth it's made of |
... |
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