Demand Cooling in Low Temp R22 w/ Jeremy Smith

HVAC School - For Techs, By Techs

Bryan Orr

Careers, Business, Self-improvement, Education

4.9 • 1K Ratings

🗓️ 21 May 2020

⏱️ 31 minutes

🔗️ Recording | iTunes | RSS

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Summary

In this podcast, Jeremy Smith joins us to discuss demand cooling in low-temperature applications that use R-22 refrigerant.

R-22 is NOT an ideal low-temperature refrigerant because it leads to high compression ratios. The discharge gas also gets really hot and can burn up the oil in the system. (The head of the compressor is even hotter than the discharge line, so if the temperature is high enough to cause oil breakdown in the discharge line, it's almost surely worse inside the compressor). However, R-22 is starting to go away in rack refrigeration.

Demand cooling injects saturated refrigerant into the compressor to help mitigate the high discharge temperature and oil damage. It may seem like demand cooling intentionally slugs the compressor. However, the saturated refrigerant should boil off almost immediately, and it should not make it to the head of the compressor under typical conditions.

On the diagnostic and repair side, demand cooling is usually pretty straightforward; if a sensor fails, then it's likely a thermistor issue. In the case of thermistor problems, you can diagnose those issues with the information given in the application engineering bulletin. Loose connections and valve restrictions can happen, but those are also pretty easy to diagnose and repair. Perhaps the most complicated issue occurs when rack systems have low liquid levels. The injector valves can't get a solid column of liquid, but many other components will work fine.

Demand cooling solutions are usually brand-specific; each manufacturer has a slightly different setup. To learn more about the Copeland Discus compressors with demand cooling, check out the AE4-1287 bulletin.

Jeremy and Bryan also discuss:

Outdoor air and head pressure
DTC valves
Desuperheaters and hot gas bypass
Tube-in-tube heat exchangers as "subcoolers"
Seasonal changes in discharge temperature
Why should we pay more attention to discharge line temperature?

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Transcript

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0:00.0	This episode of the HVAC School podcast is made possible by our excellent sponsors.
0:09.1	The first one I want to thank is Refrigeration Technologies at refrig tech.com.
0:12.8	Not only do they have the new revolutionary,
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0:38.7	You can find out more by going to Refrigetech.com or talk to your local supply house about bringing in a full supply of
0:45.0	refrigeration technologies products.
0:47.6	Navac and Navac Global.com. Navac is a long time supporter and sponsor of the
0:51.0	podcast. They make some of the best recovery machines and
0:53.8	vacuum pumps out there as well as the NEF 6 L.I. Flaring tool which is a battery-powered
1:00.2	flaring tool that just spits out perfect flares every time. Any company out there
1:04.2	seriously who's doing a lot of mini splits duckless systems VRF and you've got installers
1:08.8	out there just give them that tool and that way you don't have to worry about them making quality flares every time.
1:15.0	That's the NEFLI from navac. Go to navac global.com or truetech tools.com to find out more.
1:21.0	Use the offer code get schooled at check out for a great discount.
1:24.9	Also want to thank Speed Clean they've been with us for a long time they make the
1:28.3	mini split bib kit as well as the coil jet. The coil jet is an excellent tool for cleaning,
1:35.0	evaporator coils in place, ductless systems, condenser coils,
1:38.4	anything that you want to clean with a nice flow of water without having too much.
	...

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