Another Technique for Adjusting TXV?

[shellkamp]

this measurement method is used in some chillers, however, there is something to be noted...the temperature at the outlet of the TXV is not necessarily the same as the temperature after the distributor tubes. maybe it is in one case and not in another case. you would need to be very careful in using that method.

Exactly.

There's typically a pretty substantial pressure drop from the outlet of the TXV to the outlet of each distributor tube. Hence the requirement of an externally equalized TXV.

You're safe to use outlet of the TXV if it's a single-circuit evap coil (with an internally equalized TXV)

Sent from my Moto Z (2) using Tapatalk

[crazzycajun]

Would be curious what icemeister and a couple of other market guys say about this ie real world experience?

[icemeister]

First, regarding the video that was posted by the OP, I remember seeing that one a couple of years ago. My first reaction was that although he had the right idea for doing a two-temperature TXV adjustment, he didn't understand what jayguy mentioned about the temperature caused by the distributor tubes.

Did anybody notice his initial numbers for his "Delta T"? The reading after the TXV was 34°F and at the coil outlet it was 30°F. Duh?

If you review Sporlan's TXV selection procedure, you'll find that the typical design pressure drop from the outlet of the TXV to the coil inlet is about 35 psi.

So with R404A for example, with a 60 psig auction pressure the saturated evap temp would be about 23°F. add 35 psi to the evap pressure... 95 psig would give you about 45°F leaving the TXV...before the distributor.

Now if the evaporator doesn't have a distributor, the way he did it in the video would be correct, but then there's no way he would have gotten the same number where the inlet is higher than the outlet...ie, negative superheat?

Personally I don't like the two-temperature method. The outlet temperature is OK if it's measured at the TXV bulb location, but the inlet is a rather iffy approach to determining your true saturated evaporator temperature.

Then, if you have a high-glide refrigerant, does the two-temperature method still work?

[icemeister]

I've never seen or heard of those special flares with holes drilled in them. I thought the only thing "special" about refrigeration flares was that they had to be short-bodied for the ice-buildup possibly.

I'll have to look those TXV flares up.

Sent from my Moto Z (2) using Tapatalk

They're called frost-proof flare nuts: https://www.centurytool.net/Frost_Pr...s_s/314551.htm

I've seen at least a dozen cracked flare nuts and a lot more loose ones, all on TXV outlets due to ice.

I used to see them quite often on system that were installed prior to the 1980's, when they were considered standard equipment for a TXV outlet.

I've seen some long forged flare nuts (that weren't frost proof) cause the tubing to collapse from the ice freeze/thaw.

[icy78]

They're called frost-proof flare nuts: https://www.centurytool.net/Frost_Pr...s_s/314551.htm

I've seen at least a dozen cracked flare nuts and a lot more loose ones, all on TXV outlets due to ice.

I used to see them quite often on system that were installed prior to the 1980's, when they were considered standard equipment for a TXV outlet.

I've seen some long forged flare nuts (that weren't frost proof) cause the tubing to collapse from the ice freeze/thaw.

I had 7) R22, 50 horsepower Williams opendrive semi. They were on 7 chillers for a machine shop making firehose fittings. The fittings were all flare and the frost proof ones never leaked. The fittings that were not frost proof, would leak after a couple years. There was a lot of acid in the air too. It got to where I wouldn't go there unless they had the exhaust fans all fixed and running.
The hosers,...they asked the shop for proof of my refrigerant license and then used that to buy R22 from a supplier somewhere.

The tank operators all had that sort of fried look about them, they were either zombies or giggled alot. Wierd place.

We got , ahem , "too busy" to respond in a timely fashion.

Sent from my SM-G950U using Tapatalk

[Connor sawyer]

This is similiar to how vrf fan coils get electronically metered. The sensors are after the expansion valve bulb and other side of coil.

[hvacker]

I had 7) R22, 50 horsepower Williams opendrive semi. They were on 7 chillers for a machine shop making firehose fittings. The fittings were all flare and the frost proof ones never leaked. The fittings that were not frost proof, would leak after a couple years. There was a lot of acid in the air too. It got to where I wouldn't go there unless they had the exhaust fans all fixed and running.
The hosers,...they asked the shop for proof of my refrigerant license and then used that to buy R22 from a supplier somewhere.

The tank operators all had that sort of fried look about them, they were either zombies or giggled alot. Wierd place.

We got , ahem , "too busy" to respond in a timely fashion.

Sent from my SM-G950U using Tapatalk

Not sure how it's done today. When I was certified, my Social Sec number was my ID. If yours was also, I would not want it on any papers sent to another company or person.
Maybe just the last four.
Some of that stuff in shops can make me giggle. I used to wonder about trichloretheline in cleaning systems. Then there's the advice in a furnace book about cleaning the pilot orifice with carbon tetrichloride.
It's amazing what a company will expose their people to. Without a thought.

[WFL-TX]

"Evaporator TD". You can found it on most manufactured coils.

[checkmaster]

Yes I hear this method when I did racks everyone comments on his Y tube that's one reason he doesn't make anymore videos everything is negative and his ages was up there. Maybe you could learn something from a old time refrigeration guy. I always love to hear his story about the customer he use to service with his dad because he lived in same state that I live in before he moved. Some of the accounts he mentioned are still there but either different name or they move but the building or the streets are still there. Not everything is by the book when you learn refrigeration.

[itsiceman]

There was a older thermometer in the shop for measuring SH
Had a two temp and three temp method.
That way can be great when it works and crap when it don't. Simultaneous pressure and temperature measurements at the same spot works every time.

[ehsx]

Few notes on txv’s & dx evaps.

Confirm valve capacity using vendor corrections for as applied.

Externally equalized, balanced port…. type valves…

Insure turndown if set point changes, circuit stages or unloads.

Flash gas before entering the evap may or may not have ref at suction saturated depending on distributor.

Some evaps have liquid carry over as high as 8-10*f ssh depending on design & distribution & load. Temp probes @ 10, 2, & 8 positions on evap outlet pipe will indicate catty over if readings don’t match. Best I’ve tested were even to ~4*f ssh at full load, usually worse at light loads.

By measuring at the compressor the temps may average better and the compressor is what should be protected. Differences in measurements at the evap & condenser should be minimal, differences can be due to pipe sizing, pipe routing, tie ins, insulation.

Safe setting depends on compressor type, valve response, load & system dynamics .