Refrigeration 101

[gwynn jones]

SNIP............Adjusting a TXV aka TEV is almost always a mistake, especially when the refrigerated space is above design temp.

Oh I very much agree -I work with a few lads who will fiddle with the TEV every call - makes even more trouble

[Gary]

Oh I very much agree -I work with a few lads who will fiddle with the TEV every call - makes even more trouble

In another thread Magoo has offered a rule for judging TXV superheat. He says the superheat should be 60-70% of the TD. This makes very good sense. I like it... a lot. :

[Aik]

In another thread Magoo has offered a rule for judging TXV superheat. He says the superheat should be 60-70% of the TD. This makes very good sense. I like it... a lot. :

Acording Braydert's " Designing refrigeration installations" error-free performance of evaporator possible only with 0.5...0.7 of the TD.

[desA]

Acording Braydert's " Designing refrigeration installations" error-free performance of evaporator possible only with 0.5...0.7 of the TD.

This will very much depend on the magnitude of the TD itself.

For instance:
TD=10K ; SH = 0.5*10=5K; SH = 0.7*10=7K
TD=20K ; SH = 0.5*20=10K; SH = 0.7*20=14K
TD=30K ; SH = 0.5*30=15K; SH = 0.7*30=21K !!!

That's asking for a fair-sized SH. In all likelihood, you'd have a tremendously high Tc,discharge temperature.

The Magoo rule seems to be applicable in low TD applications & may need to be adjusted for high TD applications.

Like everything in the rhvac game, some level of sound engineering judgement will need to be made in each specific application.

[silva.foxx]

Gary...

may I first thank you for posting this "refresher" and secondly thank you for continuing your input to the Refrigeration world after your "semi-retirement".

I'm no fridgey...but at 33 and experienced it for 8 years, no quals gained, your "basics" brought it all back and has really urged me to follow the trade.

I'm an automation eng by trade, I experienced 8 years as a services eng with ammonia gas in a food factory, working with Frick and Grasso screws in pumped overfeed systems to blast & spiral freezers plus -26c cold-storeage. Looking back I loved it! It was like a black art: food at 60+ degrees going into a box and coming out frozen!!! A magic box that I knew the code of; well I assumed I did. I was working in a role that I wasn't qualified for, had no proper experience of yet getting by... really dangerous looking back. Stupid or getting by? Stupid I'd say, but someone was assessing my skills and passing me capable!

[hbguy]

Oh I very much agree -I work with a few lads who will fiddle with the TEV every call - makes even more trouble

I remember working for a parts house where about 40-50% of the tev's we sold went to ONE tech.