new to RE

[Instructor]

Hello
I am new to this site and look.forward to reading a lot of good post.
I wanted to post a question about World Skills because I have a student from the USA competinv in Germany next July at the 2012
worldskills.

This will be the first time for my State (OHIO) to have a world competitor in Refrigeration. I have no idea what to expect.

I belive in Germany all measurements are done in metric so this will be a change and a challenge for sure as we use very little metrics in US.

if anyone has anything to offer good or bad i would appriciate it.

Thank You

[al]

That will be some experience!! Si units would be a must, an ability to stay calm under pressure goes without saying!! Good luck to him.

al

[stufus]

Al is speaking from experience as he was "apprentice of the year" in Ireland in 1966.

But seriously Welcome on board and as Al stated SI is a must ,Hope he does well all the same .

Cheers
Stu

[Instructor]

Thanks guys
He does perty good took 1st in ohio as a junior in high school then took 1st in Ohio as a senior and took 2nd in the US. He is a special kid been in the field for a year and already has 6 of his NATE certifications. But even with all that the si measurements are going to confuse him.. Can you tell me what units you use to measure different things.

like in the US our manifold gauges measure in psi and F temp
we use microns for vac
our tourches are in psi
all measurements are in inches or feet
copper tubing is in inches such as 3/8"

what manufactures do you use for manifold sets ? I am trying to locate a set that will measure in Si units. not easy to find in the states

thanks for the help
Dave

[Magoo]

Hi Instructor,
greetings from New Zealand and welcome to the forum, congrats for getting to the "worlds ", surely they should cater for imperial as well as metric. Hopefully anyway.

[Instructor]

I was told everything is done in metrics and no digital gauges allowed which would convert over for him. I just found out they want him to compete in skillsAmerica which is held in Brazil. i have no idea if they use metrics. if anyone is from Brazil please let me know. Has his former instructor I really want to travel to these compititions with him.
Skills offers our young generation such a great experience and helps them build the confidence they need to be succesful in this indistry. I would incourage all of you to get involved in your country and donate the time to judge some of these contest. I think you all would be impressed.

Never thought I would be a Teacher but I must say i find great joy in helping our young learn our trade that all of us enjoy so much.

[Magoo]

Hello again Instructor.
I admire your enthusiasum and commitment to training young blokes, good on you.
Yellow Jacket do metric gauges if that helps, a metric /imperial convert calculator will also help, and pressure converstion sheets for refrigerants usually are both imperial and metric. What about hitting some company like M & M for a sponsorship and tag along support thing.
The only thing I know about Ohio is Sandusky home of Stein equipment, and lots of roller coasters.
Good on you and keep up the good work.

[Rob White]

.

I have been involved with world skills and yes SI units is a must.

The candidates will be expected to build, commision and run more than
likely one AC system and one fridge or freezer system. All work will be done
from drawings so it is very, very important to be able to read drawings and
understand them.

He will have time alowed throughout the day where he can talk to his "trainer" (coach)
and whoever that coach is can assisst with understanding the instructions given to him.

If you want you will be able to use the drawings to convert back to imperial, but all
measurements will be done in SI and if he gets it wrong he will be marked down.

All tools execpt a small selection of personal tools will be supplied, but again you
will be given all the details in advance.

You will also be given advance warning of the type of systems he will be expected
to build so you will have time to practice.

For the competion make sure his lines are straight, make sure he does not drill holes
in inapropriate places, make sure he understands electrics and electrical drawings
and more importantly teach him how to manage his time. He will have enough time
to complete the challenges but if he wastes time on somthing small he may not complete
the whole task.

Regards

Rob

.

[Instructor]

Thank.you for your kind words. I am glad you said yellow jacket because I emailed them inquiring about a metric.set of gauges. I am not sure what M&M is but we are hoping some of the companies will donate to the cause.

I realy came on board here at the site to see what I could learn about working with the metric measurments in the field. I contacted sporlan and they were able to.supply me with metric p-t charts.

thanks

[chemi-cool]

Welcome Instructor.

We hope to enjoy your wisdom.

[al]

If he has a smart phone it will have a converter app, the iphone one is pretty good, Bitzer have a great free app for refrigerant pressure/temperature conversion.

al

[Instructor]

In the US we run a 10 degree F subcooling and maybe a 15 degree F superheat.. if I just convert that to C i would have a negative value...

do you guys charge with negative values????
also we evacuate a system to 500 microns what value do you guys use?

[Tayters]

Sounds like you are just converting *F to *C. Remember they are referenced from different points.

Subcooling and superheat would be meausured in Kelvin or Rankine - a measurement of the difference between 2 values and are referenced from absolute zero so to convert you just need the 5/9 bit of the formula to convert between F and C.

For example with 10*F subcooling (or *R for the purist as we are denoting a temperature difference):

Liquid temp 86*F
Saturated condensing temp 104*F
Subcooling 104 - 86 = 18*R

the same figures in metric

Liquid temp 30*C
Saturated condensing temp 40*C
Subcooling 40 - 30 = 10K

To convert *R to K multipy by 0,55555 or 5/9

Incidently R is measured in degress but K has no unit, i.e 5*R or 5K.

Subcooling is normally around 5K, superheat around 6K.

As for vacuum measurement it differs but I've been brought up with Torr - anything below 2 torr should do.

Cheers,
Andy.

[The Viking]

Grades of vacuum .

This is the one area where the old boys are sorted from the new generation...


Back in the good old days 2 Torr was near perfect, we certainly didn't need to pull a refrigeration system any further.
But that was with old fashioned refrigerants operating in symbiosis with mineral oil. Remember, if you had a tin of mineral oil that got water in it then it was perfectly acceptable to siphon the oil out and use it?

Nowadays with refrigerants that requires synthetic oil to keep the mechanical bits lubricated it is a completely new game.
The synthetic oil is hygroscopic (= it sucks in moisture like a sponge) and with any minute amount of moisture in it the new synthetic oil will also become acidic.

Thinking back, do you remember how much more reliable the "old" systems were and how we blame the new refrigerants for leaking out here. there and everywhere? Also how compressors and other components just don't last as well as they did in the old days?

Well, with acidic oil in the systems is it surprising that there are failures?

The good news is that it is a reversible process, if the oil is put in to a deep vacuum the moisture in it will eventually boil off, and when the moisture is removed the oil will become neutral (=non acidic) again.

However, 2 Torr is not nearly at the level where you can expect the moisture to have left the oil. Some manufacturers states 800 microns other 500. The important thing is that an accurate meeter/gauge is used, one that will show minute changes in the vacuum level, say from 800 to 820 microns, this will allow you to confirm that you got rid of all the moisture in the system (Just turn the vacc pump off, take a reading then wait 30 mins and take another reading. They should both be the same)

Now, if you are installing split A/C units, you might disagree with the statement above. But there is a good reason why some A/C manufacturers has different recommendations (A cynical person might say that the acid will take longer to damage the system than the warranty lasts...). When you are installing a split you are only working on dry pipes, there is no oil in them, further more the manufacturers recommend triple vacuum broken with OFN thus ensuring that no moisture is left in the pipework or indoor unit.



BTW,
For all practical applications in our game 1 Torr = 1000 micron.
(In absolute science it is something like 999.99985 micron to 1 Torr)


.

[al]

Great post Viking, can we be absolutely certain that compressors are being charged with their oil in essentially cleanroom environments, i have my doubts, would that be adding to this perception of unreliability?

Instructor as Taytor says, subcool and superheat are measurements in difference, not absolute values in their own right, get your lad a copy of modern air con and refrigeration or Dossat's bible in SI units, this would be a great help to have a manual to pull out to refresh the memory.
al

[al]

So good i posted it twice

[Instructor]

Thanks guys
in the states we don't use K or R so i will have to train myself to work with this. we do
everything in F .
all systems are pulled down to 500 Microns before charging.

I.don't have internet at home sk I am replying from my smart phone.. i love the phone but it can be a pain to type on. so I apoligize for any typing mistakes and short replys.

[MikeHolm]

What is even easier, with my digicool, is to just cycle back and forth between units while taking measurements. It is pretty to get an idea what the values are at different conditions and get an understanding of the relationship between C and F.