How do I recover refrigerant from a non-serviceable unit?

[Newgirl]

Hi, I am new to refrigeration and recently undertook my CITB test and City Guilds in Safe Handling. I passed the C&G but on the CITB I need to go back and answer a question on recovering refrigerant from a non serviceable unit again. The question was: "describe the recovery technique for a) a serviceable unit and b) a non-servicable unit". In the last 2 weeks since the test I have looked on the internet, through the CITB safe handling book and through all my notes and I cant find any reference to a different recovery technique if the unit is non-serviceable. In my test paper I simply stated that I would use the same recovery procedure as for a serviceble unit and wrote out the procedure in full. If anyone can advise it would be much appreciated!

[philfridge]

I think by non servicable unit means a unit without access for gauges to be fitted. So you would have to fit line tap valves to suction line at the compressor to enable gauges to be fitted to reclaim the gas . Hope this helps

[Newgirl]

Ahh! I had assumed non-serviceable meant it wasnt working, not that it didnt have service valves... thanks!

[chillin out]

Quick question for you, are you really a girl?
If you are, whey to go.... good on you for entering a male dominated (or I should say 'only) trade and I hope you become one of the best.

Chillin

[Newgirl]

Definitely a girl! I hadnt realised it was so male dominated until I turned up on the trade course.... Will be going into business with my dad so he'll make sure I dont mess up!

[cmac]

Quick question for you, are you really a girl?
If you are, whey to go.... good on you for entering a male dominated (or I should say 'only) trade and I hope you become one of the best.

Chillin

Shes not alone, heard of a girl in the trade in ireland too.

[The Viking]

Good on you New.

Chillin,
You're getting old mate, I know of at least 3 other ladies in our trade. (One of whom were my apprentice for 3 months, or until she got to know me some might say).

[Lowrider]

Good on you New.

Chillin,
You're getting old mate, I know of at least 3 other ladies in our trade. (One of whom were my apprentice for 3 months, or until she got to know me some might say).

Lucky B*stard, I know zero! Give me some! Or at least one for starters!

[chillin out]

I definitely have nothing against females joining the trade, I just find it the strangest thing.

It would be really weird actually talking about fridges to a female that knows what you are talking about and not just nodding her head and sighing....lol
I had never found it the best chat up line saying I am a refrigeration engineer and them asking what the heck that was. They would never understand and usually got bored withing the first 2 minutes. (which is just 1 minute too short for me....lol)

Chillin

[Grizzly]

Hi, I am new to refrigeration and recently undertook my CITB test and City Guilds in Safe Handling. I passed the C&G but on the CITB I need to go back and answer a question on recovering refrigerant from a non serviceable unit again. The question was: "describe the recovery technique for a) a serviceable unit and b) a non-serviceable unit". In the last 2 weeks since the test I have looked on the internet, through the CITB safe handling book and through all my notes and I cant find any reference to a different recovery technique if the unit is non-serviceable. In my test paper I simply stated that I would use the same recovery procedure as for a serviceable unit and wrote out the procedure in full. If anyone can advise it would be much appreciated!

Welcome Newgirl.
If we can get away from all the testosterone thats floating about!!!
Phil the fridge may be correct, but for me.
Serviceable means is it runnable (serviceable) or not.
Because to recover refrigerant from a running unit is much quicker than one that is not runnable.
Meaning if it runs you can pump the system down.
Which in turn means that the bulk of the refrigerant is removable from the system as a liquid ( throttling the recovery units inlet valve to eliminate Liquid carry over.. on some units)
If it if non serviceable then the recovery will take a lot longer as a lot more refrigerant is in Vapour form.
WHICH HAS TO BE CONVERTED TO LIQUID prior to
being pumped into the cylinder.
Sorry it such a long winded answer.
But I have never been known for being concise..
Any how I hope you understand what I am trying to say?

When we quote for recovery of refrigerants, one of the first questions we ask is "Is there power to the unit and if so is it runnable?"
For the reason stated above!
Cheers Grizzly

[paul_h]

Unservicable unit is a hermetically sealed system, no gauge access points, ie, you can't service the refrig system like in a regular maintenance type way. Like domestic refrigerators and window mount box a/cs
Piercing valves are used (like a bullet valve), as a one time access point on the 1/4" stub that the factory used to charge the system, then the system is reclaimed of refrigerant. If the system is going back into operation a schrader valve has to welded on over the pipe peirced by the bullet valve.


meh, that's what I always thought, but maybe they do mean a running system or not. It's hard to say if they want you to know the difference between push/pull recovery and a running system, or the difference between domestic (unservicable) and commercial (serviceable gauge access points).

[Newgirl]

Hmmm..I think I need to re-read my notes! I am erring on Phil the Fridge being right as we did cover line-tap valves during one of the lessons.

[Karl Hofmann]

Hmmm..I think I need to re-read my notes! I am erring on Phil the Fridge being right as we did cover line-tap valves during one of the lessons.

Hmmm... I'm torn between a kippered compressor and a system with no service ports.. But if it was a sealed system , I would expect it to be termed non serviceable...... Splitting hairs I know but it is a poor question as it does not make itself clear.


Chillin... You have to learn to lie about your profession.... The words "I'm a heating engineer" always guarantees a telephone number... Especially just after the first frost of Autumn

[nike123]

Hmmm... I'm torn between a kippered compressor and a system with no service ports.. But if it was a sealed system , I would expect it to be termed non serviceable...... Splitting hairs I know but it is a poor question as it does not make itself clear.

Than all sealed systems (domestic fridges and freezers, window type air conditioners, mobile air conditioners etc....) will be non serviceable, and that is, simply not the case.

[The Viking]

But Nike,
It's a flaw in your reasoning.
You are assuming that the English language makes sense...


(Ask an Englishman to pronounce "Worcester", took me ages to find that one on the map)

[nike123]

But Nike,
It's a flaw in your reasoning.
You are assuming that the English language makes sense...


(Ask an Englishman to pronounce "Worcester", took me ages to find that one on the map)

Most accurate one is German language, but who wants to read (and understand) sausage words like this: Einhandmotorkettensägenführerlehrgangsteilnahmebestätigung

Or something like this:
http://tinyurl.com/kyxdr

[taz24]

Hello Newgirl.

I think if you go back to the citb centre and answer the question, giving an explanation for both posibilities.
Just state how you would pull the refrigerant out of a system that is not working and then state how you would fit line tap valves to a hermeticaly sealed system to recover the refrigerant.

All the best with the assessment and with you employment.

Cheers taz.

[Newgirl]

Thank you everyone. I think I have enough now to cover all the possibilities!

[paul_h]

Than all sealed systems (domestic fridges and freezers, window type air conditioners, mobile air conditioners etc....) will be non serviceable, and that is, simply not the case.

But they are non serviceable, 1) they are made so cheap that they don't bother putting schrader access valve in the factory. So they are sold cheap, and that says a lot for the manufacturers point of view whether they are economical to repair
2)It's costs $x for a refrig tech to come out, fit bullet peircing valve and reclaim, fit schrader, evac and recharge. So much money is wasted on labour before you can economically diagnose the system. Hence the term "unservicable" as it's cheaper to replace than repair. Unservicable from the hermitcally sealed refrig system that is, not fans, capacitors, electrical etc.

Even if it costs $300-600 more to replace than repair, you get a new unit with warranty for the extra money making it worthwhile. So anything all in one box like a fridge, window RAC etc where you don't have to pay a fridgey to install a replacement unit anyway, is termed "unservicable".
Like I mentioned in the thread about splits someone else started. The refrig industry doesn't want to deal with small scale stuff, they wanted to let the whitegoods gys deal with it. So a fridge and Window RAC is deemed "unservicable" to us, throw it out and buy a new one if the system fails.

[nike123]

But they are non serviceable, 1) they are made so cheap that they don't bother putting schrader access valve in the factory. So they are sold cheap, and that says a lot for the manufacturers point of view whether they are economical to repair
2)It's costs $x for a refrig tech to come out, fit bullet peircing valve and reclaim, fit schrader, evac and recharge. So much money is wasted on labour before you can economically diagnose the system. Hence the term "unservicable" as it's cheaper to replace than repair. Unservicable from the hermitcally sealed refrig system that is, not fans, capacitors, electrical etc.

Even if it costs $300-600 more to replace than repair, you get a new unit with warranty for the extra money making it worthwhile. So anything all in one box like a fridge, window RAC etc where you don't have to pay a fridgey to install a replacement unit anyway, is termed "unservicable".
Like I mentioned in the thread about splits someone else started. The refrig industry doesn't want to deal with small scale stuff, they wanted to let the whitegoods gys deal with it. So a fridge and Window RAC is deemed "unservicable" to us, throw it out and buy a new one if the system fails.

I think that you are wrong here, at least in case of domestic refrigerators and fridges.
They are made hermetically sealed because of critical charge they have. If you put gauge every time you want to see pressures, after two times you end up with undercharged fridge.

Second, it is not the case in entire world that is cheaper to change unit than repair it. There are countries in this world where labor is less then 1$ at hour. Here (Croatia) is average for industry 20$ (that is how much is labor charged) per hour.
Someone could pay as much as year salary for one simple fridge that you could pay with one domestic split-system install charge.

[paul_h]

I think that you are wrong here, at least in case of domestic refrigerators and fridges.
They are made hermetically sealed because of critical charge they have. If you put gauge every time you want to see pressures, after two times you end up with undercharged fridge.

Second, it is not the case in entire world that is cheaper to change unit than repair it. There are countries in this world where labor is less then 1$ at hour. Here (Croatia) is average for industry 20$ per hour.
Someone could pay as much as year salary for one simple fridge that you could pay with one domestic split-system install charge.

How often does someone check on a fridge? Only when it matters, not regular maintenance, so your point about gradual loss of refrigerant is wrong. Trust me, I used to do warranty on new fridges, gauge only goes on when a serious problem is suspected. If there was a shrader there, it would save the manufacturer or the customer a lot of money, they run at 0kpa anyway most of the time, no refrigerant would be lost.
The factory doesn't omit a service port so they don't get some crazy refrig mech losing refrig every year on annual checkups, they do it so they can save 7c per unit, they gamble on it never being necessary (hence the term "unservicable")

Unfortunately I've had to cut into systems because I was a warranty repairer, just to re-enforce my guess opinion on the state of the charge.
Older fridges, when manufacturers weren't so tight, had access fitting available. Commercial cabinets with less than 300g refrigerant and have a critcal chrage have access valves available. That doesn't make sence when you argument is only about the size of the charge and them being worried about too much lost refrigerant by wayward fridgies constantly checking the presures for fun.

It's not just the labour, but the reclaim, weld in a schrader, evac and recharge needed everytime you even want to check the charge in a new fridge. Equipment and refrigerant costs money no matter where you are or what your charge p/h.

I did my apprenticeship with a guy from india where they'd grind off hermetics, rewind the motor and reweld together because labour was that cheap compared to buying a new hermetic compressor, so I appreciate your comments on labour costs. I don't mean to offend and seem like I'm shouting you down, but the facts with critical charge systems are evident.
How are domestic systems are sealed only to prevent refrigerant loss if similar low charge commercial systems are open, ie commercial fridges, freezers etc? Domestic fridges and box WRACs are only sealed to be cheap and unservicable.

edit: Sealed systems have a life expectancy of 5 years, and they have a waranty on that so it's the factories problem. If it stuffs up after that, ie hermetic refrig system problem, your expected to throw it out and buy a new one, hence the term "unserviceable". They've made it to not be economically viable to repair due to the shortcuts they've taken in manufacture, (no service ports), due to the cost of the equipment, which makes it more attractive to owners to buy a new unit than pay some fridgey $100+ for diagnosis alone, and a lot more for actual repair due to the extra work they have to do because of the factories cost savings and lack of access ports.

[chillin out]

When they first brought out R600a they fitted a schrader valve to them.
I think this was because they knew the warranty repair guys might have to braze a fitting in and they didn't want a LTV left on which could leak.

Chillin

[philfridge]

Let us know whose right anyway Newgirl . Ive never heard of a girl engineer before fixing fridges. Normally they just stick knives threw the evaporators when defrosting them lol

[nike123]

How often does someone check on a fridge? Only when it matters, not regular maintenance, so your point about gradual loss of refrigerant is wrong. Trust me, I used to do warranty on new fridges, gauge only goes on when a serious problem is suspected.

I must admit that you are pretty much right.
Today, I was woke up and tried to drink some cold mineral water. First what I found is, that water is almost hot. Then I checked function of thermostat of my fridge and found that it is OK.
Then, I found that PTC relay is faulty. I immediately call my service part supplyer and found that he have new PTC relay for my compressor. I asked him how much, and he said 20$. OK I said, new fridge is 500$ and beyond. I changed PTC relay only to find that compressor is seized.
Then, I called some of my colleagues to argue is it plausible to change new refrigerator or fix old one, and every one of them told me that I should fix old one.

OK I said, I am going to change compressor and to fix my fridge. New compressor has cost me 100$!

Then, after replacement of compressor, I found that discharge gas temperature is to high and that I need to thoroughly check system operation conditions if I want to safe new compressor. That will cost me one more morning (or afternoon), in which I could earn at least 100$.
This has been really frustrating to me, and I decided that I am going to find some Frank-s beers in my town.

Yes, I withdrawing all my comments on this matter, and pronouncing, that if it is not thermostat, then buy new refrigerator! (I have been blind)

[Larry2]

Yes, I withdrawing all my comments on this matter, and pronouncing, that if it is not thermostat, then buy new refrigerator! (I have been blind)

You would not say this if you built your kitchen around one of these cabinet enclosed fridges. You would do most anything it took to fix that thing, to avoid installing the new kitchen your wife wants. .

Recently, I've had to install a defrost timer and a new ice maker in mine. I felt it was money well spent.

[Larry2]

I'm thinking this was a trick question, where non-servicable meant the compressor could not functional to pump refrigerant from the system. I recall some discussion on the EPA608 exam but it's fading from memory. To me, non-servicable means the compressor has failed, but there is charge to be moved out. I think many of the principles will be the same. The study materials are on www.epatest.com.

They could mean a system that lacks service access. There are a few service access valves that are suited for recovery, included ones that clamp on or solder on even with gas inside. There is even one that is a vice-grip device designed to access, recover and condemn the equipment.

[nike123]

They could mean a system that lacks service access. There are a few service access valves that are suited for recovery, included ones that clamp on or solder on even with gas inside. There is even one that is a vice-grip device designed to access, recover and condemn the equipment.

You mean like this one (14210):

[chillin out]

I used to have these, (14210 and 14200)
Very helpful tools.

Chillin

[The MG Pony]

I think that you are wrong here, at least in case of domestic refrigerators and fridges.
They are made hermetically sealed because of critical charge they have. If you put gauge every time you want to see pressures, after two times you end up with undercharged fridge.

Second, it is not the case in entire world that is cheaper to change unit than repair it. There are countries in this world where labor is less then 1$ at hour. Here (Croatia) is average for industry 20$ (that is how much is labor charged) per hour.
Someone could pay as much as year salary for one simple fridge that you could pay with one domestic split-system install charge.

No Pual is correct and described it exactly, Here in Canada is the case as well, the dump charges a reclaim fee when dropped off and they sit in a special yard where once a week a tech comes and evacuates all of them then they are compacted and recycled.

To do so he needs a line piercing valve.

[star882]

I definitely have nothing against females joining the trade, I just find it the strangest thing.

It would be really weird actually talking about fridges to a female that knows what you are talking about and not just nodding her head and sighing....lol
I had never found it the best chat up line saying I am a refrigeration engineer and them asking what the heck that was. They would never understand and usually got bored withing the first 2 minutes. (which is just 1 minute too short for me....lol)

Chillin

For your information, "fridge girls" are not *that* uncommon. When I was in high school, I thought I was going to be the prettiest HVAC/R technician in the world. In college, I know at least two other "fridge girls" who are challenging that position. They're very friendly and I actually have attended their discussion sessions about HVAC. (Of course, one knows just about as much as I do about HVAC but is nowhere near as pretty as I am, while the other is just about as pretty as I am but doesn't know as much about HVAC as I do, so I'm still in first place.)

Even more interesting than "fridge girls" are "fridge couples". The quote in my sig is probably the funniest HVAC-related quote I know of. (They consider themselves as a "well-matched system".)

BTW, during a discussion session about expansion valves, I learned a lot about expansion valves. According to them, expansion valves are often incorrectly blamed for system problems. They later went into depth about how TXVs are superior to cap tubes and how piezoelectric expansion valves might soon be the future. They also discussed how advances in embedded computing, along with switched-reluctance motors and APID (Adaptive Proportional Integral Derivative) algorithms, can greatly improve efficiency when used with piezoelectric expansion valves.

[The Viking]

When I was in high school, I thought I was going to be the prettiest HVAC/R technician in the world. In college, I know at least two other "fridge girls" who are challenging that position.
....one knows just about as much as I do about HVAC but is nowhere near as pretty as I am, while the other is just about as pretty as I am but doesn't know as much about HVAC as I do, so I'm still in first place....

Now then...

I can see a competition being required here!

My suggestion would be that all parties would have to supply 4 photos (portrait, ball gown, boiler-suit/overalls and swimsuit/bikini).
This to be combined with a Fridge/AC questionnaire.

Each part (pictures/test) would count for 50% of the overall mark.


Why haven't we thought about this before?

C'mon girls, if you send your photos to me, I will arrange a voting system on my website and I'm sure we will be able to sort a test out somehow...

And guys, spread the word!

[chillin out]

According to them, expansion valves are often incorrectly blamed for system problems.

Who are 'them'? would they happen to be over 50?
Reason I ask is because most techs over 50 always moan about us young dudes (and dudets) fiddling with expansion valve settings....lol

They later went into depth about how TXVs are superior to cap tubes

I would not have thought this was strictly true. cap tubes are just used in different applications.
Also, define superior .
Better built, better quality, better liquid control, longer lasting, most cost effective, easier to service.........?
They each have their own superior qualities.

piezoelectric

This new to me, I thought piezoelectric things were only made to give a small spark in a lighter....lol
Would you happen to have any literature on these?
Thanks.

Chillin

[star882]

Who are 'them'? would they happen to be over 50?
Reason I ask is because most techs over 50 always moan about us young dudes (and dudets) fiddling with expansion valve settings....lol

Definitely under 50. More like 20.
EDIT: One of their quotes is, "Those who do not understand the operation of a thermostatic expansion valve (TXV) blame it for system problems. Those who do understand know why a TXV is nice to have."

I would not have thought this was strictly true. cap tubes are just used in different applications.
Also, define superior .
Better built, better quality, better liquid control, longer lasting, most cost effective, easier to service.........?
They each have their own superior qualities.

They deal more with A/C than refrigeration. I have yet to find a situation in A/C where a cap tube is actually better (for the consumer) than a TXV. Small scale refrigeration is different but they mentioned that a more efficient home refrigerator would use an ice bank frozen at night (when outdoor temperatures are lower) and thus require a TXV to handle varying outdoor temperatures. And for electronics cooling (another area they're interested in), a TXV is often required to handle wildly varying loads.

This new to me, I thought piezoelectric things were only made to give a small spark in a lighter....lol
Would you happen to have any literature on these?

Basically take the TXV and replace the diaphragm assembly with a piezoelectric element. A computer can measure parameters using sensors and adjust the expansion valve along with compressor and fan speeds. Much more sophisticated control than the simple "mechanical computer" in a standard TXV. It also allows for remote troubleshooting of the system. Also, if the computer detects that the expansion valve hunts with some given settings, it can automatically change the parameters to avoid it. (That's the "adaptive" part of APID.)

[Grizzly]

Basically take the TXV and replace the diaphragm assembly with a piezoelectric element. A computer can measure parameters using sensors and adjust the expansion valve along with compressor and fan speeds. Much more sophisticated control than the simple "mechanical computer" in a standard TXV. It also allows for remote troubleshooting of the system. Also, if the computer detects that the expansion valve hunts with some given settings, it can automatically change the parameters to avoid it. (That's the "adaptive" part of APID.)

Well Star!
You have got me intrigued.
Like Chillin Out I have not heard about this piezo electric form of metering device.
Is it something you are involved in that is being developed on your side of the pond?
Has anyone else heard of this before and if so what size equipment is it used on?
Or are we just talking about a more advanced form of electronic expansion valve?
It's the reference to piezo electric that gets me?
Grizzly

[star882]

Well Star!
You have got me intrigued.
Like Chillin Out I have not heard about this piezo electric form of metering device.
Is it something you are involved in that is being developed on your side of the pond?
Has anyone else heard of this before and if so what size equipment is it used on?
Or are we just talking about a more advanced form of electronic expansion valve?
It's the reference to piezo electric that gets me?
Grizzly

It is a type of electronic expansion valve, but it uses piezoelectrics instead of a "voice coil" linear motor. As a result, it should be easier to control and the valve only draws current when opening and closing.
So far, it is still experimental. One of the problems to overcome is that the piezoelectric elements need high drive voltages (up to hundreds of volts for an A/C expansion valve), requiring expensive high voltage amplifiers. They have an idea to solve this by using a programmable switching power supply (flyback converter), but they're still working on it. In the long term, I think the solution would be a high voltage ASIC running from rectified line voltage that includes the IGBT drivers for both the fan and compressor motors, the crankcase heater PWM, current sensing, logic power supply, as well as a high voltage opamp.

[Grizzly]

It is a type of electronic expansion valve, but it uses piezoelectrics instead of a "voice coil" linear motor. As a result, it should be easier to control and the valve only draws current when opening and closing.
So far, it is still experimental. One of the problems to overcome is that the piezoelectric elements need high drive voltages (up to hundreds of volts for an A/C expansion valve), requiring expensive high voltage amplifiers. They have an idea to solve this by using a programmable switching power supply (flyback converter), but they're still working on it. In the long term, I think the solution would be a high voltage ASIC running from rectified line voltage that includes the IGBT drivers for both the fan and compressor motors, the crankcase heater PWM, current sensing, logic power supply, as well as a high voltage opamp.

Wow.
Neat answer, you say you are a student!
What are you studying?
Because that is a seriously clever and in-depth answer, especially for a humble fridge engineer like myself to take in.
You are obviously well informed on this one.
So please could you keep us up-dated on how this develops.
Many thanks Grizzly

[chillin out]

requiring expensive high voltage amplifiers
In the long term, I think the solution would be a high voltage ASIC running from rectified line voltage that includes the IGBT drivers for both the fan and compressor motors, the crankcase heater PWM, current sensing, logic power supply, as well as a high voltage opamp.

And at what cost?
This is us going back to another thread and talking about more high tech equipment and oscilloscopes to carry on an already over-crowded van.
Gee whiz, try making systems simpler and more service friendly.
Whats wrong with just using an EEV?

Chillin

[paul pursehouse]

hi,I completed my trade in the last 3 years and had a similar question,Non serviceable in our test meant there was no service ports or access valves in the system,meaning no way to attach gauges to the system.
What they wanted to know was - install bullet piercing valve or valves,connect gauges,recover refrigerant,most importantly remove bullet piercing valve and install a shroeder valve in its place,the main point being DO NOT Leave the bullet peircing valve in place as they are prone to leaks

[chillin out]

hi,I completed my trade in the last 3 years and had a similar question,Non serviceable in our test meant there was no service ports or access valves in the system,meaning no way to attach gauges to the system.
What they wanted to know was - install bullet piercing valve or valves,connect gauges,recover refrigerant,most importantly remove bullet piercing valve and install a shroeder valve in its place,the main point being DO NOT Leave the bullet peircing valve in place as they are prone to leaks

What has this got to do with this thread??

Oh yes, the original post..... this thread had got a bit side tracked since then.....lol

Chillin

[star882]

Wow.
Neat answer, you say you are a student!
What are you studying?
Because that is a seriously clever and in-depth answer, especially for a humble fridge engineer like myself to take in.
You are obviously well informed on this one.
So please could you keep us up-dated on how this develops.
Many thanks Grizzly

I'm actually an electrical engineer, but what my friends are working on caught my attention. I don't know very much about the details.

And at what cost?
This is us going back to another thread and talking about more high tech equipment and oscilloscopes to carry on an already over-crowded van.
Gee whiz, try making systems simpler and more service friendly.
Whats wrong with just using an EEV?

The development cost of an ASIC is very high, but it is non-recurrent (meaning it only has to be done once, no matter how many units are to be produced). For example, the chip in a digital clock might have costed millions to develop, but so many are produced (hundreds of millions) that the development cost per unit is negligible. Not to mention the high voltage ASICs in modern fluorescent lamps, which actually are simple inverters.

From my understanding, the "voice coil" linear motor in a standard EEV produces a force proportional to the current flowing through it, while the restriction depends on position. It results in a very complex control algorithm to hold the valve at a given position despite varying pressures.
In contrast, piezoelectrics change shape (and thus position of the valve) based on voltage. They are also affected less by pressure changes.

I think the idea with the flyback converter is to power it from the low voltage control supply, using a voltage divider for voltage sense and a H bridge for changing the polarity. Then no chips have to directly deal with high voltage, greatly decreasing costs. The requirements are probably very similar to that of a MEMS (mechanical devices on a chip) or APD (used in fiber optics) power supply.

http://www.maxim-ic.com/appnotes.cfm/an_pk/1831
http://www.maxim-ic.com/appnotes.cfm/an_pk/1751
http://www.maxim-ic.com/appnotes.cfm/an_pk/1109

[chillin out]

From my understanding, the "voice coil" linear motor in a standard EEV produces a force proportional to the current flowing through it, while the restriction depends on position. It results in a very complex control algorithm to hold the valve at a given position despite varying pressures.

The EEV's I were talking about just open and close on a pulse from the controller.

"If Hannah was an air handler, I would be a condensing unit so I could open her TXV and pump my refrigerant through her coils." - a HVAC friend of mine

Well I would be a heat pump, then she would get it both ends.

Chillin

[star882]

The EEV's I were talking about just open and close on a pulse from the controller.

They did mention about an expansion valve that is basically just a solenoid valve with a very small bore. IIRC, they said that one of the concerns is the vibrations causing leaks. Still a great concept, though.

Well I would be a heat pump, then she would get it both ends.

Actually, I think it goes, "I'll be a heat pump so I can make her coils either hot or cold."

[chillin out]

They did mention about an expansion valve that is basically just a solenoid valve with a very small bore. IIRC, they said that one of the concerns is the vibrations causing leaks. Still a great concept, though.

Yes that's the one, the 'small bore' is interchangeable to give different power.
Vibration can be a problem as you say, but it the pipes are brazed properly and secured then there isn't a problem. These are very common in the UK.

Actually, I think it goes, "I'll be a heat pump so I can make her coils either hot or cold."

Nah, I'll stick with mine...lol
(cos the 'gas' would enter at the other end due to the direction of flow...lol....forget it, this is getting too rude...hehehe)

Chillin

[star882]

Yes that's the one, the 'small bore' is interchangeable to give different power.
Vibration can be a problem as you say, but it the pipes are brazed properly and secured then there isn't a problem. These are very common in the UK.

I have just talked with them about it and I found out that Tom Stage (a pretty well known overclocker in my area) once requested a custom built Xeon CPU cooler from them. They chose to use an off-the-shelf condensing unit (1/3HP R404a IIRC) with custom evaporator blocks and solenoid expansion valves with a custom controller. They had some issues with leaks and the vibration causing the mounting screws to loosen. They got it under control with vibration dampeners and fingernail polish on the screw threads, but it left them with a bad impression.

BTW, the solenoid coils are also high voltage (typical peak voltage of 80-100v) but the drive circuit is much simpler. Their approach is to run the solenoids off the rectified line voltage (170v DC) with a MOSFET for PWM voltage regulation. The current though the solenoids must be profiled and not just turned on and off in order to keep vibration under control. (If the valve was just abruptly closed, the resulting liquid hammer could damage the pipe.) In the end, they say the piezoelectric expansion valve would avoid that issue and be roughly the same overall cost.

[chillin out]

Most supermarkets in the UK use EEvs without any problems. (Which use 240vac or 220vdc.)
If your friends experienced excessive 'hammering' then I suspect a problem with the system itself rather then the EEV.

In the end, they say the piezoelectric expansion valve would avoid that issue and be roughly the same overall cost.

Yes, but as you guys are students, I think you are wasting far too much drinking time over it...lol

Chillin

[star882]

Most supermarkets in the UK use EEvs without any problems. (Which use 240vac or 220vdc.)
If your friends experienced excessive 'hammering' then I suspect a problem with the system itself rather then the EEV.

I think the problem had to do with the frequency. While a standard refrigeration application would probably work fine with the valve opening and closing every 20 seconds or so, the CPU blocks have much lower thermal inertia so the valves switched many times every second.

Yes, but as you guys are students, I think you are wasting far too much drinking time over it...lol

They think HVAC/R is fun and building systems is just something they really like to do.