More stuff to go bad so we get to replace them more often.

 

The greatest advantage to an EXV is the ability to set limits if you need to.

Example: A chiller barrel that would freeze if you were to allow the saturated evap temp to get too low, limiting the EXV will prevent this issue.

Another advantage is being able to control a wide range of capacity with loading and unloading, especially a screw compressor.

 

Very interesting. Have not come across them yet. But they may all go that direction some day.

 

See, it went like this.

Had to get a special PC cable just to talk to the valve controller. This was very expensive for a 6' cable. Then had to download the proprietary software to interact with the valve. Fortunately, this was a free download.

I went into the store on Thursday last week on a call. Case had flooded 3 compressors (out of 4) out on the rack. I shut it down. Not having the proprietary cable and software, I could do NOTHING with the severely overfeeding EXV, so the store has gone without a service meat case for close to 6 whole days at this point.

Knowing that I couldn't properly diagnose the valve, I ordered EVERYTHING for the system including the cable. I figured that I would start it back up, figure out what was wrong and just replace the defective part. Fastest way I could figure to get it done.

Fast forward to today. Part finally arrives and is tossed directly into a truck and shipped out to me. I got the fancy cable and it worked perfectly. Turns out that the pressure transducer is reading 45# too low causing the valve to overfeed to try to maintain superheat.

Problem came when I opened the second box. EVERYTHING that I ordered turned out to be the valve controller and NOTHING else.


I should have just cut the SOB out and burned in a TXV and gone home.

 

Wow... my day seems pretty good now. Thanks JP :yes:

 

I am with you JP, they are a bastard to troubleshoot if you don't have the book, hardware, and software to do it. Even then they can be a bastard.

Then once you spend a day troubleshooting them you find out the manufacture (you know who you are) no longer makes that EXV or any of the controls that control it, and have 'upgraded' to a newer style that has more steps. To top it all off, the old EXV used a 18/3 wire but the new one requires a 18/4 wire so you have to pull new cables throughout the machine.

I hate you for that 'certain manufacturer'.

 

I had no problems with the EPR to EEPR conversion. Those were controlled through the building management system and had very few problems.

Now, this is the first of the EXV problems and I became an *instant* pro on troubleshooting them. Not that it was all that difficult in this case. Hook up PC, hook up DRSA, watch.


I'm hoping that the others that are out there just keep right on running. Of course, this is fairly easy work, so maybe I can just hope for more EXV trouble.......

At least I'm not out working on an RTU in 3 feet of snow.....

 

The main benefit with them is more accurate superheat control and the ability to drop head pressure with ambient. Me and a good friend are doing a study on a refrigerated warehouse with two identical systems. One with standard mechanical txvs and the other with EXVs.

Here's a article for you...

http://www.ashrae.org/docLib/20100804_lazzarin.pdf

 

Ity's saying article not found?

 

The head pressure is a big one IMO like dan said also you can get rid of a pump down solenoid.

RSES had a good article recently.

Forgot the month but will check unless someone getts it first.

 

I remember seeing that.

I'l have to go and re-read it.

 

http://www.rses.org/assets/rses_journal/1210_EEV.pdf

 

Great article, says theres a part 2 in the January 2011 issue , looking forward to reading that too.

 

Ever work on a refrigeration Heatcraft Beacon system.Great system.It has a EEV.you can tell the system what superheat you want and it will set it up.Valve go from full open to totally closed.No need for liquid line solenoid valve.EEV closes down when system is satisfied.You have a keypad control to adjust all defrost times,temps and settings.Great system and good example of a good EEV.True standard txv is usually enough,but this system is really nice.

 

I never worked on one yet. But heard you can use the eev as your case temp controller also. if thats the case you'll see alot tighter case temps.
I guess it would be nice instead of bending or laying half way into a case trying to superheat a valve bumping your head on the shelf above the txv. Sitting on a couple milk crates dailing in on the software. sounds nice.

 

Here is a link to five more reasons to join RSES

Link

 

thanks...

 

not to hyjack the thread but does anybody have any experience with those hybrid condensers that were featured in one of the articles in january? just wondered....

 

Jp was this a sms case?

 

Yep.


I knew they (EXVs) were out there and that more are coming. I knew what to do to deal with them, but didn't follow-through with the office to get the dongle to communicate with it.


One of the other guys said that he would have just popped an "A" valve in there and walked away.

 

I have the program and the cable but don't use it.You can troubleshoot it with the lights on the module it's much faster that way I have the light codes if ya want them.

 

They are in the book, too.

I forgot about the light codes until I had the dongle in hand and was back on-site.

I've got the manual on my laptop, now and that is always with me.


The way that this one went out, you would have needed the dongle. It wasn't a full-on bad transducer, but one that was off by about 40# I actually pulled it and ran it up and down with CO2. Consistently tracked 40# off.

Even the local H/P guy tried telling me that I was wrong.

 

The first types of EXV's they came out with were literally sh*tty, but they are getting a lot better.

 

which type were you dealing with? Stepper motor style or pulsing solenoid style...

Hopefully the stepper style! a good stepper ETXV with a good controller is the cats behind haha! those old solenoid style are a pain! IMO

 

This was a stepper motor style EXV.

I agree that, once set, it is very nice. The problem that I had was that I had no way to do anything with it in the field.

Since that has been corrected, I love them because they are guaranteed work for me as I'm the only guy so far that carries a laptop.

 

The experience I have had with exv's is on chillers. The way they control superheat so close helps the efficiency. And the level control on flooded chillers is way better than txv designs. What I have seen the most trouble comes from the thermisters on Carrier and Tranes. I can see where they are the wave of the future for refrigeration.

 

First I will say that I work for a controls manufacturer, but I have also been a field technician. I, too, used to gripe at the sight of an EXV in the field, as I did not have the proper training and know-how to setup such a sophisticated device. I will say, though, that this technology, once understood, is more advantageous to a TXV in every way, shape, or form (except for cost, of course). What you can do with head pressure controls, PRECISE superheat management, NO HUNTING, no solenoid, and increased system efficiency and stability is quite amazing. Here in the USA, we are really behind the times as far as electronic controls are concerned. In Europe, Mexico, and even Canada, electronic controls are far more widely used than here in the USA, where mechnanical controls are still the norm. I think in the future we will see energy legislation that will change this, so I recommend technicians to get acclimated to the technology sooner than later. With proper training, these devices are really exceptional.

 

I don't think they are better, but my guess is they show a slight energy savings, so the bean counters demand them. More "down time" on the electronic Master-Bilt freezers i serviced at my previous job than the old reliable's. You can't trick them or tweak them to get thru a weekend, they just quit. I left before the coolers started getting those.

 

There are so many benefits to the EEV over the TEV:

1 - No mechanical limitations to overcome (spring hysterisis, diaphragm hysterisis, etc). So, unlike a mechanical TEV whose ability to maintain a consistant superheat will vary as the system conditions vary, the EEV will remain very constant.

2 - It's easy to set (if you have the controller directions, cable, etc). You set if for your desired superheat and that's it. No playing around with an adjustment stem and watching for 1/2 hour.

3 - No need to have the display case loaded before attempting to set the valve. Again, you set it for the desired set point and that's it.

4 - On systems where you experience wide swings in load (VAV systems, etc) the EEV has the ability to throttle down to about 5% - 10% of its rated capacity and still maintain the SH set point. The mechanical TEV can regulate fairly well down to about 50% of its capacity (a balanced port TEV down to about 25% of its capacity).

5 - On refrigeration systems that float the head pressure down in the cooler ambient months to reduce compression ratio/increase efficiency, this plays havoc on a mechanical TEV. Its capacity is based in part on the pressure drop across TEV port, and as the head pressure is lowered, the TEV capacity experiences a reduction. There's a limit as to how far the head pressure can be lowered and still have sufficient TEV capacity to meet the evaporator load demand. The EEV can be greatly oversized and still maintain its SH set point during the summer months. And as an oversized valve, it will have sufficient capacity in the lower ambient months.

Drawbacks:

1 - Cost

2 - Relying on consistent performance of sensors and transducers.

3 - As JP mentioned in his original post, having the right literature and hardware for troubleshooting. Plus, troubleshooting electronic boards is at best a process of elimination. Very difficult to pinpoint how/why a board has failed...only that it isn't working correctly.

 

link went bad do you still have that article

 

Ahhh... let me jump into my time machine...