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David PS
11-08-2003, 01:18 PM
I have had some conflicting comments made concerning the suitability of electronic expansion valves when used with a single compressor condensing unit, i.e. it will not work.

Any opinions.

rbartlett
11-08-2003, 08:06 PM
yes mac and i were involved in some commissioning of a supermarket near oxford..when we found a e.e.v's on a single artic circle unit we left site..

reported to the manufacturer and they said 'oh bugger' and sent a guy to swap out all the valves for tevs

cheers

richard

Andy
11-08-2003, 10:39 PM
Hi
can't see why they wouldn't work, must be a start-up problem, getting to the stable running state. If in doubt talk to Danfoss, and possibly fit one of the better controller with the pressure transducer inlet referance, never did like the messing about with probes and positions with the probe inlet type, also they would have a high probe failure rate.
Regards. Andy.

Latte
13-08-2003, 10:37 PM
AKV 10's Wonderfull piece of equipment N O T !!!!!!!!!!!!

Once again it technology fo the sake of it. How many years have TEV Valves been available & doing the job OK. Easy to work on, Easy to change orifices & filters & reliable.

If any can think of a GOOD reason for these new valves as opposed to the old ones can you let me know.
Somerfield Stores use AKV's, weve had so many problems with them i even keep half a dozen on my van.

Andy
14-08-2003, 08:02 AM
Hi:)
in defense of AKV's, a lot of the problems are down to mis application and poorly set up controls. In my time doing supermarket work I would often check these valves, especially after a number of calls where other engineers had failed to find the fault, usually I would find faulty or misplaced probes and incorrectly configured controllers.
AKV's are a good way of acheiving low and accurate superheats, but the controllers need all to be properly networked to shutdown on plant fail:( I have seen a few smashed compressors, where the valves kept feeding, even when the suction pressure had overcome the remaining running compressors on the packs.
In short they work well, if the system is installed cleanly, i.e. if the install guys purge whilst brazing and if they are set up as per the manufacturers recomendations on say a large supermarket application.
Regards. Andy:)

Mark
24-11-2003, 07:58 PM
hi everyone
I would have to agree with andy on this .The EEV works very well and is more user friendly,if commisioned and sized properly.
the fitting of an EPR stabalizes the system alot quicker.quite often this dosent happen ,and the condensing units running pressure varies.The c/u sizing is more important though .
regards mark:)

Peter_1
24-11-2003, 10:12 PM
In the past, we used a few time AKV's on negative packs because the owner of the supermarket insisted this.
I was not aware at all of the problems with a simplex unit. It is a good lesson not to forget.
But can this not be solved with steppermotor controlled EEV's (Sporlan, Alco...)
I see in AC's that they mainly use steppermotor versions. In residential AC's, you can't afford it to have pulsations at all.
And the AKV's, you can hear them always "ticking"

Or just a thought: can the system not be used as you see in water heating systems to avoid pulsations where they use a standing vessel with a gas buffer on top of it?

Am I correct if I think that steppermotorcontrolled EEV inject better the liquid in the evaporator, more equal, with a better heat transfer? With a pulsed EEV, you experience moments with max velocity (big DP) and moments with almost 0 velocity at the inlet. You also have moments or patrs in the evaporator with almost no liquid anymore in the tubes with decreased heat exchange reduction (worser heat transfer factor) Or is this incorrect?

I shouldn't say that EEV's are more user friendly. You have almost nothing to change on a TEV when properly sized. You mount it in the system and that's it. On the other hand, a EEV once installed, you have to take the manual, attach the hand unit and you can start to program the thing. If the technician has not followed some lessons, it is not that easy to set all the parameters correct.
If you have to do a repair, you always must be sure that you have the handunit in your van. Or as we did, left one in the supermarket. In my opinion, a TEV is mutch more user friendly to maintain and to install.

Latte
25-11-2003, 02:24 AM
EEV's are good, But only as good as the probe readings it gets.
Probes only need to be slightly misplaced/loose/not sealed at the system goes tit's up. While i appreciate that all engineers do everything they can to ensure that probes are fitted corectly it only takes one to go down to mess up the EEV.
Perhaps i am getting old and not embracing new technologys with the open arms i should but personally i prefer TEV's

baker
27-11-2003, 08:21 AM
I was at a Danfoss seminar the other month and the claim was made that, all other things being equal, a pulsed EEV gave a better COP than a normal TEV. They believed that this was due to the evaporator operating more efficently if the refrigerant was pulsed in, rather than how it comes out of a TEV.

Peter_1
27-11-2003, 01:39 PM
I also was in the past at a Danfoss seminar where they told the same. I asked there the same question but they could not give independent test reports to prove this. I can't barely believe that a steady flow out of an TEV is better then a pulsed flow.

Latte
27-11-2003, 04:38 PM
i see with interest a couple of you went on danfoss seminars.
Does anyone know if such things happen over here, if so when/where. any ideas

Latte
27-11-2003, 04:49 PM
If anyone is looking for technical spec/sizes for AKV Valves go to
http://uk.refrignet.danfoss.com This puts you straight onto the refrige part of the site or if not go to www.danfoss.com & follow the menus through "industrial controlls" & "Valves & Sensors"

Latte
27-11-2003, 11:24 PM
OK Guy's Here's a problem i have, could it be the misuse of an AKV.
Large supermarket in Stevenage, Walk in freezer probably 8ft SQ.
Fed off single compressor Arctic circle unit. Problem ? Suction pressure all over place 0-15psi. Check suction BEFORE PRV Just the same. Stripped AKV all clear. Check POT all ok, head pressure good, pumps down & holds vac. Gas level OK-visible in sightglass in reciever.
Surely the only thing in the system causing this is the EEV ???
It's run off a tuscan 5 and all the probes reading OK & Secure.

QUESTION :- Should this unit be using a TEV not EEV ?????

Andy
28-11-2003, 09:35 PM
Hi Rdocwra:)
Whats the PRV, do you mean EPR, if so that will fight with the EEV, or any Expansion valve, causing the suction to hunt. A single unit will run with an EEV, but you are asking for trouble, add in an EPR and it gets plain silly:D :confused:
Regards. Andy.:)

Latte
28-11-2003, 09:37 PM
I will print off all these comments and pass it on to my supervisor.
One thing i have noticed on the unit is that it takes 2-3 mins for the EEV to open to 100%. The readings off the probes are fine. The superheat reading is therfore fine it's just the EEV seems slow to open. I assume as long as all the probes 1-5 are left on the system will still work OK nd not report any faults.
Its on a Honeywell/Elm PC Visor main monitor & tuscan 5 board

Latte
28-11-2003, 09:42 PM
Hello Andy,
I was taking about a pressure regulator thats on the suction line just before the compressor. I checked both sides because i was originally getting the strange reading with my gauges on the compressor, so i check the other side of the valve in case the valve was causing probs.

Hope this claifies what i meant

Raymond

Andy
28-11-2003, 09:51 PM
Hi rdocwra:)
The EPR problem is only when fitted to a single unit set up. You could fit say three evaporators to a unit, and providing you had a base load one, cond unit would run it all, even with EPR fitted (by base load I mean one EPR set a little lower than the other two, or one cooler without an EPR.
A CPR will work with a single unit/cooler set up, but the EEV will give you problem.
The Tuscon board will have an initialization period built in on start of injection, this opens the EEV to a present % until flow is initilized and the probes can take over.
The older Tuscon (I think) allowed you to set them up for either TEV or EEV.
What about the Inlet probe, print a graph of it against the outlet, if the outlet gets colder than the inlet the inlet probe is faulty, this would also cause a hunting suction pressure.
Regards. Andy:)

Latte
28-11-2003, 10:04 PM
Hello Andy,
Thanks, Its only a small Single Evap unit. Once i am back to work and down that way i will go in a check. From what i can remember last time i looked at it i was geting quite a good diff between p3 & p4 & superheat therefore good, it just seemed to take ages for the EEV to climb up to 100%. I know they do take time but this one seemed very slow

Raymond

winniesandar
28-07-2006, 03:56 AM
G/Day all,
This is my first post and first time I got a chance to learn in this community and signed.
Mainly, I woul like to learn more by real fridge engineer.
Rgds, Winnie