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Peter_1
16-04-2004, 09:22 AM
Another question.

Some state that the AKV’s adapt better then TEV’s to the actual load in the cold room.
I disagree with this. I follow a think pad which is perhaps not correct

Let’s say we have a cold room, normal load, set on 0°C and for the moment at 0°C.
Fans keeps running all the time so air volume the same.
Differential of thermostat set at 1 K.
As soon as temperature increases 1K due to losses over the construction, SV opens and compressor starts.
Air Entering temperature entering = 1°C. The mass air flowing over the coil possesses x enthalpy.
Temperature in the room drops to 0°C and SV closes.

Now some warmer goods are stored in the cold room. Temperature rises faster to 1°C but as soon SV opens, room starts cooling and hold it at 1°C for a longer time.
Air entering remains at 1°C for a longer time but enthalpy remains the same but evaporator has to run longer to drop the temperature.

Now lots of warm goods are stored in the cold room (no normal load anymore but more a quick chill).
Temperature rises faster to 1°C but as soon SV opens, room starts cooling and can’t hold it at 1°C any longer. Rises to let’s say 3°C. entering air now 3°C so higher load, TEV opens more and LP rises (single unit), cooling capacity of compressor increases so cools relative faster (perhaps an increase in HP due to higher load)
With a pack, LP will be held constant, so DT over evaporator will increase when room temperature increases, so it will cool faster and perhaps temperature will have never the change to swing wide away from setpoint due to increased capacity.

But in most cold room applications, as soon as SV opens due to increase in temperature, there will no further increase of temperature anymore because the then ‘injected cooling capacity’ will be much higher then the heat losses. So the load is always the same and TEV is always positioned in the same position.

Any comments?

Mark
16-04-2004, 09:44 PM
Peter :)

Indeed AKVs in my opinion should not be used in coldrooms.

There fine in larger supermarkets thats all ;)

Latte
17-04-2004, 12:05 PM
Hi Guys,
Got to admit i don't like AKV's, Too much to go wrong.
TEV's just take a reading from the feeler bulb & work.
AKV's have to get two readings, Coil in and out. Thats two extra pobes to o wrong for starters, them there is the coil. also i have found AKV's to block up easier than the old danfoss TEV's

Perhaps i am not embracing modern technology as i should but i like the old ways and as far as i am concerned if it works the old way why bother fixing somthing that isnt broken.


Regards

Raymond

chemi-cool
17-04-2004, 01:22 PM
hi guys,

got to agree with all of you.TEV's work fine and without any problems in all temperaturs. ond there is no need to chenge. I would not go for AKV on a new unit and only in supermarket I can see the need for it.

raymond, if you have a freezer using TAV, you will still need controller with two sensors for defrost control.

let me know when you start repering aircraft AC so I will catch a night flight :D
cooling units in big airplains are interesting. try something in that field.

good luck with that any way.

chemi

Mark
17-04-2004, 01:31 PM
Hi Guys,
Got to admit i don't like AKV's, Too much to go wrong.
TEV's just take a reading from the feeler bulb & work.
AKV's have to get two readings, Coil in and out. Thats two extra pobes to o wrong for starters, them there is the coil. also i have found AKV's to block up easier than the old danfoss TEV's

Perhaps i am not embracing modern technology as i should but i like the old ways and as far as i am concerned if it works the old way why bother fixing somthing that isnt broken.


Regards

Raymond

Dont worry Ray i will show you how they work when im next in cambs :D :D :D

Mark
17-04-2004, 01:45 PM
They use four or five probes actually :rolleyes:

All play a part in how the equiptment works :D :D

Peter_1
17-04-2004, 03:03 PM
They use four or five probes actually :rolleyes:

All play a part in how the equipment works :D :D

I t becomes now even worser with all that probes. All possible causes that it will one day go wrong (Murphy you know)

And why particularly in supermarkets? Freezer bins, counters ...have the most steady load of all refrigeration applications. Temperature in the store is appr. the same the whole day, delivered goods are at correct temperatures when entering, ....

AKV's are a very good option where there has to be worked in wide temperature ranges like blast freezers where temperature starts at +10°C and go down to -25°C or so.

Mark
17-04-2004, 03:23 PM
peter



I t becomes now even worser with all that probes. All possible causes that it will one day go wrong (Murphy you know)

inevitably.



And why particularly in supermarkets?


On larger supermarket pack systems AKVs can be used without having problems with suction pressure hunting,as well as other benefits.



AKV's are a very good option where there has to be worked in wide temperature ranges like blast freezers where temperature starts at +10°C and go down to -25°C or so.

This only contradicts your first point.


Kind Regards Mark :)

Peter_1
17-04-2004, 03:51 PM
On larger supermarket pack systems AK Vs can be used without having problems with suction pressure hunting,as well as other benefits.

I never saw large fluctuations on supermarket systems with TEV's. Systems are so big, so much lines, so big internal volumes that there is always a long time passing by before system stabilize back to a new condition. When it stabilize, there is always somewhere in the system a new SV which will open or close again so that the system is continuous stabilizing.

In fact, the PWM regulation also needs larger lines and volumes to use the slowness of the system. Otherwise evaporating pressure should continuous going up and down with an AKV due to the PWM.

I rather should say that you only can use the AKV's in large systems because in small systems they even won't work at all or not good because volume is too small. So there are only a few installations where they can be fit.
REason why Danfoss pushes them mostly in supermarkets and the most test cases you can find are also in supermarkets.

Seen in that vision, the stepper motor driven EV's like those made by Sporlan are a much better choice because they don't need the slowness of the system and work almost the same as a standard TEV.
Once they're opened and stabilized to the load, they inject a steady flow of refrigerant without pulsing.

Prof Sporlan is better placed to argue on this point I think.


This only contradicts your first point.

I don't understand this. Explain a little bit more Mark.

Peter.

Budokan
17-04-2004, 05:37 PM
Ignoring all opinions about what works best rom a service point of view what is best.

With an AKV there may be a few more probes but on the whole, in my opinion they are easier to maintain. As far as I am aware common faults are faulty probes (some manufacturers more than others) and the valve not closing properly, just a matter of swapping the plunger and spring or cleaning the valve, no brazing gear required that you would need for a TEV, no hot work permits etc.

Mark
17-04-2004, 05:48 PM
Peter :)

Yes i was agreeing that the AKV is only suitable in a moderate to large supermarket/pack installations.


I don't understand this. Explain a little bit more Mark.

Firstly you were talking about multiple probes failing ,then saying AKVs are the best option in a place where the probe range is taken from one extreme to the other.
Everyone has there opinion on AKVs there is no right answer :)

Regards Mark :)

Peter_1
17-04-2004, 05:58 PM
With an AKV there may be a few more probes but on the whole, in my opinion they are easier to maintain. As far as I am aware common faults are faulty probes (some manufacturers more than others) and the valve not closing properly, just a matter of swapping the plunger and spring or cleaning the valve, no brazing gear required that you would need for a TEV, no hot work permits etc.

Same for a flared TEV or the 'HEY PROF' , Sporlan Q valves. A pair of wrenches and that's it. And then the repair price for the client: 1 probe cost more then a brand new thermostatic expansion valve. A complete new valve +300% and we haven't discussed the electronic controller yet.

And let's admit it, how many times needs a TEV be replaced? and if it as to be done, it's cheap compared to a AKV. The more elements you have on a controlelr, the more chnage you have that something will go wrong one day.

When I began (the R12 century), we even didn't installed a thermostat and a defrosting controller on a cold room. We did this all with a simple LP pressostat. And it worked fine: saw end of last year a cold room I installed +/- 20 years ago and it was still working like we had installed it and still with the same TEF (do you remember, the yellow labels) The owner but also I was proud of it.

Budokan
17-04-2004, 06:19 PM
I actually agree - simple is best, when I started as an apprentice there were still a few supermarkets that had equipment that was controlled solely by an lp switch.

However everything has to be seen to be energy efficient now. As for the AKV valves I find them easier to work on, i feel you get a better or quicker picture of what is happening. If one fails you can replace the internal parts which would make it a cheaper repair than a TEV and most end user would not allow flared valves.

Peter_1
17-04-2004, 06:49 PM
If one fails you can replace the internal parts which would make it a cheaper repair than a TEV and most end user would not allow flared valves.

1. Accessories for AKV, pricelist Danfoss, gross Euro price
Piston 60.72 Euro, gasket set 1.5 euro, Upper part 91 Euro
Coil 43 Euro. A complete new TEv 76.65 Euro

2. Few of my end user know what a TEV is, so if it's soldered or flared, they don't care. The only thing they care is that they pay as less as possible for a good quality and that they don't see you back for al ong time - at least not for a repair.

I will diagnose a TEV and you an AKV. You will need a resistance meter and temperature probes or your costly hand unit (which they hopefully will not re-design when the next generation AKV comes out)
I will come with only my temperature probes.
In the time you have figured out if the coil has failed or one of the sensors perhaps failed, the electronics failed, walked through the menu of your hand unit if everyting is set as it should be, I'm long gone to my next client and bin will working again.
And then you have to be lucky that you have the spare parts in your van.

If you take then the labour cost for this repair, the AKV has to run for along time to save back this labour costs.

You always can install a Sporlan Q valve, it's a soldered version but to repair it, you only need a couple of wrenches.
Or use STEK couplings on the standard flared TEV's.

It's like in the new cars: what is in most cars the first failure: the electronics. There was another thread in MAC where they discussed this topic.


Still not convinced but it's like Mark said, everybody has his own opinion which I respect.
But till now, nobody has come with real figures, neutral test reports (do they excist?), big savings or real fiirmly based statements.

Latte
17-04-2004, 07:50 PM
Got to agrree with peter & say spot on.

What can go wrong with a tev, Either complete unit £30 or just orrifice & filter £6 (Parts Prices) now how does that compare to AKV.
An argument for an AKV could be with the use of 5 probes (Note Mark) instead of 3 on a tev is that you can get more information but do you really need it. 99% of the time the eev's suffer due to either loose or Probes gone & most engineers don't need pretty graphics on a computer to diagnose this.

Stick with Air on/ air off & defrost probes & TEV's

Mark, i thought you would prefer TEV's being a "M" dedicated engineer

Regards

Raymond

Budokan
17-04-2004, 08:41 PM
Raymond,

The AKV versus TEV debate depends on your perspective. In an ideal world all engineers working on supermarket contracts would be able to diagnose faulty TEV and replace them but due to the lack off skillbase with some contractors and end users using in store technicians to do fridge work this does not always happen. In a manager/supervisor situation it is a lot easier to diagnose online or over the phone with an AKV system, it is easy for anyone to replace a probe and relatively easy to instruct and engineer how to change the piston in an AKV.

Latte
17-04-2004, 08:51 PM
Raymond,

The AKV versus TEV debate depends on your perspective. In an ideal world all engineers working on supermarket contracts would be able to diagnose faulty TEV and replace them but due to the lack off skillbase with some contractors and end users using in store technicians to do fridge work this does not always happen. In a manager/supervisor situation it is a lot easier to diagnose online or over the phone with an AKV system, it is easy for anyone to replace a probe and relatively easy to instruct and engineer how to change the piston in an AKV.


How many of you outthere are able to go online and access readings.

somehow i don't think that i will become a often used tool for engineers for security reason although it would be a very useful one


Regards

Raymond

Budokan
17-04-2004, 08:55 PM
Raymond,

The strange thing is it has been used for years (I used it at leat 10 years ago) then all of a sudden everyone is talking about security concerns.

Shame you don't have access, it is suprising how many out of hours call outs that can be avoided once you have had a look.

Latte
17-04-2004, 09:38 PM
Hi Guys,
It is suprising how many callouts are non calls these days.
The trouble is now with more and more sites having alarm facilaties more stupid calls come in. The most common one is being called out to a coldroom alarming out high temp only to find the door is wide open.
Probe 5 faults is another one in the middle of the night is another one that wind's me up. Stupid things that can be left another few hours for want of logging on instead of getting up in the middle of the night and being knackered all day.
I hope that one day the dial in facility will be more widely used over here by engineers to save stupid calls, even if it saves one journey in summer when you have 40 outstanding calls it will help

Regards

Raymond

Peter_1
18-04-2004, 09:19 AM
Raymond,

In an ideal world all engineers working on supermarket contracts would be able to diagnose faulty TEV and replace them but due to the lack off skillbase with some contractors and end users using in store technicians to do fridge work this does not always happen. In a manager/supervisor situation it is a lot easier to diagnose online or over the phone with an AKV system, it is easy for anyone to replace a probe and relatively easy to instruct and engineer how to change the piston in an AKV.

I worked in a company which supervised +/-30 supermarkets and none of them had AKV's (except in one store where 5 bins had an AKV for testing purposes) It is not a need that there is de facto an AKV to monitor or supervise a supermarket.
You receive the same readings with a TEV (Air on, Air out , Coil temperature, SV open or closed) .
You don't need more parameters to figure out via a remote PC what's going on.

Don't tangle the fact that an AKV can only be controlled or monitored by a Danfoss system. There are a lot more other and cheaper possibilities available. And you may have the most sophisticated supervising system,; at least someone has to go on site to repair the faulty parts.

And not anyone can replace a piston in an AKV. If you let do these things by whatever tech, it's first not allowed, it's illegal.
It's even dangerous if he is not aware of the possible dangers, how he need to pump down the AKV, that gas can come out the AKV when opening it,

Correct replacing and diagnosing a TEV is in my opinion the basic of the basics of refrigeration. And if someone don't understand what the purpose of a TEV is, then h definitely won't know what an AKV is doing. You first need to know how a TEV is working before you can understand an AKV.

If you have to rely on that sort of techs, then you should better do it yourself or let the work done by companies who have techs who know what they're doing.
I don't say that you are such a tech, I'm just talking in general.

Budokan
18-04-2004, 11:05 AM
Replacing/diagnosing a TEV is on of the most basic skills however there are certain contractors who have large contracts and employ electricians or engineers with a little bit of knowledge. This is not ideal but it is comonplace.

I seem to be becoming the defender of AKV valves, which is not really the case. Most of the equipment I am involved with use TEV, personally I would much prefer a well designed conventional pack with good control system than any low energy system.

I personally know some technicians who trained as electricians and have work as in store technicians and know what a AKV is, they have never seen a TEV, they can pump down a case, strip down an AKV, replace a probe - it maybe poor or illegal but it happens and will continue to happen.

As for the remote monitoring most supermarket chains either have or are putting in place remote monitoring were a third party company will diagnose before an engineer attends and check on the engineers actions on site through an activity log.