AKV versus higher load

[Peter_1]

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]

Peter

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

There fine in larger supermarkets thats all

[Latte]

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]

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
cooling units in big airplains are interesting. try something in that field.

good luck with that any way.

chemi

[Mark]

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

[Mark]

They use four or five probes actually

All play a part in how the equiptment works

[Peter_1]

They use four or five probes actually

All play a part in how the equipment works

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.