Evaporator orientation TEV feed vs. suction

[kengineering]

I am building an air screen grab and go merchandiser and while selecting the evaporator coil the manufacturer stated an inlet and outlet on his drawing for my approval. I called to find out more on this subject and he said that it was critical but wasn't really sure why. The computer spits out the model and the engineer was away. The drawing shows the TEV feeding the top of the coil farthest from the evap fan and the suction line outlet as the top of the coil closest to the fan. The tubing circuit runs top to bottom as it flows foward. I would love an explanation, any thoughts? Ken

[Gary]

I assume the fan is push through, rather than pull through?

Heat transfer is best when the air and refrigerant flow towards each other (counter flow) and worst when they flow in the same direction (parallel flow).

Parallel flow (worst), cross flow (better), counter flow (best).

[kengineering]

Yes that is correct the fan is a push through. Counterflow makes sense. Any thoghts on the inflow and outflow both being on the top of the coil? A friend suggests that it may insure the coil is flooded before gravity affects it. Ken

[Gary]

I'm guessing that it helps flush oil out of the evaporator.

[Peter_1]

Last section will be only superheated refrigerant vapor at a low speed flowing upwards where this can be a problem returning the oil to the compressor.

You also need more refrigerant this way.

My recommendation should be that the flow in a DX evaporator must flow always downwards so that oil can't collect in the tubes.
Any commercial evaporator is made this way and I think these manufacturers did a lot of research on this issue.
This is trying re-inventing warm water.

[hendry]

my understandings so far ... unit cooler has either top feed or bottom feed coil.

the seleciton varies with the refrigerant you use & that very much has connection with relative density against lube oil.

secondly, if your unit cooler is relative higher compared to compressor, top or bottom feed issue does not exits.

thirdly, ASHRAE has advised the use of suction U-trap to recover carry-over lube oil.

probably, the above could enlighten you and others.

[Peter_1]

secondly, if your unit cooler is relative higher compared to compressor, top or bottom feed issue does not exits.

thirdly, ASHRAE has advised the use of suction U-trap to recover carry-over lube oil.

I don't think you get the point. Wherever the evaporator is located, you always can have a bottom or a top fed injection. It depends here the TEV is located on the coil.
A U-trap has nothing to do with this because the oil doesn't even has a change that it comes into the U-trap.

[hendry]

I don't think you get the point. Wherever the evaporator is located, you always can have a bottom or a top fed injection. It depends here the TEV is located on the coil.
A U-trap has nothing to do with this because the oil doesn't even has a change that it comes into the U-trap.

thank you.
let me re-study the manufacturer's in-house technical manual in unit cooler's design.

[kengineering]

Hello. Maybe a little more information is in order. The evaporator coil is entirely my choice.
This is not a unit cooler type coil with attached fan housing and fan available at the local supply house. Just a bare coil as I will be fabricating the metalwork myself.

Futhermore, I will be using a GE ECM fan motor or a similar type and 134a or 404a as my refrigerant for a 20*F, (-7* C ) evaporator coil temperature.
The condensing unit will be housed directly below the evap coil. So far I have decieded that an outside physical coil dimension of 6' X 9" X 42" ,(152mm X 228mm X 1068mm) which is the same that I currently use in another application, would be a good place to start since many of the other components will work without change.

Of course the length could change with the size of the cabnet. The tubing size, tubing wall thickness, inlet and outlet location, fin spacing, fin material thickness, and tubing circut layout are entirly my choice.
The coil fabricator has computer models based on the choices however they are hesitant in advising me. For example I have asked "what does refrigeration company XYZ use in their similar situation" and I am told this is top secret information and I completely understand this confidentiality.

So here I am needing feedback on; tubing size, tubing circut layout and inlet / outlet location for the dimensions and specs I listed. If more info is needed please do not hesitate.

Thanks Ken

[hendry]

Hello. Maybe a little more information is in order. The evaporator coil is entirely my choice.
This is not a unit cooler type coil with attached fan housing and fan available at the local supply house. Just a bare coil as I will be fabricating the metalwork myself.

Futhermore, I will be using a GE ECM fan motor or a similar type and 134a or 404a as my refrigerant for a 20*F, (-7* C ) evaporator coil temperature.
The condensing unit will be housed directly below the evap coil. So far I have decieded that an outside physical coil dimension of 6' X 9" X 42" ,(152mm X 228mm X 1068mm) which is the same that I currently use in another application, would be a good place to start since many of the other components will work without change.

Of course the length could change with the size of the cabnet. The tubing size, tubing wall thickness, inlet and outlet location, fin spacing, fin material thickness, and tubing circut layout are entirly my choice.
The coil fabricator has computer models based on the choices however they are hesitant in advising me. For example I have asked "what does refrigeration company XYZ use in their similar situation" and I am told this is top secret information and I completely understand this confidentiality.

So here I am needing feedback on; tubing size, tubing circut layout and inlet / outlet location for the dimensions and specs I listed. If more info is needed please do not hesitate.

Thanks Ken

oh i c now ...
sorry to miss the most imprtant part, my apology.

may be i could find somthing suitable for u ...