TEV selection

[lana]

In order to select a proper TEV from the manufacturer catalouge, most of the times the required capacity can not be found. For example for 9kW cooling capacity, the nearest listed capacity is 7kW or 11 kW. Each one gives different nozzle size.Which one the best choice and why?

[chemi-cool]

Hi Lana,

Its because you can adjust the TXV.

I would use the 11KW to get 9KW and just close it a bit.

Chemi

[lana]

Mr. O'Brian,
Can you explaine why 11kW? Is it possible to select the 9kW and then ajust the valve to get the required capacity?
Thanks

[Dan]

Industry convention selects the larger valve, the 11kW over the 7kW.

While I don't strongly disagree, Marc, my experience is that a slightly undersized valve will hunt less than its oversized equivalent. In cases where you are wanting to maintain as low a superheat as possible, I would favor the undersized TEV.

[lana]

Would you please give me a quick hint what is the static superheat and what's the difference between static and total superheat?
Cheers.

[Dan]

Lana, I think Marc means "Spring pressure" when he refers to static superheat. Not sure about "total superheat" but I would hazard a guess that we bring the equalizing and powerhead pressures into the picture... these, of course, are dynamic, as opposed to static, and complete the picture of an expansion valve's behavior.

[Ian Ship]

Always undersize the expansion valve. Oversized valves will hunt.

Then adjust the superheat to give 5 to 6 degrees

[Samarjit Sen]

Hi Lana,

I agree with Dan and Ian Ship. I always a slightly undersize TEV. However for the selection of a TEV, I find that using the Cool Cat of Danfoss is much better. With this you get an idea of the model, then use their Commercial Ref. Catalog to get a more accurate size.