How do you size a txv when you are the OEM

[kengineering]

In our production we use a 1/4 ton valve in a 3/8" 24 tube 30"coil, we also use a 1/4 ton valve in a 1/2" 20 tube 88" coil. The same valve for a coil more than 3 times the size. Are we just guessing? How does one calculate the right valve. Thanks, Ken

[US Iceman]

Is this a finned-tube air cooling coil?

It may have to do with pressure drop through the coil(s) and the heat transfer capacity of each coil.

The 1/2" tube is 3 times as long, but the 1/2" tube is a lot larger ID than a 3/8".

[fridg]

I say it all comes down to subcooling

design the system around subcooling

[lana]

In our production we use a 1/4 ton valve in a 3/8" 24 tube 30"coil, we also use a 1/4 ton valve in a 1/2" 20 tube 88" coil. The same valve for a coil more than 3 times the size. Are we just guessing? How does one calculate the right valve. Thanks, Ken

Hi,
In order to size the correct TEV first you have to know the refrigeration capacity. Secondly the evaporating temperature. Thirdly the pressure drop across valve which is the condensing pressure minus evaporating pressure and plus the different pressure drops in the liquid line and after TEV. Then with these three values you will refer to the TEV catalogue and select the correct size.
Cheers

[US Iceman]

review these links... they should help to explain the question about TXV selection.

http://www.sporlan.com/10-9.pdf

http://www.sporlan.com/10-10.pdf

The Sporlan website is a great place to spend some time reading!!!

[kengineering]

Thanks again for all the response. I will check out the Sporlan pages. The example in question is a finned fan coil for a open air screen self select type beverage cooler. In this case it is for R22 and desired temp is 38-40*f. Ken

[Cofreth]

Select your TXV according to your compressor capacity.

[kengineering]

design around subcooling is and interesting idea. When migyt i get more information. Ken

[US Iceman]

Ken,

If you look through the Sporlan selection and application information in the literature you will see subcooling increases the TXV capacity.

The reduced liquid temperature increases the net refrigerating effect per pound of refrigerant circulated in the system.

You can also have too much subcooling... If the liquid temperature is below the evaporating temperature, the liquid will not evaporate/boil in the coil.

Too much of something is not better...