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View Full Version : TEV superheat!!!!



bjkmiami
14-05-2013, 09:41 AM
Hi guys again,
So most TEV comes with 5K superheat as a factory setting.My question is that what happens when you turn the adjustment screw all the way to the right or left in terms of superheat values(certain range like 1K to 10K maybe????) and does this affect the capacity of the valve?? if it is 20kw valve for that specific conditions would it still be 20kw with adjustment screw opened all the way????
Appreciate your feedbacks!!!!!

PaulZ
14-05-2013, 11:52 AM
Hi bjk
The capacity of a TX valve is nominal based on a set pressure drop across the valve, basically suction to discharge. If you look at a TX valve selection chart you will see it's capacity at different evaporating temperatures and at a set condensing temperature.
If for arguments sake you have a 20 kw valve at -5oC evaporating temp and 35oC condensing this would be nominal for the stated refrigerant.
If you change the evaporating or condensing temp then the capacity will change, increasing the difference (suction / discharge) increase the capacity, decreasing the difference decrease the capacity.
I think most Danfoss valves change the superheat 1 K per turn, but I would not rely on that, nothing beats doing a proper superheat check.
By altering the superheat setting you are not changing the capacity of the valve you are either allowing more or less refrigerant to enter the evaporator depending on whether you are increasing or decreasing the superheat. Increase the superheat decrease the flow, decrease the superheat increase the flow.
If you opened the valve all the way all you will do is flood liquid back to the compressor.
Hope this helps
Paul

monkey spanners
14-05-2013, 11:40 PM
If you adjust the TEV too far open you will have no suction superheat and shortly after no compressor. I have a customer who did this trying to increase the cooling duty!
In fact if the valve is way too open the system will do little duty because the evaporating temperature will not then be low enough to pick up significant heat in the evaporator and the liquid flood back will lower the discharge temperature and pressure and so reduce the flow of refrigerant to the TEV.
If the valve is too shut, the sytem will do little duty as too little of the evaporators surface will be used for heat transfer, then the condensing pressure will be lower and so the flow to the TEV will also reduce.
Its the sweet spot in the middle where things work well!

The factory set superheat of the TEV is only 5K at design conditions, if the system has a low load the superheat may go lower, conversly if the load increases the superheat would go above 5K.

sendhilkmar
20-05-2013, 12:45 PM
TXV is designed in such a way that it starts opening at 5K superheat and 100% open when the super heat value reaches 8K. This is called factory set and Operating super heat .

By adjusting the super heat setting we can reduce the factory set super heat value. Let say if we open 2 turn then the TXV would deliver 100% capacity when the superheat value reaches 6K than the original 8K setting.

Sendhil