1 Tev 2 Evaporators

[Renato RR]

We just mount unit for climatisation on big supermarket.The manufacturer sent 4 big evaporators (125 kW cooling pover,1 x 1 in paralel) and 2 TEV s with external equalizer.
We made separation tube and conect then Tev on evaporators inlet.The sensing bulb is located after separation tube at the evaporators outlet (10 cm = 4" from end of separation tube).Used refrigerant is 407c.
I expect problem when heat exchanger gets dirty and asume that superheat level on each evaporator woudnt be equall.

Generaly opinion on this?

[US Iceman]

I would not recommend using one TXV for two evaporators.

How will the refrigerant flow be disributed uniformly into both coils????

I would expect unequal coil perfromance and lack of evaporator superheat control.

[Renato RR]

We have equal pressure drop on separation tube (equal lenght of each pipe,equal banding,equal evaporator).

[Cofreth]

Much better to install a suction accumulator for preventing liquid refrigerant flood back.

[TXiceman]

I would not attempt 2 evaps on one TXV. They willk feed different. Even with what appears to be physically identical piping you will have a slight difference in pressure drop. The same is true of the coils.

Have them do it the right way and use one TXV per coil.For the price of two more txv's you are gambling on wiping out a compressor.

I have seen this tried and it is marginal at the best.

Ken

[chiller563]

This is a very bad design. Under most conditions, even in the same ambient, each coil will have varying load conditions, i.e. one coil closer to the door, etc. If you sixed the expansion valve for the total load and one coil contains a different load the valve is going to go into a hunting scenario that it will almost never be able to overcome. If one coils load drops and the valve senses this it will begin to close, while trying to bring the superheat in the low load coil under control it will then starve the other coil and then try to open to. It would be wise to use two TEV's.

Chill

[US Iceman]

One TXV per coil is the preferred method. Attempting to save costs by using one valve (for multiple coils) will cost you more for service visits and frustration.

Using symmetrical piping for this is not the answer.

[Temprite]

Saw this on a self contained cheese case.

Two coils one valve

It never worked properly.

The end where the condenser fans were discharging there air was always starving and the other end was over feeding.

When they were taking the temperatures of the case the underfeeding end was always about 5 degrees higher in temperature.

Told them many times of the problem but they never got me to rectify it.

[star882]

Problems caused by using one TXV with multiple evaporators was actually one of the biggest concerns when Shivani was designing the cooling system for a 4 CPU Britney "server". Hence, there were 4 TXVs, one for each evaporator, along with an accumulator and receiver to ensure proper operation even during large load changes. And to top it off, there's also a PWM speed control circuit that monitors temperatures and adjusts the compressor power accordingly.

[Lc_shi]

the main concern is the unbalance of two evaporator loading which will cause the mass flow different. The inlet and outlet pressure must be equal, so the evap superheat is out of control that may one low loading evap make the Tev close. It's not a good idea but help you do brain exercise-

rgds
LC:-)

[william_wye]

Not good practice. Unbalances distibution on high loads.

[Blueboy]

don't do it! It'll cause you no end of trouble 2 X TEV is essential for this application

[chilled kiwi]

Sounds dodgy. If you cannot get more expansion valves, pipe two coils in series. Small tee flow evaporators do this. Works fine as long as the valve is set right and you don't run short of refigerant.

[chilled kiwi]

Note. The above won't work if you have a distributor on the evaporaters!!!!

[mbc]

for a lot of reasons use for each evaporator one tev especialy in larg system.