electronic expansion valve issue

[Lc_shi]

Hi sir,
Could you tell me your idea of how to match EXV with variable frequency compressor? which paremeter is good as control point?

rgds
LC

[Double V]

Hi LC

I'm not sure if i'm thinking along the same lines as what you are but you should size your valve at full load. Most EXV's are able to operate down to 10% of it's rated capacity quite accurately. As the capacity of the compressor drops your valve should shut down accordingly

[martind]

There are more approaches to control electronic expansion valve, as far as I know:
1. Two temparature sensors before and after the evaporator. Then it controls the superheat just like the normal thermostatic. It works quite fine also with variable speed compressors. This method uses also the ALCO EXV Valve with its driver.
look at this flyer (http://www.emersonclimate.com/Canada/pdf/EXD-Flyer04Eng.pdf)
2. Indirect superheat control according to discharge temperature after the compressor, but this method require special treating at frequency change as the response is slower. I do not recommend this. I think this is used only for budget reasons as there is less inputs. (Daikin Inverter Splits uses this method)

[frank]

(Daikin Inverter Splits uses this method)

From all the information I have, based on the Daikin training courses, this is an incorrect statement.

I would be interested to see the information you have.

[Walshyd]

As with any expansion device it is selected based on the tonnage/kw capacity and specific to what ever refrigerant the unit is operating on but you need correct controls in place if you where to replace a txv for a exv

[Lc_shi]

Hi dear all
Thanks for your information.

Frank,
How about Daikin split unit? Do you have some information?

rgds
LC

[martind]

to frank:
for example SiE04-306 Inverter pair wall mounted type B-series

[martind]

OK, maybe there could be some misunderstandig me, because I wrote, that only discharge temperature is used as controlled value.
If I wanted to be exact, I should write, that there are thermistors on the evaporator and condenser, and from these temperatures is the target discharge temperature calculated.

[frank]

Martind

I know understand what you were trying to say :)

[Lc_shi]

Hi Martind,
My understanding is the valve opening decided by compressor frequency and the evaporator superheat. I'm not sure if there is a control table inserted in controller. What about daikin's controller? thx

rgds
Lichuan

[martind]

We are leading this thread wrong way. It does not matter, how the proprietary control works, I used it only as an example. You cannot buy the valve and driver working this way (at least in our territory).
I did not program the controller, but there should be something :) I think there would be some given shift (so not the absolute, but the relative value of the opening)
Let it be, if you want to use electronic expansion valve, use the standard control, as I mentioned e.g. Alco or Danfoss.

[Peter_1]

My understanding is the valve opening decided by compressor frequency and the evaporator superheat. I'm not sure if there is a control table inserted in controller. What about daikin's controller?
I should say Lichuan, whatever the frequency of the compressor may be, the EEV has to be regulated in such a way that the superheat remains the same.

[Lc_shi]

Hi Peter,
Yeah. Keep the superheat same at any frequency. It's the advantage of EEV ,for TEV ,I think it couldn't control the same superheat.

thanks for Martind's offering good opinion

rgd
LC-:)

[Peter_1]

I was told by someone of Mitsibushi Belgium that they measure twice temperatures to control the EEV in the VRF but one temperature is converted via the software in the machine to a pressure.

They have installed somewhere - haven't seen it only but on the drawings - a small capillary which injects the liquid in a small tube. In that tube is one of the 2 previous mentioned themistor installed.

Due to the small isolated tube and the small amount of liquid, there's almost no heat exchange, so they're measuring almost precisely the evaporating temperature which they then convert to evaporating presure.

They avoid with this an expensive pressures sensor.

[maguro4448]

Hi,
Any body can help me for Electronic Expansion valve of Streamline Muller Industries model 2GB403144,465-PSIG-32-BAR used on Carrier water chiller of 370 KW cooling capacity.

We got problem with this valve, the valve did not open properly on maximum compressor load.
The system always shut-off caused by low suction pressure.

Please help me. Thanks for your attention.

[cre8waves]

I have worked on a few carrier flowtronics with the EXV .you can check the driver board of the exv . I think the valves have like 15000 steps and work on a pulse signal generated from the board . Most of the time i change out the valve and solves the problem . they change the style of the valve a few years back .

[non-pro]

I know that I'm "dumbing down" the conversation with my question but I'm just a flakey salesman who is making an attempt to learn. Here's my question: Doesn't an EEV automatically set the superheat when used in conjunction with thermistors and a microprosser control board? Do the thermistors on the coil merely create algorithms to develop demand defrost cycles? I apologize for asking such a pedestrian question and I appreciate any insight given.

[750 Valve]

Firstly you need to know what a superheated vapour, subcooled liquid and a saturated vapour is, perhaps google the terms to find out the meanings.

In this instance we want to control how superheated the vapour is leaving the evaporator, to do that you need to measure the difference between the temp the refrigerant is boiling off at inside the evaporator and the temperature of the vapour leaving the coil after it has turned into a vapour. For an EEV controller to measure the temp of the refrigerant boiling in the evaporator it is best to use a pressure transducer to read the pressure of the refrigerant - refrigerants have a direct pressure/temp relationship therefore the pressure can easily be turned into a temperature (saturated suction temperature), a crude way to do it is to measure the temp of the pipe where refrigerant enters the evap but this has quite a few factors that affect the pipe temp and cannot always be used accurately. By measuring the pipe temperature of the vapour leaving the coil we can determine the superheat (leaving temp - saturated suction temp = superheat).

Too much superheat and we decrease the efficiency of the coil, too little superheat and we risk liquid refrigerant spilling out of the evaporator and back to the compressor which can damage the compressor. An EEV is merely an expansion device for metering refrigerant, the amount it meters in is dependant on the programming of the microprocessor. The microprocessor uses the thermistors (and hopefully a pressure transducer) to measure the condition of the evaporator and assess the superheat, from this information it uses some user programmable parameters along with inbuilt algorithms to adjust how much refrigerant is fed to the evaporator.

Hope this helps.