Multi-set TXV

[harry_who?]

Could TXV exansion valves be adjusted for more than one conddenser temperature/pressure and refrigerant flow rate ? If so. could these different adjustments done automatically or electrically by switching on/off etc ? Are they available on the market ?

Harry

[nike123]

Could TXV exansion valves be adjusted for more than one conddenser temperature/pressure and refrigerant flow rate ?




TXV control refrigerant flow to evaporator, not condenser
TXV control superheat and not temperature or pressure
Go back to study refrigeration basics (http://www.refrigeration-engineer.com/forums/showthread.php?t=19701) and what is function of TXV (http://www.refrigeration-engineer.com/forums/showthread.php?t=19701)

http://www.mediafire.com/?z2hxz3xlzhy

[nike123]

Could TXV exansion valves be adjusted for more than one conddenser temperature/pressure and refrigerant flow rate ? If so. could these different adjustments done automatically or electrically by switching on/off etc ? Are they available on the market ?

HarryAre you talking about Thermostatic Expansion Valves (TXV) or Electronic Expansion Valves (EEV)? Make up your mind.:confused:

[harry_who?]

Nike,

There is only one flow rate in the whole refrigeration cycle. It is the same in the evaportor, compressor, and condenser. If that will make you happy, assume it is the one in the evaporator. Condenser temperature together with compressor power and
evaporator temperature and flow rate determine the superheat you are talking about. They are all linked together and one can determine the other for the given cooling capacities and refrigerant temperatures.

What I asked is very clear. Change of the flow (in your terminolgy) to the evaporator from one value to another (and hence change of superheat and cooling capacity etc). Can TVX do that or do I need the Electronic one you mentioned ?

Thanks for you interest.

Harry

[monkey spanners]

Why ask questions if you know it all?

What do you want to achieve by making these adjustments?

ms :)

[nike123]

Nike,

There is only one flow rate in the whole refrigeration cycle. It is the same in the evaportor, compressor, and condenser. If that will make you happy, assume it is the one in the evaporator. Condenser temperature together with compressor power and
evaporator temperature and flow rate determine the superheat you are talking about. They are all linked together and one can determine the other for the given cooling capacities and refrigerant temperatures.

What I asked is very clear. Change of the flow (in your terminolgy) to the evaporator from one value to another (and hence change of superheat and cooling capacity etc). Can TVX do that or do I need the Electronic one you mentioned ?

Thanks for you interest.

Harry

If you have saturated refrigerant in condenser and evaporator than saturation temperature (and corresponding pressure) is determined by heat exchanger TD and air/water entering temperature and certainly not with variation of flow of refrigerant.
Since TXV and EEV are made to maintain required superheat, that mean that in evaporator we have saturated condition as long as we have any superheat.

Change of flow is achieved with change of compressor speed or some other capacity control method and not with TXV valve or EEV. Their task is to keep required superheat no mater what is flow.

So, your question has wrong concept in its base.

[mbc]

As you know capacity of TXV is change by differential pressure (( high side ( condenser pressure) and low side (evaporator pressure) For these reason we control the condenser pressure ) Might you can use this option for your case but you have to spend more time to adjust it and also your area temperature and your condenser capacity will allow you to do it.

[harry_who?]

Nike and mbc,

Let's assume that you are only controlling the condenser pressure and the superheat at the exit of the compressor. My question is, can one change the TXV setting at the flick of a switch so that a new condenser pressure and superheat temperature is achieved (assuming that the heat exchangers and the compressor system can deal with new loads imposed by the new setting) or can the TXV programmed to control its settings electronically ?

Harry

[monkey spanners]

Its a thermostatic expansion valve and not a thermostatic condensing valve.

If you want to alter the condensing pressure/temperature you will need to alter the amount of energy rejected in the condenser by varying the air or water flow across it. This could be by altering the fan speed or the number of fans running.

Why do you want to alter the condensing conditions at the flick of a switch?

[harry_who?]

Monkey spanner,

Because I am looking for ways of operating a refrigerant unit working at two cooling capacity so that the same system can operate store room either as cold room working at around 0 deg C or a freezer working at around -20 deg C. A multi set TXV which can change setting at the flick of a switch can help achieve this multi purpose storage with one unit.

Harry

[monkey spanners]

Aha! :D

If this was a project that i was working on i would give all the relevent details to my wholesalers technical department and get them to design the system for me ;)

A lot depends on the size of the room and your budget as to which options would best suit the application.

It may be worth starting a new thread with a title such as '0c/-20c coldroom design issues' as it would give members a better idea of the problem you are looking to solve.

ms :)

[nike123]

Aha! :D

If this was a project that i was working on i would give all the relevent details to my wholesalers technical department and get them to design the system for me ;)

A lot depends on the size of the room and your budget as to which options would best suit the application.

It may be worth starting a new thread with a title such as '0c/-20c coldroom design issues' as it would give members a better idea of the problem you are looking to solve.

ms :)
http://www.refrigeration-engineer.com/forums/showthread.php?p=161429 ;)

[monkey spanners]

Aha! :D

ms :D

[elliswyatt]

Pick up an EPR (evaporator pressure regulator) with a "wide open" bypass feature. At 0C the valve modulates to maintain a higher pressure in the evaporator. At -20C the bypass solenoid energizes and holds the valve wide open so the evaporator can run at compressor suction pressure. Parker A8B or equivalent will work well.

[gregd1401]

Why not try two TXV and solenoid valves in parralel. Just switch the required solenoid in to operate the TXV that you require.