High superheat TXV

[desA]

A conventional adjustable TXV, for example Alco brand, will allow a maximum superheat setting of around 10.8-11.35K, at evaporator discharge.

I am searching for an adjustable TXV which will allow stable control at superheats higher than this, perhaps as high as up to 14-15K.

The intention is not to use a suction-line heater for this application.

If there are alternative control-valve/sensors that will allow these high superheats to be reached, then I'd be interested as well.

[Magoo]

Hi DesA
have looked at using an Air conditioning rated TX valve, that operate at a higher superheat range. Sporlan do a CP100 txv cap.
magoo

[desA]

Thanks so much Magoo. I'll follow up on the Sporlan CP100 TXV - much obliged.

(I've tried adding to your reputation, but it tells me to keep spreading it around first

[Peter_1]

Perhaps an electronic EEV like the E2V of Carel, not that expensive.

[desA]

Thanks very much Peter_1 - that's a good lead. Many thanks.

[HallsEngineer]

Danfoss ETS and controller we have controlled superheat at 25'c

[Peter_1]

You're right about the Danfoss but compare once the price for both?

[desA]

Danfoss ETS and controller we have controlled superheat at 25'c

Thanks very much, HE.

Will check prices of all options over here.

[desA]

Hi DesA
have looked at using an Air conditioning rated TX valve, that operate at a higher superheat range. Sporlan do a CP100 txv cap.
magoo

What is the maximum SH the Sporlan CP100 TXV can be pushed to?

[desA]

Are there any other non-electronic TXV's with extended super-heat capability?

Are for instance, stronger springs a possibility, for instance, for the Alco, Danfoss, Sporlan series TXV's?

Would alternative bulbs be of use? The refrigerant in use is R-134a.

[Gary]

Are there any other non-electronic TXV's with extended super-heat capability?

Are for instance, stronger springs a possibility, for instance, for the Alco, Danfoss, Sporlan series TXV's?

Would alternative bulbs be of use? The refrigerant in use is R-134a.

I am curious as to why you would want higher superheat as this would reduce the mass flow and cause the compressor to run hotter?

[Gary]

You might consider switching to an AEV, set the Te,sat where you want it, then control superheat with fan speed. The higher the fan speed/heat load, the higher the superheat.

[desA]

I am curious as to why you would want higher superheat as this would reduce the mass flow and cause the compressor to run hotter?

There is method to my madness - the Magoo SH rule.

Most conventional TXV's, cannot supply enough superheat to reach the Magoo-rule requirements.

At this point, the additional superheat penalty is not a concern & the compressor power is not affected.

[desA]

You might consider switching to an AEV, set the Te,sat where you want it, then control superheat with fan speed. The higher the fan speed/heat load, the higher the superheat.

That's a very useful thought - thanks for that. Mmhh...

So, the AEV controls the Te,sat using mass-flow to maintain pressure. The fan speed adjusts heat input & hence superheat. Ok?

[desA]

A TXV with MOP - revisited:

Can we review exactly how this works?

Acts as a normal TXV until a certain limiting pressure (determined by MOP setting) has been reached, then TXV begins shutting back mass-flow & allows the superheat to drift upwards, in the process.

[Gary]

A TXV with MOP - revisited:

Can we review exactly how this works?

Acts as a normal TXV until a certain limiting pressure (determined by MOP setting) has been reached, then TXV begins shutting back mass-flow & allows the superheat to drift upwards, in the process.

Mmmmm... not quite right. When the bulb pressure reaches its limit it cannot open the valve further, thus cannot increase the mass flow further. If the heat load then increases further, the superheat increases.

[Gary]

There is method to my madness - the Magoo SH rule.

Most conventional TXV's, cannot supply enough superheat to reach the Magoo-rule requirements.

At this point, the additional superheat penalty is not a concern & the compressor power is not affected.

I'm thinking 60-70% of dT would work better than 60-70% of TD, but again this is a rule of thumb and has its limitations and exceptions.