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NiHaoMike · 01-02-14, 08:41 PM

I'm doing that on my experimental unit, by simply leaving the TXV set to a high (20F or so) superheat and using a resistor as a small heater. The resistor must make good thermal contact with the bulb or there will be lag that can destabilize the loop.

Another approach is to replace the sensing bulb with copper bellows (like the ones found in some refrigeration thermostats) filled with oil) and a stepper motor and gear assembly to electronically adjust the valve. That's best for reusing a TXV that has lost its sensing charge.

BTW, opamps won't give you that much advantage over a plain TXV. A microcontroller is the way to go.

EEVs are hardly cheap from what I've seen. TXVs regularly go for a few dollars each on surplus sites.

01-02-14, 08:41 PM	#5
NiHaoMike Supreme EcoRenovator Join Date: Oct 2008 Location: Austin, TX Posts: 1,154 Thanks: 14 Thanked 257 Times in 241 Posts	I'm doing that on my experimental unit, by simply leaving the TXV set to a high (20F or so) superheat and using a resistor as a small heater. The resistor must make good thermal contact with the bulb or there will be lag that can destabilize the loop. Another approach is to replace the sensing bulb with copper bellows (like the ones found in some refrigeration thermostats) filled with oil) and a stepper motor and gear assembly to electronically adjust the valve. That's best for reusing a TXV that has lost its sensing charge. BTW, opamps won't give you that much advantage over a plain TXV. A microcontroller is the way to go. EEVs are hardly cheap from what I've seen. TXVs regularly go for a few dollars each on surplus sites. __________________ To my surprise, shortly after Naomi Wu gave me a bit of fame for making good use of solar power, Allie Moore got really jealous of her...