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Refrigeration question - Expansion valve regulation strategy
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Miyuki:
Hi folks, is any refrigeration expert here, or maybe just someone with better searching skills.

I'm trying to find out how are electronic expansion valves controlled in systems without pressure sensors when you have only temperature sensors.
With a pressure sensor, it is simple, you can calculate superheat and just open the valve more to decrease it.
But cannot find how they do it from temperature only, do they estimate pressure based on evaporator inlet temperature?
NiHaoMike:

--- Quote from: Miyuki on June 23, 2023, 07:51:44 am ---But cannot find how they do it from temperature only, do they estimate pressure based on evaporator inlet temperature?

--- End quote ---
That's actually a very accurate way to measure the low side pressure in steady state operation.
Miyuki:

--- Quote from: NiHaoMike on June 23, 2023, 12:36:27 pm ---
--- Quote from: Miyuki on June 23, 2023, 07:51:44 am ---But cannot find how they do it from temperature only, do they estimate pressure based on evaporator inlet temperature?

--- End quote ---
That's actually a very accurate way to measure the low side pressure in steady state operation.

--- End quote ---
It makes sense with proper coupling and insulation
I just wasn't sure if there isn't any hidden catch
Thanks
NiHaoMike:
I have done it with a diode connected transistor and a TMP513. It was at least as accurate as my Yellow Jacket HVAC gauges. (That was despite the fact I used R433b and had to interpolate a PT lookup table.) Even getting the condensing temperature was pretty easy by putting the sensor in the middle part of the condenser.
noidea:

--- Quote from: Miyuki on June 23, 2023, 07:51:44 am ---Hi folks, is any refrigeration expert here, or maybe just someone with better searching skills.

I'm trying to find out how are electronic expansion valves controlled in systems without pressure sensors when you have only temperature sensors.
With a pressure sensor, it is simple, you can calculate superheat and just open the valve more to decrease it.
But cannot find how they do it from temperature only, do they estimate pressure based on evaporator inlet temperature?

--- End quote ---

Sorry for the late reply I don't frequent the forum as much as I used to. There is nothing wrong with calculating Superheat by using sensors instead of transducers, most of the Japanese brands use this control for the expansion valve on their VRF indoor units. Two sensors minimum, midpoint of the coil for an approximation of evaporating temperature and exit of the coil for superheated temp. Better arrangements use an inlet sensor as well and calculate either Exit - inlet or Exit - midpoint to regulate the expansion valve. They will also ensure the inlet and midpoint sensors are on different circuits of the coil to take into account a blocked circuit. It all works great until you have a sensor that plays up and gives erroneous inputs when the unit is running...
You can calcualte superheat from sensors
 or I would have an
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