txv vs humidity

[paul42]

Simple question, probably the answer isn't as simple.

If you have two almost identical systems, and the difference is that one has a TXV valve, which system will remove more humidity from the air? Or does it make no difference?

[bama 101]

If both are properly charged under same conditions they will be very close but under all conditions txv might have slight advantage

[bama 101]

Also depends on air flow .but you did say same which that is what i thought

[NormChris]

Moisture removal depends upon coil temperature, coil surface area and airflow rate. Plus, compressor cycling and running time. The metering device has nothing to do with it.

[RoBoTeq]

All other considerations being the same, a TXV metered system will remove humidity better by keeping the evaporator coil colder.

[NormChris]

Originally posted by RoBoTeq
All other considerations being the same, a TXV metered system will remove humidity better by keeping the evaporator coil colder.

Colder or fully flooded?


BTW, I burned the disk I promised you but have not gotten to the post office with it.

Norm

[Panama]

Originally posted by RoBoTeq
All other considerations being the same, a TXV metered system will remove humidity better by keeping the evaporator coil colder.

If the coil is kept colder, wouldn't that make the TXV system less efficient?

[bama 101]

My question is if with both metering devices you have same superheat and same compressor as was said and of course same BTU output ,same airflow they would be same humidity removall considering the coil is the same temperatures

[BaldLoonie]

Often under cooler outdoor conditions, expecially if warm & humid inside, a fixed orifice system can have very high superheat and be properly charged. Superheats upwards of 30 degrees can be normal these days. If you have 45 degree entering refrigerant, that means that part to 1/2 of your coil could well be above the dewpoint and not dehumidifying. But the same system with a TXV will run around 15 degrees superheat and have a much colder coil. That's a more efficient use of refrigerant.

[beenthere]

Bama.
A txv will attempt to manitain the same superheat under all load circuimstances.
A pistons superheat will change as the load changes. So you wouldn't have the same superheat for both devices for the full run cycle.

[NormChris]

Originally posted by BaldLoonie
Often under cooler outdoor conditions, expecially if warm & humid inside, a fixed orifice system can have very high superheat and be properly charged. Superheats upwards of 30 degrees can be normal these days. If you have 45 degree entering refrigerant, that means that part to 1/2 of your coil could well be above the dewpoint and not dehumidifying. But the same system with a TXV will run around 15 degrees superheat and have a much colder coil. That's a more efficient use of refrigerant.

You are right Loonie. Thanks and well stated.

Norm

[paul42]

I want to thank you all for the lively discussion of the subject - especially Loonie - a name I have come to really respect on this forum.

The question was asked because on another forum, someone accused me of being a moron because I stated that a system with a TXV would do a better job of removing humidity. I may be a moron, but I was pretty sure that particular statement was not the smoking gun.

thanks again.
Paul

[RoBoTeq]

Originally posted by NormChris

Originally posted by RoBoTeq
All other considerations being the same, a TXV metered system will remove humidity better by keeping the evaporator coil colder.

Colder or fully flooded?


BTW, I burned the disk I promised you but have not gotten to the post office with it.

Norm

Fully flooded is more accurate. Being fully flooded the coil maintains being colder over a fuller range of the coil which is what I am referring to as being colder. The main point is that more of the coil surface is below dew point temperature for a longer period of operational time.

Of course, Baldy did say it better.

Colder coils in of themselves are not less efficient. Smaller coils that are caused to evaporate more refrigerant quicker become colder and are less efficient, but still do a better job dehumidifying. Less humidity equals more comfort at higher temperatures.

High efficiency ratings take into consideration only the efficiency of the equipment at the optimum operational point of operation. Since higher efficiency systems with larger coil area require longer run times to operate at optimum efficiency, they do not truly operate more efficiently all of the time. Add to that the lowering of the thermostat to compensate for higher humidity and savings become quite a "relative" subject.