R410A TXV on 13 seer?

[chade]

I know what a TXV does, but is it needed on a 13 seer unit if that is the base standard now? If it is needed, then please tell me why.

Thanks

[docholiday]

depends on the system, if you want decent performance and reliability then yes, others may disagree.

Why would you not want a TXV?

[captainrat]

economy, efficiency, reliabilty & load compensation.
i would hope a 13 seer 410A system would come with a txv
if not ,its not worth having.
with it has to be charged properly to reap the benefits
i agree with doc
what system are you looking at ?

[duct dr]

I have'nt seen any 13 SEER systems that didn't have TXV's.
The only exception being Carrier gas coils, in which case you have to field install one.

[chade]

I am talking about a TXV added at evaporator coil... I know what a txv does and why we use them, but why would one be needed at coil with a 3 ton furnace and 2 1/2 ton a/c? Couldn't you get away with a piston at coil since it is 13 seer?

[gas1]

starting NOW you should use a TXV on all 13 Plus SEER units R22 or R410

[markj]

Originally posted by chade
I am talking about a TXV added at evaporator coil... I know what a txv does and why we use them, but why would one be needed at coil with a 3 ton furnace and 2 1/2 ton a/c? Couldn't you get away with a piston at coil since it is 13 seer?

Beside the evaporator coil where elso would you locate it?
I assume you mean a furnace with a 3 ton drive?
It will work with a piston but I doubt it will still be a 13 seer unit.

[chade]

Ok, that's what I am talking about, how is it that using a piston, it wouldn't act as a 13 SEER? Is it because R410A is higher pressure? I just want to know this to understand this better.

[docholiday]

The major efficiency savings is by optimizing the evaporator in the run cycle and slowing migration in the off cycle. Both on and off cycles are considered in the SEER calcs. A piston could be used with 410A, but not as easily as R-22 because the 410 has a wider operating range in head pressure. You would see more dead compressors than you see now.

[chade]

So a TXV on R410A is a safety precaution witch helps in the on cycle but slows migration in the off cycle? How would that differ from having a piston in it? Would it just wear out the compressor more?

[docholiday]

the piston has no control over superheat or off cycle migration. It's a hole that allows refrigerant through. A TXV controls the superheat (85+% of compressor failures are from improper superheat, either high or low). The off cycle leaves the liquid in the liquid line so at restart, your indoor coil is at operating temperature much sooner with less energy used.

A piston works by feeding more refrigerant when the outdoor temps are higher (loading the indoor coil), in mild temps, the outdoor pressure is lower, thus feeding less refrigerant into the evap. These are both good things but the problem is, the compressor is sitting there trying to pump vapor and along comes some liquid, OR the motor is looking for some cooling but cannot get it. They were ok for what they were but lack efficiency, performance and reliability of a simple TXV.

[haaar]

The thermal expansion valve can adjust on the demand of the evap. therefor its peek efficency has a much wider range, of inside loads and the ambient temp.

A FO is set for a medium range of a climate. Therefor it will only perform at peek efficiency under one particular set of circumstances.

So in order to achieve higher efficiency you have to have a TEV.