Is it better to use cap tube for small capacity?

[david2008]

Because for TEV system, there will be pressure difference between two side. Small compressor will not start. Correct?:p

[GXMPLX]

Hi,

No, you can always unload and start a compressor.

If the thermal load is too small maybe yes but cap tubes are best used for constant thermal load and/or limited refrigerant charge.

Not for nothing some places are not using cap tubes anymore TEV are more efficient.

[nevgee]

Even so, It's always best to have a time delay relay to creat a rest period after the compressor has stopped and before it starts up, to allow the system pressures to equalise. If you try to start the compressor too soon after it has stopped then there will be a pressure difference between the high and low sides, this will probably cause the compressor to stall, and possibly take out a line breaker.

[david2008]

Thanks for reply. Will the pressure difference disappear if waiting more time? How to unload a compressor?

[US Iceman]

To my knowledge, small compressors, using cap tubes for expansion devices, do not have capacity control for unloading. If the compressor is off for a sufficient period of time to allow the high and low side pressures to equalize, it is essentially starting at no load (briefly).

If you try to start it before the pressures ahve equalized it is trying to start against a load (the pressure differential that exists at that specific time).

[GXMPLX]

You guys need to let your imagination fly once in a while!


Wait with a timer, more usual in Europe than here but possible.
You can use TEV with bleed (a bypass orifice) to equalize quickly
Use a small capillary in parallel with the TEV
Bypass with a solenoid valve that opens just before energizing the compressor (not usual)
Or not equalize and use a start capacitor to improve compressor torque
Set the control to start with a high enough suction pressure for the compressor not to have problems.
Use controls with mechanical delays

[US Iceman]

...TEV are more efficient.


Why, and based on what?

[GXMPLX]

Why, and based on what?

Vox populi vox dei!

[US Iceman]

Nec audiendi qui solent dicere, Vox populi, vox Dei, quum tumultuositas vulgi semper insaniae proxima sit

Et tu, Brute?:D

[GXMPLX]

If thermal load goes higher (condensing constant) a capillary tube reduces flow because it has less pressure differential.

TEV do the opposite, if thermal load goes up it senses more superheat and injects more refrigerant suction pressure goes up, thus adapting better to thermal load and therefore are more efficient.

The good thing of capillaries is that they protect the compressor better from overloading than TXV.
For this you should know that your motherland passed a bill requiring TXV to be used in all US manufactured air conditioners, because TXVs are more energy efficient, causing a word shortage of TXVs!

This is a test right?

Save yourself 25 bucks and read:
http://ecaaser3.ecaa.ntu.edu.tw/weifang/hp/Influence%20of%20the%20expansion%20device%20on%20the%20performance%20of%20a%20heat%20pump%20using%20 R407C%20under%20a%20range%20of%20charging%20conditions.pdf

[GXMPLX]

Quoque fili?

[david2008]

Save yourself 25 bucks and read:
http://ecaaser3.ecaa.ntu.edu.tw/weifang/hp/Influence%20of%20the%20expansion%20device%20on%20the%20performance%20of%20a%20heat%20pump%20using%20 R407C%20under%20a%20range%20of%20charging%20conditions.pdf

Good article!

[david2008]

You guys need to let your imagination fly once in a while!


Or not equalize and use a start capacitor to improve compressor torque



If the compressor is RSIR, not capacitor start, can we add a separate capacitor?

[GXMPLX]

If the compressor is RSIR, not capacitor start, can we add a separate capacitor?

Yes generally you can, but this is a question the compressor manufacturer or it's rep has to answer.

[GXMPLX]

Nec audiendi qui solent dicere, Vox populi, vox Dei, quum tumultuositas vulgi semper insaniae proxima sit

Et tu, Brute?:D

I can't answer, rule 6!

[nevgee]

U might get away with a hard start capacitor like the SUPCO SSP version, they're supposed to help "kick" the motor up.
We have used sol valves to relieve pressures on small units with good effect. But usually a delay timer which then limits the compressor to minimum starts / hour is an added safe guard.