Hot Gas Bypass

[jwasir]

Hi Guys,

I would like to know the % of HOT GAS that can be bypassed into the evaporator?

Also, I have a scenario where TX valve was not completely open and when HG was bypassed, the suction pressure didn't change.

I'll appreciate the comments.

Regards.

[powell]

Hi Guys,

I would like to know the % of HOT GAS that can be bypassed into the evaporator?


jwasir,

Here's a couple links to Sporlans technical forms explaining hot gas bypass. They will give you a good understanding of how a HGB valve works and how they are designed for a particular application.

Powell

Design literature: http://www.parker.com/literature/Literature%20Files/Parker.com/Literature/Sporlan/Sporlan%20pdf%20files/Sporlan%20pdf%20090/90-40.pdf

Operation and service: http://www.parker.com/literature/Literature%20Files/Parker.com/Literature/Sporlan/Sporlan%20pdf%20files/Sporlan%20pdf%20090/90-41.pdf

[US Iceman]

Typically the percentage of hot gas required is determined by the minimum step of compressor capacity if the compressor has capacity control increments,

or,

if the compressor has no capacity reduction then the hot gas would be sized for the percentage of load reduction you expect to see from the evaporator. Let's say the evaporator load has the probability of reducing to 50%. To keep the compressor operating satisfactorily the hot gas valve would be sized for 50%.

or,

you can use a variable frequency drive down to the minimum speed allowed by the compressor manufacturer.

[wambat]

To suppliment US Iceman, On air conditioning systems, the minimum allowable evaporating temperature that will avoid coil icing depends on evaporator design and the amount of air passing over the coil. The refrigerant temperature may be below 32°F, but coil icing will not usually occurwith high air velocities since the external surface temperature of the tube will be above 32°F. For most air conditioning systems the minimum evaporating temperature is 20°F to 25°F. However, when air velocities are reduced considerably, the minimum evaporating temperature should be 26°F to 28°F.

[US Iceman]

However, when air velocities are reduced considerably, the minimum evaporating temperature should be 26°F to 28°F.


I have seen this on refrigeration coils also. The return bends and deaders tend to frost up but the coil & fins stay relatively clean where uniform air flow exist.

[rcschebler]

The standard for % of hit gas bypass is no more than 50% of the compressors capacity. As far as your TX problem, the suction pressure should have gone up when the bypass valve modulated open. The addition of hot gas would increase superheat, causing the TXV to open to compensate. Check you TXV powerhead. Good luck.

[sailer]

Is this sys chill water cooled, too much cooling and the coil pressure drops that can cause the HGB to be unable to control .
What is the application?
Is the HGB adjusting it self or starting from a closed
position. On some systems you should not be
able to detect a pressure change with out digital gauges,{ if you can the unit is unstable}and the HGB should be replaced. Give the guys more info

[Aik]

The standard for % of hit gas bypass is no more than 50% of the compressors capacity. As far as your TX problem, the suction pressure should have gone up when the bypass valve modulated open. The addition of hot gas would increase superheat, causing the TXV to open to compensate. Check you TXV powerhead. Good luck.
If i not mistaken the standard for % of hit gas bypass is no more than 40% of the compressors capacity.

[Magoo]

I really dislike hot gas defrost system, should be re-named cool gas defrost and the evaporator then becomes a condenser and fires great slugs of liquid back to the plant room and low side accumulator.

[Brutus]

on a standard procedure or operation how can i know if the hot gas bypass is operating. thank you.

[jwasir]

on a standard procedure or operation how can i know if the hot gas bypass is operating. thank you.


Grab the HG line, it will be warmer/ hot!
Check the solenoid, if energised!