Maximum allowable Superheat

[hvaccaa]

Hi dear members,

I have joined this forum recently.

Can anybody tell the maximum/ minimum allowable superheat & suction gas temperature recommended for single stage R-22 sealed compressors for air-conditioning applications. To be specific the compressor in question is Bristol H2BG094DBE.

Please provide relevant web resources/ manufacture recommendations/ applicable standards for reference.

Thanks,

[Andy W]

Have a search on here http://www.bristolcompressors.com/

[Abby Normal]

For fixed metering I would say you could be anywhere from 10 to 33F. it depends on the actual load and the outdoor temperature

When it is cool out, there is a lower condensing temperature so less head pressure pushing refrigerant through the metering device and hence high superheat as the evap coil is somewhat starved.

As it gets warmer out , the condensing pressure will go up and this pushes more refrigerant through the metering device and this tends to push the superheat down.

However as it gets warmer out, it tends to get more humid out.The infiltration into the space tends to elevate the wet bulb somewhat and this increases load on the evaporator and pushes superheat up.

So with fixed metering it is a range of superheat that can be deemed normal, you really need to look at subcooling at the same time to assess the charge.

[hvaccaa]

Dear Abby Normal

The unit has installed a TXV to control the superheat of the system. However, the superheat is found more then 20F i.e. around 30-35F, whereas subcooling is around 18-25F.

[nike123]

Dear Abby Normal

The unit has installed a TXV to control the superheat of the system. However, the superheat is found more then 20F i.e. around 30-35F, whereas subcooling is around 18-25F.

Do you speak here about total or evaporator superheat?
Remove charge until you got 7-8K subcooling.
If your evaporator superheat is 30F and air flow is OK, then adjust TXV until you got 4-5K evaporator superheat.
Do you have condenser fan cycling?

[Abby Normal]

Dear Abby Normal

The unit has installed a TXV to control the superheat of the system. However, the superheat is found more then 20F i.e. around 30-35F, whereas subcooling is around 18-25F.

I would say with 30 to 35F superheat with a TX valve that you either have a very big load on the system, more than it can handle or your TX valve is undersized, it is wide open and there is not enough head pressure available to push enough liquid through the wide open valve and the evaporator coil is getting starved.

It also sounds like someone has givien it extra refrigerant as well to try and compensate.

It could also have some junk in the system clogging what enters the TX valve