Regarding air-conditioning test rig

[jaisin2000]

Hi,

I have an experimental test rig, in which I am using a centrifugal constant speed compressor of about 5 kW.
The refrigerant used is R 134a. During a test run I notice the following:

1) Setting of FCU temp 19 C
2) Temperature and pressure after evaporator 20 C, 2 bars., respectively
3) Temperature and pressure after compressor 100 C, and 11 bars (sat temp 45 C), respectively
4) Temperature at the condenser inlet 80 C

My questions:
1) What is the reason for having such a high temperature after compression? A degree of superheat of 55 C!!

2) what shall be the reason for a loss of 20 C in temperature between the compressor and the condenser despite the copper tube is well insulated?

3) Any way to reduce the temperature after compressor?

Your kind response highly appreciated.

Thank you,
Jai

[sedgy]

ni jaisin.
question 2 why 20c drop in temp between comp =conden. when its insulated? tell me why is it insulated?
for what reason?
ques 3, anyway to reduce temp after comp , yes take the duckin insulation off, is this test rig water cooñed ?

[jaisin2000]

it is insulated for t reasons:
1) for preventing heat loss ( the copper tube between compressor and condenser)
2) to not to expose the very hot pipe,

the condenser is air-cooled

[vladsabin]

Hi Jaisin,

you could try using a Liquid injection Valve, to lower the comp outlet temperature...

[DTLarca]

1) What is the reason for having such a high temperature after compression? A degree of superheat of 55 C!!

I wonder if maybe the impeller speed is too for the current conditions?

[DTLarca]

I meant "too high". This would mean more energy than necessary is inputted to the discharge gas.

[DTLarca]

Hi Jaisin,

you could try using a Liquid injection Valve, to lower the comp outlet temperature...

This could cause liquid erosion of the impeller.

[vladsabin]

This could cause liquid erosion of the impeller.

Not if properly dimensioned, desuperheating or liquid injection valves are used for a lot of compressor types(hermetic, semi-hermetic, screw) where the same problem is possible.

[DTLarca]

Not if properly dimensioned, desuperheating or liquid injection valves are used for a lot of compressor types(hermetic, semi-hermetic, screw) where the same problem is possible.

We use them a lot on screws and more often now on low temp scrolls too. But these compressors are fine taking in droplets of liquid.

Of course anything properly selected will work because we can only say it is properly selected if it works. But how tricky would it be to properly select an injection valve, i.e. to make it work, for a centrifical compressor? I've never heard of it being done.

[vladsabin]

Yes it is true, it will be tricky, but still I don't think should be impossible.
Another option could be vapor injection, but this would need far more complex injection system.
On the other hand, you said that you are using such valves for scrolls. This is something new for me too. We are you using EVI(vapor injection) on scrolls, now we even use them in Heat Pumps. I due wonder what the differences between this two methods would be, regarding efficiency, envelope...