Low condensing temperatures

[crocens]

I have a question. all compressor manufacturers tells that compressor can work e.g. at minimum condensing temperature 30*C. My question is what can hapend if i run such a compressor with condensing temp., lets say, 10*C? I know, that compressor should have very light work then. So why manufacturer forbid it, what can go wrong?

[RANGER1]

crocens,

What type of compressor,piston or screw?

[AlexG]

Your compressor doesnt work alone. It works in the systeme - compressor, evaporator, expansion valve...
So if you dont want to have LP fault maintain condensing pressure above 30C

[crocens]

RANGER,
in all types, piston, screw and scroll. I would like to know why to low condensation temperature is forbiden in some/all types of compresor. If in some of theme it is allowable then in with one?

AlexG,
I know it very well :) i like to build and test some of my ideas, now i have few ideas to build system on Very low condesing temp...

[RANGER1]

crocens,
I'm sure lots of condensing units run with below 30 C condensing in winter.
As long as system components like AlexG says, can maintain balance.

In industrial we do it all the time.

If there is other reasons I don't know what they are (compressor wise).

[crocens]

Here where I live (Poland) you cant see many (I should say there are almost none) systems designed for energy savings. Maybe heating water is popular.

But i belive there can be better way to have savings, expecialy when you have no water to warm from condensator.

I like to build some of my ideas and check them.
However i work only for 7 years... i am 26 years old and I still need advices from this forum (the best polish forum about refrigeration SUCK to the 10th power...)

So as long as the system is balanced there is no danger to go for a low condensing temps.
And how about oil? wont be any problems on that field? I will chec it by my self tomorow.

Thanks.

[mad fridgie]

Yes there are problems, with very low compression ratios.
You can get valve bounce, where there is not enough pressure to closes discharge/suction valve
You can also get premature liquification in the the compression cycle, which can cause hydraulic issues within the compression mechanism.
Also some machines need pressure difference to ensure correct internal oil flow.
With screws the VI also comes into play (not my feild)

[mikeref]

Some info about the subject.http://lvhvac.com/cope_bulletins/4-1334.pdf

[RANGER1]

Some info about the subject.http://lvhvac.com/cope_bulletins/4-1334.pdf

So it can be done, good article mikeref.

[mikeref]

Ah, thankyou Ranger 1, good to see feedback on research is appreciated. Always ready to help:D.. Mike.

[crocens]

mikeref and ranger1.

Thank You very much for your replays!
All your advises and links are very helpfull.

[JoeAT50A]

Not at all, go for it crocens, hopefully we could have a sort of COP 10 air-conditioners in near future.
Anything is possible, but nothing is easy, RE forum members are always ready to help.

[750 Valve]

I would say that screw comps without an external oil pump and rely just on pressure difference could encounter problems if the compression ratio is too low, there will be not enough oil fed to the comp to serve its needs. This being said it is worth checking with individual comp manufacturers as there are many comps that CAN operate at low compression ratios (as booster comps and as part of a 2 stage system).

[Peter_1]

If your components (like SV and TEV) are selected for low DP's, then you will not have problems. We have plants running at a DP of 5 bar with very high COP's (Bitzer pistons and standard Danfoss controls).

Some oil separators needs a certain flow at a certain temperature to work well. Check this.

A screw needs also a certain discharge temperature to heat up the oil to design conditions.

If you reduce your HP, then your COP will increase a lot. But..the biggest savings is trying to increase your LP. The savings will be a lot bigger with increasing LP compared to the same HP pressure decrease.