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View Full Version : compare ***** dx with overfeed system



COLD WANG
12-12-2006, 06:19 AM
in a factory with large cold storage and many blast freezer.the client has decided using R22, how to compare dx with overfeed system, which system is the best one? DX or overfeed? ;)

US Iceman
12-12-2006, 07:09 AM
Liquid overfeed.

These are much easier to work on and operate. And, if designed properly will use less energy than a DX system.

I don't think I have heard of very many new liquid overfeed systems being installed with R-22 though.

I might suggest the owner insist on using carbon steel pipe and no copper content. If the refrigerant leaks get to be too expensive he can always change the refrigerant to ammonia (which is a lot cheaper, at least here in the States).

COLD WANG
12-12-2006, 01:28 PM
hi iceman :
thanks for your reply, dx is less ***** charge than overfeed, dx is very simple .in your contry,***** liquid overfeed is very many few? why?***** is not available for overfeed system?

US Iceman
12-12-2006, 06:07 PM
You are correct, the refrigerant charge is much less for a DX system.

Simplicity is a strange issue. Overfeed systems have refrigerant pumps and these are frequently misunderstood or mis-applied. The hand expansion valves can be difficult to adjust for someone not familiar with them.

If the design person is aware of these issues, the overfeed system becomes very simple.

On the other hand, TXV's are also not well understood as most people tend to start adjusting these at the first sign of a problem.

You also have a minimum discharge pressure you have to maintain to provide a constant liquid supply pressure to the TXV's. Otherwise, their capacity will reduce.

The use of large "*****" overfeed systems has reduced greatly due to the impending phase-out of R-22 in the next few years. Other refrigerants would work, but at a greatly increased cost.

Ammonia is normally very cheap compared to the "*****" refrigerants.