LPR System

[kooltek]

Looking for some information on the Star LPR system and perhaps a good piping diagram I understand the concept of using the wet suction return in the LPR to subcool the condensed liquid in the coil mounted in the vessel. However I don't understand what type and the location of the "metering device" to drop from high pressure to low pressure and what balances the flow of liquid to each evap. How many evaps can be installed on a single LPR system and can this application also be applied to halocarbons as well as NH3? Thanks for the input

[Andy]

Looking for some information on the Star LPR system and perhaps a good piping diagram I understand the concept of using the wet suction return in the LPR to subcool the condensed liquid in the coil mounted in the vessel. However I don't understand what type and the location of the "metering device" to drop from high pressure to low pressure and what balances the flow of liquid to each evap. How many evaps can be installed on a single LPR system and can this application also be applied to halocarbons as well as NH3? Thanks for the input

Hi Kooltek:)
welcome to RE:)

If you send a PM to AndyP, his father was one of the original inventers, I'm sure he will be able to help you out.

Pressure drop is usually through a pair of solinoides with orifaces plates after them. Control is usually by a float switch mounted at the condenser outlet. The bleed solinoide comes on with the plant and the main solinoide is activated by the float switch, with time overides should the liquid at the condenser not make the float after a period of time.
A HP float won't work or any switch with a differential above 12mm, less is better 10mm or smaller if you can get it. There are other methods, but this I find is the most effective.

LPR systems are better as one LPR unit one cooler group. I have one site with three cooler groups and six coolers, this site always had problems with frozen coolers and poor defrosts. I changed the smaller coolers to DX with electronic controlled, keeping the larger group of coolers as flooded to overfeed liquid into the LPR for subcooling.

You can fit a max of 4 coolers in a group, but two is normal, with a simple balance pot on the expanded liquid line (much like the Kuba, Kuba Cal).

If you are thinking of LPR systems, better speak to AndyP, developing your on system is possible, but why re-invent the wheel:)

Hope this helps.

Kind Regards Andy:)

[Peter_1]

While searching for some info about LPR, I found this interesting link http://www.frperc.bris.ac.uk/home/about/je/Novel%20refrigerator%20IoR.pdf

What exactly is this system?
Did a search in this forum and there was alaready written something about it in 2005.

Is it the setup as in fugure 1 of the link I provided? If so, what about oil return to the compressor?

And how you'r sure you have 100% liquid? What if more coils are connected and several shuts off?

[Andy]

Hi Peter:)

this is a multi evaporator system that uses a kind of LPR (more a suction accumulator). An LPR has a recirculation rate of 1.1 to 1, in this case because of the number of connected circuits and the limited refrigerant charge, the recirulation rate would be hard to maintain, Isuppose the capillary tube helps, as it will reduce the volume flow to the evaporator should the subcooling decrease, controlling the level in the LPR.

Kind Regards Andy:)

[Andy P]

Looking for some information on the Star LPR system and perhaps a good piping diagram I understand the concept of using the wet suction return in the LPR to subcool the condensed liquid in the coil mounted in the vessel. However I don't understand what type and the location of the "metering device" to drop from high pressure to low pressure and what balances the flow of liquid to each evap. How many evaps can be installed on a single LPR system and can this application also be applied to halocarbons as well as NH3? Thanks for the input
Hi Kooltek,

Andy (Dunwoody) gave you good answers to most of your questions - all I can add is that the LPR as originally developed in the 1970s was for R-22 and R-502 (happy days) and they were much easier to build and operate than the ammonia LPRs we use now. The main reason is the high latent heat of ammonia, which results in the very low overfeed that Andy mentioned (typically 10%). On halocarbon it is more like 30-40%, so slight maldistribution between coolers or between circuits within a cooler is less of an issue.

If you have access to IIAR past papers you will find a couple in there - one from 1998 and one from 2003 (I think). If you need more info let me know

cheers

Andy P

[Peter_1]

Still see a problem with oil collecting in the receiver and not coming back to the compressors.
How's this solved?

[Andy P]

Still see a problem with oil collecting in the receiver and not coming back to the compressors.
How's this solved?
Hi Peter - you are absolutely right on oil return. With ***** it was quite easy - we used a distillation system to return small amounts of miscible oil to the suction line. With ammonia it is more difficult, but with PAO we have had good experience with automatic oil return. It seems that even though it is not officially miscible it can still return to the compressor because the pour point is so low. It seems to work well in practice, but I suspect would not be any good with mineral oil

cheers

Andy P