Star LPR questions

Hi guys, happy holidays:
Can anyone e-mail me an actual diagram of the piping and valve layout for a Star LPR system? I already have the basic line drawing found on Star's site, but it really doesn't explain much. I am mostly trying to understand the main TXV used in the main liquid line after the subcooling coil feeding the evaps and the type of "balancing valve" used at the evaporators. Are they like the manual hand exp, valves used in a liquid recirc system or are they electronically controlled? Also is the high side float bypassed during reverse cycle hot gas defrost? What type of high side float is used? If there is the main TXV in the main liquid line, what is the purpose of the float? I appreciate your time in helping me to understand this system there is nothing like it, that I know of, in the USA. Could the process, using reduced charge and halocarbon refrigerant be applied to supermarket refrigeration (in a modified form)?

Hi Kooltek,

There are several ways of using the LPR concept - some developed by Star and some by competitors looking for "improvements". Its important to appreciate the differences otherwise things can get a bit confusing - are you thinking of any site in particular? If so, let me know and I will try to find the relevant information.

In the meantime I can answer a couple of your questions. In a typical Star system there is a float at the condenser outlet controlling an expansion valve at the LPR's high pressure liquid line. This can be as simple as an LL float at the condenser and a solenoid plus orifice in the liquid line, but as you can imagine there are loads of ways to make this more complicated. The valves at the evaporators are usually just shut-off valves - no regulation at all. If you feed high pressure liquid to the evaporators then it is necessary to have some control there - and this in turn requires some method of sensing small amounts of overfeed at the evaporator outlet (kind of like "negative superheat" if you see what I mean). This is pretty difficult - and I suspect that something like this would be required for supermarket display cases. Small LPRs were used for supermarket cold rooms quite a lot in the early 1980s, and were very efficient, but fell out of favour when R-502 was restricted.

cheers

Andy P

Hi Andy:
Thanks for the information. I'm starting to get a handle of the concept. Like I said, to my knowledge there is nothing like this in the states, but the talk is to find creative ways to reduce charge yet keep head pressures and compression ratios as low as possible. Secondary systems are still not being used that much (energy efficiencies the reason) and mass acceptance of CO2 is a long way off (although Sam's club and the Hill Phoenix Corp. have just come out with a prototype for supermarkets that is supposed to work very well). I thought something like the LPR system would fit the bill. I guess it is not as popular as it was during the flurocarbon era. Will it work with R404A or 134A? A detailed piping and control valve diagram would help me immensely in understanding the operation. Do you know how I could go about obtaining one? Thanks again for your time.
Kevin

Hi Kooltek,

LPRs work fine with R-134a and R-404A - we've done quite a few of these - just as good as with R-502. There are two big advantages over ammonia: oil return is much easier and distribution between and within evaporators is much easier. Distribution is the main reason that the concept does not really suit a supermarket with multiple display cases, because typically the expansion valve would be back at the pack in the plant room, not at the evaporators. If you send me an e-mail address I will be able to get some more info for you - but maybe not as detailed as you are looking for

cheers

Andy P