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Thread: ORI setting
12-27-2005, 08:54 PM #1
can you tell my the rule of thumb setting on a ori. should it not go under a pressure which relates to 70*f. also what type of problems or symtoms can i expect if this ori is set to maintain too low of a head pressure. I do live in a very cold climate and see alot of these valves ori, drop leg and hold back valves some slang names for them. thanks again
12-27-2005, 09:23 PM #2
ORI, known as the "hold back" and the ord, the "receiver thing".
The ORI, what it does is holds back liquid refrigerant so the condenser fills with liquid, thus reducing effective condenser surface, thus raising head pressure. Your minnimum head setting should be found through knowing at what pressure the the TXV will begin to go nutso. Whats the minimum delta P across the valve before it goes crazy. So what ever you guys set your racks at, thats up to you. But I will tell you now, I don't beleive in all this BS about lowering too much. I think it's so stupid. Yeagh yeagh yeagh, energy. Okay great. You spend 200 bucks less in power for the month, but I bet you have service calls spending more. Suffice it to say, I hate seeing a rack dialed way down. TXV's love full column and the rated delta p, that people smarter than me come up with.
The ORD. That keeps pressure on the receiver to push the liquid out of it, cause there won't be a whole heck of a lot in there, due to the fact it's all on the roof. That must be set at 20psi lower delta p of your hold back. Sporlan rule.
12-27-2005, 09:34 PM #3
what would be the norm on this setting. and yes we are told from high above to set up our racks with floating suctions and floating heads. i do agree with you at the same time the biggest energy savings in a supermarket is controlling the lighting. but besides the 70* temp that some chains go by what would be your thoughts on what you set these valves at. how do i know about delta p across my txvs is there a rule of thumb on sporlan,alco or danfoss valves. hey i am on here to learn please bare with me,thanks
12-27-2005, 09:53 PM #4Waiting Email Confirmation
- Join Date
- Feb 2003
- Austin, Tx.
I set them at 165#.....but in Texas it only gets cold enough to worry about the settings every so often.....which is not so often.....80 degrees today....some Christmas weather huh????
I agree with D....we have been told 140 is the magic number....but in my experience it just doesn't work....
12-27-2005, 09:57 PM #5
what type of gas are those pressures for, and thanks
12-27-2005, 10:00 PM #6
and please explain why it doesn't work is it because of not enough delta p across the txv
12-27-2005, 10:52 PM #7Waiting Email Confirmation
- Join Date
- Feb 2003
- Austin, Tx.
R22 is mainly what we have down here....some 408.....I really can't give you an explanation as to why...it just doesn't work. D has much more experience than I have and can probably give a better....scientific answer....LOL
No offense D.......
12-28-2005, 07:54 AM #8
All TXV's are rated with all their specifics. One of those specifics is, their effectiveness to a minnimum Delta P. What you have to do is find out what valve attached to that rack, cause there could literally be dozens and dozens of loads, you need to find the TXV(s) that have the lowest possible rated Delta P. Then set your head pressure. This is usually a known thing if you read through the paperwork in the rack room. If not, go down on the floor and pick out the smallest load (case), dig into it and get the TXV number, go to the book and find out it's rated Delta P. Say it's 80 PSI. So if your suction is going to be 30 PSI at the lowest built into your float setting, then add 80 psi back to it. 110 psi should be the lowest pressure to set head at. So give yourself some fudge factor and add another 10 psi. This is actually written in sporlan material if I am not mistaken.
There are guys who like to get real engineer on me who will say they can dial it down more than that. It's a long thing to get into about why. But there is a balance. You can go lower than the rated delta p, and reap some capacity. But that number is a tweak and see type thing. To arrive at that can be time consuming. And then of course going any lower, screws things up. If you stick by the rated delta p rule, your good to go. If you got the time, after you benchmark to the lowest rated delta p, try playing with it and dial down a bit more, and a bit more, till you see it effing up.
Real important here too is charge. The ORD set, Gas Defrost. All Superheats good. To dial in a horked up rack is an art. It's a hard thing to explain.
If you lower your head too much, you can create a situation where the liquid gets real lazy and hits the valve with less pressure and causes the valve to not feed properly. You will see hunting. You won't get that proper flash off as it goes through the orfice and distributor causing uneven feed of vapor and liquid. It will play hell on the case temp. She won't get it. You could be flashing before the valve. When the liquid gets that lazy it tends to flash. A host of other problems.
The whole reason for an ORI and D is to keep the head pressure high enough to prevent these kinds of problems. Don't lower the head so much that the ORI and D are just there for looks.
You arrive at your minnimum head setting by looking at what the minnimum Delta P you can run the TXV at.
[Edited by Dowadudda on 12-28-2005 at 08:13 AM]
12-28-2005, 07:59 AM #9
You have mistaken a float setting here with what I was talking about, about dialing a rack down on it's head. Nothing wrong with a float setting. Tottally different than what were talking about with setting minimum head.
12-28-2005, 08:18 AM #10
dowadudda thanks for your reply i was curious though on a conventional unit what pressure do you set your ori's at. do you try to maintain a certain temp on your units which you are satisfied with.80* ,90* ?
12-28-2005, 08:39 AM #11
Whats the minnimum delta p that TXV can do. Thats the head pressure you want. And if you want, reference on the PT chart to get the temp number.
12-28-2005, 10:01 AM #12
Back some 25 years ago or so when market systems designers started seriously playing around with floating head pressures it was clear that there was a need for better expansion valves to satisfy not only the maximum summertime loads (where everybody had always selected their TEVs) but to be able to control at the lower head pressures and cooler liquid temperatures experienced during the colder winter months. This is where the small, balanced port valve designed primarily for market refrigeration came onto the scene.
Valve selection has to take into consideration the maximum and minimum expected operating conditions of the system. You have to know the max and min liquid pressures, liquid temperatures and evaporator pressures ......then select a valve that fits both conditions within its rated design.
Using the values of the liquid and evap pressures and taking into consideration the piping pressure losses and distributor pressure drops at both conditions you get the available pressure drop across the valve at the max and min conditions.
From there you calculate a capacity correction factor for the max and min liquid temperature, go to the TEV rating chart and pick the valve size to do the job.
This all sounds like a lot to do just to pick a valve, but after you've done a few it's no big deal. We in the field assume all to often that the TEV in the case has been properly selected at the factory and improper sizing likely one of the last things considered when troubleshooting at problematic system.
If you don't have balanced port valves at all evaps, stick with around 180 psig minimum liquid pressure(90 Deg F saturated condensing temp) or do the math......and add 10-20 psig for good measure.
12-28-2005, 11:48 AM #13
Continuing on with this.......
To use this info to find where you should be with your ORI, look at the existing system schedule and find the highest evap temperature circuit and use this as your base point. Say a -15 Deg circuit on a LT R404A system. The evap pressure is about 20#. To that add approximately 15# for the expected distributor pressure drop at min load and you get 35#, or the outlet pressure of the TEV.
The Sporlan data I have shows a minimum allowable available PD for a BF valve at 80# so adding that to the 35# outlet pressure gives you a 115# inlet pressure. To that add for maybe 10# for line losses and you get your minimum receiver liquid pressure for proper operation. With an ORD set at 20# differential the ORI setting should therefore be 145#, or around 70 Deg F saturated condensing temp. This is basically what the store engineer had in mind for this system, if they stopped to actually figure it.
Similarly, Sporlan's minimum allowable available pressure drop for a MT R404A system is 60#. If your highest evap circuit is say 25 DEG (62 psig), adding 15# for the distributor, 60# valve PD, 10# for the piping and 20# for the ORD, the ORI setting should be around 167# or 77 Deg F saturated condensing temp.
Clear as mud, eh?