Issues with a Tyler Rack
Hey guys, I have an issue with a Tyler NC2 rack. Everytime i put a circuit into defrost it starves the last circuit of liquid. This system has a DDPR on it with a 20# differential. It also has the liquid bypass stat set at 70 that cycles a NC solenoid valve. On the dropleg between the condenser and reciever is another NO solenoid valve (it is not a OLDR) with an IPR and a check valve around it. It is also equipped with an OPR on the gas bypass line. This is a hot gas system not latent gas. The condenser fans are cycled off of pressure as follows: bank 1-190, bank 2-215, bank 3-225, bank 4- 240. Its 90F outside today and the discharge pressure is around 250psig. R404A system. I know im probably forgetting some stuff, so just ask for more info if needed. Why is it starving the last circuit?
Im starting to think hot gas defrost was not meant for the Natures Cooling racks. After all, in the manuals it doesn't even show the NC2 rack with a piping option for hot gas defrost. Just electric or off time. Is it possible the returning liquid from the defrosting circuit is at a higher pressure than the reciever, therefore holding the freon in the reciever and starving the circuits still in refrigeration. Not getting enough liquid return from the defrosting circuit(s)? And why would the N.O. solenoid be needed in the drop leg if the differential is already being created by the DDPR valve when something is put into a defrost? The previous company i know had the same problem because they piped the liquid line to draw from further up the liquid header. But wouldnt that just cause the next circuit in line to starve? :gah:
measure the pressure differential across the OLDR valve while it is in defrost and let us know what that is.
It doesn't have a OLDR valve. Has a NO solenoid valve on dropleg wired in with a NC solenoid on the receiver bypass line. Also has a DDPR on the discharge line which is creating a 20-25# differential when in defrost.
everytime these questions come up, I try hard to spend time to figure out things. I like to do this cause I think it is good practice to always think about these different rack arrangements. I try to challenge myself to picture what is going on with out going right away to the books.
So here I go try.
With out talking about valving arrangement yet. The basic concept of HotGas Defrost, is actuating the DDPR to raise Discharge that is routed to the defrosting case(s). The other downstream side of this DDPR is now at a lesser pressure, which means the condenser is at a lesser pressure, which means the drop leg liquid line and the liquid line manifold is/should be at a lesser pressure. All at a lesser discharge pressure than what is now flowing into the branch defrosting circuit.
So it goes down as high pressure, high temperature superheated vapor. The gas in this condition, becomes saturated in the defrosting case(s) rejecting it's heat to the frost and melting it, and condensing. Still at a higher pressure than the liquid manifold at the rack. So no we leave out of the case as liquid, and were flowing back to the rack liquid manifold cause were still at a higher pressure. This liquid now is going to be used by the operating liquid branch lines.
So what happens when there is no more frost ??????????????? Does that continuous supply of high pressure, high temperature superheated vapor continue to flow if it is not stopped somehow ???? With no frost to reject it's heat to, will it condense? How can it?
The point is. If we don't end the hot gas defrost, at the point in time that frost is no longer present, were feeding the liquid manifold with high temp, high pressure vapor right? Then are we not supplying that to the other branch liquid lines??
I am wondering if your problem is occuring at the beginning of defrosts, or torwards the end. I see this a lot on old hot gas systems where we don't use termination, and we set our defrosts by time only. And often technicians who are not fully realizing and capturing the idea of what hot gas does and how it does it, they miss this while diagnosing what might be a totally different issue as to why a case may have iced up, and arbitrarily extend defrost times with out understanding the harm they are doing.
Does anyone disagree with me so far?
if it was an oldr, you always check the differential with nothing in defrost. I use to fight this concept myself. I use to argue that you check it while something is in defrost. I mean after all real world right. Well. I am stubborn and had to prove it to myself. You can actually set it wrong when you do it with something in defrost. Did it. Checked it. Been there. Got the tshirt. I really don't know why exactly, but hey, once I did it wrong and checked myself I am a believer.
if it was an oldr, you always check the differential with nothing in defrost. I use to fight this concept myself. I use to argue that you check it while something is in defrost. I mean after all real world right. Well. I am stubborn and had to prove it to myself. You can actually set it wrong when you do it with something in defrost. Did it. Checked it. Been there. Got the tshirt. I really don't know why exactly, but hey, once I did it wrong and checked myself I am a believer. I realize the OP mentioned, but just want to point out, you set an older and actuate it for adjustment with nothing in defrost.
Thanks Dow . I think we all are here to LEARN. You are very clear on your comments. The Envirogard racks with hot gas defrost, I have, the returning liquid ( I hope) is piped to the condenser. Maybe NC2 feeds it back to the liquid header?. Like you explain everything we are able to think through these different scenerios, just in case we run into these problems. .Tyler, Rest in Peace.
NC-2 is a simple idea by itself. All by itself. I always have to remind myself that sometimes things work together, while other things have there own sequences.
It is also a brand. A marketing title. Tyler was famous for this. They would add a trick to a rack and call it something.
NC-2 is simply, if the drop leg is cold enough, rather then let that liquid sub cooling diminish routing it through the receiver, were gonna bypass that receiver and send that nice sub cooled liquid straight to the liquid manifold and bypass the receiver.
So forget that it has anything to do with Hot Gas just for a second. It's either open, or it's closed based on the drop leg temp. Period. Done. Finito.
One solenoid. One T-stat. Open or close. If drop leg is below 70, were bypassing the receiver. If were above 70, were not.
The Valve is NC, opens when we want it to bypass the receiver.
This is NC-2.
So, if that was not enough to be confusing. (I had to reference my manuals, for this next part I admit). They added some bull $hit to the NC-2 arrangement and called it "Liquid-FLO". Using the Same Stat were running the NC-2, we have another normally open solenoid on the drop leg between the condenser and the receiver. When drop leg is 70 or below, we "energize and open the nc-2 bypass, normally closed solenoid valve, and we also energize and close the normally open LIQUID-FLO valve. So. If 70 or below, were bypassing the reciever. if above, were not.
Now here is the kicker. Piped around this "LIQUID-FLO" normally open valve is an IPR, and a 20# check valve in series and downstream. Read that 5 times. The IPR and downstream in series check valve is simply a bypass around the "LIQUID-FLO". This is for maintaining minimum head pressure for hot gas defrost in low ambient. It's tough to wrap your head around all of it. I don't care how good you think you are, these systems, sometimes they can throw a guy a left hook to the Jaw. Especially if you had a rack deploying all the stuff that was drempt up.
Tyler Refrigeration had great intelligent and brilliant minds on their staff, and if you knew there systems, you could appreciate why they did what they did. But in the modern world, you just don't see this sort of engineering anymore.
I have a old book, that talks all about this stuff, that I do not see in the book on hill phoenix website. It has better explanations, and better pictures. I will try to get it copied into PDF and make it available. May take a few days. I have never found the same book online. It was Tyler Equalizer Rack book.
Thanks for the comments Dow. You may be on to something with the defrost termination. This is a new store, we did the install and also service it now. Set up is this 80s era Tyler rack with brand new freezer doors and walk ins. On startup we found that all the doors had the terminations wired backwards from the factory, so the defrosts are set up on time term until this fiasco between the manufacturer and us is figured out. Although this seems to be happening at the beginning of any defrost cycle. Is it possible not enough liquid is returning from the defrosting circuit to supply the rest? Is the liquid in the reciever not in play while defrost is occuring? Is line sizing or lenghth of circuits a possible cause of reduced liquid return? Should more than one circuit be in defrost at once?
That setup is exactly what I am working with! That pdf of the manual would be awesome! I agree that Tyler definetely has some interesting setups and that brilliant minds had to be at work to think them up. Wish I had one of their phone numbers though.