Bryan you worry too much.
what are you guys setting up var speed condenser fans at?
I have racks that have a cond setpoint of 155 (507). split condensers (100,50 and 25% split capable hybrid racks). Keeprite coil lead fan on the full time 25% has a variable speed fan that has a controler for 0 to 100%(actually 97%)speed in a 40psi range (none adjustable).
I have set some up for 150psi at 100% but I think I will have to go back when it gets down to -20 because I have a feeling it might be set a little low.
100% at 160?
got an idea? lets hear it
Bryan you worry too much.
Watts New, Ohm My, I been Electrically Commutated. Are U2.
usually 105 degr codensing temp is normal, so youll have to use pressure temp chart for refrigerant your using and determine pressure.
please read the original post. its a 155psi setpoint (67 degree sat temp.) Hybrid racks keep the head down for energy savings. its not a convensional rack
run your splits off ambient.
The inactive coils in split, those fans stay off during split.
The drive looks at drop leg temp.
Splits are controled off amb temp. but the fans are controled by discharge pressure. Split fans dont run when in split. Just trying to find a happy medium for the lead fan non splitting setpoint so that its actually runs on when its warmer than -20 out. if you set the var speed down at 150 you at least have the fan run most of the time. If you set it up for 160 or more it turns at or less than 50% speed since the controler ramps up more fans to keep the head at the 155 mark.
can you explain what you mean by a hybird rack
Its best to start at the beginning. a "Conventional" rack uses a recever as a holding vestle and all the systems pull off of the recever for there liquid. On a Hybrid system the liquid has a straight shot right to the liquid headder and the recever is more a surge tank than anything else (excess refrigerant is dumped into the recever) Now this in on itself is not new or anything special (Hill has been doing surge systems for years) What is special is the desired head pressure (155psi R-507) and the recever is not tied into the liquid line only. It also has a dump line run into the suction headder to empty the recever. Lost yet? I will explain.
What this does is takes full advantage of the available sub-cooling available from the condensers to have a more efficent store. For all intents and purpose the rack is a critical charge. Too much gas and you will have excessive sub cooling. The controler (E1 and E2 on the racks we have right now) will dump the excess gas into the recever in order to reduce sub-cooling. Not enough sub-cooling and it dumps the recever contents into the suction. Now its not dumping ALL the gas at one time, it is just a 3/8" line from the liquid line into the recever threw a solenoid, and a 3/8" line into the suction headder threw a solenoid valve and a fixed orfice.
Now as you may have guessed with a Hybrid system the "Kool gas" method is out the window due to the fact that, well there is no Kool gas. Its all Hot gas defrosts. and the piping for this has to do some interesting things as well due to the fact the returning gas from the system on defrost cannot just dump into the liquid headder since the Liq headder is actually the same as the condensate (drop leg) line. The returning gas goes back into the Disc line after the DDR (Defrost Diff Reg).
The racks have 2 condensers each. 1 condenser is what is called the 50% and is the first stage to drop off. That leaves 1 other condenser that is split. So on the cold days we are down to only one half of one condenser of the two with a variable speed fan as the lead.
Clear as mud?
How do you send out Hot gas to the floor, and it not come back through the check and into the liquid header? I don't get it. And if your bringing back as your describing, wheres the differential for flow back then. I just aint getting it. Got a piping diagram.
In a normal hot gas setup or even kool gas. You diff your liquid 25 psi so your liquid manifold goes lower than discharge, suction stop your epr, open your hot gas then you send er out to the case through the DDR, (1 extra pipe), shooting it through backwards through the case, comes out through a check and back into liquid line. Your flowing back from the case cause dishcarge is now higher than liquid. Pretty shoddy way of explaining but I would think any other rack guys could follow.
I just don't get how your bringing it back. Or do you got one pipe out one pipe back somehow. I haven't been on earth long enough I guess.
And for taking liquid from the receiver to dump to suction manifold, thats wild. Are you sure there not trying to desuperheat the suction manifold using liquid and that it hasn't nothing to do to control subcooling. Why would anyone care if liquid is stacking to begin with. If my cases are satisfied thats a good thing.
I am having a hard time understanding your problem with your head. If I understand you right you got split. Then you cycle the fans on the active coils on head pressure setpoints? then you got freeq drive? Whats the point of freeq drive if your fan cycling? I suppose you could sit there and dick with it till you get the right settings and a nice tight head pressure but your not accomplishing anything but making yourself miserable that way.
And why does it have to be 155. All you want is 67 Saturated Liquid temp. Your drive should be looking to ramp on that sensor input.
You got me interested in this now.
none
[Edited by bryan l on 03-24-2005 at 01:15 PM]
sounds to me what you are calling a hybrid is what tyler calls enviroguard.
Purpose for having frequency drive on first fan is to provide more constant liquid temp in low ambient conditions. Also keeps that first fan from bangin' on & off constantly.
We have been installing drives on condensers with 10 or more hp worth of fans on the whole condenser. Each fan is individually controlled by contactor and ramps up and down based on ambient/TD setpoint. At full load, all fans are at 100%. At setpoint you might have one fan running @ 50%.
It works really good in the cooler temps, but once summer hits, TD can never be hit and they run at 100% all the time.
Originally posted by press1
Purpose for having frequency drive on first fan is to provide more constant liquid temp in low ambient conditions. Also keeps that first fan from bangin' on & off constantly.
We have been installing drives on condensers with 10 or more hp worth of fans on the whole condenser. Each fan is individually controlled by contactor and ramps up and down based on ambient/TD setpoint. At full load, all fans are at 100%. At setpoint you might have one fan running @ 50%.
It works really good in the cooler temps, but once summer hits, TD can never be hit and they run at 100% all the time.
So, why even bother with VFDs, if the final statement is true? They're a total waste of money if they're not saving any money, in a condenser application. If you're running full bore all summer, any savings are offset, and there is NO return on investment. A cheap valve or two would solve any lower ambient capacity control issues.
[Edited by condenseddave on 03-26-2005 at 10:50 AM]
Dave, not true in the climate Bryan is talking about. When it hits -40 (usually once or twice per winter), the condensor will be flooded 99.9% with 1 fan running. The liquid temp. ends up being WAY too cold. Cycling the 1st fan will eventually kill the condensor so VFD tends to be the best option.
Canadian climates (110 degrees to -40 degrees) can be quite challenging to for 'dependable' equipment.
Originally posted by mspanky
Canadian climates (110 degrees to -40 degrees) can be quite challenging to for 'dependable' equipment.
When I read 110 to minus 40 .... Texas ain't such a bad place to live afterall.......
Still not seeing it.
Cycling the 1st fan will only kill an improperly piped condenser.
We have a BUNCH of condensers installed back in the 80s still running at a 250 psi discharge pressure, cycling fans only in the winter that have never had a leak. They are piped properly.
Every header-tube sheet leak I've ever seen (and I have seen a LOT of them) were on condensers that weren't piped properly. (With and without VFDs.)
And if you're at -40, WHY would there be a fan running at all? Especially if the equipment is designed for 110 ambient. That makes no sense at all. Sure, the liquid will be cold, but, as long as you can keep it moving, there is NO SUCH THING as "too cold". In fact, the colder the liquid, the more efficient the system. You need to maintain a 50 psi delta P, which should be no problem whatsoever, unless the system load bottoms out, which, in all practical theory, would indicate that everything was damn near satisfied. If that were the case, still, no problem. This would be where proper splitting comes into play. Nothing saying you must split 50/50. We have several racks that split in 15% increments, and the loads are all over the place on them. Never have low head alarms, crashes, etc. with them.
Again, if the condenser comes up to full speed, and stays that way for months at a time, the high cost of installation and service for variable frequency drives on the fans is lost. No payback. Not ever. No way, no how. If single speed fans do it, but the coils are split in the winter, a fraction of the money has been spent, to save the same amount of electricity.
Proper splitting and capacity control from the getgo is a much better answer than vfds. Ambient be damned. Proper design and installation is the proper answer.
But, is that an accurate indication of the actual ambient in Bryan's part of Canada??????????
We swing from -10 (At the WORST) to 100, (At the WORST) but generally stay between +15 to 85.
That's what I was thinking, too.Originally posted by mccool
Bryan you worry too much.
I would probably set the 100% end at 160-170, though, after hearing all the Canadian horror stories on this thread.
As far as condensing temps, metioned by another poster, they don't apply at all in this instance. The goal is not to shoot for some rule-of-thumb condensing temp, but to keep the rack inside design specs.
On your first comment, what are you meaning by "kill" the condenser?Originally posted by condenseddave
Still not seeing it.
(1) Cycling the 1st fan will only kill an improperly piped condenser.
(2) Again, if the condenser comes up to full speed, and stays that way for months at a time, the high cost of installation and service for variable frequency drives on the fans is lost. No payback. Not ever. No way, no how.
On the second, the condenser may come up to full speed during daytime hours, but will begin ramping again once nighttime comes around. And for those nights that don't cool down much, yes, they will run all day. And those times are fewer than a handfull.
The way I remember it, the energy saved by ramping a motor is not linear, meaning at 50% speed you are not using 50% of the energy, it will be more like 25%. I don't see how you can say there will be no savings.
You said something about raising liquid temp 10deg. Just to have to drop it an extra 10 when it goes through the subcooler?
I don't want to come off negative, just that we live all over the country, energy incentives and pricing is different everywhere. Things that will work in CA might not work in Canada or Texas.
I can't say for sure, cause thats not what we do in these parts. We split on ambient, run the active condenser fans on drive to drive drop leg.
I guess I am confused. Big time. Cause your splitting we all see. Then your fan cycling like a normal deal, then your driving a fan on a freeq. The last fan. I just never seen it done that way. I don't get why. The shock of the condenser? To prevent that. Thats what you basically said. Just like Dave said, and how I see it is piping kills the condenser if not 95% of the time I have witnessed leaks at the tube sheet.
I don't know enviroguard. But I don't get this dumping into the suction manifold to reduce subcooling, or rather your saying that as subcooling increases, your dumping liquid off the receiver into suction. I don't get that. The only time I have seen anything close is when you got a horked out system, after 40 remodels and you do that to desuperheat suction manifold.
But I aint totally following this line. It's tough for me to read I guess. But you did explain about bypassing, so I am thinking your talking a surge style like receiver set up, depending on drop leg temp.
Dave, whats he saying?
Here I am sitting here feeling like an idiot. I have been killing myself with this enviroguard that junair was talking. Thats a tyler rack. Period, with, I remember this, Natures cooling.
Okay so, no big deal now that i see this pig in my head. And you need to be real carefull on them. Like Dave was saying, that delta P can only go so low. I don't buy this crap anyway about running it into the ground. Just aint right.
The condenser set up you got still makes no sense to me at all.
Course I never chased a ghost at 3 am that bad. -40? WTF. Who wants to be a refrigeration guy in -40.
In your behalf, I bet it's harder than hell to keep that liquid moving on a windy day. Screw that. I'll take the winters I get and shut up.