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Thread: Restriction and no superheat?
06-19-2008, 07:17 PM #14Regular Guest
- Join Date
- May 2008
10 ton system with 4 distributor tubes - I find it is odd ? Did not say it is wrong
Circuit #1 and #2 -- are they tied together as one common suction line out of the coil ?
30 PSIG and 16 degree suction line temp -- that gives you 9 degrees super heat and not at NO SUPER HEAT
I can get the sporlyn part number on the distributor.
my TP chart at the time i measured this units superheat was zero. i am not looking at a chart now but i think 30psi R22 = 16-18 degrees F
This unit has two compressor circuits and condenser circuits no common piping. i would like to clear my confusion and understand what can cause this symptom.
06-19-2008, 07:56 PM #15Professional Member*
- Join Date
- Aug 2006
- Marco Island, Fl
Your super heat was 9 degrees, the TXV was doing its job.
You have a two circuit, 10 ton machine, probably 5 tons each.
The 75% of the distributors were clogged AFTER the txv. All five tons were going through only 25% of the evap coil, not allowing it to boil off properly, and keeping it a saturated mixture.
The resulting 9 degree superheat is a resulting mix temperature of the clogged passes and the good pass.
0 degree superheat could have been measured depending on where your sensor was located (possibly near active section outlet)
06-19-2008, 08:18 PM #16
If it's a Sporlan, check the distributor nozzle size if you change the TEV. and make sure it's correct per your Sporlan rep.
In my experience, the second stage circuit of an intertwined evaporator has less of a load on it than the first circuit.
BTW, if you have hot gas bypass, ALL distributor feeder tubes should be sized one size larger than without hot gas.
06-19-2008, 08:43 PM #17
The key to finding this type of problem is to first confirm proper airflow, which you did. Second, if the TEV is controlling superheat properly, then something is likely odd with the evaporator coil.
You can check for plugged circuits by simply measuring the circuit temperatures as they enter the suction header. If these temperatures are holding rock steady at the same temperature as your return air, you likely have a problem. If temperatures show some fluctuation and are below return air temperature, you know refrigerant is entering the circuit.
Last edited by Andy Schoen; 06-19-2008 at 08:54 PM.
06-20-2008, 08:55 AM #18
I get 9 degrees too
Depending on your chart and whether it breaks down per degree or in even pound increments, or some of them go by 2 degrees, you get 30 psi boiling point of 7 deg. (or one of my charts shows 29.1 psi at 6 deg. and 30.9 psi at 8 deg. ergo directly proportional extrapolation gives you 30 psi at 7 deg.). (however I never looked over the ranges on the chart and I'm wondering if I'm missing something from my high school chemistry pv=nrt stuff, because I would think that the boiling point would move proportionally with pressure, but as the temperature increases the boiling pressure difference in 2 deg. increments goes from 1.8 degrees in the range we're discussing here up to almost 6 psi change per 2 degree change near the high end of the temp chart. That's not exactly a logarithmic increase, but it is more than an arithmetic straight line, it's a curve, and I'm wondering what quantity in the equation is exponented or what am forgetting. for you theory guys)
And, for the bigger hammer more solder in us all, how did the three distribution tubes get blocked by solder? Not meaning to disparage the instalation of the new TEV necessarily because you said the symptoms were the same before and after the replacement, although one supposes it is possible that the TEV charge was low and then when you put a new one in but might have accidentally blocked a few distribution tubes that you got almost an identical situation. ironic isn't it. and or since this is only one year old, could it have been running like this all along and depending on the one working circuit?
As various other threads will attest, I was confused by a low load circumstance myself last week, thinking the TEV needed adjustment when likely most of the fan coils in the house I was working on were turned off.
Circumstances were similar but not identical. low suction (mine was 48 and temp was 27 deg so I only had a couple degrees of superheat -- not factoring water temps, i'm a little confused on exactly how you add those in -- but I still had a little. But I'm getting icing back because of the line temp, not necessarily because I'm carrying a great deal of liquid.
06-20-2008, 04:51 PM #19
The Clausius-Clapeyron equation, however, can be used to estimate the P-T relationship at saturation.
06-20-2008, 08:38 PM #20Regular Guest
- Join Date
- May 2008
yep you guys have picked up on an error in my details. my suction pressures varied from 30psi-40psi and suction line temps also varied accordingly. i know the uni was flooding. I dont get it.
06-20-2008, 09:08 PM #21
are you sure
do you think it was flooding because of ice back or because of compressor noise or other physical symptoms.
OK if it was really 40 psi you had neg. 2 or 3 degrees superheat so you would have been flooding, but are you sure that the temp wasn't varying modestly over this time because of varying load conditions. What kind of pattern was the pressure change or did it drop from 40 to 30 over a cycle but not bouncing back and forth?
I got very different results while the building water coming to the chiller was still relatively warm, i.e. higher pressures and temps but once the water was chilled I think the delta T dropped before I made temp and it stabilized in the high 40s psi and 27 deg. or a few deg. superheat.
I actually stopped the frost back by raising the target temp by 10 degrees so that the chiller water never got so cold that the superheat dropped down.
Obviously not helpful on a really hot day but better than no air at all for the units that were calling. Still waiting for the next hot spell with all units calling (thankfully it ain't come yet because I'm replace a burnout on my second circuit) to test out these thoughts.
06-20-2008, 10:58 PM #22
This is a borderline hijack. sorry.
This goes against my theoretical thinking. Could you explain this a little more?
Seems to me that if the refrigerant isn't in the evap, then it's in the condenser moving slowly and giving up it's heat, at a high pressure. How can it not be condensing? Your saying it's probably all gas in there?
Actually, I would expect the superheat to be high too. It is moving slowly absorbing heat at a low pressure.
In fact, I was on one today that had 10 PSI suction and was flooding back. I flipped the newly installed blower wheel and had 10 PSI still, but a 70 degree suction line temp. Then I replaced the drier and had normal pressures.
What am I missing?Guinness for strength
06-20-2008, 11:18 PM #23
Are you asking a question or stating something.
Referring to my post you quoted i was just stating that if your not changing state one way or absorbing the latent heat necessary to evaporate, Then you cant condense now can you? If its not changing state one way it cant the other. I dont even know why i said this as i haven't read back.
06-20-2008, 11:53 PM #24
I wasnt asking a question about what I had today, I was stating my case.
I dont understand why this dude had no superheat, but he DID have enough load. It was explained earlier that less refrigerant in the circuit means less ability to absorb heat (which makes obvious sense), but I got thrown off in the description of why that could mean that the little bit of saturated refrig is still saturated as it reaches the compressor. It should have been warm in it's return to the compressor.
It's boiling off immediately any additional heat it absorbs would be superheat, assuming the pressure remains the same.
It also seems to me that you can still condense to a liquid in the condenser....even more so if you are taking on no load. The liquid should stack in the condenser. If you put all the refrigerant in one small spot (condenser), then pressurize it, it should condense. Especially if you are running a fan over it and removing heat.Guinness for strength
06-21-2008, 01:02 AM #25
when we say "condense" we are referring to taking a GAS and compressing it into a LIQUID. this action does a few things: builds pressure, and the byproduct is heat. removing the heat built up by the "condensing" of the superheated GAS is called subcooling. by the use of a metering device along with the pull of the suction valves we create a bubble point to drop the pressure. this causes the temp drop in the refrigerant that is superheated in the evap coil engineered to handle a specific amount of refrigerant based on the metering device, compressor size and air flow. the load on this coil is designed to boil off the refrigerant and return it to the compressor as a superheated gas.(PICK UP HEAT AS A GAS IN THE EVAP COIL, AND REMOVE THIS HEAT AS A LIQUID IN THE CONDENSOR.
HOW CAN YOU CONDENSE A LIQUID INTO A LIQUID?
answer: you can't
WITH THAT SAID,
having 3 of your 4 dist. tubes blocked, there is only 25% of your load that is required(return air passing through coil is the load) to properly superheat the said system in this topic. this is keeping the liquid from EVAPORATING in the evap coil and restricting flow. the restriction is dropping the pressure, and the lack of load is not boiling the refrigerant causing no superheat.
1. confirm compressor valves are ok
2. replace plugged tubes
3. clean evap coil
4. check belt tension, and blower speed for cooling.(hi)
5. cycle system and adjust charge
06-21-2008, 01:18 AM #26
after rereading your post green ears,
in your case, you had a restriction in a total different spot.
your restriction was in the filter drier, and that is before your metering device.
you had all 100% of the load you needed, but had a lack of refrgigerant in the coil causing it too pick up too much heat. the restriction caused the low pressure, and the high load caused the high superheat. typically this will look like an undercharged system. because, in effect it is doing the same thing.
undercharged system: low suction,high superheat,low head
restriction before coil: low suction, high superheat, high head
restricted distributer lines to evap: low suction pressure, low superheat, normal to high head (depending on amount of lines and size of said lines)