Freon Breakdown Question
paul milligan
at this time, and the actual readings are influenced by several factors that
are temporary.
The basic situation is a 5 ton Carrier scroll split system in a
custom application with a custom evap, and analog-controlled continuously
variable hot gas bypass at the evap for unloading.
The system runs mainly unloaded most of the time. The compressor
runs very hot ( On a recent mild day, the sump was 130F with no CC heater,
the body next to the suction line was 120F, and the head at the discharge
line was 220F. This was on a VERY mild day. Head pressure was running 275.
On hot days, head gets up to 350 - 375 - +. Ouch !!! I assume compressor
temps rise accordingly.
The system has been evacuated <VERY> well, and I know for a fact
there is no air in it. I charged it to normal pressures, with a clear
sight glass, good sub-cool & superheat, etc., and it ran fine for a while,
although the compressor is still hot ( RLA is 17, actual is 15 ), which I
assume to be due to insufficient cooling due to hot gas bypass. The suction
line comes in cold ( 40 - 56 F, the new TXV hunts due to other factors
that will be addressed ), but I suspect with insufficient volume to cool
the compressor. After a week or two, the head pressure starts to gradually
climb ( was 200 on a cool day, now 275, probably going up). There is still
lots of freon in the system, no part of the system ever got even close to
vacum ( the HG bypass also low-limits back pressure to 68 # as a default),
and the low pressure switch works, so there is no way it ran out and sucked
in air.
When the head pressure does this ( and it has happened before ), the
pressure DOES NOT RESPOND to water on the condensor, which tells me that the
problem is non-condensables, not other more common causes.
The new freon ( 2 weeks old ) smells nasty, as in acid & burned (
new suction and LL filters are in place ). So, here's the question....
What is the breakdown temperature at which R22 will start to deteriorate ?
Can an exceptionally hot compressor acheive that temperature while running
normal head pressures, if not being cooled internally by sufficient freon
flow? Can repeated passes through this super-hot compressor, running 24
hours a day, cause the Freon to break down ? If Freon breaks down in this
way, in a sealed environment ( no oxygen ), without pin-point heat such as
a flame or spark, does it break down into non-condensable components ? I
already plan to add a 1/2 ton TXV directly to the suction line at the
compressor for compressor cooling, amongst several other changes I have to
make, but I wonder if this symptomology could be caused in this way ? If
not, what else could cause slowly rising head pressure, non-responsive to
water on the coil, with increasing sub-cooling ( liquid line was warm when
I first charged it, with a full sight glass and normal pressures, now it's
very cool, lots of flash, although I have changed nothing ) ?
To copy a bit of correspondence I had with a chemist a few months
ago :
" According to the literature that I found, most of the chlorofluorocarbons
produce chloride and fluoride ions in gaseous form when they decompose due
to heat. Both of the these substances are highly toxic in this form. Some
of the refrigerant gases do indeed decompose into phosgene as well. The
ones that I looked up were Freon 31 (chlorofluoromethane), Freon 113
(trichloro-trifluoroethane), Freon 114 (dichlorotetrafluoroethane), and
Freon 11 (trichlorofluoromehane)."
So, what temperature do these little beasties wake up at, and do
they refuse to condense ?
Paul
BTW, the HVAC links page will be updated soon, give me a few more days.
Sorry about the delay.
George Goble
>
> The system runs mainly unloaded most of the time. The compressor
>runs very hot ( On a recent mild day, the sump was 130F with no CC heater,
>the body next to the suction line was 120F, and the head at the discharge
>line was 220F. This was on a VERY mild day. Head pressure was running 275.
>On hot days, head gets up to 350 - 375 - +. Ouch !!! I assume compressor
>temps rise accordingly.
If you have acid, which I suspect you do .. then R22 breakdown is probably
going on. Compressor discharge line temps (at the compressor) should
NEVER go over 300F.. or 275F to be safe.. HCFCs start breaking down then.
Although "pure" HCFCs, in sealed glass tubes, may not decompose until
500F or higher, in real life systems, the oil, metals, etc, act as
a catalyst.. and our tests show around 325F-340F range for the breakdown.
If you unsweat the compressor discharge line, you will most likely
see it caked with carbon as well.
Scrolls dont have valves, but recips can start R22 breakdown
if the discharge valves hit 325F or so. The early Copeland
residential scrolls I installed a few years back, all had
"top hat" thermostats (24V) on the compressor discharge to
shutdown on high discharge temps.. which were presumable caused
on low on charge systems (low suction pressure == higher
compression ratio, more heat of compression)
THe reason that home freezers dont use R22 anymore is for this reason.
CFCs like R-12 have slightly higher breakdown temps.. maybe 400F.
R22 has a very high "heat of compression" (that is why 502 was invented).
High compression ratios (ie low back pressure) makes the problem worse.
What are your evaporator pressure/temps?
If the suction pressure at the compressor, goes below 40-50 PSIG,
then you may have high heat of compression problems, causing breakdown.
The hot gas bypass system, may cause high suction gas temps in
certain modes of operation?? like when you are not there??
The "noncondensibles" is probably hydrogen (R22 is R12 with
one chlorine atom changed to a hydrogen == weaker bond, so lower
breakdown, lower ozone depl, etc)
We have seen hydrogen "form" when running R22 through a gas
chromatograph at slightly over 300F also.
Suggestions:
change the oil, and flush out the system if possible.. get
rid of the acid.. Check the discharge line for carbon buildup.
Run a "megger" ohm test on the compressor windings (to ground)
to check for insulation breakdown.. good should be over 100
megaohms.. If less than 50-60 megaohms, then insulation may
be damaged with a "burnout" failure to soon follow.
As you said, try liquid injection at the compressor.. I have
read, that for every degree the suction gas can be lowered,
the discharge is lowered 1 degree also. IF it were me, I would
not put a TXV there, but get a "superior" hand expansion
valve.. They have red knobs and look just like the packless
liquid line valves, but they are needle valves, so you can
adj it.. get the 1/4" size.. cost is about $40. (double a similar
liquid line valve).. This way you can set the amount of inj
you want.
Get a discharge line gas temp protector device.. and set it
for 275F or less.. just a clamp-on temp sensor for the discharge
line and cuts out if over 275F.
If you can deal with flammability issues, change the refrigerant
to R-290 (propane).. heat of compression much lower than R22,
no breakdown problems.. drop-in for 22.
TMETHOD
milligan) writes:
>
>I'll skip the background on this system, because it's only partially
fixed
>at this time, and the actual readings are influenced by several factors
that
>are temporary.
>
> The basic situation is a 5 ton Carrier scroll split system in a
>custom application with a custom evap, and analog-controlled continuously
>variable hot gas bypass at the evap for unloading.
Just to get a little better perspective, a hot gas bypass transfers load
back to the evaporator from the discharge line. It does not unload the
compressor. In fact, it adds to the load.
> The system runs mainly unloaded most of the time. The compressor
>runs very hot ( On a recent mild day, the sump was 130F with no CC
heater,
>the body next to the suction line was 120F, and the head at the discharge
>line was 220F. This was on a VERY mild day. Head pressure was running
275.
>On hot days, head gets up to 350 - 375 - +. Ouch !!! I assume
compressor
>temps rise accordingly.
Assuming this is R22, "Ouch !!!", indeed. That's 124F on a mild day and
150F + on a hot day.
>
> The system has been evacuated <VERY> well, and I know for a fact
>there is no air in it. I charged it to normal pressures, with a clear
>sight glass, good sub-cool & superheat, etc., and it ran fine for a
while,
>although the compressor is still hot ( RLA is 17, actual is 15 ), which I
>assume to be due to insufficient cooling due to hot gas bypass. The
suction
>line comes in cold ( 40 - 56 F, the new TXV hunts due to other factors
>that will be addressed ), but I suspect with insufficient volume to cool
>the compressor. After a week or two, the head pressure starts to
gradually
>climb ( was 200 on a cool day, now 275, probably going up). There is
still
>lots of freon in the system, no part of the system ever got even close to
>vacum ( the HG bypass also low-limits back pressure to 68 # as a
default),
>and the low pressure switch works, so there is no way it ran out and
sucked
>in air.
The purpose of the hot gas bypass is to prevent freezing the coil. Again
assuming R22, 68# is much too high. The compressor is experiencing high
load to higher load. Crank it down to the minimum it takes to keep the
coil from freezing (probably about 45#).
Aha, it is R22. I don't know when the refrigerant breaks down, but the oil
is certainly cooking.
IMHO, you have a combination of gross overcharge and too high a setting on
the hot gas bypass. Either one of these could also cause
TMETHOD
down at 350F. If you measure the discharge line temperature 6 inches from
the compressor and add 50-75F, that gives you the approximate temperature
at the discharge valves. The maximum acceptable discharge line temperature
is 225F. 250F indicates extreme conditions, and at 275F wave goodbye to
your compressor. (I was going to say kiss it goodbye, but then I thought
about it.)
Discharge line temperature goes up with superheat and/or head pressure.
Hope this helps.
Gary
===============================
Gary R. Lloyd CMS
TECH Method Training
HVACR Trouble Shooting Books/Software
paul milligan
~~>If you unsweat the compressor discharge line, you will most likely
~~>see it caked with carbon as well.
Yes, I just changed the TXV and there was obvious carbon tracing on
the pins.
~~>Scrolls dont have valves, but recips can start R22 breakdown
~~>if the discharge valves hit 325F or so. The early Copeland
I wonder how much the internal temperature exceeds that which I can
measure at the shell ( in a scroll unit ) ?
~~>What are your evaporator pressure/temps?
I was afraid someone was going to ask that :~( This gets into the
'other factors' area I mentioned.
A) The evap is a custom model with more
passes for greater latent removal, as the entire unit is primarily
there for humidity control. In fact, the HG bypass modulation is controlled
by an RH sensor only. Outside of that modulation, the unit is constant run.
The supposed mixing manifold head where the HG meets the TXV outlet is either
malfunctioning or incorrectly designed, as the HG comes in from the side, and
is apparently 'shooting across' in such a way that the 3 distributor tubes
directly across from the HG, and their associated evap passes, are hot
( taking all the hot gas ), while the others are simultaneously <VERY> cold,
and I suspect flooded, due to the entire output of the TXV going to approx 1/3
of the tubes. I've been told that the manifold is a special design ( the
HG inlet is a designed part of the manifold head ), but it's obviously not
mixing the inlet properly.
B) The TXV, which I just replaced, hunts like crazy, over it's full
span. I moved the bulb location further from the suction manifold, which
helped a little bit, but I think the problem is twofold - 1 ) the above
improper mixing is causing the lower coils to flood, making superheat control
almost impossible, and 2) The unit is being hot-gassed so much that the TXV
is at the extreme end of it's travel ( closed end, I think ), where it can't
settle down.
C ) There is a test going on now, 24 hours a day for the next 3
weeks, which is mission-critical, and would be invalidated if a chart
recorder on the test chamber shows variation > +/- 5% RH or > +/- 1F
beyond setpoints ( 55 RH, 70 F ), so right now I can only babysit and hope.
D ) I'm the only HVACR guy in a facility that has a normal staff of 4
plus helpers. I have 6 300 ton chillers serving 3 mission-critical areas to
watch, plus (?) ~100 small unitary AC's plus (?) ~??? pieces of lab gear. I
have to be a schizophrenic just to stay even. ~:)
~~>If the suction pressure at the compressor, goes below 40-50 PSIG,
~~>then you may have high heat of compression problems, causing breakdown.
I suspect that if the HG was turned off, that would be the case.
The HG is maintaining a 68 back in addition to riding capacity.
~~>The hot gas bypass system, may cause high suction gas temps in
~~>certain modes of operation?? like when you are not there??
No, there are no modal changes, and every minute is chart recorded.
The chart shows no unexplained changes.
~~>change the oil, and flush out the system if possible.. get
~~>rid of the acid..
On my next chance to take the system down, I will.
~~>Check the discharge line for carbon buildup.
~~>Run a "megger" ohm test on the compressor windings (to ground)
Yup.
~~>As you said, try liquid injection at the compressor.. I have
~~>read, that for every degree the suction gas can be lowered,
~~>the discharge is lowered 1 degree also. IF it were me, I would
~~>not put a TXV there, but get a "superior" hand expansion
~~>valve..
Yes, I was thinking the same way - my supervisor suggested a TXV,
but I'm going to use a hand vlave, like you say.
~~>If you can deal with flammability issues, change the refrigerant
~~>to R-290 (propane).. heat of compression much lower than R22,
~~>no breakdown problems.. drop-in for 22.
An intriguing thought, but I could never in a million years convince
my bosses to let me try it. :~(
SO, George, what do you think of the possibility of breakdown
causing non-condensability causing slowly and continuously rising head ?
Am I making stuff up, or could it be ? I'm at a loss as to what else to
think of.
Thanks for the input.
Paul
George Goble
>
>~~>If you unsweat the compressor discharge line, you will most likely
>~~>see it caked with carbon as well.
>
> Yes, I just changed the TXV and there was obvious carbon tracing on
> the pins.
Bet it is alot worse at the compressor (more carbon).
>
>~~>Scrolls dont have valves, but recips can start R22 breakdown
>~~>if the discharge valves hit 325F or so. The early Copeland
>
> I wonder how much the internal temperature exceeds that which I can
>measure at the shell ( in a scroll unit ) ?
Another posted reccommended 225F as max measured discharge temp 6inch
from the compressor.. He said Copeland says oil starts to "cook"
at 310F, and goes at 350F.. + it has some safety factor also.
Somebody should ask Copeland about measured shell temp guidline.
One also had to consider "hot bearings" in the equation.. Different
models of scrolls may have different responses..
>
>~~>What are your evaporator pressure/temps?
>
> I was afraid someone was going to ask that :~( This gets into the
>'other factors' area I mentioned.
>
> A) The evap is a custom model with more
>passes for greater latent removal, as the entire unit is primarily
>there for humidity control. In fact, the HG bypass modulation is controlled
>by an RH sensor only. Outside of that modulation, the unit is constant run.
>The supposed mixing manifold head where the HG meets the TXV outlet is either
>malfunctioning or incorrectly designed, as the HG comes in from the side, and
>is apparently 'shooting across' in such a way that the 3 distributor tubes
>directly across from the HG, and their associated evap passes, are hot
>( taking all the hot gas ), while the others are simultaneously <VERY> cold,
>and I suspect flooded, due to the entire output of the TXV going to approx 1/3
>of the tubes. I've been told that the manifold is a special design ( the
>HG inlet is a designed part of the manifold head ), but it's obviously not
>mixing the inlet properly.
What a bitch! good luck.
>
> B) The TXV, which I just replaced, hunts like crazy, over it's full
>span. I moved the bulb location further from the suction manifold, which
>
> D ) I'm the only HVACR guy in a facility that has a normal staff of 4
>plus helpers. I have 6 300 ton chillers serving 3 mission-critical areas to
>watch, plus (?) ~100 small unitary AC's plus (?) ~??? pieces of lab gear. I
>have to be a schizophrenic just to stay even. ~:)
>
WOW
Good luck
>~~>If the suction pressure at the compressor, goes below 40-50 PSIG,
>~~>then you may have high heat of compression problems, causing breakdown.
>
> I suspect that if the HG was turned off, that would be the case.
>The HG is maintaining a 68 back in addition to riding capacity.
>
>~~>The hot gas bypass system, may cause high suction gas temps in
>~~>certain modes of operation?? like when you are not there??
>
> No, there are no modal changes, and every minute is chart recorded.
>The chart shows no unexplained changes.
>
>~~>change the oil, and flush out the system if possible.. get
>~~>rid of the acid..
>
> On my next chance to take the system down, I will.
>
>~~>Check the discharge line for carbon buildup.
>~~>Run a "megger" ohm test on the compressor windings (to ground)
>
> Yup.
>
>~~>As you said, try liquid injection at the compressor.. I have
>~~>read, that for every degree the suction gas can be lowered,
>~~>the discharge is lowered 1 degree also. IF it were me, I would
>~~>not put a TXV there, but get a "superior" hand expansion
>~~>valve..
>
> Yes, I was thinking the same way - my supervisor suggested a TXV,
>but I'm going to use a hand vlave, like you say.
I just found out today that Superior discontinued their hand-expansion
valves.. If you find one.. lemme know where I can get a couple.. thanks.
>
>~~>If you can deal with flammability issues, change the refrigerant
>~~>to R-290 (propane).. heat of compression much lower than R22,
>~~>no breakdown problems.. drop-in for 22.
>
> An intriguing thought, but I could never in a million years convince
>my bosses to let me try it. :~(
>
>
> SO, George, what do you think of the possibility of breakdown
>causing non-condensability causing slowly and continuously rising head ?
>Am I making stuff up, or could it be ? I'm at a loss as to what else to
>think of.
Very good possibility of R22 and maybe some oil breaking down.. you
have carbon and acids.. The "F" will make HF (acid).. and some loose
hydrogen will appear.. and increase with time.. If there is desiccant
in the system, it will try to neutralize the HF acids, and H2 may
be given off there also.. The free hydrogen is noncondensible.
>
>Thanks for the input.
>
>Paul
You are welcome
--ghg
Allenbau
have seen this and misdiagnosed it.
Keep us posted - some good logic being used here.
Mike Allenbaugh
paul milligan
alle...@aol.com (Allenbau) wrote:
~~>This is a truly interesting thread and it makes me wonder how many times I
~~>have seen this and misdiagnosed it.
And I ! High head caused by high temp and breakdown.... I never
thought of it until now, and even then I would have laughed it off if not
for the fact that I personally have taken this system through every other
conceivable ( to me ) step. I never would have swallowed it from anyone
else. I'm still not sure I swallow it from me.
As a side-train - how about the concept that a system with 'normal'
head problems will drop head if you put a hose on the coil as a test, but a
system with non-condensables will not ? Can this be a reliable diagnostic
tool ? Almost a revelation to me if it is !
~~>Keep us posted - some good logic being used here.
I really love having the phenomenal resource of this group !
Paul
paul milligan
alle...@aol.com (Allenbau) wrote:
~~>Hate to admit it but this actually makes sense - to some degree - If there
~~>are no noncondensables then the extra cooling of the condensor caused by
~~>spraying water on it would condense more refrigerant than air alone and
~~>would lower system pressure. If the system is REALLY FULL of
~~>noncondensables one couldn't get the pressure reduction simply by cooling
~~>it.
Yes, it would certainly depend on the degree of the problem.
What made me first think of this was when I first worked on this
system - it was running around 400# head, and there was a test going on in
the chamber. I wanted the condensor as clean as possible, so I hosed it
( even though I could not shut the unit off ). Head pressure did not move,
causing me to get curious. At a later point ( after a repair and recharge
with new freon, as the old freon smelled bad ), I hosed it again just to see
what it would do - sure enough, head dropped like a stone. A few weeks later
the system was not keeping up and head was up again. In the course of
looking at it I hosed it again - head did not move. Something in there
had changed, and I can only think that it was the quality of the
condensability of the working fluid. This led me to wonder if maybe this was
actually a valid way of verifying non-condensables ( in massive quanitities)
when standard T/P results simply aren't available ( like in a system that
can't be shut down ).
~~>Seems to me a system with air or with decomposed R22 would be easy to spot
~~>with a temp/pressure chart for the refrigerant in question. I have
~~>probably cleaned up systems with damaged refrigerant thinking I was simply
~~>removing air.
Yes, we've all been through the process, and I'm sure we've all
smelled the freon, and if it smelled ok, bled off the top of the can to
remove air, and put the same freon back in. Actually, if it smells OK, it's
probably not broken down. It's interesting to think, though, that freon can
be a cause of high head without more 'normal' freon-specific things like
overcharge or air or wrong freon in system etc.
Paul
TMETHOD
success. I must be missing something. You are using a 2 ton A/C system
with a water spray on the condenser and a 5 ton A/C system with increased
coil surface area and hot gas bypass, all to cool 500 CFM of outdoor air
in order to maintain a test chamber at 70F (+/- 1F) and 55% RH (+/- 5%).
What part of Hell are you located in? My advice is to stay inside the test
chamber. : )
Ah, but then you mentioned freeze cracks in a water line, so I guess it
isn't Hell after all. Is this system providing make-up air for 500 CFM of
exhaust? Is there any preheat or reheat? What's the sequence of operation?
What happens in cold weather? In my last post, I suggested a list of
temperature measurements. It would be nice to have the same information on
the 2 ton unit as well.
I don't know about you, but I LOVE this stuff. The mental exercise is
invigorating. I can't understand why anyone would want to work in any
other trade. The only thing I have found that even comes close is computer
programming.
When everyone gets involved, kicking ideas back and forth, it just gets
even better.
Gary
======================================
paul milligan
tme...@aol.com (TMETHOD) wrote:
~~>I've been trying to form a mental picture of this system without much
~~>success. I must be missing something. You are using a 2 ton A/C system
~~>with a water spray on the condenser and a 5 ton A/C system with increased
~~>coil surface area and hot gas bypass, all to cool 500 CFM of outdoor air
~~>in order to maintain a test chamber at 70F (+/- 1F) and 55% RH (+/- 5%).
~~>What part of Hell are you located in?
The government part :~). This is a Federal installation.
'Nuff said <G>.
My advice is to stay inside the test chamber. : )
No can do. They're 2' x 2', all 10 of them ( driven by this one
system).
~~>Ah, but then you mentioned freeze cracks in a water line, so I guess it
~~>isn't Hell after all. Is this system providing make-up air for 500 CFM of
~~>exhaust? Is there any preheat or reheat? What's the sequence of operation?
The Federal Government is allowed to have freeze cracks in Hell.
They wrote a law saying so. :~)
This is the same system I posted about a while ago under 'Help me
with this load calc'. This unit's high head problem is the only remaining
issue - the rest of the beast works now. That thread will be up in 3 or 4
days in the 'Interesting Threads' section of the SEHVAC home pages, under
'problems and case studies'. It has a better description of the whole
system ( which will still be unclear, because this system is unclear ).
~~>I don't know about you, but I LOVE this stuff. The mental exercise is
~~>invigorating. I can't understand why anyone would want to work in any
~~>other trade. The only thing I have found that even comes close is computer
~~>programming.
Been there, done that. I was a systems analyst for 12 years on IBM
iron. This is more fun, and you get to breath phosgene !
~~>When everyone gets involved, kicking ideas back and forth, it just gets
~~>even better.
It's really tremendous to have a forum like this. Lynnette done
good, huh ? :~)
Paul
n7...@primenet.com
>~~>to R-290 (propane).. heat of compression much lower than R22,
>~~>no breakdown problems.. drop-in for 22.
did some casual checking, propane is a Class III refrigerant, the total charge is limited
by code. Only industrial applications would be practical.
I don't have the code here, so I won't attempt to quote.Perhaps someone
could post the information.
Jim Sullivan
David Lesher
to bore you with a naive question, but what kind of oils are used
inside such a system? Are they conventional or synthetic such as the
auto/aviation Mobil-1 brand?
--
A host is a host from coast to coast.................wb8foz@nrk.com
& no one will talk to a host that's close...........(v)301 56 LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead........vr vr vr vr.................20915-1433
paul milligan
wb8...@netcom.com (David Lesher) wrote:
~~>As a non-HVAC engineer, I've been lurking around this thread. Sorry
~~>to bore you with a naive question, but what kind of oils are used
~~>inside such a system? Are they conventional or synthetic such as the
~~>auto/aviation Mobil-1 brand?
~~>
Oil ?????
Sorry, had to do that. A layman's answer ( which is the only kind
I have ) would be special high grade, pure, dehydrated oils, of
differing viscosity, flock points, miscibility, etc for different designs.
Also some petroleum based, some synthetic. I know there are others
lurking who have a lot of specific knowledge in the area, but I think that's
the general idea.
Paul
_________________________________________________________
No Disclaimer needed - This is my own PPP account, and my
employer doesn't care what I think anyway ! :~)
_________________________________________________________
http://www.elitesoft.com/sci.hvac/ is the home page of
sci.engr.heat-vent-ac
paul milligan
~~>Paul, your refrigerant distribution situation doesn't look too good. The
~~>distributor you are referring to is probably a 'side connection' type
~~>distributor.
That would be a good description.
~~>The purpose of the extended nozzle is to
~~>prevent refrigerant flow from the TEV from being deflected by the hot gas
~~>bypass flow before it enters the distributor tubes--and messing up
~~>distribution.
How do I tell if it's 'extended' or not ? There's a stub maybe 1"
( from memory ) for the HG, but there is apparently insufficient mixing,
as described previously.
~~>BTW, what is the size of your distributor tubes? If I have it right, you
~~>have a 3 circuit, 5 ton R-22 coil. 1/4" OD tubing would be ok if you
~~>were not bypassing hot gas to the inlet of the coil. 5/16" OD tubing
~~>would be appropriate with hot gas bypass.
I'll have to check. From memory, they are 1/4, and there are 8
circuits, with extended passes ( thicker coil than normal ) for latent. I
seem to recall the coil being a 'Witt', although I don't recognize the name.
Anything smaller than 5/16" OD
~~>may cause high pressure drop conditions at the distributor tubes with
~~>hot gas bypass, causing low suction pressures and high return gas
~~>temperatures (and high discharge temperatures).
The funny thing is, my suction pressures are good ( at ~ 68 - 72 ),
and suction line is ( too ? )cold ( varies from 40 - 56 at TXV bulb, hunts
continuously ). The suction all the way back to the accumulator and
compressor is cold, and yet the compressor is hot as a .....
The last time I charged the system, a few weeks ago, after a good
evac and new filters and new freon, I ran around 200# head, 70 back, warm
LL, cold SL, clear sight glass, moderate compressor body temps, good RLA,
condensor fan cycling moderately ( on a cool morning ) to maintain head
( I bring it on at 250, off at 200 ). Since then, without touching the
system, head has risen to ~ 300 on a typical cool morning (75F OA),LL is cool,
SL still cold, lots of flash ( TXV hunting is obvious in the glass ). If
I turn a full force water hose on the coil, it changes nothing.
Non-condensables, right ? So, how ? The SL safety has been verified, the
system has been totally leak tested and leak-repaired, no part of it ever
runs less than 68#, let alone vacumn, so I have to believe no air has come
in.
{joke alert]
I know, it's because the Freon molecules started off square, but
they have become rounded at the corners by being pushed around so much !
( Yes, I actually heard this presented seriously by a 'serviceman' once ! )
>Paul, what kind of distributor are you fighting with? If you have a
>distributor with an inlet nozzle, you can't inject hot gas upstream of the
>distributor. You will end up with extremely high pressure drop conditions
>across the nozzle causing the TEV to starve.
Drat. I was picturing the pressure-imbalanced mix causing it to
starve the coil only until RH rose, the HG was backed off by the control
system, and a mix that achieved latent capacity was achieved. Why won't
this work ? Another consideration is that I can do the repiping out of
stock, whereas a new distributor would need explaing to some people who don't
know and don't want to. They refer to motors as "those big grey things", no
kidding !
>Much better to inject
>hot gas directly to the suction line and cool it with a desuperheating
>TEV. The desuperheating TEV should be sized about 25 percent of your
>hot gas bypass capacity.
That would certainly be more normal, but there ain't nothin normal
going on here, and I'm constrained to try to work within existing design.
<Sounds like some serious work needs to be done at the distributor....
Something's gonna be done, and done cheap and fast ! :~(
> As I write this, I wonder.... can a TXV work here ? Won't it see
>the effect of the HG at the leaving suction manifold, and open up to try
>to maintain superheat ?
>>Yep
> Won't the TXV try to run wide open all the time ?
Only if you are bypassing hot gas across a distributor inlet nozzle. :-)
Ouch ! <G> What's the diff, Andy ? Mix it here, mix it there, as
long as it's mixed enough to distribute when it goes out to the coil...????
~~>>already plan to add a 1/2 ton TXV directly to the suction line at the
~~>>compressor for compressor cooling, amongst several other changes I have to
~~>>make,
~~>
~~>If your return gas temperatures are high (and I'm sure they are), say >65F,
~~>a desuperheating TEV can be very effective. Figure the TEV will need to have
~~>at least 5 percent of the compressor's capacity. But you should try to figure
~~>out why you are running high return gas temperatures.
That part drives me nuts. I'm not !!! ( running high temps, that is ).
Yet the compressor, pulling below rated amps, is hot now, whereas it wasn't
when I charged it and ran it for a few hours ( and days ). This whole thing
has developed slowly over several weeks, and the unit's history makes me
believe it's happened before ! Aaaarrrggghhhh !!!!
Paul ( from the padded room )
George Goble
>( I bring it on at 250, off at 200 ). Since then, without touching the
>system, head has risen to ~ 300 on a typical cool morning (75F OA),LL is cool,
>SL still cold, lots of flash ( TXV hunting is obvious in the glass ). If
Have you checked the oil for acid? Previous burnouts? Not correctly
cleaned up? acid in the oil could be catalyzing further R22
breakdown, at lower than 330F, eating away at the motor windings..
--ghg, inventor R-406A
http://ghg.ecn.purdue.edu
http://worldserver.com/R-406A
Jim Storm
milligan) says:
>
(Major snipage to save space)
Paul..
I can't find the post or the thread I was looking for but did you say you
were controlling your HG valve with pnumatic (read air ) at 80#??
If so I would think to look for air being put into the system at the HG
valve.. I have only seen valve that were contolled by suction pressure or
thermal bulb and not pnumatic. Then again, not being there this is just a
W.A.G.
Stormy jst...@postoffice.ptd.net
paul milligan
jst...@postoffice.ptd.net (Jim Storm) wrote:
~~>I can't find the post or the thread I was looking for but did you say you
~~>were controlling your HG valve with pnumatic (read air ) at 80#??
~~>If so I would think to look for air being put into the system at the HG
~~>valve..
I will be D*****d !!!
In all the time I've fought this thing, I never thought of that even
once ! Yup, a broken diaphragm with 80# over it and 70# under it would
sure give me a slow air injection, huh ?
Thanks, Jim, I'll sure check that one out when I take the system
down!
Paul
paul milligan
~~>Paul, Sporlan type side connection type distributors will have an 'R'
~~>stamped on the distributor body.
I only got to glance at the sytem today, but the last 3
characters on the distributor are '53R' ( I didn't have a mirror with me to
see the rest ). BTW, there are 7 tubes of 1/4", and 3 are taking all the
HG. Cuts my coil down to 40 % of design, huh ? :~(
~~>Mmmmmm..... cold suction .... low superheat ? .... overheating compressor.
~~>Sounds like gremlins at work! :-)
I'm about ready to call the heeby-jeeby man in for a cure !
>> The
>>folks at Witt won't be impressed by your coil brand name recognition. :-)
A simple question of background, Andy.... Most of my work in the
last 10 years has been Witt-less. <G> Did I pull a Bohner ? <ouch>
~~>Ok, head pressure doesn't rise for no reason (unless gremlins are at
~~>work). Could you be trapping refrigerant in the condenser? Is your
~~>receiver located, like 40 ft above the condenser? Or the condenser
~~>trapped below the compressor?
Nope, both on the same level, about 10 ' away.
~~>> Drat. I was picturing the pressure-imbalanced mix causing it to
~~>>starve the coil only until RH rose, the HG was backed off by the control
~~>>system, and a mix that achieved latent capacity was achieved. Why won't
~~>>this work ?
~~>Trust me on that one. :-) That's why the distributor has a side
~~>connection in the first place.
~~>> Ouch ! <G> What's the diff, Andy ? Mix it here, mix it there, as
~~>>long as it's mixed enough to distribute when it goes out to the coil...????
~~>It's the inlet nozzle. Hot gassing ahead of it drives void fraction of
~~>the two phase flow way up, causing two phase density to drop, causing
~~>pressure drop across the nozzle to go up, causing the TEV to starving,
~~>causing mechanic to say !%#$&!?$#$
SO I can't do a magic patch out of scraps, huh ? I have seen a case
where there was a small plate pressed into the inside of a (normal)
distributor, and it was loose and rotating from the flow. First one pass
would starve and one pass flood, then reverse. Is the mixing distrib
similar inside ? Would a new distributor hopefully prevent this 'shoot
across' that I have now ? Are there other changes that would work, or have
to be done at the same time ? Obviously, it can't stay the way it is now.
~~>Andy Schoen
~~>asc...@mo.net
~~>
~~>No disclaimer on my opinions 'cause they generally right anyway.
Love your speeling too ! :~) ^^^^^^^^^
asc...@mo.net
>In article <DF4Mn...@postoffice.ptd.net>,
> jst...@postoffice.ptd.net (Jim Storm) wrote:
>
>~~>I can't find the post or the thread I was looking for but did you say you
>~~>were controlling your HG valve with pnumatic (read air ) at 80#??
>~~>If so I would think to look for air being put into the system at the HG
>~~>valve..
>
>I will be D*****d !!!
>
> In all the time I've fought this thing, I never thought of that even
>once ! Yup, a broken diaphragm with 80# over it and 70# under it would
>sure give me a slow air injection, huh ?
>
> Thanks, Jim, I'll sure check that one out when I take the system
>down!
Hey, I ran into that same problem a few years ago. The air injected into
the system was causing bubbles to form at the sight glass which alerted
me to the problem. Of course, it caused head pressures to rise also.
Good call Jim!
Andy Schoen
asc...@mo.net
paul milligan
so I dropped what I was doing and ran over. I tried to keep in mind my
list that I was preparing for 2 weeks from now, but here's what I did...
Reclaimed - could not get everything due to non-condensables.
Took hot gas piping apart to repipe - tested control for air leaks
into freon side.
BINGO !!!!!
Yup, sho nuff ! A tiny little leak ! Jim Storm nailed it with his
post. Jim, I owe you some McDOnalds coffee ! Or a Camaro axle.
Repiped HG - it now mixes properly, all distributor tubes
and coil passes are at equal temps, for the first time ever. RH oscillation
is 1/2 of what it used to be ( now +/- 2 1/2 % )for a similar OA condition.
Added compressor cooling ( BTW, the compressor megged good, and oil
tested good ). I didn't have time or budget to buy a hand valve, so I
installed a 3/16" crimp valve. FOr those who are not familiar with this type
of valve, lets just say you take a torch, some 3/16" tubing, a pair of
pliers..... <G>. But, hey, it works for now. It _will_ be replaced with a
proper valve, but I need to get through the next few weeks.
Even though it seems it wasn't freon breakdown, that was one heck
of a good thread, and it taught me a lot. Thanks to everyone who
contributed !
Paul
Speaking of good threads, I've added a few to the groups pages under
"Interesting Threads Collection". - enjoy !
paul milligan
tme...@aol.com (TMETHOD) wrote:
~~>Now that the "little beasty" has been tamed, I'm still left with one
~~>question. Is this the best way to control capacity for humidity? It still
~~>seems to me that a pneumatically controlled EPR in combination with liquid
~~>injection would do a better job and would give the compressor a break. Is
~~>there such a thing? What would be the advantages/disadvantages?
Well, the new HGBV is on order, and will take 4 weeks to arrive.
WHen it gets here, I plan to install it, add a CPR to limit compressor
intake to ~ 75 #, and put a proper hand valve on for liquid injection
( although my 3/16 " crimp valve is doing quite nicely, thank you ! :~) )
The HGBV valve has a minimum setting adjustment, which I'll target
at maybe 50 - 55 #. It then " raises system back pressure 1# for every
1# _OF APPLIED PNEUMATIC PRESSURE_".
By adding the CPR, in effect I have an EPR ( at least above the CPR
setting )controlled by the HGBV, and will be running a flooded coil most of
the time, except when the system equalizes within the range of the TXV.
There is an accumulator,BTW, which I'll leave between the CPR and the
compressor.
Here's the new question : I'm controlling RH by modulating evap
pressure. This means I'm controlling dewpoint, in relationship to SHR.
So, how to I predict the effect of a 1# change in evap pressure on
RH ? Obviously, I go to the chart for saturation point, and add in the
fact that the TXV is going to be trying to control superheat. The net
effect is in SHR, as far as latent is concerned. How do I predict it ?
I'd like to be able to go in with a setting in mind for the prop
band based in some kind of logic, rather than educated guess.
At this time, I plan on a 1:1.5 ratio on the pneumatic relay, so
that a 0 - 20 # change out of the prop controller results in 0 - 30 to
the HGBV, giving me a max evap of 55 + 30 = 85#, in other words each
1# change from the prop controller raises ( or lowers ) my evap pressure
1 1/2 #. Also, my max pneumatic pressure will never be able to exceed my
suction pressure, so the next leak will be freon out, not air in !
Paul
paul milligan
tme...@aol.com (TMETHOD) wrote:
~~>In article <44sn60$ou4...@grail917.nando.net>, p...@nando.net (paul
~~>milligan) writes:
~~>
~~>> At this time, I plan on a 1:1.5 ratio on the pneumatic relay, so
~~>>that a 0 - 20 # change out of the prop controller results in 0 - 30 to
~~>>the HGBV, giving me a max evap of 55 + 30 = 85#, in other words each
~~>>1# change from the prop controller raises ( or lowers ) my evap pressure
~~>>1 1/2 #. Also, my max pneumatic pressure will never be able to exceed my
~~>
~~>>suction pressure, so the next leak will be freon out, not air in !
~~>
~~>What's wrong with this picture? Paul, I have read this paragraph over and
~~>over and there is something wrong with the logic (last sentence in
~~>particular), but I can't quite put my finger on it. Maybe I'm missing
~~>something. Is the ratio adjustable on the HGBV? Doesn't the pneumatic
~~>pressure have to exceed the evap pressure in order to open it? Talk to me.
Not sure what you're seeing...The pressure of the control air feeding
the HGBV is variable 0 - 80. The response of the HGBV is not
adjustable, but the minimum evap pressure is. There's a spring inside,
with an adjusting stem, much like TXV, such that spring pressure plus
pneumatic pressure = total pressure, thus the spring is doing most of the
work of overcoming system pressure, and the pneumatic rides 'on top' of it.
Assuming I set the minimum pressure spring ( via the stem )to 55#,
at 0 # pneumatic I have 55 # evap, at 1 # pneumatic I have ( 55 + 1 = 56 )
back, etc. The ratio question comes in where the standard RH sensor feeds
the standard proportional band controller, with reverse action output, and
I have to determine how much of a change in sensor pressure ( varying in
10ths of lbs ) will result in what proportional span of the output ( 0 - 20),
which will then be ratio-relayed at a 1 : 1.5 factor ( as I'm thinking right
now, anyway :~) ), such that actual control to the HGBV is at a span of
0 - 30 ( over the minimum set).
To rephrase my question - let's say my RH sensor says the RH is 1%
too low ( set at 60%, reading 59% ). How do I think about how much I have
to change my evap pressure to let 1% RH more through the system ? And
what does it mean in terms of evap pressure ? Raise the back too high, and
the RH will overshoot considerably. Don't raise it enough, and the RH will
remain too low. Keep in mind that there is electric reheat coming in to
deal with the Dry Bulb effect of the system when it over-cools, I'm only
trying to worry about latent. As I see it, what I'm trying to accomplish by
changing evap pressure is to manipulate the SHR around a desired dew point,
in terms of final RH output.
So, how can I predict evap pressure vs SHR vs RH ?
Interesting question, eh ? :~)
TMETHOD
milligan) writes:
If this is the case then how could the HGBV have leaked air into the
system with a minimum setting of 68# spring pressure?
Gary
===========================================
I pretend to work. They pretend to pay me. I pretend to eat.
-Anonymous Soviet Citizen-
Gary R. Lloyd CMS
TECH Method Training
HVACR Trouble Shooting Books/Software
Tel 313-671-0188 Fax 313-676-9262
paul milligan
tme...@aol.com (TMETHOD) wrote:
~~>>now, anyway :~) ), such that actual control to the HGBV is at a span of
~~>>0 - 30 ( over the minimum set).
~~>
~~>If this is the case then how could the HGBV have leaked air into the
~~>system with a minimum setting of 68# spring pressure?
~~>
Previous set-up, as I inherited it, was resulting in the system
running at 80 - 110 # pneumatic, which is probably what broke the
diaphragm in the HGBV.
TMETHOD
milligan) writes:
>
>In article <454u97$3...@newsbf02.news.aol.com>,
> tme...@aol.com (TMETHOD) wrote:
>
>~~>>now, anyway :~) ), such that actual control to the HGBV is at a span
of
>~~>>0 - 30 ( over the minimum set).
>~~>
>~~>If this is the case then how could the HGBV have leaked air into the
>~~>system with a minimum setting of 68# spring pressure?
>~~>
>
> Previous set-up, as I inherited it, was resulting in the system
>running at 80 - 110 # pneumatic, which is probably what broke the
>diaphragm in the HGBV.
>
>
Duh...I think I'm beginning to get the picture. The HGBV was subjected to
an unregulated air supply (80-110#). A call for bypass resulted in the
HGBV being driven to it's full open position and then some, thus exceeding
the maximum operating pressure of the device. BTW, what is the max
pressure of the HGBV? Do you plan on installing a regulator in it's air
supply or are you counting on the multiplier to protect it (a very risky
proposition, IMHO)?
Will 85# evaporator pressure be enough to achieve the desired result? Not
being an engineer, and given the complexity of this system, the variables
would seem overwhelming. My unscientific approach would be to subject the
HGBV to something slightly less than its max pressure rating as a starting
point, and then gradually reduce it from there. Perhaps the engineers out
there have a better way.
Gary
================================================
Everything should be made as simple as possible, but not simpler
-Albert Einstein-
asc...@mo.net
>In article <454u97$3...@newsbf02.news.aol.com>,
> tme...@aol.com (TMETHOD) wrote:
>
>~~>>now, anyway :~) ), such that actual control to the HGBV is at a span of
>~~>>0 - 30 ( over the minimum set).
>~~>
>~~>If this is the case then how could the HGBV have leaked air into the
>~~>system with a minimum setting of 68# spring pressure?
>~~>
>
> Previous set-up, as I inherited it, was resulting in the system
>running at 80 - 110 # pneumatic, which is probably what broke the
>diaphragm in the HGBV.
Paul, an 80 - 110 psig pneumatic would not normally harm the diaphragm
of your HGBV. In fact, 200 psig shouldn't be much of a problem.
If the pneumatic signal is cycling the valve open and closed frequently,
that's another story. The signal would then be, in effect, life
cycling the valve.
I suspect moisture in the air being used is causing rust to form in
the valve above the diaphragm, and the rust is causing the diaphragm
to fail.
Andy Schoen
asc...@mo.net