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Thread: Engineering problem? Hmmmmm
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13-03-2002, 03:19 AM #1
Engineering problem? Hmmmmm
Ive got a condensor that utilizes a discharge bypass valve(a-4-0\55),desuperheating tev(egs 1\6 L1), flood control(lac-4-215)and ranco fan cycling control set at 300psi.
This condensor has 2 fans, a 12# reciever and a suction accumulator.
Compressor superheat is at 70, at -5F box temp.
The discharge bypass line is locted and piped into the suction line in the condenser 2" ahead of the accumulator.
The desuperheating tev is located and piped in the suction line in the condensor about 10" ahead of the accumulator.
The sensing bulb for the desuperheating tev is located in between the DBV piping and desuperheating piping as they
enter into the suction line.
Condenser m#KH201L6HT3A-0790 (-30f SAT SUC TEMP @80FAMBIENT=
7670 BTUS PER HOUR.
EVAPORATOR M# KTW077ED-S2A-0566 (-20F EVAP TEMP @ 10F TD=
7650 BTUS PER HOUR, box design temp is -20F
EXPANSION VALVE (EGSE-1/2-ZP) IS INSTALLED.
SYMPTOMS ARE HIGH SUCTION SUPERHEAT AT COMPRESSOR.
WHATS GOING TO HAPPEN WHEN THE WEATHER TURNS WARM?
EVERYTHING IVE READ indicates I will not get the
proper mixing of the hotgas and liquid as it was piped from the factory. The sensing bulb is also located in the wrong place.
Why with a single evaporator would the even use this type of capacity control?
Ive been on the phone all week, trying to get an explanation from keeprite, Im getting lost in email
Had the box down to -15F and suction superheat at the
compressor was 57F
Looking at the data sheets for each piece of equipment,
and utilizing the expansion valve that they are. I
believe the tev is undersized for an oversized piece of equipment. Huh?
With a superheat that high at the compressor you would expect the box temp to be suffering but this is not the
case. It is my belief that the only time you can satisisfy your box requirements and still overheat your compressor is if the equipment is oversized.In this case the evap is oversized and the expansion valve is too small to flow the required liquid to maintain a reasonable suction superheat at compressor.
Am I making any sense of this, is my thought process flawed?
To top it all off the piping arrangment dosent match
any of sporlans guidelines or the manufactures own design drawing.
Anywho, I brought this to the attention of the keeprite engineering department, sent them a digital pic of the unit.
They in turn sent me a fax with the correct piping arrangement. told me to send a quote to repair. As soon as they got the quote I got an email stating that the piping would work just fine and all I had to do was change the location of the desuperheating tev bulb. What to do?
The darn guy backtracked on me, said he had numerous of these units on the west cost and they worked fine.
R-404a system
48-50F ambient
suction pressure 12-15 psi /suction temp at comp 42F
head pressure 225 psi /liquid line temp at outlet of reciever 92F
Box temp at time of reading -5FLast edited by bernie; 13-03-2002 at 04:03 AM.
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13-03-2002, 05:52 AM #2
The subcooling at the receiver is 5F. This would indicate an undercharge. The evap TD is 19-23F, which tends to confirm undercharge, as does the high superheat. I suspect the coil outlet superheat is also high, which would leave no doubt.
I'm thinking this unit is undercharged.
I disagree with the notion that box requirements cannot be met with high compressor inlet superheat (assuming coil outlet superheat is right).
The desuperheating TEV bulb location seems wrong. Where did he tell you to relocate it to?Last edited by Gary; 13-03-2002 at 06:02 AM.
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13-03-2002, 01:59 PM #3
I don't necessarily disagree with your analysis, Mark. however...
At 50F ambient, with fan control set at 300psig, the effects of the LAC should be minimal. It should not yet be in the picture, nor should the desuperheater and/or BPV be operating with the box temp at -5F.
...ensure there is sufficient charge in the system for the LAC to properly flood the condenser with still adequate refrigerant in the receiver for proper liquid delivery.
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13-03-2002, 08:54 PM #4
Ok Gary let me say this,
I reclaimed all refrigerant, sized up my condensor for winter
charge and compensated for the 50 ambient.
At -5F box temp the flood control was infact bypassing and the desuperheater was allowing liquid into the suction line due the high return gas temperatures.
As far as the fan cycle control is concerned it wont be a factor untill My ambients raise another 10F or so.
Personally I dont see the use for it, Its not needed in this application with a flood control set at 215.
Marc,
I relocated the desuperheating sensing bulb after the accumulator just ahead of the compressor. I have to edit my self here,
The suction temp I stated in the last post of 57F was infact after I moved the bulb.
Does the desuperheater provide a positive shut off as long as the suction superheat is correct?
What about the the piping of the two, they are reversed and Im concerned that the hot gas will get thru the accumulator before the liquis can properly mix.
The frost pattern on the end of the evaporator indicates that the
superheat is high, although my box temperature falls quite well
and cycles off at -15.
It seems to me that injecting liquid due to poor system performace(compressor superheat) will cause pump down problems when ambient is low. Could liquid get trapped in the refrigerant oil and cause lenghty pump downs?
I really appreciate all your input on this matter.
Thanks
Bernie GlasgowLast edited by bernie; 13-03-2002 at 08:58 PM.
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13-03-2002, 09:34 PM #5
Head pressure control, AND fan cycle???
Should I assume the fan is not running?
Is the compressor an air cooled semi-hermitic?
Can I assume that there is a sightglass in the liquid line and it is "full" (yes, I understand that that may not be indicative of liquid at the TEV)?
First thing that I want to know is what is superheat at the evaporator OUTLET (i.e. TEV setting / operation), and if adjustment required, does it respond?
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13-03-2002, 09:42 PM #6I reclaimed all refrigerant, sized up my condensor for winter charge and compensated for the 50 ambient.
(I hate the new small font quotes)
The frost pattern tends to support my undercharge theory.
and if adjustment required, does it respond?Last edited by Gary; 13-03-2002 at 09:51 PM.
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13-03-2002, 10:07 PM #7
2nd fan is not running, the sight glass is full of liquid.
The reciever has a 12 # capacity. I agree with your undercharge theory, actually The evap and expansion valve do not matcha ccording to the data from keeprite, I should have a 1 ton valve in there.
Im not a big fan of adjusting tev's unless necessary, a 1 ton out of the box should be just rite for my application.
Knowing the operation of this system and that sporlan builds in some saftey factor to their valves, I could probably take a few turns out of the spring and achieve better results. I would prefer just to replace the cartridge a half size larger. How does this sound?
Total system charge is 12.5 #
compressor is hermatic recip # AVA2490Z.
It seems to me the manufacturer had a sale on the units,
I cant understand why they'd sell a condenser and evaporator
with an expansion valve that isnt rated to carry the load or the
liquid that the evaporator needs to properly work.
I tried to discuss this with them direct and they stated all is good
and let them do the engineering. HmmmmmmmLast edited by bernie; 13-03-2002 at 10:35 PM.
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13-03-2002, 10:44 PM #8
Hmmmmm... The plot thickens.
We have a full sight glass, and sufficient head pressure to push it through the TEV. If we can assume that the receiver is sized properly for the application, then the charge may in fact be a little excessive. Whatsmore the pulldown time is good.
I am coming around to your way of thinking, Bernie. It's looking more and more like an undersized orifice.
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13-03-2002, 10:59 PM #9
Well I took my time on this one. I initially added 9# of refrigerant
and started the machine.
After about 20 min runtime the sight glass was half full.
At that point I began charging liquid thru my lo side charger.
When the glass cleared I did the math out of my sporlan
book on winter charges and compensated for 50 ambient.
It was like 1.6# extra after that.
Im starting to come around to my way of thinking also Gary,
Thankyou.
All thats left is the DVB and desuperheater. I want to eliminate
it. I feel this set up is for units that are designed to run all the time and have mulitple evaporators. I cant see the harm in taking it out as long as the orifice and expansion valve provide proper suction temps year round.
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13-03-2002, 11:12 PM #10I cant see the harm in taking it out as long as the orifice and expansion valve provide proper suction temps year round.
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13-03-2002, 11:20 PM #11
In addition their schematic drawing of the condensor piping arrangement does match either.
They must have a lot of these out there and dont want or cant
afford the warranty claims.
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14-03-2002, 12:11 AM #12
Re: Engineering problem? Hmmmmm
Originally posted by bernie
WHATS GOING TO HAPPEN WHEN THE WEATHER TURNS WARM?
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14-03-2002, 12:13 AM #13
Units are shipped from the factory with 2 orifices loosely.
They are for r-22 and 404a #'s l3/4 or l-1 for 404a.
Im not sure which one is installed as I didnt perform the original installation. I can assure you in the coming days when I return I will check it when I replace the cartridge in the valve.
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14-03-2002, 12:15 AM #14Originally posted by Gary
I wouldn't recommend messing with the TEV adjustment
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14-03-2002, 12:17 AM #15
bernie...
we're on line at the same time, and you're responding to my posts before I edit them.... read the above, and I'll wait till I see a post from you.
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14-03-2002, 12:21 AM #16
Evap outlet superheat is at 48.
Its crazy, superheat that high yet I can satisfy the box requirements, which is -10F
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14-03-2002, 12:27 AM #17
bernie....
Start at the TEV... see if it responds.... One thing that I've noticed in a same application id the failure of TEV element head at those temperatures.... I have a -30degF application, in two years, I've gone through (2) thermostatic elements. I'm considering the application and still figuring out what the deal is.... is it a Sporlan KT53ZP element?
superheat, way too high!!!!!!!!!!!!!!!!!!!!!!
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14-03-2002, 12:29 AM #18
In my situation, the customer doesn't call until something else manifests itself...... I'LL BET MY BOTTOM DOLLAR, A NEW THERMOSTATIC ELEMENT WILL DO IT IF THAT THING IS A KT53!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Which it should be, I believe, being a "G" body. That's what I've employed in my application that I refer to.Last edited by herefishy; 14-03-2002 at 12:36 AM.
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14-03-2002, 12:34 AM #19
I would lose the zp powerhead and replace it with a Z. I would eliminate the DVB and desuperheater.
I don't follow how a 7000 btu/hr load is too much for a 1/2 ton valve. Isn't the condensing unit sized to handle a 7000 btu/hr load? If so, why are only achieving -25 with a starving coil? The desuperheater, methinks. No reason you cannot accomplish sufficient desuperheating in the coil.
The prof might hate me, but zp charges should only be used when a manufacturer intentionally slights the motor size for the displacement.
Dan
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14-03-2002, 12:35 AM #20
This equipment is less than 6 months old,
the element is a kt 43 zp
I have also had problems with the 53 elements
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14-03-2002, 12:38 AM #21
I agree. You may have a point there. Maybe the cross-charge is what is screwing you and I, huh?
I spec'd the equipment in my application, myself. What needs to be taken into consideration, is the maximum suction temperature rating of the condenser. Knowing Keeprite..... I'll bet you BETTER have that ZP charge... because they probably didn't leave much room for higher suction ratings!
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14-03-2002, 12:40 AM #22
Have you attempted adjusting the TEV?
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14-03-2002, 12:42 AM #23
From the data sheets this evaporator will provide 7650 btus,
Granted if I turn the valves adjustment out I'll probably
be close on the superheat.
The kicker is they reccomend a 1 ton valve for this specific application in those same data sheets. Yet, it shipped with a 1/2, go figure.
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14-03-2002, 12:44 AM #24
NO..... in my book, the #1 valve is a no-no.
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14-03-2002, 12:46 AM #25
mind you, the valve with the number "1" on it is not a one ton valve!!!! The rating of the valve is dependant on the application!!!! the "1" is "nominal".
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14-03-2002, 12:49 AM #26
In regard to the evaporator.... it does not provide 7,650 btuh. It provides 765 buth for every degreeF of T.D. between the S.S.T. and the "room" temperature. I can mathematically make that coil produce 1,000,000 btuh refrigerating effect!
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14-03-2002, 01:06 AM #27
Dam I hate math,
If I use a SQE valve body
A BLUE q valve cartridge
and kt 43 szp or rzp,
Ok, the element decides capacity along with cartridege selection.
I gotta ask, What book are you refering too?
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14-03-2002, 01:23 AM #28
Well said Mr O'Brien,
Are you always up this late or you a earlier riser, Either way
thanks for your input.
Were's the prof these days?
Hes lurking somewhere
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14-03-2002, 01:32 AM #29
I am certainly interested in this TEV application scenario....., because Marc, if you are right, that is probably the nature of my problem.....
but I stand by my guns, however the track record doesn'r support it, I'll admit.
I may be changing a TEV spec on the result of this diagnosis.
.....BUT I'M READING MY "201"!!!!!!!!!!!!!!!!!!!
Sporlan support ph. # 636-239-1111
I hope I don't get in trouble for that........
But I think the 1/2 is good app.
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14-03-2002, 01:38 AM #30Originally posted by Fridgetech
There is no doubt that you should have the 1 ton orifice in there...
...Then because the valve is undersised
What's undersized?... the TEV, or the orifice?
What I am really trying to visualize... is that when you decrease S.S.T., you increase Pressure drop and valve capacity increases accordingly. I don't get anyone spec'n a "1" in this app. in relation to the figures in the table.....
I'm going to my Sporlan software, now.Last edited by herefishy; 14-03-2002 at 01:43 AM.
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14-03-2002, 01:40 AM #31
I guess Im ignorant, but tell what the 201 and Ill get a copy of it for sure. Thanks herefishy
Hey Dan Im all in favor of dumping the zp charge, although with the frequent defrosts I dont think the accumulator is enough protection. Some say an pump down is all the protection you need. I dont like CPR in this specific application due to the increased pull down times also.
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14-03-2002, 01:43 AM #32
refer to edited post
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14-03-2002, 01:48 AM #33
What max. ambient do you see in chicago?
at 110 condensing the software selects the 1/2.....
In Scotland you would use a "1"
Marc.... try it at 110degF condensing, then 90degF condensing.
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14-03-2002, 01:57 AM #34
............TEV..................
call or figure it out. It's either malfunctioning or misapplied.
....I say malfunctioning......... I'm out of here, I'll check y'all out tommorow.
see ya',
Mark
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14-03-2002, 05:23 AM #35[i]Originally posted by Fridgetech[i][/B] When you decrease SST you tend lose out on net refrigeration effect faster than you gain on pressure drop. If the compressors capacity is reduced by a greater amount, which it normally is, then the net effect on comp-tev ballance is for reduced superheat operation. [/B]
As such, you should still maintain your superheat.
As valve capacity decreases, C.U. capacity decreases according to the drop in S.S.T.
As valve capacity increases, C.U. capacity increases due to resulting increase in S.S.T. As such the system maintains a balance that is inherant under any given conditions whether right or wrong (in consideration of the design criteria producing the desired effect).Last edited by herefishy; 14-03-2002 at 05:39 AM.
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14-03-2002, 01:34 PM #36Reading some of those old articles on alt.hvac I see that Gary has always had way with summary's, they a joy to reread after all these years
Okay, I'll give it a shot:
In a stabilized closed loop series system, the mass flow is identical at all points, with the mass building up behind the chokepoint(s).
Imagine that once each minute I hand you a dollar and you hand me two dollars. Before long our closed loop system will stabilize with the rate of flow at all points being one dollar per minute, and the mass buildup is in my pocket. Your ability to transfer funds (increased capacity) is overridden by my ability to hold onto them (decreased capacity). I am the overriding chokepoint.
In a refrigeration system, (assuming no other restrictions) the overriding chokepoint can be either the metering device or the compressor. And like a dam in a river, the mass rises before and lowers after.Last edited by Gary; 14-03-2002 at 02:02 PM.
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14-03-2002, 03:42 PM #37Originally posted by Fridgetech
[I]... if you're letting head drop with ambients then as the compressor power reduces the condensers total heat rejection reduces and so sat cond temp is allowed to drop closer to ambient i.e. reduced TD.
If you look at a PH chart, you can see that for any given head pressure and liquid temperature, when the sat suction drops the net refrigeration effect is reduced.. and you see the compressors capacity is reduced by the lowering of vapour density and too the reduced volumetric efficiency of account of the increased compression ratio.
(I don't know how I got that "bold" print turned on. I don't mean to yell, sorry)Last edited by herefishy; 14-03-2002 at 03:46 PM.
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14-03-2002, 04:08 PM #38
Evaporator capacity is directly related to the surface area and the temperature diffence between the surface, and the medium being cooled (refrigerated space).
Say for example, a BOHN ADT 090. The capacity of the coil in consideration of the airflow created by the fans is 900btuh per degF T.D. In a typical 10degF application (i.e., 35degF space, 25degf S.S.T.) the unit cooler will have a net refrigerating effect of 9,000 btuh.
But in a 12degF T.D. (S.S.T. @ 23degF in the above example) The net refrigerating effect of the unit cooler will be 10,800btuh
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14-03-2002, 04:22 PM #39
Marc,
Really I'm interested in learning. I know you've got a lot to offer.
LMTD?
SHF?
Anyway, have we determined that the TEV is bad yet?
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14-03-2002, 04:33 PM #40Originally posted by Fridgetech
A reduced SHF will tend to increase LMTD for a given TD by reducing dt i.e. raising leaving temperature.
But wouldn't the (properly applied) TEV's (possible) reserve capacity allow such a scenario (maintaining SH) up to the point that the unit cooler drop in T.D. would become "static" when having exceeded the range of the (expansion device)?
The system is going to balance. The whole LOT cannot simply drop, unless something is broken. Right?Last edited by herefishy; 14-03-2002 at 04:40 PM.
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14-03-2002, 04:53 PM #41Originally posted by Fridgetech
less vapour from the fed liquid, the reduced superheat closes the TEV some and the subsequent/coinciding lowering of SST reduces suction vapour density which reduces system mass flow and so a new ballance point is found at a reduced TD and SH with reduced SST and mass flow.
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14-03-2002, 05:03 PM #42
I probably do, but am not familiar with the acronym.
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14-03-2002, 05:13 PM #43Originally posted by Fridgetech
Lol, the reduced return air temp reduces evap TD and so it reduces evap capacity
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14-03-2002, 05:19 PM #44
Are you saying, that simply evaluating the TD in terms of sensible (dry bulb) temperatures is the basis of my "misunderstanding".
That actually the same amount of work is being done but as conditions near the design temp, more of the work is latent. As such the variances in the sensible TD's?
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14-03-2002, 05:43 PM #45Originally posted by Fridgetech
if the compressor is losing capacity how can the evap be increasing capacity?
Okay, only to keep beating this dead horse.... I am assuming INCREASED compressor capacity due to lower ambients. You agree with that, right?
So, compressor capacity increases, resulting in increase of evap TD, as such evap capacity increases.
Where this started was you're statement regarding lower compressor capacity resulting from lower SST due to lower PD across TEV.
Is it me, or are we debating our agreement?
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14-03-2002, 06:37 PM #46
I am not proposing a "starved" coil condition in regard to increase in evap TD.
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14-03-2002, 08:54 PM #47
Okay, Marc.
I admit it. I've never considered anything along the line of SHR. I understand the basic concept of LH+SH (since you explained it), and no, I don't know what the acronym LMTD represents.
Yes, as SST drops, so does compressor capacity.
I was engaging only on the basis of the TD*btu/hr. degF thingy.
I visualize the SST and compressor capacity reaching a "static" condition in relation to the load. And I think that the way I was addressing the subject, someone could possibly have concluded that capacity would increase infinitely as SST dropped.
Yes, as SST drops in approaching design conditions the TD is not increasing it is decreasing.
I think I may be having trouble expressing myself. My only hope is that I am at least amusing.
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14-03-2002, 11:15 PM #48
Marc, I've been to your site before, and checked out the optichiller info. Good concept. However, I'm brousing your page, now, and I'm having trouble locating the information regarding to what you reference.
Should I be observing the tabulated data page?
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14-03-2002, 11:23 PM #49I was engaging only on the basis of the TD*btu/hr. degF thingy.
Last edited by Gary; 14-03-2002 at 11:35 PM.
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14-03-2002, 11:40 PM #50
Thanks.
Has bernie been back out to that job? I hate it when someone starts all the racket, then walks out of the room while we're beating each other up!
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