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Re: TXV's To Adjust or Not to Adjust - That is ....
e
Quote:
Originally Posted by
philfridge
I have to disagree :D The orifice is not oversized it is the same size and the t.e.v will close down via the bulb sensor, and if it has not been ADJUSTED incorrectly :) liquid should not reach the compressor as the valve is shut down .System will cut out on LP control. No damage done.
Here I sit on my new deck with my trusty laptop, on the first night of the year nice enough to enjoy a glass of homebrew Ale.
I might as well jump into the fray.:D
The first thing I look for in a plant with TX valves is a Evap with the fans off, or no water flowing etc.
Tx Valves do not shut off tightly enough to completely stop the flow of refrigerant in many cases. This is very often the case with NH3 valves after a couple years.
Yes the Compressor does shut down on Low Pressure. But the unevaporated liquid continues to flow at a small rate.
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Re: TXV's To Adjust or Not to Adjust - That is ....
Quote:
Originally Posted by
philfridge
What happens if the evaporator fans stop working? The orifice is effectively oversized and so the valve will hunt and may cause premature failure of the compressor due to liquid hammer.
I have to disagree :D The orifice is not oversized it is the same size and the t.e.v will close down via the bulb sensor, and if it has not been ADJUSTED incorrectly :) liquid should not reach the compressor as the valve is shut down .System will cut out on LP control. No damage done.
I would suggest that some systems that I work on would never shut down on LP due to the fans stopping. Have look at the cut out pressures for a Daikin condensing unit, some of these are many inches of vacuum.
I would also argue the point as the gear I was commissioning and talked about in an earlier post did just this. The fire alarms were being tested whilst I was commissioning. The main fans shut down, but I had the BMS control for unit operation linked so that I could work on my kit undisturbed by on off temp control.
The result, liquid floodback to compressor, foaming oil raised noise. I shut down the kit. And had to wait for the fire alrm test to be completed. The LP switch is a factory inbuilt 1.5bar set switch. The suction pressure with the main fan operating was 4.3bar with the fans off it did not drop below 1.8bar. I dare say it would have dropped further as the coil iced over, but by that time the compressor would have been covered in frost as it was already pumping liquid.
With the fans switched off the valve orifice must become oversized as it is sized for the refrigerant mass flow rate with the fans operating, not with the fans switched off:D. With the fans off the coil becomes a static cooler and cannot possibly boil off the refrigerant that is being delivered by the now oversized compressor. Yes if we are lucky the compressor may stop via LP but not in all instances.
What I would say is that in larger systems it is usual to incorporate an evaporator fan fail switch that also shut the compressor off in the event of loss of airflow. This definitley stops the problem.
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Re: TXV's To Adjust or Not to Adjust - That is ....
philfridge, refrigerologist i apologise for the misquote - I don't know what happened... I just hit the quote button like I normally would, lots of the quotes in this thread appear to be messed up
Anyway i completely agree with US Iceman in regards to total suction superheat and mass flow rates, one of our customers - a large supermarket chain in aus specifies a maximum suction superheat (as do the comp mfg's) but fits stub probes and really likes to see around 10K at the stubs entering the suction header, which normally lands the evap superheat around the 4 to 6K mark, and yes this total superheat is affected by line sizing and insulation quality, and I guess through experience 10K provides a decent mass flow rate (when compared to say 20 - 30K). It can make setting stores up a little tedious when they are so perdantic (spelling?) about stub temps, it requires a little tweaking to keep them satisfied with both evap and total superheats but I guess it keeps us commissioners on our toes a bit.
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Re: TXV's To Adjust or Not to Adjust - That is ....
Quote:
Originally Posted by
750 Valve
philfridge, refrigerologist i apologise for the misquote - I don't know what happened... I just hit the quote button like I normally would, lots of the quotes in this thread appear to be messed up
Anyway i completely agree with US Iceman in regards to total suction superheat and mass flow rates, one of our customers - a large supermarket chain in aus specifies a maximum suction superheat (as do the comp mfg's) but fits stub probes and really likes to see around 10K at the stubs entering the suction header, which normally lands the evap superheat around the 4 to 6K mark, and yes this total superheat is affected by line sizing and insulation quality, and I guess through experience 10K provides a decent mass flow rate (when compared to say 20 - 30K). It can make setting stores up a little tedious when they are so perdantic (spelling?) about stub temps, it requires a little tweaking to keep them satisfied with both evap and total superheats but I guess it keeps us commissioners on our toes a bit.
No argument from me here! I just wish I hadn't started this thread, I knew it would be troublehttp://www.refrigeration-engineer.co...ons/icon10.gif
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Re: TXV's To Adjust or Not to Adjust - That is ....
If the fans are not runing and the valve closes, what difference does it make which orfice size is installed? Closed is closed. If the coil is flooding the valve should respond unless the piping arrangment and bulb location permit flow through the bottom of the suction pipe without cooling the bulb.
There will be little or no superheat to open the valve.:confused:
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Re: TXV's To Adjust or Not to Adjust - That is ....
Quote:
Originally Posted by Refrigerologist
I just wish I hadn't started this thread, I knew it would be trouble
Call it a community service.:D
It might seem like you opened Pandoras box, but I don't think so. These are the types of discussions that once in print help to support learning for others.
The only down side in setting the TXV's to control the total superheat is that now the compressor bodies may sweat or have frost on them depnding on the application. Then someone thinks the compressor is flooding back and resets the TXV's so the compressors run HOT AGAIN!:o
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Re: TXV's To Adjust or Not to Adjust - That is ....
Quote:
Originally Posted by NH3LVR
If the fans are not runing and the valve closes, what difference does it make which orfice size is installed? Closed is closed. If the coil is flooding the valve should respond unless the piping arrangment and bulb location permit flow through the bottom of the suction pipe without cooling the bulb.
There will be little or no superheat to open the valve.:confused:
Or unless the power element lost it's charge. Then it could potenitally seep liquid since the valve is only responding to pressure changes alone (inlet and outlet).;)
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Re: TXV's To Adjust or Not to Adjust - That is ....
Quote:
Originally Posted by
US Iceman
Or unless the power element lost it's charge. Then it could potenitally seep liquid since the valve is only responding to pressure changes alone (inlet and outlet).;)
I need to think about that awhile. The few cases I have seen the TX valve shut down when the head failed.
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Re: TXV's To Adjust or Not to Adjust - That is ....
Quote:
Originally Posted by NH3LVR
I need to think about that awhile. The few cases I have seen the TX valve shut down when the head failed.
This is a little bit of a stretch I know. But as you have stated already, if the fans shut down the TXV should close also.
This is the only way I can think of where the valve might tend to leak liquid sometimes (although I don't think it would not be a great amount by any means).
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Re: TXV's To Adjust or Not to Adjust - That is ....
Quote:
With the fans switched off the valve orifice must become oversized as it is sized for the refrigerant mass flow rate with the fans operating, not with the fans switched off:D. With the fans off the coil becomes a static cooler and cannot possibly boil off the refrigerant that is being delivered by the now oversized compressor. Yes if we are lucky the compressor may stop via LP but not in all instances
.
The fact is though the expansion valve bulb sensor clamped on the suction line will sense the freezing line :eek: and shut the valve down stopping almost any liquid flooding back to the compressor. So the evaporator will not need to boil off the refrigerant :D . The compressor is not oversized but will just not have to do much work :rolleyes: .
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Re: TXV's To Adjust or Not to Adjust - That is ....
i have enjoyed reading this discussion so far but would like to ask what should the procedure be when, in these times of energy saving, consulting engineers are requesting that operating condensing pressures be reduced from 14.5 bar to 11 bar. if the performance of the valve is in part based on the pressure drop across it, then surely a 3 to 3.5 bar decrease in pressure drop would naturally change the valve/orifice combination's capacity. this surely would therefore force a change of orifice or superheat setting. we do not however receive instruction on this with the comment "the change is not large enough to warrant replacement or adjustment". i have not yet made the time to measure any change, but the 25% change in pressure drop woluld surely have a significant effect on the system operation. does anybody have experience of this?:confused:
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Re: TXV's To Adjust or Not to Adjust - That is ....
Hav to say one of the best discussions in a long time. Spent 7 yrs at a counter now 14 years field with 7 owning my company. Same rule stands... don't mess with a valve unless you have a spare on hand. Totally agree that some techs like to think they know how to read and set properly. A couple of nightmare situations and a " good " tech learns not to touch what he can't understand. I am learning everyday MY LIMITS and look for the problem before I apply the solution. Again....great discussion!!! Thanks.
'
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Re: TXV's To Adjust or Not to Adjust - That is ....
Quote:
Originally Posted by bill1983
...consulting engineers are requesting that operating condensing pressures be reduced from 14.5 bar to 11 bar.
This is easy to do in the winter time with air-cooled condensers since the condensing pressure set point can be set to lower pressures. You have to remember in this situation the liquid coming off of the condenser has a lot of subcooling or is much colder than normal (in summer).
The colder liquid tends to increase the valve capacity, while the lower differential pressure causes the valve capacity to be reduced.
Therefore, what you loose in one condition the other helps to increase. You have to look at the manufacturers ratings and correction factors to see where indeed this balances out in the this condition.
On the other hand, trying to lower the condensing pressure in the summer is a limit of the condensing heat transfer surface available. If the condenser was sized to reject the full load heat at 14.5 bar, then that is where it will want to operate.
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Re: TXV's To Adjust or Not to Adjust - That is ....
Quote:
Originally Posted by
Refrigerologist
Many engineers' in this industry say "you should never adjust a TXV superheat setting as they are factory set".
I would welcome comments on this statement.
Personally, I will agree with this statement, many TXV is already pre-set from the factory. :);)
But certain case, only by "professional" in refrigeration, you may do some adjustment, which you can find in instruction letter come along with TXV packaging, mentioned to turn clock-wise or anticlockwise vice versa. But straightly recommend only for "professional", which they may spend whole day or even couple days for "tune" and "adjust" TXV into the right proper system they want it to be.:eek:
Hope this is usefull.:D
Regards,
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Re: TXV's To Adjust or Not to Adjust - That is ....
Quote:
Originally Posted by
jeffrey5151
Hav to say one of the best discussions in a long time. Spent 7 yrs at a counter now 14 years field with 7 owning my company. Same rule stands... don't mess with a valve unless you have a spare on hand. Totally agree that some techs like to think they know how to read and set properly. A couple of nightmare situations and a " good " tech learns not to touch what he can't understand. I am learning everyday MY LIMITS and look for the problem before I apply the solution. Again....great discussion!!! Thanks.
'
You are right - don't touch what you don't understand, but if you can't adjust a txv to maximise its operation and just change them whenever they don't do what you want, then... well.... um... I'm lost for words.
How would you go getting a butcher's coldplate to flood fully and not smash valveplates? They don't always do what you want out of the box and no amount of changing parts will help you. Sometimes you need to use the old noggin (aka grey matter) and spend the time to watch the evap operation.
Most danfoss valves require a PD of between 10 and 12 bar across the valve before capacity is dramatically reduced and as mentioned before the subcooled liquid temps decrease the percentage of flash gas and thereby allow capacity to be increased.
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Re: TXV's To Adjust or Not to Adjust - That is ....
I just want to add here, that most of the tools we have to measure superheat, are not calibrated, low accuracy and repeatability, and measurement's (pressure) are often not taken at evaporator. That fact of life also makes few more arguments in favor to not adjust TEV unless you are 100% sure that it is needed and that your measured data are of any good.
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Re: TXV's To Adjust or Not to Adjust - That is ....
Quote:
Originally Posted by nike123
I just want to add here, that most of the tools we have to measure superheat, are not calibrated, low accuracy and repeatability, and measurement's (pressure) are often not taken at evaporator. That fact of life also makes few more arguments in favor to not adjust TEV unless you are 100% sure that it is needed and that your measured data are of any good.
Some very good points! I might add some comments about the pressure/temperature relationship of the refrigerants also.
At low pressures the equivalent saturation temperature can significantly change due a small pressure loss (or bad data from gauge). While at higher pressures the effect of pressure loss ( or again bad data) present much less of an issue.
If you will forgive the IP units... A difference of 1 psi in the gauge reading can amount to as much as 5 or 6 degrees temperature change at low temperature (depending on the refrigerant). At high temperatures, a pressure difference of 1 psi may only be equivalent to 1 degree or less.
So yes, the accuracy of the gauges and data used is very important. On a low temperature display case that might be set for 6-8 degrees (evaporator superheat in Fahrenheit scale) an error of 3 or 4 degrees due to bad data could cause the compressors to run hot or flood.:o
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Re: TXV's To Adjust or Not to Adjust - That is ....
Quote:
Originally Posted by
sugino_m
But straightly recommend only for "professional", which they may spend whole day or even couple days for "tune" and "adjust" TXV into the right proper system they want it to be.:eek:
Hope this is usefull.:D
Regards,
:) Yer sounds like my kinda job spending a day or two to adjust a t.e.v . Whats the pay like :D
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Re: TXV's To Adjust or Not to Adjust - That is ....
Quote:
Originally Posted by
US Iceman
Now for the big question....
Why don't we set the superheat on the evaporator to a slightly lower setting to reduce the suction line superheat to improve the compressor performance and reduce the motor and discharge temperatures?
Lower motor and gas temperatures would increase the life of the compressor and improve the oil stability. The compressor runs cooler, so it will last longer.
A slightly lower evaporator superheat means you are using more of the evaporator surface for latent heat transfer, so you are picking up more heat with the same coil surface.;)
carrier did something like this on EVX equipt chillers , the sensor above the oil pump on the o6e compressor was the suction temp sensor , so super heat was calculated after the windings
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Re: TXV's To Adjust or Not to Adjust - That is ....
Quote:
Originally Posted by
philfridge
.
The fact is though the expansion valve bulb sensor clamped on the suction line will sense the freezing line :eek: and shut the valve down stopping almost any liquid flooding back to the compressor. So the evaporator will not need to boil off the refrigerant :D . The compressor is not oversized but will just not have to do much work :rolleyes: .
So on a large capacity system then, with the correct valve orifice installed, but an incorrectly set superheat operating at 3K superheat, the valve would fully close to prevent liquid entering the compressor? What if it is a large packaged unit with a very short suction line and a loss of duty over the evaporator? After the valve has closed there will still be a large amount of liquid in the evaporator and with no duty to heat the refrigerant, liquid will enter the compressor for a short period.
I agree in principal with what you say, but with the precursor that the TXV should be set up by the commissioning engineer and only be left at the factory set adjustment if it has been tested and found to be acceptable, or, as required by the system designer/manufacturer.
If the valves are always correct then maybe I shouldn't bother to check the superheat if I have a reasonable head pressure and 5k of subcooling at the valve inlet.
I think it is too easy for all of us, (including me), to generalise about how each system we encounter would operate in such circumstances. There are too many variables from system to system. I don't think any of us here sit on fence. Some, like me feel each valve should be checked and adjusted, others feel they should be left alone. A case for agreeing to disagree, but it is an interesting debate:)
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Re: TXV's To Adjust or Not to Adjust - That is ....
Let's compromise and say the TXV's should only be adjusted when you have a very good reason and understand what you are doing. Otherwise leave them alone.:D
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Re: TXV's To Adjust or Not to Adjust - That is ....
Quote:
Originally Posted by
Refrigerologist
Some, like me feel each valve should be checked and adjusted, others feel they should be left alone. A case for agreeing to disagree, but it is an interesting debate:)
This has to be the last comment really :rolleyes: on this debate as I think all reasons for and against the adjustment of t.e.v s have been made. But everyone has their own beliefs on this subject and must decide for themslves whenever if or why the valve should be adjusted. I personally do not interfere with the adjustment screw but i select different orifice sizes.:) A most interesting debate.
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Re: TXV's To Adjust or Not to Adjust - That is ....
Thanks guys. A very good debate. No winners or losers thoughhttp://www.refrigeration-engineer.co...ons/icon10.gif
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Re: TXV's To Adjust or Not to Adjust - That is ....
Are you throwing in the towel?:p
This was a good discussion and now it's recorded for posterity for one and all.
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Re: TXV's To Adjust or Not to Adjust - That is ....
Quote:
Originally Posted by
US Iceman
Are you throwing in the towel?:p
This was a good discussion and now it's recorded for posterity for one and all.
Yep! Towel well and truely thrown in. I couldn't take any more beatings from you guyshttp://www.refrigeration-engineer.co...ons/icon12.gif
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Re: TXV's To Adjust or Not to Adjust - That is ....
:DHello guys
I am new here
But I think superheat should be checked (and adjusted if needed)on commissioning because you can never be shore what they did in the factory
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Re: TXV's To Adjust or Not to Adjust - That is ....
Commissioning is about adjusting the system components to achieve the rated capacity and capability of the system. However, there is a logic in this same process. MRcoolingMAGIC, hits it directly. During start-ups the system/room is hot. You have to allow the system to stabilize down to operating conditions reasonably close to what the norm might be.
At that point you can adjust the pressure switches, thermostats, etc. And during this time CHECK the evaporator & suction superheats (but don't adjust them yet!).
If you try to adjust a TXV during pull-down of the load you will be on the job for weeks trying to fix it.!:D
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Re: TXV's To Adjust or Not to Adjust - That is ....
[quote=US Iceman;96656]Aha! Now we are getting down to the real basics.:cool:
You cannot get more evaporator superheat than you have temperature difference between the entering air temperature and the saturated evaporating temperature. . . Therefore, if someone tells you they have the valve set for 15°F (8.3°K) of superheat, ask them to prove it!
Oh that wonderful word "superheat" just how it evokes a discussion.
Maybe we should first all agree to the definition of superheat and what it actually is? Because I'll bet my new digital gauges that we get more than one answer to this question.
Who wants to start?:D
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Re: TXV's To Adjust or Not to Adjust - That is ....
[quote=nevgee;110646]
Quote:
Originally Posted by
US Iceman
Aha! Now we are getting down to the real basics.:cool:
You cannot get more evaporator superheat than you have temperature difference between the entering air temperature and the saturated evaporating temperature. . . Therefore, if someone tells you they have the valve set for 15°F (8.3°K) of superheat, ask them to prove it!
Oh that wonderful word "superheat" just how it evokes a discussion.
Maybe we should first all agree to the definition of superheat and what it actually is? Because I'll bet my new digital gauges that we get more than one answer to this question.
Who wants to start?:D
OK I'll bite
To measure evaporator superheat:
1) Record the actual temperature at the TXV bulb.
2) Record the evaporating pressure at the TXV bulb.
3) Convert the evaporating pressure to temperature by using those handy pocket pressure/temperature cards. These cards/charts show the saturation pressure/temperature relationship for those refrigerants.
4) Subtract the temperature you converted on the pressure/temperature card from the actual temperature you recorded at the TXV bulb.
5) The difference is the actual evaporator superheat
as you can see this is a copy and paste, the thing that is not mentioned in this is the swing you get as your TXV opens and closes with demand. It takes time to set a valve properly you have to watch the case and use your lowest temp reading and check your pressure on that swing. If you have electronic SORIT valves your pressure also changes with demand.
To set the valves properly takes time. And to answer the begining of this thread. YES every valve should be checked for proper superheat before a store is turned over.
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Re: TXV's To Adjust or Not to Adjust - That is ....
[quote=iceburg;111642]
Quote:
Originally Posted by
nevgee
YES every valve should be checked for proper superheat before a store is turned over.
Robbers dont do that over here :o
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Re: TXV's To Adjust or Not to Adjust - That is ....
The system has to be in a stable condition to adjust the TXV when you have to do it. No capacity changes, no changes in the evaporating pressure, nothing. Any chnage leads to a potentially unstable valve setting.
If the system operation is unstable, then this is what you end up doing:
http://farm2.static.flickr.com/1022/...5397681c4d.jpg
You just wear yourself out and don't get anywhere.:D
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Re: TXV's To Adjust or Not to Adjust - That is ....
I totally agree US Iceman, we spend the first week with vacuums, leak checking, gassing up, making sure all the fans are running and there are no flood backs to the compressors ect. then we leave for a week sometimes two these are new store startups so we can do that. When we get back to the store the gas and oil has found its place, that is when we start superheats. We get them as close as possible at that point, sometimes once the cases are loaded some more adjustments are needed but not much or many.
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Re: TXV's To Adjust or Not to Adjust - That is ....
Quote:
Originally Posted by iceburg
...sometimes once the cases are loaded...
This raises an interesting point.
What effect does the added mass of the product in the cases have? It helps to stabilize the loads thus reducing any erratic swings that may occur. Reducing the swings also helps to stabilize the loads, and hence smooth out the operation of the refrigeration system.
It's the same thing as an empty refrigerator. Open the door on an empty fridge and the temperatures shoot up. Open the door on a full fridge and the temperatures are moderated due to the added mass.
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Re: TXV's To Adjust or Not to Adjust - That is ....
Quote:
Originally Posted by
powell
....
Here's a link to the Parker/Sporlan (Sparker) website for more detailed info on adjusting superheat....
I'm not sure that a "newby" should be posting in this older thread, but (unfortunately) that link has gone "404". I do see wonderful Threads on this BBoard, which probably provide even better information... but is that Sporlan PDF still available anywhere else? Meanwhile- I have question, and it's exactly this topic: "TXV, stay with factory-provided non-adjustable, or replace it with an Adjustable, sized smaller to match compressor?"
Here's my sad history. I'm in USA, a homeowner with pretty much a new installation. (R410A) It's "pretty much new" due to a tech from a now-fired company trying to fix hunting and inadequate cooling, on a second call-back, by adding more charge, and more charge, and more charge... And it all blew up after he left. (Probably the Evap first, but the Compressor quickly followed.) Now to the point and question: I'm definitely not DIY, and my new tech (new company) seems way more competent. But I think that my configuration DOES call for upgrade of the factory-installed TXV to an adjustable, smaller sized TXV for several reasons:
- The Evaporator Coil (from USA company 'Advanced Distributor Products') is oversized relative to compressor (17.5 kW versus 12.25 kW), for efficiency reasons.
- altitude 5200 ft (yes, WAY up).
- lineset > 50 ft, with about seven 90 degree turns (some "sharp", others "soft").
ADP supplies this Evaporator Coil with an R410a TXV. It's a nonadjustable Emerson, the older Type-A, not the brand new Type-C. (So it's == Alco, IIRC.) Factory labels the part to be nominally capable of anything from 12.25 kW (42,000 BTUH) to the full Evaporator rating of 17.5 kW (60,000 BTUH). My Trane compressor is labeled at the absolute bottom of this range.
So, I'm thinking that the TXV had better be operating nearly closed most of the time.
And I don't like that idea, or the thought of it maybe trying to open up so wide as to generate bubbles in the incoming liquid line (from the less capable compressor). I saw severe hunting before, after the first recharge... although other service errors, including crud left in the lines, may have played a role at that time too.
The only way to tune this one-size-fits-all Emerson is by adding or removing charge. (subcooling OR superheat, not both). And the flowrate "curve" is probably too "steep" anyway.) So I'm inclined to buy a Danfoss TR6 "universal upgrade" kit for him to swap in, before doing the final N2 blow-out and charging. Nominal size 4 tons (14.0 kW). Although some of you say that Danfoss makes 'em a lot "bigger" than the BTUH rating, I think that this would still be a better match for the 12.25 kW compressor than the factory-provided Emerson. (And even if the slope is still too "steep", at least some adjustment can be done via spring tension.) Should I maybe buy the Danfoss kit all the way down at "3 tons" nominal size?
The one thing I won't like to do to the new guy is to make him charge it up, run, and test using the factory provided Emerson-- then find that I'm HATING the performance measurements, make him recover it all, then replace the TXV, then re-do the vacuum test and blow out with N2 (again) and re-vacuum (again), initial charge up (again), stabilize for measurements and charge adjustment (again), make changes, wait for it to stabilize (again) ... not a good way to win friends. So I'm inclined to ask him to take it out, replace it with the Danfoss right at the start of the call. BTW, Trane also discontinued the "factory authorized service" relationship with my original installers, and my "new" guys are Trane's current representatives here.
Thanks for reading all this. :) BTW, it's A/C only (not a Heat pump), and outdoor temps here in Reno do exceed 100F (several times each year). But humidity is extremely low, all I need is the cooling.
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Re: TXV's To Adjust or Not to Adjust - That is ....
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Re: TXV's To Adjust or Not to Adjust - That is ....
All my installation's I Check superheat A/C 10-12F medium temp 8-10F low temp 6-8F this is what Copeland requires
also doing so you will make sure that you get the most out of the coil and customer saves on electricity by unit shouting off quicker
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Re: TXV's To Adjust or Not to Adjust - That is ....
^^ Thanks nike - good to see you around.
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Re: TXV's To Adjust or Not to Adjust - That is ....
Quote:
Originally Posted by
desA
^^ Thanks nike - good to see you around.
I am little to busy these days.:)
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Re: TXV's To Adjust or Not to Adjust - That is ....
Quote:
Originally Posted by
yoelyeve
All my installation's I Check superheat A/C 10-12F medium temp 8-10F low temp 6-8F this is what Copeland requires
It is important to remember that these numbers are only valid when the refrigerated space is at design temp.
When the space temp is higher, the superheat should be higher... and vice versa.