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Hi every one I am from East Africa Tanzania I have this problem in supermarket display units previous ones used expantion valves and new ones use capillary , we usually have frequent power failures and we have to switch off main aircon and immediatly temp goes high on units but older one with expantion it used to maintain its cooling why can some one educate me on this.Thanks in advance
hi jay,
do each display unit has its oun condensing unit or its a rack?
are they pumpdown system or jujt on/off?
give us some more details please.
chemi
It has indivisual condencing units .
with mechanical defrost timer and no heater to defrost .
hi jay.
I guess in the old display units the evaporator is at the top and when the power stops the refrigerant migrates to the cold spot which in this case its the evaporator at the top. this slow circulation lasts for about two minuts before it starts to get hot. and thats explains why it stays cool.
the new units which have the evaporator at the bottom under the steel plates "pull" the hot air in dou to higher ambient air pressure and gets hoter more quickly.
I think that what is happening there.
is the serengeti park still as beutiful as used to be 20 years ago?
chemi
This thread must win the poll for bad......ahem......awful spelling!!!
But, talk of serengeti has got me going!!!
Ahhh......Ngoro goro Crater............and Mount Kilomanjaro.
Wow
Ill give my eye teeth to go there
Hey, Jay........you got a job going there??? In return for some lessons in spelling !!!
Lol
it still wild and under german management but animals are too less it is worth to visit once again you will not be dissapointed i bet you . thanks for help both have their evoporator in same position at bottom with fans blowing air through them and coming back from top, and we have many other places worth visiting but its real costly
Aiyub,Quote:
Originally posted by Aiyub
This thread must win the poll for bad......ahem......awful spelling!!!
But, talk of serengeti has got me going!!!
Ahhh......Ngoro goro Crater............and Mount Kilomanjaro.
Wow
Ill give my eye teeth to go there
Hey, Jay........you got a job going there??? In return for some lessons in spelling !!!
Lol
Sorry, I have to say this but English talking peoples - especially sorry again .....Americans - thinks that the whole world speaks English. Don't forget that the English language is only on the fifth ranking of world languages.
Also I have to use some spelling corrections - mostly typing errors - but don't let us fall in the same trap as alt.hvac where a pure technical question is mostly responded with sarcastic answers. That's the reason why I moved to here.
Don't take this personally Aiyub, but this was what I felt when I read your response. Lucky for Jay he mentioned something about Africa. I also had difficulties reading the post but I waited what others should say, ..technically.
He was understandable, because Chemi tried to help him.
I will be the first to ask to correct my spelling because I wanna write down as correct as possible.
Not everyone in this big world has the possibility to learn proper English and even worser, ...going to school to learn elementary things like reading and writing,.... let's take aside learning another language.
I once worked a time together with Romanian (here goes my spelling again) and Polish peoples (here in Belgium),... well ...you should start crying if you hear there stories and especially when you realize why they came working here in Belgium.
I will give you an example how we Flemish (Dutch speaking part of Belgium) think: if we Belgians go to Spain, we try always to speak Spanish, or Italian in Italy, or German in Germany. We (try) to adapt us to the country we're going. In the first place, we never try to speak our own language in a foreign country, we try to speak their language. If this doesn't work, we then switch to what we think they will understand the best (for example French in Italy) and last to English. And I speak much better English then French and even then, we try it in French. That's an attitude we learned in school and all the Flemish peoples I know do it like that.
I will end Aiyub with this..... all - and I mean ALL - your posts were more of worth reading them , with always a humoristic undertone.
No hard feelings at all but that's me..... I say or at least ,... I try to explain what I feel.
hi peter.
my mother never spoke to me in english so I do my best.
please dont take it personal, some people have that thing about perfect writing, some about perfect cleaness and so on.
I would like instead to be corrected when I make a spelling mistake and not use a programme to do it for me. this way I will learn better.
take it easy and have a great day.
chemi
i can't speak any other language so really apreicate how well chemi, peter etc cope with the more technical aspects..and i love miltons posts for there directness ;-)
however very often i write thinking everything was correct only to read it back with mistakes all through it....:-/
(i personally believe this has something to do with bill gates deliberately trying to undermine my obviously superior intellect ;-)
anyway nuff said...
cheers
richard
Hi:D
English is the language I am supposed to speak and my spelling is terrible. Personally I don't mind spelling as long as the point of the conversation is not lost to the reader.
Anyway I speak an english dialect, which has not really got a written form, you would not want to see the attempts people make at trying to write Ulster Scot's.
Kind Regards. Andy.:D
Hello Peter,
I know exactly where you coming from, and no, I take it on the chin and bear no hard feelings.
I am not critical of anyone whos first language is not English who makes spelling errors, in fact 100% marks to them for having tried in the first place.
I assume a very laid back and humurous stance on this forum, I never get too serious or worked up any anything. I do appreciate the fact that we are a collection of people from around the world, all with a common ground, "a love of refrigeration"
Thats all that matters, and we try and help each other out, like I have been helped out in many times.
No one is superior, there is no class or language barrier. We are all one happy big family.
I would just be estatic if a Mongolian from upper Siberia or an Argentinian from Cape of Horn posted here, good english or bad, its the contribution that counts.
My first language is not English............( surprise, surprise!!! ) so for me to be sarcastic of anyone else would be like the pot calling the kettle black!!!!
So, please, Im just the joker in the pack, and my brand of humour gets me in trouble sometimes, but I got that from the Brits........they joke about everything, from the minute they wake up in the morning.
And, lastly.......if you want me to help with a technical question.......forget it!!! I can help with legal and business issues.....but to tell you psychometric properties or enthalpy.......or why evap is not cold..........Im not your man.
Funny because I run my own fridge business
So, to all in this happy melting pot of ours...........read my lips......your spelling does not matter!!!!! Keep on posting.
And this is for Jay.
Namesti bhai, aoo be gujerati waat keroo. Mene taroo telephone dewanu, aoo tene phone keraaa
[Namesti bhai, aoo be gujerati waat keroo. Mene taroo telephone dewanu, aoo tene phone keraaa [/B][/QUOTE]
that's easy for you to say !! ;-)
cheers
richard
ok guys,
now that we have finished with language issue, lets go back to the original problem. jay's supermarket display units.
please read it again and think of an answer.
chemi
hello jay:)
surely the compressor units are integrally mounted in the base.
And the temperature rise in the case is due to the ambient temperarure in the shop rising having a proportional effect on how the unit condenses.I cant see the compressor/condenser being remotely mounted using capillary tube .
I have seen it done and im not saying it wont work,however as well as being very bad practice i think the compressor would soon reach the end of its working life.Lol
Capillary systems dont cope very well with high ambients(in the uk anyway)maybe its just the design of our equiptment in the uk.
regards mark :)
The way I read the posting.
One unit has an expansion valve
One unit has a cap tube
Air conditioning is switched off............ie: ambient increases
Display units still running.
Unit with expansion valve works better
Unit with cap tube struggles
So, I put it down simply to: Expansion valve offers superior cooling performance, especially as condensing units are remote
How far are the condensing units from the evaporator?
With remote units, cap tube is not a good idea
Replace cap system with expansion valve. You will see an improvement in efficiency
Someone can explain why on a remote system expansion valve is better then cap tube
There are also lots of other factors to consider
Are both condensing units same, same capacity, similar age, are both compressors working properly, valves in good condition
Are the line distances the same
Are condenser coils clean, condenser fans working ok
You need to log all the pressures, temperatures of both systems so an analisis can be made
hello all
Capillary tube cabinets are mostly used on small cabinets with very short pipe runs due to the critical refrigerant charge.
Lets take the scinareo that the liquid and suction line are extended, the accumulator is not sized to hold this extra volume of refrigerant the compressor goes off cycle ,the liquid refrigerant migrates to the evaparator on start up the compressor trys pumping liquid .So therefore a typical TEV/RECIEVER system would be more cost effective long term.The case temperature pull-down would be dramatically improved due to increased liquid refrigerant entering the metering device,and better heat transfer .
The cap tube is a critical charge insufficient charge starves the evaparator ,overcharge has an adverse effect on operation and any refrigerant in excess will back up into the condenser therefore the evaparator temperature would go up.
I have attended jobs in the past with capillary/liquid lines installed 30+ meters by cowboys, both times the compressors were u/s.This in my opinion is very bad practice.
hope this helps
regards mark:)
[QUOTE]Originally posted by Peter_1
[B]Aiyub,
Sorry, I have to say this but English talking peoples - especially sorry again .....Americans - thinks that the whole world speaks English. Don't forget that the English language is only on the fifth
Dear Friend,
I feel what you mean, I migrated to Australia after a Uni education
and being good in various languages. Upon working in Europe and USA I was always admired about my language knowledge by
person in which country I worked. Now being 20 years in Austrlia I am asked each time after 2 minutes of talking .Where do you come from and what an accent you still have. Writing papers in a second langauage is difficult but even proper speaking in another language ( not your own) is extremely difficult. Just let people accept what you have to say and do it as good as you can.
Anybody with comments-- shoulder it of and see it as stuped.
jg/oz
you could move to australia peter, the way things are going over here is un-uniform languages... which is really bad. i have the attitude that if you migrate to a country which speaks english, german, bolgarian or whatever language - you should learn or at least try your best to speak the native language, which is english in my case.Quote:
I will give you an example how we Flemish (Dutch speaking part of Belgium) think: if we Belgians go to Spain, we try always to speak Spanish, or Italian in Italy, or German in Germany. We (try) to adapt us to the country we're going. In the first place, we never try to speak our own language in a foreign country, we try to speak their language. If this doesn't work, we then switch to what we think they will understand the best (for example French in Italy) and last to English. And I speak much better English then French and even then, we try it in French.
the problem with our country now is we let too many foreigners into our country no questions, which is fair enough if they are willing to adapt to the aussie way of life, or are legit assylum seekers but many are not.
this causes the majority to segregate themselves from our society and many choose not to adapt into the free aussie way of life and start treating everyone in australia like their native homeland, which is sad because this great country used to provide freedom of speach, freedom of religion, a fair and just go for all. but day by day this is slowerly being erroded away by the ones who take all your handouts and agree to your way of life to get here then bite your arm off once they are.
hi all....i agree with Peter 1 but don't forget that english speaking people don't really feel the need to learn another language and anyway.......why should they?while it's true that english language ranks 5th it's true that it's the most spread around the globe!To Jay i have to say i really loved his country!The Kilimangiaro is just impressive but i enjoyed other places too!Keeping my fingers crossed i might go there again this year to follow a project in Dar Es Salaam......see you there Jay!:)
An expansion valve will (theoretically) close off when the compressor stops.
A capillary tube system will continue to feed until presssures are equalized. Hot gas in the condenser will migrate to the evaporator and condense, warming the evaporator.
And regarding the language issue, I appreciate anyone trying to communicate in a second (or more) language, especially one as strange as English.
So jay asked why do TEV cabinets work better than capillary on fluctuations in ambient temperatures
On capillary a change in load or condensing temperature has a effect on pumping capacity and flow rate in the capillary.Leading to changes in case temperarure.
The TEV with MOP limits flow at a predetermined rate therefore limiting condensing pressures and keeping refrigerated case temperatures down.Thats the fundamentals.
Hope this helps jay
regards mark:)
hi mark,
I think what jay meant is why the temperature in the cases operates with TEV, remains lower then those with cap tube when electricity supply goes off.
I need more details to come up with more then a guess.
chemi
Chemi-cool as we know language over the www is not allways easy .
A simple explanation is misinterpreted.My post was only intended to aid someone if possible.
:)
Actually, the TEV is able to respond to changes in load, while the cap tube system is not. The cap tube is designed for a given set of conditions and changes in load or condensing temperature have very little effect.Quote:
Originally posted by markfiddy
So jay asked why do TEV cabinets work better than capillary on fluctuations in ambient temperatures
On capillary a change in load or condensing temperature has a effect on pumping capacity and flow rate in the capillary.Leading to changes in case temperarure.
The TEV with MOP limits flow at a predetermined rate therefore limiting condensing pressures and keeping refrigerated case temperatures down.Thats the fundamentals.
its possible the systems are slightly undersized for there proper stand alone application, having them run with the air con on would reduce the heat needed to be removed by the cabinets as well as lower ambient and therefore lower head pressures causing units to operate properly.
turn air off, heat is too much, raising general ambient temp, therefore raising head pressures resulting in a higher COP and system stuggles to work.
the system with the TXV would tend to feed more liquid to evap when it sensed a change, becasue it would have the capacity to be able too as more then likely there would be a receiver with spare gas in it. whereas cap tube systems are designed to work within a specific ambient temp range, temp gets too low it could freeze, too high everything gets hotter because it is trying to work outside its design conditions.
hope this helps a little if you havent counted it out already...
I thank you all for the help, in fact it helped me in solving my problem.
I had to defend my case in front of engineers from south Africa KOXKA company.
With all the explanation done it shows that these units were not designed for supermarket. We have this supermarket on sea front, so we have high temp plus humidity causing this display units to fail when we loose aircon support.
I apologise for my English and thanks a million for all the support . :)
Leo 1967: Thankyou. Where r u from?
Whenever you come over to Tanzania, do get in touch. I am based in Dar-es-salaam
phone(mobile) # is +255 748 225507
Regards,
Jay
Hi jay :)
Im glad you have reached a solution.There are many genuine,methodical,helpfull people who will give advice when needed.Which not all trades have.
regards mark:)
.Quote:
Originally posted by RogGoetsch
Actually, the TEV is able to respond to changes in load, while the cap tube system is not. The cap tube is designed for a given set of conditions and changes in load or condensing temperature have very little effect.
Actually .If the condensing / evaparator temperature rises the flow through capillary remains constant.Raising superheat of vapour and saturated condensing pressure.
As the condensing pressure rises the flow through the capillary increases ,causing evaparator pressure to rise,decreasing pressure differential across the capillary until the system stabilizes.Reducing sub cooling increases flashing decreasing flow rate until system returns to normal operating conditions.
regards mark:)
hi marc
Basically my point was that cabinets working on capillary need a liquid seal at the entrance port .On the event of condenser fan failure or rise in condensing pressure ,would increase flash gas at the capillary.Until flow rate or load returns to normal .
My opinion was that yes course condensing temperatures have a large effect on how the case operates.
mark
marc
I see what you mean :o .
so marc subcooling increases flow rate.
Flashing reduces flow rate.
regards mark:)
A properly designed cap-tube system is critically charged. Under design conditions, the charge is not large enough to flood back to the compressor.
The entrance to the capillary loses its liquid seal all the time. Gas bubbles recondense in the first inches as flow slows and the seal is restored. (Most cap tubes are soldered to the suction line or coiled in the evaporator cabinet for this reason.)
Changes in condensing temperature/pressure change feed rate only minimally for two reasons:
1) The capillary tube is not a strictly pressure-dependent flow device, as an orifice would be, but as the name suggests, flow is very much dependent on the capillary effect due to the surface tension and surface wetting characterisitics of the molecule within a cylinder whose surface area is maximized while its volume is minimized.
(For example, capillary action is what allows trees to grow higher than about 33 feet, since that is the highest that water can be elevated by atmospheric pressure at sea level. Redwoods grow many times this height, in part due to the extremely powerful force of capillary action carrying water far above 33 feet.)
2) There isn't enough refrigerant to feed more than its full-flow design conditions. (See first paragraph.)
The simple fact is that capillary systems do not respond well to changes in demand. They only do three things well: cool at design conditions, starve the coil at high demand, and flood the coil if the load drops.
A TEV, on the other hand, can respond to changes in demand by monitoring superheat and increasing the feed rate. This allows the compressor to operate at a higher point on its performance curve to match the demand.
A TEV with a MOP charged bulb merely limits the top end to prevent a compressor from over-amping when coming out of defrost, for example.
Hope this helps.
Rog
hi marc,
help me to get wiser: I know the problems with capillary tubes in small refrigeration units but in air condition its a different story, from the smallest split to large rooftop units are all using cap tubes and no problems.
what is then, the difference between the two if any?
thanks
chemi
from the smallest split to large rooftop units are all using cap tubes and no problems.
what is then, the difference between the two if any?
as chemi-cool asked above I too am curious to know about it please :confused:
marc i was referring to a capillary set up.Quote:
Originally posted by markfiddy
so marc subcooling increases flow rate.
Flashing reduces flow rate.
regards mark:)
Okay, perhaps a bit of exageration to make a point. I see too many trying to apply the Bernoulli equation and coming up with faulty conclusions.Quote:
Originally posted by Marc O'Brien
Rog, lol, capillary action in cap-tubes ?? !! Lol !! That's good humour :)
Liquid flows through a cap tube easily, while vapor does not. This is the primary design principle of a cap tube.
AC systems work fine with cap tubes because after initial pull-down, air across the evaporator is almost always within a few degrees of the design value, hence the load remains relatively constant. Perfect for a cap tube.
It will starve the coil at first if the initial load is high, but that limits compressor amps, keeps condensing pressures in the ball park even on hot days and provides a simpler and lower cost system: no expansion valve or start capacitor on single phase units.
In any discussion of subcooling, it is important to remember that this involves two temperatures, i.e. SCT (saturated condenseing temperature) and liquid temperature. Lower liquid temperature is a good thing. Higher SCT is a bad thing. Therefore it is incorrect to think of increased subcooling as being good or bad. Which of the temps has increased/decreased to increase the subcooling?
Rog
I have just read your thread ,you make some valid points regarding capillary systems.
The scenario i was explaining was an extreme condition as jay was explaining.
I have to disagree that single phase units dont need a capacitor when fitted with capillary,i would say a good proportion of equiptment in the uk has capacitor start.One of The only type i have seen that dont require this are chest freezers which have adaquate time off cycle for pressures to equalize.
I think that our(uk) integral equiptment is made only to cope in cooler ambients:) Lol
mark
hello mark,
most of commercial compressors from the 1/6 hp comes with a start capacitor for the reasons you have mentioned.
if they dont, you can add one yourself by using the manufacturer instructions or use supco starting kits.
these compressors will work fine in high and low ambients, giving them long life.
chemi