Flooded Ammonia Refrigeration

[stcornish]

I am looking for information on flooded ammonia systems. Can someone give me direction.

[jheffernan]

The best information I've seen is in the RETA books (Refrigerating Engineers and Technicians Assoc.) They're a trifle spendy, but the information is great. You can go to www.reta.com and should be able to find info about a chapter in your area.

I used to think that flooded systems were the only way to go, but I'm becoming partial to pumped liquid systems. Both systems beat DX/TX systems by a wide margin for simplicity and efficiency. (my opinion).

Cheers,
Jim Heffernan
Tillamook, OR, USA

[frank]

Why don't you send a post to Frosty - he's a knowledgable guy and works with this sort of equipment every day!

[jheffernan]

Hi,
What is LPA/EEV? Taking wild guess Low Pressure Ammonia/Elecronic Expansion Valve? I'm intrigued by the prospect of improving the efficiency of a totally wetted coil.

All my experience is centered on working in a cheese factory, almost all ammonia. I sometimes mess about with smaller ***** units, but am usually humbled in the process.


Cheers,
Jim Heffernan
Tillamook, Oregon

[Andy]

Hi, I also think pumped systems are the way to go, especially where you need a large central plant with numerous evaporators all at various different levels. Also the hot gas defrost is a fast effecient means of defrosting. The only draw-back with pumped NH3 is the large charge required in the plant, this means the plant siting has to be well thought out, with out of town industrial estates being the only sane option. We also fit a plant called a low pressure receiver system, this has a minimal charge per KW duty, but works with the liquid over-feed principal, with a wet return from the evaporators into the LPR where the saturated refrigerant is boiled off by the warm liquid from the condenser in an indirect heat exchanger. The liquid enters the evaporator by means of the pressure difference from the condenser to the evaporator, not by pump pressure, although we do fit the expansion device in the liquid line within the plant room so the liquid drops it's pressure whilst travelling to the evaporator. As for defrosting the most common type used for this instalation is reverse cycle defrost, this leads to low head pressures after defrost and rapid pull-downs due to the cold condenser, which was the evaporator during defrost. Also unlike pumped NH3 there is no limit to how low you can condense the refrigerant at in the condenser, with this feature head pressures of 10c are not uncommon in plants during the winter, leading to large savings in electricity during the winter.
Regards. Andy.

[Frosty]

Andy, who's LPR do you use.....the original (Star Refrigeration) or one of the many copies...SPL (when they were in business) and Morris and Young?

Frosty

[Frosty]

Marc, there are no 'concepts' unique to the LPR....high liquid sub-cooling....effective oil recovery....reliable liquid/gas seperation.....low superheats.....effective evaporator overfeed.....floating head pressure control producing low compressor pressure ratios (increase in COsP)...reverse cycle defrost, low refrigerant charge, high refrigerating effect per kW/kg system charge etc. the list goes on!

All these attributes are found in other systems but, often not always together. The gathering of these attributes contribute to a very efficient, reliable system, best suited to one on one situations, i.e. one cooler, one evaporator - nothing beats it!

Cheers

Frosty

PS - But of course, you should know this shouldn't you - you spent a little bit of time with Star.

[Frosty]

Hi Andy

Further to the LPR conversation, you are right what you say regarding running these systems with ultra low condensing pressures. Yes, you do get phenomenal COP's but, on some systems, running with condensing pressures to low can cause problems.

It's possible that LP faults can occur and I have known issues where insufficient heat available in the condensed liquid feed, causes loss of LPR oil recovery- insufficient embolism (drive) which is required to 'force' the oil/refrigerant mix out of the LPR!

Cheers

frosty

PS It's nice to see another Star man on this site - I thought I was on my todd! (very lonely) LOL

PS - Hi Frank - I've got the numbers for the Sheffield lap dancing club that you were intersestd in!!!!!!! - I'll be in touch.

[Andy]

Hi, Frosty. Yes LPR's can be a super piece of kit. The system I was refering to was a NH3 blast employing a LPR. The complete system had been designed to have a second evaporator and compressor unit added, in any case this never happened. We took advantage of the extra heat exchange surface available and floated the head as low as possible whilst the unit was running at night. I suppose the extra surface area in the LPR heat ex allowed large amounts of subcooling to still take place even with the liquid comming off the condenser at 14c. With the addition off a shell and plate economiser the liquid was eventually subcooled to -21c before entering the evaporator at the -39c evaporating temperature. Oil return was not a problem with the oil returning by gravity assisted by the head of liquid in the LPR acting on it. As for refrigerant flow, this is controlled by the subcooling TD accross the LPR, at low heads subcooling occurs quickly so the main line solinoide is on more than the bleed solinoide creating the necessary refrigerant flow at low heads.
Nice to see someone who works for Star posting on the this Web site also.
Regards. Andy.

[Andy]

Hi, Marc. I suppose liquid over-feed is just a defination. The liquid leaving the evaporator on a LPR system may most likely not be saturated but slightly superheated. This would differ from a true pumped over-feed system where the liquid leaving the evaporator is saturated with a more refrigerant being pumped through each time that can be evaporated. Having said this more refrigerant passes through the evaporator on a LPR system than can be evaporated in the evaporator, the remainder being evaporated in the LPR. I stand to be corrected on this as I only work on the systems, not design them.
Regards. Andy.

[Frosty]

Andy, the terminology 'overfeed' when applied to the LPR system is incorrect, in fact the fluid leaving the evaporator is saturated - hence the term 'wet return'......but only just.

If the fluid left the evaporator in a superheated state, system balance would be affected, the saturated liquid stored in the shell side of the LPR would dissapear and LPR liquid sub-cooling would become non-existant....seriously effecting system performance!

Frosty

[evmnc@panafonet]

if you sucsribe your problem i might be able to help you
because i'am working in ammonia refrigeration system
thanks
Alex

[Frosty]

Wow Marc, I'm 35 now, been in the refrigeration game since I was 17 and have worked at Star all that time.

I started as an apprentice, rose to the position of engineer, then senior engineer, then supervisor.....next stop, service manager then customer support manager and now, branch manager and do you know what......I've met many, many people in my time, customers, suppliers, engineers, all sorts of people. But in all my time I have never, ever met anyone who comes anywhere near as arrogant as yourself.

What is wrong with you? Why do you feel the need to belittle people wherever possible - are you that insecure? or are you that good? Somehow I doubt it!!!!!

You say you run your own business.......do you have any many customers? If you do and you talk to them like you talk to people on this web site....how long will you have them for?

I know that I am not alone thinking the way I do, I know a lot of people who contribute to this web site and yes Marc, they all think the same as I do....your a pr*ck!

Why don't you do us all a favour, take a break from this industry for a while......go and take up something like basket weaving.

PS - One word of advice for you.....don't go onto the basket weaving world web site.....they are a bit harder than us - you never know what the consequences might be!

PPS - One last thing Marc - you might fool a good percentage of the people on this web site with your dt's and dp's - but there are a few of us here who really know the score! And you know what? maybe we are not as stupid as you think we are!!!

Nice talking to you

Frosty

[Frosty]

OOOOoooooohhhhhhhh Marc, I really do look up to you......please, please teach me all you know - i'll be forever in your debt - wan*er!!!

Don't fuc*in waste my time you arse&ole

Yours (I know **** all in comparison to the great South African fridge god)

PS - please don't talk to me like that.....your frightening me!!!!

Frosty

[Frosty]

Don't you worry......they are all lining up to have a go, of course, you won't realise that with you being a smug bas*ard. And by the way, if you really want me as a trophy, come and try your luck!!!! I'm only down the road at Star Derby - feel free to drop in at any time.....because you don't worry me one wee bit - buddy....notice that I can spell buddy and you can't!!!

I might even put the kettle on....I've got some rat poisoning that I need to get rid of!

See you soon!!!

Frosty

[Frosty]

Name the day, arsehole.....time for daddy to teach the little scared boy a lesson.....and then it's no more belittling people - is it - TW*T

Any time next week. In fact, no, what about the institute dinner tomorrow....I'll be there - might be a bit more interesting than listening to the speaker!

Email me back and tell me what table your on - or are you banned from going cause your a boring tw*t who really knows fu*k all - do you just get it all out of a book? Ooohh thats a nice paragraph, I think I'll recite a little bit of that!

Let me know, I'm interested to know - I'm one of about 630 + guests!

[WebRam]

OK, lets keep the "discussion" on a proffesional level please, no more personal attacks, thanks

[Frosty]

Marc...you are no more than a yellow-bellied FAGGOT.

N.B. Apologies webram, but theres no place for people like him on this site!

When he stops talking down to people and slating STAR (after all, I no the real reason why he 'left'), then and only then, will I leave him alone...looks like we'll have to go private FAGGOT.

[frank]

Hear, Hear, Frosty mate!!

I'm also at a loss as to why Marc seems unable to accept that other people do have an opinion, o.k. that opinion may not be as good as what Marc believes his opinion to be - but I don't see that this should result in insults and the like.

Come on Marc - ease up a little and lets get the forum back to the sort of place where we can discuss aspects of a great trade!!

[Andy]

Hi, Folks, calmed down yet?
What I was going to say, or more to the point explain was my post saying that the refrigerant leaving an evaporator of a LPR system is most likily slightly superheated. This statement is general and comes from the fact that most liquid metering devices used to feed the evaporator in an LPR system use a pulse width modulation. This is basically open/shut with the evaporator over-feed during the on pulse and slightly under-fed during the off pulse. The liquid seen in the LPR sight-glass builds up from the on pulses, creating the subcooling. As energy can neither be created or destroyed, any energy given up to the cold liquid in the LPR ends up in the suction vapour, hence Marcs interpretation that subcooling does not increase COP, but subcooling does have advantages in delivering a full head off liquid to the evaporator. With an LPR the idea is to add subcooling without superheating the suction vapour too much. The increased COP comes from the fully or nearly flooded evaporator which increases the evaporation pressure, reducing the compression ratio and the lower head pressures from a condenser which can be allowed to run to a lower condener sett point. Another advantage that is gained from the LPR being employed is a better draining of the condenser, again given a decrease compression ratio, although this can be a dis-advantage if taken too far as the heat rejected in a condenser from the trapped liquid is rejected outside the system increasing COP, a proper balance is required to acheive the best results.
Anybody fancy posting a PH diagram to explain?(I am still playing with my Iscool program)
Regards. Andy.

[Jasper]

Hi Frosty
Can't fault anything that you said about THAT S A WAN **r
Only wish he could go home and use his profound knowledge to better the lives of his fellow and much loved countrymen.

[Mike Hopkins]

Now I have a little dumb question.
Having looked at Hysave's site and what Burley's Rink Supply has done, it seems that the acronym's are starting to confuse me. I have seen LPA, LRP, and LPR. From what I understand of this theory it is not neccesarily liquid pressure amplification as I have seen it called but more of forced liquid supply or FLS, my own new acronym. What do all these acronyms mean. It is a great idea and I have seen many potential applications for it. The only exposure I have is the little 100 ton ice rink chiller that had the Burley's set up on it. The only thing I didn't like was the volute seals (orings) leaking and having to replace them. What type of pumps are used now? What kind of reliability are you having with them as far as leaking? I think the pumps I had trouble with used Buna N orings and I considered going to Viton. Never really had any seal problems, are any cropping up? The other thing I liked on the Burley's setup was they also used 2 brine pumps. Not for redundancy but for efficiency. During higher loads a larger capacity pump was used (like during pull down). At low load a smaller pump was used, kinda matched flow with load. With todays technology one could probably use one pump with a frequency drive and have the best of both if the pump curves would allow it. Wonder what the thoughts are on applying frequency drives to the liquid pumps are? Say maybe pressure or temperature controlled to ramp up/ ramp down the pump?
Mike Hopkins

[Andy]

Hi, Mike a LPR is a low pressure receiver. This is basically a suction accumulator to trap the wet return liquid from the evaporator, this liquid is then boiled off by the warmth of the liquid from the main high pressure liquid line which passes through the bottom of the LPR. (indirect heat exchange) Higher COPs are acheived by the flooded evaporator and the floating head (The expansion valve feeding the evaporator usually uses the high pressure float principle). The LPR is there to separate out the liquid from the wet return and to subcool the liquid being fed to the evaporator, it also allows reverse cycle defrosting to be utilized, as it again separates out liquid which could enter the compressor suction at the change over points to defrost or back again to refrigeration. It also holds an amount of refrigerant that keeps up the evaporation during defrost for short periods preventing the defrost from stalling at several points during the defrost cycle. A LPA pump is a liquid pressure amplification pump used to increase liquid line pressure on floating head systems, allowing the expansion valves to acheive their rated duty and to provide liquid line subcooling. Marc will explain this better as I have not used this system myself.
Regards. Andy.

[Andy]

Marc, I forgot to mention that the suction pressure is increased by the flooding of the entire evaporator. With regards to the flash gas being moved to the LPR and being released to the dry suction, this is a reconised problem high-lighted when single stage screw compressors are used with liquid injection, higher than normal discharge temperatures are encountered compaired with similar DX system. I think the normal way around this is to use Glycol/water mix oil coolers rejecting their heat to outside the system. Another way around the flash gas problem is the two stage LPR, which is basically an open flash economiser clamped onto the side of the conventional LPR. This removes some of the flash gas to the inter-stage usefully flashing off to subcool the liquid in the economiser. This should reduce the flash gas component in the main LPR. Two stage LPR's are unfortuately a thing of the past, I have only one site in N.I that has these, both are fitted to R22 blast freezers with RC4-2-11 compressors. The flash gas component is introduced at the low stage discharge where it enters the high-stage suction along with the injected liquid which de-superheats the low stage gas. Control of the liquid levels and indeed the high level cut out in the economiser is all by thermistors which are wired back to simple voltage sensor relays fitted with two 14ohm resistors accross them, liquid height is variable (a little) by adjusting the voltage sensing relays. Oh and on of these system also employs singer valves, an eairly bio-metal electronic enpansion valve.
As for NH3 LPR's the liquid is econimised in a shell and plate DX econimiser fitted with an AKVA to remove some of the flash gas conponent.
I hope what I,m saying makes sense, please feel free to comment as I am learning as I go and any imformation will assist.
Regards. Andy.

[Andy]

Hi, Marc, I forgot to mention nice Photo, youv'e aged somewhat from the last photo
Also I was thinking about the line sizes on an LPR system, I supose we could reduce the liquid line size as there's plenty of subcooling to stop flashing? What about the wet return will it be smaller than a DX system for the same mass flow? With regards to the subcooled liquid line picking up heat, I personally feel that excessive subcooling of the liquid is a no no -5c is a practical limit for an non economised liquid line, lower than this and you are subcooling for no gain and probably as you say picking up heat from the surroundings. Again if you subcool too far (a high TD setting accross the LPR) you risk holding back the liquid too long creating low suction pressures increased thermal lift and starved evaporators.
Everything in moderation.
Regards. Andy.

[Andy]

Hi, Marc, did you enjoy seeing us being stuffed at the hands of the english on Saturday, painfull wasn't it? But fear not we are now working on ways to clone Humphries. Who would have thought that we could have been so badly beaten, especially after what we did to the welsh. I normally don't follow rugby but I hope the match with Scotland goes better as another defeat like Saturday would be very bitter.

With regards to the inclusion of two stage systems, I was trying to show that by open flashing the refrigerant at inter-stage less flash gas was present in the LPR leading to cooler running compressors, by virtue of denser less superheated vapour entering the compressor inlet.
VI is another very important point often over-looked when selecting screw compressors for systems with floating head, what can I say, I personally think auto VI is the way to go Sabro and Gram have been doing it for years.
Regards. Andy.

[Sawdust]

Pump circ is definitely the way to go except for the obvious frustrations of having an accumulator with about 3 tons of ammonia and some gorilla got happy closing the pump suction valve and crushed the seat into a mangled pulp just before you had to change the shaft seal on the pump and production is waiting

Pump circ has advantages over an ammonia DX plant in reliability as the TEV tends to need replacement on a regular basis due to the erosion created by the higher density of the ammonia and this then creates slugging if it is not picked up soon enough. On bigger plants the only way to go is with pumps though. I notice that most of the various alternatives have been discussed but no one has mentioned the pump-a-drum concept yet.

Dale

[Sawdust]

There seems to be a fair liking to single compressor-single evap setups in this forum. I would assume this is because they are small plants? In my experience I have found that to be very costly in the way of power consumption and compressors. On larger plants i found the better way to go is with an economiser running of the economiser port of a screw with auto VI and that allows not only subcooling of the liquid before it feeds into an accumulator but also provides an option for small high stage loads in the event that you would like to run chill water for space cooling or a small chill room.

With regard to the oil draining on an accumulator running at -39 C, well it is like draining syrup and you are just in a vacuum so that doesn't help either. Isolating valves on the oil drain pot with a hot gas feed into the pot to build up some pressure does though.

We can go on forever discussing COP's, the benifits of the one over the other and all the rest but at the end of the day the type of installation boils down to a few factors only. Firstly the customers budget, secondly the size and requirements of the cooling system and thirdly the personal preferences of the designer.

I have seen too many good plants turned bad during upgrades or expansion phases purely because of an inept designer who failed to apply the first principles of ammonia refrigeration and just to join in on the acronyms it is KISS. That stands for Keep It Simple Stupid. Remember that the operator and the tech don't have degree's and are not rocket scientists or they would be the designers. But then there are days when I am convinced that the tech has a far greater understanding of the refrigeration process than the desk jockey designer even though he doesnt fully understand the acronyms.

Dale

[Andy]

Sawdust, Not all plant's over here are small, but it helps to discuss plant that most people are familiar with. The company I work for has just sold a pumped NH3 system to one of my customers, this system has an installed compressor capacity of 1200Kw at -8c, this size is quite tipical of what we are being asked to quote these days. Two stage NH3 systems with low and high stage drums still exist, I know of 10 or 15 such systems, these tend to be that bit older and fitted with recips. With most large low temp systems now being fitted with single stage screws with ecomisers. I suppose cost is to blame. Recently our company completed a blast freezing complex, this has the capacity to freeze 720Tons of fish in a day, every day. This job was pumped NH3 with Grasso "piggy back screws" where the low stage compressor discharges straight into the high temp compressor with liquid injection cooling at that point, these again have economisers fitted.
What type of systems do you normally fit/work on.
Regards. Andy.

[Andy]

Hi, just incase of confusion the pumped system I was refering to is a single stage pumped system servicing coolers in an abattoir -6c NH3 is pumped around the coolers with an intended room temperature of 0c.
The largest room on this system has an installed capacity just over 600Kw, this is a lamb precooler with the lambs comming off the slaughter line cools the lambs to normal storage temperature within 6Hrs. The lambs are fed in by a moving line this line traverses through the chill until the lambs come out the other side to stored or shipped out in trucks. The plan is that 3000 lambs will be cooled in the 6Hr period. Also fitted on this job are a number of low weight lost cattle chills, these have suction motorized valves fitted to control the evaporation in the coolers, this in turn controls the room humidity and minimises the weight loss or drying out of the beef in the chills. A difference or gain of 1% in lessening weight loss in a chill is a serious amount of money with the capitial investment being paid back in a short number of years.
Anyway that is probably more information than anyone wanted to know.
Regards. Andy.

[Sawdust]

Any, hi. I used to work for Grenco in South Africa (eventually spending my last 5 years with them as industrial service manager for the Johannesburg office) and we were involved in all the shapes and sizes of plant from the largest ammonia plants in South Africa to the small DX cold rooms when our clients needed a small factory shop for puplic sales.

At the moment I do expat work around Africa having spent the last 4 years between Kenya, Tanzania and Angola working on various types of plants for the fishing industry.

[Lazarus]

Yup can tell by the writing that Andy is a Star man, SPL werent they renegade Star men!!!! Spent many hours working on those LPR systems with both Star and SPL people, still not sure about the theory that you dont need a discharge NRV if you have a four way valve there !!!!!!! Morris and Young is Gary still with them!!

[Mark C]

What is wrong with you? Why do you feel the need to belittle people wherever possible - are you that insecure? or are you that good? Somehow I doubt it!!!!!

I know that I am not alone thinking the way I do, I know a lot of people who contribute to this web site and yes Marc, they all think the same as I do....your a pr*ck!

Why don't you do us all a favour, take a break from this industry for a while......go and take up something like basket weaving.

PS - One word of advice for you.....don't go onto the basket weaving world web site.....they are a bit harder than us - you never know what the consequences might be!

PPS - One last thing Marc - you might fool a good percentage of the people on this web site with your dt's and dp's - but there are a few of us here who really know the score! And you know what? maybe we are not as stupid as you think we are!!!

Nice talking to you

Frosty

LOL.... This is why I rarely offer any kind of advice at this site. I could not have said it better!

Here I thought we would have some real conversation about ammonia. Nope, it's just Marc mouthing off again! And Marc?? There are those that are far more knowledgable than you in ammonia refrigeration. One who actually works on them day in and day out for one...

And Marc is a "Moderator" here? **Rolling Eyes**

[Mark C]

Acerbic as ever, Marc.... I never said anything about my knowledge of other refrigerants.... Of which I am more than competent. I am however, pretty darned good at ammonia.

Like I said, you drive more people away from this site than you encourage. It's just a personality defect, of which you have no control. It's just your nature.

Every Forum has a denizen of the muck such as you. It's just not worth my time or effort to wrestle in the mud with a pig... It just makes the pig happy and gets you really dirty!

[Andy]

Yup can tell by the writing that Andy is a Star man, SPL werent they renegade Star men!!!! Spent many hours working on those LPR systems with both Star and SPL people, still not sure about the theory that you dont need a discharge NRV if you have a four way valve there !!!!!!! Morris and Young is Gary still with them!!

Hi Lazarus
I don't work for Star anymore and I am quite happy about that. Still they have some good people and ideas, sadly there was no room for my ideas

Kind Regards. Andy

[Lazarus]

Hi Andy,
Thats a tale i have heard before... and yes they have and had some really good engineers, though i havent spoken to any for some time i do remember that a lot of them seemed frustrated.... Maybe something to do with how there managed!! Hope you are enjoying wherever you are now...

[Peter_1]

Like I said, you drive more people away from this site than you encourage.

Very interesting. Can you perhaps prove this?

[Camille]

you may want to read one of the best
and excellent books by WF STOECKER,
Industrial refrigeration volume 1 and 2
also IIAR Ammonia refrigeration handbook

Regards
Camille

[Peter_1]

volume 2 fomr Stoecker?? Never heard of it before.
Do you have perhaps an ISBN number

[US Iceman]

Peter,

The Industrial Refrigeration book was originally published in two volumes. The current book (which you probably have) is in one volume now.

Volume 1 & 2 are the old versions.

[latent heat]

The two stage flooded ammonia system is a great system to work with. I run one myself, 87,000 lbs of nh3. The two stage is very effecient in comparison to a singal stage dry system and one of the nice things is liquid can be drawn off of multiple areas of the system at multiple liquid pressures to reudce energy consumption. Intercoolers also reduce energy consumption by removeing superheat from the first stage of compression. And everyone should remember Nh3 absorbes more latent heat per lb. than any other refrigerant (very important)

[Peter_1]

At different pressures to reduce energy consumption you said. This surprises me.

But allways higher pressures then the pressure on the main drum.

So, the main drum must work under the lowest pressure needed somewhere in the system. So the main drum is running verry unefficient because compressors has to evaporate constantly low or very low because one place needs a low pressure.

So I don't see the benefit of this statement.

Intercoolers reduce energy consumption between first and second stage. It's mainly because cooling the interstage gasses is needed for the compressors discharge valves instead of energy reduction.
Even more, the energy taken out of the interstage flow has also to be removed by the compressors, so you gain it perhaps at one point but you loose it back in another point.

[Andy]

At different pressures to reduce energy consumption you said. This surprises me.

But allways higher pressures then the pressure on the main drum.

So, the main drum must work under the lowest pressure needed somewhere in the system. So the main drum is running verry unefficient because compressors has to evaporate constantly low or very low because one place needs a low pressure.

So I don't see the benefit of this statement.

Intercoolers reduce energy consumption between first and second stage. It's mainly because cooling the interstage gasses is needed for the compressors discharge valves instead of energy reduction.
Even more, the energy taken out of the interstage flow has also to be removed by the compressors, so you gain it perhaps at one point but you loose it back in another point.

Hi Peter
it would be common to have at least one HT drum along with the LT drum, running at a intermediate pressure of say -12 deg C, pumps fitted below to feed the liquid to the HT rooms.
It is also possible to have a number a various HT drums commoned on a HT dry suction header, with evaporator pressure regulators controlling the various drum pressures.
Drum evaporations could be.

Blast chilling -18 deg c (common to header)

Cold room 0 deg c, with -10 deg drum pressure

Chilled water 3 deg c with a drum pressure of 0 deg C.

It is further possible to have a different HT drums and compressors which are only linked to their own HT load (say the 0 deg c and the -18 deg C) which do not handle any LT intermediate load, their only link is to the HT condenser. This would be the example Latent heat is talking of.

Kind Regards. Andy

[US Iceman]

It sounds like the discussion centers on the benefits of using multiple back-pressure regulators to control several temperatures higher than the common suction pressure.

If so, then this has nothing to do with energy efficiency. If a common low suction pressure is maintained by the compressors, then of course a back-pressure regulator is required to control a higher evaporating temperature. This does not make the system more efficient.

It only allows the installer to create multiple evaporating temperatures, which operates off of a common lower suction pressure. When the pressure regulator opens, the higher pressure vapor expands down to the lower pressure. In other words the compressor is still compressing the total volume of vapor at the lowest suction pressure.

If on the other hand the suction pressure is operated at a point closer to the pressure controlled by the back-pressure regulator (perhaps with no regulator at all) the efficiency of the compressor/system would be greater.

As to the multiple liquid pressures; liquid pressure has nothing to do with system efficiency. Liquid pressure is needed to provide sufficient differential pressure to achieve the rated capacity of the liquid feed valve .

Now, if the liquid is colder (lower enthalpy) then you have some benefit and increase the total heat removal by increasing the net refrigeration effect.

The intercooler de-superheats the low-stage compressor discharge gas before the gas enters the hi-stage compressor. I think we can agree on that. The de-superheating cools the gas back down close to the intermediate saturation temperature to reduce the discharge temperature of the hi-stage compressor.

The major point related to energy savings is accomplished by the reduction in pressure ratio for the lo and hi-stage compressors. When the compressors are operated with reduced pressure ratios, the compressor efficiency improves (both volumetric and mechanical). Even with two compressors operating in series, the total power use is less than a single stage compressor operating at the same conditions.

[Peter_1]

It sounds like the discussion centers on the benefits of using multiple back-pressure regulators to control several temperatures higher than the common suction pressure.

If so, then this has nothing to do with energy efficiency. If a common low suction pressure is maintained by the compressors, then of course a back-pressure regulator is required to control a higher evaporating temperature. This does not make the system more efficient.

It only allows the installer to create multiple evaporating temperatures, which operates off of a common lower suction pressure. When the pressure regulator opens, the higher pressure vapor expands down to the lower pressure. In other words the compressor is still compressing the total volume of vapor at the lowest suction pressure.

That's how I understood it, so if the compressor has to work constant at a low pressure only one coil needs it, then it's working not energy efficient.

This is a 2 stage Mycom we service.

[Andy]

Hi Peter


It is further possible to have a different HT drums and compressors which are only linked to their own HT load (say the 0 deg c and the -18 deg C) which do not handle any LT intermediate load, their only link is to the HT condenser. This would be the example Latent heat is talking of.

Kind Regards. Andy

Side loads gents It is possible to add a HT compressor, which doesnot remove any LT vapour, therefore the evaporation pressure is exactly what is required for the best effeciency of the system.
These side loads may also subcool the LT feed liquid, if they are the lowest HT evaporation.

This would be more effecient than evaporator pressure regulators However using an evaporator press reg on any system is preferable to no pressure regulator, running all the HT at -18 deg C instead of just some of the load, especially if humidity is important in the HT rooms.

Kind Regards. Andy

[US Iceman]

Hi Andy,

When I think of side loads, I think these are loads applied to the side port of the screw compressor. This is also another big area where we can have a lot of discussions.

If you are describing a HT load connected directly to a HT compressor suction pressure, then yes, this is more efficient than a HT load connected to a LT load (using back-pressure regulators). And, if the HT load also provides the subcooling for the LT load I also agree with you on this point.

However using an evaporator press reg on any system is preferable to no pressure regulator...

I think this depends on many factors.

If the evaporating pressures of the loads are fairly close, you can select the evaporators using different TD's. This would allow you to use a common suction pressure (without regulators).

There are many things to consider. The greatest loads should determine the evaporating pressure. I have seen too many systems where the larger loads at the higher temperatures are regulated down to a much lower pressure.

The performance penalty is smaller if the smaller loads are controlled at the lower pressure.

[Andy]

Hi Andy,

When I think of side loads, I think these are loads applied to the side port of the screw compressor. This is also another big area where we can have a lot of discussions.

I always thought both are types of side loads, eco ports on screws and extra load and auxiliary compressors on a two stage system ( running at a different pressure than the main HT load from the LT).
I once worked on a system that had a deep freeze running on a compound compressors, with what I suppose was a side load, the chills were DX ammonia, with the suction returns feeding into the closed flash intercooler, with addtional HT compressors to handle the "side load"

Kind Regards. Andy

[US Iceman]

I think I have it now.

Same langauge, but different definitions.

[Josip]

Hello Guys,

if you cannot understand each other how I can.

What is, by your definition, side load, extra load?

Eco port we have on screws and that is up to us if we are going to use it (with some additional investment) and get that capacity free of charge or not. We can install complete compressor or more to work at eco pressure and here we call it economizer system. No need to explain why

Anyhow, basically we have two stage system LP and HP becuse even eco compressors have comon condenser with HP compressors on LP system.


Sometimes modern designers (of refrigeration plants) drive me crazy with modern sh't design trying to invent warm water.

There are some good ideas and designs but belive me very few....