Designing a refrigeration system

[ihsan]

Dear members
I am fresh graduate and I am considerably lacking technical expertise in designing a refrigeration system from scratch. Therefore I like to ask help from you in order to design a refrigeration system. Details of the requirements are below
Required evaporating temperature: -45 Deg C
condensing temperature: about 35 Deg C
Product: Tuna
Refrigerant: Ammonia

I believe in order to achieve such a low temperature I have to go for a two stage system but i do not know how to calculate the capacities

Can anyone help me how to determine compressor capacity and condenser capacity for a plant. This plant is going to operate 04 plate freezers each one containing 1200 kg of Tuna.
Your assistance is highly appreciated
my email is hiraqul@hotmail.com

[icecube51]

i wonder in what was your graduation.
if it was in cooltechnics you didn't learn much. all these questions are pure basics.

Ice

[ihsan]

i wonder in what was your graduation.
if it was in cooltechnics you didn't learn much. all these questions are pure basics.

Ice

Thanks.
I need some guidance help me to start.

[Peter_1]

Most important questions to start: Tuna, how much, in and out temperatures do you need,..

-45°C with NH3, system will run in vacuum, are you aware of this?

Is this for a school project or for a real life project.

[ihsan]

Most important questions to start: Tuna, how much, in and out temperatures do you need,..

-45°C with NH3, system will run in vacuum, are you aware of this?

Is this for a school project or for a real life project.

Dear Peter_1
Thank you for your reply
The back ground of my assignment is as follows.
Currently we are having 4 plate freezers run by a refrigeration system working at -35 deg C evaporating temperature. Actually this refrigeration system is designed to freeze fish in freezing tunnels and it was quite recently we added these plate freezers to the system.
Now I am assigned to relocate those plate freezers with an independent refrigeration system. And we want to operate the freezers at lowest possible temperature. According to the manufacturer of the plate freezers we can use it at a min of -45 deg C.
I have recently finished my degree in mechanical engineering and I am not a specialized refrigeration engineer. What I have with me is some theoretical knowledge in thermodynamics and heat transfer and I want some help from people like you to implement my knowledge into practice. And thats why I am here searching for advice.
I would very much appreciate if anyone could help me in achieving what I am looking for. I can say I am a fast learner and I need some guidance.
Please guide me where should I start and how should I can come up with a solution to my design. I know its a laborious task that require lot of knowledge and i think i should give it a try for myself...

[mad fridgie]

You are putting the cart before the horse. You need to understand your process before you contemplate designing a refrigeration plant (Which by the way I would leave to those who have greater expertise). One thing you have in your favour is that you are using plate freezers. The plate freezers manufactures have data on different products, design temps and most important thickness, giving process times, thus load profile.
My advice is work with others first to gain an understanding of the industry
Then you can ask more specific questions, and you will recieve detailed answers,

[ihsan]

You are putting the cart before the horse. You need to understand your process before you contemplate designing a refrigeration plant (Which by the way I would leave to those who have greater expertise). One thing you have in your favour is that you are using plate freezers. The plate freezers manufactures have data on different products, design temps and most important thickness, giving process times, thus load profile.
My advice is work with others first to gain an understanding of the industry
Then you can ask more specific questions, and you will recieve detailed answers,

The 04 plate freezers (1200 kg of fish each) is going to be used to freeze fish (Tuna). the package size is 75 mm. These freezers needs to be run at -35 deg C evaporating temperature. If I can still lower it i would like to make it something like -45 deg C but it is not a strict requirement for now.
We already have an ammonia system but that system is designed to operate at -17.5 deg C. I would like to find ways so that we can modify that system to operate at -35 deg C (or -45 deg C). I think we cannot achieve this without going for a two stage system. I am trying to figure out how I can calculate the capacity of compressors and condensers to achieve what I require. If you need more details i would love to share with you as I am desperately in need of help from experts. I can also be reached through my e mail
hiraqul@hotmail.com

Hoping to hear from you.... I need your help pls

[abet_meneses]

contact a refrigeration supplier in your area and have them designed the system to suit your requirements,and an experience refrigeration engineer will do the job,and you will learn step by step from professional.

[winks]

Hi for all,
Im an electrical engineer and I need any cooling capacity calculation softwear or program.
Thanks,
winks@y.net.ye

[mad fridgie]

The 04 plate freezers (1200 kg of fish each) is going to be used to freeze fish (Tuna). the package size is 75 mm. These freezers needs to be run at -35 deg C evaporating temperature. If I can still lower it i would like to make it something like -45 deg C but it is not a strict requirement for now.
We already have an ammonia system but that system is designed to operate at -17.5 deg C. I would like to find ways so that we can modify that system to operate at -35 deg C (or -45 deg C). I think we cannot achieve this without going for a two stage system. I am trying to figure out how I can calculate the capacity of compressors and condensers to achieve what I require. If you need more details i would love to share with you as I am desperately in need of help from experts. I can also be reached through my e mail
hiraqul@hotmail.com

Hoping to hear from you.... I need your help pls

You need to go to your plate manufacturer, give him your product data "Tuna, 75mm thick", tell him what evap temp you will be using.
This will give you a process length "Time". and normally duty.
When you have this, you then can calculate the refrigeration system.
or if you are not sure
You know your product, how long do you want it to take to freeze? then go the plate manufactures giving them this detail andd they give you a required plate temp (evap temp)
Either way sort your process out first, then call in experts. "pay"

[ihsan]

Thanks for your comment. I have consulted the freezer manufacturer and he said he will forward me the capacity and I am awaiting for his reply which I expect will receive by this week.
Since I am living in different country I can only contact him through e mail and I would love to work beside such a professional.
My aim to join this forum is to learn. If i have the chance to work with a pro i am sure i will learn a lot. But believe me....by living in Maldives you hardly have a chance to work with a pro and that's my problem.
I would love if someone can guide me the steps to design even a simple ref system. (Forget the plate thingy). How the calculation for the compressor and condenser is made.. assuming i have the required parameters like evaporating temperature, condensing temperature, operating pressures and so on...

[Peter_1]

As soon your plate mfr gives you your capacity, we can go on further.
Still my questions remains unanswered:how many kg's/batch, required realistic and needed freezing time, temperature in and req. temp out...
This will give you already an estimate.

((kg'/batch x DT from temp in to 0°C) + (kgs/batch x 86 ) x (kgs/batch x DT from 0°C to req freezing temp ) ) x 1.16/1000/required time gives you kW you will need.
Select a compressor which will give you at TE -31°C this needed cooling capacity and select a condenser with a TD of 10 K or lower with ambient temperature to release this capacity again.
Then you need to select your vessel, regulating devices,....

[Peter_1]

http://www.scribd.com/doc/21207371/H...ng-Manual-2008

[mad fridgie]

Thanks for your comment. I have consulted the freezer manufacturer and he said he will forward me the capacity and I am awaiting for his reply which I expect will receive by this week.
Since I am living in different country I can only contact him through e mail and I would love to work beside such a professional.
My aim to join this forum is to learn. If i have the chance to work with a pro i am sure i will learn a lot. But believe me....by living in Maldives you hardly have a chance to work with a pro and that's my problem.
I would love if someone can guide me the steps to design even a simple ref system. (Forget the plate thingy). How the calculation for the compressor and condenser is made.. assuming i have the required parameters like evaporating temperature, condensing temperature, operating pressures and so on...

Good you are now moving in the right direction, At some point you will need to contact a refrigeration supply company (this is not a cheap process). I suggest that you purchase a packaged deal, including commissioning. (if you want manage interconnecting pipe work with their design, then this is a good method of learning the process.) You are not in a position to undertake this process without full technical backup. This forum is excellent but it is not a free consulantcy service. All information is given with care, but no responsibilty, on a project like this you need some one to take responsibilty, your client needs to allow for this.

[ihsan]

As soon your plate mfr gives you your capacity, we can go on further.
Still my questions remains unanswered:how many kg's/batch, required realistic and needed freezing time, temperature in and req. temp out...
This will give you already an estimate.

((kg'/batch x DT from temp in to 0°C) + (kgs/batch x 86 ) x (kgs/batch x DT from 0°C to req freezing temp ) ) x 1.16/1000/required time gives you kW you will need.
Select a compressor which will give you at TE -31°C this needed cooling capacity and select a condenser with a TD of 10 K or lower with ambient temperature to release this capacity again.
Then you need to select your vessel, regulating devices,....

Dear Peter_1
Thank you very much for your kind reply. Here is the answer to your question
We need to freeze 4800 kg (Lets say 5000 kg) of tuna per batch and they enter the freezer at a temperature of 20 deg C and leave -25 deg G at the core. Our ambient temperature is around 30 deg C.
Your post is very helpful to me but i would appreciate you if you could define those constants for me... 86 and 1.16.. are they specific heats of Tuna???

[ihsan]

The book is very helpful.... Very much appreciated. Thanks a bunch Peter_1

[Peter_1]

you need +/- 86 cal to convert 1 gr of water to ice (phase change) and 1.16 is the conversion from cal to W or kcal to kW.
Fish is mostly water and it gives you also some margin.
So in your case for one batch ((5000 x 20) + (5000x 86) + (5000 x 25 x 0.85)/1000)*1.16 divided once again by the hours to freeze you batch gives you your needed kW.

So in 2 hours you will need 370 kW at -31°C.
All figures are +/-

[SreekanthP]

You can search the website for the software coolpack it is very good and help you in calculating the heat load calculations as well.

[tuga2000]

Ishan
look for Ashrae handbook refrigeration and fundamentals Freezing times tables are there.
Mean time request help to plates manufactures they know about it. They deal with this daily.
Usually process altered with temperatures gives you a different performance. As compressors, evap and condensers. I hope you are not pretending re-use existent equipment.

Your load is like this
Q = C X m x DT

freezing latent heat
sensible prior freezing
and sensible after frozen
coefficients change as soon is frozen, shape and sizes affect the time.
Estimating cooling load as water if fine, be sure times are possible with experts.
packaging dimensions and air distributions play here too.

I can help you with the refrigeration pack, oil separator, oil management system and control panel.

-35ºC SST / SDT 45ºC in one stage with a J&E HALL Screw compressor, is possible.

Is more than just put little things together. I thing they put you in a position to do magic, there are companies and contracting refrigeration engineers without idea how to design a blast freezer, so be care full in what to trust.
My first advice: get advice from a consultant, they quote equipment with written specifications.

[ihsan]

you need +/- 86 cal to convert 1 gr of water to ice (phase change) and 1.16 is the conversion from cal to W or kcal to kW.
Fish is mostly water and it gives you also some margin.
So in your case for one batch ((5000 x 20) + (5000x 86) + (5000 x 25 x 0.85)/1000)*1.16 divided once again by the hours to freeze you batch gives you your needed kW.

So in 2 hours you will need 370 kW at -31°C.
All figures are +/-

Thanks again Peter_1
It really helped me a lot and I am now able to start. Here I have another question again for you. You have calculated that I will need a capacity of 370 kW. In choosing compressor can I choose 02 units of something about half of that capacity. Adding both will I get the required capacity?
I am trying to get an online manufacturer's specification for compressors and condensers. Is there any way i can have such info for various models in a single site? I live in the Maldives and here we don't have that kind of industry so I have to find someone from whom i can get spares most cheaply.

[ihsan]

Ishan
look for Ashrae handbook refrigeration and fundamentals Freezing times tables are there.
Mean time request help to plates manufactures they know about it. They deal with this daily.
Usually process altered with temperatures gives you a different performance. As compressors, evap and condensers. I hope you are not pretending re-use existent equipment.

Your load is like this
Q = C X m x DT

freezing latent heat
sensible prior freezing
and sensible after frozen
coefficients change as soon is frozen, shape and sizes affect the time.
Estimating cooling load as water if fine, be sure times are possible with experts.
packaging dimensions and air distributions play here too.

I can help you with the refrigeration pack, oil separator, oil management system and control panel.

-35ºC SST / SDT 45ºC in one stage with a J&E HALL Screw compressor, is possible.

Is more than just put little things together. I thing they put you in a position to do magic, there are companies and contracting refrigeration engineers without idea how to design a blast freezer, so be care full in what to trust.
My first advice: get advice from a consultant, they quote equipment with written specifications.

Thank you Tuga2000
I have already contacted the plate freezer manufacturer. It is supplied by a company in Denmark. REFTEC A/S. They also supply compressors and the engineer has told me that he will give me a specs of a screw compressor which can handle -45 deg C evaporating/30 deg C condensing. We are already using their equipments and I have personally met the said engineer too. So i think i am with a trust-able person after all. Thanks a lot for your input.
I know its more than putting little things together but also trying to learn those things is my first intention. I have recently graduated and now its my use the knowledge in practice. Here in Maldives we dont have companies manufacturing those sort of things. So its really hard to work alongside a professional and I always love to do that

[tuga2000]

Ihsan
Just one more thing, Evaporation temperature is selected by the process, (freezing time, shape, sizes, etc).
The condensing is selected considering a differential, be careful with 30ºC for condensing as your design temp in Maldivas is 30ºC.
I recommend to you a healthy 10K differential for the condenser as minimum, that means 40ºC condensing if is air cooled. Or lower if you consider water cooled, heat recovery in any other process, cooling tower, etc) . Lower differential implies expensive condenser. As well with electric consumption increase with condensing temp, so max 15K, because you don't want increase discharge pressure to fit a smaller condenser.
This company that you mentioned work representing the Vilter compressor packs, a little rustic for my opinion compare with HALLSCREW, same single screw technology.

You may want to have a redundancy with 2 compressors for this is typical. Sometimes is recommendable to have in remote areas 100% stand by, as the process cost could be representative.
There is a company called Jackstone freezers in UK, go for tree different enquiries to manufactures, then compare support, prices, after service, etc
Just don't go for the first shot because you already have something with them.
Think about the freight as well, nothing cheep or expensive is recommendable so don't go for chinesse stuff for price. Stay away of big corps too. As Johnson controls, Mycom, Grasso as they would initially increase your budget.
Don't go for semi industrial compressors neither as Bitzer, Refcom, etc. They are not as reliable as a industrial pack.
Remember Energy consumption and shut-down times cost money.

[ref717]

Our friends are right. Designing an ammonia refrigeration system is not for newly grads. You should consult an Approved ammonia ref. designer and contractor for your plant. Yes you can easily compute heat loads and select the right equipments, but the critical parts are the design and installation of pipings, valves, equipment, accessories, controls,etc. plus the commissioning works.
Ammonia is a very hazardous refrigerant, Safety First..

[Romanicus]

I think that if you will use hot gas to take out the frozen fish from the plates, you must take into consideration the hot gas valve kit and also that you must run at least 2 freezers and one in defrost in order to have enough hot gas.

[sterl]

The compiliation source for the basic thermal calcs, mass and energy balances, etc: would be Stoecker; "Industrial Refrigeration Handbook"

There are a bunch of sources on the web for the pure theory:


http://books.google.com/books?id=Pr0...page&q&f=false


http://www.scribd.com/doc/29348262/M...ration-Systems

But neither really cover what it takes to design a functional process system...and the manufacturers of the key equipment can tell you what capacity the compressors and condensers and so on should be; but the criteria for selecting vessels, hot gas arrangements, control scheme overall and a variety of piping details, control valve selections and other topics is dependent on a broader set of parameters: like how many days per week and hours per day are you going to operate; what is the consequence of an hour's worth or a day's worth of downtime; what are you paying for power; how fast can you load and unload these freezers; and so on.

[bobkerry]

hey you can check them all on various webpages...along with this i would like to add that this is an inetresting field and it can help your qualification as well as learning alot

[ihsan]

Thanks sterl
Those are very informative

[ihsan]

Most important questions to start: Tuna, how much, in and out temperatures do you need,..

-45°C with NH3, system will run in vacuum, are you aware of this?

Is this for a school project or for a real life project.

What are the consequences of running the system in vacuum??

[Romanicus]

What are the consequences of running the system in vacuum??

Air can enter into the system, and you can have problems with the condensing temp. You must use a gas purger.

[Peter_1]

It runs now on -35°C, so why try to decrease this temperature. Lowering your LP will decrease your COP seriously. Avoid running in vacuum and increase therefore a little bit your freezing time and run just above vacuum. It will save you a lot of troubles.
Don't forget that lowering the LP will drop your COP much more then increasing your HP with the same degrees, especially in that low working region of -35°C.

[ihsan]

you need +/- 86 cal to convert 1 gr of water to ice (phase change) and 1.16 is the conversion from cal to W or kcal to kW.
Fish is mostly water and it gives you also some margin.
So in your case for one batch ((5000 x 20) + (5000x 86) + (5000 x 25 x 0.85)/1000)*1.16 divided once again by the hours to freeze you batch gives you your needed kW.

So in 2 hours you will need 370 kW at -31°C.
All figures are +/-

After i calculate the required power can i divide it between the compressor. For example if I get 300 kW can i choose 2 compressors with of kW cooling capacity???

[sachin230]

peter_1 & sterl
Thanks for the link.very informative