Commercial

[suny]

Hi every body

Could you please all there tell me the basis of calculation to select the two stage compressor, once we know the cooling capacity? As an example to blast freeze chicken from +25° C to -25° C. Here to calculate the cooling load I have assumed the room temperature is -35° C & Te is -45° C. Period to pull down time is 4 hours. As such we have to have a two stage compressor installed & may be a Tandem two stage compressor.

I know if you give the cooling capacity all other details to the compressor selection software it will give the necessary compressor model.

But I want to know from you all learned & experience guys up to what temperature first stage works and the second stage starts from what temperature & how we select from the compressor’s manufacturers charts.

Best Regards
Suny

[Eeram]

To pull down chicken from +25 degrees C to -25 degrees C in 4 hours would probably dim your city's lights because you are going to need a lot of capacity, unless it is 1 chicken at a time!

What is the room size, the amount of chicken, whole birds or cutlets, ambient temperature, other heat loads, etc?

Copeland or Bitzer standard 2 Stage compressors can go down to -67 degrees C on R-507 refrigerant and low temperature oils and can be used in Multiplex Systems (2 or more compressors in parallel.)

Give the design data and we can help.

[lana]

Hi there,
Two stage compressor (internally compounded) selection is like single stage.
Data required :
te, tc, Refrigerant, capacity, with or without sub-cooler.
Two stage compressor is physically one compressor but the compression occurs at two stages in cylinders. For example, first 4 cylinders are in parallel and act as first stage and then the next two cylinders act as second stage. The next two cylinders are in series with the first four cylinders.
The main difference is you have an extra connection from liquid line to the intermediate stage for cooling with a small TEV or CIC module in Bitzer.

On the cooling load calculation side you have to be very careful about the amount of the product and also the cooling time. Short cooling times and high product load give higher capacity.
Rule of thumb : 1200kg of poultry in 8 hours require one 30HP double-stage Bitzer compressor at room temperature of -35°C.

You also have to use TEV with MOP.

Cheers

[suny]

Thank you, Eeram & Lana for your comments & advice. I will give you all details.

[Samarjit Sen]

A two stage compressor is like a single stage unit. lana has well very explained the same. As regards the load calculation, if you can provide the informations such as the quantity of chicken by weight, the incoming temperature and the pull down time required, the same can be worked out. There are good two stage compressors available such as Copeland, Bitzer, Dorin, Gelfred(they have recently started producing two stage compressors) and some others.

[Tapas K Mitra]

You can use two Single Stage compressor to act as one two stage. In fact that will give you ahigher COP.
You can post your exact requirement, based on which I can give you a suitable solution.

[Peter_1]

I agree Eera, freeezing chickens will be very hard to accomplish in 4 hours.
I have aclient (poultry slaughtery) 6000 pieces/hour and they also have a blast freezer, partially a 2 stage Mycom and the other part an NH3 system.
Don't forget that a blast freezer isn't that easy to calculate.
You better should be do first some tests in a standard freezer room where you install some additional fansso that you have optimum flow over the product and determine first the real/actual freezing time.
Use the same enclosures/cratings as the freezer will be loaded.
Increasing the capacity will not change the freezing time, only lowering the evaporating temperature will decrease this.

[Samarjit Sen]

Hi Sunny,

Please let me know the quantity of chicken in terms of weight that you propose to freeze. From your post you want the freezing time to be 4 hrs. It is good that you have thought of using a two stage compressor. What would be the hourly loading.

[suny]

My Dear Members

Please find the following information of the proposed blast freeze 3000 kgs of chicken. Based on the data I have calculated the total cooling load will be about 77Kw, with out adjusting for the DX evaporator losses such as Heaters, Fans, correction factor & gas multiplier etc.

1 Chicken Inlet Temperature Deg C 24
2 Chicken Temperature Deg C -20
3 Chicken Room Temperature Deg C -30
4 Evaporating Temperature Deg C -40
5 Chicken Room Capacity (20'x15'x8') Cu Feet 2,400
6 Chicken Room Insulation Inches 8
7 Chicken Blast Freezing Time Hours 4
8 Chicken Freezing Capacity at a Time Kgs 3,000
9 Ambient Temperature Deg C 35
10 Calculated Cooling Total Load Kw 77
11 Total Capacity Production per hour Kgs. 3,000


I prefer to install Bitzer brand as such please let me know appropriate compressor model and how you selected the second stage capacity from compressor manual. They need four units of these Blast freezers to freeze their production capacity depending on the demand. Furthermore they are going to use the present blast freezer facility (you can not call them as blast freezers) to store the blast frozen chicken by modifying them as storage. This was started in a small scale and now it has grown up to large scale production unit and they are very weak from the refrigeration aspect.

Hope the above information will be sufficient to select the compressor model.

Best regards
Suny

[aqui]

for a R404a system, if saturated suction temp is -20 F, the corresponding saturated condensing temp is up to 130 F max.

[Samarjit Sen]

Since you are proposing to use Bitzer compressor, you get the Selection Software from them. They have the selection of double stage compressors.

I will also work out the details and send the same to you soon.

[Samarjit Sen]

I had worked out the load and it is 78 kw. Any way you will have to use 2 nos of compressors each of 50 % capacity. Each compressor shall be suitable for 42 kw at -40 C Te and 40 C Tc with R 22. The suitable model of Bitzer is S66F-60.2-40P.

I would prefer to use Blasr Freezer Coils of Frigabohn. They are very effective. If you want further details do send me a PM

[suny]

Mr. Samarjit,

Thank you for providing me with the information. I have the Bitzer software.

Suny

[Eeram]

From the data you gave, I came to the following:

To freeze a chicken portion 200mm X 200mm X 200m from +24 deg C to -25 deg C would take 6.5 Hours, minimum.

To freeze 3000kg of chicken in 6 hours with your data supplied, would need 104 kw of refrigeration at -40 deg C evaporating temperature and 35 deg C condensing temperature on R-507 refrigerant.

With Bitzer, you are going to need 1 X S66J-32.2Y and 1 X S66F-60.2Y compressor in parallel. That is basically a 60 and 35 horsepower in parallel.

The evaporator(s) would be based on what your supplier can come up to.

[Eeram]

From the data you gave, I came to the following:

To freeze a chicken portion 200mm X 200mm X 200m from +24 deg C to -25 deg C would take 6.5 Hours, minimum.

To freeze 3000kg of chicken in 6 hours with your data supplied, would need 104 kw of refrigeration at -40 deg C evaporating temperature and 35 deg C condensing temperature on R-507 refrigerant.

With Bitzer, you are going to need 1 X S66J-32.2Y and 1 X S66F-60.2Y compressor in parallel. That is basically a 60 and 35 horsepower in parallel.

The evaporator(s) would be based on what your supplier can come up to.

Somewhere a bug slipped into my reply (don't know how) Sorry for that!

The capacity needed is 87.91 kw and not 104 kw! at -40 deg C evaporation and 35 deg C condensing. The room temperature should run at -30 deg C.

The compressor models I gave is correct. The bigger compressor should be the lead compressor

The evaporator fans are 1.5 kw and with 225.7 air changes at 4.06 cu.m/s