How to calculate the power of the shock freezing chamber

The power of the cooling system of the freezer is one of the determining factors of its performance. On the other hand, the value of this parameter is directly proportional to the unit price. To calculate the power of the refrigeration chamber or the installation of Express freezing, it is required to perform quite complex thermal calculations taking into account a variety of variables and patterns. However, in some cases, a very approximate calculation is enough, which will help to understand the order of prices. This approach is relevant at the stage of assessing the attractiveness of the business in specific market conditions.

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What is the total capacity of the cooling system?

Electric drives are usually equipped with two elements of the system — a compressor and a cooler. The cooler is a separate unit with an evaporative circuit on which the fans are mounted. Accordingly, the power of the cooling system is equal to the sum of the compressor and cooling fans.

The main factors influencing the capacity

The performance of shock freezing is measured both in technical terms and in kind. Under natural refers to the amount (weight) of a certain food product that you want to freeze for a certain time.

Productivity factors in kind:

Product type (meat, fish, vegetables, different types of semi-finished products or ready dishes).
Demanded temperature (final) and the speed of freezing. Are set in Celsius degrees and minutes.
The sizes and weight of the frozen elements according to the accepted high-quality cutting / cutting. For example, meat for shock freezing can be cut the pieces having thickness no more than 2.5 cm and weight no more than 400 g
Natural capacity of the camera of box type. Usually is accepted in dimension of kg/h.
A section operation mode (the number of changes in day, a number of hours in change).

The factors that determine the capacity from the equipment:

Air temperature in boxing.
Temperature and air humidity in workshop.
Camera sizes.
Type and thickness of the used thermoinsulator. For different walls, a ceiling and half of the box isolation can be arranged differently.
A type of the used coolant. As system efficiency depends on its brand, and the required power of the compressor will differ depending on the selected heat carrier.
Compressor operation mode, hour/day.

Example of calculations

Any randomly selected online calculator determines the useful capacity of the compressor required for processing a certain mass of the product under the established modes. However, such calculators do not take into account the power losses that occur due to heat flows through the walls of the chamber.

The approximate calculation of the performance of the shock freezing chamber should begin with the determination of the useful weight of the load and the internal dimensions of the box. To do this, you must have the technological requirements for the processing of the product you are interested in. For example, for meat cut across fibers, the starting data may look as follows:

item size 20 x 10 x 2.5 cm;
the mass of the elements 400 g;
location on the tray size of 80 x 50 cm (trolley size in plan — 900 x 55 cm) — 9 PCs. on the tray;
step trays height in the rack (cart) — 10 cm.
freezing mode — from 20 °C to -28 °C for 60 min.

Then, asking the capacity of the section (for example, 2000 kg. per shift (shift duration 420 min), defined productivity shock freezing in one loading chamber: Zagruzki = Rcmenu x tзагрузки/tсмены = 2000 x 60/420 = 285 (kg) (value rounded up). On one tray we placed 3.6 kg. Then the number of trays 285/3,6 = 79 (PCs.) (rounded).

Taking into account the architectural binding of the site, we take the maximum internal height of the chamber 2.5 m. the recommended height of the rack should be less than 0.5 m. Then 20 trays are placed on one rack. Accordingly, for a single download should be placed in the chamber 4 racks (rounded up). Taking into account the minimum gaps (10 cm) between the carts, we determine the dimensions of the block of 4 racks. The length of the front of the trucks: 900 x 4 + 100 x 3 = 3900 mm. dimensions of 3900 x 550 x 2000 mm.

The volume of the chamber is recommended to be taken at the rate of 1.0 m3 per 10 kg of frozen products at one load. In our case, the camera V is assumed equal to 28 m3. Based on the size of the block, assign the width of the box 4.5 m. Then its depth will be 28/(2.5 x 4.5) = 2.48 m. Round to 2.4 m.

Accordingly, the refined internal volume of the box V = 2,5 x 4,5 x 2,4 = 27 m3, and the area of the inner surface S = 78,6 m2. The ratio of V/S = 27/78,6 = 0.34.

Then you can calculate the approximate flow of heat into the chamber through its walls. To do this, it is enough to find in the table the value V/S, the most approximate to the obtained by calculation. The same table helps to determine the required insulation material and its thickness.

Table of typical values of specific heat inflow into the shock freezing chamber (operating temperature -32 °C) of the box type, kW/m3

V/S	0,17	0,33	0,38	0,50	0,55	0,67
EPPS 100 mm	0,13	0,07	0,06	0,05	0,05	0,04
EPPS 150 mm	0,09	0,04	0,04	0,03	0,03	0,03
EPPS 200 mm	0,07	0,03	0,03	0,03	0,02	0,02
Polyureth. 100 mm	0,09	0,04	0,04	0,04	0,03	0,03
Polyureth. 150 mm	0,06	0,03	0,03	0,02	0,02	0,02
Polyureth. 200 mm	0,04	0,02	0,02	0,02	0,02	0,01

For example, we choose as a thermal insulator EPPS 150 mm thick with the corresponding value of the specific power loss through the walls of the chamber 0,04 kW/m3. Multiply by the volume of our camera and get the power loss ΔNst = 0.04 x 27 = 1.08 kW.

Now let's get to the main part of the calculation of the performance of the shock freezing chamber. Determine the power required to freeze the meat. Choose an arbitrary online calculator, enter the type of product (eg, beef), as well as the load weight, freezing time and temperature values. Get N freeze = 32,3 kW.

Then the minimum useful power of the compressor will be Ncommin = Nzamorozki + ΔNst = 32,3 + 1,08 = 33,38 kW. Choosing a compressor from the catalog, it should be borne in mind that the power consumption of the machine will be more useful by the amount of efficiency, and the efficiency, in turn, depends on the type of refrigerant used. Having determined the brand of coolant, you can choose the compressor model.

To get the total capacity of our installation, it is necessary to choose the model of the chiller (evaporator) and to sum the values of the Nкомп and Nисп. The characteristics of the coolers usually contain recommendations on the parameters of suitable compressors.

Having done the work described in this section, it is possible to estimate the cost of all mechanisms and components of the chamber of the box type, including the cost of equipping the installation housing.

Precise determination of the required power of the shock freezing chamber

To get the exact value of the power of the shock freezing chamber, it is necessary to fill in the questionnaire on the main page of our website in as much detail as possible. In addition to the values of the model parameters to the engineers to select reasonable technical solutions require further information regarding the General descriptions of the proposed or existing manufacturing process.

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