Direct product cooling

Direct product cooling heat transfer

In view of the specific needs and expectations of our customers in the field of heat transfer in the case of direct product cool down, we provide the calculations on one hand and the manufactured technical systems and components on the other hand. Consequently, both are tailored to functionality and efficiency, but also never to loose sight of process stability of the respective field of application. Our ice water systems, falling film chillers, ice banks or heat exchange systems have this stability to ensure that the direct product cooling process chain is not interrupted.

Ice water systems as washing line for fruit and vegetables

Ice water is required for the washing lines in all fruit and vegetable processing plants. This ice water is then usually to be produced with a state-of-the-art refrigeration system and the washing lines are to be supplied with a constant temperature of +1°C. In the same plants hot water is usually also required for cleaning purposes. The clarification of the power requirement of the refrigeration plant considers the ice water and hot water requirements. In most cases, it is found locally that this fluctuates greatly depending on the season.

Ice water systems as washing line for fruit and vegetables

There are not many cooling systems that allow water to be cooled down to +0.5°C. Usually, there are only two alternatives, the falling film chiller and the static ice bank It quickly becomes clear that an ice storage system can be operated more energetically by taking advantage of the favourable low tariff period. However, this argument is directly offset by the much lower investment costs of the falling film chiller. After examining the running time of the refrigeration system, there are usually indications that the optimal balance between investment costs and operational reliability for charging a certain kW value for an ice storage system is achieved, but the argument that actually decides everything is outweighed by the necessary hourly withdrawal of ice water in the processing process and overlaps of the withdrawal with low-tariff times. In the selection of refrigerants, today's choice falls on the one hand on natural refrigerants such as NH3, CO2 or propane, and on the other hand on refrigerants such as R448A, R449A, R407A, R407C or R507C. In addition, systems are increasingly being operated with refrigerants such as propylene and ethylene glycol-water mixtures in various concentrations. When choosing the refrigeration concept, a flooded system is usually selected for refrigerants for reasons of low operating costs. For refrigerants with temperature glide, all units are designed for dry expansion (dx operation). Here, flooded evaporators are not used. Finally, in order to make the right decision, many individual aspects have to be considered, evaluated and calculated. In the end, this determines the choice of a falling film chiller or a static ice bank, depending on the advantage calculated on the basis of current data.

Animation for understanding the structure and the process of hydrocooling

This animation shows the construction of a stainless steel hydrocooler, as well as the sequence of a cooling process. In particular for the following applications:

  • Fruits or vegetables
  • Meat or fish
  • Ready-made meals or sauces
Hydrocooler outside installation
Hydrocooler outside installation
Hydrocooler inside installation
Hydrocooler inside installation
Ice water sprinkling onto the conveyor belt
Ice water sprinkling onto the conveyor belt
Product cooling white asparagus
Product cooling white asparagus
Product cooling ready salads cut
Product cooling ready salads cut
Direct product cooling with 6-8mm ice thickness of -0.5°C
Direct product cooling with 6-8mm ice thickness of -0.5°C

Alternative primary refrigerants and secondary refrigerants

In the selection of refrigerants, the current choice is primarily R134a, R404a, R407C, but also occasionally R448a and R449a. These refrigerants each have the best values for dry expension and the second best for flooded operation. When choosing the refrigeration concept, a flooded system is usually chosen for reasons of low operating costs. Finally, to make the right decision, many individual aspects must be considered, evaluated and calculated. In the end, this is the decisive factor for the selection of a falling-film chiller or an ice bank system, depending on the calculated advantage based on current data.

System comparison ice bank / falling film chiller

  • Both systems fulfil the conditions
  • Investment costs of the falling-film chiller are much lower
  • No partial load operation (power fluctuations) with the ice bank variant
  • Energy cost savings (night charging) with the ice bank variant per year
  • Longer payback period of the additional investment of the ice bank variant

Direct product chilling with Ice water temperatures of 0.5°C

Ice water with temperatures of 0.5°C can perform very well for direct product chill down
of large quantities of product in a very short time. As a result it has been used for many years in food cooling and process cooling wordwide. Ice water slightly over 0°C has no risk of freezer burn and is ideal for direct product cooling as such in most of the applications. Many customers are critical about the use of ice water due to too moisture, but they forget, that fruits and vegetables are resistant to rain by nature. Fish and seafood are naturally under water.

Direct product chilling option with 0.5°C ice water till -0.5°C chip ice

Furthermore, the overall product is a combination of the heat transfer calculation of the final product and the calculation of the economics of these heat exchangers (author is head of our R&D department). Both are therefore prior components of the overall system, which are not negligible. In addition, we calculate the necessary quantities of water or ice in the case of direct product cool down. However, the components of ice water (0.5 ° C) and / or chip ice (-0.5 ° C) are of primary importance to us in this heat transfer calculation. In cases where ice water (0.5 ° C) is insufficient for the cooling process, mainly in the meat industry and the fish processing, ice (-0.5 ° C) must be used.

Energy consumption advantage of a BUCO Industrial Ice machine in direct product cooling

To produce ice, we do have the efficiency in prior focus. Only by melting of the ice, the heat for cooling of the water is taken from the surrounding. Ice is melting at a temperature of 0°C to water and gives 335 kj per kg ice. Therefor we do produce ice with an evaporation temperature T0= -10°C, which generates ice at a temperatures of  T= -0.5°C to -1.0°C. The idea is simple, as the cooling gain for subcooling of the Flake Ice in conventional drum systems is down to T= –8°C, which is only approx. 8% of a higher melting capacity. Unfortunately this has a high energy consumption impact for the drum ice machines as such:

Energy cost comparison of a BUCO Industrial Ice machine and a conventional drum system as main cost factor for direct product chilling

Example: 30 to ice / day
Necessary refrigeration power including losses: ca. 150 kWref

Electric power for the drive of the refrigeration machine:
-30 / 35 °C with COP = 1,8 Pel = 84 kWel – Drum system – Flake Ice
-10 / 35 °C with COP = 3,6Pel = 42 kWel – BUCO Ice Pack
Additional drives: 6 kW
Price for electricity: 0,15 € /k Whel
Running costs at -30 °C : 324 € / day or 11 € / to ice – Drum system
Running costs at -10 °C : 173 € / day or 6 € / to ice – BUCO Ice Pack
Savings: 151 € / day
for 300 days production: 45.300,-€ / year savings of electricity costs

The manufactured products that generate this are basically the falling film chiller (ice water 0.5 ° C) and the industrial ice maker (plate ice -0.5 ° C) to serve the following products of industrial food refrigeration:

  • Fish, meat, poultry
  • Fruit Vegetable
  • Milk, milk products
  • beverage production
  • Bakery production

Customer questions and applications for product cooling:

We have always assimilated engineering science and thermodynamics optimally in the various manufacturing processes.

Thermodynamicists,mechanical engineers and welding engineers define the dimensioning, design and construction of customised heat exchanger panels and systems in materials ranging from mild and austenitic steels through to titanium, and ensure successful distribution of their work worldwide.

In doing so they fall back on production engineering expertise and calculations developed in the course of the past hundred years that are still being continuously optimised in an ongoing process.

In the perception of our customers, the Buco product stands for:

Technical and process-oriented consulting
Thermodynamic efficiency
Quality and longevity