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.
There are not many cooling systems that allow water cooling to +1°C. Usually there are only two alternatives, the falling-film chiller and the ice bank. It quickly becomes clear that an ice bank unit can be operated more efficiently in terms of energy by exploiting the favourable low tariff period. However, this argument is directly opposed by the much lower investment costs of the falling-film chiller. After investigating the running time of the refrigeration plant, there are usually indications that the optimum balance between investment costs and operational safety is achieved for charging a certain kW value for an ice bank unit, but the argument that actually decides everything is predominant, how high the hourly required volume flow of ice water in the processing process and overlapping of acceptance with low tariff periods is. 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 cooling with 6-8mm ice thickness of -0.5°C
Direct product chilling with heat transfer temperatures of 0.5°C till -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.
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 €/kWhel
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