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3 September 2021
Autoclave hybrid cooling system


Polish industry is responsible for approx. 40% of energy consumption, i.e. 65 TWh (Central Statistical Office data for 2019). Estimated half of this power is used for thermal processes (including pumps, compressors, fans, etc…). Reducing this value can be achieved by modernizing worn-out installations or building new energy-saving ones.

All industries, such as air conditioning, refrigeration or electricity production, are characterized by heat emission. Some of this energy can be recovered and reused, e.g. to heat water. The rest of the non-useful heat must be dissipated due to the low energy content. Industrial cooling systems are systems in which excess heat is removed from the medium (water, glycol, refrigerant, etc.) while lowering its temperature to the ambient temperature. Most often, heat utilization is carried out using water and/or air to the external environment.

A cooling system should be designed and used that will ensure appropriate technological conditions, including start-up, operation and shutdown of cooled equipment in the most effective and durable manner. Local factors limit design possibilities. Such factors include climate, access to water, space available for construction, and location and related restrictions, such as noise emissions or environmental pollution.

Evaporative cooling

One of the most important factors, however, is the local climate, as it directly affects the final temperature of the medium or air used as coolant. Refrigeration equipment is designed so that maximum cooling capacity is achieved under the least favorable environmental conditions. These temperatures are the dry bulb and the wet bulb, which depends on the humidity of the air.

Depending on which temperature, wet or dry, we design a refrigeration system, we distinguish dry and wet cooling, also known as evaporative cooling. In addition, you can distinguish adiabatic cooling, otherwise hybrid, i.e. a combination of dry and wet cooling.

On the psychometric chart, the reference points for individual cooling methods are marked, including dry cooling (+35oC) in red, evaporative cooling in blue (+23oC) and adiabatic cooling in orange (+25oC). The arrow points to the initial parameters, which are constant for all and are:

  • Dry bulb: +35oC
  • Relative humidity: +35%

The difference between the wet and dry bulb for the Polish climate is about 12K. This is a value that allows you to realistically reduce the direct and indirect energy consumption of the refrigeration system.

The difference between the wet and dry bulb for the Polish climate is about 12K. This is a value that allows you to realistically reduce the direct and indirect energy consumption of the refrigeration system.

Evaporative cooling is characterized by high thermal efficiency, thanks to the natural effect of water evaporation, with minimal energy consumption and recirculation of approx. 95% of water. Evaporative technologies allow the temperature of the process to be lowered below the ambient temperature (dry bulb). Compared to dry air cooling, evaporative cooling is more effective because 1 kilogram of water is able to remove 2,200 kJ of heat (evaporation heat) while 1 kilogram of air only approx. 1 kJ per 1 K.

Another example of a device using the effect of water evaporation is also an adiabatic cooler equipped with an adiabatic panel, PVC covered with viscose, ensuring effective operation of the system in wet mode. The built-in controller automatically switches the operating modes (dry and wet) of the device in the most effective way. The appropriate geometry of the adiabatic panel allows free flow of water, which does not need to be treated, because there is no evaporation of water.

The use of viscose (increased water absorption), compared to other types of adiabatic panels, allows for short water cycles (a few seconds every 10-15 minutes). Thanks to this, water consumption is minimal and electricity consumption is optimized to a minimum. An additional advantage of using this material is the lack of risk of Legionella infection (Legionella), which is crucial in the case of food plants. This is possible because the additional protection of the surface prevents the formation of bacterial foci. In addition, the controller reduces the rotational speed of the fans at the time of the adiabatic panel wetting cycle. This prevents the entrainment of water droplets and its splashing. Another protection is the cyclic refreshing of water in the tank of the water recirculation system.

Case study – hybrid autoclave cooling, poultry industry

For one of the Polish producers – a leader in the poultry industry – a hybrid autoclave cooling system was designed and delivered. The most important task set by the client was to select devices so that they use as little media as possible, i.e. electricity and water.

Design assumptions:

  • medium: propylene glycol 37%,
  • capacity: 480 kW,
  • medium inlet temperature: +60oC
  • medium outlet temperature: +20oC
  • location: Poznan

With EcoCooler software from MITA Cooling Technologies, an analysis was prepared. The analysis consisted in checking the distribution of ambient temperatures for Poznań, which is shown in the chart below.

After analyzing the graph, it was proposed to use a hybrid adiabatic cooler PAD-V 2/5 (400 kW) together with a water chiller (80 kW). The cold store will cool down the glycol to +25oC at the time of the highest external temperatures. For less than 200 hours per year, the unit will cool the glycol from 25oC to the required +20oC. The remaining time of the year, the cold store is an independent source of cooling.

the software also allows you to analyze what will be the consumption of energy and water throughout the year of operation of the adiabatic cooling tower. For such an analysis, a year-round operation at full thermal load was adopted. The graph below shows the instantaneous consumption depending on the ambient temperature, taking into account the temperature of switching between dry and wet mode.

After summing up all the data, the cold store will consume:

19,584 kWh of electricity,
159 m3 of untreated water.


Every industrial cooling installation is different. When designing and selecting devices, attention should be paid to a number of aspects. The final installation must ensure the continuity of production in the most optimal way. Not always the simplest and cheapest solution is the best one. For the indicated temperature profile, an open cooling tower can be used, where the CAPEX is the most advantageous, but the OPEX is less.

Thanks to the use of a combination of a hybrid cold store and an aggregate, the customer received an energy-saving system that will secure the need for cooling throughout the year, at high and low ambient temperatures. The software that the manufacturer has at its disposal allows for the selection of devices in a way that is best suited to a given location. The unique characteristics of the PAD-V cooler also reduce the costs associated with service (panel made of durable PVC material) and water preparation (no water treatment). Such an installation, despite the increased CAPEX, will guarantee the lowest possible OPEX. The payback time of the installation is expected after 2.5 years of installation operation.