Refrigeration design

REFRIGERATION DESIGN

Designing refrigeration includes the development of design and estimation documentation for construction and commissioning. This is an important stage of the investment project that determines the efficiency of the planned construction works. It is prohibited in the Russian Federation to build, install and adjust without the design estimates.

The design performance specification must be developed first to clarify and meet all the requirements of the customer. The three main choices should be made:

  • Coolant
  • Cooling system
  • Refrigeration supply system
  1. Choosing a coolant

Current main refrigeration systems in the food industries use ammonia, freons and carbon dioxide as refrigerants. During the intermediate cooling water is used to refrigerate products at positive temperatures and aqueous solutions (most often water / propylene glycol) at negative temperatures.

One of the refrigerants is ammonia NH3 (R 717) — a colourless gas with a characteristic pungent smell, toxic and explosive. Ammonia is one of the best cooling agents due to its thermodynamic properties.

Fluoride coolants (freons). Freon is a colourless and  tasteless gas without smell, non-flammable, non-explosive. Freon is more expensive, there may occur some difficulties with separating the oil, the leak can only be determined by special devices but  freons have extremely high fluidity.

Carbon dioxide as refrigerant CO2 (R 744). Carbon dioxide is a colourless, acid gas, non-flammable, non-explosive.

The refrigerant is most commonly used in CO2/NH3 cascade refrigerating plants.

  1. Choosing a cooling system

Three main broadly used cooling systems:

  • Refrigerant vaporization in processing vessels (direct expansion)
  • Product refrigerating with intermediate coolant (brine circulation coolhouse)
  • Cascade scheme

Direct expansion. In this cooling system the liquid refrigerant enters directly into the cooling devices. Due to the heat of the ambient air the refrigerant boils and that cools it. The refrigerant vapor is sucked off by the compressor. According to the way the refrigerant is soaked into the devices the systems are divided into pumping and non-pumping. Pumping systems are usually installed in large freezers and non-pumping in trade and public catering companies.

Intermediate cooling. In this cooling system, liquid refrigerant enters the evaporator, where, by removing heat from the coolant, boils and thereby cools it. Refrigerant vapor is sucked off by the compressor and the coolant is supplied to the cooling devices by pumps. In addition, the intermediate cooling system can be open and closed, single-circuit and dual-circuit. The advantages of the intermediate cooling include the reduction of the space of the system, relative simplicity of controlling the air temperature in the cooled chamber. in the capacity of the system filled with the refrigerant, the relative simplicity of controlling the air temperature in the cooler compartment. The disadvantage of the intermediate system is a high cost of cold, especially for compartments with low temperatures for storing frozen items.

Cascade scheme. This system consists of two separate cooling circuits. The cascade capacitor combines two circuits: high-temperature one as a condenser and low-temperature one as a vaporizer. Each of these circuits can use a different refrigerant selected for its needs. For example, NH3 refrigerant can be used in a high-temperature circuit and CO2 in a low-temperature one. This is a cascade NH3 / CO2 system.

  1. Choosing a refrigeration supply system

There can be local and district (central) cooling systems. Local refrigeration is most commonly installed in small enterprises to cool one production facility or several chilled product chambers. In that case packaged equipment or standard split-systems are applied. This cooling solution has its advantages: the extreme simplicity of installation, economical, user-friendly. However, in large industries this method of refrigeration supply is completely inappropriate. The operation of each unit is accompanied by noise and heat. If in small quantities this does not cause inconvenience, when there is a lot of equipment, heat inflows will be significant, the noise level will also increase.

The refrigeration systems of industrial enterprises are mainly the district ones, when the cold comes from one powerful installation located in a special production facility. This solves the problems of noise, heat inflows, simplifies equipment maintenance and ensures the stability of cooling supply for all facilities, processing lines and production areas. Quite often district cooling is supplemented with useful options that bring benefits and increase their efficiency. For example, the use of the steam heat released by compressors.

Main advantages of district cooling systems

  1. In case of failure of one or more compressors the remaining compressors will maintain the required temperature until troubleshooting.
  2. Microprocessor based control of the district cooling system allows one specialist to monitor, diagnose and regulate all the necessary parameters and operating modes of cold consumers effectively. For that one computer workstation in the enterprise is sufficient.
  3. Microprocessor based control makes it possible to adjust the condensation temperature depending on the weather conditions and time of day, what significantly reduces energy costs.
  4. Microprocessor based control allows to maintain more precisely the temperature of food storage that leads to better preservation of products and also reduces energy costs.
  5. Preventive maintenance of the refrigeration equipment is carried out in a special compressor compartment, what helps to perform works in a high qualitative level without interfering with the normal operation process of trading halls and technological facilities.
  6. Another advantage of central cooling systems is their high reliability and durability due to the use of high-power compressors.

District cooling systems design

District cooling systems are designed for longer service lives. Disadvantages of using these systems are: the considerable length and branching of pipelines, the presence of a large number of fittings and refrigerant, large amount of installation and commissioning work, the relative complexity of automation. However, as it was said above, in large industries the preference should be given to district cooling supply.

 

The Project Office of TEHNOMIR company offers complex design services and engineering systems estimation of industrial establishments in different fields.

While designing we apply modern technologies and self-developed engineering decisions.

Our accumulated experience helps to develop a custom technical solution for the specific task.

Our project documentation is based on the principles of production processes optimization.

We consider all the rules of fire safety, operating safety, ecology and energy efficiency.

The documentation meets all the statutory and regulatory requirements.

The professionalism of our engineers and installation staff will guarantee correct and safe operation of the refrigerating equipment.

If you are interested in further information on designing, please, contact us by e-mail or call us (812) 346-56-66.

 

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