Overview
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ABSTRACT
The aim of refrigerating machines is to place or maintain a system at an inferior temperature to that of the environment. This equipment can come in the form of two types: direct or indirect. The design of an industrial refrigerating machine is based upon both the objective of the system (cooling, freezing, etc.), its thermal balance, the heat condition of the environment and economic considerations. This article details the direct and indirect cooling processes by presenting their ground principles, the technologies involved as well as the dimensioning of the installations. It finally resents the installation and operation stages, from the preliminary studies to the delivery of the machine.
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Read the articleAUTHOR
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Georges VRINAT: Engineer from the Conservatoire national des arts et métiers and the Institut français du froid industriel - Member of the French Refrigeration Association – Expert frigoriste
INTRODUCTION
The complete definition of a refrigeration plant is the result of a logical analysis, starting from the type of application (air conditioning, freezing, refrigeration, etc.), its refrigeration balance and the thermal conditions of the ambient heat extraction and rejection media.
There are only two types of systems for distributing refrigeration energy:
the direct system, with evaporation of the refrigerant in the evaporator-cooler of a gas, liquid or solid cooling process;
the indirect system, with forced circulation of a refrigerant or heat transfer fluid between the production machine and the process heat exchangers.
In some cases, these two systems can solve the same problem, but with different technologies, energy consumption and economics. In other cases, on the contrary, site-specific economic and feasibility criteria will decide. For example, urban air-conditioning systems require chilled water distribution, whereas office air-conditioning systems accept direct VRV-type circuits.
In economic terms, a well-designed direct evaporation system is less expensive in terms of investment and energy consumption than an indirect system. The latter requires an exchanger-cooler for the refrigerant, implying additional cost, space and energy expenditure, on the one hand because of the temperature difference required by the exchanger-cooler, and on the other because of the energy supplied to the refrigerant by pumping and external heat inputs to the refrigerant pipes.
In the case of premises where staff are working, or where the public is staying, the use of a suitable, safe refrigerant carrier eliminates any risk of pollution or panic in the event of a refrigerant leak.
What's more, it's obvious that the refrigerant charge of an indirect system is lower, easier to contain and monitor than that of a direct circuit, geographically developed with difficult access.
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Industrial refrigeration machines