Tuesday, December 2, 2014

Introduction To Refrigeration equipment servicing and installation

Introduction

To be able to install, commission and carry out maintenance or repairs to even the most basic refrigeration system, it is essential that the engineer has a sound knowledge of the system operation, the functions of the various valves, the controls employed in the system, and the specialist tools or equipment necessary to carry out those tasks.

Generally, larger refrigeration companies employ engineers who specialize in servicing and others involved only with the installation of equipment. Smaller companies require engineers to be proficient in both service and installation practice.

This manual deals with the fundamental principles of service, installation and commissioning, but not necessarily to any specific manufacturer’s recommendation or equipment.

The service engineer

Obviously the need for service and maintenance on existing plant exceeds the demand for new installations and for this reason it is essential that all engineers are conversant with the various service operations and diagnostic procedures; they are dealt with in Part One.

The engineer must be conversant with the type and location of system service valves, with the gauge manifold and all types of gauges used with refrigeration equipment.

The ability to diagnose why a system is not operating correctly, or merely to establish that it is providing optimum service, starts with the fitting of gauges to record either the operating or static pressure of the plant, depending upon the circumstances.

A high percentage of service calls are due to refrigerant leakage either from fractured pipework joints or from defective components which have been subjected to internal or external corrosion to cause a leak.

Often a service call can result in the replacement or relocation of a component, necessitating a change in the pipework design or route so the two

aspects, servicing and installation, cannot be completely divorced from each other.

The response to a service call is a venture into the unknown and the engineer must be prepared for every eventuality.

Installation procedures

Part Two starts with the most commonly encountered pipework fittings, methods of joining and supporting pipework and the important subject of oil traps to ensure oil return to the compressor for adequate lubrication at all times.

Installations vary according to system design, system application and the location of major components, of which the most important aspects are discussed. The requirement for ancillary controls and components also depends upon the system design.

The installation of compressors and drive couplings, including the correct alignment of drive options and drive belt tensioning, is of utmost importance, whether in a new installation, in replacement or during commissioning. The necessity to provide electrical protection for both equipment and personnel must not be overlooked.

System evacuation for newly installed systems and after remedial service has taken place must be given priority if reliability is to be achieved. Decontamination of systems often presents problems unless the prescribed and proved procedures are adopted.

For all of these requirements the correct, logical and safe practices are explained. Unless good refrigeration practices are observed, not only does a system’s reliability become suspect; there is also the danger of polluting the atmosphere in general, including the immediate vicinity where other people may be affected to the detriment of their health and working conditions.

Vapour compression systems

The basic refrigeration system comprises four major components (Figure 1):

1 The evaporator or cooling coil, which creates a cool surface to which heat may transfer from the refrigerated space or product and be absorbed by the cooling agent (refrigerant) circulated within.

2 The compressor, which circulates the cooling agent and changes its state by compression, creating a pressure differential at B.

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3 The condenser, which provides a sufficient surface area to be able to reject the heat absorbed by the cooling agent or refrigerant, conveyed from the evaporator.

4 The expansion device or refrigerant metering control, which regulates

the flow of refrigerant to the evaporator and creates a pressure differential at A.

Some systems include a liquid receiver, which acts as a storage container for surplus refrigerant during normal operation and is able to retain the bulk of the system operating charge whilst certain service operations are performed.

Refrigerant is conveyed to and from these components by interconnecting pipework, as in Figure 2.

It will be seen from Figures 1 and 2 that the system is divided. The low side runs from the outlet of the expansion device to the inlet of the compressor, and the high side from the outlet or discharge of the compressor to the inlet of the expansion device. The compressor and expansion device are the two components which create a pressure differential within the system, and malfunction of either will affect the system operation.

Obviously, the presence of high and low pressures within the system necessitates the use of valves to isolate those pressures during service operations (Figure 2). These valves are known as service valves and, although the design and position of the valves may vary, their function remains the same.

Part One Servicing

Since this handbook was first published changes have taken place which affect some of the previous recognized practices.

New and replacement refrigerants and lubricating oils have been introduced and no doubt many more are contemplated. A selection of these are dealt with in this edition.

It will also be noted that some refrigerants which have been phased out and some which will be phased out by the year 2000 are still mentioned. They have been included in this edition for reference and comparison.

Some calculations based on the use of these substances remain to describe the principle. Systems charged with these refrigerants are still operating nationwide and need to be considered.