Compressors for Challenging Environments

Cabinet Optimization

One of the most vital elements of compressor technology is the cabinet. Secop is continuously searching for improved solutions and ensures global support in order to provide optimal reliability and high efficiency. Secop compressor components are subject to stringent testing. However it is important to point out that all components require caution with regard to handling and application.

Evaporator, Condenser, and Accumulator

For successful evaporation, we recommend taking note of the following issues:

• Large evaporator area
• Sufficient air ventilation
• In case of capacity problems in the freezing compartment of double door cabinets use the O type instead of C type
• Optimal channel cross sections depending on  refrigerant type and compressor capacity

Always use the largest possible condenser size with the best air ventilation. Appropriate tube dimension is necessary in order to avoid a drop in pressure or too much refrigerant charge. When using the accumulator, be aware that the size and shape has to be adapted for the different refrigerants.

Internal Heat exchanger for Capillary Tube

Always use an internal heat exchanger. The capillary dimensions should be determined depending on:

• Refrigerant type
• Compressor size
• Application

Charge Determination, Optimal Compressor Size and Thermostat Values

The right amount of charge is the premise for ensuring low consumption and high efficiency. Compressor size is just as important as charge determination. The rule is simple: compressors should be as small as possible. Too much capacity can lead to increased energy consumption. In order to establish efficient conditions smaller, compressors should run at:

• Possible high evaporation temperature t₀
• Possible low power condensing temperature t_C

Variable capacity compressors such as the Secop NLV or SLVE compressors can increase system efficiency. Please be advised that too small capacity can lead to insufficient cabinet temperatures at extreme conditions. 
The thermostat influences compressor running time and as a result it also influences the average condition (pressure) and energy consumption. The rule of thumb for fixed speed compressors is that long compressor run times lead to low average evaporation temperatures and too much energy consumption.

Avoid Electrical Heating

It is important at all times to avoid electrical heating:

• Anti-condensation heaters should be an extension of the condenser tube
• Insulation thickness and the proper placement of frame heaters (anti-condensation heater) can avoid sweating
• Double-door evaporators should be designed to prevent a geyser-effect from occurring. Placing a heater on a refrigerator evaporator plate is not required
• Secop can provide support for evaporator designs

Equal and Sufficient Insulation, Door Gap Design, and Gaskets

In order to maintain equal and sufficient insulation, please avoid thermal bridges and be sure to have sufficient sealing gaskets and door labyrinths (door gaps). 
Please notice that doors with gaskets are a general weak point in heat transfer. A sufficient door labyrinth, though, will support the gasket. Secop can provide support for new labyrinth (door gaps) designs. Furthermore, gaskets have to be designed so as to minimise heat transfer. This can be done with different chambers, sufficient overlay, especially at corner sections, and a flat front on the appliance housing.

Reliability and Performance

Reliability is everybody’s major concern in refrigeration applications along with the level of performance. In order to meet these two requirements, Secop has engineered a step-by-step-procedure for ensuring products and solutions continue to set a global standard.

Step 1

Application Analysis 

A new compressor model always starts out with a thorough check of functionalities and performance.

• Defining performance targets
• Running special operation tests with regard to cooling cabinets
• Drawing information about measurements and needed operation range

Step 2

Definition of Compressor Specifications

Using an application analysis, Secop creates a CRD (Customer Requirements Document) for the new compressor type. The CRD summarises all demands which the compressor has to fulfil.

• Operation envelope (ranges of voltage, pressures, temperature)
• Cooling performance (capacity, energy efficiency, start, stall)
• Noise performance (noise, vibration, pulsation)
• Reliability demands and special functions

Different market needs can lead to special variants of a CRD (e.g. “normal use” and “special use”). The CRD covers all possible variables involved in using the compressor.

Step 3

Performance Tests, Targets, and Evaluations 

The Secop R&D team set up performance tests, targets and evaluations according to CRD definitions,

• Extreme load conditions: winding temperature, protector function, motor load
• Optimisation conditions: cooling capacity, energy efficiency, noise
• Pull down and start: maximum pressures, minimum voltage, reverse rotation
• Overload situation: fan out failure - maximum pressures
• Transportation: wear, particles, etc.

Before a prototype is released, all details and designs must be measured and documented. All tests are run inside Secop and according to Secop test specifications (1 and 2).

Step 4

Reliability Tests and Evaluation of Results

Based on various extreme operation conditions and linked impact time, specialists define conditions for the reliability tests. All reliability tests are accelerated tests and coincide with the refrigerant.
Secop´s  reliability tests are conducted to visualise behaviour of wear and fatigue of compressor components after a “working life” of 15 years.
All reliability tests are run, analysed and documented according to Secop specifications and in Secop laboratories (3).

Step 5

Release of a New Compressor Type

Prior to the release of a new compressor type, Secop run final release tests with pilot series compressors.
This extensive step-by-step procedure ensures the reliability and high performance synonymous with Secop compressors.

Reliability and Performance

Pertains in particular to the Middle East, South Asia and Africa. Ranges of target values or boundary conditions can be different but the testing, which examines reliability and performance, always follows the same rules. This ensures that the quality of Secop compressors is always of the highest level, regardless of the application or operation environment.

Special Boundary Conditions

Compressors and unstable power sources are a challenge. In order to ensure the best conditions, please note the following:

• Start at very low voltage up to very high voltage must be possible
• Short time (<30 min) operation at very high voltage must be possible
• Fast restart after power source blackout must be possible
• Reverse rotation after power source brownout must be avoided or possible
• Operation at very high ambient temperatures and extreme voltages must be possible

Boundary conditions, as described above, will be linked to the application-related compressor demands. Unique compressors can be produced if the exact specifications are known.