System Savings – Why You Should Always Consider The Whole System

conveyor-systemsavingsRegardless of whether the energy efficiency of a new or existing process/machine shall be improved, the whole system must always be considered.

Existing installations have the advantage that measurements can be made to determine the losses in the installation, creating a benchmark as to whether improvements to the system are working as expected or not.

The figure below illustrates a drive system operating a conveyor showing the majority of components which can be found in a drive system.

The setup and the whole dimensioning of the system depend on the application (transmission, motor, output filter and motor cable) and its environment (EMC filter, output filters, cables, mains, climate, etc.).

SystemSavings-1

Therefore the engineering and the energy saving assessment should always start with the application assessment. It makes no sense to select one or two highly- efficient components if they have a negative impact on the system efficiency. This is illustrated in the following example.

Before deciding to make an investment, it is necessary to examine not only the technical, but also the commercial and logistical aspects, so that measures which are not cost-effective, or which are counter-productive, can be avoided or minimised. TCO (Total Cost of Ownership = total costs within a certain timeframe) and LCC (Life Cycle Costs = costs incurred within a lifecycle) are methods used for such an evaluation.

A life cycle cost analysis includes not only the procurement and installation costs, but also the costs of energy, operation, maintenance, downtime, the environment and disposal. Two factors – energy cost and maintenance cost, have a decisive effect on the life cycle cost.

LCC = Cic + Cin + Ce + Co + Cm + Cs + Cenv + Cd

Cic = initial capital cost (procurement cost)
Cin = installation and commissioning costs
Ce = energy cost Cs = downtime and lost production costs
Co = operating cost Cenv = environmental cost
Cm = maintenance cost Cd = decommissioning and disposal costs

One of the biggest factors in the life cycle cost formula is the energy cost. Higher Investments which bring the energy consumption down will, in many applications, have only a minor impact.

SystemSavings-2

Fan 1 is a direct-driven type and the system effi ciency increases when more efficient motors (better IE class) are used. Fan 2 is EC fan with a high-efficiency motor. The lower system efficiency results from the fan design. As the motor is placed as hub in the EC fan the air fl ow is disturbed and the system efficiency decreases.

The majority of applications are suitable for speed control but it must be validated case by case. For example, not all compressors are designed for speed control and their minimum and maximum speed limits must be respected and too short or too fast ramp times can be critical.

From Danfoss’ Facts Worth Knowing About Frequency Converters – free download here

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