Economic optimisation, both for new and existing fan ventilation systems. Emphasis is given to the need for considering the complete ventilation system, including the secondary costs of carrying out such an optimisation. Usually it is the ducting system cost and the energy cost which are the two most important factors in fan system life cycle costs.

Energy consumption is greatly dependent on the flow variation required and upon the choice and methods of control and regulation. Economic assessment criteria of various types are used to determine the viability of alternative ventilation system proposals. When calculating the profitability of an investment, it is important to consider the rate of increase of energy costs when compared with general inflation, together with the returns on.

Fan economics, optimisation, alternative ventilation

An important characteristic of a fan system, from an economic point of view, is its efficiency factor, i.e. the efficiency with which it converts the absorbed energy, usually electrical energy, into air power. This is especially important, since efficiency factors normally have extremely low values, much lower than usually quoted.

Reasons for low efficiency factors are discussed and suggestions for improvement are presented. The secondary costs for the main process, of which the fan unit is a part, can be considerable if factors such as process adaptation and available capacity are not considered when designing the plant. The most precious form of energy in ventilation is air energy, which warrants attention because of the parameters which not only determine the air power requirements but also the energy consumption. The basic requirement of every fan installation is to transport air or some other gas.

The object of economic optimisation is to enable the air conveyance to be carried out at the lowest possible cost. The actual liquid transportation, however, often constitutes a small part of a much larger process. An evaluation of the air transport costs must, therefore, also include the costs of adaptation to the main process, or if adaptation is not carried out, the resultant costs of a less effective main process.

How to: Replace an Entire Ceiling Fan

Since the required air movement cannot be accomplished without the contribution of all components in the ventilation plant, the complete system should be considered when carrying out economic optimisation. Only when the remaining costs are not affected, can partial optimisations give completely accurate results. Partial optimisations do, however, have the advantage that they are easier to evaluate and are therefore applied extensively, despite the risk of certain errors.

The cost which should be minimised is the plant whole-life cost, i.e. the summation of all the costs which occur during the total economic life span of the plant. This begins with planning and drafting and ends when the plant is written off or otherwise disposed of. Whole-life costs are traditionally divided into investment and operating costs.

New and existing plant

The design and layout of new plant offers a greater freedom of choice for economic optimisation than is the case for existing plant. For new plant the conditions are more favourable for total optimisation, since all the plant components can be chosen freely. Normally, economic optimisation is carried out for a number of technically feasible alternatives.

The costs for the various items are determined and summate as in Section 19.1.2. The alternative selected is that which fulfils the gas transportation requirements whilst incurring the lowest whole-life costs. The opportunities presented by a new plant should be seized upon to achieve good adaptation to the process. Since the major costs are often associated with the main process, of which gas transportation is only a part, considerable cost reductions can be achieved by suitably designing the ventilation plant.