Speed variation and air renewal

Michel, a french member of the community sent us this article, and we tought it was interesting for you to read it and give your impressions.

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Inserted into ventilation and air renewal systems in the buildings, the speed variator can deliver the right air flow in real time. Some considerable assets in terms of energy performance and maintenance equipments.

In addition to the use of electric motors at high-yield, the speed variator contribute to the reducing of energy consumption. Concerning the business buildings – service sector ones, and also the industrial buildings, two main categories of application are targeted. First, ventilation and then, domestic water pumping, notably in tall buildings or skyscrapers.

Adjusting flows to reduce consumption

Of course, depending on the way the premises are occupied, the needs vary and it’s not necessary to constantly deliver an air flow or a nominal pressure. Today, this logic of energy performance is backed up with three facts – the increasing costs of energy, the national thermal regulations more and more severe and the decreasing costs of the electronic equipments made for piloting.

Let’s remember that electric energy consumed by pumps, fans and compressors represents a significant part of the electric energy consumption around the world. In the industrial process and the building trade, more than 70% of electricity is consumed by motors and more than 60% of its energy is used for the stream of fluids.

HVAC, variable flow for a constant comfort

The speed variation in air treatment plants is known for a long time. Its debuts were arduous at times in terms of regulation, but today the solutions are finalized.

Yet, the way the flow varies impacts on the stand-alone ventilation solutions or coupled with an air preheating/pre-cooling. The idea consists in measuring the way each room is occupied to adapt the air renewal flow necessary and sufficient for each air vent. Upstream from the air vent, one or several variable-speed motors carries out the variation of the air flow. Some systems works at constant pressure in the air duct, some much more elaborated systems compile in real time the air blowing needs of each air vent in order to give a speed set point to the variator. The speed variator remains the masterpiece of the planting, linked with the electronic of regulation. To know how occupied a room is, a detector warns of the presence or concentration of CO2 thanks to a signal from which the modulation could occur.

Indirect benefits

In most cases, without any variator, fans are sized for a maximal flow greater than the useful one. In that particular case, registers are installed to reduce the air or speed flow when they quit the circuit. Then these registers are adjusted during the commissioning of the installation. As a result, a loss of charge which harms energetic efficiency is noticed.
Yet, indirect benefits spring from the integration of the speed variation. Optimized, the flows lower to the nominal flow will permit to reduce the sounding level of the installation.

Moreover, in some cases, the abundance of the in-rush flows permits to reduce the parts of air ducts. To finish, running an equipment low-speed permits to extend the maintenance intervals for the most fragile items like bearings, pulleys, belts…and motors.