HVAC Ventilation Requirements

Ventilation is produced by two basic methods: natural and mechanical. Natural ventilation is obtained by open windows, vents, or drafts, whereas mechanical ventilation is produced by the use of fans.

Thermal effect is possibly better known as flue effect. Flue effect is the draft in a stack or chimney that is produced within a building when the outdoor temperature is lower than the indoor temperature. This is caused by the difference in weight of the warm column of air within the building and the cooler air outside.

Air may be filtered by two ways: dry filtering and wet filtering. Various air-cleaning equipments (such as filtering, washing, or combined filtering and washing devices) are used to purify the air. When designing the duct network, ample filter area must be included so that the air velocity passing through the filters is sufficient. Accuracy in estimating the resistance to the flow of air through the duct system is important in the selection of blower motors. Resistance should be kept as low as possible in the interest of economy. Ducts should be installed as short as possible.

The effect of dust on health has been properly emphasized by competent medical authorities. Air-conditioning apparatus removes these contaminants from the air and further provides the correct amount of moisture so that the respiratory tracts are not dehydrated, but are kept properly moist. Dust is more than just dry dirt. It is a complex, variable mixture of materials and, as a whole, is rather uninviting, especially the type found in and around human habitation. Dust contains fine particles of sand, soot, earth, rust, fiber, animal and vegetable refuse, hair, and chemicals.

Humidifiers add moisture to dry air. The types of humidifiers used in air-conditioning systems are spray-type air washers, pan evaporative, electrically operated, and air operated.

The function of an air washer is to cool the air and to control humidity. An air washer usually consists of a row of spray nozzles and a chamber or tank at the bottom that collects the water as it falls through the air contacting many baffles. Air passing over the baffles picks up the required amount of humidity.

Dehumidification is the removal of moisture from the air and is accomplished by two methods: cooling and adsorption. Cooling-type dehumidification operates on the refrigeration principle. It removes moisture from the air by passing the air over a cooling coil. The moisture in the air condenses to form water, which then runs off the coil into a collecting tray or bucket.

Ventilation is the process of supplying or removing air to or from any building or space. Such air may or may not have been conditioned. Methods of supplying or removing the air are accomplished by natural ventilation and mechanical methods. The treatment of air, both inside and out is very important in any ventilation system.

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