Category: Ventilation Requirements

HVAC Air-Duct Calculations

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HVAC Air-Duct Calculations

For the sake of convenience, this section outlines a simplified air-duct sizing procedure, which eliminates the usual complicated engineering calculation required when designing a duct system. Refer to Figs. 3-23 to 3-25, which show the plans of a typical family residence having a total cubic content of approximately 19,000 ft3. It is desired to provide […]

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HVAC Suitable Air-Duct Velocities

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HVAC Suitable Air-Duct Velocities

Table 3-2 gives the recommended air velocities in feet per minute for different requirements. These air velocities are in accordance with good practice. It should be understood that the fanoutlet velocities depend somewhat on the static pressure, as static pressures and fan-housing velocity pressures are interdependent for good operating conditions. Fan-outlet velocities are also affected […]

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Heat Gains in Air-Duct

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In any air-conditioning installation involving a duct system, invariably there is an accession of heat by the moving air in the ducts between the coils and supply grilles when air is supplied below room temperature. If the ducts are located through much of their length in the conditioned space, then, of course, this heat absorption […]

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HVAC Air-Duct Systems

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Air ducts for transmission of air in a forced-air heating, ventilation, or air-conditioner system must be carefully designed from the standpoint of economy, as well as for proper functioning. When designing air ducts, the following methods may be used: ? Compute the total amount of air to be handled per minute by the fan, as […]

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Adsorption-Type Dehumidifiers

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Adsorption-Type Dehumidifiers

Adsorption-type dehumidifiers operate on the use of sorbent materials for adsorption of moisture from the air. Sorbents are substances that contain a vast amount of microscopic pores. These pores afford a great internal surface to which water adheres or is adsorbed. A typical dehumidifier based on the honeycomb desiccant wheel principle is shown schematically in […]

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Dehumidifier Control

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Dehumidifier Control

As mentioned previously, the dehumidifier (see Fig. 3-19) operates on the principles of the conventional household refrigerator. It contains a motor-operated compressor, a condenser, and a receiver. In a dehumidifier, the cooling coil takes the place of the evaporator, or chilling unit in a refrigerator. The refrigerant is circulated through the dehumidifier in the same […]

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Electric Dehumidification

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An electric dehumidifier 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. The amount of water removed from the air varies, depending on the […]

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Air-Operated Humidifiers

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Air-Operated Humidifiers

Air-operated humidifying units operate in the same manner as electrical units, except that they utilize a pneumatic hygrostat as a humidity controller and an air operator to open or close the steam valve (see Fig. 3-17). Adecrease in relative humidity increases the air pressure under a springloaded diaphragm to open the steam valve wider. An […]

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Electrically Operated Humidifiers

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Electrically Operated Humidifiers

Dry-steam electrically operated humidifiers operate by means of a solenoid valve, which is energized by a humidistat. When the relative humidity drops slightly below the desired level set by the humidistat (see Fig. 3-16), a solenoid valve actuated by the humidistat admits steam from the separating chamber to the reevaporating chamber. Steam passes from this […]

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Pan Humidifiers

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Pan Humidifiers

Figure 3-15 shows the essential parts of the pan-type humidifier. The main part is a tank of water heated by low-pressure steam or forced hot water where a water temperature of 200°F (93°C) or higher is maintained. The evaporative-type humidifier is fully automatic, the water level being controlled by means of a float control. In […]

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