The routine of operation to secure the best and most efficient results with an attic fan is important. Atypical operating routine might require that, in the late afternoon when the outdoor temperature begins to fall, the windows on the first floor and the grilles in the ceiling or the attic floor be opened and the […]
Read More…Category: Ventilation Requirements
HVAC Attic-Fan Installation
Because of the low static pressures involved (usually less than 1/8 in. of water), disk or propeller fans are generally used instead of the blower or housed types. It is important that the fans have quiet operating characteristics and sufficient capacity to give at least 30 air changes per hour. For example, a house with […]
Read More…HVAC Fan Operation
Fans may be centrally located in an attic or other suitable space (such as a hallway), and arranged to move air proportionately from several rooms. A local unit may be installed in a window to provide comfort cooling for one room only when desired. Attic fans are usually propeller types and should be selected for […]
Read More…HVAC Fan Applications
The numerous applications of fans in the field of air-conditioning and ventilation are well known, particularly to engineers and air-conditioning repair and maintenance personnel. The various fan applications are as follows: ? Exhaust fans ? Circulating fans ? Cooling-tower fans ? Kitchen fans ? Attic fans Exhaust fans are found in all types of applications, […]
Read More…HVAC Fan Selection
Most often, the service determines the type of fan to use. When operation occurs with little or no resistance, and particularly when no duct system is required, the propeller fan is commonly used because of its simplicity and economy in operation. When a duct system is involved, a centrifugal or axial type of fan is […]
Read More…HVAC Fan Drive Methods
Whenever possible, the fan wheel should be directly connected to the motor shaft. This can usually be accomplished with small centrifugal fans and with propeller fans up to about 60 in. in diameter. The deflection and the critical speed of the shaft, however, should be investigated to determine whether or not it is safe. When […]
Read More…HVAC Fan or Blower Horsepower Requirements
The horsepower required for any fan or blower varies directly as the cube of the speed, provided that the area of the discharge orifice remains unchanged. The horsepower requirements of a centrifugal fan generally decrease with a decrease in the area of the discharge orifice if the speed remains unchanged. The horsepower requirements of a […]
Read More…HVAC Ventilation Air Volume
The volume of air required is determined by the size of the space to be ventilated and the number of times per hour that the air in the space is to be changed. Table 3-4 shows the recommended rate of air change for various types of spaces. In many cases, existing local regulations or codes […]
Read More…HVAC Fans and Blowers
Various types of fans are used in air-conditioning applications and are classified as propeller, tube-axial, vane-axial, and centrifugal. The propeller and tube-axial fans consist of a propeller or disk-type wheel mounted inside a ring or plate and driven by a belt or direct drive motor. Avane-axial fan consists of a disk-type wheel mounted within a […]
Read More…Resistance Losses in HVAC Duct Systems
In general, it can be said that duct sizes and the depth of a duct in particular are affected by the available space in the building. For this reason, although the round duct is the most economical shape from the standpoint of friction per unit area and from the standpoint of metal required for construction […]
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