In order to make the right fan choice for your application, it is important to understand how differing factors can affect fan performance in a given application. This post will look at understanding how temperature and altitude affect fan selection.
Altitude Effects on Fan Performance
The performance of a fan fluctuates with the density of the gas involved in the application. For this reason, fans specifications are typically listed with a standard condition defined as: 70°F. air, at sea level, with a gas density of .075 lb./ft.3 at a barometric pressure of 29.92″ Hg. As conditions vary, the fan’s ability to develop pressure and its horsepower requirement will change. If the density of the gas stream involved in your application is anything other than the standard .075 lb./ft.3 , correction factors should be made to select the correct fan, motor, and drive.
Temperature and Fan Speed Safety
The maximum safe speed of a wheel, shaft, or bearing can also vary. This can be due to an alloy becoming too brittle or too pliable at temperatures other than 70°F. Temperature adjustments should be applied to the maximum safe fan speed to avoid overspeed situations.
Applications that require a fan to move air at temperatures substantially above or below 70°F. it is critical that the safe speeds of wheel and shaft are not exceeded, and that bearing temperature and lubrication are also satisfactory.
The maximum safe speed of a fan in a given application must be determined by calculations or actual tests. Safe fan speed is based on the assembly of the wheel and shaft ability to withstand the centrifugal forces created by the fan’s own weight. Higher temperatures can have an impact on the ability of the wheel and shaft to withstand these forces. Most metals lose strength at higher temperatures, and the loss is measurable in terms of yield and creep strength. These factors can be applied in formulas that determine the safe speed of a wheel and shaft assembly at its tested maximum speed under standard conditions. Fan manufacturers provide safe speed reductions in their catalogs based on the alloy that was used to manufacture the wheel and/or shaft.
G Squared is highly experienced in calculating proper fan adjustments and selecting specific fans for the best application performance. We are always available to help with your fan selection needs.