Term

FS: FanGrid redundant fan

Explanation

When dimensioning a FanGrid (radial or axial fans arranged in parallel), the user has the option to define one or more so-called redundant fan(s). This ensures the FanGrid is dimensioned in a way that allows it to meet all defined operating points even in case one or more fans fail.

Relevance

Operating a number of fans in parallel makes it possible to achieve high air performances beyond 50,000 m3/h. For high air performances, e.g. in centralized air-conditioning systems or for data center cooling, a number of fans may be operated in parallel quite easily. However, when installing the fans, great care has to be taken to ensure there is sufficient distance between the fans. Analyzing measuring data has found that with a distance between the fans of more than half the impeller diameter, the air performance of the individual fans is not negatively impacted. If distance is reduced, deductions on the air performance have to be taken into consideration. The current version of the FanScout takes this into account accordingly.
With redundancy, there are also issues to be taken into account. For one thing, the reserve of the remaining fans must be dimensioned sufficiently to allow the missing air volume of the inoperative fans to be compensated for. On top of that, the air volume flowing back through the fans in standstill mode must also be compensated. These aspects are also taken into account in FanScout. With redundancy, we have to differentiate between the “non-return flap” and “without non-return flap” variant.

Illustration

 

The illustration shows three types of operation in a FanGrid with the specification “Redundancy n+1”, i.e. one fan as reserve.
1. Normal case:
All fans are available. The specified operating point (red) is met with larger reserve.
 
2. One fan failing with return flow (without non-return flap):
One fan failed, i.e. the characteristic with 4 fans is no longer available. The characteristic in green is the one for 3 fans with the return flow losses due to the failed fan already deducted. The FanGrid is dimensioned in such a way as to make sure there is sufficient reserve to compensate for the redundant fan and the occurring return flow by increasing the speed of the remaining fans.
qv_lek=sqrt(2*dp/rho)*A*K
(see function calculate_the_leakage() in unit uChart)

 
3. One fan failing, no return flow (with non-return flap):
One fan failed, i.e. the characteristic with 4 fans is no longer available. The characteristic in green is the one for 3 fans. Return flow losses are prevented using a non-return flap.

 

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