Fault -Tolerant Fan (FTF) Systems; Now Easily Accomplished
By Application Engineer (Comair Rotron)

Introduction

The need for reliability in electronic equipment does not stop at using the highest quality fans, such as Comair Rotron fans. There is an ever-increasing need to use additional fans as added insurance in the event of a fan failure. For example, a system that would normally use 4 Muffin fans would be equipped with 2 additional Muffin fans for redundancy; bringing the total to 6 Muffin fans. The additional 2 fans gives peace of mind to customers who rely heavily on their equipment operating; but it also produces additional noise that nobody wants.

As a way to provide redundant cooling and reduce noise emission, Comair Rotron has developed the Fault Tolerant Fan (FTF) system. Under normal operation, the fans are run at a reduced speed that provides the necessary airflow for cooling. In the event of a fan failure, the remaining fans increase their speed to compensate for the failed fan. The end result is quiet operation with the reliability that our customers have come to expect.

Comair Rotron's FTF systems have several advantages:

1. Ease of installation
2. Uninterrupted cooling
3. Lower noise; same airflow
4. Higher reliability per fan
5. Eliminates fan redundancy

Description

Many engineers design redundant fan systems, which over compensate for potential failures by putting extra fans into their system. By taking advantage of modern day electronics located in the fans themselves, a simple redundant system can be created. This system would use Comair Rotron's ThermaPro-V technology with a Fan Performance Sensor. The ThermaPro-V option includes a programmable capability that is tied to the alarm output.

Unfortunately, AC fans do not have the programmable ability and will still require over compensation or and external control circuit.

Fan noise increases and decreases proportionally with rpm. When comparing the noise dBA of one Patriot fan at full speed vs. two Patriot fans at 1/2 speed, we see a noise reduction from 54.9 dBA to 49.9 dBA. This 5 dBA reduction in noise is clearly noticeable. In terms of airflow, the two-1/2 speed Patriots will deliver 235 CFM at free delivery the same as one fan at full speed.

Higher reliability per fan is obtained by running the fans at a lower rpm. The two main factors which come into play are bearing wear and internal temperature rise.

1. Each fan, at low speed, will be using less power and dissipating less heat internally. As a result, the bearings will run cooler.

2. The propeller/shaft/bearing assembly will be turning at fewer revolutions per minute, creating less wear on the bearings.

A fault tolerant system can be applied with the fans in series, parallel, both, or multiple fans and at various speeds. Multiple fans (3 or more) require different circuitry than a system with 2 fans. Both methods are described later. Fault Tolerant Fan systems can be supplied as part of a tray assembly or can be integrated into the system logic by the customer.

more..........