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Using a Mass Airflow Sensor to correct for altitude or airflow variations in computer system cooling designs

IP.com Disclosure Number: IPCOM000033493D
Original Publication Date: 2004-Dec-13
Included in the Prior Art Database: 2004-Dec-13
Document File: 3 page(s) / 60K

Publishing Venue

IBM

Abstract

Typical computer cooling solutions employ temperature feedback to regulate the speed of the fans. As either the in-box or ambient temperature varies, a control circuit varies the fan speed to compensate. However, temperature is not the only variable that affects the system cooling performance. At high altitudes, the fans must rotate faster than they would at sea level to move the same mass of air. This increased fan speed leads to more system noise. Since current cooling solutions employ no mechanism to determine air density or altitude, the system fan speed must be calibrated to assume that they are operating at high altitude. This results in the system fans spinning at higher speed and creating more noise at lower altitudes than is necessary. As system airflow demands increase, it becomes more important to regulate accompanied system noise output to meet workplace standards. This article describes a mechanism to use a Mass Airflow Sensor to modulate fan speed in a server or Blade chassis thereby cooling the system more efficiently.

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Using a Mass Airflow Sensor to correct for altitude or airflow variations in computer system cooling designs

     This invention consists of a fan control circuit, a temperature sensor, a Mass AirFlow(MAF) sensor, and a fan. All of these devices are part of a larger computer system or chassis. The fan control circuit contains algorithms to take the measurements from one or many temperature and MAF sensors and create an output suitable to drive a fan. The MAF sits in the airstream of the fan and measures the mass of air moving through the system. The system components are connected as shown in the figure below. (fig. A)

     For the system to operate properly, it must first be calibrated for a particular application. A system thermal profile is created to determine the mass airflow required to appropriately cool the devices contained within the chassis at all operational temperatures. (fig. B) This thermal profile information can be organized as a simple look-up table or as an equation that correlates temperature and mass airflow. This thermal profile information is then stored in the fan control circuit typically a microcontroller or other programmable device that resides within the chassis.

     During normal operation the fan control circuit first reads the temperature sensor. The fan control circuit uses the measured temperature and the stored thermal profile information to determine the required mass airflow. The fan control circuit adjusts the fan speed such that the readi...