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Rack Cooling Solutions from ebm-papst


The Hidden Equipment That We All Rely On

Internet traffic these days is measured in ‘Exabytes’ (EB) of data. 1 Exabyte is equal to 1,000,000,000,000,000,000 (1018) bytes and each year the level of data traffic is rapidly increasing. To put it into context, it is reported that 5 Exabytes would be equal to all of the words spoken throughout history and in physical context, if the Earth was considered to be the size of a gigabyte, the Sun would be the size of an Exabyte. From 11.51EB of data transmitted in 2017 to a predicted 77.5EB transmissions in 2022, the growth in infrastructure to manage these flows of data relies on a basic piece of equipment used in datacentre sites worldwide.

The 19-inch Rack

Housing data storage and processing equipment, the 19-inch rack is a fundamental part of the ubiquitous manifestation of the internet. From small mobile cabinets to larger static ‘cupboard’ arrays, 19-inch racks come in a variety of formats, either open fronted or enclosed. Whilst the outward appearance may vary, the physical layout of the structural elements inside conforms to a long existing international standard.

The 19-inch rack was first established as a standard in the 1920’s by the American Telephone and Telegraph company (AT&T), to provide a compact mounting system for repeater and termination equipment in a telephone company central office. The equipment housed within the rack is fixed upon two parallel vertical metal "posts" or "panel mounts". The posts are 0.625 inches (15.88 mm) wide and are separated by a gap of 17.75 inches (450.85 mm), giving an overall rack width of 19 inches (482.60 mm).

In addition to the width, there is a specification for equipment height related to measurement units called ‘Rack Units’ (RU) or more simply known as a ‘U’. A single U space (1U), is equivalent to 1.75 inches in height (44.45mm) and equipment housed within the rack will be sized in multiples of these units, (1U, 2U, 3U, etc…).

Applications and Equipment Mounted in a 19-inch rack

As mentioned above, the 19-inch rack was originally designed for telecommunications equipment enabling us to talk to each other in a variety of formats: voice calls, faxes, telex, basic data transmission. As our need for data has grown, more sophisticated data transmission methods have digitised the world of communication increasing speed and reliability. Digitisation has also enabled miniaturisation which means the equipment we use to store data; house computer servers and networking hardware can now be accommodated within the confines of a 19-inch rack. Other industries involved in power transmission, control cabinets, audio visual and scientific equipment have all made use of the 19-inch rack as a common platform for equipment design.

The Requirement for Rack Cooling

Modern equipment housed in racks now provide high power output in a compact space envelope. This increase in power density can cause localised hotspots within the equipment which if left unchecked can cause component damage and potential equipment failure. This is particularly pertinent during periods of high demand whether it is general internet use or emergency response, an increase in data traffic forces more power into the equipment resulting in greater heat dissipation. For a variety of reasons, some essential services require guaranteed connectivity without interruption requiring that heat loads within the equipment are monitored and managed effectively. Managing the dissipated heat requires fans to force cool air through and over the components inside the equipment housed in the rack.

Information and Communication Technology (ICT) equipment dissipates energy in the form of what is known as Sensible Heat. When an electrical or electronic circuit is working, there are losses due to the resistance of the components in the circuit. The greater the power flowing through the circuit the greater the temperature rise of the components.

Sensible heat is a dry heat which can be removed by convection. If the heat load is small or the circuit is low power, natural convection over the components may be sufficient to draw away the heat generated by the dissipation of energy. With larger heat loads, such as high capacity ICT equipment, forced cooling using a fan may be required. The amount of airflow required for cooling is calculated using a simple formula.

The formula considers the power being dissipated with the difference between the ambient air temperature and the maximum allowable operating temperature of the components in the equipment.

Fans and Controllers Used for Rack Cooling

The types of fan used in this application can be compact high-speed axial for high volume flow against high resistance when localised cooling is required and mounting space is at a premium. Alternatively, backward curved motorised impellers can be used for collective cooling on higher pressure applications consisting of equipment with densely packed components or applications with high grades of filtration (removal of fine particulates).

Controllers that have multiple sensor inputs can be used to monitor the temperature at specific points within the rack. The controller can be set to control based on an average of the two sensor readings, use the highest reading to set the speed of the fans or use the specific sensors to control specific fans installed within the rack.

Products from RS Components that can be Installed in Rack Cooling Systems

Axial Fans

High Performance 24V DC axial fans available via RS components include

400 series (840-5560)

600 series (878-1050)

8000 series (749-6966)

4000 series (055-7701)

High performance 24V DC Diagonal flow fans available from RS Components include

DV4000 series (826-1165)

DV5000 series (826-1171)

DV6000 series (826-1193)

Radial Fans

High Performance 24V DC Centrifugal fans available from RS Components include

RG160 series (825-7901)

RER101 series (2508416513)

RER175 series (860-0223)

RER190 series (920-9206)


CPCXX – DCP Temperature based fan speed controller with open collector PWM output

The controller includes

  • Fan monitoring
  • Pre-set temperature profile controls the fan from 15-100% speed
  • Alarm output
  • Compatible temperature sensor on 2m lead

RS Components part numbers:

  • Supply voltage 11-57V DC & Control range 20-40oC – RS165-1397 - CPCXX2040SC-R
    See (165-1397)
  • Supply voltage 11-57V DC & Control range 20-40oC – RS165-1398 - CPCXX3555SC-R
    See (165-1398)

CPCXX – A2P Analogue 0-10V input to open collector PWM output fan speed controller

The controller includes:

  • Fan monitoring
  • Pre-programmed control response
    • 0V input = 0% PWM output (signal low)
    • 10V input = 100% PWM output (signal high)

RS Components part number:

  • Supply voltage 11-57V DC & Control range 0-10V input 0-100%PWM Output – 165-1401 – CPCXXVV10UN-R
    See - (165-1401)

CECXX – Temperature based fan speed controller with 0-10V DC analogue output

The controller includes

  • Fan monitoring
  • Pre-set temperature profile controls the fan from 15-100% speed
  • Alarm output
  • Compatible temperature sensor on 2m lead

See RS Components part numbers:

  • Supply voltage +10V DC with Control range 20-40oC – RS165-1399 - CECXX2040SC-R
    See (165-1399)
  • Supply voltage +10V DC with Control range 20-40oC – RS165-1400 – CECXX3555SC-R
    See (165-1400)

CGCXX – User Configurable Temperature / 0-10V based fan speed controller – one fan output

Fan controller that combines the features of both the CPC and CEC product ranges with a Microsoft Windows™ based Graphical User Interface (GUI) software package to allow the controller to be configured according to requirements. The controller includes

  • Wide operating voltage range (+10V to +57V DC)
  • Configurable control input (Thermistor / 0-10V DC analogue signal)
  • Configurable output signal (Open collector PWM / 0-10V analogue signal)
  • Configurable set-points
    • Simple control profile (4 program points)
    • Multi-point profile (up to 256 program points)
  • Minimum speed cut-off
  • Programmable Open Collector Alarm Trigger (Fan fail / Over temperature / Under temperature)
  • Maximum fan speed limitation

See RS Components part numbers

  • Supply voltage +10V to 55V DC User configurable controller – RS165-1402 – CGCXX00000
    See - (165-1402)
  • Controller configuration lead – RS 769-2726 – 210-HAR11887
    See (769-2726)
  • Graphical User Interface and instruction manuals (Free to download)

Thermal Management System (TMS) Controller

The Thermal Management System controller is fully configurable and can speed control 4 fans independently based on either a temperature sensor or an analogue 0-10V control signal input. The fans can either be 4-wire open collector PWM control or 4-wire 0-10V analogue control.

See RS Components part numbers

  • Development Kit with +12V to 57V DC User configurable controller – RS769-2732 – TMSB11111-01
    See (769-2732)
  • Boxed controller only +12V to 57V DC User configurable controller – RS769-2722 – TMSB00000-01
    See (769-2722)
  • Controller configuration lead – RS 769-2726 – 210-HAR11887
    See (769-2726)
  • Graphical User Interface and instruction manuals (Free to download)


Ever increasing data transmission rates, demand for information without interruption and requirements to deliver these requirements in equipment installed in a 19-inch rack, requires close management of temperature. Fans and controllers responding to variances in demand can deliver cooling when required to optimise equipment performance and maintain operational reliability.


My background is in Mechanical & Production Engineering however working for ebm-papst that has expanded into electro-mechanical, some electronic and acoustic engineering. When it comes to acquiring and passing on knowledge, I try to keep it as simple and as least painful as possible. I am happy to receive feedback and if there are any questions that arise from anything that gets published. If I don't know the answer to your question immediately, I am sure that I know someone that can help.

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