The Facts Behind Cooling Towers

Since the opening credits of US cartoon series The Simpsons, cooling towers have become synonymous with heavy industry and power. Similarly cooling towers have become familiar facets in the skylines of industry-focused cities such as Birmingham and Sheffield. So what are the facts behind these devices that are increasingly becoming part of the industrial landscape?

To begin, a tower's purpose is to remove hot air and are commonly used to shift excess heat from sites such as power plants, oil refineries and large scale factories. Cooling towers measure - on average - around 200 meters tall and 100 meters wide and are often a fluted, vase-like shape made from cement.

Towers used in heavy industry ensure machinery and production facilities are kept at a comfortable and safe working temperature by disposing of excess heat into the atmosphere or by flushing cooled water back into natural water supplies; without damage to the local ecosystem. Cooling towers that do not have access to bodies of water or where activity would raise water temperatures above suitable levels for organisms often opt to dispose of excess heat via evaporation.

Many towers produce a recognisable plumes of fog. In humid conditions, the levels of water discharge from the towers can cause low lying fog in areas around the towers as the level of water in the air becomes saturated. Tower operators need also be careful of freezing conditions which can affect the productivity of the tower. Residual ice which gathers in areas of moisture also adds weight to the tower's structural load which - in very, very rare conditions - can lead to cracks which could potentially cause collapse.

Naturally, the level of maintenance and expertise required to keep a tower in optimal condition has lead to the increased popularity of cooling tower rentals where manufacturers and construction sites can obtain towers on a temporary basis.

Harvey McEwan writes to offer information amd advice on a variety of areas, from technology to holiday destinations. Read through Harvey's other articles here to find out more.

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History of the Computer - Cooling, Part 2 of 2

Computer manufacturers specified the heat load required to be handled, the required flow of conditioned air, and the temperature to be measured at the cabinet entry points. Most systems were installed on false floors, with a space of about 1 meter or 3ft below the floor. This allowed the air conditioning to be supplied under the floor, and exhausted through the false ceiling. This space was also used for cabling the systems. An air lock was often provided for entry and exit.

Other components of the computer system, such as disks, also generated heat and had to be considered. Tape drives were particularly large producers of heat. It was common, on large scale systems, for the tapes and disks to be installed in a separate room, or partitioned off from the mainframe, so that air conditioning requirements could be better controlled. (Printers were also partitioned, but mainly for noise, dust, and publishing requirements.

For instance disks are sensitive to rapid changes in humidity, as condensation forming on the disk surface can cause head crashes, due to the small height the head flies at. Tapes produce a lot of heat due to the powerful motors they use, but are more tolerant of temperature changes.

Integrated circuits, or chips, introduced at the end of the 1960s, produced a similar escalation in heat generation and tolerance. As they became more sophisticated, and LSI (large scale integration) was common the escalation continued. This problem is still with us today - have you tried using a laptop on your lap lately? Apart from ever more sophisticated fan design, coupled with heat sinks and air flow funnels or plenums, another approach has been used from time to time. This is the system we mentioned above, water cooling.

The computer user already provides a close tolerance power supply, sometimes at different frequencies, such as 400Hz instead of 50 or 60. He must also supply air conditioning with temperature and humidity gradients specified within tight limits. Now he is required to supply chilled water, also to tight tolerances.

The computer logic circuits were assembled on multilayer PCBs (or PCAs - Printed Circuit Boards or Arrays) which were 'plugged in' to the backplane. The Backplane was a large multilayer printed circuit panel, of varying size, depending on the system, but normally around one metre or 3ft square. Approximately 60-100 PCBs would be plugged in to this panel via a multipin connector, with several hundred pins, on the board.

The multilayer PCB or backplane had been necessary since the early 1970s, due to the incorporation of many more circuits on the board. A single two-dimensional plane could not hold all the interconnections required for this multitude of circuits. The multilayer board incorporates circuits on each layer, with links through the layers, to accomplish the required connections.

For water cooling, the PCB consisted of a large heat sink, around which the circuit components were assembled, through which the chilled water flowed. When the PCB was plugged into the backplane, it also connected via special leak proof connectors to the chilled water supply flowing in the backplane. In turn, the backplane was connected with larger leak proof connectors to the customer supply.

Today's systems are usually physically smaller for the same computing power, and are designed to have a larger tolerance of air conditioning requirements, some in a so-called 'office environment'. They are designed with a wind tunnel approach, and require all doors to be closed.

Tony is a retired computer engineer, with 40 years experience, building on his previous electronics engineering on radar and automatic controls. He is now working from home on the internet. This article, brought up to date, with diagrams and illustrations, forms part of his latest book. For further information and details, please visit the website Computer Fundamentals

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